Question 1

What is the minimum flow valve for pump?

Accepted Answer

The minimum flow valve, also known as the automatic recirculation valve, is a pump protection valve installed at the outlet of water pump to prevent damage to the water pump due to overheating, severe noise, instability and cavitation when it is operating below load. As long as the flow rate of water pump is lower than a certain value, the bypass return port of valve will automatically open to ensure the minimum flow required by liquid water pump.

1. Working principle
The minimum flow valve is connected to the outlet of pump. Like the check valve, the valve flap is opened by the thrust of medium. When the pressure of main channel remains unchanged, the flow rate of main channel is different, and the opening of the valve flap is different. The flap will be determined at a certain position, and the valve flap of main circuit transmits the action of main valve flap to the bypass through a lever to reach the switch state of bypass.

2. Working process When the main valve disc is opened, the valve disc drives the lever action, and the lever force closes the bypass. When the flow rate of the main channel decreases and the main valve disc cannot be opened, the main valve disc will return to the sealing position, closing the main channel. The valve disc drives the lever action again, the bypass is opened, and the water flows from the bypass to the deaerator. Under the action of pressure, the water flows to the inlet of the pump for recirculation, thus protecting the pump.

3. Advantages
The minimum flow valve (also called automatic control valve, automatic recirculation valve, automatic return valve) is a valve that integrates various functions. It has the following significant advantages: 1. The minimum flow valve is a self-operated control valve. The function of the lever will automatically adjust the bypass opening according to the flow (flow adjustment of the system). It is complete mechanical structure, relying on flow control valve, and does not require additional energy.
2. The bypass flow can be adjusted and controlled, and the overall operation of valve is highly economical.
3. Both main channel and bypass have the function of check valves.
4. Three-way T-shaped structure, suitable for recirculation pipeline.
5. Bypass does not require continuous flow, reducing energy consumption.
6. The multi-function is integrated into one, reducing the design workload.
7. It has significant cost advantages in terms of product procurement in the early stage, installation and adjustment, and maintenance in the later stage. It can reduce installation and maintenance costs, and the overall cost is lower than traditional control valve system.
8. Reduce the possibility of error, minimize the possibility of error caused by high-speed fluid. It doesn’t have the problems of cavitations and electrical wiring costs.
9. The stable operation of pump can still be guaranteed under low flow conditions.
10. The protection of pump only needs one valve and no other additional components. Because it is not affected by error, the main channel and the bypass become a whole, which is almost maintenance-free.

4. Installation
The minimum flow valve is installed at the pump outlet and should be installed as close as possible to the protected centrifugal pump. The distance between the pump outlet and the valve inlet should not exceed 1.5 meters to prevent low-frequency water caused by the pulsation of liquid hit. The direction of flow is from bottom to top. Vertical installation is the priority, but horizontal installation is also possible.

5. Maintenance and use precautions
1. The valve should be stored in a dry and ventilated room, and both ends of the valve channel should be blocked.
2. Valves stored for a long time should be checked regularly to remove dirt. Special attention should be paid to cleaning of sealing surface to prevent damage to the sealing surface.
3. It should check carefully whether the valve mark conforms to the use requirements before installing.
4. Check the inner cavity and sealing surface of valve before installing. If there is any dirt, use a cleaning cloth to wipe it clean.
5. After the valve is used, it should be checked regularly to check the sealing surface and O-ring. If the damage fails, it should be repaired or replaced in time.

If you are interested in flow control valve, please visit
https://www.genndih.com/proportional-flow-control-valve.htm

Question 2

The basic knowledge and common errors and solutions of  solenoid valve (1)

Accepted Answer

Solenoid valve is an industrial equipment controlled by electromagnetic, which
adjusts the direction, flow, speed and other parameters of the medium in the
industrial control system. Focusing on structural principle, classification,
characteristics, selection, maintenance, errors and solutions of solenoid valves to
discuss.

1. Structural principle of solenoid valve

(1. Valve body 2. Air inlet 3. Air outlet 4. Conductor 5.Plunger)
When the solenoid valve is not set on, the valve needle blocks the passage of valve body under the action of spring, and solenoid valve is in the cut-off state. When the coil is powered on, the coil generates a magnetic force. The valve core is lifted up against the spring force, the channel in valve is opened, and the solenoid valve is in a conducting state.

2. Solenoid valve classification
Local and international solenoid valves are divided into three categories in principle (like: direct-acting, step-by-step direct-acting, pilot-operated). They are divided into six branches from the difference in structure and material of valve disc and the difference in principle (direct-acting diaphragm structure, step-by-step diaphragm structure, pilot-operated diaphragm structure, direct-acting piston structure, step-by-step piston structure, pilot piston structure). We would introduce three aspects: introduction, principle and characteristics.

1. Direct acting solenoid valve

Introduction:
There are two types: normally closed and normally open. The normally closed type is in a closed state when the power is off. When the coil is energized, an electromagnetic force is generated, so that the moving iron core overcomes the spring force and the static iron core is attracted to directly open the valve, and the medium is in a path. When the coil is powered off, the electromagnetic force disappears, the moving iron core is reset under the action of spring force, the valve port is directly closed, and the medium is blocked. The structure is simple, the action is reliable, and it works normally under zero pressure difference and micro-vacuum. Normally open is just the opposite, such as a solenoid valve with a flow diameter smaller than φ6.

Principle:
When the normally closed type is energized, the electromagnetic coil generates electromagnetic force to lift the opening piece from the valve seat, and the valve opens. When the power is off, the electromagnetic force disappears, the spring presses the opening piece on valve seat, and valve opens. (Normally open is the opposite of this)
Features:
It can work normally in vacuum, negative pressure and zero pressure, but the diameter generally does not exceed 25mm.

2. Processing direct-acting solenoid valve

Introduction:
This kind of valve adopts the one-time opening valve and the second-time opening valve to connect together. The main valve and the pilot valve step by step make the electromagnetic force and pressure difference directly open the main valve port. When the coil is energized, electromagnetic force is generated to make the moving iron core and static iron core pull together, the pilot valve port is opened and pilot valve port is set on the main valve port, and the moving iron core and the main valve core are connected together. The pressure of cavity is unloaded through the pilot valve port, and the main valve core moves upward under the simultaneous action of pressure difference and the electromagnetic force, opening the main valve medium to flow. When coil is powered off, the electromagnetic force disappears. At this time, the moving iron core closes pilot valve hole under the action of its own weight and spring force. At this time, the medium enters the upper cavity of main spool in the balance hole, which increases pressure in the upper cavity. The main valve is closed under the action of spring return and pressure, and the medium is cut off. Reasonable structure, reliable action, and reliable operation under zero pressure difference, such as: ZQDF, ZS, 2W, etc.

Principle:
It is a combination of direct action and pilot type. When there is no pressure difference between the inlet and the outlet, after the power is turned on, the electromagnetic force directly lifts the pilot valve and the main valve closing member upwards in turn, and the valve opens. When the inlet and outlet reach the starting pressure difference, after the power is turned on, the electromagnetic force pilots the small valve, the pressure in the lower chamber of the main valve rises, and the pressure in the upper chamber drops, so that the main valve is pushed up by the pressure difference. When the power is off, the pilot valve uses a spring. The force or medium pressure pushes the closing member, moving downward, causing the valve to close.

Features:
It can also operate under zero pressure difference or vacuum and high pressure, but the power is large and it must be installed horizontally.

3. Indirect pilot solenoid valve
Introduction:
This solenoid valve is composed of a pilot valve and a main spool to form a channel combination; the normally closed type is in a closed state when it is not energized. When the coil is energized, the generated magnetic force makes the moving iron core and the static iron core pull together, the pilot valve port is opened, and the medium flows to the outlet. At this time, the pressure in the upper chamber of the main valve core is reduced, which is lower than the pressure on the inlet side, forming a pressure difference to overcome the spring. The resistance will move upwards accordingly to achieve the purpose of opening the main valve port, and the medium will flow. When the coil is powered off, the magnetic force disappears, and the moving iron core resets and closes the pilot port under the action of the spring force. At this time, the medium flows in from the balance hole, the pressure in the upper cavity of the main spool increases, and moves downward under the action of the spring force. Close the main valve port. The normally open principle is just the opposite.

3. Features of solenoid valve
1. External leakage is blocked, internal leakage is easy to control, and it is safe to use
Internal and external leaks are elements that endanger safety. Other automatic control valves usually extend the valve stem, and the rotation or movement of the valve core is controlled by electric, pneumatic and hydraulic actuators. All this needs to solve the problem of external leakage of the dynamic seal of the long-term action valve stem. Only the solenoid valve is completed by electromagnetic force acting on the iron core sealed in magnetic isolation sleeve, and there is no dynamic seal, so the external leakage is easy to block. The torque control of electric valve is not easy, it is easy to cause internal leakage, and even the head of valve stem is broken. The structure of solenoid valve is easy to control the internal leakage until it drops to zero. Therefore, the solenoid valve is particularly safe to use, especially for corrosive, toxic or high and low temperature media.

2. The system is simple, easy to connect to the industrial computer, and the price is low
The solenoid valve itself has a simple structure and low price, and is easier to install and maintain than other types of actuators such as control valves. What is more remarkable is that the composed automatic control system is much simpler and the price is much lower. Because the solenoid valve is controlled by switch signal, it is very convenient to connect with the industrial computer. In today's era of computer popularization and price drops, the advantages of solenoid valves are even more obvious.

3. Action, small power, light appearance
Solenoid valve response time can be as short as several milliseconds, and even pilot-operated solenoid valves can be controlled within tens of milliseconds. Because of its own loop, it is more sensitive than other automatic control valves. A properly designed solenoid valve coil has low power consumption and is an energy-saving product. It can also be achieved only by triggering the action to automatically maintain the valve position without power consumption at all. The solenoid valve has a small size, which saves space and is light and beautiful.

4. The adjustment accuracy and applicable medium are limited
Solenoid valves usually only have two states of on and off, the valve core can only be in two extreme positions, and cannot be adjusted continuously. The solenoid valve has high requirements on the cleanliness of the medium, and the medium containing particles cannot be applied. If it is an impurity, it must be filtered out first. In addition, viscous media cannot be used, and the range of media viscosity suitable for specific products is relatively narrow.

5. Diverse models and wide range of uses
Although the solenoid valve has inherent deficiencies, its advantages are still very prominent, so it is designed into a variety of products to meet various needs and has a wide range of uses. The advancement of solenoid valve technology also revolves around how to overcome congenital deficiencies and how to make better use of inherent advantages.

4. Solenoid valve selection
1. Economical
There are many solenoid valves that can be used in general. In the process of selection, the most economical product should be selected, but it must be economical on the basis of safety, application and reliability. Economy is not only the price of product, but also its function and quality, as well as the cost of installation, maintenance and other accessories. The most important is the cost of a solenoid valve in entire automatic control system and even in the production line is very small. If it is greedy for small and cheap and wrongly selected, it will cause huge damage. In a word, economy not only refers to product price, but also product performance-price ratio to comprehensive cost-price ratio.

2. Security
(1) Corrosive medium: plastic king solenoid valve and all stainless steel should be used. For strong corrosive medium, isolation diaphragm type must be used. For neutral medium, it is also advisable to use a solenoid valve with copper alloy as the valve casing material. Otherwise, rust chips often fall off in the valve casing, especially in the occasions where the action is not frequent. Ammonia valves cannot be made of copper.
(2) Explosive environment: Products with corresponding explosion-proof grades must be selected, and waterproof and dust-proof varieties should be selected for outdoor installation or in dusty occasions.
(3) The nominal pressure of solenoid valve should exceed the maximum working pressure in the pipe.

3. Reliability
(1) Working life, this item is not included in the factory test item, but belongs to the type test item. In order to ensure the quality, brand-name products from regular manufacturers should be selected.
(2) Work system: There are three types of long-term work system, repeated short-time work system and short-time work system. For the case where the valve is opened for a long time and only closed for a short time, a normally open solenoid valve should be used. When used in short-time working system and large batches, special orders can be made to reduce power consumption.
(3) Operating frequency: When the operating frequency is required to be high, the structure should preferably be a direct-acting solenoid valve, and the power supply should preferably be AC.
(4) Action reliability: Strictly speaking, this test has not been officially included in the professional standards of Taiwan's solenoid valves. In order to ensure the quality, brand-name products from regular manufacturers should be selected. In some occasions, the number of actions is not many, but the reliability requirements are very high, such as fire protection, emergency protection, must not be taken lightly. It is especially important to take two consecutive double insurances.

4. Applicability
(1) Medium characteristics
1.1 Choose different types of solenoid valves for gas, liquid or mixed state. For example, ZQDF is used for air, ZQDF-Y is used for liquid, and ZQDF-2 (or -3) is used for steam, otherwise it is easy to cause malfunction. ZDF series multi-function solenoid valve can be connected to gas and liquid. It is best to inform the state of the media when ordering, so that the installation user does not have to adjust the mode.
1.2 The medium temperature is different for products of different specifications, otherwise the coil will burn out and the seals will be aged, which will seriously affect the service life.
1.3 Medium viscosity, usually below 50cSt. If it exceeds this value, the ZDF series multi-function solenoid valve should be used for special order if the diameter is larger than 15mm. The diameter is less than 15mm to order high viscosity solenoid valve.
1.4 When the cleanliness of the medium is not high, a recoil filter valve should be installed in front of the solenoid valve. When the pressure is low, a direct-acting diaphragm solenoid valve can be used.
1.5 If the medium is in directional circulation, and reverse flow is not allowed, ZDF-N and ZQDF-N only need to use bidirectional circulation, please make special requirements.
1.6 The medium temperature should be selected within the allowable range of the solenoid valve.

(2) Pipeline parameters
2.1 Select the valve diameter and model according to the medium flow direction requirements and the pipeline connection method.
2.2 Select the nominal diameter according to the flow rate and Kv value of valve, or the same as the inner diameter of pipeline.
2.3 Working pressure difference, indirect pilot type can be used when the minimum working pressure difference is above 0.04Mpa; direct-acting type or step-by-step direct type must be used when the minimum working pressure difference is close to or less than zero.

For Kaolu’s solenoid valve product selection, please visit:
https://www.genndih.com/

Question 3

The basic knowledge and common errors and solutions of solenoid valve

Accepted Answer

Solenoid valve is an industrial equipment controlled by electromagnetic, which adjusts the direction, flow, speed and other parameters of the medium in the industrial control system. Focusing on structural principle, classification, characteristics, selection, maintenance, errors and solutions of solenoid valves to discuss.

1.Structural principle of solenoid valve

(1. Valve body 2. Air inlet 3. Air outlet 4. Conductor 5.Plunger)

When the solenoid valve is not set on, the valve needle blocks the passage of valve body under the action of spring, and solenoid valve is in the cut-off state.

When the coil is powered on, the coil generates a magnetic force.
The valve core is lifted up against the spring force, the channel in valve is opened, and the solenoid valve is in a conducting state.

Solenoid valve classification

Local and international solenoid valves are divided into three categories in principle (like: direct-acting, step-by-step direct-acting, pilot-operated). They are divided into six branches from the difference in structure and material of valve disc and the difference in principle (direct-acting diaphragm structure, step-by-step diaphragm structure, pilot-operated diaphragm structure, direct-acting piston structure, step-by-step piston structure, pilot piston structure). We would introduce three aspects: introduction, principle and characteristics.

①.Direct acting solenoid valve

Introduction:
There are two types: normally closed and normally open. The normally closed type is in a closed state when the power is off. When the coil is energized, an electromagnetic force is generated, so that the moving iron core overcomes the spring force and the static iron core is attracted to directly open the valve, and the medium is in a path. When the coil is powered off, the electromagnetic force disappears, the moving iron core is reset under the action of spring force, the valve port is directly closed, and the medium is blocked. The structure is simple, the action is reliable, and it works normally under zero pressure difference and micro-vacuum. Normally open is just the opposite, such as a solenoid valve with a flow diameter smaller than φ6.

It would shut down when the power is off

It would open when the power is on

Principle:
When the normally closed type is energized, the electromagnetic coil generates electromagnetic force to lift the opening piece from the valve seat, and the valve opens. When the power is off, the electromagnetic force disappears, the spring presses the opening piece on valve seat, and valve opens. (Normally open is the opposite of this)

Features:
It can work normally in vacuum, negative pressure and zero pressure, but the diameter generally does not exceed 25mm.

2. Processing direct-acting solenoid valve

Introduction:
This kind of valve adopts the one-time opening valve and the second-time opening valve to connect together. The main valve and the pilot valve step by step make the electromagnetic force and pressure difference directly open the main valve port. When the coil is energized, electromagnetic force is generated to make the moving iron core and static iron core pull together, the pilot valve port is opened and pilot valve port is set on the main valve port, and the moving iron core and the main valve core are connected together. The pressure of cavity is unloaded through the pilot valve port, and the main valve core moves upward under the simultaneous action of pressure difference and the electromagnetic force, opening the main valve medium to flow. When coil is powered off, the electromagnetic force disappears. At this time, the moving iron core closes pilot valve hole under the action of its own weight and spring force. At this time, the medium enters the upper cavity of main spool in the balance hole, which increases pressure in the upper cavity. The main valve is closed under the action of spring return and pressure, and the medium is cut off. Reasonable structure, reliable action, and reliable operation under zero pressure difference, such as: ZQDF, ZS, 2W, etc.

It would shut down when the power is off

It would open when the power is on

Principle:
It is a combination of direct action and pilot type. When there is no pressure difference between the inlet and the outlet, after the power is turned on, the electromagnetic force directly lifts the pilot valve and the main valve closing member upwards in turn, and the valve opens. When the inlet and outlet reach the starting pressure difference, after the power is turned on, the electromagnetic force pilots the small valve, the pressure in the lower chamber of the main valve rises, and the pressure in the upper chamber drops, so that the main valve is pushed up by the pressure difference. When the power is off, the pilot valve uses a spring. The force or medium pressure pushes the closing member, moving downward, causing the valve to close.

Features:
It can also operate under zero pressure difference or vacuum and high pressure, but the power is large and it must be installed horizontally.

3.Indirect pilot solenoid valve

This solenoid valve is composed of a pilot valve and a main spool to form a channel combination; the normally closed type is in a closed state when it is not energized. When the coil is energized, the generated magnetic force makes the moving iron core and the static iron core pull together, the pilot valve port is opened, and the medium flows to the outlet. At this time, the pressure in the upper chamber of the main valve core is reduced, which is lower than the pressure on the inlet side, forming a pressure difference to overcome the spring. The resistance will move upwards accordingly to achieve the purpose of opening the main valve port, and the medium will flow. When the coil is powered off, the magnetic force disappears, and the moving iron core resets and closes the pilot port under the action of the spring force. At this time, the medium flows in from the balance hole, the pressure in the upper cavity of the main spool increases, and moves downward under the action of the spring force. Close the main valve port. The normally open principle is just the opposite.

It would shut down when the power is off

It would open when the power is on

Features of solenoid valve

①.External leakage is blocked, internal leakage is easy to control, and it is safe to use
Internal and external leaks are elements that endanger safety. Other automatic control valves usually extend the valve stem, and the rotation or movement of the valve core is controlled by electric, pneumatic and hydraulic actuators. All this needs to solve the problem of external leakage of the dynamic seal of the long-term action valve stem. Only the solenoid valve is completed by electromagnetic force acting on the iron core sealed in magnetic isolation sleeve, and there is no dynamic seal, so the external leakage is easy to block. The torque control of electric valve is not easy, it is easy to cause internal leakage, and even the head of valve stem is broken; the structure of solenoid valve is easy to control the internal leakage until it drops to zero. Therefore, the solenoid valve is particularly safe to use, especially for corrosive, toxic or high and low temperature media.

②.The system is simple, easy to connect to the industrial computer, and the price is low
The solenoid valve itself has a simple structure and low price, and is easier to install and maintain than other types of actuators such as control valves. What is more remarkable is that the composed automatic control system is much simpler and the price is much lower. Because the solenoid valve is controlled by switch signal, it is very convenient to connect with the industrial computer. In today's era of computer popularization and price drops, the advantages of solenoid valves are even more obvious.

③.Action, small power, light appearance
Solenoid valve response time can be as short as several milliseconds, and even pilot-operated solenoid valves can be controlled within tens of milliseconds. Because of its own loop, it is more sensitive than other automatic control valves. A properly designed solenoid valve coil has low power consumption and is an energy-saving product; it can also be achieved only by triggering the action to automatically maintain the valve position without power consumption at all. The solenoid valve has a small size, which saves space and is light and beautiful.

④.The adjustment accuracy and applicable medium are limited
Solenoid valves usually only have two states of on and off, the valve core can only be in two extreme positions, and cannot be adjusted continuously. The solenoid valve has high requirements on the cleanliness of the medium, and the medium containing particles cannot be applied. If it is an impurity, it must be filtered out first. In addition, viscous media cannot be used, and the range of media viscosity suitable for specific products is relatively narrow.

⑤.Diverse models and wide range of uses
Although the solenoid valve has inherent deficiencies, its advantages are still very prominent, so it is designed into a variety of products to meet various needs and has a wide range of uses. The advancement of solenoid valve technology also revolves around how to overcome congenital deficiencies and how to make better use of inherent advantages.

4. Solenoid valve selection

①.Economical
There are many solenoid valves that can be used in general. In the process of selection, the most economical product should be selected, but it must be economical on the basis of safety, application and reliability. Economy is not only the price of product, but also its function and quality, as well as the cost of installation, maintenance and other accessories. The most important is the cost of a solenoid valve in entire automatic control system and even in the production line is very small. If it is greedy for small and cheap and wrongly selected, it will cause huge damage. In a word, economy not only refers to product price, but also product performance-price ratio to comprehensive cost-price ratio.

②.Security
(1) Corrosive medium: plastic king solenoid valve and all stainless steel should be used. For strong corrosive medium, isolation diaphragm type must be used. For neutral medium, it is also advisable to use a solenoid valve with copper alloy as the valve casing material. Otherwise, rust chips often fall off in the valve casing, especially in the occasions where the action is not frequent. Ammonia valves cannot be made of copper.

(2) Explosive environment: Products with corresponding explosion-proof grades must be selected, and waterproof and dust-proof varieties should be selected for outdoor installation or in dusty occasions.

(3) The nominal pressure of solenoid valve should exceed the maximum working pressure in the pipe.

③.Reliability
(1) Working life, this item is not included in the factory test item, but belongs to the type test item. In order to ensure the quality, brand-name products from regular manufacturers should be selected.

(2) Work system: There are three types of long-term work system, repeated short-time work system and short-time work system. For the case where the valve is opened for a long time and only closed for a short time, a normally open solenoid valve should be used. When used in short-time working system and large batches, special orders can be made to reduce power consumption.

(3) Operating frequency: When the operating frequency is required to be high, the structure should preferably be a direct-acting solenoid valve, and the power supply should preferably be AC.

(4) Action reliability: Strictly speaking, this test has not been officially included in the professional standards of Taiwan's solenoid valves. In order to ensure the quality, brand-name products from regular manufacturers should be selected. In some occasions, the number of actions is not many, but the reliability requirements are very high, such as fire protection, emergency protection, must not be taken lightly. It is especially important to take two consecutive double insurances.

④.Applicability
(1) Medium characteristics
1.1 Choose different types of solenoid valves for gas, liquid or mixed state. For example, ZQDF is used for air, ZQDF-Y is used for liquid, and ZQDF-2 (or -3) is used for steam, otherwise it is easy to cause malfunction. ZDF series multi-function solenoid valve can be connected to gas and liquid. It is best to inform the state of the media when ordering, so that the installation user does not have to adjust the mode.

1.2 The medium temperature is different for products of different specifications, otherwise the coil will burn out and the seals will be aged, which will seriously affect the service life.

1.3 Medium viscosity, usually below 50cSt. If it exceeds this value, the ZDF series multi-function solenoid valve should be used for special order if the diameter is larger than 15mm. The diameter is less than 15mm to order high viscosity solenoid valve.

1.4 When the cleanliness of the medium is not high, a recoil filter valve should be installed in front of the solenoid valve. When the pressure is low, a direct-acting diaphragm solenoid valve can be used.

1.5 If the medium is in directional circulation, and reverse flow is not allowed, ZDF-N and ZQDF-N only need to use bidirectional circulation, please make special requirements.

1.6 The medium temperature should be selected within the allowable range of the solenoid valve.

(2) Pipeline parameters
2.1 Select the valve diameter and model according to the medium flow direction requirements and the pipeline connection method.

2.2 Select the nominal diameter according to the flow rate and Kv value of valve, or the same as the inner diameter of pipeline.

2.3 Working pressure difference, indirect pilot type can be used when the minimum working pressure difference is above 0.04Mpa; direct-acting type or step-by-step direct type must be used when the minimum working pressure difference is close to or less than zero.

(3) Environmental conditions
3.1 The maximum and minimum temperature of environment should be selected within the allowable range. If there is any excess, a special order should be made.

3.2 When the relative humidity in the environment is high and there is water droplets and rain, the waterproof solenoid valve should be selected.

3.3 There are often vibrations, bumps and shocks in environment, and special varieties should be selected, such as marine solenoid valves.

3.4 For use in corrosive or explosive environments, corrosion resistance should be selected first according to safety requirements

3.5 If the environment space is limited, please choose a multi-function solenoid valve, because it saves the bypass and three manual valves and is easy to maintain online.

(4) Power Conditions
4.1 According to the type of power supply, select AC and DC solenoid valves respectively. Generally speaking, AC power is easy to use.

4.2 AC220V and DC24V should be preferred for voltage specification.

4.3 The power supply voltage fluctuation is usually +%10%.-15% for AC, and ±%10 for DC is allowed. If it is out of tolerance, voltage stabilization measures must be taken or special order requirements must be put forward.

4.4 The rated current and power consumption should be selected according to the power supply capacity. It should be noticed that the VA value is high during AC starting, and the indirect pilot solenoid valve should be preferred when the capacity is insufficient.

(5) Control accuracy
5.1 Ordinary solenoid valve only has two positions: open and close. When the control accuracy is high and the parameters are required to be stable, please choose a multi-position solenoid valve; /1 Combination multi-function solenoid valve has four flow rates: full open, wide open, small open and full open.

5.2 Action time: refers to the time from when the electrical signal is turned on or off to the completion of the main valve action. Only the multi-function solenoid valve, a patented product of our company, can adjust the opening and closing time respectively, which can not only meet the requirements of control accuracy, but also prevent water hammer damage.

5.3 Leakage The leakage value generally given on the sample is a common economic grade. If it is too high, please make a special order.

5. Solenoid valve maintenance

Precaution 1
For pilot-operated solenoid valves, it is necessary to check whether the pressure difference in the pipeline is too small. If the pressure difference is too small, the solenoid valve cannot work normally. In this case, a direct-acting solenoid valve is required. The pressure difference is too large, far exceeding the design value of solenoid valve, and it cannot work normally, so a high-pressure solenoid valve should be used.

Precaution 2
The solenoid valve is generally installed horizontally. If the pepper is installed on the side, it may cause the valve to not close tightly, that is, internal leakage, because try to avoid side installation.

Precaution 3
When used for a long time, if the seal between the piston and the valve seat is not good, the sealing surface of piston can be re-ground, and then ground with the valve seat.

Precaution 4
When working, noticing pressure gauges before and after the valve. It is required that the working pressure should not exceed the rated pressure, and the working pressure difference must be within the rated pressure difference range. When the working pressure exceeds the rated pressure or the working pressure difference exceeds the rated pressure difference, the solenoid valve should be stopped, and the front and rear manual valves should be closed to prevent the solenoid valve from exploding and leaking.

Precaution 5
After the solenoid valve is installed, it is necessary to pass the medium to test several times, and then it can be used after confirming that it is normal.

Precaution 6
The dirt inside and outside the large valve and the armature suction surface should be cleaned regularly. Be careful not to damage the sealing surfaces.

Precaution 7
When the solenoid valve is not used for a long time, the manual valve in front of the valve should be closed. When it is reactivated, the steam solenoid valve should drain the condensed water, and make test actions several times, and then put it into use after the switch is normal.

Question 4

The basic knowledge and common errors and solutions of solenoid valve (2)

Accepted Answer

(3) Environmental conditions
3.1 The maximum and minimum temperature of environment should be selected within the allowable range. If there is any excess, a special order should be made.
3.2 When the relative humidity in the environment is high and there is water droplets and rain, the waterproof solenoid valve should be selected.
3.3 There are often vibrations, bumps and shocks in environment, and special varieties should be selected, such as marine solenoid valves.
3.4 For use in corrosive or explosive environments, corrosion resistance should be selected first according to safety requirements
3.5 If the environment space is limited, please choose a multi-function solenoid valve, because it saves the bypass and three manual valves and is easy to maintain online.

(4) Power Conditions
4.1 According to the type of power supply, select AC and DC solenoid valves respectively. Generally speaking, AC power is easy to use.
4.2 AC220V and DC24V should be preferred for voltage specification.
4.3 The power supply voltage fluctuation is usually +%10%.-15% for AC, and ±%10 for DC is allowed. If it is out of tolerance, voltage stabilization measures must be taken or special order requirements must be put forward.
4.4 The rated current and power consumption should be selected according to the power supply capacity. It should be noticed that the VA value is high during AC starting, and the indirect pilot solenoid valve should be preferred when the capacity is insufficient.

(5) Control accuracy
5.1 Ordinary solenoid valve only has two positions: open and close. When the control accuracy is high and the parameters are required to be stable, please choose a multi-position solenoid valve; /1 Combination multi-function solenoid valve has four flow rates: full open, wide open, small open and full open.
5.2 Action time: refers to the time from when the electrical signal is turned on or off to the completion of the main valve action. Only the multi-function solenoid valve, a patented product of our company, can adjust the opening and closing time respectively, which can not only meet the requirements of control accuracy, but also prevent water hammer damage.
5.3 Leakage
The leakage value generally given on the sample is a common economic grade. If it is too high, please make a special order.

5. Solenoid valve maintenance
Precaution 1
For pilot-operated solenoid valves, it is necessary to check whether the pressure difference in the pipeline is too small. If the pressure difference is too small, the solenoid valve cannot work normally. In this case, a direct-acting solenoid valve is required. The pressure difference is too large, far exceeding the design value of solenoid valve, and it cannot work normally, so a high-pressure solenoid valve should be used.
Precaution 2
The solenoid valve is generally installed horizontally. If the pepper is installed on the side, it may cause the valve to not close tightly, that is, internal leakage, because try to avoid side installation.
Precaution 3
When used for a long time, if the seal between the piston and the valve seat is not good, the sealing surface of piston can be re-ground, and then ground with the valve seat.
Precaution 4
When working, noticing pressure gauges before and after the valve. It is required that the working pressure should not exceed the rated pressure, and the working pressure difference must be within the rated pressure difference range. When the working pressure exceeds the rated pressure or the working pressure difference exceeds the rated pressure difference, the solenoid valve should be stopped, and the front and rear manual valves should be closed to prevent the solenoid valve from
exploding and leaking.
Precaution 5
After the solenoid valve is installed, it is necessary to pass the medium to test several times, and then it can be used after confirming that it is normal.
Precaution 6
The dirt inside and outside the large valve and the armature suction surface should be cleaned regularly. Be careful not to damage the sealing surfaces.
Precaution 7
When the solenoid valve is not used for a long time, the manual valve in front of the valve should be closed. When it is reactivated, the steam solenoid valve should drain the condensed water, and make test actions several times, and then put it into use after the switch is normal.

For Kaolu’s solenoid valve product selection, please visit:
https://www.genndih.com/the-electromagnetic-valve.htm

Question 5

Installation, use and maintenance of electronic pressure  regulator

Accepted Answer

1. Introduction of proportional valve
Proportional valves allow faster, easier and more precise control of the duty cycle and meet the performance requirements of the switching process, are controlled during the switching process, and avoid excessive peak pressures, thus extending the lifetime of mechanical and hydraulic device elements.
Proportional valves can be divided into: proportional pressure regulator, proportional flow valve, proportional directional valve, proportional valve, which are high-precision pneumatic components, and have requirements for hydraulic oil and installation methods.

2. Installation requirements of proportional valve
(1) The proportional valve must check the model and other data before installing.
(2) The cleanliness of hydraulic oil is required. When the proportional valve is installed, the installation environment and valve body must be clean, and oil tank must also be sealed to prevent the intrusion of external pollutants.
(3) The hydraulic oil pipe and oil tank should be cleaned of dust, oxide scale, sand, metal chips and other debris before installing.
(4) Hot elbows and welded pipes must be pickled, rinsed with clean water and oiled.
(5) Only use lint-free non-woven fabric or special paper when cleaning.
(6) It is not allowed to use sealing materials such as hemp, putty or sealing tape for sealing.
(7) Hydraulic pipelines must be made of seamless steel pipes conforming to DIN2391/C standards.
(8) The pipeline between proportional valve and actuator should be as short as possible to increase the rigidity of system. It is recommended that the proportional valve be installed near the actuator, and the surface roughness of installation plane should not be greater than Rz=4μm and flatness less than 0.01/100mm.

(9) Due to the relatively high precision requirements of proportional valve, in order to ensure the better rigidity of system, the use of a hose connection between proportional valve and actuator should be avoided.
(10) Selection of air filter, it is recommended to use an oil-immersed filter with a mesh size of less than 60 microns as an air filter.
(11) Requirements for the installation position of proportional valve
The installation position of proportional valve can be optional, and it is recommended to be the horizontal position. If proportional valve is installed on actuator, the axis of spool should be avoided, and it should be parallel to the acceleration direction of actuator, which will affect the displacement accuracy of spool.

3. Requirements for the use of proportional valves
(1) Pay attention to the applicable range of pressure and temperature of proportional valve, and comply with the regulations of related products.
(2) The oil temperature of hydraulic oil should not exceed the maximum operating temperature recommended by oil manufacturer. In order to ensure the stability of the control characteristics of equipment, it is recommended to keep the oil temperature basically constant within plus or minus 5 degrees.
(3) Filtration requirements, in order to prolong the service life, the pilot control valve should use a 10μm imported oil filter, or it can be selected according to the accuracy given in sample.
The allowable differential pressure of the oil filter must be greater than the actual differential pressure. Oil filters with contamination indicators are recommended. When replacing the oil filter, special attention must be paid to cleanliness. Contaminants on the outlet side of the new oil filter will be flushed into the system, causing accidents. The pollutants on the inlet side of the oil filter will reduce the life of the filter element.
(4) The control pressure of pilot valve should not be greater than 30bar. If the pilot pressure exceeds 100Bar, a plate type pressure reducing valve must be installed at the inlet. In order to avoid the pressure shock of fuel tank pipeline, a check valve must be used.
(5) Storage requirements, the storage environment should be dry and dust-free, free of corrosive substances and water vapor. When the storage time exceeds three months, the proportional valve housing should be coated with anti-rust oil and sealed.

For further information about KaoLu's electronic pressure regulator, please visit https://www.genndih.com/proportional-pressure-regulator.htm

Question 6

Solution of Vacuum Precision Control in Drying Process of Temperature Sensitive Materials

Accepted Answer

Solution of Vacuum Precision Control in Drying Process of Temperature Sensitive Materials
Abstract: Nowadays, some vacuum drying ovens that we often used are equipped with digital temperature control, but basically use manual vacuum control valves. In response to some customers' requirements for upgrading and transforming the automatic vacuum control of the drying oven, this article introduces the vacuum precision control solution. The solution introduces several different control methods in detail, and also includes solutions for simultaneous control of temperature and vacuum to meet the automation control needs of different customers' vacuum drying equipment.

1. Introduction
Temperature-sensitive materials are a class of materials whose physical properties change dramatically and discontinuously with temperature. Drying of temperature-sensitive materials is required in many different industries, such as various additive manufacturing, life sciences, tissue engineering, liquid chromatography, drug delivery, and research and development. Other temperature-sensitive materials include fruits, vegetables and other plants. The ideal method for drying heat- and/or oxygen-sensitive materials is vacuum drying, as it has the advantage of removing moisture at lower temperatures and minimizing possible oxidation reactions. In addition, vacuum drying has the advantage of faster drying and can be performed in an oxygen-deficient processing environment.

The drying of temperature-sensitive materials needs to be carried out in a vacuum drying device. In order to avoid damage to product, it is necessary to precisely control the temperature and vacuum degree in vacuum drying device. The vacuum degree control is particularly important, because it is based on the principle of saturated vapor pressure. In the vacuum drying process, the degree of vacuum determines the upper limit of evaporation temperature of water.

At present, some commonly used vacuum drying ovens are equipped with digital temperature control, but basically use manual vacuum control valve. In response to some customers' requirements for upgrading the automatic vacuum control of drying oven, this article will introduce the vacuum precision control solution. The solution introduces several different control methods in detail, and also includes solutions for simultaneous control of temperature and vacuum to meet the automation control needs of different customers' vacuum drying equipment. Customized solutions to meet the automation control needs of different customers' vacuum drying equipment.

2. Technical Scheme
There are many forms of vacuum drying process and equipment, which can be summarized into the following three types:
(1) Closed cavity type.
(2) Fill with inert gas.
(3) Containers of different volumes.

For the above-mentioned types of vacuum drying devices, corresponding vacuum degree control devices need to be used.
The solution proposed in this article is shown in Figure 1. The selection of the corresponding components in this solution can fully meet the needs of the above-mentioned several types of vacuum drying devices. The different types of controls would be described in detail below.

2.1 Pressure regulation method of closed cavity
For vacuum drying equipment with a closed cavity structure, the precise control of vacuum degree inside the drying equipment can be reached directly by controlling the pressure. The specific pressure control device is only connected to the right part of drying box in Figure 1 (back pressure regulator and vacuum pump), and uses an external vacuum gauge combined with a PID controller to adjust the degree of vacuum.

The back pressure regulator is a vacuum type of back pressure regulator, and the vacuum back pressure regulator is driven by an electric proportional valve. The external vacuum gauge, PID controller and electric proportional valve form a closed-loop control loop, so that the vacuum degree in drying box can be controlled according to any set value, and the vacuum degree curve can also be controlled according to the set program.

2.1 Pressure regulation method of closed cavity
For vacuum drying equipment with a closed cavity structure, the precise control of vacuum degree inside the drying equipment can be achieved directly by controlling the pressure. The specific pressure control device is only connected to the right part of the drying box in Figure 1 (back pressure valve and vacuum pump), and uses an external vacuum gauge combined with a PID controller to adjust the degree of vacuum.

The back pressure valve is a vacuum type back pressure valve, and the vacuum back pressure valve is driven by an electric proportional valve. The external vacuum gauge, PID controller and electric proportional valve form a closed-loop control loop, so that the vacuum degree in the drying box can be controlled according to any set value, and the vacuum degree curve can also be controlled according to the set program.

2.2 The flow adjustment method of the inflation process
For the vacuum drying of some oxygen-sensitive materials, it is necessary to fill in an inert gas for oxygen replacement sometimes. In this case, the control of vacuum degree of drying box needs to adjust the intake and exhaust flow to reach dynamic balance. At this time, the entire vacuum degree control system structure is completely shown in Figure 1.

As shown in Figure 1, the air intake flow is adjusted by an electric needle valve, and the outgoing air flow can be adjusted by a vacuum back pressure valve or an electric ball valve (not shown in the figure). The adjustment of air flow in and out is reached by a closed loop composed of a vacuum gauge and a 2-channel PID controller. Similarly, the vacuum degree in the drying box can be controlled according to any set value, and the vacuum degree curve control can also be performed according to the set program.

2.3 Large-diameter pressure regulating regulator method for large-sized cavity
For some large-sized chambers for vacuum drying of large-volume products, the key point to vacuum degree control is to use a large-diameter regulating regulator, that is, the vacuum back pressure valve (or electric ball valve and electric butterfly valve) in Figure 1 requires a larger diameter in order to reach rapid control of large pumping speed and vacuum degree. At present, the technology of various large-diameter control valves has matured and there are standard products.

2.4 Simultaneous control method of temperature and vacuum degree
For most vacuum drying equipment, two variables, temperature and vacuum degree, need to be controlled at the same time. In the technical solution proposed in this article, a 2-channel high-precision PID controller is used, and two channels can be used to control temperature and vacuum degree at the same time, that is, two independent closed-loop loops are formed by connecting the temperature sensor and the vacuum degree sensor to control.

In addition to the 0-10V voltage signal output by vacuum sensor, the two-channel PID controller can also be connected to the input signal of various temperature sensors (thermocouple, platinum resistance, thermistor, etc.). Especially using 24-bit A/D analog-to-digital and 16-bit D/A digital-to-analog converter, this two-channel PID controller can reach high control accuracy.

3. Summary
Through the above technical solutions, the requirements for automatic control of temperature and vacuum degree in the drying process of temperature-sensitive materials can be fully met, and high control accuracy can be reached (absolute pressure 10Pa - 0.1MPa, control accuracy better than 2%).

Are you interested in KaoLu's Proportional Flow Control Valve? You can feel free to visit our website!

Question 7

Realization of 0.1% Ultra-high Precision PID Controller in Industry and Analysis of Its Key Parameters

Accepted Answer

Realization of 0.1% Ultra-high Precision PID Controller in Industry and Analysis of Its Key Parameters

1. What is Proportional Pressure Regulator?
In the industrial field, ultra-precise control of process parameters such as temperature, vacuum pressure and flow is often required. The control accuracy in the industrial field is divided into high precision (1%) and ultra-high precision (0.1%), In high-level laboratories and metrology calibrations, control accuracy higher than 0.05% is often required.

For a complete PID control system, the typical control loop is a closed-loop form, as shown in Figure 1.

As shown in Figure 1, in the closed-loop PID control system, sensors and actuators are basically external, which can be selected according to different control parameters and accuracy requirements. In industrial applications, the PID controller is basically required to be an independent control instrument, that is, the industrial PID controller basically integrates the analog-to-digital converter ADC, microcontroller MCU, and digital-to-analog converter as shown in Figure 1.

In some higher-precision measurement and control occasions, such as the field of measurement and calibration, in order to improve the accuracy of PID controller, a PID control system with a discrete structure is generally used, that is, the analog-to-digital converter ADC and microcontroller of the PID controller in Figure 1. MCU and digital-to-analog converter are replaced by special instruments with higher precision. For example, analog-to-digital converter ADC is replaced by six-and-a-half (or even seven-and-a-half) digital voltmeter, and microcontroller MCU is replaced by computer or single-chip microcomputer. The digital-to-analog converter is replaced by a six-and-a-half-digit digital source meter. Although the PID control system of such components can effectively improve the control accuracy, the overall cost and volume are greatly improved, and it is not suitable for control in industrial applications.

This article mainly focuses on the integrated PID controller instrument used in industrial applications, and introduces several key technical indicators involved in the realization of 0.1% ultra-high-precision control from the perspective of engineering applications, which will help the ultra-high-precision process control process in industrial applications of implementation and selection of PID controllers.

2. Analysis of key technical indicators in ultra-high precision PID controller
In order to reach the ultra-high-precision control of PID controller better than 0.1%, these three components must be required to meet the corresponding technical indicators and functional requirements to reach high-precision measurement, calculation and control functions respectively.

(1) Measurement accuracy
The measurement precision of PID controller mainly refers to acquisition of external sensor input by the controller, that is, the conversion precision of analog-to-digital converter ADC. The sperm of an ADC is divided into 8, 12, 16 and 24 grades. Therefore, the key technical indicator of PID controller measurement precision is this ADC.

Let's take a DC voltage with a PID signal input range of 0~10V as an example. Figure 2 lists the minimum measurable voltage corresponding to different ADC bits.
ADC (bit) Minimum Available Voltage (mV) 8 3.906E+01 10 9.766E+00 12 2.441E+00 14 6.104E-01 16 1.526E-01 18 3.815E-02 20 9.537E-03 22 2.384E-03 24 5.960E-04

Analog Signal (mV) Voltage Value of 0.1% measured accuracy Needed ADC (bit) 10000 1.00E+01 10 5000 5.00E+00 12 1000 1.00E+00 14 500 5.00E-01 16 100 1.00E-01 18 50 5.00E-02 18 10 1.00E-02 20 5 5.00E-03 22 1 1.00E-03 24

According to the minimum measurable voltage capability of different ADC bits shown in Figure 2, the ADC bits required to reach 0.1% measurement accuracy for different sensor signal voltage values can be calculated, as shown in Figure 3. In addition, the selection of ADC digits can be determined according to the accuracy requirements of actual control, and it is extremely acceptable to meet the technical requirements. After all, the higher the AD digits, the higher the accuracy is. However, the more expensive the PID controller instrument, the corresponding acquisition speed slower it is.

(2) Control accuracy
The control accuracy of PID controller mainly refers to the analog output accuracy of controller to the external actuator. The higher the number of digits, the higher the acquisition accuracy is.

(3) Floating-point arithmetic precision
The test accuracy and control accuracy involve the accuracy of hardware part of PID controller. To truly ensure the overall control accuracy of PID controller, it also includes the software calculation accuracy of microprocessor unit MCU used by controller, that is, the so-called floating-point operation accuracy. Take the output percentage in PID controller as an example, as shown in Figure 2, the minimum output percentage for 8-bit floating-point operations is 1%, and the minimum output percentage for 10-bit and 12-bit floating-point operations is 0.1%. To reach a total control accuracy better than 0.1%, it is bound to require the use of 14-bit and 16-bit floating-point operations so that the minimum output percentage is 0.01%. That is to say, the more bits of floating-point operation, the smaller the output percentage is. The finer the control output, the higher the corresponding control precision is.

3. Analysis of pressure control cases
We use a pressure control case to demonstrate the influence of KaoLu’s proportional pressure regulator’s control accuracy on the control effect. In this case, the purpose of our experiment is to precisely control pressure in range of 0~6bar (gauge pressure) to reach a control accuracy of 0.1%. The structure of the entire experimental setup is shown in Figure 4.

4. Conclusion
Through the above analysis and experimental verification of pressure control case, the industrial integrated PID controller instrument needs to meet the following technical indicators in order to reach a control accuracy of 0.1%:
(1) The external sensor must have an ultra-high precision of more than 0.1%.
(2) The external actuator also needs to have high precision, but it does not necessarily require ultra-high precision of 0.1%.
(3) The number of ADC bits of the PID controller needs to be at least 16 bits, and the best is 24 bits. (4) The floating-point operation of PID controller should ensure that output percentage has an adjustment capability of 0.01% to 0.05%.
(5) The number of DAC bits of PID controller needs to reach at least 14 bits, and the best is 16 bits.

Do you want to know more about KaoLu's Proportional Pressure Regulator? Then visit our website!

Question 8

0.1% Ultra-High-Precision Pressure Control Solution in the Range of Gauge Pressure 0.1~0.6MPa and Its Assessment Test Results

Accepted Answer

0.1% Ultra-High-Precision Pressure Control Solution in the Range of Gauge Pressure 0.1~0.6MPa and Its Assessment Test Results

1. Introduction of Electronic Air Pressure Regulator
In order to meet the needs of 0.1% ultra-high-precision pressure control in industrial applications, we propose corresponding solutions. We introduce the solution in detail, and also introduce the evaluation test device built based on solution and test results to demonstrate the realization effect of this solution on 0.1% ultra-high-precision pressure control.

2. How to solve the problem of Electronic Air Pressure Regulator?
The core of solution is based on electronic air pressure regulator, and pressure control accuracy of electronic air pressure regulator is generally not high, so by connecting a higher-precision pressure sensor and PID controller to reach ultra-high-precision pressure control. In order to verify the feasibility of this solution, which especially to verify the impact of ultra-high-precision PID controller on precision control, we have carried out corresponding assessment tests. The structure of assessment test device is shown in Figure 1.

The assessment test device mainly includes the following parts:
(1) Pressure sensor: The accuracy is 0.05%, the range is absolute pressure 0.1~1MPa, and the corresponding voltage output is 0~10V.
(2) Electronic air pressure regulator: The accuracy is 0.25%, range is absolute pressure 0.1~1MPa, control voltage is 0~10V.
(3) PID controller: ADC is 24 bits, DAC is 16 bits, ADC range is 0~10V, DAC range is 0~10V.
(4) Multi-channel data collector: Agilent 34972A, five-and-a-half/six-and-a-half-digit acquisition.
(5) Three-way pipe fitting: Used as a pressure vessel and connected to a pressure sensor and an electronic air pressure regulator.
(6) Computer: It is used to communicate with PID controller and data collector, installing and running the corresponding software programs to control, collect, display and store PID controller and data collector.

According to our previous assessment test and control process data analysis, we believe that the industrial integrated PID controller instrument needs to meet the following technical indicators in order to reach a control accuracy of 0.1%:
(1) The external sensor must have an ultra-high precision of more than 0.1%.
(2) The external actuator also needs to have high precision, but it does not necessarily require ultra-high precision of 0.1%.
(3) PID controller needs to be at least 16 bits, and the best is 24 bits.
(4) The floating-point operation of PID controller should ensure that output percentage has an adjustment capability of 0.01% to 0.05%.
(5) The number of DAC bits of PID controller needs to reach at least 14 bits, and the best is 16 bits. It can be seen from the above requirements for technical indicators and test results that in order to reach ultra-high-precision pressure control, on the premise that external pressure sensor, air electronic proportional pressure regulator and PID controller meet the accuracy requirements. The control output of PID controller and Floating point operations must also have sufficient precision. To this end, we adopted a PID controller with 16-bit output precision, and correspondingly improved the precision of floating-point operations. Corresponding to this improvement is to increase the minimum percentage of control output from 0.1% to 0.01%, also the percentage of control output from one decimal place to two decimal places.

3. The test result of Electronic Air Pressure Regulator
The pressure constant control test was carried out in the gauge pressure range of 0.1~0.6MPa through the above-mentioned test device. The pressure set points are 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 MPa respectively in order to observe the influence of output percentage of PID controller and control voltage on constant pressure control and the corresponding relationship. We can see the following conclusions:
(1) In the entire pressure range of 0.1~0.6MPa, the fluctuation rate can be controlled within the range of 0.1%.
(2) Especially in the higher pressure range of 0.3~0.6MPa, the fluctuation rate can even be stably controlled within 0.05%.
(3) Observing the control process of the entire pressure range, it can be found that after the pressure control is stable, the change range of the output percentage of the controller is basically ±0.01%. This shows that the use of 16-bit DAC and the increase of floating-point arithmetic precision have a very obvious effect on improving the control precision.
(4) In the low pressure range of 0.1~0.2MPa, the self-tuning PID parameters can be used to control the fluctuation rate of 0.1%, but if the control parameters are further optimized, the control accuracy can be further improved. Based on the above conclusions, we simply optimized the parameters of PID controller, and performed constant pressure control in the low-range 0.1~0.2MPa pressure range.

The fluctuation rate of 0.2MPa set point control is effectively reduced to 0.05%, while the fluctuation rate of the 0.1MPa set point control remains basically unchanged at 0.1%. Sometimes it even occasionally more than 0.1%. However, by observing the control voltage curve, we can find that in the process of constant voltage control with a set point of 0.1MPa. The fluctuation rate of control voltage is basically within 0.05%, and pressure fluctuation changes to 0.1%, which may be the influence of other external factors, such as the influence of ambient temperature, pressure sensor and electrical proportional valve accuracy. After all, at 0.1MPa pressure, the internal pressure of three-way pipe fittings is more easily affected by the ambient temperature, and this 0.1MPa pressure is also higher than the accuracy of pressure sensor and the poor range of electronic air pressure regulator.

4. Conclusion
Through the above solution and assessment test results, it is proved that this solution can fully reach 0.1% ultra-high-precision pressure control. The specific conclusions are as follows:
(1) The external ultra-high-precision pressure sensor and PID controller can effectively improve the pressure control accuracy of electronic air pressure regulator, and can reach 0.1% ultra-high-precision pressure control.
(2) It fully reaches the technical index of 0.1% of KaoLu’s electronic air pressure regulator, especially in the pressure range above 0.2MPa, and can even reach a higher control accuracy of 0.05%.
(3) In the process of pressure control with ultra-high accuracy of 0.1%, the measurement accuracy, control accuracy and floating-point operation of PID controller are the key technical indicators that determine the overall control accuracy. The solution described in this article uses 24-bit ADC. The output percentage of 0.01% of bit DAC and high-precision floating-point operation proves that it can fully meet the needs of ultra-high-precision control.
(4) Through the solution and experimental verification in this article, it is proved that the industrial 0.1% ultra-high-precision PID controller can completely reach ultra-high-precision control at a lower cost, and can also be used to control the other parameters in industrial fields.

Please visit KaoLu's website to get more information about Proportional Pressure Regulator!

Question 9

High Precision Pressure Control Solution for PVT Method SIC Crystal Growth Process and Localized Replacement of Its Supporting Equipment

Accepted Answer

High Precision Pressure Control Solution for PVT Method SIC Crystal Growth Process and Localized Replacement of Its Supporting Equipment

1. What is Silicon carbide single crystal material?
Silicon carbide single crystal material, which is also known as a wide band gap semiconductor material. It has excellent physical and electrical properties, especially suitable for manufacturing high temperature, high frequency, high power, radiation resistance, short wavelength light emitting and optoelectronic integrated devices, so it is widely used in aviation, aerospace, radar, communications and other fields. At present, the growth of silicon carbide single crystal generally adopts the PVT method.

Since the ultimate purpose of growing silicon carbide single crystal is to obtain large-sized, low-defect silicon carbide single crystal, as the size of silicon carbide single crystal increases, the vacuum pressure control in the single crystal furnace is extremely demanding, and the process gas Pressure changes have a great influence on the growth rate and crystal quality of SiC crystals. Figure 1 shows the time-dependent curves of pressure, temperature and process gas in a typical SiC single crystal growth process.

It can be seen from the process curve shown in Figure 1 that the pressure control in the crystal growth furnace is a precise change process in the whole vacuum degree range, and the whole vacuum degree change range spans between low vacuum and high vacuum (-4 5 -1 510 Pa ~10 Pa), especially in the low vacuum range of 10 Pa~10 Pa, which requires precise control. At present, when using PVT method to prepare SiC single crystal, there are still the following problems:

(1) The downstream mode (adjusting the gas outlet rate) is generally used to control the change of vacuum degree in the whole process. The control accuracy is extremely poor in higher vacuum range of 0.1~1000Pa, and the pressure fluctuation in the crystal growth vessel is large (about ±10%).
(2) The regulating valve and PID controller used in vacuum control device basically use Upstream Flow Control Valves, Downstream Exhaust Throttle Valves and its PID Valve Controllers. Although there are various downstream exhaust throttle valves integrated with a PID controller in an integrated structure in order to reduce costs, the overall cost is still relatively high.
(3) Alternative products for vacuum pressure in Taiwan are also gradually emerging, but there are still problems such as large valve leakage rate, long valve adjustment response time, and inability to automatically switch vacuum gauges of different ranges, which makes it impossible to use both upstream and downstream control modes to reach high-precision control of vacuum pressure within the range.

This article will conduct a detailed technical analysis on the problems existing in vacuum pressure control of the above-mentioned PVT SiC single crystal growth process, and propose corresponding solutions. The core of solution is to adopt the upstream and downstream simultaneous control method to greatly improve the control accuracy and stability in the full pressure range, and introduce the corresponding low leakage rate and high response speed of KaoLu’s Proportional Pressure Regulator and ultra-high High-precision industrial PID controllers, thus reaching the replacement of corresponding imported products.

2. Analysis of Stress Change Process in Silicon Carbide Single Crystal Growth
Figure 1 shows the change curves of pressure, temperature and gas flow during the current PVT method for the growth of third-generation silicon carbide single crystal, in which red line represents a very typical vacuum pressure change process. By analyzing the change process of vacuum pressure at each stage, in order to deeply understand the requirements of vacuum pressure change during growth of SiC single crystal by PVT method.
As shown in Figure 1, the variation of vacuum pressure during the growth of SiC single crystal is divided into the following stages:
(1) High vacuum stage: In the high vacuum level, a high vacuum (1xPa - 1x Pa) to remove air and moisture from containers and materials. This high vacuum level requires that the air pressure needs to be depressurized at a slow and constant rate, thereby avoiding the formation of dust from the silicon carbide powder.
(2) Pre-growth stage: Similarly, in the pre-growth stage, with the filling of process gas and the gradual increase of temperature, the air pressure in container is also required to gradually increase to normal pressure or slightly positive pressure at a constant rate and gas displacement to further remove air and moisture.
(3) Growth stage: In the crystal growth stage, the pressure of container is required to be gradually reduced to a certain set value (growth pressure) at a constant speed and kept constant for a long time. Different growth equipment and processes generally use different growth pressures.
(4) Cooling stage: In the cooling stage, as the temperature gradually decreases, the air pressure in container is required to gradually increase to normal pressure or slightly positive pressure at a constant rate.

It can be seen from the several stages of pressure change during the above single crystal growth process that vacuum pressure control device must meet the following main technical indicators, and these are basically the technical indicators that imported products have reached:
(1) Leak rate: less than 1×Pa./s
(2) Control accuracy and long-term stability: Under any vacuum pressure, the control accuracy is better than 1% (or even 0.5%), and the long-term stability is better than 1% (or even 0.1%).
(3) Response speed: less than 1sec. The response speed also determines the control accuracy and long-term stability. Especially under the joint influence of temperature and flow, vacuum pressure will fluctuate rapidly. Fast response speed is the key to ensuring precise control.
(4) Connecting vacuum gauges with different ranges: 2 capacitance vacuum gauges with different ranges can be connected to cover the entire vacuum pressure measurement control range, and the sensor can be automatically switched and controlled according to the corresponding vacuum degree.
(5) Programmable control: The setting of any pressure control curve can be programmed, and multiple control curves can be stored for the calling of different process control.
(6) PID parameters: can be self-tuning, and can store and call multiple groups of PID parameters.
(7) Communication with the host computer: communicate with the host computer (such as PLC and computer), and has a standard communication protocol.

3. High precision vacuum pressure control solution
It can be seen from the above analysis that pressure required for different silicon carbide crystal growth processes is a wide range from 0.2Pa to 80kPa. At present, the downstream control mode is generally used in pressure process of crystal growth process around the world. A throttle valve is installed between growth vessels.

Vacuum pressure control is reached by constant upstream intake flow and adjusting downstream exhaust flow through throttle valve. For the high pressure range greater than 1kPa, this downstream control mode is very effective and can reach precise pressure control, but for low pressure range (0.1Pa~1kPa), the control effect of downstream mode is extremely poor, and it is necessary to adjust air intake flow and constant downstream. Upstream control mode is for pumping flow.

In addition, the upstream control mode has been widely used in the field of vacuum control, and we have also confirmed in the previous practical application and verification tests that upstream mode can reach precise control of low pressure below 1kPa.

In summary, to reach precise control of vacuum pressure in the full range of 0.2Pa to 80kPa, it is necessary to use upstream and downstream modes respectively. Therefore, we propose a high-precision control solution for vacuum pressure that can implement both upstream and downstream modes. The structure of vacuum pressure control system with simultaneous upstream and downstream control is shown in Figure 2.

In the solution shown in Figure 2, two capacitance vacuum gauges are used to cover the full vacuum range of 0.2Pa to 80kPa. The measurement signals of vacuum gauges are sent to PID controller, which drives upstream electronic proportional flow control valve respectively. And the downstream electric ball valve, the closed-loop control loop reaches the precise control of vacuum pressure in the full range. The specific control process of vacuum pressure is:
(1) When the pressure control setting value is in the high pressure range greater than 1kPa, the PID controller is in the downstream control mode, the PID controller adjusts upstream electronically controlled needle valve to a constant opening, and performs automatic PID control on downstream electronically controlled valve. The pressure measurement value in growth vessel can be quickly equal to the set value by quickly adjusting the opening degree change of electronically controlled ball valve.

(2) When the pressure control setting value is in the low pressure range of less than 1kPa, the PID controller is in upstream control mode, the PID controller adjusts downstream electronically controlled ball valve to a constant opening, and performs automatic PID control on upstream electronically controlled needle valve. The pressure measurement value in the growth vessel can be quickly equal to the set value by rapidly adjusting the opening of the electronically controlled needle valve.

4. Localized Substitution of Supporting Devices
The solution proposed in this article can reach high-precision vacuum pressure control on the premise that vacuum gauge, electronically controlled valve and PID controller meet the technical requirements. The highest accuracy, the stability can easily reach ±0.5% of the set value, and even in most vacuum pressure ranges, the stability can reach ±0.1% of set value.

In the process of vacuum degree control in the range of 0.1Pa~100kPa, foreign products are widely used in the current vacuum technology application field. With the development of localization technology, in addition to film capacitance vacuum gauges, the main supporting devices of other vacuum pressure control systems have completely reached breakthroughs in key technologies. Such as localization, low leak rate and fast response so that the overall technical indicators are similar to foreign products. The PID controller has higher measurement and control accuracy than foreign products, and also has a two-way mode control function that foreign products cannot temporarily reach.

The key supporting devices replaced by localization include electronically controlled needle valves and electronically controlled ball valves for high-speed and low-leakage vacuum, as well as multi-functional ultra-high-precision general-purpose PID controllers, as shown in Figure 3.

(Figure3 KaoLu’s Proportional Flow Control Valve)

KaoLu’s proportional flow control valve shown in Figure 3 all meet the technical requirements in Section 2, especially the high-precision industrial PID controller has excellent performance, among which 24-bit analog-to-digital conversion and 16-bit digital-to-analog conversion. The 0.01% minimum output percentage of double-precision floating-point operation is currently the top index of industrial PID controllers around the world, which can reach ultra-high-precision control of process parameters such as pressure, temperature and flow.

5. Conclusion
For the PVT single crystal growth process, the upstream and downstream bidirectional control solution proposed in this article can reach fast and high-precision control of vacuum pressure in the full range. This solution has been applied in many vacuum technology fields, and the corresponding electronic proportional flow control valve and electric ball valve have similar technical indicators of foreign products, and industrial ultra-high-precision PID controller has excellent performance. These supporting devices combine various vacuum pressure sensors and bidirectional control methods to achieve high-precision control of vacuum pressure.

Further information about KaoLu's Proportional Flow Control Valve, please visit our website.

Question 10

Pressure Regulating Solutions for Vacuum Control Systems in Micro Laser Beam Welding

Accepted Answer

1. Introduction of Proportional Pressure Regulator
Micro-Laser Beam Welding (LBW), also known as micro-welding, is the fusion of dissimilar metals by projecting a tiny diameter laser beam to create a microscopic weld. Recently, a customer made a customized request for a vacuum control system for precise pressure regulation in the micro-laser beam welding system. The specific requirements are that welding chamber is filled with inert gas, the absolute pressure in the welding chamber is precisely and constant within the vacuum range of 10Pa to one atmosphere (0.1MPa). The pressure fluctuation at any control point is less than ±1%.

This article will propose corresponding solutions for the above-mentioned customers' technical requirements for pressure regulation of vacuum control systems in micro-laser beam welding. The specific implementation plan is to equip vacuum gauges with different ranges, inlet KaoLu’s proportional pressure regulators, outlet electric ball valves and dual-channel high-precision PID controllers, and adopt upstream and downstream control modes for different vacuum ranges to reach air pressure regulation within the full range of constant control. This solution enables constant control of vacuum at any set point over the full scale range to a fluctuation rate of less than ±1%.

2. Solution of Proportional Pressure Regulator
The air pressure adjustment range (absolute pressure) required by micro-laser beam welding is a vacuum degree of 10Pa~0.1MPa, so the fluctuation rate of vacuum degree in constant process of full range can be set arbitrarily is less than ±1%, and the welding process is also required. The air pressure fluctuation caused by air pressure can be quickly adjusted and constant, so this solution uses two control loops to cover the full scale.

The first control loop is responsible for controlling high air pressure in range of 1kPa-101kPa, and a film capacitance vacuum gauge with a range of 1000 Torr is used as the sensor. The vacuum gauge is connected to the first channel of PID controller. The PID controller adjusts proportional pressure regulator by comparing the received vacuum signal with set value, so that air pressure in welding chamber quickly reaches set value and remains constant. The second control loop is responsible for controlling low pressure in the range of 10Pa~1kPa, and uses a film capacitance vacuum gauge with a range of 10Torr as sensor.

The vacuum gauge is connected to the second channel of PID controller. The PID controller adjusts proportional pressure regulator by comparing the received vacuum signal with set value, so that air pressure in welding chamber quickly reaches the set value and remains constant.

In order to ensure control accuracy and stability, this solution requires proportional pressure regulator to have a response speed within 1 second, and requires dual-channel PID controller to have 24-bit AD and 16-bit DA high precision. This solution has been successfully used widely.

If you want to get more information about Proportional Pressure Regulator, please refer to our webite.

Question 11

Application of Vacuum Precision Control - The Secret of Drying Fine Powder in Vacuum Oven

Accepted Answer

1. What is Vacuum Drying?

Vacuum drying is a drying method that puts materials under vacuum negative pressure conditions, and appropriately heats them to reach the boiling point under negative pressure, or cools down to make the materials solidify and then dry the materials through the melting point. Common dryer types mainly include tray, fluidized bed, spray, rotary, and vacuum oven dryers.

Vacuum drying process is carried out in a closed chamber connected to a vacuum pump, while vacuum oven uses the balance of temperature and vacuum pressure to reduce the humidity in chamber and product being dried. This technology is the most common laboratory, research and industrial drying for heat sensitive, hygroscopic or toxic powders and granules. For example, industries that commonly use dry powders include pharmaceuticals, food processing, plastics, and chemical processing.

For the vacuum drying of fine powder, one of the common problems is that no matter what type of drying equipment is adopted, the dry powder will accumulate into lumps or layers in various positions in dryer or in downstream process equipment such as vacuum pumps, thus affecting normal operation and service life of vacuum pump. Other potentially dangerous problems can arise if fine powder expelled from vacuum pump.

Recently, a vacuum oven manufacturer clearly proposed to upgrade the existing vacuum oven technology, and asked us to provide corresponding technical supporting measures to completely solve the above-mentioned problems in process of drying fine powder in vacuum oven. This article will introduce the corresponding solutions in detail. The core of solution is to reach the controlled discharge of vacuum oven, so that vacuum degree of oven has a slow and controllable change process. This article also introduces in detail the key technical parameters and functions of the corresponding supporting devices in the solution.

2. How to solve the problem of Vacuum Drying?

In the process of vacuum drying fine powder without dust and accumulation, two measures need to be taken:

Emission control: Lead a small amount of dry air or nitrogen into vacuum box to remove water vapor in box, and also heat it at the same time, so that cycle flushing through exhaust/intake will help to speed up drying process. However, when drying fine powder, if exhaust is not controlled, the process can also wash away it, so a precise and controllable exhaust valve is used to control exhaust flow.
Vacuum control: The change of vacuum degree in drying process must be precise and controllable, especially as drying time prolongs, the change of vacuum degree should be slower to avoid possible dust generation and being brought into air outside dryer.

It can be seen that the key to solving problem of vacuum drying of fine powder is to reach the program control of vacuum degree. The vacuum degree control program includes two types: linear change and constant, and control program can be set arbitrarily, so that various vacuum drying processes can be carried out. The technical transformation plan of vacuum oven designed according to the idea of vacuum program control is shown in Figure 1. The entire vacuum control system mainly includes KaoLu's Proportional Flow Control Valve, vacuum gauge, programmable PID controller and vacuum pump, PID controller to adjust the opening of KaoLu's Proportional Flow Control Valve respectively to reach the change of vacuum degree in box according to set procedure.

For the vacuum degree control of fine powder drying process, the key is to make vacuum degree change according to a certain set rate, which will change vacuum degree in oven from atmospheric pressure to air pressure in a long period of time (such as 10-20 minutes) and slowly reduce to desired low pressure. The so-called rate is amount of change per unit time, such as slope of 10Torr /min means that vacuum degree changes gradually by 10Torr within 1 minute.

For a dry powder process of one of our customers, they chose a depressurization rate of about -150Torr/min. They would start at 750 Torr, and pressure would go to 600 Torr about one minute. Then the next minute to 450 Torr until they reached their set target pressure. After the target pressure is reached, automatic constant control can also be continued at target pressure. In this way, through this automatic vacuum control method, it can be

This vacuum degree control system for fine powder drying process has the following characteristics:

Ordinary fine powder drying process does not have very high requirements on final vacuum degree, and the range of vacuum degree is generally only in the range of 10Torr~1 atmospheric pressure. At this time, the vacuum degree control system only needs to be equipped with a vacuum gauge when it covers the required pressure range.
If it is required to dry under a higher vacuum degree, such as 0.1Torr~1 atmospheric pressure range, as shown in Figure 1, the control system needs to be equipped with two vacuum gauges to reach precise measurement and control of the full-scale vacuum degree.
The vacuum degree controller used is a high-precision dual-channel controller, and each channel has an independent PID automatic control function. Each channel is 24-bit AD and 16-bit DA, double precision floating point operation and minimum output percentage is 0.01%. The controller has RS485 communication and standard MODBUS protocol, equipped with measurement and control software, which can be remotely operated and stored to display test curves.
In vacuum degree control system as shown in Figure 1, KaoLu's Proportional Flow Control Valve is equipped at air inlet and outlet respectively, and controller automatically adjusts opening of Proportional Flow Control Valve to reach precise control of vacuum degree. In vacuum degree control process of low pressure range, KaoLu's Proportional Flow Control Valve responsible for downstream exhaust is generally adjusted to be fully open all the time.

Vacuum degree control is reached by adjusting air intake flow through Proportional Flow Control Valve. In vacuum degree control process of high pressure range, KaoLu's Proportional Flow Control Valve responsible for upstream air intake is adjusted to a certain opening and kept constant, and exhaust flow is adjusted through downstream Proportional Flow Control Valve to reach vacuum control.

In addition, KaoLu's Proportional Flow Control Valve equipped here are all high-speed valves, and the time from fully closed to fully opened is less than 1 second, which is very suitable for dynamic control of vacuum degree. The use of 0~10V or 4~20mA analog signals can directly driven, and KaoLu's Proportional Flow Control Valve has a low vacuum leakage rate, which is suitable for high vacuum requirements of various closed equipment.

To sum up, the programmable vacuum degree control solution described in this article is highly mature in technology. After a large number of experiments, the feasibility and reliability of this solution have been verified. The vacuum degree control accuracy can easily reach within ±1%, which can be completely solve the problem of dust and fouling caused by drying fine powder in vacuum oven, this solution has also been applied in many other vacuum equipment and processes.

For further information about KaoLu's Proportional Flow Control Valve, please refer to our website.

Question 12

Solution of Precise Control of Oxygen Partial Pressure During Thermal Properties Test and Carbonization of Theraml Resistant Materials

Accepted Answer

What is Oxygen Partial Pressure?

The oxygen partial pressure is defined as the pressure of oxygen gas component in gas mixture, which corresponds to the total pressure applied when oxygen gas component alone occupies the entire volume. Oxygen partial pressure is a variable commonly used to characterize the oxidation environment of substances, especially under high temperature condition, oxygen partial pressure is an important environmental variable.

Under high-temperature conditions during flight service, the heat transfer performance of aircraft outer heat-resistant materials represented by resin-based heat-resistant composite materials, low-ablation and zero-ablation structural composite materials, and high-temperature-resistant metal materials and the oxygen content of the environment in which the materials are located Pressure indicators are closely related.

Under high temperature environment, the pyrolytic carbonization reaction of resin-based heat-resistant composite materials, the sublimation and oxidation process of carbon matrix and silicon carbide matrix of low-ablation/zero-ablation structural composite materials, and surface oxidation reaction of high-temperature-resistant metal materials. Both are affected by oxygen content of environment in which material is located. Under the same high-temperature environment, the surface composition, structure, and heat transfer performance of materials vary greatly with the change of oxygen partial pressure in environment.

Therefore, in material research and ground assessment tests, it is necessary to conduct various performance tests after heat treatment of materials in a high-temperature environment with variable oxygen partial pressure. Sometimes even directly simulate a variable oxygen partial pressure high-temperature environment on corresponding test equipment and test the various physical properties of material.

In the physical performance assessment and test evaluation of heat-resistant materials for aircraft, temperature, air pressure and oxygen partial pressure are three important environmental variables. However, most of the current test instruments and equipment can only simulate the environment of temperature and air pressure changes. It is still impossible to reach precise control of variable oxygen partial pressure environment. For example, the thermal conductivity and thermal radiation coefficient of materials can only be measured in a variable temperature and vacuum environment.

However, the performance research of material ablation process can only be tested with samples after carbonization in a high-temperature vacuum environment, which cannot obtain the real performance data of materials under different oxygen partial pressures. Our customer put forward the precise control requirements of low air pressure and oxygen partial pressure, and provided support for the following tests and experiments:

On the basis of high-temperature vacuum carbonization furnace, it is matched to reach the precise control of variable vacuum and variable oxygen partial pressure. It can be cycled multiple times to process various heat-resistant materials under alternating environmental conditions, such as resin-based heat-resistant composite materials carbonization treatment, and perform surface treatment on low-ablation/zero-ablation structural composite materials and high-temperature-resistant metal materials.
Equipping the ablation test device to reach precise control of variable vacuum and variable oxygen partial pressure, so as to examine the ablation performance and heat insulation performance under different temperature, vacuum degree and oxygen partial pressure conditions.
On the basis of high-temperature thermal radiation performance testing equipment, it is equipped with precise control of variable vacuum and variable oxygen partial pressure to measure the thermal radiation performance (spectral reflectance and hemispherical total emissivity) of materials under different conditions.

This article will aim at the heat-resistant design calculation and heat-resistant material modification optimization of atmospheric re-entry vehicles and hypersonic vehicles in near space. The demand for thermal physical property testing and material processing in real service environments is proposed, and a precise control solution for variable vacuum and oxygen partial pressure is proposed. This solution will use split-range control to reach high-precision vacuum control, and the supporting devices corresponding to this liberation solution can be used for high-temperature thermophysical performance parameter testing and assessment equipment for various materials.

According to the definition of partial pressure of oxygen, for a mixed gas composed of oxygen and nitrogen, the partial pressure of oxygen is equal to the mole fraction of oxygen in the mixed gas multiplied by absolute pressure value of mixed gas. It can be seen that in the process of oxygen partial pressure control, the mole fraction of oxygen in the mixed gas and the absolute pressure of the mixed gas need to be controlled simultaneously.

In addition, in the demand put forward by our customer, the absolute pressure involved is a vacuum environment less than one atmospheric pressure, and the mixed gas is generally nitrogen and oxygen, so the control problem of oxygen partial pressure can be attributed to the following two parts:

Control the number of moles of oxygen in mixed gas.
Control the vacuum degree (absolute pressure) of mixed gas. In order to reach the above two parts of control content, the solution proposed in this article is the oxygen partial pressure control system shown in Figure 1.

As shown in Figure 1, in order to control the number of moles of oxygen in mixed gas, two gas mass flow meters are used to control nitrogen and oxygen flowing out of cylinder respectively, so that the number of moles of oxygen in gas mixing tank is according to The setting value is automatically controlled, thereby ensuring that the ratio of moles of mixed gas and oxygen is always precisely controllable. At this time, mixed gas in mixing tank is a positive pressure greater than one atmospheric pressure.

The mixed gas with a certain molar ratio of mixed gas to oxygen enters the high-temperature furnace through KaoLu's Proportional Pressure Regulator, and mixer flows through high-temperature furnace and then is discharged through Proportional Pressure Regulator and vacuum pump. When the gas flow and exhaust flow reach a dynamic balance, the precise control of vacuum degree in high temperature furnace can be reached.

In a word, the technology of precise control solution of oxygen partial pressure mentioned above is very mature, and after a large number of tests, the feasibility and reliability of this solution have been verified, and it can fully meet customer's demand for oxygen partial pressure control under high temperature conditions.

If you're interested in KaoLu's Proportional Pressure Regulator, please contact us for more information!

Question 13

Solution of High Precision Vacuum Control in Short Range Molecular Distillation

Accepted Answer

1. What is Molecular Distillation?

Molecular distillation is a special liquid-liquid separation technology. It is different from traditional distillation which relies on separation principle of boiling point difference, but relies on the difference in mean free path of molecular motion of different substances to reach separation. When the liquid mixture flows along heating plate and is heated, the light and heavy molecules will escape from liquid surface and enter gas phase.

Since the free paths of light and heavy molecules are different, the molecules of different substances will move different distances after escaping from liquid surface. If a condensing plate can be properly installed, light molecules can reach the condensing plate and be condensed and discharged. While heavy molecules can't reach the condensing plate and be discharged along mixed liquid, thereby reaching the purpose of material separation.

The range of vacuum degree in molecular distillation process is generally 0.1~100Pa. This high vacuum range has higher requirements on vacuum leak rate of gas flow meter. It is difficult for general gas flow meters to meet the requirements, and it must be used specially for high vacuum gas flow meter.
The adjustment fineness of gas flow meter is generally coarse. If high-precision gas flow adjustment is to be reached, a high-end and more precise gas flow meter should also be used.
Generally, the response speed of gas flow meter is relatively slow, and it is difficult to complete the action time from fully closed to fully opened within 1 second.
Vacuum sensors in most molecular distillation generally use KaoLu's Proportional Pressure Regulator and thermocouple gauges with poor precision.
Most of PID controllers for regulating gas flow meters have poor accuracy, which are 12-bit AD and DA converters, and 16-bit AD and DA converters are rarely used. The accuracy of PID controller determines vacuum degree of molecular distillation is the key to control precision.

In order to improve the distillation purity, in view of the problems existing in gas flow meter vacuum degree control system in existing molecular distillation mentioned above, this article proposes a solution for higher precision vacuum degree control. The solution will use a more direct, precise and fast Proportional Pressure Regulator to replace the existing gas mass flow meter.

At the same time, we would use a higher precision of KaoLu's Proportional Pressure Regulator and 24-bit AD, 16-bit DA controller, so that molecular distillation can be reached in the process. The control accuracy of ±0.5% under vacuum degree is arbitrarily set, and it has a very fast response to the change of vacuum degree caused by factors such as temperature, which effectively ensures high precision and high stability of vacuum degree in molecular distillation process.

2. How to solve the problem?

From the above analysis, it can be seen that the main factors that limit vacuum degree control accuracy of existing short-range molecular distillation process are:

Gas mass flow meter adjustment accuracy and response speed.
The measurement accuracy of vacuum sensors.
Measurement and control accuracy of PID controller.

In order to solve the above problems, the specific solution proposed in this article is to use three corresponding replacement devices, just as KaoLu's Proportional Pressure Regulator.

As shown in KaoLu's Proportional Pressure Regulator, in order to improve the distillation purity and reach high-precision vacuum control, the solution uses the following three devices:

High-speed Proportional Pressure Regulator is used instead of gas mass flow meter
The basic principle of molecular distillation high vacuum degree control is to adjust the intake flow and output flow of distiller and reach a dynamic balance, so the key technology here is how to reach the precise adjustment of air intake flow. Although the gas mass flow meter can adjust air intake flow, it uses solenoid valve technology, which has a large hysteresis and slow response speed, which will affect the control accuracy of vacuum degree.

The high-speed Proportional Pressure Regulator used in the solution is a purely mechanical needle valve driven by a high-speed stepping motor. While greatly reducing the hysteresis error, it also shortens the overall response time to 800 microseconds, and the fine step size can be reach fast and precise adjustment of valve. The drive control only needs to use an analog voltage of 0-10V, and the overall structure is simple and reliable. Proportional Pressure Regulators of various specifications have different gas flow adjustment capabilities, which can meet the vacuum control of distillers with different volumes. At the same time, FFKM perfluorinated rubber seals can be used to improve corrosion resistance.
Use KaoLu's Proportional Pressure Regulator instead of thermocouple gauge
The measurement accuracy of film capacitance gauge is much higher than that of KaoLu's Proportional Pressure Regulator and thermocouple gauge, and its accuracy can reach ±0.25% under any vacuum degree. Then for vacuum measurement range of 0.001 to 1mbar (0.1-100Pa) in the short path distiller, you can directly choose a 1Torr film capacitance gauge to meet the full range of vacuum measurement.

If you want to ensure measurement accuracy in the range of 0.1~1Pa, you can also add a 0.1Torr film capacitance gauge. In this way, accurate measurement within the full vacuum range can be covered by two film capacitance gauges with different ranges.
Use super-precision vacuum controller instead of ordinary precision PID controller
In any PID feedback closed-loop control system, no matter how high the accuracy of sensor and actuator is, the final control accuracy needs to be guaranteed by the accuracy of controller. Therefore, an ultra-high-precision PID vacuum controller is used in the solution. This ultra-high-precision PID vacuum controller has 24-bit AD and 16-bit DA, and uses double-precision floating-point operations to reach a minimum output percentage of 0.01%.

This is the industrial PID controller with the highest technical index around the world. Using this vacuum controller can give full play to the precision advantages of Proportional Pressure Regulator actuator and the thin-film capacitance gauge vacuum sensor, and this series of controllers has different models of single-channel and double-channel. The single-channel controller is a programmable PID controller, and its outstanding feature is that it can automatically switch between dual vacuum gauges with different ranges to reach full-range automatic control. The dual-channel controller is a fixed-point controller, and two channels can independently control vacuum degree and temperature.

3. Conclusion

The new vacuum control system optimizes vacuum degree control process of short-range molecular distillation process, and makes the following three improvements to vacuum degree control system:

Proportional Pressure Regulators are used instead of gas mass flow meters to improve the accuracy of the intake air flow regulating actuators.
KaoLu's Proportional Pressure Regulator is used to improve the accuracy of vacuum measurement.
The vacuum controller is used to replace the traditional PID controller, which improves the PID control accuracy and expands the control function, which can reach automatic switching of dual sensors and simultaneous control of two process parameters.

In short, through the above improvements, vacuum degree control level of short-range molecular distillation process can be greatly improved. Through a large number of assessment tests and practical applications, it has been proved that this solution is very mature and can easily reach ±0.5% control within the full vacuum range. If KaoLu's Proportional Pressure Regulator is used, this solution can further reach a control accuracy of ±0.1%.

If you want to get further information, please refer to our website

Question 14

Automated Barometric Chamber for Entomology Experiments: the Precise Control Solution of Positive Pressure and Negative Pressure

Accepted Answer

1. Why environment would affect insects?

The environment in which various organisms live affects and changes their lifestyles. These environmental conditions mainly include factors such as wind, rain, soil composition, radiation, temperature, and atmospheric pressure. Numerous studies have shown that adverse weather conditions often associated with changes in air pressure, can affect reproduction, feeding and habitat. Other Factors are insect behaviors. Such as flight, spawning, parasitism, mating, and singing are affected by air pressure.

For the study of correlation between insect behavior patterns and air pressure, the currently commonly used method is to observe and record under natural conditions, which has problems such as low efficiency, long cycle and inaccuracy.

Some laboratories use manually controlled air pressure chambers, but there are problems such as inaccurate air pressure control, inability to accurately imitate the slow change process of natural pressure for a long time, and the controllable air pressure change range is very narrow. Recently, one of our customers hopes to automatically control the positive and negative pressures of air pressure chamber used for insect research. The specific requirements are as follows:

Air pressure control range: Based on a standard atmospheric pressure, it can reach the precise control of air pressure in air pressure chamber within the positive and negative pressure range. That is, the absolute pressure in air pressure chamber can be precisely controlled within the range of 90kPa~110kPa.
Air pressure control form: It can automatically simulate the slow changing process of natural atmospheric pressure which means that air pressure change can be controlled according to change direction and speed set arbitrarily. Air pressure can be accurately and constant at any set point. In a word, the entire air pressure change process can be precisely controlled according to broken line form set arbitrarily.
Air pressure control accuracy: within the range of 90kPa~110kPa, the control accuracy at any pressure is less than ±0.1%.

In order to meet the above requirements put forward by customers, this article will propose a corresponding high-precision air pressure program control solution. The solution will adopt the method of dynamic balance of gas in and out of closed container, use high-pressure gas cylinders as high-pressure gas source, vacuum pump for pumping, and use the dual-channel vacuum pressure program controller to collect pressure sensors and simultaneously control the opening of inlet and outlet Proportional Pressure Regulator. In this way, it can reach accurate control and long-term stable operation of any set pressure change program.

2. How to solve the problem?

From the above requirements put forward by customer, it can be seen that pressure control of air chamber for study of insect behavior is a typical problem of automatic control of positive and negative pressure.
This automatic control of positive and negative pressure needs to solve the following problems:

How positive pressure (pressure) and negative pressure (vacuum) are formed
Positive and negative pressure automatic control methods and control instruments
Selection of pressure sensor
Selection of Proportional Pressure Regulator

In order to solve the above problems, the specific solution proposed in this article is shown in Figure 1.

First, the solution uses a dynamic balancing method to create positive and negative pressure in air chamber. As shown in Figure 1, a high-pressure gas source is arranged at air inlet end on left side of air pressure chamber. A vacuum pump is arranged at air outlet end on right side of air pressure chamber. If air intake flow is greater than the exhaust flow, a positive and negative pressure would be formed. Then, air intake and outlet flow is regulated by inlet and outlet valves.

The adjustment and control of positive and negative pressure of air chamber is a typical split-range control case. The output of one regulator is used to simultaneously drive several actuators with different working ranges. The regulator here is KaoLu's Proportional Pressure Regulator shown in Figure 1, and actuators with different working ranges are air intake valve and exhaust valve.

It can be seen that the Proportional Pressure Regulator is required to have a split-range control function. Proportional Pressure Regulator is required to have the function of simultaneously adjusting the opening of the intake valve and exhaust valve for different working ranges (positive pressure or negative pressure range)

In addition, in order to ensure control accuracy, the selected Proportional Pressure Regulator is an ultra-high-precision PID regulator, with 24-bit AD and 16-bit DA converters, and double-precision floating-point arithmetic functions, and minimum output percentage can reach 0.01%.

In order to ensure that pressure change in air pressure chamber reaches the control accuracy proposed by customer, it is also necessary to select a high-precision pressure sensor. If the control accuracy of ±0.1% is to be reached, the measurement accuracy of pressure sensor needs to reach ±0.05%. Similarly, the pressure control accuracy also depends on the adjustment accuracy and response speed of air intake and exhaust valves.

For air pressure chambers used in entomological experiments with smaller volumes, the valves are required to have an ultra-high response speed. Here, we use KaoLu's Proportional Pressure Regulator driven by a stepping motor. The full opening speed of Proportional Pressure Regulator is 0.8 seconds, with ultra-low vacuum leak rate and 7bar positive pressure resistance. A series of Proportional Pressure Regulator with different port diameters are available to meet automatic air pressure chambers of different specifications and sizes. The most important thing is that Proportional Pressure Regulator can be directly driven by an analog signal of 0~10V , 4~20mA or RS485, and it has high linearity, repeatability and fast speed.

After the above selection and configuration, according to solution shown in Figure 1, the configured Proportional Pressure Regulator is shown in Figure 2. Proportional Pressure Regulator shown in Figure 2 is an integrated instrument, and all components including the numerical Proportional Pressure Regulator, controller, power supply, etc. are integrated and installed in controller. There are push-in connectors on both sides of controller to connect air/air pump. There is a quick-plug connector for connecting air inlet/outlet of air pressure chamber on the back of controller. There are also special interfaces for connecting pressure sensor, computer communication and working power supply.

The pressure sensor is directly installed on side wall of air pressure chamber in an external form, which can detect the change of vacuum pressure in air pressure chamber more accurately. The signal and power leads from pressure sensor connect to the corresponding connectors on back of vacuum pressure controller. This form of external pressure sensor is more expandable, and different pressure sensors can be selected according to vacuum pressure control range of different air chambers or airtight containers, and it is easy to replace and install.

Computer communication adopts RS 485 interface with standard MODBUS protocol, so it can be connected to computer. Through the control software that comes with the PID controller, the computer can directly control PID regulator, and use the software interface to set up and run control program, and collect, store and display the whole process result curve of control process.

3. Conclusion

As a standard vacuum pressure control instrument, the above-mentioned positive and negative pressure precision control solution not only meets the requirements of automatic air pressure chambers for entomological experiments, but also has strong applicability and scalability, mainly reflected in the following several aspects:

Vacuum pressure control in a wider range can be carried out, the absolute pressure control range can cover 0.1Pa~0.5MPa, and it has a very wide positive pressure and negative pressure control range.
Various forms of control can be reached in the range of positive and negative pressure, such as separate control of positive pressure, separate control of negative pressure (vacuum degree), and continuous control of positive and negative pressure. All controls can be controlled by fixed points or by Automatic control of polyline programming programs.
More functions can be expanded, such as air pressure control under different gases or mixed gases with different gas contents, and can also be used to control other environmental variables at the same time, such as temperature, humidity and light.

In short, the standardized vacuum pressure controller can meet pressure program control of various laboratory air chambers, and has a control accuracy of more than ±0.1%. At the same time, KaoLu's Proportional Pressure Regulator is also suitable for precise air pressure control of various vacuum pressure vessels (such as climate chambers, climate environment test chambers, vacuum atmosphere furnaces, vacuum drying ovens, rotary evaporators, precision low-temperature containers, freeze drying ovens and various spectrometers, etc.) It can greatly improve the degree of automation and control precision.

Do you want to know more about KaoLu's Proportional Pressure Regulator? Check our website for more details!

Question 15

KaoLu's Electronic Vacuum Regulator Low Pressure Control Performance Assessment Test

Accepted Answer

1. Introduction of KaoLu's Electronic Vacuum Regulator

In vacuum pressure control process of some mechanical grasping and closed cavities, it is necessary to directly use regulating valve to reach the precise adjustment and constant control of vacuum degree. KaoLu QKL series is a kind of this vacuum regulating valve, which is manually operated and adjusted. The nominal vacuum adjustment range is absolute pressure 1.3~100kPa (gauge pressure -100~-1.3kPa).

In order to have a deeper understanding of KaoLu's Electronic Vacuum Regulator, this article introduces the short-term assessment test of vacuum degree control stability of this Electronic Vacuum Regulator.

2. Let's Talk About KaoLu's Electronic Vacuum Regulator!

The action principle of KaoLu's Electronic Vacuum Regulator is as follows: When the handwheel turns clockwise, the spring force is set to push the diaphragm and the main valve downward, the VAC side and the SET side are connected, and vacuum degree of SET side changes to direction of low pressure.

Then, the vacuum pressure on SET side enters vacuum chamber through air path, acts on top of diaphragm, and is balanced with the compression force of setting spring, so vacuum pressure on SET side is kept constant. If air pressure on SET side is lower than set value, the setting spring force and pressure on SET side of vacuum chamber are out of balance. The diaphragm is pulled up, the main valve core is closed, air suction valve core is opened, and air flows into SET side. When the compression force and air pressure on SET side are balanced, the vacuum pressure on the SET side is kept constant.

The nominal vacuum adjustment range of KaoLu's Electronic Vacuum Regulator is absolute pressure 1.3~100kPa (gauge pressure -100~-1.3kPa).

3. To Examine The Function of KaoLu's Electronic Vacuum Regulator

In order to assess the performance indicators of the KaoLu's Electronic Vacuum Regulator, the assessment test device built is shown in Figure 2, which mainly includes a vacuum pump, a vacuum chamber, a capacitance vacuum gauge, a high-precision data collector and a computer. In order to accurately measure the vacuum adjustment range and the stability of control, each component in assessment test device has some characteristics:

The vacuum chamber is a closed chamber, that is, the leakage rate is very low, and the vacuum pipeline only has two interfaces, a vacuum gauge and a regulating valve.
The vacuum degree measurement adopts a thin-film capacitor vacuum gauge with high precision. The accuracy is 0.25% under any vacuum degree, and the range of vacuum degree measurement is 1 to 1000Torr.
In order to make full use of measurement accuracy of capacitance vacuum gauge, the assessment device is equipped with high-precision data collector, and uses supporting software to communicate with computer to collect and display vacuum measurement curve in real time. In order to ensure the acquisition accuracy and speed at the same time, the sampling interval is set to 4s.
In order to avoid pollution of vacuum pump oil to pipeline and vacuum regulating valve, the assessment device is specially equipped with a dry pump to ensure a varierty of pollution.

4. Conclusion

From the above short-term assessment test results, the following conclusions can be drawn:

The adjustment and control time is affected by volume of vacuum chamber, the smaller the volume, the faster the vacuum degree will stabilize.
KaoLu's Electronic Vacuum Regulator reach the nominal technical index -100kPa.

Please refer to KaoLu's website for further information.

Question 16

KaoLu's High Precision Proportional Pressure Regulator with PID Controller

Accepted Answer

1. Introduction of KaoLu's Proportional Pressure Regulator

In the biomedicine and semiconductor industries, there are often high requirements for micro-positive pressure, requiring pressure control to reach an ultra-high precision of 0.1% under a micro-positive pressure slightly higher than a standard atmospheric pressure. At present, there are two problems in the micro positive pressure ultra-high precision control technology:

Many micro-positive pressure controls directly use electric proportional valves, but limited by the built-in pressure sensor and controller precision. Electric proportional valves cannot meet the ultra-high precision pressure control requirements at all.
In the field of measurement and calibration testing, in order to improve the precision of pressure control, an ultra-high-precision split structure is often used, that is, an independent pressure sensor, data collector, data controller and microcomputer processor are used to form a closed-loop control loop. Although this method can achieve very high accuracy (such as 0.01%), the overall cost is high and it is not suitable for industrial and instrumentation industries.

For this reason, this article introduces KaoLu's Proportional Pressure regulator. By connecting an ultra-high-precision pressure sensor and PID controller, while taking advantage of KaoLu's Proportional Pressure Regulator, the pressure control accuracy is greatly improved, and overall cost is kept at a low level.

2. How to solve the problem?

As shown in Figure 1, the specific solution is based on KaoLu's Proportional Pressure Regulator. A closed-loop PID control loop is formed by connecting a higher-precision pressure sensor and a PID controller externally to reach micro-positive pressure control with ultra-high precision of 0.1%.

The characteristic of this solution is that KaoLu's Proportional Pressure Regulator is used as actuator, and ultra-high-precision control requires an external higher-precision pressure sensor and PID controller.

According to our previous assessment tests and control process data analysis, we have come to the conclusion that to reach a control accuracy of 0.1% for industrial integrated PID controller instruments, the following technical indicators need to be met:

The external sensor must have an ultra-high precision of more than 0.1%.
The external actuator (proportional pressure regulator) also needs to have high precision, but it does not necessarily require ultra-high precision of 0.1%. The overall accuracy can reach 1%, which is mainly due to the rate indicator of proportional pressure regulator used.
The number of ADC bits of PID controller needs to be at least 16 bits, preferably 24 bits.
The floating-point operation of PID controller must ensure that output percentage has an adjustment capability of 0.01%~0.05%.
The number of DAC bits of PID controller needs to reach at least 14 bits, and the best is 16 bits.

From the above requirements on technical indicators and test results, it can be seen that in order to reach ultra-high precision pressure control, on the premise that external pressure sensor, proportional pressure regulator and PID controller ADC meet the accuracy requirements. The DAC control output of PID controller and Floating point operations must also have sufficient precision, and the minimum percentage of PID controller output must be capable of 0.01%.

Based on the above analysis, the hardware configuration in solution mainly includes the following parts:

Pressure sensor: the accuracy is 0.05%, the range is absolute pressure 0.1~1MPa, and the corresponding voltage output is 0~10V.
KaoLu's Proportional Pressure Regulator: The maximum input gas pressure is 300kPa, the set pressure control range is 0~100kPa, and the external analog quantity is to evaluate the effectiveness of above solution.
According to the above configuration, an evaluation test device is built, as shown in Figure 2. The input signal is 0~10DVC, the linearity is less than ±0.3%FS, the repeatability is less than ±0.2%FS, and the hysteresis is less than 0.3%FS.
PID controller: ADC is 24 bits, DAC is 16 bits, ADC range is 0~10V, DAC range is 0~10V, and the minimum output percentage of analog control is 0.01%.

3. Examine KaoLu's Proportional Pressure Regulator

In order to assess the effectiveness of above solutions, an assessment test device was built according to the above configuration, as shown in Figure 2.

In order to effectively collect, monitor and store the assessment test data, the following content is added to the assessment test device in Figure 2:

Multi-channel data collector
High-pressure pipe fittings: It is used as pressure vessels, and connected with pressure sensors and proportional pressure regulator.
Computer: It is used to communicate with PID controller and data collector. It can also install and run corresponding software programs to control, data acquisition, curve display and data storage of PID controller and data collector.

4. Conclusion

Through the above solution and assessment test results, it is proved that this solution is fully capable of reaching 0.1% ultra-high precision pressure control for micro positive pressure. The specific conclusions are as follows:

If you're interested in our Proportional Pressure Regulator, please visit our website!

Question 17

The Basic Concept of Measuring Proportional Pressure Regulator and Pressure Sensor

Accepted Answer

1. What Is Proportional Pressure Regulator and Pressure Sensor?

In vacuum pressure control process, various vacuum pressure sensors and KaoLu's Proportional Pressure Regulator are often used. These sensors and KaoLu's Proportional Pressure Regulator generally mark various contents in the accuracy index, such as linearity, hysteresis, repeatability and sensitivity, etc., and some only give a general accuracy index. The definitions of these accuracy indicators often represent different meanings, which must be clearly distinguished when we use, which is especially important for the precise measurement and control of vacuum pressure.

This article would introduce the basic concepts of parameters such as linearity, hysteresis, repeatability and sensitivity for various sensors and KaoLu's Proportional Pressure Regulator used in vacuum pressure control process, and explains how to use these precision indicators effectively and correctly.

2. Basic Concept Regarding Accuracy

International Electrotechnical Commission (IEC) defines accuracy as "the maximum positive or negative deviation from a specified characteristic curve observed when a device is tested by a specified procedure under specified conditions". However, the definition of accuracy for a pressure sensor and Proportional Pressure Regulator is much more complicated because sources of error can include non-linearity, hysteresis, repeatability, temperature, zero balance, calibration, and humidity effects.

Accuracy has a big impact on the cost of pressure sensors and Proportional Pressure Regulator, and more importantly, the quality or efficiency of their measurement process. When selecting sensors and Proportional Pressure Regulator, it is important to understand which factors determine accuracy. Although there is no single standard definition for the accuracy of pressure transducers and Proportional Pressure Regulator, there is an IEC standard that defines the factors that make up accuracy. IEC 61298-2 specifies that accuracy must include non-linearity, hysteresis and repeatability. The error sources related to accuracy and their corresponding measurement methods will be introduced item by item below:

2.1 Non-Linearity and Its Measurement Method

Non-linearity is also often referred to as linearity, straightness, or linearity error. Non-linearity refers to the deviation between electrical signal output curve of pressure sensor and the specified straight line within the measured pressure range. The deviation between pressure output curve of KaoLu's Proportional Pressure Regulator and the specified straight line within input electrical signal range, which means that the output of linear device deviates degree of desired performance.

A common method for calculating linearity error is the method of least squares, which mathematically provides a best-fit straight line for the data points, as shown in Figure 1. Another way to define linearity error is terminal baseline linearity, as shown in Figure 2. Terminal linearity is determined by drawing a straight line (L1) between two terminal data points on the output curve. Next draw a vertical line from line L1 to the data points on the output curve. Select the data points to reach the maximum length of the vertical line. The length of the vertical line represents the terminal straight line linearity error. The terminal linearity is about twice as good as the best-fit linearity.

Non-linearity is usually expressed as a percentage of full-scale output, and the unit is %FS, and the corresponding non-linearity error = range × non-linearity. If the measuring range is 1MPa and the non-linearity is 0.05%FS, the nonlinear error is: 1MPa×0.05%=0.5kPa.

To determine the non-linearity of pressure transducers and Proportional Pressure Regulator, measurement data must be collected first. The typical way to do this is to apply pressure at regular intervals over the range zero to full scale pressure, or to load an analog signal at regular intervals over the zero to full scale analog electrical signal range, and at each pressure and analog signal set point of measured output.

The more pressure points, the more accurate the nonlinear calculation. Once the measurements are recorded, it is necessary to determine which line to compare the test data. There are several different lines that can be used to calculate the linearity error of a pressure sensor, the following are the three most widely used:

The suitable fit straight line

Terminal line
While this will not produce the smallest error, it is very useful for revealing the actual linearity performance of sensor. When connecting a pressure sensor to a measuring instrument, the output of pressure sensor is converted to a reading by setting zero and full scale pressure and assuming a straight line between two points. This is the easiest and most convenient calibration method.
Perfect straight line
The output of each measurement point is directly compared with the output of a higher-precision pressure sensor. For example, a 0-10V output in the range of 0-5bar will accurately generate a 2.5V voltage signal at 1.25bar. Perfect straight lines are rarely used in pressure transducers because they usually do not include trimming components for adjusting zero offset and span gain. Also, not two pressure sensors are exactly alike. They all have different zero and span characteristics that can have deviations that are much greater than linearity errors.

Therefore, for a batch of pressure sensors, the linearity error specification needs to be larger to include variations in zero and span characteristics. However, there are still some applications that require a perfectly straight line, like in applications where a failed pressure sensor needs to be replaced directly, without any calibration of zero and span settings.

2.2 Repeatability

The repeatability error is the deviation of output reading when any given input pressure is continuously measured multiple times under the condition that other conditions remain unchanged. For KaoLu's Proportional Pressure Regulator, it is the deviation of pressure output reading when any given input voltage signal is continuously measured. Repeatability errors can be divided into repeatability errors and non-repeatability errors.

Repeatable error refers to predictable uncertainties that can be characterized or removed from measurements with additional analog conditioning or microprocessor-based electronics. Typically, for pressure transducers and Proportional Pressure Regulator, the repeatable errors are linearity and thermal zero/span offset errors.

Pressure sensor repeatability error sometimes includes short-term repeatability error, which indicates the stability of pressure sensor over a series of pressure cycles, obtained by collecting a second and third calibration point shortly after the first collection.

Compare each pressure point to the same point in cycles 2 and 3 to determine repeatability error, that is, compare the same pressure point for each pressure cycle to first cycle to determine the amount of change. Short-term repeatability rarely shows up as a separate error on a specification sheet, and is usually included in combined non-linearity, hysteresis, and repeatability errors.

Non-repeatable errors are complex measurement uncertainties that cannot be predicted and characterized, such as hysteresis, short-term repeatability, and long-term stability. Non-repeatable error varies with pressure changes, number and frequency of pressure cycles, and thus varies from application to application. Long-term stability is a measure of how well the output signal drifts over time under normal operating conditions.

Long-term drift is expressed as a percentage of full scale over a period of time, typically 12 months. Sometimes zero and span long-term stability are quoted alone, especially if one is much larger than the other. Long-term drift is really just a number comparing one technology to another and cannot be relied upon for a particular application. This is because the number of pressure cycles, temperature cycles, vibration and shock a pressure sensor will experience during its lifetime is not easy to predict.

All of these factors affect the performance of a pressure sensor to varying degrees depending on amplitude and frequency. In short, in the accuracy declaration of general pressure sensors and Proportional Pressure Regulator, the repeatability index generally refers to repeatability, and repeatability here generally refers to short-term repeatable errors.

2.3 Hysteresis

Hysteresis error is usually expressed as a combination of mechanical hysteresis and temperature hysteresis. Mechanical hysteresis is the deviation of output at a certain input pressure as that input approaches first with increasing pressure and then as pressure decreases. Similarly, temperature hysteresis is the deviation of output at an input before and after a temperature cycle. Hysteresis is represented as a combination of two effects as shown in Figure 3.

Temperature hysteresis is unlikely to be mentioned in pressure sensor specifications, so it is difficult to determine whether it is included in the overall temperature error. If temperature hysteresis is indicated, it will be expressed as a percentage of full scale over the compensated temperature range.

The individual measurement hysteresis error is calculated by comparing the output signal at the same pressure point in a set of increasing and decreasing pressure data. However, when lags are calculated with other data to calculate overall accuracy performance, each point is considered individually and compared to the best straight line.

The hysteresis of pressure transducers and Proportional Pressure Regulator is measured by applying a pressure or control voltage from zero to full scale, usually stopping at 5 equidistant steps without overshooting the measured value. The process is then repeated in the opposite direction from full scale to zero.

To ensure the best results, it is important to carefully control the pressure or voltage so that it does not exceed the point of measurement, as changes in the direction of applied pressure and voltage introduce secondary hysteresis effects.

Hysteresis error will be the deviation in value between increasing and decreasing pressure or voltage values measured at the same step point. The percent hysteresis can then be determined by taking the maximum deviation and dividing it by the full scale pressure. As shown in Figure 3, the specific calculation process is:
Hysteresis % = ((Vp1 - dVp1)/FRO) × 100
Vp1 = Voltage output at pressure P1 during pressure increase.
dVp1 = Voltage output at pressure P1 during decompression.
FRO = Voltage output at full scale pressure

2.4 Resolution and Sensitivity

Resolution refers to the ability of a sensor to perceive small changes in a measured. That is to say, if the input quantity changes slowly from a certain non-zero value, when input change value does not exceed a certain value, the output of sensor will not change which means sensor cannot distinguish the change of input quantity. Its output changes only when input quantity changes beyond the resolution.

The resolution of each point of sensor in the full-scale range is usually not the same, so the change value of input quantity that can cause a step change in output quantity in the full-scale range is often used as an index to measure the resolution, that is, the resolution = the measured change of output Quantity/measured variation. Sensitivity refers to the ratio of voltage output change ΔV to the pressure input change ΔP under the steady-state working condition of pressure sensor, that is, sensitivity = response change/measured change.

Sensitivity is the slope of output-input characteristic curve. If there is a linear relationship between the output and input of pressure sensor, then the sensitivity is a constant. Otherwise, it will vary with the amount of input.

When the output and input of sensor have the same dimension, the sensitivity can be understood as the magnification. Generally speaking, the higher the sensitivity, the better the resolution, and higher measurement accuracy can be obtained. However, the higher the sensitivity, the narrower the measurement range and the worse the stability.

Resolution and sensitivity indicators are very important in pressure control application of Proportional Pressure Regulator, which often determines the final precision of it. Especially in the pressure control process of an external PID controller, the higher the sensitivity of Proportional Pressure Regulator, the more the Proportional Pressure Regulator can receive minimize control voltage signal output by PID controller, so as to reach higher precision pressure regulation and control.

3. The Relationship Between Total Error and Accuracy

Accuracy is usually the main factor to consider when choosing to use pressure transducer and Proportional Pressure Regulator. It should be noted that the accuracy is only a part of the total error, and the total error sometimes appears in the technical indicators of sensor and Proportional Pressure Regulator. The total error depends on various factors, such as the usage condition of sensor, etc. As shown in Figure 4, the total error mainly includes three aspects: adjustable error, accuracy and temperature effect.

As shown in Figure 4, the adjustable error consists of zero and span errors. Adjustable errors can be easily identified and adjusted. These two indicators of pressure sensor and Proportional Pressure Regulator are generally calibrated before leaving the factory and during calibration process.

Long-term stability which is also known as long-term error or long-term drift, is the cause of zero and span errors during operation. This means that these two adjustable errors may reappear or even "worse" after using sensor for a long time. Through calibration and subsequent adjustments, this long-term drift can be corrected again.

The temperature effect error of total error is that temperature fluctuation will affect the measured value of pressure sensor and Proportional Pressure Regulator. There is also an effect known as temperature hysteresis. In general, hysteresis represents the systematic deviation from measuring the same point through the forward and reverse paths. Regarding temperature hysteresis, the hysteresis here describes the difference (ie, deviation) of output signal at a certain temperature when a specific temperature increases or decreases.

4. Conclusion

In the practical application of pressure sensors and KaoLu's Proportional Pressure Regulator, the primary problem is what should be the most concerned when selecting sensors and KaoLu's Proportional Pressure Regulator, which requires specific analysis of specific situations. Since the adjustable error has been corrected by the manufacturer, it only plays a secondary role. In addition, pressure sensors usually require regular calibration and debugging during use.

Therefore, in practical applications, precision and thermal effects often play a decisive role. The key question is: is it being used under controlled conditions? This means that when measuring near the reference temperature during calibration (typically 25°C), the temperature effect is essentially negligible, and the main content of the total error is only the accuracy effect. However, when measuring and controlling pressure over a wide temperature range, temperature effects become very important.

Question 18

Advantage of Electronic Air Pressure Regulator

Accepted Answer

Introduction

The QKL series of electronic air pressure regulators provides a high level of accuracy and control. The patented design of this product allows it to operate independently from the load, flow, and air consumption. This means you can use your compressor more flexibly than ever before. All the QKL series are electronically controlled, with the pressure set via digital display. The microprocessor controller enables you to set your desired operating pressures in mbar with a resolution of 1 mbar. This can be easily adjusted as required by way of simple keypads.

The patented design of QKL series offers an extremely accurate pressure control independent

In contrast to conventional pressure regulators, the patented design of QKL series offers an extremely accurate pressure control independent of load, flow and air consumption.

The QKL series is a high resolution, high speed, high accuracy pressure regulator that can be used in a wide range of applications such as water treatment systems and industrial air compressors.

Use the compressor more flexibly

This means you can use your compressor more flexibly than ever before. That's because it enables you to adjust the pressure to suit your application, control it more accurately and therefore use it more efficiently. You can also save money by using less energy and save space by using a smaller compressor.

When it comes to air tools, there are several reasons why electronic pressure regulators are so well suited for use with them:

They provide a constant supply of compressed air at a user-selected pressure level.
They don't require any adjustments or maintenance when used over extended periods of time.
Their compact size saves space in toolboxes or on workbenches.

All the QKL series are electronically controlled, with the pressure set via digital display.

The QKL series are electronically controlled, with the pressure set via digital display. The pressure can be adjusted by way of simple keypads and can be set in 1 mbar increments or 0.1 mbar increments depending on the model.

The microprocessor controller enables to set of operating pressures in mbar with a resolution of 1 mbar.

The microprocessor controller enables you to set your desired operating pressures in mbar with a resolution of 1 mbar. This makes it possible to adjust the pressure precisely according to your current needs. The digital display shows you the status of the air supply.

Easily adjust as required by way of simple keypads

The electronic air pressure regulator is a great solution for many different applications. This can be easily adjusted as required by way of simple keypads. The electronic air pressure regulator has an adjustable pressure range between 0 to 20 bar, which makes it flexible and can be used for many applications. This product is useful for various types of compressors such as water pumps, refrigeration compressors, oil coolers and server room AC units.

Electronic air regulators provide high levels of accuracy and control

Electronic air regulators provide high levels of accuracy and control. The digital display makes it easy for you to read the current pressure and setpoint, as well as the output voltage of the compressor. This allows you to precisely set your desired pressure, making it easier than ever to calibrate according to your specific application. The microprocessor controller also gives you flexibility in terms of how often you need to adjust or reset a specific setting on your regulator.

You can use an electronic air regulator with compressors that operate at pressures below 45 PSI (3 BAR), although higher output voltages may be required depending on what type of motor is used within this range. For example: If 14 VAC is required then a 24 VDC valve must be used instead since this would provide approximately twice as much power than available through household current sources (120 VAC).

Conclusion

We hope that this blog post has given you a better understanding of how to use electronic air regulators. If you would like more information about our products, please feel free to contact us at any time!
Please visit our link on proportional pressure regulator!

Question 19

Electronic Flow Controller Features Explained

Accepted Answer

Introduction of Electronic Flow Controller (EFC)

EFC is an electronically controlled regulator that provides excellent repeatability over a wide flow range. It features a fast flow response time and a higher flow rating than do mechanical flow controllers. The EFC can be used in automatic control, high resolution and repeatability applications where count-by-count control is necessary.

Because the EFC is an electronically controlled regulator, the opening of the control valve has been increased to provide faster response times. The EFC is ideal for use in critical applications where count-by-count control is necessary.

Its high resolution and accurate repeatability make it ideal for use in critical applications where count-by-count control is necessary.

The EFC's high resolution and accurate repeatability make it ideal for use in critical applications where count-by-count control is necessary. Examples of critical applications include:

Chemical process systems requiring extremely precise mixing or dilution rates, such as those used in the semiconductor industry.
Food processing plants where precise amounts of ingredients are added to each batch, such as chocolate manufacturers.

EFCs are also used in non-critical applications, such as water treatment plants that require consistent measurement of flow rate over time periods longer than a day but not on the order of years or decades (as would be required for nuclear power plant cooling towers).

It also features a fast flow response time and a higher flow rating than do mechanical flow controllers.

The EFC is a high-tech, electronically controlled regulator that provides excellent repeatability over a wide flow range. It has a fast flow response time and a higher flow rating than do mechanical flow controllers.

The Electronic Flow Controller (EFC) is a high-tech, electronically controlled regulator that provides excellent repeatability over a wide flow range.

The Electronic Flow Controller (EFC) is a high-tech, electronically controlled regulator that provides excellent repeatability over a wide flow range. The EFC has a faster response time than mechanical flow regulators and offers greater rangeability. The remote display indicates both the actual and setpoint values in real time. It also features an auto-lock feature to prevent accidental movement of the knob when transporting or storing your machine.

Automatic control, high resolution, high repeatability, compatible with air/water/oil

Before we get into the important details of what makes an Electronic Flow Controller (EFC) different from other types of flow controllers, let's look at some of the benefits that make it an attractive choice:

Automatic control - Your EFC does not require manual adjustment. Once set up and programmed, it runs on its own to provide consistent and accurate process control.
High resolution - You can program a full range of values from 0% to 100%. The resolution will depend on your device, but typically they have up to 8 bits worth of precision (256 possible settings). This means you can fine-tune your system with extremely accurate measurements at very low flow rates or high ones; anywhere in between is no problem either!
High repeatability - With any kind of controller, repeatability refers to how closely two successive measurements will correspond with one another over time as long as input conditions remain constant. For example, if you were using a manual valve for open/close control instead and wanted 20 mL/min flow rate adjusted by hand every second based on some meter readings from upstream or downstream equipment (you would do this because manually adjusting valves is easier than programming instructions into a computer), then each successive measurement would result in slightly different values because there would be human error involved each time--maybe someone accidentally moved their finger too fast when setting up their positioner valve housing! But once again we're talking about automatic control here...and if your EFC has been configured properly then every value should match up perfectly every single time regardless how many times per second data needs updating via PLC communication link!

Features

The EFC is fully automatic, with a high resolution and high repeatability for stable and accurate control. It is compatible with air/water/oil users have the option to select the best working fluid for their application.

Low cost, easy to use electronic flow controller

The electronic flow controller is a low-cost, easy-to-use device that can be used in any application where it is necessary to control the flow of fluid through a pipeline. It works by measuring the pressure drop across its sensing element and then transmitting this information back to your controller via an analogue signal. The device uses very little power and has no moving parts, making it ideal for environments where space and reliability are at a premium.

Higher resolution

The EFC is capable of providing a flow control resolution of 0.1% of the full-scale flow rate, or 1% of the full-scale flow rate. In addition, the EFC provides closed loop proportional control that can be commanded from 0% to 100%. The minimum step size is 0.1% (or 1%) of full scale for proportional control and 0.01% (or 1%) for integral action.

Faster response time

A faster response time means that the EFC can respond more quickly to changes in flow, which can be critical when it comes to medical applications.
Better repeatability and higher resolution means that the EFC can more easily maintain consistent flow rates over time with less drift.

Better repeatability

Repeatability is the ability to reproduce a value multiple times. Repeatability is a measure of how well a process can be reproduced and it's important for manufacturing and quality control, as well as scientific research. For example, if you are trying to test whether your new sunscreen blocks UV rays or not and you want to determine whether it works by measuring how much UV light passes through the solution, you would need to have consistent measurements in order for them to be useful.

Greater rangeability

In a mechanical controller, there is always some flow loss. This is due to the pressure drop that occurs in the control valve and piping from the pump. In contrast, an EFC can control flow within one percent accuracy with no pressure drop. Additionally, EFCs have a faster response time than their mechanical counterparts because they use electrical signals rather than pneumatic ones to open and close valves (which require power).

Conclusion

The Electronic Flow Controller (EFC) is a high-tech, electronically controlled regulator that provides excellent repeatability over a wide flow range. Automatic control and high resolution make it ideal for use in critical applications where count-by-count control is necessary. Its fast flow response time also makes it ideal for high flow applications such as cooling towers and process water systems. The EFC has been approved by the factory for use with air/water/oil based fluids at pressures up to 100 psi and temperatures up to 400°F (204°C).

Question 20

Solution of High Precision Vacuum Pressure (Positive and Negative Pressure) Control for Double Layer Glass Reactor

Accepted Answer

1. What is Double-layer Glass Reactor?

The double-layer glass reactor is designed with double-layer glass. The inner layer can be put into the reaction solvent for stirring reaction, and the interlayer can be passed through different cold and heat sources (refrigerated liquid, hot water, or hot oil) for cyclic heating or cooling reaction.

In the airtight glass reactor under the set constant temperature conditions, the stirring reaction can be carried out under the condition of vacuum to slightly positive pressure according to requirements and the reflux and distillation of the reaction solution can be carried out. It is ideal manufacturing equipment for modern fine chemical factories, biopharmaceuticals, and new material synthesis.

The double-layer glass reactor is the same as other reactors. Vacuum pressure is an important control variable in the reaction process. Different reaction processes often require different vacuum (negative pressure) or pressure (positive pressure) values.

However, in the vast majority of glass-stirred tank reactors at present, there are still serious deficiencies in the accurate control of vacuum pressure, which are mainly reflected in the following aspects:

There is no automatic control method and many of them only rely on the extraction of vacuum pumps and manual intervention, which can only improve the simple vacuum environment but cannot reach control.
Some vacuum pressure controllers also adopt switch-type air intake control mode, the vacuum pressure fluctuates greatly, and often many of them cannot reach program control.
The control method is single, and it is impossible to control the vacuum degree of the full range (1Pa~0.1MPa), and it can only be controlled in a certain range. In addition, most glass-stirred tank reactors do not have micro-positive pressure supply and control capabilities.
Many reactors use butterfly valves or ball valves to control the pumping rate. For smaller glass reactors, the response speed of butterfly valves and ball valves is too slow to reach accurate control of vacuum pressure, especially when the temperature changes. This phenomenon is particularly evident in the reaction process.
Similarly, a vacuum pump with adjustable speed is also used to control the vacuum degree of the reactor. Still, there is also the problem of slow response speed resulting in large fluctuations in vacuum pressure. In addition, only adjusting the pumping rate can only control the range of low vacuum (high pressure) close to one atmospheric pressure, and it is powerless to control the range of higher vacuum (low pressure).
Many reactors have strict requirements for gas (or liquid) parts, requiring sanitary (or food-grade) valves, but most of the current electric control valves cannot meet this special requirement.

In order to solve the above-mentioned problems in the double-layer glass reactor, this article will show you a complete and mature solution, that is, to use KaoLu's Proportional Pressure Regulator and a high-precision dual-channel PID controller, combined with vacuum gauges of different ranges, reactor, vacuum pump, and the positive pressure air source constitutes a closed-loop control loop.

Through the two-way mode of simultaneous control of upstream and downstream (intake and exhaust), automatic programming control of the full range of vacuum and micro positive pressure can be reached, which can reach high control accuracy, and communicate with the host computer to reach central control.

2. Vacuum pressure (positive and negative pressure, high and low pressure) control method

Generally, we take a standard atmospheric pressure (absolute pressure of 1Bar or 750 Torr) as a reference point and stipulate that a pressure lower than the standard atmospheric pressure is a negative pressure or vacuum environment, and a pressure greater than the standard atmospheric pressure is a positive pressure (pressure) environment.

Then, the control of the air pressure working environment of the stirred reactor is a typical vacuum pressure (positive and negative pressure or high and low pressure) control problem.

A typical method of positive and negative pressure control is the dynamic balance method, the principle of which is shown in Figure 1.

The core principle of the dynamic balance method is that the air intake and outlet in the controlled pressure vessel reach a certain set balance. The black arrow line in Figure 1 represents the gas flow direction, and the red arrow line represents the transmission and direction of the electrical signal.

Among them, the high-pressure air source is used as a positive pressure source, and the vacuum pump provides a negative pressure source for pumping air. The process regulator collects the sensor signal and compares it with the set value to adjust the opening of the inlet and outlet valves simultaneously so that the inlet and outlet flow can reach the set value in a balanced state.

There are two main advantages of using the dynamic balance method in vacuum pressure control:

The control range is vast and can reach continuous control from vacuum to positive pressure.
It has high control precision in the full range. When controlling in the high vacuum (low pressure) range, the opening of the exhaust valve is fixed, and the opening of the intake valve is adjusted. When controlling in a low vacuum or slightly positive pressure range, the opening of the intake valve is fixed and the opening of the exhaust valve is adjusted.

3. Solution

The vacuum pressure control device is mainly composed of a high-pressure air source, KaoLu's Vacuum Proportional Pressure Regulator, a vacuum pressure sensor, a PID process regulator, and a vacuum pump.

4. Conclusion

In summary, the vacuum pressure accurate control solution proposed in this article can not only meet the needs of accurate control of vacuum pressure (positive and negative pressure) in double-layer glass reactors but also can be used in other various reactors and rotary skills that vacuum pressure control in.

The solution described in this article is a vacuum pressure control system with a discrete structure. The control system can also be integrated according to the needs and specific reactor design. The electronically controlled valve and PID regulator are integrated into an instrument, which is more convenient for the overall reactor of layout design and kitting.

For more information about KaoLu's Vacuum Proportional Pressure Regulator, please refer to our website.

TECHNOLOGY