Question 1

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 2

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 3

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 4

Technical Scheme of Vacuum Precision Control in Lunar Soil Environment Ground Simulation Test Device

Accepted Answer

Abstract: In the lunar exploration project, it is necessary to collect lunar soil samples in the vacuum environment of the lunar surface. It is necessary to establish a ground test device to simulate the vacuum thermal environment of the lunar surface to test the performance of the sample in vacuum thermal environment. Therefore, the degree of vacuum is required and it can achieve precise control. In this article, a technical scheme for accurate vacuum control using FC series proportional flow control valve is proposed for the ground simulation test device of vacuum thermal environment.

1. Question
In the lunar exploration project, it is necessary to collect lunar soil samples in the vacuum environment of the lunar surface. Therefore, a ground test device needs to be established to simulate the vacuum thermal environment of the lunar surface to test the performance of sample in the vacuum thermal environment, and accurate vacuum control is required to reach precise control. Due to the particularity of the lunar soil, vacuum control in current lunar soil ground model test device still needs to solve the following problems:
(1) Lunar soil and simulated lunar soil samples are generally powdery particles, so the pumping rate in the initial time should be strictly controlled to avoid dust generation.
(2) The current vacuum measurement and control also uses a Pirani vacuum gauge, which makes the matching control system unable to reach precise control of the vacuum, resulting in poor repeatability of the test results.
(3) The lunar soil ground simulation test device is generally small in size, and it has always been difficult to achieve precise control within a wide range of vacuum degrees. The fluctuation of vacuum degree is large, which is also one of the reasons for the poor repeatability of test results. Aiming at the above problems existing in the lunar soil ground model test device, this article focuses on corresponding technical solutions and introduces the detailed implementation process.

2. Technical Scheme
The overall structure of vacuum density control system of lunar soil environment ground simulation test equipment is shown in Figure 1. The whole system mainly includes a vacuum gauge, two proportional flow control valve, a PID controller and a vacuum pump. In order to do the precise control of the full range of vacuum degree, three capacitance vacuum gauges are generally required, and the measurement accuracy of vacuum gauge is 0.25%. In order to match the measurement accuracy of capacitance vacuum gauge, the controller adopts a high-precision PID controller with 24-bit A/D and 16-bit D/A, and the independent dual-channel facilitates the gas flow adjustment and control of the upstream proportional flow control valve and downstream proportional flow control valve control. The precise control of vacuum degree uses dynamic control mode, that is, the downstream proportional flow control valve is adjusted under low vacuum conditions, and the upstream proportional flow control valve is adjusted under high vacuum conditions. This is a typical forward and reverse control method, which can effectively ensure the control accuracy of vacuum degree. In conclusion, with this proven accurate vacuum control scheme, a control accuracy of better than 1% vacuum over the full scale range can be achieved.

For further information on different models of proportional flow control valve, please visit https://www.genndih.com/proportional-flow-control-valve.htm

Question 5

Precision Vacuum Control to Reduce Solvent Loss in Evaporation and Concentration Process

Accepted Answer

Abstract: Aiming at the problems of precision vacuum control to reduce solvent loss in evaporation and concentration process, this article focuses on vacuum evaporation techniques, including the precise control method of vacuum degree, the simultaneous control method of vacuum degree and temperature, and the use of strong resistance of the corrosive electronic valve acts as a vacuum regulator.

1. Question
In the process of solvent extraction, the vacuum evaporation and concentration process is generally used. Since the solvent often has good volatility, the solvent is prone to loss during the vacuum extraction process, and sometimes the loss can reach 5~8%. Therefore, in order to solve the loss of solvent in the evaporation and concentration process, the following problems need to be solved:
(1) The precise control problem of vacuum degree, such as fixed-point control and program control, which is the key to reducing solvent loss.
(2) Simultaneous control problem of vacuum degree and temperature. This is because different vacuum degrees determine the boiling point of the solution. Through coordinated control of vacuum degree and temperature at the same time, the yield of the solvent can be greatly improved.
(3) In the vacuum evaporation and concentration process, many solvents and solutions are often corrosive to a certain extent, which requires the vacuum regulating valve to have good corrosion resistance. In order to solve the requirement of reducing solvent loss in the evaporation and concentration process, this article proposes a solution for precise control of vacuum degree, including the use of electronic flow control valve with strong corrosion resistance as vacuum degree control valves.

2. Solution
For the precise control of vacuum degree and temperature in the evaporation and concentration process, the overall structure of control system is shown in Figure 1.

(Figure 1 Schematic diagram of the vacuum degree and temperature control system structure of the evaporation and concentration process)

The basic principle of precise vacuum control is the dynamic control method, that is, according to the control set value and the measured value of vacuum gauge, the intake flow and exhaust flow of vacuum container are adjusted respectively, so that the flow in and out can reach a dynamic balance. If automatic control is required, PID control algorithms and corresponding controllers are required.

As shown in Figure 1, the accurate control proposal for vacuum degree control in this article adopts a dynamic control method, using an electronic flow control valve to adjust the intake flow, using an electronic ball valve or an electronic needle valve to adjust the exhaust flow, and the vacuum pump is used as a vacuum source. The automatic control of vacuum degree adopts PID controller.

In order to reach the temperature control function at the same time, this scheme adopts a dual-channel PID controller, one channel is used to control the vacuum degree, and another channel is used to control the temperature. This PID control has 24-bit A/D and 16D/A, with 47 input signal forms (thermocouple, thermal resistance, DC voltage), and can be connected to various vacuum and temperature sensors for measurement, display and control. It also has 2 independent measurement control channels, two-wire RS485, standard MODBUS RTU communication protocol.

(Figure 2 FC series electronic needle valve)

In order to reach high-precision adjustment in the vacuum degree control process, an electronic needle valve with fine adjustment by a numerically controlled stepping motor is used, as shown in Figure 2. The hysteresis of this FC series proportional needle valves is much smaller than that of solenoid valves, and has a high-speed response within 1 second, especially the use of fluorine rubber (FKM) sealing technology, which makes the valve have superior corrosion resistance. Equipped with a stepper motor drive circuit module with the numerical control proportional needle valve, it provides the required power supply (24VDC) and control signal (0~10VDC) for the numerical control needle valve, and can also provide direct control of RS485 serial communication.

For larger-diameter air-extraction pipelines, a miniature proportional needle valve is used in this scheme, as shown in Figure 2. This series of proportional needle valve is a small electronic valve. The valve opening can be adjusted continuously according to the change of control signal (0~10VDC). The fastest opening and closing time is less than 7 seconds, and the opening and closing time can also reach less than 1 second. The integrated design of the valve and the valve body reduces external volume and is low in price. It is often installed between the sealed container and the vacuum pump to adjust pumping rate.

In short, through the solution described in this article, the vacuum degree control accuracy in the evaporation and concentration process can reach 1%, and the corresponding temperature control can also be carried out. The vacuum regulating valve has super corrosion resistance, which can effectively reduce the loss of solvent concentration during the vacuum evaporation process.

Question 6

Proposal for Vacuum Precision Control in Low Pressure Carburizing (LPC) Process

Accepted Answer

Abstract: In order to meet the requirements of precise control of vacuum degree in low-pressure carburizing process (vacuum carburizing), corresponding solutions are proposed in this article, including adding a gas mixing tank for permeate gas mixing, using upstream and downstream dynamic vacuum level control methods and vacuum degree by coordinating the control method with the temperature, the rapid and precise control of the vacuum degree and temperature in the infiltration process can be reached.

1. Question
Low-pressure carburizing, also known as vacuum carburizing, is a process in which a carburizing medium is passed into a high-temperature furnace for rapid carburizing under a low-pressure vacuum state. The vacuum carburizing process can be divided into one-stage type, pulse type and swing type. Among them, the degree of vacuum, temperature and carburizing time will change according to the specific requirement, especially the degree of vacuum will change drastically with the temperature change. Therefore, in the vacuum carburizing process, the following problems need to be solved in terms of vacuum degree control:

(1) The problem of fast and accurate control of vacuum degree, such as fixed-point control, program control and fast pulse control, requires the vacuum control system to have high response speed and control accuracy. Especially to achieve precise control in the full range of vacuum, it is necessary to use different vacuum sensors and corresponding upstream and downstream control modes according to different ranges.

(2) Simultaneous control problem of vacuum degree and temperature. The carburizing is carried out in a high temperature environment, requiring simultaneous control of vacuum degree and temperature.
In order to meet the requirements of precise control of vacuum degree in low-pressure carburizing process, this article focuses on a solution for precise control of vacuum degree, and adopts dual-channel PID control to reach synchronous temperature control.

2. Solution
The overall structure of the vacuum degree and temperature control system in the low pressure carburizing process is shown in Figure 1.

Figure 1 Schematic diagram of the structure of vacuum degree and temperature control system in low pressure carburizing process

The basic principle of precise control of vacuum degree is the dynamic control method, that is, according to the control set value and the measured value of vacuum gauge, the air intake flow and exhaust flow of the carburizing chamber are adjusted respectively, so that the flow in and out can reach a dynamic balance. If automatic control is required, PID control algorithms and corresponding controllers are required.

As shown in Figure 1, the precision control solution for vacuum degree proposed in this article adopts a dynamic control method, using an electronic needle valve to adjust the air intake flow, using an electronic ball valve or an electronic needle valve to adjust the exhaust flow, and the vacuum pump is used as a vacuum source. The automatic control of vacuum degree adopts PID controller.

For different low pressure carburizing processes, the control range of the vacuum degree is 1Pa~100kPa. Therefore, in the specific process, different dynamic control modes need to be adopted for the control in different vacuum degree ranges. For the vacuum degree control in the high vacuum range of 1Pa~1kPa, the upstream control mode of fixed exhaust flow and adjustable intake flow is adopted; for the vacuum degree control in the low vacuum range of 1kPa~100kPa, fixed intake flow and adjustable exhaust downstream control mode of the flow.

As shown in Figure 1, in order to reach the adjustment and control of air intake flow, a gas mixing tank is added to the intake end of carburizing chamber, and a gas mass flow meter is used to distribute various permeated gases into the gas mixing tank. The gas flows through the electronic needle valve for flow regulation and control.

In order to reach the temperature control function at the same time, this scheme adopts a dual-channel PID controller, one channel is used to control the vacuum degree, and the other channel is used to control the temperature. This PID control has 24-bit A/D and 16-bit D/A, with 47 input signal forms (thermocouple, thermal resistance, DC voltage), and can be connected to various vacuum and temperature sensors for measurement, display and control of 2 independent measurement control channels, two-wire RS485, standard MODBUS RTU communication protocol.

Figure 2 FC series electronic needle valve

In order to reach high-precision adjustment in the vacuum degree control process, an electronic needle valve with fine adjustment by a numerically controlled stepping motor is used, as shown in Figure 2. The hysteresis of FC series of needle valves is much smaller than that of solenoid valves, and has a high-speed response within 1 second, especially the use of fluorine rubber (FKM) sealing technology, which makes the valve have superior corrosion resistance. Equipped with a stepper motor drive circuit module with the numerical control electronic needle valve, it provides the required power supply (24VDC) and control signal (0~10VDC) for the numerical control needle valve, and can also provide direct control of RS485 serial communication.

In conclusion, through the solution described in this article, the vacuum degree control accuracy in the low pressure carburizing process can reach 1% in the full scale range, and the corresponding temperature control can also be carried out.

Question 7

Ultra-Low Loss Single-Mode Optical Fiber Fused Taper Production by Accurate Vacuum Level Control Adsorption Fixture

Accepted Answer

Abstract: In the fiber fused taper system of fusion method, the fiber coupling with minimal loss corresponds to the optimal vacuum degree for adsorbing and fixing the optical fiber. Therefore, it is necessary to precisely control the adsorption vacuum degree and find the optimal vacuum degree value. In this article, focusing on the stable batch production of fiber fused taper system with minimal loss, an improvement scheme of vacuum system using FC series proportional flow control valve is proposed, which can reach precise control of vacuum degree.

1. Question
In the process of making optical fiber couplers and optical fiber cones in the optical fiber taper system, two or more optical fibers are generally positioned and clamped on the optical table by means of vacuum adsorption and special fixtures, and the two or more optical fibers are fixed in a certain way. A plurality of bare fibers are rotated and moved closer to the axis, heated and melted by a hydrogen-oxygen flame or a laser, and stretched to both sides at a certain speed, and finally a special waveguide structure in the form of a double cone is formed in the heating zone.

The current optical fiber taper technology is difficult to produce optical fiber couplers stably with a loss of less than 0.1 in batches, which is mainly due to the fact that optical fibers are fixed too tightly by vacuum adsorption. Some literatures reported that the vacuum system for adsorption and fixation fixture was improved, and the corresponding fiber couplers were fabricated under a series of different adsorption and fixation vacuum degrees, and it was proved that coupling loss in the entire vacuum degree range has a minimum area, When the vacuum degree is 120mBar, the minimum loss is 0.05dB.

The higher the vacuum degree, the tighter the fiber is fixed, and the coupling loss will be larger. It can be seen that in order to obtain an ultra-low loss fiber coupling device, it is necessary to precisely control the vacuum degree of the vacuum adsorption device.

In this article, according to the requirements for precise control of vacuum degree in the process of fabricating ultra-low loss optical fiber coupling devices by fiber taper method, a technical scheme of vacuum control system and corresponding supporting contents are proposed to reach precise and rapid control of vacuum degree.

2. Technical Scheme
In order to reach the precise control of adsorption vacuum degree in the left and right stretching fixtures, a vacuum tank is added to the original vacuum system. As long as the vacuum pressure in the vacuum tank is controlled, the adsorption vacuum degree of the left and right stretching fixtures can be controlled which shown in figure 2.

The vacuum degree control system shown in Figure 2 mainly includes an electronic needle valve, a vacuum gauge, a PID controller and a vacuum pump. The precise control of the vacuum degree adopts the dynamic control method, that is, according to the comparison between the measured value of the vacuum gauge and the set value, the PID controller adjusts the intake air flow and the exhaust air flow at the same time to quickly achieve dynamic balance and control the vacuum degree to the set value. , the control accuracy can reach ±1%.

In conclusion, through precise control of vacuum degree, stable mass production of ultra-low-loss fiber-coupled devices can be reached.

Figure 2 Schematic diagram of the vacuum degree control system of the fiber taper machine

Question 8

A Precise Control Method of Temperature and Pressure in Rayleigh-Brillouin Scattering Spectrometry

Accepted Answer

A Precise Control Method of Temperature and Pressure in Rayleigh-Brillouin Scattering Spectrometry

Abstract: For the Rayleigh-Brillouin scattering (RBS) spectroscopy experimental device, users proposed to reach high-precision control of temperature and pressure of measuring gas chamber. This article introduces a specific implementation, in which high-precision temperature control is implemented using semiconductor TEC modules and proportional control flow valve. Pressure control adopts a high-precision vacuum pressure control system, which includes a high-precision pressure sensor, a precision proportional control flow valve and a 24-bit acquisition precision PID controller. This temperature and pressure control scheme has been widely used and proven.

The introduced proportional flow control valve is introduced in https://www.genndih.com/proportional-flow-control-valve.htm

1. Technique requirement
According to customer requirements, temperature and pressure in Rayleigh-Brillouin scattering (RBS) spectroscopy as shown in Figure 1(the content of the red box area) for precise control, the specific requirements are as follows:
(1) Temperature range is 300K~318K; temperature control accuracy is ±0.02K.
(2) Pressure range is 30kPa~90kPa (absolute pressure); pressure control accuracy is ±0.1kPa; atmosphere is 99.9trogen.

2. Temperature control scheme
For high-precision temperature control near room temperature, it is proposed to use semiconductor heating and cooling technology shown in Figure 2 to reach, the specific contents include:
(1) Heating refrigerator: TEC module.
(2) Sensor: platinum resistance or thermistor temperature.
(3) PID controller: high-precision 24-bit temperature and pressure controller.

3. Pressure control scheme
The absolute pressure range required for experimental device to work is 30kPa~ 90kPa, and pressure within this range is required to be accurate and constant at any set point. Using KaoLu’s proportional control flow valve is the best choice.

(1) Using a capacitance pressure gauge with a range of 1000torr for pressure measurement, its accuracy can reach ±0.2%. A vacuum pressure sensor with a higher accuracy of ±0.05% can also be used for measurement.
(2) The high-precision PID vacuum pressure controller with 24-bit A/D acquisition is used to match the measurement accuracy of high-precision vacuum pressure sensor and ensure control accuracy.
(3) Install a proportional flow control valve at air inlet and exhaust port of air chamber respectively. The proportional flow control valve is directly installed at air inlet.

https://www.genndih.com/proportional-flow-control-valve/mid-flow-proportional-valve-0-130L-min.html

(4) During the control process, the pumping speed is guaranteed to be constant after vacuum pump is turned on. First, you need to set the air intake electronic needle valve so that pressure and flow of intake port are constant, and then perform self-tuning of PID parameters. Last, realize precise control of air chamber pressure by automatically adjusting the flow rate of exhaust port.

Question 9

Vacuum Level and Temperature Control Method in Glove Box

Accepted Answer

A Detailed Tutorial on Vacuum Degree and Temperature Control Method in Glove Box

Abstract: In order to reach powerful functions of glove box for two environmental variables of vacuum and temperature in glove box. This article focuses on integrated solution for accurate measurement and control of vacuum and temperature, and describes the upstream, downstream, bi-directional methods. Also introduces the specific application of switching control mode in different vacuum degree ranges, and demonstrates the new proportional flow control valve and 24-bit ultra-high-precision PID controller used in the control.

1. Questions
Vacuum glove boxes are often used for readily oxidizable and deliquescent substances. Chemical reactions, material processing and performance testing that require manual operations in an anaerobic and anhydrous environment are very helpful. The core function of glove box is to provide a vacuum environment and easy to use, but in current practical applications most glove boxes only use anaerobic environment and manual operation functions of glove box, and do not give full capacity to the role of glove box. The more powerful application of glove box is also reflected in the following two aspects:

(1) The vacuum glove box is a hermetic environmental box, and the ultimate vacuum degree can generally reach about 10Pa, so that vacuum degree in glove box can be controlled at any set point between 10Pa and atmospheric pressure as required. Various chemical reactions, experiments and tests that are sensitive to vacuum can be carried out; also various manual operations can be carried out without changing and destroying the vacuum environment.

(2) In addition to vacuum, temperature is another important environmental variable for many reactions, experiments and tests. By placing the corresponding heating device in the glove box, various experimental studies under the combined environment of temperature and vacuum degree can be carried out. And so on, other physical quantity environmental conditions can also be configured to form multi-physical quantity coupling test conditions under various boundary conditions. In order to achieve the full performance of a vacuum glove box, it focuses on two environmental variables of vacuum degree and temperature in the glove box.

This article introduces in detail the integrated solution for accurate measurement and control of vacuum degree and temperature, and introduces the different vacuum degree ranges of upstream, downstream and bidirectional control modes in vacuum control process.

2. Vacuum control in glove box
Glove box belongs to a low vacuum environment cavity. The vacuum degree of the glove box using a mechanical pump can generally reach an absolute pressure of about 10Pa. By vacuuming and filling with inert gas, the vacuum degree of the glove box can be controlled from 10Pa to one atmosphere (absolute pressure 0.1MPa). For control in such a vacuum range spanning four orders of magnitude, vacuum sensors with different precisions will be used according to actual needs, and there will be different control modes accordingly. The following is the specific content of each control mode.

2.1 Upstream Control Mode
As shown in Figure 1, under the condition that the pumping speeds of downstream vacuum pump is kept constant. The upstream control mode is to adjust the opening of proportional flow control valve of upstream air intake port through PID vacuum pressure controller according to the measurement signal of vacuum gauge, that is, by controlling intake flow to keep pressure in glove box at the set point. Upstream mode is often used for high vacuum control.

2.2 Downstream Control Mode
As shown in Figure 2, under the condition that the pumping speed of downstream vacuum pump is kept constant, the downstream control mode is to adjust the opening of proportional flow control valve of downstream air outlet through PID vacuum pressure controller according to the measurement signal of vacuum gauge, that is, by controlling the air flow rate, the pressure in glove tank is controlled at the set value. We can see that downstream mode is often used for low vacuum control.

2.3 Bi-directional Control Mode
The above upstream and downstream control modes have their own advantages, and are rarely used alone in practical applications. Generally, the upstream and downstream modes are integrated together, which is the so-called bi-directional control mode, as shown in Figure 3. In bi-directional control mode, the vacuum pressure controller is required to have forward and reverse control functions, that is, reverse control for upstream proportional flow control valve and reverse control for downstream proportional flow control valve.

2.4 Dual sensor automatic switching mode
As mentioned above, if the accurate measurement and control of vacuum degree is carried out in the full range of 10Pa~0.1MPa, it is generally necessary to configure two high-precision diaphragm pressure gauges of 1000Torr and 10Torrswitch automatically. As shown in Figure 4, the high switching point (2-3) is the high point where low vacuum sensor works, and the low switching point (1-2) is the low point where high vacuum sensor works. The controller performs smoothing calculation between these two points. When the continuous sampling of low vacuum measurement PV1 and high vacuum measurement PV2 is below the lower switching point, switching to the rough vacuum sensor. When continuous sampling of low vacuum measured value PV1 and high vacuum measured value PV2 is above the upper switching point, the switch to high vacuum sensor is made.

3. Selection of vacuum gauge, valve and controller

3.1 Selection of vacuum sensor
Like other sensors, various vacuum sensors also have a certain measurement range and accuracy. The basic rule is that a sensor with a wide measurement range has poor accuracy; a sensor with high measurement accuracy has a narrower measurement range. For glove box, as shown in Figure 5, the used vacuum sensors generally have the following three categories:
(1) Conventional vacuum gauge: Pirani vacuum gauge, the accuracy is ±(15~50)% of the full scale, but one vacuum gauge can cover the full scale.
(2) High-precision vacuum gauge: diaphragm pressure gauge, the accuracy is ±2.5% of the full scale, if it covers the range of 10Pa~0.1MPa, two vacuum gauges of 1000Torr and 10Torr are generally required.
(3) Ultra-high precision vacuum gauge: semiconductor vacuum gauge, the accuracy is ±0.05% of the full scale, and the effective range is 50Pa ~ 0.1MPa, which cannot cover higher vacuum.

3.2 Selection of electric valve
In glove box of vacuum control, two types of valves are generally involved: one is an air intake valve that adjusts the flow at air intake, and the other is an exhaust valve that adjusts the exhaust flow. Air intake valves are mostly used for small flow regulation, so needle valves are generally selected. Exhaust valves are mostly used for vacuuming, so ball valves with larger diameters are generally required.

Due to the automatic control, both needle valves and ball valves are required to be driven by DC voltage, DC current or digital signal (RS485) which is the so-called proportional flow control valve. Proportional flow control valve selects a small-sized stepper motor-driven proportional flow control valve, as shown in Figure 6. This proportional flow control valve has high response speed (within 1s) and linearity (within 1%). For FC series proportional flow control valve, please visit https://www.genndih.com/proportional-flow-control-valve.htm

3.2 Selection of controller
From the above various control modes of vacuum degree of glove box, it can be seen that control process of vacuum degree puts forward high requirements for the controller. As shown in Figure 7, the selected controller must meet the following criteria:

(1) At least it is a PID controller, and has the function of PID parameter self-tuning.
(2) The accuracy of vacuum gauge itself is high. In order to give full play to the measurement accuracy of vacuum gauge, PID controller that needs data acquisition and control must have high accuracy. It is recommended that controller should be 24-bit A/D acquisition and 16-bit D/A output. (3) At least 2 channels are required to achieve simultaneous measurement and control of temperature and vacuum degree, also to reduce installation space.
(4) Multiple input signal access functions, which can directly connect the input signals of different types of sensors such as thermocouple, thermal resistance, DC voltage, etc., to achieve simultaneous testing, display and control of different parameters.
(5) Forward and reverse control function to reach two-way control mode.
(6) With dual sensor switching function, each channel can support dual sensor switching of high and low temperature and high and low vacuum. Two channels can form a control combination with a total of four sensors connected.
(7) Program control function, you can create and save multiple control programs by yourself, and you only need to select and call to start (program control mode).
(8) It has a communication interface to connect with computer, such as the RS485 interface of the standard MODBUS protocol.

4. Temperature control of the glove box
In addition to providing a vacuum environment, the glove box can also put a heating device in the glove box to perform various experiments and tests at different temperatures, so it is necessary to introduce temperature control function into glove box application. Temperature control is a very mature and classic technology, which is generally realized by using a PID controller in combination with a temperature sensor. In order to reduce the cost and installation volume, a multi-channel PID controller is generally used to control temperature and vacuum degree at the same time. The controller communicates with a computer to display and store measurement control data and curves. The working temperature in glove box is generally not required to be too high, but if thermal protection and cooling are done well, the working temperature range above 1000°C can also be achieved. The temperature measurement sensor generally chooses a thermocouple. If the measurement accuracy is high, the thermal resistance and the thermistor temperature sensor can also be selected. These sensors can be directly connected to the above-mentioned high-precision PID controller.

5. Conclusion
Through the introduction of above content, the various control methods of vacuum degree and temperature in glove box and the main sensors, proportional flow control valve and PID controllers involved are basically explained. In specific applications, partial improvements can be made to the specific structure and function of glove box, and the overall design, installation and integration of glove box can also be carried out according to actual requirements.
Although this article only introduces the measurement and control of vacuum degree and temperature in glove box, these methods and specific implementation contents can also be extended and applied to the control of test parameters in other fields that are more sensitive to the atmosphere environment, such as low temperature, geometric quantity, optics and acoustics.

Question 10

KaoLu's Electronic Air Flow Control Valve

Accepted Answer

KaoLu's Electronic Air Flow Control Valve

1. Overview
KaoLu's Electronic Air Flow Control Valve is actually the exact same control valve, only the OEM is different. As shown in Figure 1, this gas control valve is a needle valve driven by a stepper motor, which can convert an external control signal into a prescribed valve needle position, thereby adjusting the opening of the valve to reach gas flow control. The external control signal can be in the following three types :
(1) DC simulation voltage (0~10VDC)
(2) Interface module
(3) RS232 interface
For this gas control valve, INFICON and Pfeiffer provided matching controllers, as shown in Figure 2, the models are: INFICON: VCC500-Z; Pfeiffer: RVC 300.
This article will introduce the corresponding technical indicators for the above-mentioned control valves and controllers, and introduce the corresponding localized alternative products and their technical indicators, so as to provide cost-effective products for localized substitution.

2. Technical indicators of foreign products

2.1 Controller Technical Indicators

Operating Mode	Pressure Control, Gas flow regulation
Analog Output	4 channels: vacuum pressure sensor signal, valve signal(0-10VDC), valve position, +10VDC reference voltage(10mA)
Number Output	8 channels: open valve, closed valve, valve position, valve error, sensor error, preparation, divergence, sensor condition
Analog Input	2 channels: vacuum pressure set point (standard value),flow set point (standard value)
Number Input	8 channels: flow reduction, flow addition, external closure, external open, flow mode, pressure mode, discharge open, exhausting open
Characteristic	After power outage, turn on output "reach the standard value", then it can adjust tolerance
Display Unit	mbar, Pa, Torr, mV
Language	English, German
Communication Interface	RS232C, RS485

Controller type	PI automatic: it can choose control speed step 1-99 PID: Users can define parameters
Control Accuracy	±5% FS sensor
Display Accuracy	±0.2% FS sensor
Power Supply	Voltage90 ~250VAC

Weight

1.65kg

From the above-mentioned controller technical indicators and practical application experience, it can be found that:
(1) Single-channel measurement and control: that is, only one vacuum gauge signal and one control valve can be collected. Although there are multiple analog and digital input and output channels, only one closed-loop control can be performed. This single channel controller will not be able to cover the wide range that requires two vacuum gauges to cover.
(2) No PID self-regulating function: Sometimes the optimal PID parameters cannot be obtained in the end, which seriously affects the control effect.
(3) Poor control accuracy: The control accuracy is ±5% of the full scale of sensor, which basically shows that acquisition and control circuit in the controller uses 12-bit A/D and D/A converters, which is the key to determining the control accuracy.

3. KaoLu’s electronic air flow control valve replaces INFICON and PFA control valves
The control valve of KaoLu's Electronic Air Flow Control Valve is a typical electronic air flow control valve driven by stepper motor. The performance indicator is very superior. The only disadvantage is that the opening of needle valve is small, thus it causes a small flow. Moreover, the price is too expensive.
In order to reach the replacement of gas flow control valve and improve the low cost high performance, KaoLu also used stepper motor in needle valve technology for localization, and developed a series of electronic air flow control valve with different flow rates.

As shown in Figure 3, fully realized it has been replaced, and the price is only one-third of foreign products. The detailed technical indicators are shown in Figure 4. Please visit https://www.genndih.com/proportional-flow-control-valve.htm

(Figure3 KaoLu’s FC electronic air flow control valve)

Model	FC-20	FC-120	FC-300	FC-1000
Valve type	Needle Valve
Spool Drift Diameter	0.9mm	2.25mm	2.75mm	4.10mm
Actuator	Bipolar stepper motor control
Response time	0.8sec(Open to close)
Standard size	G1/8”			G3/8”
Fluid	Inert gas and liquid
Contact Materials	Stainless Steel
Pressure Range	-1 ~ 7bar			-1 ~ 5bar
Maximum Flow	50L/min @7bar	240L/min @7bar	290L/min @7bar	600L/min @7bar

Linearity	±2%	±0.1 ~ 1%	±0.2 ~ 5%	±11%
Repeatability (Full scale)	±0.1%
Flow Resolution (Step length)	0.1L/min	0.1 ~ 0.2L/min	0.2 ~ 0.75L/min	1L/min
Shift Resolution (Step length)	12.7um		25.4um
Operating Temperature Range	0 ~ 84ºc
Seal	Standard FKM or other choices of seals

Control Signal	DC: 0 ~ 10V (or 4 ~ 20mA)
Power Supply	DC: 24V (12W)

(Figure4 Technical indicators of KaoLu’s FC electronic air flow control valve)

3. Localized high-precision dual-channel PID controller replaces INFICON and PFA controllers
In order to use the measurement accuracy of vacuum gauges fully (such as capacitive film pressure gauges), at least 16-bit analog-to-digital and digital-to-analog converters are required for data acquisition and control of controller. In recent years, KaoLu have developed the FC series of high-precision 24-bit general-purpose PID controllers, as shown in Figure 5. This series of PID controllers is far more powerful than foreign products, but the price is only one-eighth of foreign products. Its main performance indicators are as follows:
(1) Precision: 24-bit A/D, 16-bit D/A.
(2) Multi-channel: independent 1-channel or 2-channel. 2 channels can realize the simultaneous measurement and control of temperature and pressure.
(3) A variety of output parameters: 47 kinds of input signals (thermocouple, thermal resistance, DC voltage) can reach simultaneous test, display and control of different parameters.
(4) Multi-function: forward, reverse, forward and reverse two-way control.
(5) PID control: The improved PID algorithm supports PV differential and differential advance control. There are 20 groups of PIDs.
(6) Dual sensor switching: Each channel can support dual sensor switching of high and low temperature and high and low vacuum. Two channels can form a control combination with a total of four sensors connected.
(7) Program control: You can create and store up to 20 condensation programs by yourself, and you only need to select and call to start condensation (program control mode).

In the vacuum degree control, downstream control mode is more suitable for vacuum degree close to atmospheric pressure, but upstream air intake control mode is required for vacuum degree control of less than 10mbar. Therefore, in order to satisfy the full control degree of vacuum, the dual sensor and two-way control mode as shown in Figure 6 can be used.
In the control mode shown in Figure 6, it is necessary to use the forward and reverse control and dual sensor automatic switching functions of the above FC-20 series dual-channel controller, that is, during different air pressure control processes; the controller automatically switches the corresponding range. Vacuum gauge, and select the corresponding electronic air flow control valve for control.

Question 11

Atmosphere Pressure Control in Vacuum Laser Powder Bed Fusion

Accepted Answer

Atmosphere Pressure Control in Vacuum Laser Powder Bed Fusion

Low pressure SLM fusion process
Features: The molten pool is more stable and reduces porosity. Low-pressure atmosphere requirements: Fast and accurate air pressure control is reached within the process window of 5kPa~101kPa.

Pressure Control
Control method: two-way control method, adjusting upstream air intake electronic air flow control valve and downstream electric ball valve at the same time. It can also adjust the air intake flow and vacuum pump exhaust rate. For further information on electronic air flow control valve, please visit https://www.genndih.com/proportional-flow-control-valve.htm

Sensor: vacuum pressure sensor, the measurement range is 5kPa~101kPa, and the accuracy is ±0.2%.
Controller: two-way PID controller, two-way control function

Question 12

Proportional Flow Control Valve

Accepted Answer

These are some of our proportional flow control valve applications:
1. Torque control
2. Vacuum generator
3. Gas control
4. Gas blending
5. Cooling

We have been offering various models of proportional flow control valve that can be used to control the flow rate of gas, liquid, oil. Customers often uses our valves to replace solenoid valves, where our FC series could act as on/off control and at the same time control the flow rate. We have succesfully replaced Clippard (SCPV), and Burkert flow control valve.

Advantage:

Compact
Low cost
High sensitive
Analog / Digital signal
Easy-control
Full scale linearity flow rate control
control up to 20 L/min of water flow (customisable)

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