Question 1

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 2

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 dual-channel PID controller is shown in Figure 2. 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 VPC2021 series dual-channel PID controller)

(Figure 3 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 3. 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 3. 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 3

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 dual-channel PID controller is shown in Figure 2. 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 VPC2021 series dual-channel PID controller

Figure 3 FC series electronic needle valve

Figure 4 LCV-DS series electronic ball 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 3. 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.

For the larger diameter of the suction pipeline, this scheme uses a miniature electronic ball valve, as shown in Figure 4. This series of electronic ball valve is a small electronic valve. The valve opening can be adjusted continuously according to the change of the 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 the external volume and is low in price. It is often installed between the sealed container and the vacuum pump to adjust the pumping rate.

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 4

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, as shown in Figure 1.

As you can see from the results in Figure 1, it is not that the higher the vacuum degree, the better vacuum degree would be. 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.

Fig.1 Coupling loss under different vacuum pressures

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 5

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. Because of it, vacuum pressure control system as shown in Figure 2 is proposed to be implemented, and details are as follows:

(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 6

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 7

Localized Electronic Air Flow Control Valve

Accepted Answer

Localized Substitution of INFICON VDE016 and Pfeiffer EVR116 Gas Control Valves and PID Controllers
Abstract: Not only comparing to VDE 016 of INFICON and EVR 116 gas control valve of Pfeiffer but VCC500 of INFICON and RVC 300 controller of Pfeiffer. This article introduces the corresponding localized alternative products electronic air flow control valve and multi-function of high-precision PID controller. Also introduces the corresponding features and technical indicators of localized alternative products.

1. Overview
The gas control valve of INFICON 's VDE 016 and Pfeiffer's EVR 116 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 Specifications of gas control valve
The performance parametersof INFICON and Pfeiffer’s control valves are shown in Table 1, and the technical indicators are shown in Table 2.

2.2 Controller Technical Indicators
The technical indicators of controller performance of INFICON and Pfeiffer are shown in Table 3.

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 INFICON and Pfeiffer controllers have the following deficiencies:
(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: The biggest disadvantage of INFICON and Pfeiffer controllers is the lack of PID parameter self-tuning function, which brings inconvenience in practical applications, requiring users to find suitable PID parameters by themselves. 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 INFICON and Pfeiffer 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 8

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 9

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)

We hope you have enjoyed reading the article. Please remember to visit our product page.

Question 10

Electronic Flow Valve

Accepted Answer

What is an Electronic Flow Valve?

An Electronic Flow Valve is a device that is able to control the flow rate of fluid (liquid and gas) with electronic signal. Ideally, the output flow rate is linearly proportional to input signal. Depend on the type of medial it is regulating, when it’s air, it is called electronic flow regulator, electronic air flow control valve, electronic pneumatic flow control valve; and when the media is water, it’s called electronic water flow control valve, digital flow control valve, digital flow controller, or proportional needle valve for both types.

There are different types of working principle, and in this article we will be introducing you the proportional needle valve type driven by a stepper motor powered linear actuator. We will firstly introduce you what type of electronic flow valve we offer, followed by the working principle and with what is the main advantage of KaoLu’s proportional needle valve, and then conclude with what you should think about before purchasing an electronic flow valve.

What type of Electronic Flow Valve does KaoLu offer?

KaoLu offers 5 types of digital flow control valve. One advantage is that it can control both gas and liquid. Please click on the photo link below for further information

FC20 : Flow rate up to 45 L/min of nitrogen gas @ 6 bar or 750 mL/min of water @ 6 bar
FC120: Flow rate up to 200 L/min of nitrogen gas @ 6 bar or 3.5 L/min of water @ 6 bar
FC300: Flow rate up to 450 L/min of nitrogen gas @ 6 bar or 8 L/min of water @ 6 bar
FC1000: Flow rate up to 650 L/min of nitrogen gas @ 5 bar or 12 L/min of water @ 5 bar
FC2000: Flow rate up to 2000 L/min of nitrogen gas @ 5 bar or 30 L/min of water @ 5 bar

Please refer to our youtube channel for some of the interesting applications:

What is working principle of an Electronic Flow Regulator?

There are different types of Electronic Flow Regulator. Here we will be explaining the type that utilizes a linear stepper motor actuator and proportional needle valve.

So, what is the advantage of KaoLu’s electronic air flow control valve or electronic water flow control valve?

Our parameters tells all the story. With FC series electronic flow valve, we are able to withstand 7 bar of perpendicular operating pressure, with a resolution as high as 20 mL/min of air, repeatability of 0.1% F.S, and 0.1% of linearity. This is due to the motor we used, the extremely low tolerance of mechanical parts, the fine thread needle we used which is extremely difficult to reproduce by others, and the control system we designed.

What should you consider when purchasing an electronic flow regulator?

You should consider 3 main factors ( we called CPR)

Compatibility: Medium, flow range, compatibility with the valve material, and operating pressure
Performance: Resolution, starting flow point, and linearity
Control system

It is important to understand whether the media you used falls into the flow range of the operating valve. As each media has different density so the flow range would be different from the nominal flow range. Next is whether the media used is compatible with the wet material and whether you would also need the body to be special material. The operating pressure is another caveat, where if you simply needs flow control, sometimes it would not be a very important factor.

Next is the performance, with some applications that needs fine control and adjustment between steps, such as laser cutting, the resolution dictated by the control logic and motor performance plays an important role here. Furthermore, as the motion system requires to overcome initial inertia, the start flow point is should be considered.

Then comes the control system where the you should check what type of control system do suppliers offer? Here we provide an external driver that has a cable connected to the control valve. The great advantage that we offer is that should you want to operate the valve from distant away from the site, we offer RS485 modbus where you could control the valve up to half a mile away from the valve.

We hope you have enjoyed reading the article, understand about stepper motor driver electronic flow control valve, understand about our products, and finally help you with selecting the right valve.

We hope you have enjoyed reading the article. Please remember to visit our product page.

Question 11

Proportional valve and proportional control system

Accepted Answer

Proportional control technology is a control technology developed in the late 1960s that is reliable, inexpensive, and has control accuracy and response characteristics that can meet the actual needs of industrial control systems. Electro-pneumatic proportional control technology is a control method between the on-off control technology of ordinary pneumatic valves and electro-pneumatic proportional control technology. It can continuously and proportionally follow the control signal to change the air pressure. Therefore, the control performance of the electro-pneumatic proportional control technology is better than the on-off control of ordinary pneumatic valves. Comparing with the servo valve, due to the proportional valve has a dead zone in neutral position, there is still a slight gap in the control accuracy and response speed. However, its obvious advantage is that it has strong anti-pollution ability, which greatly reduces the working failure of pneumatic system caused by contaminant. On the other hand, the cost of proportional valve is lower than servo valve, and the structure is also simple, which has been widely used in many occasions.
After decades of continuous development, proportional control technology has reached a relatively complete level. It is mainly manifested in three aspects. First, feedback and electrical correction methods such as pressure, flow rate, displacement and dynamic pressure are adopted, which improves the steady-state accuracy and dynamic response quality of the valve. It indicates that the design principle of proportional control has been perfected. Second, Proportional technology and cartridge valve have been combined to give birth to proportional cartridge technology. Last, the birth of proportional volume components represented by proportional control pumps further expands the application of proportional control technology.

1. Types of Electro-Pneumatic Proportional Valves and how they work
There are many structural forms of electro-pneumatic proportional valve, similar to electro-pneumatic pressure regulator, usually composed of electro-mechanical converter, pneumatic amplifier (pilot valve and power main valve) and detection feedback mechanism. If it is a single valve, there is no pilot valve or it is a multi valve.
Electromechanical converters such as proportional electromagnetic valve, force motors or torque motors are used to convert the input electrical signal into force or torque through a proportional amplifier to generate displacement or rotation angle that drives the movement of the pilot valve. The pilot valve, also known as the pre-stage (can be a spool valve, a poppet valve, a nozzle flapper valve or a cartridge valve), is used to receive the displacement or rotation angle signal input by a low-power electrical-mechanical converter to convert the mechanical quantity. The main valve (spool valve, poppet valve or cartridge valve) converts the pneumatic pressure of the pilot stage valve into flow or pressure output, the detection feedback mechanism (which can be hydraulic, mechanical, electrical feedback, etc.) The pressure, flow or spool displacement of the main valve control port is fed back to
input end of pilot valve or input end of proportional amplifier to reach the balance of input and output.
The core of proportional control is proportional valve. The input unit of proportional valve is an electro-mechanical converter, which converts the input signal into a mechanical quantity. Converters are in the form of servo motors and stepper motors, force motors and torque motors, and proportional electromagnetic valve. However, most common proportional valves use proportional electromagnetic valve. The proportional electromagnetic valve is designed according to the principle of
electromagnetic valve, so that the mechanical quantity (force or torque and displacement) generated input electrical signal (current), and then continuously controlled the position of hydraulic valve spool, thereby reaching continuous control of pressure, direction and flow of pneumatic system. The structure of proportional electromagnetic valve is shown in Figure 2. It consists of a coil, an armature, a putter,etc. When there is a signal input to the coil, the magnetic field in the coil produces a force on the armature, and the armature is in the magnetic field according to the magnitude and direction of signal current. It moves proportionally and continuously, and then drives the push rod to move through fixed pins, so as to control the movement of spool valve. The most widely used proportional electromagnetic valve is the high voltage DC proportional electromagnetic valve.

The types of proportional electromagnetic valves are mainly divided into the following categories according to their working principles:
(1) Force control type
The stroke of this type of electromagnetic valve is short, only 1.5mm, and the output force is proportional to the input current. It is often used in the pilot control stage of the proportional valve.
(2) Stroke control type
It is composed of a force control type plus a load spring. The force output by the electromagnetic valve is converted into an output displacement through the spring. The output displacement is proportional to the input current. The working stroke reaches 3mm and has good linearity. It can be used in direct Controlled proportional valve.
(3) Position adjustment type
After the position of the armature is detected by the sensor in the valve, an in-valve feedback signal is sent out, and the position of the armature is re-adjusted after the comparison in the valve, forming a closed-loop control in the valve, with high precision. Regardless of the force, it can almost be compared with the servo valve in terms of accuracy. The proportional valve produced by many famous companies in the world adopts this structure.
Proportional valves are classified into four categories according to their main functions: proportional pressure regulators, flow control valves, directional control valves, and proportional compound control valves:
(1) Electro-Pneumatic Pressure Regulator
There are relief valve, pressure reducing valve, sequence valve, which can continuously adjust the system pressure.
(2) Proportional directional valve
The polarity of the input current determines the flow direction of the air flow, the stroke of the valve core is proportional to the size of the input current, and the directional valve is divided into two categories: with position sensor and without position sensor.
(3) Proportional flow control valve
There are proportional speed regulating valve and proportional overflow flow control valve, which can continuously adjust the system flow or speed.
(4) Proportional composite control valve
Generally, it is composed of two kinds of valves with different functions, suitable for use in open-loop control systems. Each type can be divided into two structural forms: direct control and pilot control. Direct control is used in low-flow and low-power systems, and pilot control is used in large-flow and high-power systems to form electro-pneumatic proportional valves.

2. Selection of proportional valve
(1) Select the type of proportional valve according to the purpose and the controlled object.
(2) Understand the dynamic and static indicators of proportional valve correctly, mainly including rated output, initial current, hysteresis, repeatability, rated pressure loss, temperature drift, response characteristics, frequency characteristics, etc.
(3) Select the accuracy of proportional valve according to the working accuracy requirements of actuator, and the valve with feedback closed loop has good steady-state and dynamic quality. If the inherent characteristics of proportional valve, such as hysteresis, nonlinearity, etc., cannot make the controlled system achieve the desired effect, software programs can be used to improve the performance ofsystem.
(4) If you choose a proportional valve with a pilot valve, notice the requirements of pilot valve on oil pollution degree. Generally, it should meet the ISO18/15 standard, and install a 10 oil inlet oil filter on the oil road.
(5) The orifice of proportional valve should be the flow of actuator at the maximum speed. If the orifice is too large, the resolution of system will be reduced. The proportional valve must use the matching amplifier. The distance between the valve and the amplifier should be as short as possible. The amplifier adopts current negative feedback, and sets the ramp signal generator to control the boosting, decreasing time or motion acceleration and deceleration. When power is off, the spool can be placed in a safe position.

3. Proportional control system
The proportional control system has direct proportional control and electro-pneumatic proportional control, which is similar to the servo system control in essence, and can be analyzed with reference to the servo system. According to whether there is feedback, it is divided into open-loop control and closed-loop control. The proportional valve-controlled hydraulic cylinder or motor system can control parameters such as speed, displacement, rotational speed and torque.

4. Comparison of Electro-hydraulic Servo System and Proportional Servo System

Type	Commonality	Difference
Electro-pneumatic Servo System	(1) The input is a low-power electrical signal (2) The output has a linear relationship with the input (3) Continuous control is possible	(1) Both are closed-loop control (2) The output is various physical quantities such as position, speed, force, etc. (3) The control element is a servo valve (4) High control precision and high response speed (5) For high-performance occasions
Proportional Servo System		(1) Generally open-loop control, closed-loop control can also be used when performance requirements are high (2) General output is speed or pressure, and it can also be displacement when closed-loop. (3) The control element is a proportional valve (4) Low control precision and low response speed (5) For general industrial automation occasions

For further information about electro-pneumatic proportional pressure regulator, please
visit https://www.genndih.com/proportional-pressure-regulator.htm

Question 12

Common errors of proportional valves and cause root analysis

Accepted Answer

What are the common errors of proportional valves? What is the reason of these errors? How to avoid them?

1. Proportional electromagnet error
① Due to the aging of wiring socket (base) of plug assembly, poor contact, and de-soldering of electromagnet lead, the proportional electromagnet cannot work (cannot pass current). At this time, the meter can be used for testing. If the resistance is found to be infinite, the lead wire can be re-soldered, the socket can be repaired and the socket can be inserted firmly.

② The errors of coil components include coil aging, coil burnout, internal disconnection of the coil, and excessive temperature rise of the coil. If the temperature of coil is too high, the output force of proportional electromagnet will be insufficient, and the rest will make the proportional electromagnet unable to work.

If the temperature of coil rises too high, you can check whether the passing current is too large, whether the insulation of enameled wire of coil is poor, whether the valve core is stuck due to dirt to find out the reasons and eliminate them one by one. For disconnection, burnout, the coil must be replaced.

③ The error of armature assembly is mainly due to the wear of the friction pair formed by the armature and the magnetic guide sleeve during use, which leads to an increase in the force hysteresis of the valve. There is also a misalignment between the push rod guide and the armature, which will also cause an increase in the force hysteresis, which must be ruled out.

④ The welding part of the magnetic guide sleeve is broken due to the weak welding or the pulse pressure of the proportional valve during use, so that the proportional electromagnet loses its function.

⑤ The magnetic guide sleeve is deformed under the impact pressure, and the friction pair formed by the magnetic guide sleeve and the armature is worn during use, resulting in an increase in the force hysteresis of the proportional valve.

⑥ The proportional amplifier is shut down, causing the proportional electromagnet not working. At this time, various components of amplifier circuit should be checked to eliminate the error of proportional amplifier circuit.

⑦ The connection between proportional amplifier and the electromagnet is broken or the connection of amplifier terminal is disconnected, so that the proportional electromagnet does not work. At this time, the broken wire should be replaced and reconnected firmly.

2. Error analysis and elimination of proportional pressure regulator
Since the proportional pressure regulator is just based on the ordinary pressurevalve, the pressure regulating handle is replaced by a proportional electromagnet. Therefore, the various errors caused by ordinary pressure valves will also cause error and troubleshooting methods of ordinary pressure valves, which are also completely applicable to the corresponding proportional pressure valves (such as the relief valve corresponding to proportional relief valve), and can be handled with reference.
Beside this there is:

① When the voltage regulation fails, you can first check the current value with electric meter to determine whether there is a problem with the control circuit of electromagnet, proportional electromagnet, or valve part, which can be treated symptomatically.

②Although the current flowing through proportional electromagnet is the rated value, but the pressure cannot go up at all, or the required pressure cannot be obtained, between proportional pilot pressure regulating valve (relief valve) and the main relief valve. The pilot-operated manual pressure-regulating valve of common pilot-operated relief valve is still retained, which acts as a safety valve here. When the regulating pressure of valve is too low, although the passing current of proportional electromagnet is the rated value, the pressure cannot rise. If the set pressure of valve is too low, the pilot flow will flow back to the tank from valve, so that the pressure cannot rise. At this time, the set pressure of valve should be adjusted to be about 1MPa higher than the maximum working pressure of valve.

③ The current flowing through proportional electromagnet has been too large, but the pressure still cannot go up, or the required pressure cannot be obtained. At this time, the coil resistance of proportional electromagnet can be checked. If it is far less than the specified value, then the coil of electromagnet is internally open circuited. If the solenoid coil resistance is normal, then the connection line connected to proportional amplifier is short-circuited. At this time, the proportional electromagnet should be replaced, the wiring should be connected, or the coil should be rewound
and installed.

④ When the pressure is changed stepwise, the pressure fluctuation of small amplitude is continuous, and the reason for the instability of the set pressure is mainly due to the adhesion of dirt between the iron core of the proportional electromagnet and the guide part (guide sleeve), which hinders the movement of the iron core. In addition, the sliding part of the main spool is stuck with dirt, which hinders the movement of the main spool. Due to the influence of these contaminants, the hysteresis is increased. In the range of hysteresis, the pressure is unstable and the pressure fluctuates continuously. Another reason is the wear of the iron core and the magnetic guide sleeve, the gap increases, and the adjusted pressure (through a certain current value) is unstable.

⑤ The pressure response is delayed and the pressure changes slowly because the air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the movement of proportional electromagnet core and the main valve core is unnecessarily hindered. In addition, air enters the system, which usually occurs when the equipment starts to run after being installed or after an occasion of long-term shutdown.

The solution is to loosen the bleed screw before the proportional pressure regulator starts to use, and let out clean air until the oil flows out. In the case of dirt blocking the damping hole, the proportional solenoid and the main valve should be disassembled for cleaning, and at the highest position of the system oil circuit where the air is easy to concentrate, it is best to set the air release valve to release air or loosen the pipe joint to release air.

⑤ The pressure response is delayed and the pressure changes slowly because the
air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the
movement of proportional electromagnet core and the main valve core is
unnecessarily hindered. In addition, air enters the system, which usually occurs
when the equipment starts to run after being installed or after an occasion of long-
term shutdown.

⑤ The pressure response is delayed and the pressure changes slowly because the
air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the
movement of proportional electromagnet core and the main valve core is
unnecessarily hindered. In addition, air enters the system, which usually occurs
when the equipment starts to run after being installed or after an occasion of long-
term shutdown.

⑤ The pressure response is delayed and the pressure changes slowly because the
air in the proportional electromagnet is not cleaned. It is blocked by dirt, and the
movement of proportional electromagnet core and the main valve core is
unnecessarily hindered. In addition, air enters the system, which usually occurs
when the equipment starts to run after being installed or after an occasion of long-
term shutdown.

⑥Two faults of electro-hydraulic proportional relief valve
a. When the rated current (50mA) is input to the coil, the inlet pressure cannot reach the rated working pressure (21MPa), but is 2-6MPa lower than the rated pressure. The reason is: after long-term use, due to the loosening of the fastening screws of the magnetic gap adjustment gasket, the magnetic gap increases, and the magnetic resistance of the magnetic gap (air gap) in the magnetic circuit is very large.

F=k(iN/Rm)2S

where k-constant;
i——the coil input current;
N - the number of turns of the coil;
Rm - magnetoresistance;
S - the cross-sectional area of the magnetic circuit.

It can be seen that as long as the magnetic gap is slightly increased, the reluctance Rm increases significantly, and the electromagnetic force F decreases in a square relationship. The hydraulic clearance increases, the pressure upstream of the nozzle decreases, so the pressure in the upper chamber of the main spool decreases. The force added by reduced pressure and weak spring in the upper chamber of the main valve decreases, so that the opening pressure of the main spool decreases, that is, the inlet pressure decreased, and the maximum pressure (21MPa) could not be reached.

Solution: Appropriately increase or decrease the thickness of the magnetic gap adjustment gasket, tighten the fastening screws of the magnetic gap adjustment gasket, and reduce the magnetic gap, which can increase the inlet pressure. The initial setting of the magnetic gap should be 0.89 ~ 0.94mm.
b. When the input current of the coil is zero, the initial pressure of the valve is too high (4-7MPa). Normally, the initial pressure should be about 1MPa. The minimum set pressure mainly depends on the initial gap 8 of the nozzle baffle. The normal gap is 0.1 to 0.13 mm. If it is too small, the initial pressure will be too high.

3. Error analysis and elimination of proportional flow valve
①The flow cannot be adjusted, and the throttling adjustment function is invalid. In addition to the error analysis and troubleshooting method of speed control valve, there are the following two points: a. Proportional electromagnet failed to energize.
The reasons are: aging of the proportional electromagnet socket and poor contact; unsoldering of the electromagnet lead; wire breakage inside the coil, you can refer to the above "(1) Proportional electromagnet error" method for troubleshooting.

b. Proportional amplifier error. Same as ①, ⑤, ⑥ in the above (2).
②The adjusted flow is unstable. The flow adjustment of the proportional flow valve is reached by changing the current flowing into its proportional electromagnet. When the input current value remains unchanged, the adjusted flow rate should remain unchanged. But in fact, the adjusted flow rate (when the same signal value is input) often changes in the working process, which is caused by the increase of the force hysteresis. Hysteresis means that when the same signal (current) value is input, the maximum change value of the output flow (or pressure) is caused when the same current signal value is passed due to different input directions (forward and reverse directions).

The factors affecting the force hysteresis are mainly caused by the existence of radial unbalanced force and mechanical friction. Then measures such as reducing the radial unbalanced force and reducing the friction factor can reduce the influence of mechanical friction on the hysteresis. The hysteresis is reduced, and the natural change of the adjusted flow is small. The following measures can be taken specifically:
a. Minimize the wear of the armature and the magnetic guide sleeve.
b. The push rod guide rod and the armature should be same.
c. Pay attention to the cleaning of the oil to prevent the dirt from entering the gap between the armature and the magnetic guide sleeve and jam the armature, so that the armature can move evenly in proportion to the input current value without sudden jumping. Once the sudden jump phenomenon occurs, the output flow of the proportional flow valve will also follow the sudden jump and make the adjusted flow unstable.
d. After the magnetizing sleeve armature is worn, noticing repair, so that the gap between the two is kept within an appropriate range. These measures are quite beneficial and effective to maintain the stability of the flow rate adjusted by the proportional flow valve.

In addition, the hysteresis of proportional valve driven by the general proportional electromagnet is 3% to 7%, the hysteresis of proportional valve driven by the torque motor is 1.5% to 3%, and the proportional valve driven by the servo motor is about 1.5%. The proportional flow valve driven by the servo motor has a relatively small change in flow.

For further information about electro-pneumatic pressure regulator, please visit https://www.genndih.com/proportional-pressure-regulator.htm