Question 1

What Is A Pinch Valve?

Accepted Answer

A pinch valve is a type of fluid control valve. It applies a pinching force to the outer surface of flexible tubing. While pinching it collapses and seals the tubing to control fluid flow or pressure.
The main body of a pinch valve is not in direct contact with the gas or the liquid, and only the inside of the tube will have direct contact with the liquid and gas fluid flowing through. Therefore, the pinch valve is not in direct contact with the fluid.

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Question 2

Gas Blending

Accepted Answer

Gas blending is a critical process in many semiconductor or industrial application, such as when one needs to regulate the percentage composition of nitrogen and helium gas in a tank. Here we show how to set up a high precision gas blending schemes.

Functions of Proportional Pressure Regulator
Our QKL electronic proportional pressure regulators ( I/P converter) help with gas blending applications that need repeatable pressure control. By controlling the pressure of each specific gas to a tank through a pre-defined orifice, a tailored blend can be achieved. Here two QKL proportional pressure regulator ( I/P converter) are controlling the pressure of two types of media in a gas blending application.

Adding an extra proportional flow control valve
Our proportional pressure regulator can also work in tandem (upstream of) with the proportional flow control valve to stabilise the inlet air pressure, and thus stabilise the flow rate after the flow control valve. Proportional flow control valve acts as variable orifice, whereas proportional pressure regulator regulates and stabilizes the upstream air pressure.

Benefits
Using proportional pressure regulator to control the flow rate has several benefit: high speed flow rate change, high accuracy, and high resolution. Using our high resolution QKL proportional pressure regulator can achieve turndown ratio up to 1: 500.

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Question 3

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

Accepted Answer

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

1. Structural principle of solenoid valve

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

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

1. Direct acting solenoid valve

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

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

2. Processing direct-acting solenoid valve

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Question 4

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%).

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Question 5

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

Accepted Answer

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

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

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

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

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

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

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

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

Let's take a DC voltage with a PID signal input range of 0~10V as an example. Figure 2 lists the minimum measurable voltage corresponding to different ADC bits.

ADC (bit)	Minimum Available Voltage (mV)
8	3.906E+01
10	9.766E+00
12	2.441E+00
14	6.104E-01
16	1.526E-01
18	3.815E-02
20	9.537E-03
22	2.384E-03
24	5.960E-04

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

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

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

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

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

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

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

Question 6

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

Accepted Answer

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

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

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

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

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

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

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

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

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

Question 7

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 8

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

Accepted Answer

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

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

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

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

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

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

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

Question 9

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 10

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

Accepted Answer

What is Oxygen Partial Pressure?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Question 11

Solution of High Precision Vacuum Control in Short Range Molecular Distillation

Accepted Answer

1. What is Molecular Distillation?

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

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

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

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

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

2. How to solve the problem?

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

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

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

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

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

3. Conclusion

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

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

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

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

Question 12

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

Accepted Answer

1. Why environment would affect insects?

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

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

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

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

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

2. How to solve the problem?

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

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

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

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

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

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

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

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

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

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

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

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

3. Conclusion

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

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

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

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

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