Question 1

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.

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

Question 2

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 3

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 4

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 5

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 6

Solution of High Precision Vacuum Control in Short Range Molecular Distillation

Accepted Answer

1. What is Molecular Distillation?

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

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

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

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

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

2. How to solve the problem?

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

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

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

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

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

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

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

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

3. Conclusion

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

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

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

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

Question 7

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

Accepted Answer

1. Why environment would affect insects?

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

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

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

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

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

2. How to solve the problem?

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

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

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

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

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

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

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

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

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

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

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

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

3. Conclusion

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

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

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

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

Question 8

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

Accepted Answer

1. Introduction of KaoLu's Electronic Vacuum Regulator

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

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

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

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

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

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

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

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

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

4. Conclusion

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

Please refer to KaoLu's website for further information.

Question 9

KaoLu's High Precision Proportional Pressure Regulator with PID Controller

Accepted Answer

1. Introduction of KaoLu's Proportional Pressure Regulator

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

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

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

2. How to solve the problem?

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

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

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

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

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

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

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

3. Examine KaoLu's Proportional Pressure Regulator

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

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

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

4. Conclusion

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

The external ultra-high-precision pressure sensor and PID controller can effectively improve the pressure control accuracy of KaoLu's Proportional Pressure Regulator, and can reach 0.1% ultra-high-precision pressure control.
In the ultra-high-precision 0.1% pressure control process, 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, 16-bit DAC and high-precision floating-point operation with an output percentage of 0.01%, which proves that it can fully meet the needs of ultra-high-precision control.
Through the solution and test verification in this article, it is proved that KaoLu's Proportional Pressure regulator can reach ultra-high-precision control at a lower cost.
The solution in this article has great flexibility, pressure sensors and KaoLu's Proportional Pressure regulator with different ranges can be selected. Ultra-high-precision control in different pressure ranges can be reached through a general-purpose ultra-high-precision PID controller.

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

Question 10

The Basic Concept of Measuring Proportional Pressure Regulator and Pressure Sensor

Accepted Answer

1. What Is Proportional Pressure Regulator and Pressure Sensor?

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

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

2. Basic Concept Regarding Accuracy

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

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

2.1 Non-Linearity and Its Measurement Method

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

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

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

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

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

The suitable fit straight line

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

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

2.2 Repeatability

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

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

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

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

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

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

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

2.3 Hysteresis

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

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

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

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

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

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

2.4 Resolution and Sensitivity

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

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

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

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

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

3. The Relationship Between Total Error and Accuracy

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

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

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

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

4. Conclusion

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

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

Question 11

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

Accepted Answer

1. What is Double-layer Glass Reactor?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

3. Solution

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

4. Conclusion

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

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

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

Question 12

Solution of Precise Control of Vacuum in Liquid Thickness Adjustment of Liquid Phase Transmission Electron Microscope

Accepted Answer

1. What is Liquid Phase Transmission Electron Microscope?

In recent years, liquid-phase transmission electron microscopy based on transmission electron microscopy, micro-nano processing, and thin-film manufacturing technologies have been used to build micro-experiment platforms at various nanoscale resolution scales and develop new nano-characterization techniques and related fields. We provide an effective way here. As shown in Figure 1, a standard liquid cell is a silicon microchip with two electronically transparent silicon nitride (SiN) film windows supported by an isolation material, between which a liquid sample is filled.

Theoretically, the thickness of liquid can be set by a spacer between microchips, but in actual observation, the microchip needs to be placed in an ultra-high vacuum environment of the transmission electron microscope, so that the pressure inside and outside of the membrane window is different. It will cause the membrane window to protrude and expand, causing the thickness of the liquid to change, and this change is often more than several times.

Therefore, unless bubbles are produced, this thickness variation will seriously affect the resolution of observation. In addition, pillars can be used to connect the top and bottom membrane windows to minimize expansion, but this kind of liquid pool with a fixed thickness cannot be loaded with different samples for observation, which is not universal and applicable.

It can be seen that the convex deformation and expansion of the liquid pool in the ultra-high vacuum environment of the transmission electron microscope is actually a usable characteristic. Through this expansion, liquid samples of different thicknesses can be reached under the condition of ensuring high resolution is more versatile and applicable to observing a variety of liquid samples. However, the premise that liquid thickness can be adjusted is that it can be accurately controlled.

Therefore, in order to reach the adjustable thickness of a liquid sample in the liquid phase electron microscope, it is necessary to try to precisely control the pressure difference between the inside and outside of the membrane window of the liquid pool. This article will introduce corresponding solutions for vacuum degree control inside the liquid pool. The high-precision control of vacuum degree will adopt the dynamic balance method, which can reach a control accuracy of ±1% under any vacuum degree within the range of 0.1~100kPa and can precisely adjustable and constantly control liquid sample thickness.

2. Solution

The solution described in this article also uses the above-mentioned dynamic balance method to control the vacuum degree of the liquid sample. The difference is that it is further refined, and the specific implementation plan and detailed description are given.

According to the vacuum degree control range corresponding to the adjustment of liquid thickness described in the above literature, we first determined that the vacuum degree control range that the solution needs to cover is 0.1~100kPa, which can basically satisfy all liquid samples under the liquid phase transmission electron microscope. Also, the need for thickness adjustment, while the vacuum degree control accuracy is required to be better than ±1%. The device is shown in Figure 2.

The vacuum degree control system for liquid sample thickness adjustment in the liquid phase electron microscope shown in Figure 4 mainly includes vacuum gauges, KaoLu's Proportional Pressure Regulator, vacuum pumps, vacuum pressure controllers, computers and their software, their respective functions and their details described as follows:

Vacuum gauge
used to precisely measure the vacuum degree of liquid samples. The vacuum gauge adopts a thin-film capacitor vacuum gauge with high measurement accuracy. In order to meet the needs of full-scale vacuum measurement, two vacuum gauges with different ranges are equipped.
KaoLu's Proportional Pressure Regulator
used to precisely adjust the intake and exhaust flow. KaoLu's Proportional Pressure Regulator is a high-speed needle valve driven by a stepping motor. It can precisely and quickly adjust the opening of the needle valve in less than 1s through an analog voltage signal of 0~10V to reach high-precision flow adjustment. It is very suitable for small sizes of vacuum control in the space. We equip two QKL series Proportional Pressure Regulators to adjust air intake and exhaust flow respectively to reach high-precision control of vacuum degree.
Vacuum pump
It is used as a vacuum source. The vacuum pump used as a vacuum source generally adopts a low-pollution dry vacuum pump and reduces the impact of vibration and noise on the entire transmission electron microscope.
Vacuum pressure controller
It is used to receive the measurement signal of the vacuum gauge, and automatically control the Proportional Pressure Regulator according to the set value of vacuum degree by PID so that the vacuum degree of the liquid sample can quickly reach the set value and keep it constant for a long time.

For high vacuum control within the range of 0.1~1kPa, the controller needs to collect the vacuum gauge 1 signal with a range of 10Torr, and at the same time, fix the Proportional Pressure Regulator for the exhaust to a fully open state, the controller automatically adjusts the opening of Proportional Pressure Regulator for air intake.

For low vacuum degree control in the range of 1~100kPa, the controller needs to collect the signal of vacuum gauge 2 with a range of 1000Torr, and at the same time fix the Proportional Pressure Regulator for the air intake at a certain opening state, and the controller controls Proportional Pressure Regulator for exhaust. The opening is automatically adjusted. In order to reach this kind of vacuum degree control in a wide range, it is equipped with an independent dual-channel KaoLu's QKL series high-precision Proportional Pressure Regulator. The two channels correspond to the signal acquisition of two vacuum gauges and form two independent channels. The closed-loop control loop automatically controls the vacuum degree in different ranges.
Computer and software
The computer is used to communicate with the vacuum pressure controller, and the computer software can perform various parameter settings, operation control, digital display, graphic display, storage, and call of the vacuum pressure controller through the interface form. Although the vacuum pressure controller can be used alone to control the vacuum degree, it needs to be manually operated through the buttons on the controller, which is complicated to operate, but it is more intuitive and simple to operate the controller through computer software.

In order to meet the high-precision requirements of liquid thickness adjustment and control, the main technical indicators of the above key components are as follows:

3. Conclusion

Liquid-phase transmission electron microscopy has become a basic technique for the real-time monitoring of nanomaterial processes in liquids. Due to the pressure difference between the liquid and high vacuum of the transmission electron microscope, the silicon nitride membrane window is usually bent, which can be adjusted by adjusting the liquid pool. Vacuum pressure is used to dynamically adjust the liquid thickness, resulting in an ultra-thin liquid layer in the central window region for high-resolution imaging.

Through the solution proposed in this article, an independent vacuum degree control device can be built for automatic adjustment and constant control of various thicknesses of microchip liquid samples in liquid transmission electron microscopy and can reach high control accuracy. In addition, the automatic control of high-precision vacuum inside the liquid pool also provides the possibility for dynamic change of liquid thickness according to the program, which is very beneficial to overcome the diffusion limitation and reach the bulk dissolution condition.

In summary, the solution provides a fundamental method for measuring and dynamically adjusting liquid thickness by using KaoLu's Proportional Pressure Regulator, enabling new experimental designs and better control of solution chemistry.

Do you want to know more about KaoLu's Proportional Pressure Regulator?
Welcome you to visit our website and our YouTube channel!

Electronic Proportional Pressure Regulator Applications