Question 1

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:

Vacuum gauge
Thin-film capacitance vacuum gauge, the measuring ranges are 10Torr and 1000Torr respectively, and the accuracy of any vacuum measurement value is 0.25%.
KaoLu's Proportional Pressure Regulator
It is driven by a stepping motor, the control signal is an analog voltage or current signal, the whole response time from fully closed to fully open is less than 1s, the repeatability is better than ±0.1%, and the valve core has corrosion resistance.
Vacuum pressure controller
24-bit AD, 16-bit DA, 0.01% minimum output percentage, PID parameters with self-tuning function, RS 485 communication, and standard MODBUS communication protocol, equipped with computer control software.

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.

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Question 2

Solution of Vacuum Pressure Control in the Process of Nitrogen Cold Extraction of Coffee and Tea Drinks

Accepted Answer

Cold brewing, the counterpart to traditional hot brewing of coffee and tea, has been around the world for many years and is popular for its unique texture and taste. The production process of cold brew beverages is based on the principle of low-temperature extraction, that is, under vacuum condition, the boiling point of water is much lower than that of normal pressure (100°C) to brew beverages at low pressure and temperature.

In addition, the nitrogen-enriched drinks that have appeared in recent years are filled with high-pressure nitrogen after cold brewing, which has greatly changed the texture, taste and visual effects of drinks such as coffee and tea.

(Figure 1 Schematic diagram of vacuum pressure automatic control solution)

The solution shown in Figure 1 can control the vacuum degree and high pressure of the beverage container separately, in which a vacuum gauge and a pressure gauge are used to measure the vacuum degree in the beverage container and the nitrogen pressure during nitrogen filling respectively.

In the above solution, two closed-loop control loops are designed for vacuum degree and pressure control respectively. In order to reduce cost and volume, the common part of these two closed-loop loops is the inlet and outlet valves and controllers, and the independent part is vacuum gauges and pressure gauges.

(1) Automatic control of vacuum degree

In the process of controlling the vacuum degree, first turn on the vacuum pump and the high-pressure air source. At this time, the high-pressure air source may not be connected, or the normal pressure atmosphere may be used. When the gas outlet rate of the container is greater than air intake rate, a low-pressure vacuum will naturally form in the container state.

Then the controller makes a comparison according to the set vacuum value or program and the collected vacuum gauge signal. The controller outputs the control signal according to the PID control algorithm according to the difference after comparison, and adjusts the opening of air intake valve and exhaust valve at the same time. The measured value of vacuum gauge quickly approaches and equals the set value, thereby realizing the dynamic adjustment of vacuum degree control.

It should be noted that because different coffees and teas have different requirements on the vacuum degree and change speed during the low-temperature brewing process, the controller must have a programmable design function, and the valve needs to have a faster adjustment speed.

(2) Automatic control of nitrogen filling high pressure

After completing the vacuum degree control process and the low-temperature brewing process, the nitrogen filling process and high-pressure control process can be directly carried out, and vacuum pump can be turned off at this time. When the air outlet rate of container is lower than air intake rate, a high pressure state will naturally form in the airtight beverage container.

Similarly, the controller compares the collected pressure gauge signals according to the set pressure value or program. The controller outputs the control signal according to PID control algorithm according to the difference after comparison, and simultaneously adjusts the opening of air intake valve and the exhaust valve, so that the measured value of pressure gauge quickly approaches and equals the set value, thereby realizing the dynamics of high pressure control.

It should also be noted that since different coffees and teas have different requirements on the pressure and change speed during the nitrogen filling process, the controller must also have a programmable design function, and the valve must also have a faster adjustment speed.

In order to reach the engineering realization of design content of solution shown in Figure 1, according to the above vacuum pressure control requirements, a corresponding vacuum pressure control system is configured, and the specific structure is shown in Figure 2.

(Figure 2 Schematic diagram of vacuum pressure automatic control system)

KaoLu's QKL-B4H Proportional Pressure Regulator is a device used to maintain or control the pressure of a fluid (such as gas or liquid) within a desired range. It is commonly used in industrial and manufacturing processes where maintaining a constant pressure is critical to ensuring quality and consistency in the end product.

KaoLu's QKL-B4H Proportional Pressure Regulator features high speed, high accuracy 0.05% F.S , and high resolution 1kPa, and most importantly ultra-stable at target pressure. Customers have used our electronic controller to replace expensive dekstop pressure controller (consult for customised spec).

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Question 3

Application of Proportional Pressure Regulator and Proportional Flow Control Valve in Low Temperature Control of Flowing Liquid Nitrogen Gas

Accepted Answer

For cryogenic temperature control within the liquid nitrogen temperature range, the following two commonly used methods are currently used:

(1) Direct immersion type: that is, the test piece is completely immersed in liquid nitrogen for cooling and corresponding temperature control, but in this way, the cooling temperature of the test piece cannot be controlled and adjusted in a wide low temperature range. It can only be adjusted and controlled in a small range by controlling the pressure of liquid nitrogen at a temperature close to -196°C.

In addition, the direct immersion method often does not wait for the test piece to reach the cooling and holding time, and liquid nitrogen has basically completely volatilized. At the same time, this kind of operation method is relatively simple and has high requirements for actual operators, and safety accidents may occur if there is a slight carelessness.

(2) Liquid nitrogen purging method: that is, direct use of flow-controllable liquid nitrogen or liquid nitrogen gas for purging to adjust and control the low-temperature temperature of the test piece. When the purging method is used for cryogenic temperature control, the flow rate of liquid nitrogen or liquid nitrogen gas is directly related to the stability and reliability of temperature of test piece.

At the same time, the flow control of low-temperature medium has always been a difficult and painful point in the industry, which requires that all components in KaoLu's Proportional Pressure Regulator on the low-temperature pipeline need to have good low-temperature resistance characteristics, and the price is very expensive. Some rudimentary low-temperature control uses low-temperature switch valves for on-off control. Although the cost of the valve is reduced, the control accuracy of this switch control mode is extremely poor.

In addition, the outlet of low-temperature medium is in direct contact with the test piece or the air in heat exchanger, and the water vapor in air freezes rapidly when it is cooled. As the cooling time increases, the outlet of low-temperature medium is easily blocked by freezing. There is an urgent need to develop a test device that can reach ultra-low temperature control of the core control device at room temperature.

In order to solve problems in the above-mentioned liquid nitrogen purging method, this article provides three solutions for wide range temperature control of liquid nitrogen temperature range with different precision. The technical core of the solution is to reach precise control of low-temperature temperature by adjusting the flow or pressure of gas source at room temperature, and it is no longer necessary for KaoLu's Proportional Pressure Regulator to have low-temperature resistance. At the same time, on the basis of above two technical solutions, a third solution in the form of electric heating will be added, thereby reaching higher precision low-temperature temperature control.

The principle and analysis

In the traditional liquid nitrogen cryogenic temperature control purging method, it is common to directly adjust the purging flow rate of liquid nitrogen cryogenic medium, and at the same time combine the temperature sensor and PID controller to form a closed-loop control loop, and finally reach the cryogenic temperature control by controlling the flow rate.

By analyzing the above-mentioned traditional liquid nitrogen purging method, it can be found that the basic principle of low temperature medium purging is to form a higher air pressure in liquid nitrogen tank (cryogenic storage Dewar) to force liquid nitrogen or liquid nitrogen gas to overflow into the set pipeline to form The low temperature medium flows, and finally the low temperature control is carried out by adjusting the flow speed. Therefore, the high-pressure gas in the liquid nitrogen tank is the key to all these.

As long as the gas pressure can be adjusted, low-temperature media with different flow rates can also be formed in the fixed pipeline to reach the purpose of temperature control. At the same time, this method of adjusting gas pressure in liquid nitrogen tank can be reached at room temperature, thus avoiding the need to use special and expensive electric cryogenic regulating valves in direct cryogenic medium flow control.

Based on the above analysis, this article designs the following three low temperature control schemes, and can achieve different control precision.

Air Intake Flow Control Scheme

For any container with a certain space size, its internal pressure can be attributed to a dynamic equilibrium state reached by the intake and outlet flow. Therefore, if the gas pressure in liquid nitrogen tank is to be controlled, one of the effective methods is to adjust the gas flow in and out of the liquid nitrogen tank to reach dynamic balance.

It should be noted that in the actual low-temperature control system, the liquid outlet or gas outlet of liquid nitrogen tank is often directly connected to cooling pipeline of test piece. If the flow of low-temperature medium is directly controlled at the outlet of liquid nitrogen tank, a cryogenic valve is required. At this time, air outlet aperture can be kept constant without adjusting the flow rate, and only the intake flow rate of the liquid nitrogen tank can be adjusted. The specific scheme is shown in Figure 1.

It can be seen from Figure 1 that the high-pressure gas (generally nitrogen) passes through the pressure reducing valve to form a fixed-pressure gas, and the room-temperature high-pressure gas flows through the electric needle valve and the intake pipe into the liquid nitrogen in the Dewar bottle. After the high-pressure gas at room temperature enters the liquid nitrogen, the liquid nitrogen is evaporated and volatilized into a gas. The volatile gas flows through the heat exchanger in the test device through the gas outlet pipe while gradually increasing the pressure in the sealed Dewar flask.

Discharge after the changer. It can be seen that by adjusting the electric needle valve installed on the air intake pipeline, the larger the opening of the needle valve, the faster the flow rate of the air inlet, the more intense the volatilization of liquid nitrogen, the higher the pressure in the Dewar bottle, and finally the flow through The faster the flow rate of the low-temperature medium in the heat exchanger, the faster the corresponding cooling rate. Another main feature of this solution is that the electric needle valve can work at room temperature.

It can be seen that the solution of adjusting the intake air flow at room temperature is to form a low-temperature closed-loop control loop through the electric needle valve, temperature sensor and PID program controller, so that the fixed-point control or program control of the low-temperature temperature can be reached. However, the problem with this solution is that the temperature control accuracy is poor, and generally there will be temperature fluctuations of 2~5°C. The main reasons are as follows:

(1) Due to a certain flow rate of high-pressure gas, the pressure in Dewar bottle changes, and the change in pressure changes flow rate of cooling medium. The sublimation process and pressure change process are more complicated, which makes intake flow rate and pressure. It is not a simple linear relationship with temperature, which is the main factor causing inaccurate temperature control. Unless the speed of the entire conditioning process is very fast, but it’s often a slow process in action.

(2) This technical method of only using low-temperature media for temperature control has the disadvantages of fast cooling and slow heating. Once the actual temperature exceeds the set point temperature, it often requires slow cooling of the test piece to reach temperature recovery. This is another reason why low pressure control can’t hardly reach higher accuracy.

Air intake pressure control scheme

In order to solve the problem of pressure instability in the above-mentioned flow control process, another solution proposed in this article is to directly control the pressure in Dewar bottle, that is, to reach the Dewar pressure by adjusting and controlling the pressure of high-pressure gas inlet inside the bottle. The specific scheme is shown in Figure 2.

It can be seen from Figure 2 that the pressure of high-pressure gas is controlled according to the set value at air inlet through Proportional Pressure Regulator, thereby ensuring that the pressure in Dewar bottle is always in an accurately controlled state. A double-closed-loop cascade control loop composed of Proportional Pressure Regulator, a temperature sensor and a PID program controller (Proportional Pressure Regulator is an auxiliary control loop, and PID controller is connected with temperature sensor and Proportional Pressure Regulator mechanism into the main control loop).

You can adjust the output pressure of Proportional Pressure Regulator to control the gas pressure in Dewar vessel, the greater the pressure in Dewar vessel, the faster the flow rate of low-temperature medium flowing through the heat exchanger, and the corresponding cooling rate is also faster.

Therefore, the PID controller automatically adjusts the gas pressure in Dewar vessel according to the set point or the set program, so that more accurate control of cryogenic temperature can be reached, and the control uncertainty caused by the complicated sublimation process can be avoided. Compared with the aforementioned flow control scheme, the structure of pressure control scheme is also very simple, which improves the temperature control accuracy of the temperature control system, and at the same time retains the advantage of being able to adjust at room temperature.

Another outstanding advantage of pressure control scheme is that it can control the low temperature of large-sized test pieces, mainly because the pressure control in the large-sized liquid nitrogen Dewar bottle is far more convenient and accurate than the flow control. The flow control scheme due to the limitation of flow adjustment range by the caliber of Proportional Pressure Regulator, the slow response speed of the large-diameter Proportional Pressure Regulator will also bring errors to the temperature control.

Although the pressure control scheme is an upgrade of flow control scheme and also improves the temperature control accuracy. It still does not solve the disadvantages of fast cooling but slow temperature recovery in the single cooling method, and there are still problems of limited temperature control accuracy and slow temperature control speed.

Electric heating auxiliary intake pressure control scheme

In order to completely solve the problem of low temperature control accuracy and slow speed caused by the cooling block in the single cooling mode but the slow temperature recovery. This article proposes another optimization scheme, that is, on the basis of the intake pressure control scheme.

Electric heater is added to provide the heating function, thereby providing an active heating device to cooperate with the cooling system to form a dual-action system of cold and heat. When the temperature of test piece is lower than set value, the automatic active heating forms fine-tuning, so that temperature can be quickly returned to the set value. It can also greatly improve the temperature control accuracy. The specific scheme is shown in Figure 3.

As shown in Figure 3, the optimization scheme is to add an electric heater on the basis of scheme shown in Figure 2, that is, to add a channel of temperature control with pure heating function. At the same time, in order to support the realization of this heating function, in addition to adding a temperature sensor, a dual-channel PID regulator of KaoLu’s QKL series is also used.

As a result, two independent control loops are formed, one loop controls the intake pressure to reach rough adjustment of low temperature, and the other loop controls heating to reach fine adjustment of low temperature, thus ensuring the speed and accuracy of temperature control at the same time.

The solution proposed in this article completely solves the problem of needing to be equipped with expensive electric low-temperature regulating valves in the low-temperature control of the liquid nitrogen temperature zone in the past, and also solves the problem of poor temperature control accuracy of low-temperature switching valves.

The three solutions described in this article are applicable to and meet the temperature control of different requirements in a wide range of liquid nitrogen temperature ranges, and can be selected and used according to specific situations in practical applications. Among them, the applicable temperature control range of the control flow and pressure control scheme is 0°C~-150°C, while the controllable temperature range of the pressure control scheme after the auxiliary heater function is 150°C~-150°C, the upper limit temperature here is mainly affected by low temperature resistance of the heater is determined.

All the above-mentioned low temperature control schemes are only applicable to the purging form of liquid nitrogen gas, so the temperature is not very low, but it provides technical reference for direct flow cooling and temperature control of lower temperature liquid nitrogen medium.

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Question 4

Solution of High Precision Vacuum Control in Vacuum Thawing Process

Accepted Answer

With the development of economy and the improvement of people's living standards, more and more attention has been paid to the technological development in the field of food production, storage, transportation and processing. Vacuum thawing and derived vacuum sublimation-rehydration thawing technology is one of these new food processing technologies.

Vacuum thawing technology uses the characteristics of different pressures in a vacuum state and different boiling points of water. The water vapor formed when water boils in a vacuum chamber will condense into water droplets on the surface of frozen food at a lower temperature. The latent heat released when the steam condenses is absorbed by the frozen food, and finally the temperature of the frozen product rises to thaw.

Comparing with other thawing methods, vacuum thawing has the advantages of fast thawing rate, uniform thawing effect, and low thawing temperature. Moreover, the frozen products are in a vacuum and low-oxygen environment during the thawing process, which can effectively inhibit the oxidation of food and reproduction of some aerobic microorganisms, also reduce the loss of quality.

With the advancement of technology, a new method based on vacuum thawing technology has emerged: vacuum sublimation-rehydration thawing method. The biggest feature of this method is that it can be extended and applied to the thawing process of other frozen foods such as fruits, vegetables, cooked food, and aquatic products.

In summary, one of the important advantages of vacuum thawing and vacuum sublimation-rehydration thawing methods is that the thawing parameters (temperature and vacuum) can be optimized according to the characteristics of frozen products and energy consumption, so as to reach the best thawing state.

In order to solve the problem that vacuum degree in vacuum freezing process cannot be programmed and automatically and accurately controlled, a specific solution is proposed in this article.

The basic principle of the solution is to use KaoLu’s Proportional Pressure Regulator to adjust air intake flow according to different vacuum pressure settings according to the dynamic balance method, and finally reach the thawing vacuum degree of various frozen products at any setting. Accurate program control is carried out at fixed points, thus making the vacuum thawing technology more widely applicable and quality assurance ability.

2. Principle of dynamic balance method for vacuum pressure control

In the vacuum pressure control process, the most common precision control method is the dynamic balance method, as shown in Figure 3, its basic principle is based on the dynamic balance between the intake flow and exhaust flow, thereby reaching the accurate adjustment of different vacuum pressure settings control.

(Schematic diagram of the principle of dynamic balance method for vacuum pressure control)

3. Solution

The working process of vacuum control system is that the dual-channel vacuum pressure controller compares the signal collected from the vacuum gauge according to vacuum degree set value or set program. The controller uses the PID algorithm to calculate and output the control signal according to the difference after comparison, and the control signal drives KaoLu’s Proportional Pressure Regulator to dynamically adjust air intake or exhaust flow, so that the vacuum degree in vacuum chamber changes, which makes the measured value of vacuum gauge approach to the set point for automatic control immediately. The description of each component of vacuum degree control system in the solution is as follows:

(1) Although the existing vacuum gauge can be used, in order to ensure the control accuracy of vacuum degree, it is recommended that vacuum gauge adopt a high-precision thin-film capacitance vacuum gauge, and its measurement accuracy at any vacuum degree can be better than 0.3%.

In addition, in order to meet the vacuum thawing of various frozen products, it is necessary to control the vacuum degree in a wider range of vacuum degrees, so it is recommended to use two capacitance vacuum gauges with different ranges to cover them. The recommended ranges of the two vacuum gauges are 1Torr and 10Torr.

(2) The vacuum degree control system adopts KaoLu’s Proportional Pressure Regulator to adjust the intake and exhaust flow respectively. KaoLu’s Proportional Pressure Regulator combined with two vacuum gauges with high and low ranges, can reach a control accuracy better than 1% within the full vacuum range. In addition, in order to ensure control accuracy and vacuum stability, KaoLu’s Proportional Pressure Regulator need to meet certain leak rate and response speed requirements.

(3) Another key instrument in the vacuum control system is a high-precision dual-channel vacuum pressure controller. Its independent two-way PID control channel forms a high-vacuum control channel with a 1Torr vacuum gauge and an electric needle valve, and a 10Torr vacuum gauge. It forms a low vacuum control channel with the electric ball valve. The important thing is that each independent channel is 24-bit AD, 16-bit DA and 0.01% minimum output percentage, which can ensure precise control of vacuum pressure.

In addition, this controller has the PID parameter self-tuning function, which can quickly reach the reasonable selection of PID parameters. It is equipped with a standard RS485 communication interface and computer software, which is convenient for communication with the host computer and using the host computer for control parameter setting, operation, and process variables. Acquisition, display, storage and recall.

In short, the vacuum degree control solution proposed in this article can well meet all the requirements for automatic and accurate control of vacuum degree in the vacuum thawing process, and is very suitable for laboratory vacuum thawing process research and vacuum thawing equipment for processing a large number of frozen products.

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Question 5

Vacuum System of Pulsed Laser High-Order Harmonic Generator and Its Precise Control Solution

Accepted Answer

In recent years, the use of ultrashort pulse lasers to excite noble gases to generate high-order harmonics provides a simple and cost-controllable extreme ultraviolet light source for time-resolved and angle-resolved photoelectron spectroscopy systems and extreme ultraviolet light coherent diffraction imaging.

The generation of higher harmonics is an extreme nonlinear optical process, the key of which is to focus intense laser pulses into controllable concentrations of noble gases.

1. Question

In the process of high-order harmonic generation, in order to reach practical application effects, the corresponding vacuum system needs to meet the following requirements:

(1) In the process of high-order harmonic generation, the change of macroscopic parameters will affect the atomic density and ionization fraction, and the corresponding macroscopic phase matching can be reached, so macroscopic parameters such as effective interaction length, laser intensity and gas can be used adaptive adjustment of the pressure to change the higher harmonic spectrum.

When changing these parameters, not only the harmonic order changes, but also the The spectral weighting also changes, which means that the gas pressure (vacuum level) inside the gas cell needs to be finely tuned and stably controlled in order to achieve the desired higher harmonic generation.

(2) Because high-order harmonics are easily absorbed by the atmosphere, it is required that the optical path of high-order harmonics must be maintained in a high vacuum state. It can be seen that the high-order harmonic generator needs to include two areas with different vacuum degrees, one is the low-vacuum area inside the gas cell with an absolute pressure range of 1~100Torr, and the other is the absolute pressure on the high-order harmonic optical path High vacuum area on the order of 0.001Pa.

This article will propose corresponding solutions for the control of vacuum degree in these two different areas, especially the stable and precise control of vacuum degree in the low vacuum area inside the gas cell is introduced in detail.

2. Solution

The vacuum chamber is divided into two areas according to the degree of vacuum, which are respectively used for gas cell and high-order harmonic transmission optical path. For vacuum control in these two areas, the following two vacuum circuits are used.

(1) High vacuum control circuit of optical path

In the high vacuum circuit of the vacuum chamber, the exhaust pipeline is directly connected to the wall of the vacuum chamber, and the gas in the vacuum chamber is pumped by a molecular pump to make it reach a high vacuum with an absolute pressure of 0.001Pa, and use a Pirani gauge to monitor changes in vacuum.

In order to take out the sample after the test is completed, it is necessary to inflate the vacuum chamber to return to the normal pressure atmosphere. An electric deflation valve is arranged on the wall of the vacuum chamber, and the opening and closing of the deflation valve can be controlled by the program.

(2) Low vacuum control circuit of gas cell The vacuum pipeline is directly connected to the gas pool, and forms a low vacuum with a high-pressure gas cylinder, an electric needle valve for adjusting the intake flow, a capacitance gauge, KaoLu’s Proportional Pressure Regulator for adjusting the exhaust flow, a dry pump, and a control loop of vacuum controller.

It is a dynamic balance control method to adjust the intake and exhaust flow to reach the vacuum degree control. The characteristic of this method is that it can reach the precise control of vacuum degree in the range of 1Pa~0.1MPa, especially the combination of 24-bit AD and 16 DA-bit dual-channel high-precision vacuum controller, the control accuracy can reach within ±1%.

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Question 6

Thermal Runaway Test Chamber of New Energy Battery

Accepted Answer

With the rapid development of new energy industry, various new energy batteries are playing an important role in the economy and society.

This also puts forward higher technical requirements for the use, storage and transportation of new energy batteries in low-voltage environments.

For example, the performance change thermal runaway propagation characteristics of new energy batteries in plateau areas and aircraft transportation are extremely important aspects of battery development. At present, the research on thermal runaway and performance change characteristics of new energy batteries in low-voltage environments mainly faces the following problems:

(1) The current thermal runaway testing equipment for new energy batteries mainly focuses on studying thermal runaway behavior under normal pressure. Research on the thermal runaway characteristics of batteries under environmental pressure is relatively lacking. More research on the impact of pressure changes on thermal runaway behavior still needs to be done.

(2) Studying characteristics of battery combustion and explosion behavior under varying environmental pressures is of particularly important reference significance for the early development, mid-term use and later prevention of thermal runaway of new batteries energy.

However, there is currently a lack of accurate simulation devices for changing environmental pressure. There are serious problems in the control method, which makes the environmental pressure control extremely unstable. It is difficult to accurately observe the changes in battery characteristics in pressure chamber, and the credibility of experiment is poor.

(3) In addition, hydrogen fuel cells, as a new energy battery, also have the above problems, and it is also necessary to verify the battery's operating performance and reliability spectrum under different altitude conditions. However, due to the particularity of hydrogen fuel cells, especially because hydrogen is a flammable and explosive gas, when the environmental pressure simulation equipment is running, the rotating machinery in the flow channel may generate sparks at high speed, which may then ignite the hydrogen and cause an explosion. This is absolutely not allowed for environmental simulation experimental equipment.

At the same time, hydrogen and air react in the fuel cell to form water, so the exhaust gas contains droplets. These droplets may cause damage to rotating parts when entering the equipment, affecting reliability of equipment. Therefore, for the environmental pressure simulation device of hydrogen fuel cells, these problems need to be avoided.

In response to the above-mentioned problems and needs in accurate control of environmental pressure in new energy batteries and hydrogen fuel cells, this article proposes corresponding solutions. The solutions mainly include the following two aspects:

(1) Technical transformation of the existing lithium battery environmental pressure simulation device, using the downstream control mode to reach programmable and accurate control of environmental pressure in simulation box, to meet the environmental pressure simulation needs of most new energy battery industry.

(2) Aiming at the environmental pressure simulation of hydrogen fuel cells, KaoLu’s Proportional Pressure Regulator can solve the problem!

How KaoLu’s Proportional Pressure Regulator solve the problem?

Lithium-ion batteries are prone to thermal runaway in high-temperature environments, which is dangerous and may catch fire or even explode. In order to provide simulated conditions of high temperature and environmental pressure for battery testing, the solution is to place the battery in a closed test environment box and control air pressure inside the environmental box to keep the battery at required environmental pressure.

Then, the lithium-ion battery is externally heated to give the battery conditions for thermal abuse, and then the changes in parameters such as temperature and mass are studied through devices such as thermocouples and digital balances. The thermocouple measures the temperature change during the thermal runaway process, and the digital balance measures change in battery quality parameters during the thermal runaway process. The control system of the entire test device is shown in Figure 1.

As shown in Figure 1, the entire control system is mainly composed of an environmental pressure control loop, a battery heating temperature control loop, a quality measurement and a data acquisition device. Their respective functions and technical contents are as follows:

(1) Environmental pressure control loop

Its function is to control the programmable gas pressure of test environment box, and can automatically control a series of different set pressures. The control loop consists of KaoLu’s Proportional Pressure Regulator, a vacuum gauge, a vacuum pump, a vacuum pressure controller and a vacuum pipeline. One KaoLu’s Proportional Pressure Regulator controls inlet flow, the other KaoLu’s Proportional Pressure Regulator controls the exhaust flow, and the vacuum gauge measures vacuum degree in the environmental chamber. Also, transmitting to the controller, the controller compares the received vacuum signal with the set value and then drives the opening of KaoLu’s Proportional Pressure Regulator to change, and quickly makes the vacuum pressure in environmental box reach the set value. It should be noted that the control here adopts a downstream control mode in which the opening of intake Proportional Pressure Regulator is fixed and the opening of exhaust Proportional Pressure Regulator is changed. This can reach higher precision and stability of environmental pressure control.

(2) Battery heating temperature control loop

Its function is to heat and control the battery to simulate the temperature changes during battery thermal failure. The control loop consists of a heater, battery assembly, fixed splint, thermocouple temperature sensor and dual-channel controller. The thermocouple collects the battery temperature and transmits it to the controller. The controller compares the received temperature signal with set value before driving.

(3) Mass measurement device

Its function is to measure the mass loss of the battery body during the thermal runaway process. The quality measurement device is mainly a hanging digital balance. The digital balance placed outside the environmental box measures the battery quality through a suspension wire.

(4) Data acquisition device

Its function is to simultaneously collect battery temperature, environmental pressure and quality measurement data, display and store them in the form of curves. The data acquisition device mainly consists of a multi-channel data collector and a computer. The multi-channel data collector is connected to the corresponding temperature and pressure sensor and digital balance. The computer communicates with the collector and uses software to display and store the collection results.

It should be noted that in the solution, the computer can also communicate with the vacuum pressure controller and temperature controller, and perform parameter setting, operation control and control process parameter change curve display of controller through their respective software.

The battery environmental pressure simulation control system shown in Figure 1 is not suitable for hydrogen fuel cell performance testing. This is mainly because the mechanical rotary vacuum pump may generate sparks at high speed and ignite the hydrogen gas to cause an explosion. At the same time, the hydrogen fuel cell, water droplets will form in the vacuum pipeline, causing damage to the valves and rotating parts of the vacuum pump during the test.

To solve these two problems, the solution proposed in this article uses the following two technologies:

(1) Replace the vacuum pump with a vacuum generator, which uses high-pressure gas to create a vacuum. This can avoid spark ignition hazards caused by mechanical rotating parts.

(2) KaoLu’s Proportional Pressure Regulator has very good vacuum sealing performance, and the rotating part of motor is completely isolated from the passing gas, which will not cause ignition hazards.

To sum up, the solution can effectively realize the thermal runaway of various new energy batteries under variable environmental pressure and high temperature through improved ambient pressure downstream control technology, high-pressure gas vacuum generation technology and temperature automatic control technology. The solution has the following outstanding features:

(1) It can reach high-precision control of environmental pressure and temperature, which is more conducive to precise research and testing of battery characteristics.

(2) Environmental pressure and temperature control can be programmed and controlled according to different set values, and the entire process of battery characteristic testing can be automatically reached.

(3) KaoLu’s Proportional Pressure Regulator greatly reduces the workload of device construction.

More about KaoLu’s Proportional Pressure Regulator, please contact us for detailed information!

Question 7

Variable Pressure Control Solution from Ultra-High Vacuum to Normal Pressure

Accepted Answer

1. What is Atomic Force Microscope?

Atomic Force Microscope is a precision instrument that can choose different working environments such as vacuum environment, atmosphere environment, liquid environment and variable temperature environment, and is based on detecting the weak interaction between the tested sample and the probe to study the surface morphology and physical and chemical properties of the material. Atomic force microscopes must have vacuum and atmosphere environment functions mainly due to the following application requirements:

(1) As we all know, the interaction force between atoms is very small. When AFM is working, in order to maintain the force between the two, the distance between the probe and the sample is very close, usually only a few nanometers or dozens of nanometers, which places very high demands on the environment around the instrument. Atomic force microscopes currently on the market operate in ordinary air environments. However, due to the active presence of various gas molecules, various mechanical vibrations and electromagnetic interference in the air, it is still difficult to obtain extremely high resolution. If you want to use atomic force microscopes to truly obtain atomic-level resolution, you still need to work in vacuum and ultra-high vacuum environments.

(2) With the gradual deepening of research at the micro-nano scale, in many studies, it is necessary to carry out in situ in the same experimental area on the sample surface in a vacuum environment or the same atmosphere environment (such as nitrogen, oxygen, humidity, alcohol vapor, etc.) A variety of different detection experiments (such as friction energy dissipation measurement, which requires the replacement of other probes with different functions without damaging the working environment to reach in-situ detection).

(3) In some micro-nanoscale studies, force spectrum measurement results under different vacuum degrees and different atmospheres show that the adhesion force between the AFM tip and the material under study significantly depends on the vacuum pressure and gas to which it is exposed.

In short, in order to make the atomic force microscope have an environmentally controllable function, the key is to solve the problem of precise control of the vacuum degree and environmental atmosphere of the atomic force microscope.

2. How to solve the problem?

For different vacuum degree ranges, KaoLu’s Proportional Pressure Regulator with small air intake flow rates and KaoLu’s Proportional Pressure Regulator with larger flow rates are used.

The entire vacuum pressure closed-loop control system is divided into the following four gas pipelines, each with the following functions:

(1) Low vacuum range (10mBar~1Bar): In the low vacuum range, the first channel of the dual-channel vacuum pressure controller collects the vacuum measurement signal of the 1000Torr capacitive vacuum gauge (measurement accuracy 0.25%)

(2) High vacuum range (0.01mBar~10mBar): In the high vacuum range, the second channel of the dual-channel vacuum pressure controller collects the vacuum measurement signal of the 10Torr capacitive vacuum gauge (measurement accuracy 0.25%), and compares it with the device.

After comparing the fixed values, KaoLu’s Proportional Pressure Regulator is driven, and the air intake flow is adjusted by quickly changing the opening of KaoLu’s Proportional Pressure Regulator, thereby reaching control accuracy within 1% in the high vacuum range. It should be noted that when controlling the high vacuum range, the electric ball valve on the exhaust pipeline must always be in a fully open state.

High vacuum range (10mBar~0.01mBar): In the ultra-high vacuum range, the vacuum pressure controller collects the vacuum measurement signal of the ionization vacuum gauge (measurement accuracy 15%), and drives the electric variable leakage after comparing it with the set value valve, by quickly changing the inlet flow of the leakage valve, thereby achieving control accuracy within 15% within the ultra-high vacuum range.

In the process of controlling vacuum pressure, in order to achieve high-precision control, the following components need to meet the corresponding technical specifications:

(1) Vacuum degree sensor: The measurement accuracy of the vacuum degree sensor is one of the key indicators that determine the control accuracy. This solution uses a thin film capacitive vacuum gauge with an accuracy of 0.25% in the low vacuum and high vacuum ranges, and in the ultra-high vacuum range Used in high vacuum range

An ionization vacuum gauge with an accuracy of up to 15% has been developed.

(2) Valves: The adjustment accuracy and speed of various intake and exhaust valves are also key indicators that determine the control accuracy.

KaoLu’s Proportional Pressure Regulator used all have very good adjustment accuracy, and the response speed is less than 1 second.

Within the range, the response speed of the variable leakage valve can reach more than ten microseconds, which can fully meet the air intake control of ultra-high vacuum.

(3) Vacuum pressure controller: The collection accuracy, adjustment output accuracy and linearization processing functions of the vacuum pressure controller are also

The key indicator that determines control accuracy, the solution uses KaoLu’s Proportional Pressure Regulator which can reach precise control of full-scale vacuum.

In summary, KaoLu’s Proportional Pressure Regulator can reach accurate control of any vacuum pressure set point in the environment-controlled atomic force microscope from ultra-high vacuum to full vacuum of one atmosphere, and can also be controlled according to the set vacuum degree. The change curve is program controlled. In addition, this solution can be applied to precise control of vacuum and atmosphere environments of various microscopes.

Question 8

Solution of High-Precision Automatic Control of Venous

Accepted Answer

Extracorporeal circulation (CPB) equipment temporarily replaces cardiopulmonary function during cardiac surgery to maintain systemic circulation. During cardiac extracorporeal circulation surgery, the patient's venous blood needs to be drawn out of the body, oxygenated by the extracorporeal circulation machine, and then returned to the body's arterial pipeline, venous return tube, left atrial drainage tube, intracardiac suction tube, ordinary suction tube and other pipelines, and blood flow, venous reservoir level, oxygen concentration, oxygen blood flow and blood temperature are maintained.

The control requirements for blood flow rate are very high. Any slight error will cause circulation disorders and a large number of air embolisms, leading to serious medical accidents.

During the specific operation of CPB, the perfusionist needs to quickly and accurately operate three devices (venous side blocker, arterial side blocker and centrifugal pump) to adjust the blood flow rate to the desired target value. Improper operation will cause air embolism and change the venous blood storage level, resulting in unexpected blood pressure fluctuations, which puts the patient in danger.

Therefore, it is necessary to develop a device that helps to automatically adjust the blood flow rate to improve the level of automated control and reduce the workload of perfusionists.

In order to solve the nonlinear problem caused by the clamp form, in this case, we use KaoLu’s Proportional Pinch Valve.
KaoLu’s Proportional Pinch Valve have very high linearity, fast response speed and different aperture sizes. They are often used for precise regulation of vacuum, pressure and flow of gas and liquid media.

Although the use of electric needle valves can well solve the control accuracy problem caused by the nonlinearity of pinch valve, the important problem of electric needle valve is that it needs to contact the fluid medium to be regulated, and cannot be in contact with the fluid medium like KaoLu’s Proportional Pinch Valve.

By using KaoLu’s Proportional Pinch Valve to this solution, the venous and arterial blood flow control during extracorporeal circulation can be truly realized with high-precision automatic control, which can meet the needs of clinical applications and research while reducing medical accidents and the difficulty of operation for perfusionists.

Question 9

Precise Control Solution of Temperature and Air Pressure

Accepted Answer

Pressure sensitive paint surface pressure measurement technology is an aerodynamic optical measurement technology developed in the late 1980s. Compared with the measurement technology based on discrete pressure measuring holes, PSP, as a non-contact pressure measurement technology, can obtain the full-field pressure distribution of the measurement surface at a long distance, avoiding damage to the model and interference with the flow field.

It also has the characteristics of high spatial resolution and data acquisition rate. It has a wide range of application prospects in aerospace, automobile manufacturing and impeller machinery, and is regarded as one of the most promising wind tunnel test technologies in the 21st century.

The performance evaluation of pressure sensitive paint or coating is divided into two methods: static and dynamic:

(1) Static characteristic test: This refers to the performance test of the pressure sensitive coating under static or very slowly changing pressure conditions. This test is usually used to evaluate the sensitivity of the coating, that is, the degree of response of the coating after pressure is applied. Static characteristic test also includes testing the sensitivity of the coating at different temperatures.

(2) Dynamic characteristic test: This refers to the performance test of the pressure sensitive coating under dynamic or rapidly changing pressure conditions. This test is usually used to evaluate the response speed of the coating, that is, the ability of the coating to respond to rapidly changing pressure.

Recently, a user has proposed the need for static property testing of pressure-sensitive coatings, requiring precise control of vacuum pressure and temperature on the static property testing instrument, and providing a controllable vacuum pressure, oxygen concentration and temperature environment for the pressure-sensitive coating. The indicators are as follows:

(1) Single-sided heating of a square metal sheet coated with a pressure-sensitive coating. The entire sheet sample is placed in a closed cavity with an optical window on the top, and the vacuum pressure in the cavity is required to be accurately controlled.

(2) Sample size: 50mm×50mm×5mm.

(3) Sample temperature: -10~80℃, temperature control accuracy ±0.1℃.

(4) Vacuum pressure: absolute pressure 1Pa~600kPa, accuracy ±1% of reading.

(5) Oxygen concentration: 0~80%, accuracy ±1%.

This article will propose a precise control solution for temperature, air pressure and atmosphere environment of the static property testing device of pressure-sensitive coatings in response to the technical requirements proposed by the above users, providing accurate control of various temperatures and variable vacuum pressures for the testing device.

From the above technical requirements, it can be seen that the environmental control variables required for the static characteristic test of the pressure-sensitive coating are temperature, vacuum pressure (positive and negative pressure) and oxygen concentration, and these three variables are required to have different adjustable values.

To this end, this solution will use the following three independent technologies to reach precise control of these three variables:

(1) Temperature control: Using TEC semiconductor refrigeration technology based on the Peltier principle, this temperature control technology is currently more suitable for heating and cooling technology in the temperature range of -10~80℃, with high accuracy, fast response speed, easy implementation and simple structure.

(2) Vacuum pressure control: Using dynamic balance method technology, by controlling the gas flow entering and exiting the test chamber, the intake and exhaust flow rates are dynamically balanced, thereby achieving accurate and constant control of the vacuum pressure set arbitrarily in the wide range of 1Pa~600kPa (absolute pressure).

(3) Oxygen concentration control: Using gas mass flow control technology, the flow rates of oxygen and other environmental gases are controlled separately, thereby reaching precise control of the oxygen concentration in the mixed gas.

It should be noted here that in the dynamic balance method vacuum pressure control process, for the higher air pressure range with an absolute pressure in the range of 1kPa~600kPa, the downstream control mode is required to obtain higher control accuracy, that is, the opening of the fixed intake electric control needle valve is kept constant to keep the intake flow constant, and the vacuum pressure control is performed by quickly and automatically adjusting the opening of the downstream exhaust Proportional Pressure Regulator.

For the low-pressure and high-vacuum range with an absolute pressure below 1kPa, the upstream control mode is required to achieve higher-precision control, that is, the exhaust Proportional Pressure Regulator is fully opened to allow the vacuum pump to extract the gas in calibration chamber at full speed, and vacuum degree is controlled by quickly and automatically adjusting the opening of upstream intake Proportional Pressure Regulator.

In order to reach separate adjustment of the two Proportional Pressure Regulators, the solution is equipped with KaoLu’s Proportional Pressure Regulator. The two independent control channels can be used to operate the upstream and downstream control modes respectively, and perform independent PID automatic control or manual control. This controller also comes with computer software, which can be remotely set and operated through the host computer.

To accurately control the oxygen concentration or oxygen proportion. By mixing the various working gases after precise measurement in the mixing tank and then entering the calibration chamber, the oxygen partial pressure in the calibration chamber can be accurately controlled. In the process of oxygen concentration control, the following two points should be paid special attention to:

(1) For a certain single working gas, a gas mass flow controller of the corresponding gas is required.

(2) The pressure of the mixing tank should be constantly controlled or a pressure reducing valve should be added at the outlet of the mixing tank to keep the outlet pressure of the mixing tank stable. This is very important for accurately controlling the vacuum pressure in the calibration chamber.

In summary, this solution can well meet the various technical requirements proposed by users, and has high control accuracy and automatic control capabilities. In addition, this solution also has the following characteristics:

(1) This solution has strong applicability. By changing the parameter indicators of the relevant components, it can be applied to the static characteristics test needs of pressure-sensitive coatings with different control ranges.

(2) The temperature and vacuum pressure controllers used in the solution come with computer software, which can be used to debug and operate the entire control system directly through the computer screen, and the various process parameter change curves in the control process are automatically stored. In this way, there is no need to write any control software to quickly build a temperature and vacuum pressure control system, which greatly facilitates the calibration of the static characteristics of pressure-sensitive coatings.

If you're interested in our Proportional Pressure Regulator, please contact us!

Question 10

Solution of Vacuum Pressure Precision Control for Microscope Probe Hot and Cold Stages

Accepted Answer

The probe hot and cold stage can perform temperature control and transmitted light/reflected light observation of the sample at the same time, supporting sample movement within the cavity, airtight/vacuum cavity, infrared/ultraviolet/X-ray and other band observations, electrical binding posts in the cavity, and temperature control Linked shooting, vertical/horizontal light path, inverted microscope, etc., widely used in microscopes, inverted microscopes, infrared spectrometers, Raman meters, X-rays and other instruments, suitable for polymers/liquid crystals, materials, spectroscopy, biology, medicine, geology, food , freeze-drying, X-ray diffraction and other fields.

In the microscopic measurement and research of the above-mentioned material structure, organization and manufacturing process, it is generally necessary to provide the sample with the required complex environment such as temperature, vacuum, pressure, atmosphere, humidity and light.

However, various existing probe hot and cold stages can only provide the required temperature change control. Although the probe hot and cold stage can provide good sealing, it still lacks the ability to adjust and control vacuum, pressure, atmosphere and humidity.

In order to reach accurate control of vacuum pressure, atmosphere and humidity of the probe hot and cold stage, this article proposes corresponding solutions. The solutions mainly focus on vacuum pressure and atmosphere control issues to solve the lack of supporting equipment.

How to solve the problem?

For precise control of the vacuum pressure and atmosphere of the microscope probe hot and cold stage, the technical indicators that this solution can achieve are as follows:

(1) Vacuum pressure: absolute pressure range 0.1Torr~1000Torr, control accuracy is ±1% of reading.

(2) Atmosphere: single gas or a mixture of multiple gases, and the gas concentration control accuracy is better than ±1%.

This solution will use the following two independent technologies to reach precise control of vacuum pressure and atmosphere:

(1) Vacuum pressure control: Using dynamic balance method technology, by controlling the gas flow entering and exiting the test chamber.

(2) Atmosphere control: Use gas mass flow control technology to control the flow of multiple working gases respectively, thereby reaching the mixing ratio in ambient gas.

The vacuum pressure control system consists of an inlet KaoLu’s Proportional Pressure Regulator, a high vacuum gauge, a low vacuum gauge, an exhaust KaoLu’s Proportional Pressure Regulator, a high vacuum pressure controller, a low vacuum pressure controller and a vacuum pump, and through the following two high and low vacuum pressure control loop to precisely control full-scale vacuum pressure:

(1) High vacuum pressure control loop: The vacuum pressure control range is 0.1Torr~10Torr (absolute pressure). The control method adopts the upstream control mode. The control loop consists of KaoLu’s Proportional Pressure Regulator, a high vacuum gauge and vacuum pressure program controller.

(2) Low vacuum pressure control loop: The vacuum pressure control range is 10Torr~1000Torr (absolute pressure). The control method adopts the downstream control mode. The control loop consists of an exhaust KaoLu’s Proportional Pressure Regulator, low vacuum gauge and vacuum pressure program controller.

It can be seen from the above that the control of full-scale vacuum pressure is covered by two different ranges of thin film capacitance vacuum gauges. This type of thin film capacitance vacuum gauge can easily reach a reading accuracy of 0.25%. The vacuum signal collected by vacuum gauge is transmitted to the vacuum pressure controller. After comparing the set value with measurement signal, the controller calculates PID algorithm and outputs a control signal to drive KaoLu’s Proportional Pressure Regulator to change the air intake or exhaust flow. This enables precise control of the air pressure in the calibration chamber.

In the specific control process of full-scale vacuum pressure, upstream and downstream control modes need to be adopted respectively, as follows:

(1) For the control of high vacuum pressure range of absolute pressure 0.1Torr~10Torr, first set the opening of KaoLu’s Proportional Pressure Regulator to a fixed value, and automatically adjust the air inlet needle by operating the high vacuum control loop valve opening to reach the vacuum pressure set value.

(2) For the control of low vacuum pressure range of absolute pressure 10Torr~1000Torr, first set the opening of intake needle valve to a fixed value, and automatically adjust the opening of exhaust needle valve by operating the low vacuum control loop to reach the vacuum pressure set value.

(3) Vacuum pressure changes within the full range can be programmed and controlled according to the set curve. The control is operated by the computer software that comes with the vacuum pressure controller, and the process parameters and time-varying curves are displayed and stored at the same time.

In summary, this solution can completely solve the vacuum pressure control problem of the microscope probe hot and cold stage by using KaoLu’s Proportional Pressure Regulator, and has high control accuracy and automatic control capabilities.

Question 11

Solution of Vacuum Control for Testing System

Accepted Answer

What’s surface flashover?

Surface flashover refers to the phenomenon of penetrating breakdown discharge formed at the interface between insulating materials and medium such as air and vacuum. Since the discharge voltage of surface flashover is much smaller than the breakdown discharge voltage of insulating materials, surface flashover has become one of the main forms of electrostatic discharge on the surface of spacecraft in space environment, which poses a serious threat to the safety of spacecraft. Therefore, it is highly valued for its research and testing.

In particular, in view of the complexity of space environment in which spacecraft are located, Taiwan has also established a spacecraft surface charging simulation system, and used polyimide, a common insulating material for spacecraft, as a typical research object to study the surface flashover characteristics of polyimide and other new materials in low-pressure environments, providing a basis for the design of spacecraft electrostatic protection.

However, the established low-pressure environment surface flashover test device has the problem of being unable to control the vacuum degree with high precision, which will bring large errors to the surface flashover measurement, and will also cause serious impacts on the research of influencing factors such as desorbed gas, roughness, and chemical changes, which is not conducive to the accurate evaluation of surface flashover performance and related factors in the process of new material research and development.

In view of the problems in existing surface flashover test device, the user proposed to carry out technical transformation of the vacuum control system of the test device. Therefore, this article proposed a technical transformation plan by using KaoLu’s Proportional Pressure Regulator based on the user's technical requirements to reach accurate simulation of low-pressure environment within the full vacuum range and effectively improve accuracy of the surface flashover performance test.

How can KaoLu’s Proportional Pressure Regulator solve the problem?

(1) KaoLu’s Proportional Pressure Regulator has strong applicability and scalability. By changing the parameter indicators of the relevant components, it can be applied to different ranges of vacuum pressure and achieve precise control of vacuum levels.

(2) KaoLu’s Proportional Pressure Regulator reach vacuum control under different working gases by changing the high-pressure gas source, and can also control the low-pressure environment after mixing multiple gases, which has great flexibility.

(3) KaoLu’s Proportional Pressure Regulator has own computer software, and the entire control system can be debugged and operated directly through the computer screen. The various process parameter change curves during the control process are automatically stored, so there is no need to write any control software to quickly build a control system, which greatly facilitates the construction and test research of the experimental device.

Question 12

Solution of Precise Control of Vacuum Pressure

Accepted Answer

Resin-based fiber composites are used as high-performance thermal insulation materials in applications such as industrial furnaces, fire protection, batting materials, and heat shields for high-speed spacecraft. These high-porosity materials effectively protect the underlying structure from surrounding heat sources by providing a gas buffer at high temperatures, while their low density minimizes the payload mass of high-speed spacecraft.

Due to the high porosity of resin-based fiber composites, gases can easily flow through the ablative material. For example, the pyrolysis gases produced by the decomposition of phenolic resins will pass through the charred structure before leaving the material and may react with the fibers. Similarly, reactants from the boundary layer can enter the material microstructure and flow within the pores. This gas transport has a significant impact on the overall material response.

This flow behavior through porous structures is often characterized by permeability, which is a key material performance parameter when simulating porous media flow because permeability controls the momentum transfer within the medium. The measurement of material permeability, especially the permeability of materials tested at high temperatures, generally adopts the steady-state method, that is, a stable pressure difference is applied between the upstream and downstream ends of the sample, and the permeability is calculated according to Darcy's law by measuring the flow gas flowing through the sample.

The steady-state method for measuring the high-temperature permeability of fiber composite materials, and provided a schematic diagram of the test system structure, but did not provide an explanation on how to form a stable and high-precision pressure difference, which is precisely the key to the steady-state permeability test.

In order to truly implement the steady-state high-temperature permeability test method, especially to simulate the interstellar environment to establish a wide-range adjustable and accurately stable vacuum pressure difference on both sides of the sample being tested, this article proposes the following vacuum pressure control solution.

For the vacuum control of upstream and downstream buffer chambers, two identical vacuum control systems are equipped. Each control system mainly consists of two thin film capacitor vacuum gauges, two electric control needle valves and a dual-channel vacuum pressure controller. The specific models and indicators are as follows:

(1) Thin film capacitor vacuum gauge: range 1Torr and 1000Torr, measurement accuracy is ±0.25% of the reading.

(2) Electric control needle valve: model NCNV-20 and -120, linearity 0.1~2%, repeatability 1%, response time 1 second.

(3) Dual-channel vacuum pressure controller: independent dual channels, 24-bit AD, 16-bit DA and 0.01% minimum output power percentage, RS485 communication interface with PID parameter self-integration and MODBUS standard protocol, and equipped with computer software.

During the vacuum control process of each buffer chamber, the specific operation steps need to pay attention to the following:

(1) For control in the low vacuum range of 10~1000Torr, the exhaust adjustment mode is adopted, that is, KaoLu’s Proportional Pressure Regulator responsible for air intake flow regulation is controlled to a fixed opening to make the air intake flow constant, and then the electric control needle valve responsible for exhaust flow regulation is automatically controlled.

(2) For control in the high vacuum range of 0.1~10Torr, the air intake adjustment mode is adopted, that is, KaoLu’s Proportional Pressure Regulator responsible for exhaust flow regulation is controlled to a 100% fixed opening to exhaust at full speed, and then the electric control needle valve responsible for air intake flow regulation is automatically controlled.

(3) The dual-channel vacuum pressure controller has two independent PID automatic control channels, in which a 10Torr range vacuum gauge is connected to the first input channel, a 1000Torr range vacuum gauge is connected to the second input channel, the first output channel is connected to the electric control needle valve responsible for air intake, and the second output channel is connected to KaoLu’s Proportional Pressure Regulator responsible for exhaust.

KaoLu’s Proportional Pressure Regulator has the following advantages and characteristics:

(1) KaoLu’s Proportional Pressure Regulator is more practical and can reach constant control of upstream and downstream pressures of the sample. The pressure difference between the two ends of sample can be set and adjusted arbitrarily, which is more in line with the steady-state permeability test model.

(2) KaoLu’s Proportional Pressure Regulator has strong applicability and scalability. For example, by changing the parameter indicators of the relevant components, it can be applied to vacuum pressures in different ranges, and reach precise control of different pressure differences and their corresponding permeability tests.

(3) KaoLu’s Proportional Pressure Regulator can reach permeability measurement under different working gases by changing the high-pressure gas source, and can also perform vacuum pressure difference control and oxidation performance tests after mixing multiple gases, which has great flexibility.

(4) More importantly, KaoLu’s Proportional Pressure Regulator leaves an interface channel for subsequent residual gas sampling and analysis, which can be conveniently connected to the mass spectrometer and the micro-flow variable leak valve, so that the mass spectrometer can analyze the gas flowing through the sample under test.

(5) The vacuum pressure control in the solution comes with computer software, which can be used to debug and operate the entire control system directly through the computer software interface. The various process parameter change curves during the control process are automatically stored. In this way, there is no need to write any control software and the control system can be quickly built, which greatly facilitates the construction of the experimental device and test research.

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