Positive pressure leak hole calibration method and device with small leakage rate

Abstract

The present invention relates to a calibration method for a small leakage rate positive pressure leak hole. A calibration chamber and a reference chamber made of the same material as the calibration chamber are provided, and the two are separated by a differential pressure diaphragm gauge and a stop valve; the gas quantity Q·t is proportional to the reading P of the differential pressure diaphragm gauge, and it can be obtained that #imgabs0# where Q represents the leakage rate, t represents the time, and k = P0·x·A / (P2 - P1); a piston is arranged in the calibration chamber. By first measuring the pressure difference caused by pushing the piston, which is equivalent to the gas quantity flowing into the leak hole, the volume coefficient k is calculated, where: A is the cross-sectional area of the piston; x is the moving distance of the piston; P1 and P2 are the indicated values of the diaphragm before and after the piston moves; then, the change rate of the pressure P with time t caused by the leak hole to be detected flowing into the calibration chamber is measured, so as to obtain the leakage rate of the leak hole to be detected.

Description

Technical Field

[0001] The present invention relates to a calibration method and device for a positive pressure leak hole with a small leakage rate, belonging to the technical field of vacuum metrology. Background Art

[0002] The positive pressure leak hole is the leakage rate standard during positive pressure leak detection, and its leakage rate accuracy is directly related to the leak detection sensitivity and effectiveness of the leak detector. Therefore, the calibration of the positive pressure leak hole is crucial.

[0003] The working principles of the existing positive pressure leak hole calibration devices are divided into the constant pressure method and the constant volume method. Under the condition of constant temperature, the gas quantity is represented by the product PV of the pressure P and the volume V. At this time, the leakage rate Q of the leak hole is the total differential of PV with respect to time t, that is: If the volume remains unchanged, it is the constant volume method; if the pressure remains unchanged, it is the constant pressure method.

[0004] The constant pressure method is applicable to the calibration of positive pressure leak holes with a leakage rate greater than 1×10 -6 Pa·m 3 / s. Otherwise, the pressure fluctuation caused by moving the piston has too much influence. Therefore, for the leakage rate calibration less than 1×10 -6 Pa·m 3 / s, the constant volume method is adopted.

[0005] The existing constant volume method has the following deficiencies:

[0006] 1. In the traditional constant volume method, the leak hole to be calibrated is connected to the calibration chamber. As gas leaks into the calibration chamber through the leak hole to be calibrated, the indicated value of the differential pressure diaphragm gauge will change. Assuming that the volume of the calibration chamber remains unchanged, calculating the change rate of the pressure indicated value of the differential pressure diaphragm gauge with respect to time can obtain the leakage rate of the leak hole to be calibrated. However, the differential pressure diaphragm gauge measures pressure based on the elastic deformation principle of the diaphragm. While the diaphragm gauge shows the pressure change in the calibration chamber, its own diaphragm will deform, resulting in changes in the volumes of both the calibration chamber and the reference chamber. Therefore, it is not possible to directly assume that the volume remains unchanged to calculate the leakage rate, and the deformation amount of the diaphragm needs to be considered.

[0007] 2. Since the internal pressure of the positive pressure leak hole is above 1×10 5 Pa, there are many gas molecules, and the pressure is greatly affected by temperature. Therefore, the virtual leakage amount caused by the change in the pressure at the outlet end of the positive pressure leak hole due to the change in the calibration temperature is the main problem affecting the measurement lower limit and accuracy. Although in the calibration work, the method of first measuring the virtual leakage amount and then subtracting it can be used to improve the measurement lower limit, temperature change is still an important factor affecting the measurement lower limit and accuracy.

[0008] 3. There are various gases inside the positive pressure standard leak hole. Different gases are very likely to react when mixed together. When the traditional positive pressure leak hole calibration device finishes detecting one leak hole and continues to detect another leak hole with a different gas, it has to wait at least 4 hours until the gas stabilizes before starting the measurement, resulting in low efficiency. Summary of the Invention

[0009] The object of the present invention is to enable the effective traceability of the value of a positive pressure leak hole with a small leak rate, making the measurement result more accurate.

[0010] The present invention adopts the following technical solutions:

[0011] A calibration method for a positive pressure leak hole with a small leak rate. A calibration chamber and a reference chamber made of the same material as the calibration chamber are provided. The two are separated by a differential pressure diaphragm gauge and a stop valve. An exhaustable vent valve 6 is provided on the pipeline of the reference chamber, and a test valve 14 is provided on the pipeline of the calibration chamber. The calibration chamber is connected to the leak hole through the test valve 14. The leak rate Q is proportional to the reading P of the differential pressure diaphragm gauge. It can be obtained that where t represents time. A piston 10 is provided in the calibration chamber. By first measuring the pressure difference caused by pushing the piston 10, which is equivalent to the gas volume flowing into the leak hole, the volume coefficient k is calculated, k = P 0 ·x·A / (P 2 -P 1 ); where: A is the cross-sectional area of the piston; x is the moving distance of the piston; P 1 、P 2 are the indicated values of the diaphragm gauge before and after the piston moves. Then measure the change rate of the pressure P with time t caused by the gas flowing into the calibration chamber from the leak hole to be detected, so as to obtain the leak rate of the leak hole to be detected.

[0012] Preferably, both the calibration chamber and the reference chamber are arranged in a closed space, and temperature control is implemented on the closed space.

[0013] Further, the temperature control adopts a PID control system 2 to implement temperature control on the semiconductor refrigeration constant temperature control system.

[0014] Preferably, connect the leak hole to be calibrated to the calibration chamber through the test valve, read the indicated value P1 of the differential pressure diaphragm gauge, pneumatically control the piston to advance a certain distance △L, and read the indicated value P2 of the differential pressure diaphragm gauge. Then the pressure change amount △P1 = P2 - P1. Retract the piston to the original position, read the indicated value P3 of the differential pressure diaphragm gauge, △P2 = P3 - P1, then the pressure change amount △P caused by the piston advancing volume = △P1 - 1 / 2△P2; repeat the measurement N times like this, and take the average value of the N measurements.

[0015] A calibration device for a small leakage rate positive pressure leak hole adopts the above-mentioned calibration method for a small leakage rate positive pressure leak hole; the piston 10 is controlled by a pneumatic control device 16, and a capacitive grating ruler 9 is used to measure the piston stroke. The piston 10, the pneumatic control device 16, and the capacitive grating ruler 9 form a capacitive grating ruler piston measurement system; a semiconductor refrigeration module 4 is provided on the sealed space to make the sealed space into a constant temperature box 5; the semiconductor refrigeration constant temperature control system includes a power supply module, a semiconductor refrigeration module, and a temperature detection module connected in sequence, and the control module is connected to the input end of the power supply module and the output end of the temperature detection module at the same time.

[0016] Preferably, the leak hole is arranged in a space, and a three-dimensional moving workbench is arranged in the space. The leak hole is arranged on the three-dimensional moving workbench, which is convenient for the sealed connection between the leak hole and the calibration chamber. During detection, an isolation cover is used to isolate the leak hole and the connection part between the leak hole and the calibration device from the air.

[0017] Preferably, a vent valve 6 is arranged on the reference chamber pipeline. The vent valve 6 is connected to an external mechanical pump through a pipeline; when the gas of the next leak hole is different from that of the previous leak hole, after the detection of the previous leak hole is completed, the test valve 14 is closed, the stop valve 7 and the vent valve 6 are opened, and the mechanical pump is started to quickly evacuate the gas inside the calibration chamber and the reference chamber.

[0018] Preferably, it further includes a data acquisition and control system, and the data acquisition and control system is signal-connected to the PID control system 2, the differential pressure diaphragm gauge 8, and the three-dimensional moving workbench.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1) Through theoretical derivation and calculation, it is found that the amount of leaked gas and the pressure value of the differential pressure diaphragm gauge are approximately linearly related. Then, a piston is connected to the calibration chamber. By first measuring the pressure difference caused by pushing the piston, which is equivalent to the amount of gas flowing into the leak hole, the volume coefficient k is calculated. Then, the change rate of the pressure P with time t caused by the gas flowing into the calibration chamber from the leak hole to be detected is measured, so as to obtain the leakage rate of the leak hole to be detected. The detection result obtained in this way takes into account the change in the volume of the calibration chamber and the reference chamber caused by the deformation of the film, and the detection result is more accurate;

[0021] 2) The sealed space is set as a constant temperature box, and a semiconductor refrigeration module and a PID control system are used for temperature control to avoid the influence of temperature change on the detection result and improve the accuracy of detection.

[0022] 3) By setting structures such as a stop valve, a test valve, a vent valve, and a mechanical pump, the gas inside the reference chamber can be quickly evacuated, and the time interval between the detection of the previous leak hole and the next leak hole can be quickly shortened, improving the detection efficiency.

[0023] 4) A three-dimensional moving workbench is provided, and the leakage hole is arranged on the three-dimensional moving workbench, which is convenient for the sealed connection between the leakage hole and the calibration chamber. During detection, the isolation cover is used to isolate the leakage hole and the connection part between the leakage hole and the calibration device from the air, facilitating the installation of the leakage hole and the connection work before testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the front view of the calibration device for small leakage rate positive pressure leakage holes of the present invention.

[0025] Figure 2 is the perspective view of the calibration device for small leakage rate positive pressure leakage holes of the present invention.

[0026] Figure 3 is the perspective view of the capacitance grating ruler piston measurement system.

[0027] Figure 4 is the schematic diagram of semiconductor refrigeration principle.

[0028] Figure 5 is the structural diagram of the semiconductor refrigeration constant temperature control system.

[0029] Figure 6 is the schematic diagram of the installation of the semiconductor refrigeration module.

[0030] Figure 7 is the schematic diagram of the installation of the leakage hole to be calibrated.

[0031] Figure 8 is the schematic diagram of the method for improving the efficiency of continuously detecting the leakage rate of positive pressure leakage holes of different gases by using a mechanical pump.

[0032] In the figure, 1. Thin film gauge display instrument, 2. PID control system, 4. Semiconductor refrigeration module, 5. Constant temperature box, 6. Vent valve, 7. Stop valve, 8. Differential pressure thin film gauge, 9. Capacitance grating ruler, 10. Piston, 11. Temperature probe, 12. Three-dimensional moving workbench, 13. Isolation cover, 14. Test valve, 16. Pneumatic control device. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0034] See Figure 1-2 , Figure 1-2 is the schematic diagram of the positive pressure leakage hole calibration device developed by ourselves. It mainly consists of a volume measurement system composed of a capacitance grating ruler and a piston, a constant temperature system composed of a semiconductor refrigeration module and PID control, a differential pressure thin film gauge, three high-precision pneumatic surface seal valves and a vacuum pipeline. Among them, the pipeline between the differential pressure thin film gauge, the test valve and the stop valve forms a calibration chamber, and the pipeline between the differential pressure thin film gauge, the vent valve and the stop valve forms a reference chamber.

[0035] In the traditional calibration method for positive pressure leak holes, the leak hole to be calibrated is connected to the calibration chamber. As gas leaks into the leak hole to be calibrated, the indicated value of the differential pressure diaphragm gauge will change. Assuming that the volume of the calibration chamber remains unchanged, the leak rate of the leak hole to be calibrated can be obtained by calculating the change rate of the pressure indicated value of the differential pressure diaphragm gauge over time. However, the differential pressure diaphragm gauge measures pressure based on the principle of elastic deformation of the diaphragm. While the diaphragm gauge shows the pressure change in the calibration chamber, its own diaphragm will deform, resulting in changes in the volumes of both the calibration chamber and the reference chamber. Therefore, it is not possible to directly assume that the volume remains unchanged to calculate the leak rate. Through theoretical derivation and calculation, our institute has found that the amount of gas leaking in and the pressure value are approximately linearly related.

[0036] According to the ideal gas state equation under constant temperature conditions, we have:

[0037] P 0 ·V r =P r ·(V r -ΔV)

[0038] From the above equation, we get: P 0 ·V x =P x ·(V x +ΔV)+Q·t

[0039]

[0040] When ΔP is less than 1 kPa, P x / P 0 and P r / P 0 are approximately equal to 1, then

[0041] where, P 0 - atmospheric pressure, P r - pressure of the reference chamber, P x - pressure of the calibration chamber, V r - volume of the reference chamber, V x - volume of the calibration chamber, △V - change in volume of the calibration chamber, Q - leak rate of the leak hole to be calibrated, t - time, P - indicated value of the differential pressure diaphragm gauge.

[0042] According to the working principle of the differential pressure diaphragm gauge, ΔV is proportional to P, then Q·t is proportional to P, and we can get:

[0043] where: k is the volume coefficient.

[0044] Based on the above derivation, a piston can be connected to the calibration chamber. By first measuring the pressure difference caused by pushing the piston, which is equivalent to the amount of gas flowing in through the leak hole, the volume coefficient k can be calculated. Then, by measuring the change rate of the pressure P in the calibration chamber caused by the gas flowing in through the leak hole to be detected over time t, the leak rate of the leak hole to be detected can be obtained.

[0045] k=P 0 ·x·A / (P 2 -P 1 )

[0046] Where: A is the cross-sectional area of ​​the piston; x is the distance the piston moves; P1 and P2 are the values ​​indicated by the film meter before and after the piston moves.

[0047] At the same time, part of the volume will be introduced when the calibrated leak hole is connected to the calibration chamber. Although the volume introduced by the calibrated leak hole is usually very small, it directly limits the measurement limit and uncertainty of the device. The shapes of the calibrated pressure leak holes are different, and the volumes introduced are also very different, which leads to different volume coefficients of different calibrated leak holes. Therefore, it is one of the key technologies to expand the measurement limit and improve the measurement uncertainty to realize continuous measurement of the piston propulsion volume and calculate the volume coefficients of different leak holes each time calibration. The present invention adopts a method of combining a pneumatically controlled piston and a capacitive scale measurement system to realize continuous, automatic and accurate measurement of the propulsion volume.

[0048] The capacitive gate measurement system is a closed-loop control system with zero differential regulation. Its basic measurement part is a differential capacitor. Its function is to use the charge coupling method of the capacitor to convert the mechanical displacement into the corresponding change of the electrical signal. After the electrical signal is sent to the electronic circuit, it will display the size of the mechanical displacement after a series of transformations and operations. Due to the principle and advanced structural design of the capacitive gate measurement system, it has many outstanding advantages: 1. High resolution and fast measurement speed. When the resolution is 0.01mm, the measurement speed can reach 1.5m / s; 2. The structure of the sensor is simple, easy to be integrated with the integrated circuit, and easy to carry out mechanical design. The mechanical part of the sensor is mainly composed of two sets of plates, and the structure is compact, which makes the structure of the measurement system simple and low-cost. This advantage is also unmatched by other types of displacement measurement systems; 3. It has low requirements for the use environment. It can resist the interference of electric and magnetic fields and is not sensitive to air humidity. This is also a very prominent advantage of the capacitive gate measurement system; 4. Low energy consumption. This is because the dielectric loss and electrostatic attraction of the sensor itself are very small. The circuit uses large-scale CMOS integrated circuits, which enables the circuit to work under low power consumption; 5. Serial code data output can be used for computer processing and printer data recording, which provides convenient conditions for product quality control.

[0049] At the same time, in order to reduce the error caused by human operation, this device uses pneumatic control piston to change manual operation into automatic operation. Pneumatic control has the characteristics of low price, strong reliability, long life, safety and convenience, and is very suitable for piston propulsion in this device. Figure 3As shown in the figure, the piston is connected to the capacitive grating ruler through a certain mechanical structure. The piston is pushed forward a certain distance by pneumatic control, driving the capacitive grating ruler to move, and the capacitive grating ruler automatically measures the moving displacement.

[0050] When measuring the volume pushed by the piston and the resulting pressure difference, the leakage hole will also leak into a part of the volume of the calibration chamber, resulting in the measured pressure difference being caused by both the piston pushing and the leakage hole leaking. Therefore, the influence of the volume leaked by the leakage hole needs to be eliminated. The specific method is as follows:

[0051] Connect the leakage hole to be calibrated to the calibration chamber through the test valve, read the indication value P1 of the differential pressure diaphragm gauge, pneumatically control the piston to push forward a certain distance △L, and read the indication value P2 of the differential pressure diaphragm gauge. Then the pressure change amount △P1 = P2 - P1. Retract the piston to the original position, read the indication value P3 of the differential pressure diaphragm gauge, △P2 = P3 - P1, and the pressure change amount △P caused by the volume pushed by the piston is △P = △P1 - 1 / 2△P2. Repeat the measurement three times and take the average of the three measurements. This method can achieve volume compensation for leakage holes of different shapes, expand the measurement range, and improve the measurement uncertainty.

[0052] Since the internal pressure of the positive pressure leakage hole is above 1×10 5 Pa, there are many gas molecules, and the pressure is greatly affected by temperature. Therefore, the virtual leakage amount caused by the change in the outlet pressure of the positive pressure leakage hole due to the change in calibration temperature is the main problem affecting the measurement lower limit and accuracy. Although in the calibration work, the method of first measuring the virtual leakage amount and then subtracting it can be used to improve the measurement lower limit, temperature change is still an important factor affecting the measurement lower limit and accuracy. Therefore, achieving good constant temperature and reducing the measurement error caused by temperature change is one of the key technologies for developing this device.

[0053] This device combines semiconductor refrigeration technology with a PID control system to achieve temperature control inside the device. As a new type of temperature regulation technology, semiconductor refrigeration technology is increasingly favored in the world today. Compared with traditional temperature control technologies, it has both heating and cooling effects at the same time and can be switched at any time by changing the direction of the current. Semiconductor refrigeration technology is based on the Peltier principle. As Figure 4 shown, the semiconductor thermocouple is composed of an N-type semiconductor and a P-type semiconductor. The N-type semiconductor has extra electrons and a negative thermoelectric potential difference, while the P-type semiconductor has a shortage of electrons and a positive thermoelectric potential difference. When electrons pass from the P-type through the junction to the N-type, the temperature of the junction decreases. On the contrary, when electrons flow from the N-type to the P-type semiconductor, the temperature of the junction will increase. Connect several pairs of P-type semiconductor and N-type semiconductor elements in series in the way shown in Figure 4 the figure and then connect them to a DC power supply to form a semiconductor refrigerator. Compared with traditional refrigeration technologies, semiconductor refrigeration has the following characteristics:

[0054] 1. Simple structure. The whole refrigerator is composed of a thermopile and wires, with low requirements for the working environment. 2. No refrigerants, no mechanical moving parts, no noise, no wear, high reliability, long life, and convenient maintenance. 3. Small size and light weight, especially having unique advantages in the applications with small cooling capacity and small volume. 4. Fast startup and flexible control. As long as the power is connected, it can cool rapidly. Both the cooling speed and the refrigeration temperature can be achieved by adjusting the working current. 5. The operation is reversible. It can be used for refrigeration and can also be used for heating by changing the current direction. Therefore, it can be used as a thermostat above or below room temperature.

[0055] The semiconductor refrigeration technology can realize the cooling or heating of a sealed space. By effectively combining the semiconductor refrigeration technology with the automatic control technology, the constant temperature control of the space can be achieved. Figure 5 The figure shows the semiconductor refrigeration constant temperature control system diagram.

[0056] The power supply module supplies power to the semiconductor refrigeration module. The refrigeration module realizes cooling or heating. The space temperature is detected by the temperature detection module, compared with the target temperature to obtain the difference value, and through the adjustment of the error value by the control module, the goal of stable control is finally achieved. Since the model of this control object is relatively simple, the PID control method with good stability and simple structure can be used to control the temperature in the box to make it reach a constant temperature.

[0057] PID control, that is, proportional-integral-derivative control. This control method also needs to set a target value for the control object. The temperature control system compares the currently collected temperature value with the set target value, takes the difference value as the input of the PID control system, and the control system calculates the output control quantity according to the PID parameters to modify the control variable. It is a closed-loop control method. The PID controller is a linear controller, and its rule is:

[0058]

[0059] In the formula, K p represents the proportional coefficient, K i represents the integral coefficient, K d represents the derivative coefficient. Proportional control has the advantages of small error, high sensitivity, and fast dynamic response, etc.; integral control has the advantages of small steady-state error of the system and high control accuracy, etc.; derivative control can improve the dynamic characteristics of the system, reduce the overshoot, and shorten the adjustment time.

[0060] It can be seen from the formula that the relationship between the outputs of the proportional, integral, and derivative control laws and the deviation is linear. The linear operation laws are usually the simplest and most easily controllable. Therefore, the PID control has the advantages of good stability, convenient adjustment, simple structure, reliable operation, high control accuracy, and low price, and has important applications in many fields.

[0061] Since the entire calibration device is almost a system symmetric about the differential pressure diaphragm gauge and the shut-off valve, the semiconductor refrigeration module can be installed at the center position at the top inside the box, as Figure 6 shown. Two high-precision temperature probes are respectively placed at both ends of the test valve and the bleed valve close to the shut-off valve to monitor the temperatures of the calibration chamber and the reference chamber. Set the temperature of the constant temperature system to be between (23±5)°C and close to a value of the current room temperature to reduce the refrigeration or heating time. The housing can be made of stainless steel, and the heat insulation layer is made of polyethylene foam, also known as EPE pearl cotton. Polyethylene foam has the characteristics of environmental protection, light weight, long service life, very low thermal conductivity, excellent heat insulation performance, and very good chemical resistance. Therefore, it is a very good choice to use polyethylene foam as the heat insulation layer.

[0062] Due to the different sizes and shapes of the leak holes to be calibrated, the present invention is equipped with a three-dimensional moving workbench to adjust the positions of the leak holes, facilitating the sealed connection between the leak holes and the calibration device. At the same time, to reduce the influence of air flow on the leak holes to be calibrated, during detection, an isolation cover is used to isolate the leak holes and the connection parts between the leak holes and the calibration device from the air, as Figure 7 shown.

[0063] The leak rate measured by this device is as low as 1×10 -7 Pa·m 3 / s, and the airtightness requirement is very high. Therefore, all-metal sealed valves are used to prevent air leakage and bleeding. At the same time, all valves are pneumatically controlled, and the opening and closing of the valves are automatically completed through a computer program, thus avoiding the temperature influence and time error of manual valve operation. Secondly, this device adopts an automatic control program design, which can automatically collect the advancing volume of the capacitive grating ruler and the indication value of the differential pressure diaphragm gauge, and can automatically calculate the leak rate value.

[0064] The specific operation steps are as follows:

[0065] 1) Install the leak hole to be calibrated and cover the isolation cover;

[0066] 2) Connect the air source and the power supply;

[0067] 3) Close the evacuation valve and the shut-off valve;

[0068] 4) Input the laboratory atmospheric pressure and the piston advancing distance, and the system automatically collects the differential pressure change value and calculates the coefficient;

[0069] 5) Input the sampling time interval. After the measured leak rate value is stable, record the measured value;

[0070] 6) After the test record is completed, open the test record data and archive it;

[0071] 7) After the test is completed, close the test valve. Remove the leak hole to be detected.

[0072] There are various gases inside the positive pressure standard leak hole, and different gases are very likely to react when mixed together. When the traditional positive pressure leak hole calibration device finishes detecting one leak hole and continues to detect another leak hole with a different gas, it has to wait at least 4 hours until the gas stabilizes before starting the measurement, resulting in low efficiency. This project proposes a method to improve the detection efficiency, as Figure 8 shown. If the gas of the next leak hole is different from that of the previous one, after the detection of the previous leak hole is completed, close the test valve, open the stop valve, connect the vent valve to the mechanical pump, and quickly evacuate the internal gas. This method can greatly improve the detection efficiency. If the internal vacuum degree is monitored with a pressure gauge, the leak rates of standard leak holes with different outlet pressures can also be measured, preparing for the research on the calibration technology of positive pressure leak holes that require specific outlet pressures.

[0073] The above are the preferred embodiments of the present invention. Those of ordinary skill in the art can also make various transformations or improvements based on this. Without departing from the general concept of the present invention, these transformations or improvements should fall within the scope of protection required by the present invention.

Claims

1. A calibration method for a small leakage rate positive pressure leak hole, characterized in that : a calibration chamber and a reference chamber made of the same material as the calibration chamber are provided, and the two are separated by a differential pressure diaphragm gauge and a stop valve; an exhaust vent valve (6) that can exhaust gas is provided on the pipeline of the reference chamber, and a test valve (14) is provided on the pipeline of the calibration chamber. The calibration chamber is connected to the leak hole through the test valve (14); The gas quantity Q·t is proportional to the differential pressure diaphragm gauge reading P; it can be obtained that where Q represents the leakage rate and t represents time; a piston (10) is provided in the calibration chamber. By first measuring the pressure difference caused by pushing the piston (10), which is equivalent to the amount of gas flowing into the leak hole, the volume coefficient k is calculated; k = p 0 ·x·A / △P; where: A is the cross-sectional area of the piston; x is the moving distance of the piston; △P is the pressure change amount caused by the volume pushed by the piston; then measure the change rate of the pressure P with time t caused by the leak hole to be detected flowing into the calibration chamber, so as to obtain the leakage rate of the leak hole to be detected; both the calibration chamber and the reference chamber are arranged in a sealed space, and temperature control is implemented on the sealed space; the temperature control uses a PID control system (2) to implement temperature control on the semiconductor refrigeration constant temperature control system; Connect the leak hole to be calibrated to the calibration chamber through the test valve, read the indicated value P1 of the differential pressure diaphragm gauge, pneumatically control the piston to push a certain distance △L, and read the indicated value P2 of the differential pressure diaphragm gauge, then the pressure change amount △P1 = P2 - P1; return the piston to the original position, read the indicated value P3 of the differential pressure diaphragm gauge, △P2 = P3 - P1, then the pressure change amount △P caused by the volume pushed by the piston = △P1 - 1 / 2△P2; repeat the measurement N times like this, and take the average value of the N measurements.

2. The calibration method for a small leakage rate positive pressure leak hole according to claim 1, characterized in that: the piston (10) is controlled by a pneumatic control device (16), and a capacitive grating ruler (9) is used to measure the piston stroke. The piston (10), the pneumatic control device (16), and the capacitive grating ruler (9) form a capacitive grating ruler piston measurement system; a semiconductor refrigeration module (4) is provided on the sealed space to make the sealed space into a constant temperature box (5); the semiconductor refrigeration constant temperature control system includes a power module, a semiconductor refrigeration module, and a temperature detection module connected in sequence. The control module is connected to the input end of the power module and the output end of the temperature detection module at the same time.

3. The calibration method for a small leakage rate positive pressure leak hole according to claim 2, characterized in that: The leak hole is arranged in a space, and a three-dimensional moving workbench is arranged in the space. The leak hole is arranged on the three-dimensional moving workbench to facilitate the sealed connection between the leak hole and the calibration chamber. During detection, an isolation cover is used to isolate the leak hole and the connection part between the leak hole and the calibration device from the air.

4. The calibration method for a small leakage rate positive pressure leak hole according to claim 2, characterized in that: An exhaust vent valve (6) is provided on the pipeline of the reference chamber, and the exhaust vent valve (6) is connected to an external mechanical pump through a pipeline; When the gas of the next leak hole is different from that of the previous leak hole, after the detection of the previous leak hole is completed, close the test valve (14), open the stop valve (7) and the exhaust vent valve (6), start the mechanical pump, and quickly evacuate the gas inside the calibration chamber and the reference chamber.

5. The calibration method for a small leakage rate positive pressure leak hole according to claim 3, characterized in that: It further includes a data acquisition and control system, and the data acquisition and control system is respectively connected to the PID control system (2), the differential pressure diaphragm gauge, and the three-dimensional moving workbench in a signal connection manner.

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