A loop-type natural gas secondary calibration system and calibration method

Abstract

This invention discloses a loop-type natural gas secondary calibration system and calibration method, including a loop unit, a flow and pressure control unit, a temperature control unit, a leak detection unit, and a control unit. Natural gas circulates within the loop unit. The flow and pressure control unit, temperature control unit, and leak detection unit are all electrically connected to the control unit. The flow and pressure control unit stabilizes the flow rate and pressure of the natural gas within the loop unit; the temperature control unit stabilizes the temperature of the natural gas within the loop unit; the leak detection unit detects whether leaks have occurred at both ends of the flow meter under test. The loop unit also includes a first electric ball valve, a differential pressure transmitter, a second temperature transmitter, and a sonic nozzle standard gauge. The calibration method includes calibration preparation, calibration operation, and leak detection operation. This system simplifies the natural gas verification and regulation process, reduces dependence on natural gas transmission stations, and has leak detection capabilities, making it worthy of widespread application.

Description

Technical Field

[0001] This invention relates to the field of natural gas metering technology, specifically to a loop-type natural gas secondary calibration system and calibration method. Background Technology

[0002] The loop-type natural gas secondary calibration system is an important device in the field of natural gas metering for calibrating natural gas flow meters. Its working principle is based on the temperature, pressure, and flow stability requirements of the verification procedure. Natural gas is injected into the circulating process system. When the required verification pressure is reached, the injection process is closed to maintain pressure stability. The gas medium in the loop system will also remain stable. The loop power equipment (circulating fan) is then started, and the required verification flow rate is set according to the verification procedure. Because the verification condition adjustment process is usually cumbersome and highly dependent on the operating conditions of the natural gas transmission station, the verification process is lengthy, consuming a large amount of manpower and resources, resulting in poor overall uncertainty and low verification efficiency. Summary of the Invention

[0003] The purpose of this invention is to provide a loop-type natural gas secondary calibration system and calibration method. This system can simplify the natural gas verification and adjustment process, reduce dependence on natural gas transmission stations, and also has leak detection capabilities, making it worthy of widespread application.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A loop-type natural gas secondary calibration system includes a loop unit, a flow and pressure control unit, a temperature control unit, a leak detection unit, and a control unit, wherein natural gas circulates within the loop unit; the flow and pressure control unit, the temperature control unit, and the leak detection unit are all electrically connected to the control unit;

[0006] The flow and pressure control unit is used to stabilize the flow and pressure of natural gas in the loop unit, including a circulating compressor installed on the loop unit and a bypass pipeline connected in parallel with the circulating compressor, and a bypass regulating valve and an ultrasonic flow meter installed on the bypass pipeline.

[0007] The temperature control unit is used to stabilize the temperature of natural gas in the loop unit, and includes a heat exchanger installed on the loop unit and a cooling module for cooling the heat exchanger.

[0008] The leak detection unit includes a first forced shut-off valve and a second forced shut-off valve spaced apart on the loop unit. A flow meter under test, an absolute pressure transmitter, and a first temperature transmitter are arranged between the first and second forced shut-off valves. A one-way detection pipeline is respectively arranged at one end of the first and second forced shut-off valves, and one end of the two one-way detection pipelines is connected to a pressure detection pipeline. A manual ball valve, a first solenoid valve, and a check valve are arranged on the one-way detection pipeline, and a gauge pressure transmitter and a second solenoid valve are arranged on the pressure detection pipeline.

[0009] The loop unit is also equipped with a first electric ball valve, a differential pressure transmitter, a second temperature transmitter, and a sonic nozzle standard gauge.

[0010] Preferably, a gas replenishment unit is provided at one end of the loop unit, and the gas replenishment unit injects natural gas into the loop unit at a preset pressure.

[0011] Preferably, the gas replenishment unit includes a gas storage cylinder group, an intake and exhaust compressor disposed at one end of the gas storage cylinder group, and a second electric ball valve sealed and installed on the loop unit; when the gas pressure in the loop unit is lower or higher than a preset value, the control unit controls the intake and exhaust compressor and the second electric ball valve to replenish or exhaust gas.

[0012] Preferably, when the natural gas pressure is adjusted by the flow and pressure control unit so that the sonic nozzle standard meter reaches the back pressure ratio condition, the flow rate through the sonic nozzle standard meter is a constant value, and the calibration operation of the flow meter under test is performed under this state.

[0013] Preferably, multiple sets of the first electric ball valve, differential pressure transmitter, second temperature transmitter, and sonic nozzle standard meter are connected in parallel. When calibrating the flow meter under test, the calibration flow value of the flow meter under test is adjusted by the combination of the sonic nozzle standard meter pipeline.

[0014] A calibration method for a loop-type natural gas secondary calibration system, the calibration method comprising the following steps:

[0015] Step 1, calibration preparation: Install the flow meter to be calibrated on the loop unit, and start the flow and pressure control unit and temperature control unit through the control unit to make the flow, pressure and temperature of natural gas in the loop unit stable within the preset range.

[0016] Step 2, calibration operation: When the back pressure ratio of the sonic nozzle standard gauge drops to the critical value or below, and the temperature value of the first temperature transmitter stabilizes at the preset value, the flow meter under test is calibrated.

[0017] Step 3, leak detection: After one flow meter under test has been calibrated, a leak detection operation is required before replacing it with another flow meter under test. First, the control unit stops the operation of the flow, pressure, and temperature control units and closes the first and second forced shut-off valves. At this time, the manual ball valve remains open, and the control unit controls the first and second solenoid valves to open. The second solenoid valve automatically closes after a delay of 5 to 15 seconds. The control unit determines the leakage of the first or second forced shut-off valve based on the reading of the gauge pressure transmitter. If there is no leakage, the flow meter under test can be replaced.

[0018] Preferably, in step three, when the gauge pressure transmitter value continues to rise, either the first forced shut-off valve or the second forced shut-off valve leaks; when the gauge pressure transmitter value remains unchanged, neither the first forced shut-off valve nor the second forced shut-off valve leaks.

[0019] Preferably, when the first or second forced shut-off valve leaks, both first solenoid valves or manual ball valves are closed simultaneously. Then, the first solenoid valve or manual ball valve in a one-way detection line is opened separately, connecting the one-way detection line to the pressure detection line. After a period of time, if the gauge pressure transmitter reading continues to rise, then the first or second forced shut-off valve in the corresponding one-way detection line is leaking.

[0020] In this invention, the flow and pressure control unit and temperature control unit can regulate the natural gas in the loop unit to within preset temperature, flow, and pressure ranges, ensuring the accuracy of the verification and calibration operations. The differential pressure transmitter has a small range and high measurement accuracy, improving the overall system uncertainty.

[0021] This self-contained system largely eliminates reliance on the gas stability of natural gas transmission stations, simplifies the traditional gas regulation process dependent on these stations, and offers high calibration efficiency. Multiple primary electric ball valves enable rapid adjustment for different flow levels, making it suitable for calibrating various sizes of flow meters. The integrated circulating compressor and bypass pipeline can quickly provide natural gas at specified flow rates and velocities, with simple and convenient adjustment.

[0022] The leak detection unit can automatically perform sealing tests on both ends of the replaced flow meter, preventing safety accidents caused by leakage. It has high detection efficiency and reduces the cost of manual testing. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the system principle of the present invention;

[0024] Figure 2This is a schematic diagram of the flow and pressure control unit and the temperature control unit of the present invention;

[0025] Figure 3 This is a schematic diagram of the leak detection unit of the present invention;

[0026] In the diagram: 1. Loop unit; 2. Flow and pressure control unit; 3. Temperature control unit; 4. Leak detection unit; 5. Control unit; 6. Gas supply unit; 7. First electric ball valve; 8. Differential pressure transmitter; 9. Second temperature transmitter; 10. Sonic nozzle standard gauge; 11. Flow meter under test; 12. Absolute pressure transmitter; 13. First temperature transmitter; 20. Circulating compressor; 21. Bypass pipeline; 22. Bypass regulating valve; 23. Ultrasonic flow meter; 30. Heat exchanger; 31. Cooling module; 40. First forced shut-off valve; 41. Second forced shut-off valve; 42. One-way detection pipeline; 43. Pressure detection pipeline; 44. Manual ball valve; 45. First solenoid valve; 46. One-way valve; 47. Gauge pressure transmitter; 48. Second solenoid valve; 60. Gas storage cylinder group; 61. Inlet and outlet compressor; 62. Second electric ball valve. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings:

[0028] like Figures 1-3 The illustrated loop-type natural gas secondary calibration system includes a loop unit 1, a flow and pressure control unit 2, a temperature control unit 3, a leak detection unit 4, and a control unit 5. Natural gas circulates within the loop unit 1. The flow and pressure control unit 2, temperature control unit 3, and leak detection unit 4 are all electrically connected to the control unit 5. In this embodiment, the main control unit 5 is an industrial computer that communicates via an RS485 bus. It has a display, memory, and is equipped with the Modbus communication protocol for data interaction with a host computer. The display shows the values ​​of various parameters measured in the system. The main control unit 5 contains a built-in program for the system's operation. This program is set up by those skilled in the art according to operational requirements and is well-known in the field, so it will not be described in detail here. The control unit 5 is located in the calibration room cabinet. The main control unit 5 collects the temperature, pressure, differential pressure, and flow meter pulse signals from the loop unit 1.

[0029] A gas replenishment unit 6 is installed at one end of the loop unit 1. The gas replenishment unit 6 injects natural gas into the loop unit 1 at a preset pressure. The gas replenishment unit 6 includes a gas storage cylinder group 60, an intake and exhaust compressor 61 sealed at one end of the gas storage cylinder group 60, and a second electric ball valve 62 sealed on the loop unit 1. One end of the intake and exhaust compressor 61 is sealed to the second electric ball valve 62. When the gas pressure in the loop unit 1 is lower or higher than the preset value, the control unit 5 controls the start and stop of the intake and exhaust compressor 61 and the opening and closing of the second electric ball valve 62 to replenish or exhaust gas. This ensures that the pressure of the natural gas in the loop unit 1 is within the preset range.

[0030] The flow and pressure control unit 2 is used to stabilize the flow and pressure of natural gas in the loop unit 1. The flow and pressure control unit 2 includes a circulating compressor 20 installed on the loop unit 1 and a bypass pipeline 21 installed in parallel with the circulating compressor 20 on the loop unit. A bypass regulating valve 22 and an ultrasonic flow meter 23 are installed on the bypass pipeline 21. The opening degree of the bypass regulating valve 22 is controlled by the main control unit 5, and in conjunction with the regulation of the circulating compressor 20, the precise control of the flow and pressure of natural gas in the loop unit 1 is realized.

[0031] The ultrasonic flow meter 23 used does not need to be in direct contact with the fluid during measurement, so it will not interfere with the fluid flow state. It has a wide measurement range and can maintain high measurement accuracy under different flow rates. It only requires the ultrasonic transducer to be installed on the outer wall of the pipe, without the need for large-scale modification of the pipe. The installation process is simple and quick, and has little impact on the production process.

[0032] The circulating compressor 20 comes in various forms, including external motor and internal motor. The circulating compressor 20 provides the power source for the fluid in the circulating unit 1. By controlling the power or frequency of the circulating compressor 20, the pressure and flow rate of the fluid can be controlled.

[0033] The loop unit 1 is also equipped with a first electric ball valve 7, a differential pressure transmitter 8, a second temperature transmitter 9, and a sonic nozzle standard gauge 10. In this embodiment, multiple sets of the first electric ball valve 7, differential pressure transmitter 8, second temperature transmitter 9, and sonic nozzle standard gauge 10 are connected in parallel. Three sets are used in this specification, and three sets are also illustrated in the attached drawings. The calibration flow value of the flow meter under test 11 is adjusted by the combination of the piping of the sonic nozzle standard gauge 10. When calibrating the flow meter under test 11, it can adapt to calibration operations with different ranges of flow values ​​of the flow meter under test 11.

[0034] For example, using the following specifications for a sonic nozzle, as shown in Table 10, the flow rate is 8m³ / s. 3 / h, 16m 3 / h、32m 3 / h、64m 3 / h, 128m3 / h、256m 3 / h, the verification procedure "JJG 643-2024 Standard Meter Method Flow Standard Device" stipulates that the standard meter used for a fixed flow range should have no less than 10 flow points within the flow range, and each flow point should be verified no less than 6 times. By simultaneously opening one or more sonic nozzle standard meter (10) pipelines, the measurement range of 8m can be achieved. 3 / h-400m 3 The turbine flow meter standard gauge was calibrated at multiple flow points. The flow calibration points are as follows:

[0035] Qmin (8m) 3 / h), Qt (40m) 3 / h), 0.2Qmax(80m 3 / h), 0.25Qmax(100m 3 / h), 0.4Qmax(160m 3 / h), 0.5Qmax(200m 3 / h), 0.7Qmax(280m 3 / h), 0.8Qmax(320m 3 / h), 0.9Qmax(360m 3 / h), Qmax (400m 3 / h).

[0036] For example, 0.25Qmax(100m 3 / h) The usable flow rate is 32m 3 / h and 64m 3 The two sonic nozzles of standard Table 10 are combined (the deviation of the calibration point is within 5%) to form a 96m... 3 / h at 95m 3 / h-105m 3 / h, meets the requirements); 0.7Qmax (280m 3 / h) The usable flow rate is 32m 3 / h and 256m 3 The two sonic nozzles of standard Table 10 are combined (the deviation of the calibration point within 5% is acceptable), resulting in a combined 288m. 3 / h at 273.6m 3 / h-302.4m 3 / h, meets the requirements); Qmax (400m 3 / h) Usable flow rate is 256m 3 / h, 128m 3 / h and 16m 3 The three sonic nozzles of / h are combined according to Table 10.

[0037] The differential pressure transmitter 8 is used to measure the pressure difference between the inlet and outlet of the flow meter under test 11 and transmit the pressure difference to the control unit 5. The differential pressure transmitter 8 has a small range and high accuracy, thereby improving the uncertainty of the overall system and providing measurement accuracy.

[0038] When the natural gas pressure in the loop unit 1 is adjusted by the flow and pressure control unit 2 so that the sonic nozzle standard gauge 10 reaches the back pressure ratio condition, the flow rate through the sonic nozzle standard gauge 10 is a constant value. Under this condition, the calibration operation of the flow meter 10 under test is performed.

[0039] Temperature control unit 3 is used to stabilize the temperature of natural gas within loop unit 1. Temperature control unit 3 includes a heat exchanger 30 installed on loop unit 1 and a cooling module 31 for cooling the heat exchanger 30. The cooling module 31 can be a commercially available air-cooled, water-cooled, or refrigeration-type cooling device; its specific structure is not described in detail in this specification. Heat exchanger 30 is used to cool the natural gas passing through it. Heat exchanger 30 can be a commercially available shell-and-tube heat exchanger, plate heat exchanger, or finned heat exchanger; its specific structure is not described in detail in this specification. Controlling the temperature and flow rate of the circulating water in cooling module 31 indirectly controls the heat exchange efficiency of heat exchanger 30, thereby achieving the purpose of cooling the outlet medium temperature of circulating compressor 20. Heat exchanger 30 is located at the air outlet of circulating compressor 20.

[0040] The leak detection unit 4 includes a first forced shut-off valve 40 and a second forced shut-off valve 41 spaced apart on the loop unit 1. A flow meter under test 11, an absolute pressure transmitter 12, and a first temperature transmitter 13 are disposed between the first forced shut-off valve 40 and the second forced shut-off valve 41. When the first forced shut-off valve 40 and the second forced shut-off valve 41 are open, natural gas can sequentially pass through the first forced shut-off valve 40, the absolute pressure transmitter 12, the first temperature transmitter 13, the flow meter under test 11, and the second forced shut-off valve 41. The absolute pressure transmitter 12 is used to detect the natural gas pressure at the inlet of the flow meter under test 11 and transmit the value to the control unit 5. The first temperature transmitter 13 is used to detect the natural gas temperature at the inlet of the flow meter under test 11 and transmit the value to the control unit 5.

[0041] A one-way detection line 42 is provided on one end of the first forced shut-off valve 40 and the second forced shut-off valve 41 respectively, and one end of the two one-way detection lines 42 is connected to the pressure detection line 43; the one-way detection line 42 can discharge the gas leaked from the first forced shut-off valve 40 or the second forced shut-off valve 41 to the pressure detection line 43.

[0042] A manual ball valve 44, a first solenoid valve 45, and a check valve 46 are sequentially arranged on the one-way detection line 42, with the check valve 46 positioned near the pressure detection line 43. A gauge pressure transmitter 47 and a second solenoid valve 48 are installed on the pressure detection line 43. The control unit 5 controls the opening and closing of the first solenoid valve 45 and the second solenoid valve 48. The gauge pressure transmitter 47 measures the gas pressure at that point and transmits the pressure value to the control unit 5. A temperature transmitter and a pressure transmitter are installed between the sonic nozzle standard gauge 10 and the second electric ball valve 62; between the second electric ball valve 62 and the circulating compressor 20; and between the heat exchanger 30 and the first forced shut-off valve 40. The control unit 5 uses these three temperature and pressure transmitters to monitor the temperature and pressure at different locations throughout the loop unit 1 in real time, enabling more accurate detection of the temperature and pressure conditions of the loop unit 1.

[0043] like Figures 1-3 The calibration method shown is a calibration method for a loop-type natural gas secondary calibration system, which includes the following steps:

[0044] Step 1: Calibration preparation. Install the flow meter 11 to be calibrated on loop unit 1. Start the flow and pressure control unit 2 and temperature control unit 3 through control unit 5. According to the flow value to be calibrated by the flow meter 11, adjust the natural gas in loop unit 1 to the specified pressure and flow rate through the circulating compressor 20 and bypass regulating valve 22. Adjust the temperature of the natural gas in loop unit 1 through heat exchanger 30, so that the flow rate, pressure and temperature of the natural gas in loop unit 1 are stable within the preset range.

[0045] Step two, calibration: When the back pressure ratio of the sonic nozzle standard gauge 10 decreases to or below the critical value, the instantaneous flow rate reaches a stable state, and the temperature value of the first temperature transmitter 13 stabilizes within the preset range, the flow meter under test 11 is calibrated. The calibration flow value of the flow meter under test 11 can be adjusted by combining the pipelines of the sonic nozzle standard gauge 10. This allows for the calibration of different flow values ​​of the same flow meter under test 11.

[0046] Step 3: Leak Detection. After one flow meter 11 under test has been calibrated, a leak detection operation is required before replacing it with another flow meter 11. First, control unit 5 stops the operation of flow and pressure control unit 2 and temperature control unit 3, and closes the first forced shut-off valve 40 and the second forced shut-off valve 41. At this time, manual ball valve 44 remains open, and control unit 5 controls the first solenoid valve 45 and the second solenoid valve 48 to open. The second solenoid valve 48 automatically closes after a delay of 5-15 seconds. Control unit 5 determines the leakage status of the first forced shut-off valve 40 or the second forced shut-off valve 41 based on the reading from the gauge pressure transmitter 47. If there is no leakage, the flow meter 11 under test can be replaced. Manual ball valve 44 is normally open, but can be manually closed in case of emergencies.

[0047] Specifically, the second solenoid valve 48 automatically closes after a 10-second delay. If the reading on the gauge pressure transmitter 47 continues to rise after the second solenoid valve 48 closes, it indicates that either the first forced shut-off valve 40 or the second forced shut-off valve 41 is leaking. Conversely, if the reading on the gauge pressure transmitter 47 remains unchanged, it indicates that neither the first forced shut-off valve 40 nor the second forced shut-off valve 41 is leaking.

[0048] When the reading on the gauge pressure transmitter 47 continues to rise, it indicates a leak in either the first forced shut-off valve 40 or the second forced shut-off valve 41. However, it's impossible to directly determine which valve is leaking. To pinpoint the leak, both first solenoid valves 45 or manual ball valves 44 are simultaneously closed. When using automatic control with the control unit 5, the first solenoid valve 45 is closed; when using manual control, either the first solenoid valve 45 or the manual ball valve 44 can be closed. Then, a single first solenoid valve 45 or manual ball valve 44 in a one-way detection line 42 is opened, connecting it to the pressure detection line 43. After maintaining this connection for a period, if the reading on the gauge pressure transmitter 47 continues to rise, it indicates a leak in either the first forced shut-off valve 40 or the second forced shut-off valve 41 in that one-way detection line 42. After the test is completed, close the one-way detection line 42, and then open the first solenoid valve 45 or manual ball valve 44 in another one-way detection line 42 to connect the one-way detection line 42 with the pressure detection line 43. After a period of time, when the value of the gauge pressure transmitter 47 continues to rise, it corresponds to a leak in the first forced shut-off valve 40 or the second forced shut-off valve 41 of the one-way detection line 42.

[0049] The above embodiments are merely illustrative of the concept and implementation of the present invention and are not intended to limit it. Under the concept of the present invention, technical solutions without substantial changes are still within the scope of protection.

Claims

1. A loop natural gas secondary calibration system, characterized by: The application relates to a natural gas calibration device, which comprises a loop unit (1), a flow and pressure control unit (2), a temperature control unit (3), a leak detection unit (4) and a control unit (5), and natural gas circulates in the loop unit (1); the flow and pressure control unit (2), the temperature control unit (3) and the leak detection unit (4) are electrically connected with the control unit (5); The flow and pressure control unit (2) is used for stabilizing the flow and pressure of natural gas in the loop unit (1) and comprises a circulating compressor (20) arranged on the loop unit (1) and a bypass pipeline (21) arranged in parallel with the circulating compressor (20), a bypass adjusting valve (22) and an ultrasonic flowmeter (23) are arranged on the bypass pipeline (21); The temperature control unit (3) is used for stabilizing the temperature of natural gas in the loop unit (1) and comprises a heat exchanger (30) arranged on the loop unit (1) and a cooling module (31) for cooling the heat exchanger (30); The leak detection unit (4) comprises a first forced sealing valve (40) and a second forced sealing valve (41) which are arranged at intervals on the loop unit (1), a detected flowmeter (11), an absolute pressure transmitter (12) and a first temperature transmitter (13) are arranged between the first forced sealing valve (40) and the second forced sealing valve (41), one-way detection pipelines (42) are arranged at one end of the first forced sealing valve (40) and the second forced sealing valve (41) respectively, one ends of the two one-way detection pipelines (42) are connected to a pressure detection pipeline (43), a hand-operated ball valve (44), a first electromagnetic valve (45) and a one-way valve (46) are arranged on the one-way detection pipeline (42), and a gauge pressure transmitter (47) and a second electromagnetic valve (48) are arranged on the pressure detection pipeline (43); A first electric ball valve (7), a differential pressure transmitter (8), a second temperature transmitter (9) and an acoustic nozzle standard table (10) are further arranged on the loop unit (1).

2. The loop natural gas secondary calibration system of claim 1, wherein: A gas supplement unit (6) is arranged at one end of the loop unit (1), the gas supplement unit (6) injects natural gas into the loop unit (1) according to a preset pressure.

3. The loop natural gas secondary calibration system of claim 2, wherein: The gas supplement unit (6) comprises a gas storage bottle group (60), an air intake and exhaust compressor (61) arranged at one end of the gas storage bottle group (60) and a second electric ball valve (62) sealingly arranged on the loop unit (1), when the gas pressure in the loop unit (1) is lower than or higher than a preset value, the control unit (5) controls the air intake and exhaust compressor (61) and the second electric ball valve (62) to supplement or exhaust gas.

4. The loop natural gas secondary calibration system of claim 1, wherein: When the pressure of natural gas is adjusted by the flow and pressure control unit (2) so that the acoustic nozzle standard table (10) reaches a back pressure ratio condition, the flow through the acoustic nozzle standard table (10) is a constant value, and the calibration operation of the detected flowmeter (11) is carried out under the condition.

5. The loop natural gas secondary calibration system of claim 1 or 4, wherein: The first electric ball valve (7), the differential pressure transmitter (8), the second temperature transmitter (9) and the sonic nozzle standard table (10) are arranged in parallel in multiple groups, and when the calibration operation of the detected flowmeter (11) is performed, the detected flowmeter (11) is adjusted by the combination of the sonic nozzle standard table (10) pipeline.

6. A method of calibrating a loop natural gas subcalibration system according to any one of claims 1 to 5, characterized in that: The calibration method comprises the following steps: Step one, calibration operation preparation, the detected flowmeter (11) to be calibrated is installed on the loop unit (1), the flow and pressure control unit (2) and the temperature control unit (3) are started by the control unit (5), so that the flow, pressure and temperature of the natural gas in the loop unit (1) are stabilized in the preset value range; Step two, calibration operation, when the back pressure ratio of the sonic nozzle standard table (10) is reduced to the critical value and below, and the temperature value of the first temperature transmitter (13) is stabilized at the preset value, the detected flowmeter (11) is calibrated; Step three, leak detection operation, after the calibration of a detected flowmeter (11) is completed, before another detected flowmeter (11) is replaced, the leak detection operation needs to be performed first, first, the flow and pressure control unit (2) and the temperature control unit (3) are stopped by the control unit (5), and the first forced sealing valve (40) and the second forced sealing valve (41) are closed; At this time, the manual ball valve (44) remains open, the control unit (5) controls the first electromagnetic valve (45) and the second electromagnetic valve (48) to open, the second electromagnetic valve (48) is automatically closed after a delay of 5-15s, and the control unit (5) judges the leakage of the first forced sealing valve (40) or the second forced sealing valve (41) according to the value of the gage pressure transmitter (47); When there is no leakage, the detected flowmeter (11) can be replaced.

7. The method of calibration of claim 6, wherein: In the step three, when the value of the gage pressure transmitter (47) continuously rises, the first forced sealing valve (40) or the second forced sealing valve (41) leaks; When the value of the gage pressure transmitter (47) remains unchanged, neither the first forced sealing valve (40) nor the second forced sealing valve (41) leaks.

8. The method of calibration of claim 7, wherein: When the first forced sealing valve (40) or the second forced sealing valve (41) leaks, both the first electromagnetic valve (45) or the manual ball valve (44) are closed, and then one of the first electromagnetic valve (45) or the manual ball valve (44) in the one-way detection pipeline (42) is opened alone, so that the one-way detection pipeline (42) is connected with the pressure detection pipeline (43), and after a period of time, when the value of the gage pressure transmitter (47) continues to rise, the first forced sealing valve (40) or the second forced sealing valve (41) corresponding to the one-way detection pipeline (42) leaks.

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