Calibration cylinder capacity calibration device and method

Abstract

The present invention discloses a device and method for calibrating the capacity of a calibration cylinder, belonging to the technical field of measuring devices. The calibration device includes a data acquisition system, a pipeline assembly, a windshield, and a support frame. The calibration cylinder capacity is calibrated using a negative pressure suction substitution measurement method. Specifically, the mass and temperature of the liquid medium sucked into a transition container, as well as the temperature, relative humidity, and pressure of the environment, are measured. The calibration cylinder capacity is then calculated from the liquid volume, allowing the capacity value to be traced back to mass, temperature, and pressure. The present invention solves the problem of piston leakage caused by the medium entering the calibration cylinder piston cavity during conventional static weighing and volume comparison calibration methods, thereby achieving the advantages of rapid calibration of the calibration cylinder capacity and measurement performance evaluation.

Description

Technical Field

[0001] The present invention relates to a device and method for calibrating measuring instruments in the field of measurement, and in particular to a device and method for calibrating the capacity of a calibration cylinder (hereinafter referred to as a calibration cylinder) for a pulmonary function meter, and is suitable for calibrating the capacity of a calibration cylinder with a capacity of 200mL to 7L. Background Art

[0002] Spirometers are the most commonly used instruments in clinical medicine for assessing respiratory physiology. They primarily consist of a spirometer and gas analyzer, providing analytical data for diagnosis and research. Spirometers are used to measure vital capacity, forced vital capacity, maximum minute ventilation, and to perform bronchodilator tests. Their quality is a key factor influencing the reliability of test results.

[0003] According to the Guidelines for Pulmonary Function Testing (Part II) - Spirometry, to ensure reliable clinical data from spirometers, spirometers must be calibrated before routine use. JJF 1213-2008, Specification for Pulmonary Function Instrument Calibration, stipulates the use of a calibration cylinder (standard breathing simulator) to calibrate the spirometer. The volume measurement of the calibration cylinder directly impacts the accuracy of spirometry data, and thus the reliability of pulmonary function and respiratory physiological indicators.

[0004] The calibration cylinder generally consists of a cylinder body, a piston, a piston rod and a vent, such as Figure 8 As shown, the inner surface of the cylinder and the piston are in close contact, sealed by a sealing ring, forming a sealed piston chamber (a) and (b). Pulling the piston rod moves the piston, changing the volume of the piston chamber. Maximum displacement occurs when the piston moves to the rightmost end, while zero displacement occurs when it moves to the leftmost end. The corresponding difference in piston chamber volume is the maximum volume of air displaced during use, which is the total capacity of the calibration cylinder.

[0005] In recent years, the country has placed particular emphasis on basic medical science, and hospitals and health checkup centers are now equipped with spirometers. Currently, tens of thousands of spirometers nationwide are equipped with calibration cylinders suitable for subjects ranging from infants to adults. The smallest calibration cylinder has a capacity of 200mL, while the largest holds 7L. According to the Pulmonary Function Testing Guidelines (Part 2) - Spirometry, the accuracy of the calibration cylinder volume value must reach 0.5% of the total range.

[0006] Calibration of the volume of calibration cylinders falls under the purview of small and medium-capacity measurement. Currently, the national metrology technical specifications for small and medium-capacity measuring instruments primarily include JJG 259-2005 Standard Metal Scales, JJG 18-1990 Medical Syringes, JJG 20-2001 Standard Glass Scales, and JJG 10-2001 Special Glass Scales. Calibration based on these specifications, whether using the static weighing method or the volume comparison method, requires the liquid medium to be injected into the piston cavity of the calibration cylinder. Practice has shown that liquid intrusion into the piston cavity can cause the piston seal to fail, leading to leakage and, consequently, the accuracy of the calibration cylinder volume measurement results cannot meet the requirements of spirometry testing.

[0007] In summary, existing capacity verification devices and methods are not suitable for accurate calibration of calibration cylinder capacity, resulting in a lack of effective traceability of the capacity values ​​of tens of thousands of calibration cylinders nationwide. To objectively and effectively evaluate the performance indicators of calibration cylinders and confirm whether their capacities meet the ±0.5% requirement, it is urgent to develop a calibration device and method that meets these requirements. Summary of the Invention

[0008] The present invention addresses the current state of calibration cylinder capacity testing by providing a device and method for calibrating the capacity of a calibration cylinder. This method utilizes a novel capacity calibration principle: the negative pressure aspiration substitution measurement method. During calibration, the mass and temperature of the liquid medium aspirated into a transition container are measured, along with the ambient temperature, relative humidity, and pressure. The calculated liquid volume is used to determine the calibration cylinder capacity, enabling traceability of the capacity value back to mass, temperature, and pressure.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A device and method for calibrating the capacity of a calibration cylinder include data acquisition system hardware, a pipeline component, a wind shield, and a support frame.

[0011] The data acquisition system consists of a weighing module, a temperature and humidity sensor, an atmospheric pressure sensor, two temperature sensors, a temperature acquisition module and a computer.

[0012] The pipeline assembly consists of a water tank, a container, a pipeline and a weighing bucket; the pipeline includes a liquid injection pipe, a liquid level control valve, a liquid inlet pipe, a liquid inlet valve and an air pipe, so that the water tank, the container, the weighing bucket, the calibration cylinder and the atmospheric pressure sensor are interconnected.

[0013] In the present invention, in order to isolate the weighing module and weighing bucket from the external environment and reduce the influence of external airflow on the weighing, a windshield is designed and used. The left panel, right panel and upper panel of the windshield can be pushed and pulled back and forth; to facilitate pipeline connection, a row of holes with a diameter of 2 cm are provided at 3 / 4 of the height of the left and right panels; the weighing module and weighing bucket are placed during calibration to reduce the influence of the external environment on the measurement.

[0014] In this invention, transparent pneumatic hoses are used for the liquid injection pipe, liquid inlet pipe, and air pipe in order to observe the flow of pure water during calibration. A support frame for fixing the calibration cylinder is designed to ensure accurate positioning of the piston rod of the calibration cylinder during calibration. In order to ensure the temperature stability of the liquid medium, a large-capacity water tank is used and filled with pure water before calibration.

[0015] In the present invention, in order to prevent pure water from entering the piston chamber of the calibration cylinder during calibration, a negative pressure suction replacement measurement method is adopted, namely: the piston rod of the calibration cylinder moves to increase the capacity of the piston chamber from 0 to the maximum, causing the pressure in the piston chamber to drop to less than the atmospheric pressure, forming a negative pressure, and the pressure in the weighing barrel connected to it drops accordingly. Under the action of negative pressure, pure water is sucked in; when the pressure difference is 0, the flow of pure water stops; the capacity value of the calibration cylinder can be determined by measuring the volume of pure water flowing in. During calibration, first open the liquid inlet valve, push the piston rod of the calibration cylinder to 0 displacement and hold it; on an empty scale, collect the measurement data of the weighing module and the measurement data of the atmospheric pressure sensor; then, slowly pull the piston rod of the calibration cylinder to the maximum displacement and hold it until the difference between the atmospheric pressure sensor data and the atmospheric pressure measurement value measured on the empty scale does not exceed ±10Pa, and then close the liquid inlet valve; on an actual scale, collect data from the weighing module, temperature and humidity sensor, atmospheric pressure sensor, and temperature sensor. Finally, based on the measurement data, the capacity V of the calibration cylinder is calculated by the formula 20 .

[0016] The data acquisition system of the calibration device developed by this invention essentially comprises calibration software and data acquisition hardware. The calibration software manages the entry and modification of calibration information, as well as the acquisition and processing of measurement data. During calibration, it automatically collects data such as ambient temperature and humidity, atmospheric pressure parameters, mass, and temperature, and displays the relevant information on the current interface. After calibration is complete, the raw calibration data is automatically processed to generate a calibration record and a calibration certificate.

[0017] The calibration cylinder capacity calibration software installed on the computer connects the sensor and temperature acquisition module through the RS232 serial port and RS485 serial port to realize data acquisition control and data transmission; the capacity V of the calibration cylinder at the standard temperature is calculated using the universal pure water density formula, air density formula and static weighing method capacity calculation formula. 20 .

[0018] The computer's RS232 serial port communicates with the weighing module and the atmospheric pressure sensor to collect mass and atmospheric pressure data; the RS485 serial port communicates with the ambient temperature and humidity sensor and the temperature acquisition module to collect ambient temperature, humidity and pure water temperature data;

[0019] In specific practice, a liquid level control valve is used to keep the pure water level in the container at a set height; two temperature sensors are used to measure the pure water temperature, and the average value is used as the pure water temperature.

[0020] In order to cooperate with the system application, the present invention also develops a calibration method for the capacity of the calibration cylinder, which includes the following steps:

[0021] ①. Fix the calibration cylinder on the support frame, empty the weighing barrel and fasten the barrel cover, and connect other piping components;

[0022] ②. Enter the basic information of the calibration cylinder;

[0023] ③. Check the sealing performance of the calibration cylinder: Close the liquid inlet valve, slowly pull the piston rod of the calibration cylinder until the pressure sensor reading reaches the set value, and hold for 1 minute; observe the changes in the atmospheric pressure sensor reading to confirm its sealing performance;

[0024] ④. Perform an air weighing: Open the liquid inlet valve, push the piston rod of the calibration cylinder to the zero displacement position and hold it until the atmospheric pressure sensor measurement value stabilizes; collect and record the initial air pressure value p 0i and weighing module measurement value I 0i ;

[0025] ⑤. Liquid inlet: slowly pull the piston rod of the calibration cylinder to the maximum displacement and keep it there. Under the action of negative pressure, the liquid medium flows from the container into the weighing barrel. When the atmospheric pressure sensor measures the value p 1i With p 0i The absolute value of the difference between |p 1i -p 0i |≤10Pa, close the liquid inlet valve; collect and record the measured value of the weighing sensor I 1i , and the measured value p of the atmospheric pressure sensor 1i , the measured value of the ambient temperature and humidity sensor t ai , rhi, collect liquid medium temperature measurement data t 1i , t 2i ;

[0026] ⑥. Empty the liquid medium in the weighing barrel and connect the pipeline components;

[0027] Repeat ④ to ⑥ for a total of 6 times;

[0028] In the present invention, according to each collection of I 0i , I 1i , t 1i , t 2i 、p 1i , t ai 、rhi,calculate the volume value V of the calibration cylinder 20i ; Take the average value of 6 measurements As the calibration cylinder volume;

[0029] In the present invention, after the measurement is completed, data processing is performed, including:

[0030] ①. Calculate the air density ρ for each measurement ai , pure water density ρ wi , and the standard volume V 20i ;

[0031] ②Calculate V 20i Average value As the calibration cylinder capacity measurement result V 20 ;

[0032] ③. Calculate the measurement uncertainty U c (k=2);

[0033] In the present invention, the automatically generated calibration original record includes the following information:

[0034] ①. The unit, model, serial number, manufacturer and calibration date of the calibration cylinder;

[0035] ②. Air pressure data p 0i , weighing module data I 0i ;

[0036] ③. Actual atmospheric pressure data p 1i , weighing module data I 1i , temperature sensor data t 1i , t 2i , ambient temperature data t ai 、Ambient humidity data rh i ;

[0037] ④. Calculation results: air density ρ ai , liquid medium density ρ wi , and the standard volume V 20i ;

[0038] ⑤.Capacity calibration result V 20 , the uncertainty of the capacity calibration result Uc (k=2).

[0039] In the present invention, the calibration original record can be saved as an original data file in Excel format or Word format.

[0040] Compared with existing technologies, the present invention offers the following advantages: It utilizes the negative pressure generated within the piston chamber when the piston rod of the calibration cylinder is pulled to its maximum displacement to draw pure water into the weighing bucket. By collecting ambient temperature, humidity, pressure, and pure water mass and temperature data, the pure water volume is calculated as the calibration cylinder capacity. This improves calibration efficiency, avoids damage to the cylinder's seal caused by liquid entering the cylinder, and prevents residual liquid from affecting measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the overall structure of the calibration cylinder capacity calibration device provided by the present invention.

[0042] Figure 2 This is a schematic diagram of the data acquisition system provided by the present invention.

[0043] Figure 3 This is a structural schematic diagram of the pipeline assembly provided by the present invention.

[0044] Figure 4 4.a is a schematic diagram of the structure of the windshield provided by the present invention, and 4.b is a schematic diagram of the relationship between the windshield and the weighing module.

[0045] Figure 5 This is a schematic structural diagram of the support frame provided by the present invention.

[0046] Figure 6 6.a is a schematic diagram of the pallet structure provided by the present invention, and 6.b is a schematic diagram of the positional relationship between the weighing module and the pallet.

[0047] Figure 7 This is a schematic flow chart of the calibration method for the capacity of a calibration cylinder provided by the present invention.

[0048] Figure 8 This is a schematic diagram of the calibration cylinder structure in the background technology provided by the present invention.

[0049] 11. Weighing module; 111. Tray; 1111. Main body; 1112. Positioning pin; 12. Temperature and humidity sensor; 13. Atmospheric pressure sensor; 14. Temperature sensor; 15. Temperature acquisition module; 16. Computer; 2. Pipeline assembly; 21. Water tank; 22. Container; 23. Pipeline; 231. Liquid filling pipe; 232. Liquid level control valve; 233. Liquid inlet pipe; 234. Liquid inlet valve; 235. Air pipe; 24. Weighing barrel; 241. Barrel cover; 242. Barrel body; 3. Wind shield; 31. Frame; 32. Left panel; 33. Upper panel; 34. Right panel; 4. Support frame; 41. Left baffle; 42. Right baffle; 43. Screw slide; 5. Calibration cylinder; 51. Housing; 52. Piston rod; 53. Calibration cylinder air port. DETAILED DESCRIPTION

[0050] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and specific implementation methods.

[0051] like Figure 1 As shown, a calibration device for the capacity of a calibration cylinder includes a data acquisition system 1, a pipeline assembly 2, a wind shield 3 and a support frame 4.

[0052] like Figure 2 As shown, the data acquisition system consists of a weighing module 11, a temperature and humidity sensor 12, an atmospheric pressure sensor 13, two temperature sensors 14, a temperature acquisition module 15, and a computer 16. The computer 16 is an industrial computer with one RS232 serial port and one RS485 serial port, and its display is a 12-inch touch screen. The weighing module 11 is a force-compensated high-precision weighing sensor with a maximum weighing capacity of 8200g, a resolution of 0.01g, an uncertainty of 0.05g, and an RS232 serial port. The temperature and humidity sensor 12 has a temperature resolution of 0.1°C, a measurement tolerance of 0.1°C, a humidity resolution of 1%, a measurement uncertainty of 10% (k=2), and an RS485 serial port. The atmospheric pressure sensor 13 is a precision barometer with an accuracy level of 0.05 level, with RS232 serial port; the temperature sensor 14 is an immersion RTD sensor (Pt100) with a measurement uncertainty better than 0.02℃; there are two in total, measuring the temperature of the upper and lower parts of the liquid in the weighing barrel respectively; the temperature acquisition module 15 is a multi-channel data acquisition module with an RS485 communication port, and its terminal blocks are connected to the two temperature sensors; the weighing module 13 and the atmospheric pressure sensor 13 communicate with the computer 16 via the RS232 serial port; the temperature and humidity sensor 12 and the temperature acquisition module 15 communicate with the computer 16 via the RS485 serial port.

[0053] like Figure 3As shown, the piping assembly 2 consists of a water tank 21, a container 22, piping 23, and a weighing bucket 24. The water tank 21 is used to store pure water, and the container 22 is used to maintain the liquid level inside at a set position. Piping 23 includes a liquid injection pipe 231, a liquid level control valve 232, a liquid inlet pipe 233, a liquid inlet valve 234, and an air pipe 235. The liquid injection pipe 231 is connected to the water tank 21 at one end and to the liquid level control valve 232 at the other end. The liquid level control valve 232 is mounted on the container 22 and automatically supplies water and controls the liquid level at a set height. The air pipe 235 is connected to the atmospheric pressure sensor 13, the weighing bucket 24, and the calibration cylinder 5. The left end of the liquid inlet pipe 233 is inserted into the container 22, with the liquid inlet valve 234 installed in the middle. The right end is connected to the weighing bucket 24 and inserted into the bottom. Two air pipes 235 are provided, one connecting the atmospheric pressure sensor 13 to the weighing barrel 24, and the other connecting the weighing barrel 24 to the calibration cylinder air port 53. The weighing barrel 24, consisting of a lid 241 and a body 242, is placed on the tray 111 of the weighing module 11 during calibration. It serves as a transitional container, holding pure water for calibrating the calibration cylinder 5. The lid 241 is equipped with two temperature sensors and three pipe connectors, and is tightly sealed to the body 242 via a snap fastener and sealing ring.

[0054] like Figure 4 As shown, the windshield 3 is composed of a frame 31, and front, rear, left, right and upper panels. Among them, the frame 31 is made of aluminum profiles, and the left panel 32, upper panel 33, and right panel 34 can be pushed and pulled back and forth. They are made of the same material as the front panel, which are transparent organic glass panels. Figure 4 As shown in .b, the weighing module 11 and the weighing bucket 24 are placed inside the windproof cover, separated from the external environment, to reduce the impact of the external environment on the weighing; the weighing bucket 24 is placed on the tray 111 of the weighing module 11.

[0055] like Figure 5 As shown, support frame 4 is used to securely support housing 51 of calibration cylinder 5, facilitating the positioning of the calibration cylinder piston rod 52. The support frame comprises a main body 41, baffles 41 and 42, and a guide rail 43. The position of baffle 42 can be adjusted via guide rail 43 to accommodate the axial dimensions of calibration cylinder 5.

[0056] like Figure 6 As shown in FIG. a, the tray 111 is mounted horizontally on the weighing module. Figure 6As shown in .b, the tray 111 consists of a main body 1111 and a positioning pin 1112. A series of concentric circles centered on the center of the disc are drawn on the surface, and there are three countersunk holes in the middle. The main body 1111 is disc-shaped and is made of aluminum alloy; the positioning pin 1112 is 30 mm long and 6 mm in diameter, and the center of its threaded mounting hole is located on a circle with a diameter of 210 mm and is evenly distributed. The main body 1111 uses three hexagon socket bolts passing through the countersunk holes 1113 to cooperate with the weighing module 11 to achieve horizontal installation and fixation of the tray. The use of the positioning pin 1112 and the concentric rings can improve the positioning accuracy of the central placement of the weighing bucket 24 and reduce the weighing overload.

[0057] like Figure 7 The figure shows a flow chart of a calibration method for the capacity of a calibration cylinder. A specific embodiment is as follows: Before calibration, fix the cylinder 51 of the calibration cylinder 5 to the support frame and connect the pipe assembly 2. Then, start calibration according to the following steps:

[0058] Information entry: enter the calibration cylinder related information;

[0059] Start testing and open the computer serial port;

[0060] a. Check the sealing performance to confirm that the calibration cylinder 5 is well sealed;

[0061] b. Empty scale: measure and record the initial air pressure value p0 and the measured value I0 of the weighing module 11;

[0062] c. Add liquid.

[0063] d. Actual weighing: Measure and record the measured value I1 of the weighing module 11, the measured value p1 of the atmospheric pressure sensor 13, and the measured value t of the ambient temperature and humidity sensor 12. a , rh, pure water temperature measurement data t1, t2;

[0064] e. Empty the weighing bucket 24; repeat b to e for a total of 6 times;

[0065] f. I collected by measurement 0i , I 1i , t 1i , t 2i 、p 1i , t ai 、rh i , calculate the calibration cylinder volume measurement value V 20i ; Take 6 measurements of V 20i Average value As the calibration cylinder volume V 20 ; Calculate the uncertainty Uc (k=2) of the calibration result.

[0066] After the calibration is completed, save the data manually and generate the calibration cylinder calibration original record and calibration certificate.

[0067] In this specification, reference to terms such as "specific embodiment" and "specific example" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example.

[0068] The foregoing description is merely an embodiment of the present invention and is not intended to limit the present invention. The present invention is susceptible to various suitable modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A calibration device for the capacity of a calibration cylinder, characterized in that: It includes a data acquisition system, a pipeline assembly, a windshield and a support frame; the data acquisition system is composed of a weighing module, a temperature and humidity sensor, an atmospheric pressure sensor, a temperature sensor, a temperature acquisition module and a computer; The pipeline assembly consists of a water tank, a container, a pipeline and a weighing bucket. The water tank is used to store pure water, and the container is used to maintain the internal liquid level at a set position. The pipeline includes a liquid injection pipe, a liquid level control valve, a liquid inlet pipe, a liquid inlet valve and an air pipe; one end of the liquid injection pipe is connected to the water tank and the other end is connected to the liquid level control valve; the liquid level control valve is installed on the container for automatic water supply and control of the liquid level at a set height; the air pipe is connected to the atmospheric pressure sensor, the weighing bucket and the calibration cylinder; the left end of the liquid inlet pipe is inserted into the container, the liquid inlet valve is installed in the middle, and the right end is connected to the weighing bucket and inserted into the bottom; there are two air pipes, one of which connects the atmospheric pressure sensor and the weighing bucket, and the other connects the weighing bucket and the air port of the calibration cylinder; the weighing bucket consists of a bucket cover and a barrel body, and is placed on the tray of the weighing module during calibration; as a transition container, the weighing bucket is used to hold pure water for calibrating the capacity of the calibration cylinder; the bucket cover is installed with two temperature sensors and three pipe joints, and is tightly sealed with the barrel body by buckles and sealing rings; Wherein, the support frame is used to fix and support the outer shell of the calibration cylinder; Wherein, the tray is horizontally mounted on the weighing module.

2. A calibration device for a calibration cylinder according to claim 1, characterized in that: The left panel, right panel and upper panel of the wind shield can be pushed and pulled forward and backward. The support frame and the front vertical baffle are fixedly installed, and the rear vertical baffle is installed on the screw slide rail. The horizontal position can be adjusted to fix the outer shell of the calibration cylinder.

3. The calibration device for a calibration cylinder according to claim 1, characterized in that: The weighing module is a force-compensated high-precision weighing sensor with a maximum weighing capacity of 8200g, a resolution of 0.01g, an uncertainty of 0.05g, and an RS232 serial port; the temperature and humidity sensor has a temperature resolution of 0.1°C and a measurement tolerance of 0.1 ℃, humidity resolution is 1%, measurement uncertainty is 10%, and it has an RS485 serial port; the atmospheric pressure sensor is a precision barometer with an accuracy level of 0.05 and an RS232 serial port; the temperature sensor is an immersion RTD sensor with a measurement uncertainty better than 0.02℃, with two sensors in total, measuring the temperature of the upper and lower parts of the liquid in the weighing barrel respectively; the temperature acquisition module is a multi-channel data acquisition module with an RS485 communication port, and its terminal blocks are connected to two temperature sensors. The weighing module and atmospheric pressure sensor communicate with the computer through the RS232 serial port, and the temperature and humidity sensor and temperature acquisition module communicate with the computer through the RS485 serial port; the computer is an industrial computer with one RS232 serial port and one RS485 serial port.

4. A method for calibrating the capacity of a calibration cylinder, applied to the calibration device according to any one of claims 1 to 3, characterized in that: During calibration, the negative pressure suction replacement measurement method is adopted. The piston rod is slowly pulled out, and the pressure in the piston cavity of the calibration cylinder drops, which is lower than the atmospheric pressure to form a negative pressure. The pressure in the weighing barrel also drops, and pure water is sucked in. When the pressure difference is 0, the flow of pure water stops. By measuring the volume of pure water flowing in, the capacity value of the calibration cylinder can be obtained.

5. A method for calibrating the capacity of a calibration cylinder according to claim 4, characterized in that: The following steps are included ①Fix the calibration cylinder to the support frame, empty the weighing barrel and fasten the barrel cover, and connect other piping components; ② Check the sealing performance of the calibration cylinder: Close the liquid inlet valve, slowly pull the piston rod of the calibration cylinder until the atmospheric pressure measurement value reaches the set value and maintain it, and observe the changes in the atmospheric pressure sensor indication; if the pressure change does not exceed ±10Pa within 1 minute, it is considered that the calibration cylinder is well sealed; ③ Empty scale: Open the liquid inlet valve and push the piston rod to 0 position. After the atmospheric pressure sensor shows a stable value, record the measured value. p 0i , and record the measured value of the weighing module at this time I 0i ; ④ Water inlet: slowly pull the piston rod of the calibration cylinder to the maximum extension position and keep it, pure water enters the weighing barrel from the container, when the reading of the atmospheric pressure sensor is consistent with the p 0i When the absolute value of the difference is less than 10Pa, close the liquid inlet valve; ⑤ Actual weighing: Measure and record the measured value of the weighing module I 1i , the measurement value of the atmospheric pressure sensor is p 1i , measure and record the measured value of the ambient temperature and humidity sensor t ai 、 rh i , collect pure water temperature measurement value t 1i 、 t 2i ; ⑥ Empty the pure water in the weighing bucket, fasten the bucket cover, and connect other pipeline components; ⑦Repeat ③~⑥ for 6 times in total.

6. A method for calibrating the capacity of a calibration cylinder according to claim 5, characterized in that: By measurement I 0i 、 I 1i 、 t 1i 、 t 2i 、 p 1i 、 t ai 、 rh i , calculate the calibration cylinder volume measurement value V 20i ; 6 measurements V 20i Average value 20 , as the calibration cylinder volume V 20 ; According to formula (1): V 20 =( I 1- I 0).(1- ρ A / ρ B ) / ( ρ w - ρ A ).[1- α .( t -20)] Calculate the capacity of the calibration cylinder at a standard temperature of 20°C V 20 ,in: I 1 is the actual weighing value, kg; I 0 is the weight indication when the scale is empty, kg; t is the pure water temperature (the average value of the two temperature sensors), °C; ρ w for t Density of pure water at ℃, kg / m 3 ρ A is the air density, kg / m 3 ; α is the expansion coefficient of the calibration cylinder, ℃ -1 ρ B is the weight density, 7850 kg / m 3。 7. A method for calibrating the capacity of a calibration cylinder according to claim 5, characterized in that: The ambient temperature, humidity, and pressure data measured by the temperature and humidity sensor and the atmospheric pressure sensor are calculated based on the simplified air density formula (2) recommended by CIPM: ρ A =[0.34848 .p- 0.

009. rh . e 0.061.ta ] / (273.15+ t a ) to calculate the air density, where: p is the atmospheric pressure, hPa; rh is the relative humidity, %; t a is the air temperature, ℃.

8. A method for calibrating the capacity of a calibration cylinder according to claim 6, characterized in that: According to the Tanaka formula for pure water density: ρ w = a 5. [1 - ( t + a 1) 2 .(t+ a 2) / a 3 / (t+ a 4)]+ ( s 0+ s 1. t ) to calculate the density of pure water, where: a 1 = -3.983035℃, a 2 =301.797 ℃, a 3 = 522528.9℃, a 4 = 69.34881 °C, a 5 = 999.974950kg / m -3 , s 0 = -4.612 × 10 -3 kg / m 3 , s 1 = 0.106×10 -3 kg / m 3 ℃ -1 , t is the pure water temperature, ℃.

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