Calibration device of self-circulation piston

Abstract

The calibration device comprises a standard volume tube and a detection control system, the standard volume tube comprises a metering cylinder body and a piston which forms sliding sealing with the inner wall of the metering cylinder body, the interior of the metering cylinder body is divided into a left metering cavity and a right metering cavity by taking the piston as a boundary, and the metering cylinder body is used for measuring fluid to be measured; the detection control system comprises a detection element, a detection calibration module, a circulation pipeline and a control module, the control module controls liquid feeding of the left metering cavity or the right metering cavity, the piston is pushed to move in the direction of one side, and after the piston moves in place, the detection element is matched with the control module to switch liquid to enter the left metering cavity or the right metering cavity, so that the detection calibration module is started. Compared with a traditional standard volume provided with an external driving mechanism, self-circulation movement of the piston is achieved under the condition that no external driving mechanism exists, and therefore the requirement for detecting the small flow of liquid is met, and repeated use is achieved.

Description

Technical Field

[0001] The invention relates to the field of standard volume tubes, in particular to a calibration device for a self-circulating piston. Background Art

[0002] As a flow standard device for calibrating liquid flow meters, the standard volume tube allows liquid to flow through the volume tube and the meter being tested in turn, and records the volume change and time in the cavity to calculate the volume flow rate. This method has the advantages of simple structure, easy use, good repeatability, and the measurement results can be directly traced back to length and time.

[0003] Standard volume tubes can be divided into active piston type and passive piston type according to the driving method. The active type needs to be driven by a mechanism such as a screw. In contrast, the passive type relies on the on-site liquid itself to push the piston to move, and has the advantages of simple structure and few moving parts. In the semiconductor field, many kinds of process liquid media are needed, which have the characteristics of small flow, high precision, and low impurity content. At the same time, the flow controller cannot be easily removed for inspection, so in-situ calibration is required. In the existing scheme, the structure of the active piston is relatively complex, and the moving parts are prone to liquid contamination, leakage and other problems, while the passive piston has the problem of difficulty in resetting, and the upper limit of the calibration flow is limited by the working volume. Summary of the invention

[0004] Aiming at the disadvantage of the prior art passive piston being difficult to reset, the present invention provides a calibration device for a self-circulating piston.

[0005] In order to solve the above technical problems, the present invention is solved by the following technical solutions: a self-circulating piston calibration device, comprising a standard volume tube, the standard volume tube comprising a metering cylinder and a piston forming a sliding seal with the inner wall of the metering cylinder, characterized in that the metering cylinder is divided into a left metering cavity and a right metering cavity by the piston, the metering cylinder is used to measure the volume of the measured fluid, and the liquid small flow calibration device also includes a detection control system, The detection control system includes a detection element, a detection module, a circulation pipeline and a control module. The detection element comprises a left in-position detection sensor arranged at the extreme sliding position of the piston at one end of the metering cylinder body and a right in-position detection sensor arranged at the extreme sliding position of the piston at the other end of the metering cylinder body, wherein the left in-position sensor generates a piston left in-position signal when detecting the piston, and the right in-position sensor generates a piston right in-position signal when detecting the piston; The detection module includes a detection unit, which generates single movement distance information and standard flow value information according to the piston left position signal and the piston right position signal. The circulation pipeline includes a liquid inlet control valve and a liquid discharge control valve, and the left metering cavity and the right metering cavity are both connected to the liquid inlet control valve and the liquid discharge control valve. The control module controls the inlet and outlet of the left metering chamber or the right metering chamber through the inlet control valve and the discharge control valve. When the inlet control valve controls the inlet of the left metering chamber, the discharge control valve controls the outlet of the right metering chamber, and the piston moves toward the right in-place detection sensor. When the inlet control valve controls the inlet of the right metering chamber, the discharge control valve controls the outlet of the left metering chamber, and the piston moves toward the left in-place detection sensor.

[0006] By adopting the above technical scheme, the control module controls the liquid inlet into the left metering cavity or the right metering cavity, thereby pushing the piston to move, which can effectively push the piston into place, and the detection element cooperates with the control module to perform multiple self-circulating small flow detections. The control module controls the liquid inlet into the left metering cavity or the right metering cavity to push the piston to move in one direction. After the piston moves into place, the detection element cooperates with the control module to switch the liquid to enter the left metering cavity or the right metering cavity, driving the piston to move in the opposite direction. Compared with the traditional standard volume with an external driving mechanism, the present invention realizes the self-circulating movement of the piston without an external driving mechanism, thereby meeting the calibration requirements for small liquid flows and repeated use.

[0007] The present invention is further configured as follows: the liquid inlet control valve includes a left inlet switch valve and a right inlet switch valve, the liquid discharge control valve includes a left outlet switch valve and a right outlet switch valve, the left inlet switch valve and the left outlet switch valve are both connected to the left metering chamber, the right inlet switch valve and the right outlet switch valve are both connected to the right metering chamber, the measured fluid enters the metering cylinder from the left inlet switch valve or the right inlet switch valve, When the control module receives a piston right in-position signal, the control module controls the left inlet switch valve and the right outlet switch valve to be closed, and the control module controls the left outlet switch valve and the right inlet switch valve to be opened. When the measured fluid flows into the right metering chamber from the right inlet switch valve, the measured fluid drives the piston to move to the left until the piston moves to the piston limit sliding position and is arranged opposite to the left in-position sensor; When the control module receives the piston left in-position signal, the control module controls the left outlet switch valve and the right inlet switch valve to be closed, and the control module controls the left inlet switch valve and the right outlet switch valve to be opened. When the measured fluid flows into the left metering chamber from the left inlet switch valve, the measured fluid drives the piston to move to the right until the piston moves to the piston limit sliding position and is set opposite to the right in-position sensor.

[0008] By adopting the above technical solution, the reciprocating motion of the piston can be controlled in real time through the left-in switch valve, the right-in switch valve, the left-out switch valve and the right-out switch valve, thereby realizing the self-circulating motion of the piston, meeting the calibration requirements of small liquid flows and enabling repeated use.

[0009] The present invention is further configured as follows: a left inlet and outlet connected to a left metering cavity and a right inlet and outlet connected to a right metering cavity are respectively provided at two ends of the metering cylinder body; the left inlet and outlet and the right inlet and outlet are both used for fluid to flow in or out; the left inlet switch valve and the left outlet switch valve are both connected to the left inlet and outlet, and the right inlet switch valve and the right outlet switch valve are both connected to the right inlet and outlet.

[0010] By adopting the above technical solution, the advantage of fluid entering or flowing out of the common inlet and outlet is that errors are minimized to the greatest extent and the installation of pipelines is facilitated.

[0011] The present invention is further configured as follows: the liquid inlet control valve and the liquid discharge control valve are both directional valves that are switched to communicate with the left metering cavity or the right metering cavity. When the control module receives a piston right in-position signal, the control module controls the inlet control valve to switch to communicate with the right metering chamber, and the control module controls the discharge control valve to switch to communicate with the left metering chamber. When the measured fluid flows from the right inlet switch valve into the right metering chamber, the measured fluid drives the piston to move to the left until the piston moves to the piston limit sliding position and is arranged opposite to the left in-position sensor. When the control module receives the piston left position signal, the control module controls the inlet control valve to switch and connect with the left metering chamber, and the control module controls the discharge control valve to switch and connect with the right metering chamber. When the measured fluid flows into the left metering chamber from the left inlet switch valve, the measured fluid drives the piston to move to the right until the piston moves to the piston limit sliding position and is arranged opposite to the right position sensor.

[0012] By adopting the above technical solution, the advantage of using reversing valves for both the liquid inlet control valve and the liquid discharge control valve is that the number of control valves can be saved and industrial costs can be reduced. At the same time, the reversing valve can also more easily control the circulation pipeline.

[0013] The present invention is further configured as follows: the left arrival detection sensor and the right arrival detection sensor both adopt reflective photoelectric switches, the metering cylinder body is provided with mounting holes at the extreme sliding positions at both ends of the piston, and the reflective photoelectric switches are sealed and connected to the mounting holes.

[0014] By adopting the above technical solution, in order to accurately detect the movement of the piston, the photoelectric detection system is designed to include a PLC timer, a fiber optic sensor, and a fiber optic amplifier. The fiber optic sensors are installed at both ends of the calibrated effective distance of the cavity. The transmitter emits a light beam into the device. When the piston passes by, the intensity and path of the reflected light change, which is transmitted to the receiver and the fiber optic signal is transmitted to the amplifier. After amplification and processing, the fiber optic amplifier triggers the PLC internal clock timing through its pulse signal to obtain the detection time.

[0015] The present invention is further configured as follows: the piston includes a sealing section and a sliding section that slides with the metering cylinder body, a sliding section is arranged on each side of the sealing section, a V-shaped sealing ring is arranged on the sealing section, at least two sealing rings are arranged along the sliding direction of the piston, and the two sealing rings are arranged in a mirror image.

[0016] By adopting the above technical solution, the technical problem solved by the sealing ring is how to achieve better bidirectional sealing. By setting two groups of V-shaped sealing rings in a mirror image, the bidirectional sealing structure of the piston is completed.

[0017] The present invention is further configured as follows: an external clamp-on ultrasonic pressure gauge is arranged on the outside of the metering cylinder.

[0018] By adopting the above technical solution, an external clamp-on ultrasonic liquid pressure measuring instrument is used, which has the characteristics of fast response, strong dynamic monitoring capability, and no destruction of physical fluidity. Ultrasonic waves are used as the detection object and are attached to the outside of the hydraulic pipeline for pressure measurement. The system obtains the liquid pressure in the pipe based on the model of the relationship between the propagation speed of ultrasonic waves in the liquid and the pressure change. The pressure curve in the cavity is obtained through multiple experimental fitting and the stage of stable pressure is selected as the effective distance.

[0019] The present invention is further configured as follows: the detection control system also includes an in-place detection module, the in-place detection module includes a magnetic sliding member slidably arranged on the outside of the metering cylinder body and a distance sensor for detecting the relative position of the magnetic sliding member, the piston and the magnetic sliding member are both provided with magnetic members that magnetically attract each other, the metering cylinder body is provided with a slide groove for the sliding of the magnetic sliding member, and the length of the slide groove is greater than the maximum moving distance of the piston in the metering cylinder body.

[0020] By adopting the above technical solution, when impurities enter the metering cylinder, the in-place detection unit detects that the piston is in place, but due to the obstruction of the impurities, the piston is actually still some distance away from the limit position. By checking the relative position of the magnetic suction part that follows the piston, it is possible to detect whether the piston has reached the limit position.

[0021] The present invention is further configured as follows: the in-place detection module further includes A detection unit, wherein the distance detection unit detects a single movement distance of the magnetic sliding member through a distance sensor, and generates a single movement distance of the piston and a single correction detection time; The error calculation unit calculates the volume of fluid discharged by a single movement of the piston according to the single movement distance of the piston and the area of ​​the cross section of the metering cylinder, and generates single correction fluid volume data.

[0022] By adopting the above technical solution, the distance sensor detects the distance of the magnetic sliding member, and the error calculation unit can correct the actual flow volume discharged by the piston.

[0023] The present invention is further configured as follows: at least one magnetic sliding member is disposed on each side of the metering cylinder body, and each of the magnetic sliding members is provided with a distance sensor in cooperation with the other.

[0024] By adopting the above technical solution, multiple magnetic sliding parts can limit the rotation of the piston when encountering a circular cylinder body, making the piston sliding state more stable. It is also possible to monitor the distance of multiple magnetic sliding parts to detect whether the piston is tilted at an angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a metering cylinder in a calibration device for a self-circulating piston in Example 1; Figure 2 is a combined cross-sectional view of the standard volume tube in Example 1; Figure 3 It is a simplified view of the circulation pipeline in the first embodiment; Figure 4 is a schematic diagram of the states of the various switch valves when the piston is facing rightward in the first embodiment; Figure 5 is a schematic diagram of the states of the various switch valves when the piston is facing left in the first embodiment; Figure 6 It is a simplified view of the circulation pipeline in the second embodiment; Figure 7 is a schematic diagram of the switching state of the control valve when the piston is facing rightward in the second embodiment; Figure 8 It is a schematic diagram of the switching state of the control valve when the piston is facing left in the second embodiment.

[0026] The parts indicated by the numbers in the above drawings are as follows: 1. Standard volume tube; 11. Measuring cylinder; 111. Left metering chamber; 112. Right metering chamber; 12. Piston; 121. Sealing section; 122. Sliding section; 123. Sealing ring; 13. Mounting hole; 2. Detection element; 21. Left in-position detection sensor; 22. Right in-position detection sensor; 3. Circulation pipeline; 31. Liquid inlet control valve; 32. Liquid discharge control valve; 311. Left inlet switch valve; 312. Right inlet switch valve; 321. Left outlet switch valve; 322. Right outlet switch valve; 4. Magnetic sliding part; 41. Slide; 42. Magnetic part; 5. Flow meter. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0028] Embodiment 1: A liquid small flow calibration device for a self-circulating piston 12, first see Figure 1 and Figure 3 , including a standard volume tube 1, the standard volume tube 1 includes a metering cylinder 11 for measuring the measured fluid and a piston 12 forming a sliding seal with the inner wall of the metering cylinder 11, the metering cylinder 11 is in the shape of an elongated strip, and the inside of the metering cylinder 11 is divided into a left metering cavity 111 and a right metering cavity 112 with the piston 12 as the boundary, and a left inlet and outlet connected to the left metering cavity 111 and a right inlet and outlet connected to the right metering cavity 112 are respectively opened at both ends of the metering cylinder 11, and the left inlet and outlet and the right inlet and outlet are both used for the fluid to flow in or out, and the flow calibration device can be a flowmeter 5 that cooperates with the standard volume tube 1.

[0029] The detection control system includes a detection element 2, a detection calibration module, a circulation pipeline 3 and a control module.

[0030] See also Figure 3 The detection element 2 includes a left in-position detection sensor 21 arranged at the extreme sliding position of the piston at one end of the metering cylinder body 11 and a right in-position detection sensor 22 arranged at the extreme sliding position of the piston at the other end of the metering cylinder body 11. Mounting holes 13 are respectively opened on the metering cylinder body 11 at the extreme sliding positions at both ends of the piston 12. The left in-position detection sensor 21 and the right in-position detection sensor 22 both adopt reflective photoelectric switches. The reflective photoelectric switches are sealed and connected to the mounting holes 13. The transmitter and receiver of the reflective photoelectric switches are installed on the same side. In this embodiment, the mounting hole 13 adopts a threaded hole installation method to reduce or avoid fluid leakage when the piston 12 moves in the cylinder body. When the piston 12 reciprocates, the left in-position sensor generates a piston left in-position signal when detecting the piston 12, and the right in-position sensor generates a piston right in-position signal when detecting the piston 12.

[0031] The circulation pipeline 3 includes a liquid inlet control valve 31 and a liquid discharge control valve 32. In this embodiment, the liquid inlet control valve 31 includes a left inlet switch valve 311 and a right inlet switch valve 312, and the liquid discharge control valve 32 includes a left outlet switch valve 321 and a right outlet switch valve 322. The left inlet switch valve 311 and the left outlet switch valve 321 are both connected to the left inlet and outlet through a pipeline, and the right inlet switch valve 312 and the right outlet switch valve 322 are both connected to the right inlet and outlet through a pipeline. The left inlet switch valve 311 and the right inlet switch valve 312 are both connected in parallel and connected to the flow meter 5 through a pipeline.

[0032] The control module is used to control the left metering chamber 111 to enter the liquid, the right metering chamber 112 to exit the liquid and the left metering chamber 111 to exit the liquid, and the right metering cylinder 11 to exit the liquid. The switching of the two inlet and outlet directions causes the piston 12 to reciprocate. Figures 3 to 5 , the control module controls the left inlet switch valve 311 and the right outlet switch valve 322 to be closed, and controls the left outlet switch valve 321 and the right inlet switch valve 312 to be opened. When the measured fluid flows into the right inlet switch valve 312, the measured fluid drives the piston 12 to move to the left, the volume of the right metering chamber increases to show the fluid entering state, and the volume of the left metering chamber decreases to show the fluid discharging state, until the piston 12 moves to the piston limit sliding position relative to the left in-position detection sensor 21, and the left in-position detection sensor 21 generates a piston left in-position signal. The control module is electrically connected to the detection element 2. When the control module receives the piston left in-position signal, the left outlet switch valve 321 and the right inlet switch valve 312 are both closed, and the left inlet switch valve 311 and When the right-outlet switch valve 322 is opened and the measured fluid flows in from the left-inlet switch valve 311, the measured fluid drives the piston 12 to move to the right, the volume of the left metering chamber increases and the fluid enters, and the volume of the right metering chamber decreases and the fluid is discharged, until the piston 12 moves to the piston limit sliding position relative to the right in-position detection sensor 22, and the right in-position detection sensor 22 generates a piston right in-position signal. When the control module receives the piston right in-position signal, the control module controls the left-inlet switch valve 311 and the right-outlet switch valve 322 to close, and controls the left-outlet switch valve 321 and the right-inlet switch valve 312 to open. When the measured fluid flows in from the right-inlet switch valve 312, the measured fluid drives the piston 12 to move to the left, thereby reciprocating.

[0033] The detection and calibration module includes a detection unit, a timing unit and a calibration unit. The detection unit generates single detection information according to the piston left position signal and the piston right position signal. The timing unit obtains the single detection time of the piston left position signal and the piston right position signal according to the single detection information. When the circulation pipeline 3 does not drive the piston 12 to perform reciprocating cycle detection, the calibration unit is used to compare the single flow volume with the standard volume of the metering cylinder 11. The calibration unit corrects the flow meter 5 in real time according to the single detection time.

[0034] The piston 12 includes a sealing section 121 and a sliding section 122 that slides with the metering cylinder 11. A sliding section 122 is provided at each end of the sealing end. The diameter of the sealing section 121 is smaller than that of the sliding section 122. A sealing ring 123 is sleeved on the sealing section 121. At least two groups of sealing rings 123 are arranged side by side along the sliding direction of the piston 12. In this embodiment, only two groups are provided, but it is not limited to two groups. Four groups or more can also be provided. The cross-section of the sealing ring 123 is V-shaped. The function of the sealing ring 123 is to prevent the fluid in the left metering cavity 111 and the fluid in the right metering cavity 112 from circulating with each other when the piston 12 moves repeatedly, so as to avoid affecting the metering result. An external clamp-on ultrasonic pressure gauge is provided on the outside of the metering cylinder 11. The ultrasonic pressure gauge is used to analyze the position of the photoelectric switch to ensure that the movement distance of the piston 12 between the photoelectric sensors is a stable section. It is necessary to study the liquid pressure distribution formed by the movement of the piston 12 inside the cylinder, so as to facilitate the improvement of the calibration device.

[0035] The detection control system also includes an in-place detection module, which includes a magnetic sliding member 4 slidably arranged on the outside of the metering cylinder 11 and a distance sensor for detecting the relative position of the magnetic member. The distance sensor adopts a laser rangefinder, which is fixedly connected to the outside of the metering cylinder 11 and arranged opposite to the magnetic sliding member 4. In this embodiment, two magnetic sliding members 4 are provided, and both magnetic sliding members 4 are provided with a distance sensor, but are not limited to two magnetic sliding members 4. At least one magnetic sliding member 4 is provided on the metering cylinder 11, and the magnetic sliding member 4 and The sliding sections 122 of the piston 12 are all provided with magnetic parts 42 that are magnetically attracted to each other. In this embodiment, the magnetic parts 42 are magnets. A slide groove 41 is opened on the outer side of the metering cylinder body 11 along the axial direction. A graphite layer for lubricating the magnetic part 42 is arranged in the slide groove 41. The magnetic sliding part 4 includes a magnetic sliding section slidably connected to the slide groove 41 and a detection section extending out of the slide groove 41 and used for distance sensor detection. The length of the slide groove 41 is greater than the maximum moving distance of the piston 12 in the metering cylinder body 11, and both ends of the slide groove 41 exceed the limit moving position of the piston 12.

[0036] The in-place detection module also includes a correction detection unit, an error calculation unit and a correction comparison unit. The distance detection unit detects the single movement distance of the magnetic sliding member 4 through the distance sensor, and generates the single movement distance of the piston 12 and the single correction detection time; The error calculation unit calculates the volume of fluid discharged by a single movement of the piston 12 according to the single movement distance of the piston 12 and the area of ​​the cross section of the metering cylinder 11, and generates single correction fluid volume data; The correction comparison unit obtains the flow volume of the flow meter 5 within the time interval according to the single correction detection time, and compares it with the single correction fluid volume. When the flow volume of the flow meter 5 within the single correction detection time is not equal to the single correction fluid volume, an auxiliary calibration abnormality signal is generated.

[0037] The operator can repair or replace the flow meter 5 according to the calibration abnormality signal, can repair or replace the flow meter 5 according to the auxiliary calibration abnormality signal, or can remove impurities or replace the standard volume tube 1.

[0038] Embodiment 2: The difference between this embodiment and the first embodiment is that Figure 6 In this embodiment, both the liquid inlet control valve 31 and the liquid discharge control valve 32 adopt a reversing valve, and the reversing valve is a three-position three-way or two-position three-way solenoid valve. In this embodiment, a three-position three-way solenoid valve is adopted, and the function of the reversing valve is to switch between the left metering chamber 111 and the right metering chamber 112.

[0039] See also Figure 7 When the control module receives the piston left in-position signal, the control module controls the inlet control valve 31 to switch to communicate with the left metering chamber 111, and the control module controls the discharge control valve 32 to switch to communicate with the right metering chamber 112. When the measured fluid flows from the left inlet switch valve 311 into the left metering chamber 111, the measured fluid drives the piston 12 to move right until the piston 12 moves to the piston limit sliding position and is arranged opposite to the right in-position sensor. See also Figure 8 When the control module receives the piston right in-position signal, the control module controls the liquid inlet control valve 31 to switch and connect with the right metering chamber 112, and the control module controls the liquid discharge control valve 32 to switch and connect with the left metering chamber 111. When the measured fluid flows from the right inlet switch valve 312 into the right metering chamber 112, the measured fluid drives the piston 12 to move to the left until the piston 12 moves to the piston limit sliding position and is arranged opposite to the left in-position sensor.

[0040] Therefore, the switching between the liquid inlet control valve 31 and the liquid discharge control valve 32 using the reversing valve is more convenient, and the same technical effect as that of the first embodiment can be achieved.

Claims

1. A self-circulating piston calibration device, comprising a standard volume tube (1), wherein the standard volume tube (1) comprises a metering cylinder (11) and a piston (12) forming a sliding seal with the inner wall of the metering cylinder (11), characterized in that: The metering cylinder (11) is divided into a left metering cavity (111) and a right metering cavity (112) by the piston (12). The metering cylinder (11) is used to measure the volume of the measured fluid. The liquid small flow calibration device also includes a detection control system. The detection control system comprises a detection element (2), a circulation pipeline (3) and a control module. The detection element (2) comprises a left in-position detection sensor (21) arranged at the extreme sliding position of the piston (12) at one end of the metering cylinder (11) and a right in-position detection sensor (22) arranged at the extreme sliding position of the piston (12) at the other end of the metering cylinder (11), wherein the left in-position sensor generates a piston left in-position signal when detecting the piston (12), and the right in-position sensor generates a piston right in-position signal when detecting the piston (12); The circulation pipeline (3) comprises a liquid inlet control valve (31) and a liquid discharge control valve (32), and the left metering chamber (111) and the right metering chamber (112) are both connected to the liquid inlet control valve (31) and the liquid discharge control valve (32). The control module controls the inflow and outflow of liquid into the left metering chamber (111) or the right metering chamber (112) through the inflow control valve (31) and the discharge control valve (32); when the inflow control valve (31) controls the inflow of liquid into the left metering chamber (111), the discharge control valve (32) controls the outflow of liquid into the right metering chamber (112), and the piston (12) moves in the direction of the right in-place detection sensor (22); when the inflow control valve (31) controls the inflow of liquid into the right metering chamber (112), the discharge control valve (32) controls the outflow of liquid into the left metering chamber (111), and the piston (12) moves in the direction of the left in-place detection sensor (21).

2. A calibration device for a self-circulating piston according to claim 1, characterized in that: The liquid inlet control valve (31) comprises a left inlet switch valve (311) and a right inlet switch valve (312); the liquid discharge control valve (32) comprises a left outlet switch valve (321) and a right outlet switch valve (322); the left inlet switch valve (311) and the left outlet switch valve (321) are both connected to the left metering chamber; the right inlet switch valve (312) and the right outlet switch valve (322) are both connected to the right metering chamber; the measured fluid enters the metering cylinder (11) from the left inlet switch valve (311) or the right inlet switch valve (312); When the control module receives a piston right position signal, the control module controls the left inlet switch valve (311) and the right outlet switch valve (322) to be closed, and the control module controls the left outlet switch valve (321) and the right inlet switch valve (312) to be opened. When the measured fluid flows from the right inlet switch valve (312) into the right metering chamber (112), the measured fluid drives the piston (12) to move to the left until the piston (12) moves to the piston (12) limit sliding position and is arranged opposite to the left position sensor; When the control module receives a piston left position arrival signal, the control module controls the left outlet switch valve (321) and the right inlet switch valve (312) to be closed, and the control module controls the left inlet switch valve (311) and the right outlet switch valve (322) to be opened. When the measured fluid flows from the left inlet switch valve (311) into the left metering chamber (111), the measured fluid drives the piston (12) to move rightward until the piston (12) moves to the piston (12) limit sliding position and is arranged opposite to the right position arrival sensor.

3. A calibration device for a self-circulating piston according to claim 2, characterized in that: The two ends of the metering cylinder (11) are respectively provided with a left inlet and outlet connected to the left metering cavity (111) and a right inlet and outlet connected to the right metering cavity (112). The left inlet and outlet and the right inlet and outlet are both used for fluid to flow in or out. The left inlet switch valve (311) and the left outlet switch valve (321) are both connected to the left inlet and outlet, and the right inlet switch valve (312) and the right outlet switch valve (322) are both connected to the right inlet and outlet.

4. A calibration device for a self-circulating piston according to claim 1, characterized in that: The liquid inlet control valve (31) and the liquid discharge control valve (32) are both reversing valves that are switched to communicate with the left metering chamber (111) or the right metering chamber (112). When the control module receives a piston right position signal, the control module controls the inlet control valve (31) to switch to communicate with the right metering chamber (112), and the control module controls the discharge control valve (32) to switch to communicate with the left metering chamber (111). When the measured fluid flows from the right inlet switch valve (312) into the right metering chamber (112), the measured fluid drives the piston (12) to move to the left until the piston (12) moves to the piston (12) limit sliding position and is arranged opposite to the left position sensor; When the control module receives a piston left-positioned signal, the control module controls the inlet control valve (31) to switch and communicate with the left metering chamber (111), and the control module controls the discharge control valve (32) to switch and communicate with the right metering chamber (112). When the measured fluid flows from the left inlet switch valve (311) into the left metering chamber (111), the measured fluid drives the piston (12) to move rightward until the piston (12) moves to the piston (12) limit sliding position and is arranged opposite to the right-positioned sensor.

5. A calibration device for a self-circulating piston according to claim 1, characterized in that: The left-in-place detection sensor (21) and the right-in-place detection sensor (22) both adopt reflective photoelectric switches. The metering cylinder (11) is provided with mounting holes (13) at the extreme sliding positions at both ends of the piston (12). The reflective photoelectric switches are sealed and connected to the mounting holes (13).

6. A calibration device for a self-circulating piston according to claim 1, characterized in that: The piston (12) comprises a sealing section (121) and a sliding section (122) that slides with the metering cylinder body (11), the sliding section (122) being arranged on both sides of the sealing section (121), the sealing section (121) being provided with a V-shaped sealing ring (123), at least two sealing rings (123) being arranged along the sliding direction of the piston (12), and the two sealing rings (123) being arranged in a mirror image.

7. A calibration device for a self-circulating piston according to claim 1, characterized in that: An external clamp-on ultrasonic pressure gauge is arranged on the outside of the metering cylinder (11).

8. A calibration device for a self-circulating piston according to claim 1, characterized in that: The detection control system further comprises an in-position detection module, the in-position detection module comprising a magnetic sliding member (4) slidably arranged on the outside of the metering cylinder (11) and a distance sensor for detecting the relative position of the magnetic sliding member, the piston (12) and the magnetic sliding member (4) are both provided with magnetic members (42) that magnetically attract each other, the metering cylinder (11) is provided with a slide groove (41) for the magnetic sliding member (4) to slide, and the length of the slide groove (41) is greater than the maximum moving distance of the piston (12) in the metering cylinder (11).

9. A calibration device for a self-circulating piston according to claim 7, characterized in that: The in-place detection module also includes A detection unit, wherein the distance detection unit detects a single movement distance of the magnetic attraction sliding member (4) through a distance sensor, and generates a single movement distance of the piston (12) and a single correction detection time; An error calculation unit is provided, wherein the error calculation unit calculates the volume of fluid discharged by a single movement of the piston (12) based on the single movement distance of the piston (12) and the area of ​​the cross section of the metering cylinder (11), and generates single correction fluid volume data.

10. A calibration device for a self-circulating piston according to claim 7, characterized in that: At least one magnetic sliding member (4) is provided on the side of the metering cylinder body (11), and each of the magnetic sliding members (4) is provided with a distance sensor.

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