System and method for measuring effective area of piston

Abstract

The invention relates to the technical field of physical quantity precision measurement, in particular to a piston effective area measurement system and method. The system comprises an optical pressure measuring device and a piston pressure gauge pressure measuring device. The optical pressure measuring device comprises a box body, a measuring cavity, a reference cavity and a laser refractometer. The measuring cavity is used for filling a gas medium; the reference cavity maintains a vacuum state; the laser refractometer emits laser to the measuring cavity and the reference cavity. The piston pressure gauge pressure measuring device comprises a piston pressure gauge which comprises an air cylinder and a piston. The piston divides the cylinder into a first space and a second space. The gas source is communicated with the second space and the measuring cavity through the three-way valve, the refractive index of gas in the measuring cavity is obtained through the laser refractometer, and the pressure of the gas is determined through the refractive index of the gas. Calibration of the effective area of the piston is traced to basic physical constants and high-precision measured physical quantities, the pressure is accurately measured, and high precision and reliability of a calibration result are guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of precise measurement of physical quantities, and in particular to a piston effective area measurement system and method. BACKGROUND

[0002] Pressure (unit: Pascal, Pa) as a basic physical quantity, the accurate reproduction and transmission of its value is the basis of scientific research and industrial production. In metrology, it is traditionally defined as the force acting on the unit effective area. The world currently recognizes that the most core primary reference instrument for realizing and propagating the unit of Pascal is the piston pressure gauge, whose working principle is based on force balance, i.e. P=F / A, and its measurement accuracy directly depends on the accurate measurement of three core physical quantities: the applied mass M, the local gravity acceleration g, and the effective area A of the piston-cylinder assembly T,P . Among them, the effective area A T,P of the piston is not a fixed geometric quantity, but an elastic deformation and thermal expansion with pressure and temperature conditions, and is one of the main sources of uncertainty in pressure measurement. Therefore, accurate calibration of the effective area A T,P of the piston is a prerequisite for ensuring the accuracy of pressure value transmission.

[0003] The traditional effective area calibration of the piston pressure gauge mainly relies on two methods: (1) Geometric size measurement method, i.e. determining the effective area of the primary piston pressure gauge by precisely measuring the diameters of the piston and the cylinder and the gap (geometric size measurement), and combining complex fluid dynamics and elastic distortion models for calculation. However, this method requires extremely high manufacturing precision. Due to the challenges of geometric measurement itself and the complexity of fluid dynamics modeling, the uncertainty of the effective area of the piston is still difficult to break through a certain limit.

[0004] (2) Cross-floating method, i.e. using a calibrated piston pressure gauge to compare with a reference standard piston pressure gauge with a known effective area. This method is the current mainstream value transmission method, but its core limitation is the core limitation of uncertainty accumulation. The uncertainty of the calibration result inevitably contains the uncertainty of the reference standard itself, resulting in that the longer the value transmission chain, the larger the uncertainty, and the problem of high uncertainty of the effective area of the piston cannot be fundamentally solved.

[0005] Based on the above problems, developing a new method and new system that can balance high precision and traceability to accurately characterize and calibrate the core parameter A T,P of the traditional piston pressure gauge has become a difficult problem to be solved in this technical field. SUMMARY

[0006] The present application provides a piston effective area measurement system and method based on thermal pressure-mechanical pressure balance principle to solve the defects of mechanical measurement limitation, size modeling or inherent cumulative uncertainty of workpiece reference in the prior art.

[0007] The present application provides a piston effective area measurement system, comprising: an optical pressure measuring device and a piston pressure gauge pressure measuring device. The optical pressure measuring device comprises: A box body; A measuring cavity arranged in the box body and in communication with the outside of the box body for filling gas medium; A reference cavity arranged in the box body and maintained in a vacuum state; A laser refractometer arranged in the box body and used for emitting laser to the measuring cavity and the reference cavity respectively; The piston pressure gauge pressure measuring device comprises: A piston pressure gauge arranged in the box body, comprising: A cylinder; A piston movably arranged in the cylinder and dividing the cylinder into a first space and a second space, the first space being used for containing a weight of a predetermined weight; A gas source in communication with the second space and the measuring cavity respectively through a three-way valve, the refractive index of the gas in the measuring cavity being obtained through the laser refractometer, and the pressure of the gas being determined through the refractive index of the gas.

[0008] The piston effective area measurement system provided by the present application further comprises: A gas storage cylinder; A pressure relief valve, A first stop valve, the pressure relief valve and the first stop valve being connected in sequence between the gas storage cylinder and the inlet of the three-way valve.

[0009] The piston effective area measurement system provided by the present application further comprises: A vacuum cover arranged on the outside of the piston pressure gauge; A first vacuum pump group in communication with the inside of the vacuum cover.

[0010] The piston effective area measurement system provided by the present application further comprises: An ultra-low expansion glass spacer arranged in the box body, the measuring cavity and the reference cavity being fixed on the ultra-low expansion glass spacer respectively.

[0011] The piston effective area measurement system provided by the present application further comprises: A first mirror is arranged at the first end of the ultra-low expansion glass spacer and is arranged opposite the laser emission end of the laser refractometer. The reference cavity comprises: A second mirror is arranged at the second end of the ultra-low expansion glass spacer and is arranged opposite the laser emission end of the laser refractometer.

[0012] According to the piston effective area measurement system provided by the application, the optical pressure measuring device further comprises: A second vacuum pump group is in communication with the inside of the reference cavity.

[0013] According to the piston effective area measurement system provided by the application, the optical pressure measuring device further comprises: A second stop valve; A third vacuum pump group, the second stop valve and the third vacuum pump group are sequentially connected to the box.

[0014] According to the piston effective area measurement system provided by the application, the box is a thermostat; and the optical pressure measuring device further comprises: A temperature controller is arranged in the thermostat.

[0015] The application provides a method for measuring the effective area of a piston by using the piston effective area measurement system. S1, the refractive index of laser is measured by a laser refractometer, and then the gas pressure value is obtained by theoretical calculation; S2, the obtained gas pressure value is equal to the pressure applied to the piston in the piston pressure gauge, and according to the working principle of the piston pressure gauge, the effective area of the piston is obtained by reverse calculation of the gas pressure value.

[0016] According to the method for measuring the effective area of a piston by using the piston effective area measurement system, the S1 specifically comprises: The laser frequency is locked to the resonant frequency of the reference cavity and the measurement cavity by the laser refractometer, the frequencies of the two groups of lasers are measured and recorded by the frequency meter inside the laser refractometer, and then the gas pressure in the measurement cavity is calculated.

[0017] The application provides a piston effective area measuring system and method, which comprises an optical pressure measuring device and a piston pressure gauge pressure measuring device. The optical pressure measuring device comprises a box, a measuring cavity, a reference cavity and a laser refractometer. The measuring cavity is arranged in the box and communicates with the outside of the box and is used for filling gas medium. The reference cavity is arranged in the box and is kept in a vacuum state. The laser refractometer is arranged in the box and is used for emitting laser to the measuring cavity and the reference cavity respectively. The piston pressure gauge pressure measuring device comprises a piston pressure gauge, which comprises a cylinder and a piston. The piston is movably arranged in the cylinder and divides the cylinder into a first space and a second space. The first space is used for containing a weight of a preset weight. A gas source communicates with the second space and the measuring cavity through a three-way valve. The refractive index of the gas in the measuring cavity is obtained through the laser refractometer. The pressure of the gas is determined through the refractive index of the gas. The application provides a piston effective area measuring system and a new method for balancing thermal pressure and mechanical pressure. The application converts the measurement of the piston effective area into the precise measurement of the thermal pressure of the gas. The piston effective area is inversely calculated through the principle of the piston pressure gauge. The calibration of the piston effective area is traced to the basic physical constant and the physical quantity of high-precision measurement. The dependence on the specific geometric size workpiece or the real object reference of the traditional method is completely eliminated. The optical pressure measuring method has high sensitivity and accuracy. The calibration result has high precision and reliability. T,P The application provides a piston effective area measuring system and method, which comprises an optical pressure measuring device and a piston pressure gauge pressure measuring device. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the application or prior art, the following will briefly introduce the drawings needed in the embodiments or prior art description.

[0019] Figure 1 FIG. 1 is a structural schematic diagram of the piston effective area measuring system provided in one embodiment of the application.

[0020] REFERENCE SIGNS 1, gas storage bottle; 2, pressure relief valve; 3, first stop valve; 4, three-way valve; 5, piston pressure gauge; 6, first vacuum pump set; 7, cylinder; 8, piston; 9, weight tray; 10, weight; 11, vacuum cover; 12, measuring cavity; 13, reference cavity; 14, temperature controller; 15, laser refractometer; 16, constant temperature box; 17, second vacuum pump set; 18, second stop valve; 19, third vacuum pump set. DETAILED DESCRIPTION

[0021] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below with reference to the drawings in the present application. Obviously, the described embodiments are only some, but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0022] In the description of the present embodiment, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the purpose of facilitating the description of the present embodiment and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present embodiment.

[0023] In addition, the terms "first" and "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first" and "second" can explicitly or implicitly include at least one of the features. In the description of the present embodiment, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise explicitly specified and limited.

[0024] In the present embodiment, unless otherwise explicitly specified and limited, the terms "arrangement", "installation", "connection", "connection", "fixation" and the like should be understood broadly, for example, can be fixedly connected, or can be detachably connected, or can be integrated; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those of ordinary skill in the art, the specific meaning of the above terms in the present embodiment can be understood according to the specific circumstances.

[0025] In the embodiments of the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature is "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or only means that the first feature is higher in horizontal height than the second feature. The first feature is "below", "under" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or only means that the first feature is lower in horizontal height than the second feature.

[0026] The following will be described in conjunction with Figure 1 A piston effective area measurement system is described. The piston effective area measurement system comprises an optical pressure measurement device and a piston pressure gauge pressure measurement device.

[0027] The optical pressure measurement device comprises a box, a measurement cavity 12, a reference cavity 13 and a laser refractometer 15. The measurement cavity 12 is arranged in the box and communicates with the outside of the box, and is used to fill with a gas medium; the reference cavity 13 is arranged in the box and is maintained in a vacuum state; the laser refractometer 15 is arranged in the box and is used to emit laser light to the measurement cavity 12 and the reference cavity 13 respectively.

[0028] The piston pressure gauge pressure measurement device comprises a piston pressure gauge 5 arranged in the box, which comprises a cylinder 7 and a piston 8. The piston 8 is movably arranged inside the cylinder 7 and divides the cylinder 7 into a first space and a second space, and the first space is used to hold a pre-set weight.

[0029] The gas source communicates with the second space and the measurement cavity 12 through a three-way valve 4, the refractive index of the gas in the measurement cavity 12 is obtained through the laser refractometer 15, and the pressure of the gas is determined through the refractive index of the gas.

[0030] Specifically, the piston effective area measurement system is composed of an optical pressure measurement device and a piston pressure gauge pressure measurement device. The optical pressure measurement device comprises a box, a measurement cavity 12, a reference cavity 13 and a laser refractometer 15; and the piston pressure gauge pressure measurement device comprises a piston pressure gauge 5.

[0031] The box is a shell structure of the optical pressure measurement device, mainly plays a temperature control and external barrier function, reduces the influence on the pressure measurement process. In the following embodiments, the box adopts a thermostat 16, which is used to accommodate the components that are easily affected by temperature, reduce the influence of temperature change on measurement, and further improve the measurement accuracy of each component.

[0032] The measuring cavity 12 and the reference cavity 13 are respectively formed by two pairs of mirrors fixed at two ends of an Ultra-Low Expansion (ULE) glass spacer, wherein the reference cavity 13 is always maintained in a vacuum state as a reference, and the measuring cavity 12 is in communication with the outside and can be filled with gas. The ULE glass is a special glass material with extremely low thermal expansion coefficient, mainly composed of silicon dioxide and a small amount of titanium dioxide, belonging to titanium silicate glass, and its average linear thermal expansion coefficient can be as low as ±0.030 × 10 -6 / ℃ in the range of 0~50℃, even close to zero expansion, so that the measurement of the measuring cavity 12 and the reference cavity 13 is not affected when the temperature changes.

[0033] The laser refractometer 15 is a refractive index measuring instrument using laser as a light source, which includes two sets of auxiliary elements such as laser, frequency meter, electro-optic modulator, isolator, polarization beam splitter prism and photodetector, so as to better lock the laser on the measuring cavity 12 and the reference cavity 13 respectively, and timely measure and record the absolute frequency of the laser, so as to calculate the refractive index of the gas in the measuring cavity 12, and then obtain the pressure value through theoretical calculation.

[0034] The piston pressure gauge 5 includes a cylinder 7 and a piston, and the piston divides the cylinder 7 into a first space located at the upper part and a second space located at the lower part, and the first space is used to hold a pre-set weight of a weight, for example, a weight 10. The weight 10 is pressed on the piston 8 (i.e. the first space) through a weight tray 9, and the pressure value below the piston 8 is equal to the gas pressure calculated by the optical pressure measuring device.

[0035] The gas source is in communication with the second space and the measuring cavity 12 through the three-way valve 4, that is, the same gas source is used to be respectively introduced into the second space and the measuring cavity 12, so as to ensure that the gas source pressure is the same, the gas source medium type is the same, etc. Since helium is the best working gas for realizing ultra-precision and primary measurement of quantum pressure standard by optical method at present, helium is used as the gas in the experiment; of course, the working medium is not limited to helium, and according to the set working temperature interval, neon, argon, nitrogen, etc. can also be selected; the basic principle of selection is to ensure that the working medium always remains in a single gas phase state in the whole temperature and pressure range of the experiment, and avoid liquefaction or solidification.

[0036] In addition, the replacement scheme of the refractive index measurement scheme: the device for measuring the refractive index of the gas in the application is not limited to the optical Fabry-Perot cavity, and a microwave resonant cavity can also be used, which is placed in a low-temperature thermostat, and the refractive index of the gas is inversely calculated through the resonant frequency of the quasi-spherical microwave resonant spherical cavity, so as to realize the same pressure measuring purpose.

[0037] In addition, the pressure measurement method is replaced: the method for measuring the pressure of the gas in the application is not limited to obtaining by measuring the refractive index of the gas, but can also use acoustic or dielectric constant method to obtain the pressure value of the gas based on theoretical calculation through obtaining the sound velocity or dielectric constant.

[0038] The application provides a piston effective area measurement system, which accurately determines the gas thermodynamic pressure P in a closed system through an optical pressure measuring device, then, the accurate known thermodynamic pressure P is applied to the lower end of the piston of the piston pressure gauge 5 as a reference, so that the mechanical pressure (generated by the weight M and the gravity g) applied to the upper end of the piston pressure gauge 5 is balanced. Finally, the effective area A of the piston is inversely solved according to the force balance equation of the piston pressure gauge 5 T,P .

[0039] The application provides a new method for measuring the effective area of the piston balanced by the thermal pressure and the mechanical pressure, establishes and utilizes the balance relationship of the thermal pressure and the mechanical pressure, converts the measurement problem of the effective area of the piston into the accurate measurement problem of the gas thermal pressure, constructs a measurement link of “resonant frequency-gas refractive index-gas pressure-effective area”, that is, the pressure is accurately determined through the gas refractive index method, and then the effective area of the piston is inversely calculated through the principle of the piston pressure gauge 5; the laser refractometer 15 is arranged in the closed box, and the measurement temperature is defined at the room temperature point of the international temperature scale or other temperature points which can be accurately measured and controlled, so that the influence of the thermal fluctuation on the pressure measurement accuracy is maximally inhibited.

[0040] It can be seen that the application has the following advantages: 1、The calibration of the effective area of the piston in the application is traced back to the basic physical constant (such as the Boltzmann constant k B ) and the physical quantity (frequency v and temperature T) measured with high precision, and is completely free from the dependence on the specific geometric size workpiece or the real object reference of the previous level in the traditional method; the pressure measurement based on the optical method (Fabry-Perot cavity) has extremely high sensitivity and accuracy, and fundamentally guarantees the high precision and reliability of the calibration result of A T,P .

[0041] 2、The scheme is an “absolute” measurement method rather than a “comparison” method; the uncertainty thereof only depends on the optical pressure measuring system and the force balance system (the weight M and the gravity g) itself, and avoids the defect that the uncertainty is accumulated step by step in the traditional cross-floating method.

[0042] 3、The pressure measurement of the application is carried out under the optical standard, which can provide fast and stable pressure readings, greatly reduces the workload, shortens the required time, and maximally reduces the measurement error caused by the operator compared with the manual and patient balance of the weight 10 by the operator in the traditional cross-floating method.

[0043] This invention provides a piston effective area measurement system, comprising: an optical pressure measuring device and a piston pressure gauge measuring device. The optical pressure measuring device includes: a housing, a measuring cavity 12, a reference cavity 13, and a laser refractometer 15. The measuring cavity 12 is located inside the housing and communicates with the outside of the housing, used to fill it with a gaseous medium; the reference cavity 13 is located inside the housing and maintained in a vacuum state; the laser refractometer 15 is located inside the housing and is used to emit laser light into the measuring cavity 12 and the reference cavity 13 respectively. The piston pressure gauge measuring device includes: a piston pressure gauge 5, which includes: a cylinder 7 and a piston 8. The piston 8 is movably disposed inside the cylinder 7, dividing the cylinder 7 into a first space and a second space. The first space is used to hold a weight of a preset weight. A gas source is connected to the second space and the measuring cavity 12 respectively through a three-way valve 4. The refractive index of the gas in the measuring cavity 12 is obtained by the laser refractometer 15, and the gas pressure is determined by the refractive index of the gas. This invention provides a piston effective area measurement system, proposing a novel method for measuring the piston effective area by balancing thermal and mechanical pressure. It establishes and utilizes the balance relationship between thermal and mechanical pressure, transforming the problem of measuring the piston effective area into a problem of precisely measuring gas thermal pressure. The pressure is accurately determined using the gas refractive index method, and then the piston effective area is calculated using the principle of a piston pressure gauge. This invention traces the calibration of the piston effective area back to fundamental physical constants and high-precision measured physical quantities, completely eliminating the dependence of traditional methods on workpieces with specific geometric dimensions or higher-level physical references. The pressure measurement based on optical methods has extremely high sensitivity and accuracy, fundamentally ensuring A T,P The calibration results are highly accurate and reliable.

[0044] In one embodiment of the present invention, the piston effective area measurement system further includes: a gas storage cylinder 1, a pressure relief valve 2, and a first shut-off valve 3; the pressure relief valve 2 and the first shut-off valve 3 are sequentially connected between the gas storage cylinder 1 and the inlet of the three-way valve 4. The gas storage cylinder 1 provides a gas source and stores helium; the pressure relief valve 2 is used to reduce the gas pressure to prevent the high-pressure gas from the gas storage cylinder 1 from directly impacting the pipeline; the first shut-off valve 3 is used to control the gas flow rate. The piston pressure gauge 5 is connected to the measuring chamber 12 through the three-way valve 4, and the gas pressures measured by both are equal.

[0045] In one embodiment of the present invention, the piston pressure gauge measuring device further includes a vacuum shroud 11 and a first vacuum pump assembly 6. The vacuum shroud 11 is disposed on the outside of the piston pressure gauge 5; the first vacuum pump assembly 6 is in communication with the inside of the vacuum shroud 11 and can evacuate the internal space of the vacuum shroud 11.

[0046] In one of the embodiments of the present application, the optical pressure measuring device further comprises: an ultra-low expansion glass spacer (ULE spacer) arranged in the box, and the measuring cavity 12 and the reference cavity 13 are fixed on the ULE spacer. Specifically, the ULE spacer is formed with two pairs of grooves for fixing the measuring cavity 12 and the reference cavity 13, respectively. The ULE spacer is used because of its ultra-low expansion property, which will not affect the measurement due to temperature changes.

[0047] In one of the embodiments of the present application, the measuring cavity 12 comprises: a first mirror arranged at a first end of the ULE spacer and opposite to the laser emitting end of the laser refractometer 15; and the reference cavity 13 comprises: a second mirror arranged at a second end of the ULE spacer and opposite to the laser emitting end of the laser refractometer 15. Specifically, the laser reflected by the mirror is received by the photodetector and the gas refractive index is calculated.

[0048] In one of the embodiments of the present application, the optical pressure measuring device further comprises: a second vacuum pump group 17 in communication with the inside of the reference cavity 13, for vacuumizing the reference cavity 13 to ensure a stable and continuous vacuum environment.

[0049] In one of the embodiments of the present application, the optical pressure measuring device further comprises: a second stop valve 18 and a third vacuum pump group 19. The second stop valve 18 and the third vacuum pump group 19 are connected to the box in sequence. Specifically, the measuring cavity 12 is in communication with the box, and the measuring cavity 12 is vacuumized before the experiment starts by opening the second stop valve 18 and the third vacuum pump group 19, to avoid the subsequent gas from being contaminated; when it is needed to fill the gas medium into the measuring cavity 12, the second stop valve 18 is closed, and the pressure relief valve 2 and the first stop valve 3 are opened, to fill the gas into the inside of the box and the measuring cavity 12. The reference cavity 13 is always in a sealed state, i.e., not in communication with the box, and the vacuum environment in the inside thereof is maintained by the second vacuum pump group 17.

[0050] In one of the embodiments of the present application, the box is a thermostat 16. The optical pressure measuring device further comprises: a temperature controller 14 arranged in the thermostat 16, to monitor and control the temperature of the gas in the thermostat 16, to ensure the accuracy and stability of the temperature of the gas in the measuring cavity 12 during the measurement.

[0051] In one of the embodiments of the present application, the piston effective area measuring system further comprises: a weight 10 arranged in the first space and placed on the piston 8. The piston effective area measuring system further comprises: a weight tray 9 arranged in the first space and placed on the piston 8, and the weight 10 is placed on the weight tray 9. Specifically, the weight tray 9 is placed on the piston 8, and the calibrated weight 10 is added on the weight tray 9.

[0052] The application further provides a method of the piston effective area measuring system in the embodiment of the application. S1, the refractive index of laser is measured by the laser refractometer 15, and then the gas pressure value is obtained by theoretical calculation; S2, the obtained gas pressure value is equal to the pressure applied to the piston in the piston pressure gauge 5, and the effective area of the piston is obtained by reverse calculation according to the working principle of the piston pressure gauge 5.

[0053] In one of the embodiments of the application, S1 specifically comprises: the laser frequency is locked to the resonance frequencies of the reference cavity 13 and the measuring cavity 12 by the laser refractometer 15, and the frequencies of the two groups of laser are measured and recorded by the frequency meter inside the laser refractometer 15, and then the gas pressure in the measuring cavity 12 is calculated.

[0054] The specific measurement steps are as follows: First step: the internal space of the reference cavity 13 and the measuring cavity 12 is respectively vacuumized by the second vacuum pump set 17 and the third vacuum pump set 19, then the calibrated weight 10 is added to the weight tray 9 of the piston pressure gauge 5, and the space in the vacuum cover 11 is vacuumized by the first vacuum pump set 6.

[0055] Second step: when the vacuum degrees of the internal spaces of the reference cavity 13, the measuring cavity 12 and the vacuum cover 11 reach 10 -4 -10 -5 Pa order of magnitude, the thermostat 16 is opened to control the temperature of the internal space of the laser refractometer 15; when the temperature of the thermostat 16 reaches room temperature 20 ℃ and remains unchanged, the second stop valve 18 is closed, the pressure relief valve 2 and the first stop valve 3 are opened, and the gas in the gas cylinder 1 flows into the lower space (i.e. the second space) of the piston pressure gauge 5 through the pressure relief valve 2 after being relieved; Third step: the gas flow into the piston pressure gauge 5 is controlled by the first stop valve 3, so that the piston floats in the cylinder 7 and remains at a certain height; Fourth step: the gas enters the measuring cavity 12, the temperature of the gas in the cavity is monitored by the temperature controller 14, and the temperature of the gas in the measuring cavity 12 is controlled by the temperature control system of the temperature controller 14, so that the temperature remains at room temperature 20 ℃; Fifth step: after the height of the piston and the temperature of the gas in the measuring cavity 12 are stable, the laser frequency is accurately locked to the resonance frequencies of the reference cavity 13 and the measuring cavity 12 by the laser refractometer 15, and then the frequencies of the two groups of laser are measured and recorded by the frequency meter contained in the laser refractometer 15, and then the gas pressure in the measuring cavity 12, i.e. the lower gas pressure P of the piston pressure gauge 5, is calculated according to the frequency. Step 6: The effective area of the piston can be calculated reversely according to the pressure measurement principle of the piston pressure gauge, and then the piston area can be calibrated.

[0056] The relevant calculation ideas and methods are described below: For the piston pressure gauge, the measured gas pressure P can be calculated by the following formula.

[0057] Where A T,P represents the effective area of the piston, m 2 ; M represents the load mass, kg; P HA represents the static pressure correction corresponding to the height difference between the reference position of the piston pressure gauge and the center position of the Fabry-Perot cavity, Pa; P vac represents the residual pressure above the piston, Pa; g represents the local gravitational acceleration, m / s 2 . In the experiment, the reference position of the piston pressure gauge and the center position of the Fabry-Perot cavity can be kept at the same height, and the temperature of the optical pressure measurement system and the piston pressure gauge measurement system during pressure measurement is room temperature, so the influence of static pressure correction on measurement can be ignored, P HA ≈0.

[0058] For the optical pressure measurement system, P is calculated based on the determination of the gas refractive index by the Fabry-Perot cavity. The specific principles and calculation methods are as follows.

[0059] When laser passes through gas medium, its wavelength will change with the change of gas refractive index, and the Fabry-Perot cavity can be used to monitor the laser wavelength. When the laser half-wavelength is an integer multiple of m times the cavity length L, the laser will resonate with the Fabry-Perot optical cavity, and the resonance frequency can be calculated by the formula.

[0060] Where c is the speed of light in vacuum, m / s; n is the refractive index of the medium in the cavity. When a laser is locked on the longitudinal mode of the optical cavity, the laser resonance frequency will change due to the change of gas refractive index, and the relationship is shown in the formula.

[0061] Where represents the change of laser frequency; represents the change of gas refractive index.

[0062] Using this method, first measure the resonance frequency of the laser when the optical cavity is in high vacuum (n = 1), then measure the resonance frequency when the optical cavity is filled with a certain pressure of gas, and then calculate the refractive index of the gas, which is shown in the following formula.

[0063] Where, △v =v i -v f +△m×FSR represents the absolute frequency change of the laser before and after inflation, in Hz; △m represents the change in modulus; FSR represents the free spectral range, in Hz; v i The absolute frequency of the laser before inflation, i.e., the absolute frequency of the laser in the vacuum cavity, is expressed in Hz; v f The absolute frequency of the laser after inflation, i.e., the absolute frequency of the laser in the measuring cavity, is expressed in Hz. ρ represents the pressure change before and after inflation, in Pa; K represents the bulk modulus of the ULE material, in Pa.

[0064] Furthermore, by combining the Lorentz-Lorentz equation and the virial equation of state, the gas pressure can also be obtained from the refractive index inversion. Here, only the first-order approximation is mainly explained, and its calculation formula is shown in the following formula.

[0065] Where, k B Boltzmann constant (J / K); T is the temperature of the gas inside the measuring cavity (K); N A A is Avogadro's constant; ε m is the molar polarizability. 3 / mol; A μ m is the molar magnetic susceptibility. 3 / mol; n is the refractive index of the gas.

[0066] By combining the equations, the area measurement result can be obtained, as shown in the following equation.

[0067] Where T is the temperature of the gas inside the measuring cavity, K, which remains constant during the experiment and can be room temperature or other thermodynamic temperatures, and can be measured by acoustic methods, dielectric constant methods, or other temperature measurement methods; during the experiment, the reference position of the piston pressure gauge can be kept at the same height as the center position of the optical Fabry-Perot cavity, thereby reducing the influence of static pressure correction on the measurement, P HA ≈ 0.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A piston effective area measurement system, characterized in that, include: Optical pressure measuring device and piston pressure gauge pressure measuring device; The optical pressure measuring device includes: Box; A measuring chamber (12) is located inside the box and communicates with the outside of the box, and is used to fill the gas medium; The reference cavity (13) is located inside the box and maintained in a vacuum state; A laser refractometer (15) is installed inside the housing and is used to emit lasers into the measuring cavity (12) and the reference cavity (13), respectively. The piston pressure gauge measuring device includes: Piston pressure gauge (5), located inside the housing, includes: Cylinder (7); The piston (8) is movably disposed inside the cylinder (7) and divides the cylinder (7) into a first space and a second space. The first space is used to hold a weight of a preset weight. The gas source is connected to the second space and the measuring cavity (12) respectively through the three-way valve (4). The refractive index of the gas in the measuring cavity (12) is obtained through the laser refractometer (15), and the gas pressure is determined by the refractive index of the gas.

2. The piston effective area measurement system according to claim 1, characterized in that, Also includes: Gas storage cylinder (1); Pressure relief valve (2); The first shut-off valve (3), the pressure relief valve (2) and the first shut-off valve (3) are connected in sequence between the gas storage cylinder (1) and the inlet of the three-way valve (4).

3. The piston effective area measurement system according to claim 1, characterized in that, The piston pressure gauge measuring device also includes: A vacuum shroud (11) is provided on the outside of the piston pressure gauge (5); The first vacuum pump unit (6) is connected to the inside of the vacuum shroud (11).

4. The piston effective area measurement system according to claim 1, characterized in that, The optical pressure measuring device also includes: An ultra-low expansion glass spacer is disposed inside the box, and the measuring cavity (12) and the reference cavity (13) are respectively fixed on the ultra-low expansion glass spacer.

5. The piston effective area measurement system according to claim 4, characterized in that, The measuring cavity (12) includes: The first reflector is located at the first end of the ultra-low expansion glass spacer and is positioned opposite to the laser emitting end of the laser refractometer (15); The reference cavity (13) includes: The second reflector is located at the second end of the ultra-low expansion glass spacer and is positioned opposite to the laser emitting end of the laser refractometer (15).

6. The piston effective area measurement system according to claim 1, characterized in that, The optical pressure measuring device also includes: The second vacuum pump assembly (17) is connected to the interior of the reference cavity (13).

7. The piston effective area measurement system according to claim 1, characterized in that, The optical pressure measuring device also includes: Second shut-off valve (18); The third vacuum pump assembly (19), the second shut-off valve (18), and the third vacuum pump assembly (19) are sequentially connected to the housing.

8. The piston effective area measurement system according to claim 1, characterized in that, The chamber is a constant temperature chamber (16); the optical pressure measuring device also includes: A temperature controller (14) is located inside the constant temperature chamber (16).

9. A method for measuring the effective area of ​​a piston according to any one of claims 1 to 8, characterized in that, include: S1. The refractive index of the laser is measured by a laser refractometer (15), and the gas pressure value is obtained by theoretical calculation. S2. The obtained gas pressure value is equal to the pressure applied to the piston (8) in the piston pressure gauge (5). According to the working principle of the piston pressure gauge (5), the effective area of ​​the piston (8) is calculated in reverse by the gas pressure value.

10. The method for measuring the effective area of ​​a piston according to claim 9, characterized in that, S1 specifically includes: The laser frequency is locked to the resonant frequency of the reference cavity (13) and the measurement cavity (12) by the laser refractometer (15). The frequencies of the two lasers are measured and recorded by the frequency meter inside the laser refractometer (15), and then the gas pressure in the measurement cavity (12) is calculated.

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