SF6 gas density measurement and error compensation system based on dynamic segmented calibration

Abstract

The invention discloses an SF6 gas density measurement and error compensation system based on dynamic segmented calibration, and relates to the technical field of gas pressure and density measurement, the SF6 gas density measurement and error compensation system comprises a gas pressure sampling module used for amplifying weak analog signals output by a pressure sensor and completing analog-to-digital conversion to obtain digital sampling data used for pressure calculation; the gas density calculation module is used for establishing a density solving model based on a preset physical state equation and outputting a gas density calculation value; and the gas density calibration module is used for carrying out segmented calibration on a pressure interval corresponding to a density calculation value by taking a preset reference pressure point as a reference and outputting a calibrated density measurement result. The invention provides a method for carrying out high-precision sampling and amplification on a weak signal, and solving the density based on rapid iteration of a Betti-Bridgman equation; the invention relates to an SF6 gas density high-precision measuring system which is linked with three systems and is dynamically segmented and asymmetrically calibrated by taking 0.5 MPa as a benchmark.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of gas pressure and density measurement, and particularly relates to an SF6 gas density measurement and error compensation system based on dynamic segmented calibration. BACKGROUND

[0002] SF6 gas is used in gas insulated switchgear (GIS) to maintain insulation and arc extinguishing performance. The density of SF6 gas changes with temperature fluctuation and leakage. If the density is lower than a threshold value, the insulation performance will be significantly reduced, and a safety risk will be caused. Therefore, a real-time density monitoring system is required according to relevant standards.

[0003] The existing density monitoring scheme has the following problems: a weak voltage signal is easily disturbed by noise in the sampling link, resulting in insufficient precision; a single calibration strategy is difficult to compensate for the nonlinear error of the sensor in different pressure intervals; and when a complex physical state equation is used, the limited computing power of an embedded device makes it difficult to achieve fast solving and real-time output. SUMMARY

[0004] The application aims to provide an SF6 gas density measurement and error compensation system based on dynamic segmented calibration to solve the problems in the background.

[0005] To solve the above technical problems, the application provides the following technical scheme: an SF6 gas density measurement and error compensation system based on dynamic segmented calibration, comprising a gas pressure sampling module, a gas density calculation module and a gas density calibration module.

[0006] According to the above technical scheme, the gas pressure sampling module comprises a pressure sensor interface unit, an instrument amplification unit, an analog-to-digital conversion unit and a sampling calculation unit, wherein the pressure sensor interface unit is used to access a 0-20 mV level sensor output signal, the instrument amplification unit is used to amplify the signal to a voltage range suitable for the ADC reference voltage, the analog-to-digital conversion unit is used to output a digital sampling value, and the sampling calculation unit is used to convert the digital sampling value to obtain a pressure initial value. The gas density calculation module comprises an equation construction unit, a density equation transformation unit, an iterative solution unit and a convergence determination unit, wherein the equation construction unit is configured to load a parameterized model of the Bethe-Bridgman equation, the density equation transformation unit is configured to form a root-finding equation with density as an unknown quantity, the iterative solution unit is configured to quickly iterate to obtain a density value under embedded computing power conditions, and the convergence determination unit is configured to determine whether the iteration result meets a preset accuracy threshold; The gas density calibration module comprises a reference point setting unit, a low-pressure section calibration unit, a high-pressure section calibration unit and an adaptive adjustment unit, wherein the reference point setting unit is configured to set 0.5 MPa as a calibration reference point, the low-pressure section calibration unit and the high-pressure section calibration unit are respectively configured to apply a proportional coefficient and an offset in a corresponding pressure interval, and the adaptive adjustment unit is configured to update the proportional coefficient and the offset according to an error direction.

[0007] According to the above technical solution, the following steps are included: S1: Perform pressure signal acquisition, acquire an analog voltage signal output by a pressure sensor, and perform amplification processing on the analog voltage signal to meet the input range requirements of subsequent analog-to-digital conversion; S2: Perform analog-to-digital conversion and pressure initial value calculation, perform analog-to-digital conversion on the amplified voltage signal to obtain a digital sampling value, and obtain a pressure initial value based on a sampling calculation relationship; S3: Perform density calculation, convert a physical state equation into a density solving model, and obtain a density calculation value through iteration to meet the real-time calculation requirements of embedded devices; S4: Perform dynamic segmented calibration, divide a full-range pressure into at least two pressure intervals with reference to a preset reference pressure point, and apply different calibration parameters in different pressure intervals to compensate for nonlinear errors; S5: Output measurement results, output the calibrated density measurement results to a display, communication or monitoring interface, and meet the response time requirements of industrial real-time monitoring.

[0008] According to the above technical solution, the S1-S2 are specifically as follows: S1-1: Signal conditioning and amplification, the analog voltage signal output by the pressure sensor is connected to the input end of the instrument amplifier, the analog voltage signal is a weak signal of 0-20 mV order of magnitude; the resistance network of the instrument amplifier is set to have a fixed gain G=85.32, so that the sampling voltage after amplification falls within the range of 0-2.5V and matches the ADC reference voltage, thereby improving the signal-to-noise ratio on the hardware side and avoiding ADC input overload; wherein G is the amplification factor of the instrument amplifier, and the sampling voltage after amplification is denoted as Vs; S2-1, analog-digital conversion and digital quantity definition, analog-digital conversion is performed on the sampling voltage Vs under the ADC reference voltage Vref, and the following is met: Vs / Vref=Nadc / NFS; wherein Nadc is an ADC output code value obtained by one sampling, and NFS is an upper limit value of an ADC range, and NFS is 4095; a one-to-one correspondence between the analog quantity Vs and the digital quantity Nadc is established through the proportional relationship, so that subsequent pressure initial value calculation and error compensation are performed in a digital manner; S2-2: inverse calculation of amplification and formation of pressure initial value, the sampling voltage Vs is inversely calculated according to the Nadc, NFS and Vref, and the sampling voltage is converted into a raw voltage at the output end of the sensor in combination with the amplification G, and then the raw voltage is converted into the pressure initial value Praw according to the pre-stored pressure sensor calibration curve; wherein Praw is a pressure value before the segmented calibration is performed, and is used as an input quantity for subsequent density equation solving and segmented calibration, so as to ensure that the input definition of the calculation link is single and traceable.

[0009] According to the technical scheme, the S3 is specifically: S3-1: density solving model construction, the Betti-Bridgman equation is parameterized and loaded on the controller side, and the equation is equivalent transformed in the form of density as an unknown quantity to form a density solving equation f(D)=0; wherein D is a SF6 gas density to be solved, and f(D) is a density residual function, which is obtained by substituting the pressure initial value Praw obtained in step S2 into the parameterized equation, so that the subsequent solving target is clear as a root-finding problem of making the residual zero; S3-2: iterative update and derivative meaning limitation, the Newton-Leibniz iteration method is used to iteratively update the density solving equation, and the iterative relationship is: D{n+1}=Dn−f(Dn) / f'(Dn); wherein Dn is the density value of the nth iteration, D{n+1} is the density value of the n+1th iteration, and f'(Dn) is the derivative value of the density residual function f(D) with respect to the density D at Dn; by introducing f'(Dn), the iteration direction and step length are adaptively changed with the local slope of the residual curve, so as to improve the convergence speed under the embedded condition and reduce the number of iterations; S3-3: initial value and convergence output rule, the density value D0 is initialized as 0, and the convergence threshold ε is set; when |D{n+1}−Dn|≤ε is met, it is determined that the iteration result converges and the density calculation value Dout is output; Dout is the density calculation output before the segmented calibration is performed, and is used to enter the subsequent segmented calibration link, so as to clearly determine when to stop iteration and output which density value.

[0010] According to the technical scheme, the S4 includes the following sub-steps: S4-1: The reference point is set for the purpose of alignment, and the reference pressure point Pb=0.5 MPa is set as the demarcation point between the low pressure section and the high pressure section; the measured value and the theoretical value are obtained at the reference pressure point and compared, which is used to determine which point is used as the overall error alignment point to avoid the magnification of interval non-linear error caused by the full range unified coefficient; S4-2: The slope correction coefficient is introduced, and the slope correction coefficient ks is calculated based on the measured value and the theoretical value, wherein the ks is 0.981, which is used to uniformly correct the proportional error accumulated with the increase of the range in the pressure link; the coefficient is used as a common multiplier for subsequent segmented linear correction to ensure that the segmented calibration does not damage the overall scale consistency; S4-3: The segmented interval and parameter set are defined, and the pressure full range is divided into a low pressure section ΓL and a high pressure section ΓH, wherein ΓL is a 0-0.5 MPa interval, and ΓH is a 0.5-1 MPa interval; the proportional coefficient ratioL and the offset offsetL are set for ΓL, and the proportional coefficient ratioH and the offset offsetH are set for ΓH; wherein ratioL and ratioH are used to represent the segmented proportional correction strength, and offsetL and offsetH are used to represent the segmented zero point compensation amount, so that the calibration parameters of different pressure intervals are independent of each other; S4-4: The segmented linear correction and the output pressure are defined, and the segmented linear correction is performed on the pressure initial value Praw to obtain the calibrated pressure Pcal: when Praw falls into the low pressure section ΓL, the linear correction is completed by using ks, ratioL and offsetL; when Praw falls into the high pressure section ΓH, the linear correction is completed by using ks, ratioH and offsetH; wherein Pcal is the calibrated pressure output, which is used as the final output basis of the density measurement result, thereby defining the execution rule of using different correction parameters in different intervals for the same pressure initial value.

[0011] According to the above technical solution, the S4 further comprises an adaptive calibration sub-step: S4-5: The segmented error amount calculation and the sign meaning fixing, the corresponding reference calibration points are selected in the low pressure section ΓL and the high pressure section ΓH, the calibrated pressure Pcal and the reference pressure Pref at the reference calibration points are compared to obtain the low pressure section error eL and the high pressure section error eH; wherein the positive and negative signs of eL and eH are used to represent the deviation direction, e>0 indicates that the calibrated output is higher than the reference value, and e<0 indicates that the calibrated output is lower than the reference value, thereby converting the error direction into an executable parameter update trigger condition; S4-6: Deterministic update rule based on error direction, when eL>0, decrease ratioL and offsetL by preset update step simultaneously; when eL<0, increase ratioL and offsetL by preset update step simultaneously; when eL=0, keep ratioL and offsetL unchanged; the same update rule is applied to ratioH and offsetH for high pressure error eH; wherein the update step is a positive number fixed in advance, so that the parameter update has a deterministic direction and a deterministic amplitude in each adaptive iteration, thereby avoiding the understanding obstacle that adjustment is made but it is unclear how to adjust; S4-7: Closed-loop calibration termination condition, after completing a parameter update, execute step S4-4 again to obtain new Pcal, and recalculate eL and eH; when the full-range error is less than 0.1%, terminate the adaptive calibration process and fix the current ratioL, offsetL, ratioH, and offsetH; wherein the full-range error is the maximum value of the relative error at each calibration point, which is used as the only judgment index for whether to end the adaptive calibration.

[0012] According to the above technical solution, the S5 includes the following constraints and output control: S5-1: Real-time linkage scheduling boundary, pressure sampling, density calculation and segmented calibration are executed as a serial processing link in the same measurement period, and one measurement result is output after completing one link processing, so that the response time of the whole process of sampling-processing-output is less than 10ms; wherein the response time is defined as the time interval from triggering one ADC sampling to obtaining the final output result, so as to give a clear and verifiable measurement criterion for real-time index; S5-2: Density calculation accuracy constraint and output association, in the link, the solving error of the density calculation module is controlled to be less than 0.05%, and the density calculation output Dout that meets the accuracy constraint is taken as the input of segmented calibration, so that the density calculation result meets the basic accuracy requirement before entering the segmented calibration, thereby ensuring that the subsequent calibration is mainly used to compensate the segmented nonlinear error of the sensor rather than to compensate the model solving error; S5-3: Final output quantity definition, form the final density measurement result Dcal based on the calibration pressure Pcal and output, the Dcal is the density result compensated by the segmented calibration parameters, which is used for real-time monitoring and safety threshold judgment of GIS equipment, so that the output object remains unique and consistent.

[0013] Compared with the prior art, the present application has the beneficial effects that: the present scheme amplifies the 0-20mV level weak signal through the instrument amplifier and maps it into the ADC reference range, realizes high-precision sampling of the low-level signal and calculation of the pressure initial value; the Betty-Bridgman equation is converted into a density solving equation and the iterative method is used for fast convergence on the embedded side, realizing microsecond-level solving and reducing the calculation burden; at the same time, the low-pressure section and the high-pressure section are set with independent proportional coefficients and offsets based on the 0.5MPa reference point, and the error direction is combined for adaptive adjustment, so that the full-range error is controlled within 0.1%; the three modules are linked in real time, so that the sampling-processing-output whole process response is less than 10ms, meeting the real-time and precision requirements of GIS online monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0014] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, illustrate the present application together with the embodiments thereof, and explain the present application, but do not constitute a limitation of the present application. In the drawings: Figure 1 is a schematic diagram of the overall module structure of the present application. DETAILED DESCRIPTION

[0015] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0016] Please refer to Figure 1 , the present application provides a technical solution: a SF6 gas density measurement and error compensation system based on dynamic segmented calibration, comprising a gas pressure sampling module, which is used for amplifying the weak analog signal output by the pressure sensor and completing analog-digital conversion, to obtain digital sampling data for pressure calculation; a gas density calculation module, which is used for establishing a density solving model based on a preset physical state equation and outputting a gas density calculation value; and a gas density calibration module, which is used for segmenting and calibrating the pressure interval corresponding to the density calculation value with reference to a preset reference pressure point and outputting the calibrated density measurement result. The gas pressure sampling module comprises a pressure sensor interface unit, an instrument amplification unit, an analog-digital conversion unit and a sampling calculation unit, wherein the pressure sensor interface unit is used for accessing the 0-20mV level sensor output signal, the instrument amplification unit is used for amplifying the signal to a voltage range suitable for the ADC reference voltage, the analog-digital conversion unit is used for outputting the digital sampling value, and the sampling calculation unit is used for converting the digital sampling value to obtain the pressure initial value. The gas density calculation module comprises an equation construction unit, a density equation transformation unit, an iterative solution unit and a convergence determination unit, wherein the equation construction unit is configured to load a parameterized model of the Bethe-Bridgman equation, the density equation transformation unit is configured to form a root-finding equation with density as an unknown quantity, the iterative solution unit is configured to quickly iterate to obtain a density value under embedded computing power conditions, and the convergence determination unit is configured to determine whether the iteration result meets a preset accuracy threshold; The gas density calibration module comprises a reference point setting unit, a low-pressure section calibration unit, a high-pressure section calibration unit and an adaptive adjustment unit, wherein the reference point setting unit is configured to set 0.5 MPa as a calibration reference point, the low-pressure section calibration unit and the high-pressure section calibration unit are respectively configured to apply a proportional coefficient and an offset in a corresponding pressure interval, and the adaptive adjustment unit is configured to update the proportional coefficient and the offset according to an error direction; The method comprises the following steps: S1: performing pressure signal acquisition, acquiring an analog voltage signal output by a pressure sensor, and amplifying the analog voltage signal to meet the input range requirements of subsequent analog-to-digital conversion; S2: performing analog-to-digital conversion and pressure initial value calculation, performing analog-to-digital conversion on the amplified voltage signal to obtain a digital sampling value, and obtaining a pressure initial value based on a sampling calculation relationship; S3: performing density calculation, converting a physical state equation into a density solving model and obtaining a density calculation value through iteration to meet the real-time calculation requirements of embedded devices; S4: performing dynamic segmented calibration, dividing a full-range pressure into at least two pressure intervals with a preset reference pressure point as a reference, and applying different calibration parameters in different pressure intervals to compensate for nonlinear errors; S5: outputting measurement results, outputting the calibrated density measurement results to a display, communication or monitoring interface, and meeting the response time requirements of industrial real-time monitoring; S1-S2 are specifically: S1-1: signal conditioning and amplification, connecting the analog voltage signal output by the pressure sensor to the input end of the instrument amplifier, the analog voltage signal being a weak signal of 0-20 mV order of magnitude; setting the resistance network of the instrument amplifier to make its gain fixed at G=85.32, so that the amplified sampling voltage falls within the range of 0-2.5V and matches the ADC reference voltage, thereby improving the signal-to-noise ratio on the hardware side and avoiding ADC input overload; wherein G is the amplification factor of the instrument amplifier, and the amplified sampling voltage is denoted as Vs; S2-1, analog-digital conversion and digital quantity definition, analog-digital conversion is performed on the sampling voltage Vs under the ADC reference voltage Vref, which satisfies: Vs / Vref=Nadc / NFS; wherein Nadc is the ADC output code value obtained by one sampling, and NFS is the upper limit value of the ADC range, and NFS takes 4095; the one-to-one correspondence between the analog quantity Vs and the digital quantity Nadc is established through the proportional relationship, so that the subsequent pressure initial value calculation and error compensation are performed in a digital manner; S2-2: inverse calculation of amplification factor and formation of pressure initial value, the sampling voltage Vs is inversely calculated according to Nadc, NFS and Vref, and the sampling voltage is converted into the original voltage at the output end of the sensor in combination with the amplification factor G, and then the original voltage is converted into the pressure initial value Praw according to the pre-stored calibration curve of the pressure sensor; wherein Praw is the pressure value before the segmented calibration is performed, which is used as the input quantity for subsequent density equation solving and segmented calibration, so as to ensure that the input definition of the calculation link is single and traceable; S3 is specifically: S3-1: density solving model construction, the Betti-Bridgman equation is parameterized and loaded on the controller side, and the equation is equivalent transformed according to the form that the density is unknown, to form the density solving equation f(D)=0; wherein D is the SF6 gas density to be solved, and f(D) is the density residual function, which is obtained by substituting the pressure initial value Praw obtained in step S2 into the parameterized equation, so that the subsequent solving target is clear as a root-finding problem of making the residual zero; S3-2: iterative update and derivative meaning limitation, the Newton-Leibniz iteration method is used to iteratively update the density solving equation, and the iterative relationship is: D{n+1}=Dn−f(Dn) / f'(Dn); wherein Dn is the density value of the nth iteration, D{n+1} is the density value of the n+1th iteration, and f'(Dn) is the derivative value of the density residual function f(D) with respect to the density D at Dn; by introducing f'(Dn), the iteration direction and step length are adaptively changed with the local slope of the residual curve, so as to improve the convergence speed under the embedded condition and reduce the number of iterations; S3-3: initial value and convergence output rule, the density value D0 is initialized as 0, and the convergence threshold ε is set; when |D{n+1}−Dn|≤ε is satisfied, it is determined that the iteration result converges and the density calculation value Dout is output; Dout is the density calculation output before the segmented calibration is performed, which is used to enter the subsequent segmented calibration link, so as to determine when to stop iteration and output which density value; S4 includes the following sub-steps: S4-1: The reference point is set for the purpose of alignment, and the reference pressure point Pb=0.5 MPa is set as the demarcation point between the low pressure section and the high pressure section. The measured value and the theoretical value at the reference pressure point are compared to determine which point is used as the overall error alignment point, so as to avoid the magnification of interval non-linear error caused by the full-range uniform coefficient; S4-2: The slope correction coefficient is introduced, and the slope correction coefficient ks is calculated based on the measured value and the theoretical value. The ks is 0.981, which is used to uniformly correct the proportional error accumulated with the increase of the range in the pressure link. The coefficient is used as a common multiplier for subsequent segmented linear correction to ensure that the segmented calibration does not damage the overall scale consistency; S4-3: The segmented interval and parameter set are defined. The pressure full range is divided into a low pressure section ΓL and a high pressure section ΓH, wherein ΓL is the 0-0.5 MPa interval, and ΓH is the 0.5-1 MPa interval. The proportional coefficient ratioL and the offset offsetL are set for ΓL, and the proportional coefficient ratioH and the offset offsetH are set for ΓH. The ratioL and the ratioH are used to represent the segmented proportional correction strength, and the offsetL and the offsetH are used to represent the segmented zero point compensation amount, so that the calibration parameters of different pressure intervals are independent of each other; S4-4: The segmented linear correction and the output pressure are defined. The segmented linear correction is performed on the pressure initial value Praw to obtain the calibrated pressure Pcal: when Praw falls into the low pressure section ΓL, the linear correction is completed by using ks, ratioL and offsetL; when Praw falls into the high pressure section ΓH, the linear correction is completed by using ks, ratioH and offsetH; wherein Pcal is the calibrated pressure output, which is used as the final output basis of the density measurement result, thereby defining the execution rule of using different correction parameters in different intervals for the same pressure initial value; S4 further comprises an adaptive calibration sub-step: S4-5: The segmented error amount calculation and the sign meaning fixing are performed. The corresponding reference calibration points are selected in the low pressure section ΓL and the high pressure section ΓH, and the calibrated pressure Pcal and the reference pressure Pref at the reference calibration points are compared to obtain the low pressure section error eL and the high pressure section error eH. The positive and negative signs of eL and eH are used to represent the deviation direction, e>0 represents that the calibrated output is higher than the reference value, and e<0 represents that the calibrated output is lower than the reference value, thereby converting the error direction into an executable parameter update trigger condition; S4-6: Deterministic updating rule based on error direction, when eL>0, decrease ratioL and offsetL by preset updating step simultaneously; when eL<0, increase ratioL and offsetL by preset updating step simultaneously; when eL=0, keep ratioL and offsetL unchanged; the same updating rule is applied to ratioH and offsetH for high pressure error eH; wherein the updating step is a positive number fixed in advance, so that the parameter updating has a deterministic direction and a deterministic amplitude in each adaptive iteration, thereby avoiding the understanding obstacle that adjustment is made but it is unclear how to adjust; S4-7: Closed-loop calibration termination condition, after completing a parameter updating, new Pcal is obtained by re-executing step S4-4, and eL and eH are recalculated; when the full range error is less than 0.1%, the adaptive calibration process is terminated and the current ratioL, offsetL, ratioH and offsetH are fixed; wherein the full range error is the maximum value of the relative error at each calibration point, which is used as the only judgment index for whether to end the adaptive calibration; S5 includes the following constraints and output controls: S5-1: Real-time linkage scheduling boundary, pressure sampling, density calculation and segmented calibration are executed as a serial processing link in the same measurement period, one measurement result is output after completing one link processing, and the response time of the whole process of sampling-processing-output is less than 10ms; wherein the response time is defined as the time interval from triggering one ADC sampling to obtaining the final output result, so as to give a clear and verifiable measurement criterion for real-time index; S5-2: Density calculation accuracy constraint and output association, the solving error of the density calculation module in the link is controlled to be less than 0.05%, and the density calculation output Dout that meets the accuracy constraint is taken as the input of segmented calibration, so that the density calculation result meets the basic accuracy requirement before entering the segmented calibration, thereby ensuring that the subsequent calibration is mainly used to compensate the segmented nonlinear error of the sensor rather than to make up the model solving error; S5-3: Final output quantity definition, the final density measurement result Dcal is formed based on the calibration pressure Pcal and output, Dcal is the density result compensated by the segmented calibration parameters, which is used for real-time monitoring and safety threshold judgment of GIS equipment, so that the output object remains unique and consistent.

[0017] It should be noted that, in the present document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprising", "including", "containing", or any other similar terms are intended to be non-exclusive and non-limiting, such that a process, method, article, or apparatus that comprises, includes, or contains a list of elements is not required to include only those elements on the list, but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0018] Finally, it should be noted that the above-described embodiments are merely possible examples of implementing the present application, and thus do not limit the present application. Accordingly, numerous modifications and variations are possible in the light of the above teachings without departing from the spirit and scope of the application, and it should be understood that all modifications and variations fall within the scope of the application.

Claims

1. A system for measuring and compensating the density of SF6 gas based on dynamic segmented calibration, characterized in that: It includes a gas pressure sampling module, which amplifies the weak analog signal output by the pressure sensor and performs analog-to-digital conversion to obtain digital sampling data for pressure calculation; and a gas density calculation module, which establishes a density solution model based on a preset physical state equation and outputs the calculated gas density value. The gas density calibration module is used to perform segmented calibration of the pressure range corresponding to the density calculation value with a preset reference pressure point and output the calibrated density measurement results.

2. The SF6 gas density measurement and error compensation system based on dynamic segmented calibration according to claim 1, characterized in that: The gas pressure sampling module includes a pressure sensor interface unit, an instrument amplification unit, an analog-to-digital conversion unit, and a sampling calculation unit. The pressure sensor interface unit is used to receive the output signal of a 0–20mV level sensor, the instrument amplification unit is used to amplify the signal to a voltage range that matches the ADC reference voltage, the analog-to-digital conversion unit is used to output digital sampled values, and the sampling calculation unit is used to calculate the initial pressure value from the digital sampled values. The gas density calculation module includes an equation construction unit, a density equation transformation unit, an iterative solution unit, and a convergence determination unit. The equation construction unit is used to load the parameterized model of the Bertie-Bridgeman equation, the density equation transformation unit is used to form a root-finding equation with density as the unknown, the iterative solution unit is used to quickly iterate to obtain the density value under embedded computing power conditions, and the convergence determination unit is used to determine whether the iteration result meets the preset accuracy threshold. The gas density calibration module includes a reference point setting unit, a low-pressure section calibration unit, a high-pressure section calibration unit, and an adaptive adjustment unit. The reference point setting unit is used to set 0.5MPa as the calibration reference point. The low-pressure section calibration unit and the high-pressure section calibration unit are used to apply a proportional coefficient and an offset in the corresponding pressure range, respectively. The adaptive adjustment unit is used to update the proportional coefficient and the offset according to the error direction.

3. The SF6 gas density measurement and error compensation system based on dynamic segmented calibration according to claim 2, characterized in that: Includes the following steps: S1: Perform pressure signal acquisition, obtain the analog voltage signal output by the pressure sensor, and amplify the analog voltage signal to meet the input range requirements of subsequent analog-to-digital conversion; S2: Perform analog-to-digital conversion and initial pressure calculation. Perform analog-to-digital conversion on the amplified voltage signal to obtain digital sampled values, and obtain the initial pressure value based on the sampling calculation relationship; S3: Perform density calculation, transform the physical state equation into a density solution model and obtain the density calculation value through an iterative method to meet the real-time computing requirements of embedded devices; S4: Perform dynamic segmented calibration, using a preset reference pressure point as a reference, divide the entire pressure range into at least two pressure intervals, and apply different calibration parameters in different pressure intervals to compensate for nonlinear errors; S5: Output measurement results. Output the calibrated density measurement results to the display, communication or monitoring interface, and meet the response time requirements of industrial real-time monitoring.

4. The SF6 gas density measurement and error compensation system based on dynamic segmented calibration according to claim 3, characterized in that: Specifically, S1-S2 are: S1-1: Signal conditioning and amplification. The analog voltage signal output by the pressure sensor is connected to the input of the instrumentation amplifier. The analog voltage signal is a weak signal in the range of 0–20mV. By setting the resistor network of the instrumentation amplifier to fix its gain at G=85.32, the amplified sampling voltage falls into the range of 0–2.5V and matches the ADC reference voltage, thereby improving the signal-to-noise ratio on the hardware side and avoiding ADC input overload. Here, G is the amplification factor of the instrumentation amplifier, and the amplified sampling voltage is denoted as Vs. S2-1. Analog-to-digital conversion and digital quantity definition: The sampling voltage Vs is converted from analog to digital under the ADC reference voltage Vref, satisfying: Vs / Vref=Nadc / NFS; where Nadc is the ADC output code value obtained from one sampling, and NFS is the upper limit of the ADC range, with NFS set to 4095. S2-2: Amplification factor back calculation and initial pressure value formation. Based on Nadc, NFS and Vref, the sampling voltage Vs is back calculated, and combined with the amplification factor G, the sampling voltage is converted into the original voltage of the sensor output terminal. Then, according to the pre-stored pressure sensor calibration curve, the original voltage is converted into the initial pressure value Praw; where Praw is the pressure value before segmented calibration is performed.

5. The SF6 gas density measurement and error compensation system based on dynamic segmented calibration according to claim 4, characterized in that: Specifically, S3 is: S3-1: Density solution model construction. The Bertie-Bridgeman equation is parameterized on the controller side, and the equation is equivalently transformed with density as the unknown quantity to form the density solution equation f(D)=0; where D is the density of SF6 gas to be determined, and f(D) is the density residual function. The residual function is obtained by substituting the initial pressure value Praw obtained in step S2 into the parameterized equation. S3-2: Iterative Update and Derivative Meaning Definition. The Newton-Leibniz iterative method is used to iteratively update the density solution equation. The iterative relationship is: D{n+1}=Dn−f(Dn) / f'(Dn); where Dn is the density value of the nth iteration, D{n+1} is the density value of the (n+1)th iteration, and f'(Dn) is the derivative of the density residual function f(D) with respect to density D at Dn. By introducing f'(Dn), the iteration direction and step size are adaptively changed with the local slope of the residual curve. S3-3: Initial value and convergence output rules. Initialize the density value D0=0 and set the convergence threshold ε. When |D{n+1}−Dn|≤ε is satisfied, the iteration result is determined to be converged and the density calculation value Dout is output. Dout is the density calculation output before the piecewise calibration is performed.

6. The SF6 gas density measurement and error compensation system based on dynamic segmented calibration according to claim 5, characterized in that: S4 includes the following sub-steps: S4-1: The purpose of setting and aligning the reference point is to set a reference pressure point Pb=0.5MPa and use this reference point as the boundary between the low-pressure section and the high-pressure section; the measured value and the theoretical value are obtained at the reference pressure point and compared. S4-2: Slope correction coefficient is introduced. The slope correction coefficient ks is calculated based on the measured value and the theoretical value. The ks is 0.981 and is used to uniformly correct the proportional error that accumulates with the increase of the range in the pressure link. S4-3: Definition of segmented intervals and parameter sets. The full pressure range is divided into a low-pressure segment ΓL and a high-pressure segment ΓH, where ΓL is the 0–0.5MPa range and ΓH is the 0.5–1MPa range. A proportional coefficient ratioL and an offset L are set for ΓL, and a proportional coefficient ratioH and an offset H are set for ΓH. Among them, ratioL and ratioH are used to characterize the segmented proportional correction strength, and offsetL and offsetH are used to characterize the segmented zero-point compensation amount. S4-4: Piecewise linear correction and output pressure definition. Piecewise linear correction is performed on the initial pressure value Praw to obtain the calibrated pressure Pcal. When Praw falls into the low-pressure range ΓL, linear correction is performed using ks, ratioL, and offsetL. When Praw falls into the high-pressure range ΓH, linear correction is performed using ks, ratioH, and offsetH. Pcal is the calibrated pressure output.

7. The SF6 gas density measurement and error compensation system based on dynamic segmented calibration according to claim 6, characterized in that: S4 further includes an adaptive calibration sub-step: S4-5: The calculation and symbol meaning of segmented error are fixed. Corresponding reference calibration points are selected in the low-pressure segment ΓL and the high-pressure segment ΓH respectively. The calibration pressure Pcal at the reference calibration point is compared with the reference pressure Pref to obtain the low-pressure segment error eL and the high-pressure segment error eH. The positive and negative signs of eL and eH are used to characterize the direction of deviation. e>0 indicates that the calibration output is higher than the reference value, and e<0 indicates that the calibration output is lower than the reference value. S4-6: Deterministic update rule based on error direction. When eL>0, ratioL and offsetL are simultaneously decreased by a preset update step size; when eL<0, ratioL and offsetL are simultaneously increased by a preset update step size; when eL=0, ratioL and offsetL remain unchanged; the same update rule is applied to ratioH and offsetH for the high-voltage section error eH; wherein the update step size is a pre-fixed positive number, so that the parameter update has a definite direction and a definite magnitude in each adaptive iteration; S4-7: Closed-loop calibration termination condition. After completing one parameter update, step S4-4 is executed again to obtain the new Pcal, and eL and eH are recalculated. When the full-range error is less than 0.1%, the adaptive calibration process is terminated and the current ratioL, offsetL, ratioH, and offsetH are fixed. The full-range error is the maximum value of the relative error at each calibration point.

8. The SF6 gas density measurement and error compensation system based on dynamic segmented calibration according to claim 7, characterized in that: S5 includes the following constraints and output controls: S5-1: Real-time linkage scheduling boundary, pressure sampling, density calculation and segment calibration are executed as a series processing link within the same measurement cycle. After completing one link processing, one measurement result is output, so that the entire process response time of sampling-processing-output is less than 10ms; where response time is defined as the time interval from the start of triggering an ADC sampling to the end of obtaining the final output result; S5-2: Density calculation accuracy constraint and output association. In the link, the solution error of the density calculation module is controlled to be less than 0.05%, and the density calculation output Dout that meets the accuracy constraint is used as the input for segment calibration, so that the density calculation result meets the basic accuracy requirements before entering the segment calibration. S5-3: Final output definition: Based on the calibration pressure Pcal, the final density measurement result Dcal is generated and output. Dcal is the density result after compensation by segmented calibration parameters, which is used for real-time monitoring and safety threshold determination of GIS equipment.

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