Method for improving temperature compensation precision of pressure sensor

Abstract

The invention provides a method for improving the temperature compensation precision of a pressure sensor, and the method comprises the steps: obtaining the output-pressure-temperature data of a pressure sensor sample through an experiment by employing calibrated high-precision equipment, carrying out the polynomial fitting based on a least square method, calculating the coefficient of a multi-term expression, optimizing the polynomial times of the multi-term expression, and obtaining the temperature compensation precision of the pressure sensor. And the polynomial piecewise function is combined to obtain the highest fitting precision, the function piecewise of the polynomial piecewise function is optimized, and the optimized polynomials are combined into the polynomial piecewise function to serve as a temperature compensation function for improving the temperature compensation precision of the pressure sensor. According to the method provided by the invention, the temperature compensation precision can be further improved, the fitting precision can be effectively improved, the fitting mean square error can be improved from 4.993 e-05 to 1.013 e-05, and the precision is improved by about 80%.

Description

Technical Field

[0001] The present invention belongs to the technical field of pressure detection, and more specifically relates to a method for improving the temperature compensation accuracy of a pressure sensor. Background Art

[0002] Micro-electro-mechanical system, also known as MEMS (Micro-Electro-Mechanical-System), is an advanced technology for large-scale manufacturing of miniature high-performance devices, such as pressure sensors, accelerometers, etc. MEMS pressure sensors mainly include piezoresistive pressure sensors and capacitive pressure sensors. Among them, piezoresistive pressure sensors are the most widely used MEMS devices. Piezoresistive pressure sensors rely on a layer of pressure film to sense the pressure of the external medium. Through micro-machining technology, piezoresistive elements can be made on the pressure film. The characteristic of these piezoresistive elements is that their resistance value is very sensitive to stress. When external pressure is applied, the pressure film will deform and generate stress. These stresses are transmitted to the piezoresistive element, which will cause the resistance value of the piezoresistive element to change. By measuring the change in resistance, the external pressure change can be converted into an electrical signal output. The existing technology uses MEMS pressure sensors, which have a very significant limitation in use, that is, at different temperatures, the sensitivity and linearity of the pressure sensor will be different, which leads to different sensor output errors at different temperatures. For example, the accuracy of 0.1% FS at room temperature will reach 3% or even higher at minus 40 degrees or 150 degrees. Therefore, many different methods are used to compensate for temperature in practical applications. The current temperature compensation method is mainly completed by hardware or software. Among them, hardware compensation optimizes the configuration of the measurement circuit by changing the circuit parameters, but hardware compensation generally has the disadvantages of increased cost, weak process flexibility, difficulty in debugging, limited accuracy, etc., which are not conducive to production promotion. Software compensation has gradually become a hot spot and has received widespread attention because it avoids the above shortcomings. The most commonly used software compensation algorithm is the piecewise linear interpolation method, which performs temperature compensation by storing the calibration data obtained from the experiment in the pressure sensor memory (EPROM) as the interpolation point.

[0003] Chinese patent application No. CN201710009360.1 discloses a temperature and pressure compensation method for improving the output accuracy of an embedded pressure sensor. The method uses a sensor signal processing chip to collect the pressure signal of the pressure sensor and the change in bridge resistance, and converts the pressure output into a polynomial expression based on temperature and pressure. The upper computer then performs polynomial fitting based on the least squares method on different temperature and pressure conditions to calculate the coefficients of the polynomial expression.

[0004] Chinese patent application No. CN201710302488.7 discloses a temperature compensation method for a silicon piezoresistive transmitter, which uses a second-order fitting method to obtain a polynomial temperature compensation model. First, a polynomial least squares fitting is performed on the standard pressure input value-pressure measurement value at a specified temperature point to obtain a polynomial function mapping relationship between the standard pressure input value and the pressure measurement AD value at the specified temperature value and a first-stage coefficient matrix. Then, a least squares fitting with a fitting number of l is performed on the m specified temperature AD values ​​and the coefficient row vectors of length m in the first-stage coefficient matrix to obtain the polynomial function mapping relationship between the temperature AD value and the first-stage coefficient row vector and the coefficient matrix of the temperature compensation model.

[0005] The existing temperature compensation method for the output accuracy of pressure sensors adopts a polynomial fitting output-pressure-temperature function to flexibly realize the fitting calculation of multiple temperature points and multiple pressure points. The temperature points and pressure points can be effectively set based on the experience of piezoresistive pressure sensors to obtain a more effective fit; however, due to the existence of nonlinearity of piezoresistive pressure sensors, it is difficult to further improve the temperature compensation accuracy after the compensation accuracy reaches a certain level. Summary of the invention

[0006] Based on the technical problems existing in the prior art, the present invention provides a method for improving the temperature compensation accuracy of a pressure sensor, aiming to solve the technical problem in the prior art that the compensation accuracy is difficult to further improve after reaching a certain level due to the existence of nonlinearity.

[0007] To achieve the above object, according to a first aspect of the present invention, a method for improving the temperature compensation accuracy of a pressure sensor is provided, which comprises the following steps:

[0008] Step S1, using calibrated high-precision equipment to obtain output-pressure-temperature data of a pressure sensor sample through experiments;

[0009] Step S2, segmenting the output-pressure-temperature data obtained in step S1 according to temperature;

[0010] Step S3, performing polynomial fitting based on the least squares method on each segment of data obtained in step S2 to calculate the coefficients of the polynomial expression;

[0011] Step S4, optimizing the polynomial degree of the polynomial expression to obtain the highest fitting accuracy;

[0012] Step S5, optimizing the function segmentation of the polynomial piecewise function;

[0013] Step S6, combining the optimized polynomials into a polynomial piecewise function as a temperature compensation function for improving the temperature compensation accuracy of the pressure sensor.

[0014] The temperature compensation function obtained in step S6 is stored in the memory of the pressure sensor data processing chip. During measurement, the pressure sensor output value and the corresponding temperature value are substituted into the temperature compensation function to obtain the pressure value, thereby completing the temperature compensation of the pressure.

[0015] Preferably, step S1 includes using a standard pressure source and a temperature control device to perform calibration according to the measurement environment, and using a data acquisition system to record the standard measurement environment data and the calibration data of the standard pressure source and the temperature control device.

[0016] Furthermore, the standard pressure source is selected from Yokogawa test and measurement instrument Yokogawa 2558A or WIKA CPP1000-L.

[0017] In addition, the temperature control equipment uses a constant temperature box. The temperature control equipment uses a German Binder KBF series constant temperature box.

[0018] Preferably, a standard pressure source is used as a pressure sensor and connected to a data acquisition system, such as an STM32-based system for data reading and processing; different predetermined known pressures are applied to the pressure sensor through a pressurizing device and varied within a certain temperature range to simulate an actual working environment.

[0019] Preferably, a standard pressure source is used as a pressure sensor and connected to a data acquisition system, and a system based on STM32 is used for data reading and processing.

[0020] More preferably, during the data acquisition process, the raw data of the output signal of the standard pressure source as the pressure sensor at different pressures and temperatures are preprocessed, including filtering, sampling, normalization and other operations, to facilitate subsequent data analysis.

[0021] In another embodiment, the output-pressure-temperature data obtained in step S1 is segmented according to the temperature cuts with 10° C. or 20° C. as a segment.

[0022] Compared with the prior art, the method of improving the temperature compensation accuracy of the pressure sensor of the present invention has the following beneficial effects:

[0023] (1) The method proposed in the present invention can further improve the temperature compensation accuracy. Compared with the segmented fitting in the prior art, which is limited in the temperature compensation accuracy due to the nonlinearity of the pressure sensor, the present invention can effectively improve the fitting accuracy. The present invention can increase the mean square error of the fitting from 4.993e-05 to 1.013e-05, and the accuracy is improved by about 80%.

[0024] (2) Since the present invention reduces the temperature range, the response of the output signal to the pressure is closer to a linear relationship, and the fitting can obtain higher accuracy than the full / large temperature range. For the output-pressure-temperature relationship with stronger nonlinearity, the fitting effect on the segment will be better. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0026] Figure 1 Experimental data of temperature compensation of the pressure sensor according to the present invention;

[0027] Figure 2 It is a schematic diagram of the segmented fitting of the temperature compensation function of the pressure sensor according to the present invention;

[0028] Figure 3 A schematic diagram of optimizing the polynomial degree of the temperature compensation function of the pressure sensor according to the present invention;

[0029] Figure 4 A graph showing the variation of the unsegmented fitting accuracy with the degree of the polynomial according to the present invention;

[0030] Figure 5 FIG. 4 is a schematic diagram of a system for improving the temperature compensation accuracy of a pressure sensor according to the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] It should be noted that when an element is referred to as being "fixed to" or "arranged on" another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or indirectly connected to the other element. In the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0033] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0034] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0035] The present invention provides a method for improving the temperature compensation accuracy of a pressure sensor, which uses a calibrated high-precision device to obtain the output-pressure-temperature data of a pressure sensor sample through an experiment, performs polynomial fitting based on the least squares method, calculates the coefficients of the polynomial expression, optimizes the polynomial degree of the polynomial expression to obtain the highest fitting accuracy, optimizes the function segmentation of the polynomial piecewise function, and combines the optimized polynomial into a polynomial piecewise function as a temperature compensation function to improve the temperature compensation accuracy of the pressure sensor. The method proposed by the present invention can further improve the temperature compensation accuracy and can effectively improve the fitting accuracy. The present invention can improve the mean square error of the fitting from 4.993e-05 to 1.013e-05, and the accuracy is improved by about 80%.

[0036] In order to illustrate the technical solution of the present invention, the following is a description with reference to specific drawings and embodiments.

[0037] like Figure 1-Figure 4 As shown, the present invention provides a method for improving the temperature compensation accuracy of a pressure sensor, which comprises the following steps:

[0038] Step S1, using calibrated high-precision equipment, obtain the output-pressure-temperature data of the pressure sensor sample through experiments (such as Figure 1 shown);

[0039] Step S2, segmenting the output-pressure-temperature data obtained in step S1 according to temperature;

[0040] Step S3, respectively perform polynomial fitting based on the least squares method on each segment of data obtained in step S2 to calculate the coefficients of the polynomial expression (such as Figure 2 shown);

[0041] Step S4, optimizing the polynomial degree of the polynomial expression to obtain the highest fitting accuracy (such as Figure 3 shown);

[0042] Step S5, optimizing the function segmentation of the polynomial piecewise function;

[0043] Step S6, combining the optimized polynomials into a polynomial piecewise function as a temperature compensation function for improving the temperature compensation accuracy of the pressure sensor.

[0044] Furthermore, the temperature compensation function obtained in step S6 is stored in the memory (EPROM) of the pressure sensor data processing chip. During measurement, the pressure sensor output value and the corresponding temperature value are brought into the temperature compensation function to obtain the pressure value, thereby completing the temperature compensation of the pressure (e.g. Figure 5 shown).

[0045] like Figure 1 As shown, step S1 uses calibrated high-precision equipment to obtain pressure-temperature data of the pressure sensor sample through experiments, which specifically includes the following technical contents:

[0046] Step S11, using a standard pressure source and a temperature control device to calibrate according to the measurement environment, and using a data acquisition system to record the standard measurement environment data and the calibration data of the standard pressure source and the temperature control device.

[0047] The standard pressure source is Yokogawa 2558A, WIKA CPP1000-L, etc.; the temperature control equipment is a constant temperature box, such as the German Binder KBF series constant temperature box. The calibration of the standard pressure source and temperature control equipment includes the following steps: First, ensure that the calibration environment meets the setting requirements of the standard pressure source and temperature control equipment, and then use standard equipment that has been certified by the standard to compare or calibrate the measurement technology of the measuring equipment (the measuring equipment is the standard pressure source and temperature control equipment), and record the calibration data; secondly, analyze and determine the measurement accuracy of the measuring equipment (standard pressure source and temperature control equipment), and make adjustments before the experimental data measurement if necessary; then issue a calibration report or calibration report, and determine the cycle of the next calibration. The entire process must ensure traceability to ensure the reliability and consistency of the measurement results of the standard pressure source and temperature control equipment.

[0048] Step S12, connecting the standard pressure source (as a pressure sensor) to a data acquisition system, for example, using an STM32-based system to read and process data.

[0049] Step S13, applying different predetermined known pressures to the pressure sensor (standard pressure source) through a pressurizing device, and changing within a certain temperature range to simulate the actual working environment. The data acquisition system will record the output value of the pressure sensor at different pressures and temperatures in real time. In a preferred embodiment, a high-precision thermostat (such as Binder KBF series thermostat) is used to control the temperature conditions during the measurement process, and a standard pressure source is used to provide an accurate pressure reference value. The data acquisition system can be a PC software or a PLC control system, and the data acquisition system records the output signals of the pressure sensor at different pressures and temperatures. These output signal data include changes in voltage or current, and data analysis and processing are performed on the recorded output signals.

[0050] In another preferred embodiment, during the data acquisition process, the raw data of the output signal of the pressure sensor (standard pressure source) at different pressures and temperatures are preprocessed, including filtering, sampling, normalization and other operations, to facilitate subsequent data analysis. In addition, in order to ensure the accuracy of the data, the pressure sensor (standard pressure source) needs to be calibrated and corrected regularly to eliminate drift caused by environmental changes or long-term use. In some cases, simulation software can also be used to obtain accurate results of the pressure sensor (preferably a piezoresistive pressure sensor), and the accuracy of the simulation can be verified by experimental comparison. The output data of the pressure sensor at different pressures and temperatures obtained in this step provides a basis for further performance evaluation and application.

[0051] In step S2, the output-pressure-temperature data obtained in step S1 is segmented by temperature, for example, using 10°C or 20°C as a segment; the output-pressure-temperature data obtained in step S1 is set to three dimensions, namely temperature t, pressure p and sensor output signal u, and the data can be segmented by temperature. In one embodiment, the temperature segmentation is -40°C≤t<-30°C, -30°C≤t<-20°C.

[0052] like Figure 2 As shown, in step S3, each segment of data obtained in step S2 is respectively subjected to polynomial fitting based on the least square method to calculate the coefficients of the polynomial expression; which specifically includes the following steps:

[0053] Step S31, the data of sensor output u and temperature t are respectively substituted into the formula Where k is the polynomial index, n is the highest degree of the polynomial, and we get a k The coefficient matrix of Where m is a data index, here we assume that the form is The experimental data has m+1 rows; then the corresponding pressure p is formed into a vector y, and the transposed matrix X of X is calculated respectively. T , the matrix product XT X, X T y;X T The inverse matrix of X (X T X) -1 Finally, by the formula a=(X T X) -1 X T Get the fitted coefficient vector of the polynomial.

[0054] like Figure 3 and Figure 4 As shown, the polynomial degree of the polynomial expression is optimized to obtain the highest fitting accuracy.

[0055] The polynomial degree n is changed, the fitting accuracy is investigated with the polynomial degree n, and the n value that minimizes the root mean square error (RMSE) is found. In the present invention, the root mean square error RMSE of the segmented fitting can reach 1.013e-05, which is better than 4.993e-05 of the non-segmented fitting.

[0056] Step S5, optimizing the function segmentation of the polynomial piecewise function includes changing the range of each temperature segment t to minimize the mean square error RMSE / mean absolute error MAE of the fitting of each temperature segment, and finally obtaining the fitting polynomial of each segment.

[0057] Step S6, combining the optimized polynomials into a polynomial piecewise function as a temperature compensation function to improve the temperature compensation accuracy of the pressure sensor, including writing the fitted polynomials into the following form: The temperature compensation function obtained in step S6 is stored in the memory (EPROM) of the pressure sensor data processing chip. During measurement, the pressure sensor output value and the corresponding temperature value are brought into the function to obtain the pressure value, thus completing the temperature compensation of the pressure (such as Figure 5 A system for improving the temperature compensation accuracy of a pressure sensor as shown).

[0058] The present invention provides a system for improving the temperature compensation accuracy of a pressure sensor, which comprises the following standard pressure source, a constant temperature box, a pressure transmitter, a temperature transmitter, an analog-to-digital conversion module and a temperature compensation device, and further comprises a data display device; pressure and temperature signals are obtained respectively through the pressure transmitter and the temperature transmitter, and converted into numerical values ​​by analog-to-digital conversion and input into a data processor.

[0059] Among them, in the temperature compensation function fitting stage: the pressure transmitter is provided with pressure by a standard pressure source, including but not limited to Yokogawa Test Measurement (Yokogawa) 2558A, etc., which is used to apply accurate pressure to the pressure sensor and obtain the required pressure data; the constant temperature box, including but not limited to the German Binder KBF series, etc., is used to control the temperature environment required for measurement and obtain the temperature data of the pressure sensor sample;

[0060] The pressure transmitter gives the response current / voltage value at the specified pressure and temperature;

[0061] The above acquired data is used to obtain a polynomial piecewise fitting temperature compensation function according to the above steps S1-S6.

[0062] Temperature compensation application stage Figure 5 As shown:

[0063] The temperature transmitter is used to obtain the ambient temperature data of the pressure sensor; the pressure transmitter is used to obtain the response current / voltage value under the pressure to be measured;

[0064] The analog-to-digital conversion module is used to convert the acquired sensor output data from analog signals into numerical values ​​to be transmitted to the subsequent data processor, which calculates the pressure value through the pre-stored fitted piecewise polynomial compensation function and then displays it through the data display device. The pressure value calculated by the piecewise polynomial compensation function is obtained by using the method of the present invention to improve the temperature compensation accuracy of the pressure sensor.

[0065] The temperature compensation device is used for temperature compensation of the output data of the pressure transmitter, that is, converting the voltage / current value of the pressure transmitter in response to the pressure output into the pressure value after correcting the temperature influence;

[0066] The data display device is used to display the pressure value after temperature compensation.

[0067] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the temperature compensation accuracy of a pressure sensor, characterized in that: It includes the following steps: Step S1, using calibrated high-precision equipment to obtain output-pressure-temperature data of a pressure sensor sample through experiments; Step S2, segmenting the output-pressure-temperature data obtained in step S1 according to temperature; Step S3, performing polynomial fitting based on the least squares method on each segment of data obtained in step S2 to calculate the coefficients of the polynomial expression; Step S4, optimizing the polynomial degree of the polynomial expression to obtain the highest fitting accuracy; Step S5, optimizing the function segmentation of the polynomial piecewise function; Step S6, combining the optimized polynomials into a polynomial piecewise function as a temperature compensation function for improving the temperature compensation accuracy of the pressure sensor.

2. The method for improving the temperature compensation accuracy of a pressure sensor according to claim 1, characterized in that: The temperature compensation function obtained in step S6 is stored in the memory of the pressure sensor data processing chip. During measurement, the pressure sensor output value and the corresponding temperature value are substituted into the temperature compensation function to obtain the pressure value, thereby completing the temperature compensation of the pressure.

3. The method for improving the temperature compensation accuracy of a pressure sensor according to claim 2, characterized in that: Step S1 includes using a standard pressure source and a temperature control device to perform calibration according to a measurement environment, and using a data acquisition system to record standard measurement environment data and calibration data of the standard pressure source and the temperature control device.

4. The method for improving the temperature compensation accuracy of a pressure sensor according to claim 3, characterized in that: The selection of standard pressure sources is not limited to Yokogawa test and measurement instruments such as Yokogawa 2558A or WIKA CPP1000-L.

5. The method for improving the temperature compensation accuracy of a pressure sensor according to claim 3, characterized in that: The temperature control equipment is a constant temperature box.

6. The method for improving the temperature compensation accuracy of a pressure sensor according to claim 3, characterized in that: The temperature control equipment is not limited to the German Binder KBF series thermostats.

7. The method for improving the temperature compensation accuracy of a pressure sensor according to claim 3, characterized in that: The standard pressure source is used as a pressure sensor and connected to a data acquisition system, such as an STM32-based system for data reading and processing. Different predetermined known pressures are applied to the pressure sensor through a pressurizing device and varied within a certain temperature range to simulate the actual working environment.

8. The method for improving the temperature compensation accuracy of a pressure sensor according to claim 3, characterized in that: The standard pressure source is used as a pressure sensor and connected to the data acquisition system, and the STM32-based system is used to read and process the data.

9. The method for improving the temperature compensation accuracy of a pressure sensor according to claim 3, characterized in that: During the data acquisition process, the raw data of the output signal of the standard pressure source as a pressure sensor at different pressures and temperatures are preprocessed, including filtering, sampling, normalization and other operations, to facilitate subsequent data analysis.

10. The method for improving the temperature compensation accuracy of a pressure sensor according to claim 3, characterized in that: The output-pressure-temperature data obtained in step S1 are segmented according to the temperature cuts of 10°C or 20°C.

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