A method for over-range calibration of small-range measuring equipment

Abstract

The invention discloses an over-range calibration method for a small-range metering device, which is used to solve the problems that the existing calibration method for small-range metering devices is unstable and has a large amount of calculation. The steps of the invention are as follows: through experimental induction and high-concentration standard gas, a nonlinear curve of response value and concentration value is established for the small-range metering device; the zero point of the small-range metering device is calibrated by standard to generate a zero-point correction factor; the fixed value beyond the range is calibrated to generate an over-range calibration factor; the nonlinear curve is corrected by the zero-point correction factor and the over-range calibration factor to obtain a correction nonlinear curve; the correction nonlinear curve is used to calculate the true concentration value of the small-range metering device. The invention has low requirements on device parameters and standard sources for calibration, and has fast calibration, flexible adjustment, and high precision, which reduces the production cost of the enterprise and is easy to realize mass production.

Description

Technical Field

[0001] The invention relates to the technical field of calibration of measuring equipment, and in particular to an over-range calibration method of a small-range measuring equipment. Background Art

[0002] For small-scale measuring equipment, such as low-concentration gas detector equipment, low-concentration standard gas needs to be used for calibration during the equipment production and calibration process. Due to the characteristics of low-concentration standard gas, such as short shelf life, difficulty in storage, large external interference factors and difficulty in purchasing some low-concentration standard gases, currently in the production process of small-scale measuring equipment, low-concentration standard gas is purchased or substitute standard gas is used to calibrate the small-scale measuring equipment. Due to the disadvantages of low-concentration standard gas being difficult to store and being greatly affected by external interference factors, the calibration of the measuring equipment is very unstable. Since each batch of sensors is different, each batch of sensors needs to be tested when using substitute standard gas to calibrate the measuring equipment. The substitute standard coefficient of each batch of sensors is obtained through test calculation, which increases the workload in the production process of small-scale measuring equipment.

[0003] The invention patent with application number 20201157833.4 discloses a response model and concentration compensation method based on the sensor characteristic curve, which can realize the concentration calibration of the current sensor through a small number of concentration points, and has the characteristics of few calibration points, high precision, good accuracy, and high versatility; when performing concentration compensation, the model, characteristic values, and characteristic parameters are built into the detector. If it is necessary to predict gas leakage, it is necessary to adjust the characteristic values ​​and characteristic parameters that affect the sensor response time, and based on the built-in response curve model, perform compression fitting, establish a new response model, and improve the response time of the detector, thereby realizing the early prediction of the current gas concentration, shortening the alarm time, and solving the problem of accidents caused by short response time. However, this compensation method is used to solve the impact of temperature on concentration, and it fits the relationship curve between temperature and concentration, and cannot solve the calibration problem of small-range measuring equipment. Summary of the invention

[0004] In view of the technical problems that the existing calibration methods for small-range measuring equipment are unstable and have a large amount of calculation, the present invention proposes an over-range calibration method for small-range measuring equipment. The small-range measuring equipment is calibrated using high-concentration standard gas that is easy to store and has high stability. The calibration speed is fast and the requirements for the calibration standard are low.

[0005] In order to achieve the above object, the technical solution of the present invention is implemented as follows: a method for over-range calibration of a small-range measuring device, the steps of which are as follows:

[0006] Step 1: Through experimental induction and high-concentration standard gas, a nonlinear curve between response value and concentration value is established for small-range measuring equipment;

[0007] Step 2: Perform standard calibration on the zero point of the small-range measuring equipment to generate the zero point correction factor;

[0008] Step 3: calibrate the fixed value that exceeds the range to generate an over-range calibration factor;

[0009] Step 4: Correct the nonlinear curve by using the zero correction factor and the over-range calibration factor to obtain a corrected nonlinear curve;

[0010] Step 5: Use the nonlinear correction curve to calculate the true concentration value of the small-range measuring equipment.

[0011] In the step 1, the test data and the parameters of the nonlinear curve are stored. Before the step 2 is implemented, the test data is read and the fitting parameters are obtained by using the least squares method. The correctness of the parameters of the nonlinear curve in step 1 is determined by using the fitting parameters.

[0012] The implementation method of step one is:

[0013] S1, obtain the collected value of this small-range measuring device in air (non-target gas) and record it as y1;

[0014] S2. Select m different concentration points within the full range of the small-range measuring device, and mark the concentration points in ascending order as x2, x3, ... m ;

[0015] S3. According to the technical manual of the small-range measuring equipment, the response values ​​at the above concentration points are calculated and marked as

[0016] S4. The response value and concentration point of the small-scale measuring equipment satisfy the univariate linear regression equation. Suppose the univariate linear regression equation is: So for every known concentration point x i , with a predicted response value of Where, i = 1, 2, ..., n, α and β are parameters of the univariate linear regression equation;

[0017] S5, input x2, x3... into the small-range measuring equipment in sequence. m For gases of different concentrations, the actual response values ​​of the small-range measuring equipment at different concentrations are marked as y2, y3...y m ;

[0018] S6. To obtain the best fitting equation, it is necessary to make each concentration point x of the small-scale measuring device iThe true response value y i and the predicted response value The sum of squares of the differences between the two is the smallest:

[0019] S7. Solve the optimization problem of step S6 using the least square method to obtain a nonlinear curve y=αx+β between the response value and the concentration value.

[0020] The solution method of the least square method for solving the minimization problem in step S6 is:

[0021] make The original minimization problem is transformed into finding the minimum value of a binary function. From the relevant knowledge of calculus, we know that:

[0022]

[0023]

[0024] make and The values ​​of parameters α and β can be found:

[0025]

[0026]

[0027] The test data of the small-range measuring equipment (x1, y1), (x2, y2), (x3, y3)…(x m ,y m ) as sample data, where y1 is the response value of the small-range metering device in non-target gas, and the zero-point concentration value x1 is 0; the values ​​of parameters α and β are calculated respectively, and a relationship curve between the response value y and the concentration value x is established in the MCU: y = αx + β;

[0028] At the same time, the test data (x1,y1), (x2,y2), (x3,y3)…(x m ,y m ) and the calculated parameters α and β values ​​are stored in the MCU built-in memory respectively.

[0029] The method for generating the zero point correction factor in step 2 is: recording the current display value y of the small-range measuring device in the air 11 , calculate the current display value y 11 The offset Δy from the measured data acquisition value y1 is 11 -y1, Δy is the zero point correction factor, and the zero point correction factor Δy is stored in the MCU built-in memory; at this time, the relationship between the response value and the concentration value is: y=αx+β+Δy.

[0030] The method for generating the over-range calibration factor is: introducing the concentration value x of the standard gas with a known over-range value into the small-range metering device. n , and x n >x m MCU collects the concentration value x of the small-scale measuring device n The response value y n , use the formula y = αx + β + Δy to reversely calculate the response value y n The corresponding gas concentration value x nn , calculate x n / x nn The ratio is marked as γ b , γ b This is the overrange calibration factor.

[0031] The method of the correction processing in step 4 is: correcting the nonlinear curve through the zero point and the over-range calibration point, and the correction process operation expression is:

[0032]

[0033] Among them, x is the true concentration value obtained after correction, Δy is the zero point correction factor, γ b is the over-range calibration factor, α and β are parameters of the nonlinear curve, and y is the measured response value.

[0034] Read the test data and the parameters α and β of the nonlinear curve stored in the memory of the MCU, calculate the fitting parameters of the nonlinear curve by using the test data and the least squares method, and determine whether the calculated fitting parameters are the same as the read parameters α and β of the nonlinear curve. If they are the same, the nonlinear curve is correct.

[0035] The MCU sends a zero-point correction instruction to the small-range measuring device through the human-computer interaction interface, measures the display value corresponding to the zero point and obtains the zero-point correction factor; introduces a standard gas concentration exceeding the range value into the small-range measuring device, and after the reaction is stable, sends an over-range calibration instruction to the small-range measuring device through the human-computer interaction interface to generate an over-range calibration factor; The nonlinear curve stored in the MCU is corrected, and the true concentration value is calculated according to the corrected curve; the human-computer interaction interface is one of an infrared interface, a Bluetooth interface, a button interface or a command interface.

[0036] The correction method is to load the over-range calibration factor γ from the MCU internal memory b , determine the over-range calibration factor γ b Is it greater than 0, γ b >0 is valid data, according to the formula Calculate the final concentration.

[0037] The beneficial effects of the present invention are as follows: based on the previous experimental data model, the correction factor of the zero calibration and the calibration factor of the over-range calibration, the calibration speed is fast, the efficiency is high, the calibration accuracy is high, the requirements for the calibration design technology are low, the cost of the calibration equipment is reduced, the requirements for the nominal accuracy of the device parameters are reduced through the compensation correction of the correction algorithm, the cost is low, the software configuration is flexible, etc. The present invention is applicable to all small-range measuring equipment. The method has the characteristics of low requirements for device parameters, low requirements for the standard source used for calibration, fast calibration, flexible adjustment, high accuracy, etc., which reduces the production cost of the enterprise and is easy to realize mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, 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 work.

[0039] Figure 1 It is a flow chart of the present invention.

[0040] Figure 2 The present invention is a flow chart of the deviation correction method for small-range measuring equipment. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Example 1

[0043] A method for over-range calibration of a small-range measuring device, for example, a high-concentration, easy-to-store standard gas can be used to calibrate the small-range gas detector during its production process. The method can also be used for calibration of other types of small-range measuring devices. The method comprises the following steps:

[0044] Step 1: Establish a built-in nonlinear curve model through experimental induction; the specific implementation steps are as follows:

[0045] S1. Take the same type of small-range gas detector as an example (the air does not contain gases that can make this type of sensor respond), obtain the collection value of this sensor in the air and record it as y1 (this value is the zero-point collection value of the sensor);

[0046] S2. Select m different concentration points within the full range of this small-range gas detector. These concentration points are sorted from small to large and marked as x2, x3, ..., x m ;

[0047] S3. According to the technical manual of small-range gas detector, calculate the response value of the gas detector at the above concentration points and mark it as

[0048] S4. The response value and concentration value of the small-range gas detector satisfy the univariate linear regression equation. Suppose the univariate linear regression equation is: So for every known concentration point x i , with a predicted response value of

[0049] S5, pass x2, x3, .... x into this small-range gas detector in sequence m Different concentrations of gas, the collected values ​​of the gas detector at different concentrations are marked as y2, y3...y m ;

[0050] S6. To obtain the best fitting equation, it is necessary to minimize the sum of squares of the difference between the actual response value and the predicted response value of each sample point of the small-range gas detector, that is, the optimization problem:

[0051]

[0052] make The original problem is transformed into finding the minimum value of a binary function. From the knowledge of calculus, we know that

[0053]

[0054]

[0055] make and The values ​​of α and β can be obtained

[0056]

[0057]

[0058]

[0059] Take the gas detector test data (x1,y1), (x2,y2), (x3,y3)…(x m ,y m) as sample data, where y1 is the response value of the sensor in non-target gas (sensor zero-point response value), so the zero-point concentration value x1 is 0; the values ​​of parameters α and β are calculated by formula (1) and formula (2) respectively, and a relationship curve between the response value and concentration value of this gas detector is established inside the MCU, which is:

[0060] y=αx+β Formula (3)

[0061] At the same time, the test data of the gas detector (x1, y1), (x2, y2), (x3, y3)…(x m ,y m ) and the calculated parameters α and β values ​​are stored in the MCU built-in FLASH memory respectively.

[0062] Step 2: Calibrate the zero point of the small-range gas detector to generate a zero point correction factor;

[0063] During the use of the gas detector, the sensor baseline drift (sensor zero drift) is caused by environmental factors or its own signal attenuation. Therefore, when calibrating the gas detector, it is necessary to first calibrate the zero point of the gas detector and record the current display value of the sensor in the air as y. 11 , calculate y 11 The offset from y1 is denoted as Δy=y 11 -y1, Δy is the zero point correction factor, and the zero point correction factor Δy is stored in the MCU internal FLASH memory. At this time, the relationship between the response value and concentration value of the MCU built-in gas detector is:

[0064] y=αx+β+Δy Formula (4)

[0065] Step 3: calibrate the fixed value that exceeds the measuring range and generate the calibration factor;

[0066] A gas concentration known to exceed the sensor range is introduced into the gas detector (the gas concentration value is marked with x). n ), the MCU collects the response value of the gas detector under this standard gas concentration and marks it as y n , use formula (4) to reversely calculate the sensor response value y n The corresponding gas concentration value is marked as x nn , calculate x n / x nn The ratio is marked as γ b , γ b This is the overrange calibration factor.

[0067] Step 4: Correct the built-in curve model through the zero point and over-range calibration points. The correction process calculation expression is:

[0068]

[0069] Where x is the true concentration value obtained after correction, Δy is the generated zero point correction factor, γ b is the calibration factor generated during the overrange calibration process.

[0070] Step 5: Use the nonlinear correction curve to calculate the response value of the small-range measuring equipment at different concentration points.

[0071] This embodiment uses a small-range gas detector as an example to describe this method in detail, but this method is not limited to small-range gas detectors. This method is applicable to all small-range measuring equipment. It is not necessarily the gas that needs to be calibrated because the range is low or the target value that needs to be calibrated is much higher than the range value set by the product. This is true for gas, pressure, etc.

[0072] Example 2

[0073] like Figure 1 The figure shows an over-range calibration method for a small-range measuring device, which includes the following steps:

[0074] (1) Load the preset parameters from the MCU internal FLASH memory to the MCU internal RAM. The preset parameters are the test data in the experimental model and the parameter α and β values ​​calculated by the test data. The parameter α and β values ​​are calculated by the test data in the experimental model and formula (1) and formula (2). The calculated parameter α and β values ​​are compared with the α and β values ​​read from the MCU internal FLASH memory. If the two values ​​are the same, the model is correct. If the two data are not the same, recalibrate the model.

[0075] (2) If the model is correct, a zero point correction instruction is sent to the small-scale measuring device through a human-machine interaction interface such as an infrared interface, a Bluetooth interface, a key interface or a command interface, and the zero point correction process, i.e., step 2, is entered, and the zero point correction factor is recorded.

[0076] (3) After completing the zero point correction, a gas concentration of a standard gas exceeding the range value is introduced into the small-range measuring device. After the reaction is stable, an over-range calibration instruction is sent to the small-range measuring device through a human-machine interaction interface such as an infrared interface, a Bluetooth interface, a key interface or a command interface, and the over-range calibration, i.e., step three, is entered, and an over-range calibration factor is generated and recorded.

[0077] (4) After completing the above steps, the original curve built into the MCU is corrected using formula (5). Calculate concentration information.

[0078] Example 3

[0079] like Figure 2 The figure shows a deviation correction method in the over-range calibration method of a small-range measuring device, which includes the following steps:

[0080] (1) Load preset parameters from the MCU's internal FLASH memory to the MCU's internal RAM. The preset parameters are the test data in the experimental model and the α and β values ​​calculated using the test data. Calculate the α and β values ​​using the test data in the experimental model and formulas (1) and (2). Compare the calculated α and β values ​​with the α and β values ​​read from the MCU's internal FLASH memory. If the two values ​​are the same, the model is correct.

[0081] (2) Load the preset parameters from the MCU internal FLASH to the MCU internal RAM, that is, the over-range calibration factor γ b , γ b If it is greater than 0, it is valid data and the parameters are correct. b =0, the small-range measuring equipment needs to be recalibrated for over-range.

[0082] (3) According to formula (5), the final concentration is calculated by substituting the original parameters α and β, the zero correction factor and the over-range calibration factor, and the result is output.

[0083] The implementation of the over-range calibration method for the small-range metering equipment provided by the present invention relies on the constraints of embedded devices (such as MCU storing test data for establishing a curve and coefficients of the nonlinear relationship curve between the sensor response value and the concentration value), the need to calculate the relationship curve between the sensor response value and the concentration value, and a calibration standard gas source (the standard gas used is used to calibrate the sensor). High-concentration and easy-to-store standard gas can be used, the requirements for the calibration standard source are low, and the calibration is fast, the adjustment is flexible, and the accuracy is high.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for over-range calibration of a small-range measuring device, characterized in that: The steps are as follows: Step 1: Through experimental induction and high-concentration standard gas, the linear curve relationship between the response value y and the concentration value x of the small-range measuring equipment is established as follows: y = αx + β, where α and β are parameters of the linear curve; In the step 1, the test data and the parameters of the linear curve are stored, and before the step 2 is implemented, the test data is read and the fitting parameters are obtained by using the least squares method, and the correctness of the parameters of the linear curve in the step 1 is determined by using the fitting parameters; Step 2: Perform standard calibration on the zero point of the small-range measuring equipment to generate the zero point correction factor; The method for generating the zero point correction factor in step 2 is: recording the current display value y of the small-range measuring device in the air 11 , calculate the current display value y 11 The offset Δy from the measured data acquisition value y1 is 11 -y1, Δy is the zero point correction factor. At this time, the relationship between the response value and the concentration value is: y=ax+β+Δy; Step 3: calibrate the fixed value that exceeds the range to generate an over-range calibration factor; The method for generating the over-range calibration factor is: introducing the concentration value x of the standard gas with a known over-range value into the small-range metering device. n MCU collects the concentration value x of the small-scale measuring device n The response value y n , use the formula y = αx + β + Δy to reversely calculate the response value y n The corresponding gas concentration value x nn , calculate x n / x nn The ratio is marked as γ b , γ b This is the over-range calibration factor; Step 4: Correct the linear curve by using the zero correction factor and the over-range calibration factor to obtain a correction linear curve; The method of the correction processing in step 4 is: correcting the linear curve through the zero point and the over-range calibration point, and the correction process operation expression is: Among them, x is the true concentration value obtained after correction, and y is the measured response value; Step 5: Use the correction linear curve to calculate the true concentration value of the small-range measuring equipment.

2. The over-range calibration method for a small-range measuring device according to claim 1, characterized in that: The implementation method of step one is: S1, obtain the collection value of this small-range measuring device in non-target gas and record it as y1; S2. Select m different concentration points within the full range of the small-range measuring device, and mark the concentration points in ascending order as x2, x3, ... x m ; S3. According to the technical manual of the small-range measuring equipment, the response values ​​at the above concentration points are calculated and marked as S4. The response value and concentration point of the small-scale measuring equipment satisfy the univariate linear regression equation. Suppose the univariate linear regression equation is: So for every known concentration point x i , with a predicted response value of Where, i = 1, 2, ..., m, α and β are parameters of the univariate linear regression equation; S5, input x2, x3…x into the small-range measuring equipment in sequence m The actual response values ​​of the small-range measuring equipment at different concentrations are marked as y2, y3, ...y m ; S6. To obtain the best fitting equation, it is necessary to make each concentration point x of the small-scale measuring device i The true response value y i and the predicted response value The sum of squares of the differences between the two is the smallest: S7. Solve the optimization problem of step S6 using the least square method to obtain a linear curve y=αx+β between the response value and the concentration value.

3. The over-range calibration method for a small-range measuring device according to claim 2, characterized in that: The solution method of the least square method for solving the minimization problem in step S6 is: make The original minimization problem is transformed into finding the minimum value of a binary function. From the relevant knowledge of calculus, we know that: make and The values ​​of parameters α and β can be found: The test data of the small-range measuring equipment (x1, y1), (x2, y2), (x3, y3)…(x m ,y m ) as sample data, where y1 is the response value of the small-range metering device in non-target gas, and the zero-point concentration value x1 is 0; the values ​​of parameters α and β are calculated respectively, and a relationship curve between the response value y and the concentration value x is established in the MCU: y = αx + β; At the same time, the test data (x1,y1), (x2,y2), (x3,y3)…(x m ,y m ) and the calculated parameters α and β values ​​are stored in the MCU built-in memory respectively.

4. The over-range calibration method for a small-range measuring device according to claim 3, characterized in that: The zero point correction factor Δy is stored in the MCU built-in memory.

5. The over-range calibration method for a small-range measuring device according to any one of claims 1 to 4, characterized in that: Read the test data and the parameters α and β of the linear curve stored in the internal memory of the MCU, calculate the fitting parameters of the linear curve by using the test data and the least squares method, and determine whether the calculated fitting parameters are the same as the read parameters α and β of the linear curve. If they are the same, the linear curve is correct.

6. The over-range calibration method for a small-range measuring device according to claim 5, characterized in that: The MCU sends a zero-point correction instruction to the small-range measuring device through the human-computer interaction interface, measures the display value corresponding to the zero point and obtains the zero-point correction factor; introduces a standard gas concentration exceeding the range value into the small-range measuring device, and after the reaction is stable, sends an over-range calibration instruction to the small-range measuring device through the human-computer interaction interface to generate an over-range calibration factor; The linear curve stored in the MCU is corrected, and the true concentration value is calculated according to the corrected curve; the human-computer interaction interface is one of an infrared interface, a Bluetooth interface, a button interface or a command interface.

7. The over-range calibration method for a small-range measuring device according to claim 1, characterized in that: The correction method is to load the over-range calibration factor γ from the MCU internal memory b , determine the over-range calibration factor γ b Is it greater than 0, γ b >0 is valid data, according to the formula Calculate the final concentration.

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