KR100279049B1 - A device and techique of the calibration of piezo-electric pressure transducer - Google Patents

Abstract

The present invention relates to a dynamic pressure calibration device and a calibration method of a piezoelectric pressure sensor, and to improve the performance and accuracy of the system by applying the automatic hybrid calibration method using the absolute calibration method and the comparative calibration method and a new error correction algorithm to the calibration system will be.

Description

Dynamic pressure calibration device and calibration method of piezoelectric pressure sensor {A DEVICE AND TECHIQUE OF THE CALIBRATION OF PIEZO-ELECTRIC PRESSURE TRANSDUCER}

The present invention relates to a dynamic pressure calibration device of a piezoelectric pressure sensor.

Piezoelectric pressure transducers (piezoelectric pressure transducers) are used to measure the sound generated from performance tests of various weapon systems, and can be classified into low pressure sensors or high pressure sensors according to the pressure level. The present invention mainly relates to a piezoelectric low pressure sensor that measures a low pressure whose pressure range is between 0.3 psi and 500 psi, but is also applicable to a high pressure sensor. Piezoelectric pressure sensor is composed of a piezoelectric element (piezoelectric element) for generating an electrical signal proportional to the pressure, because it is susceptible to external impact, physical properties may vary depending on the frequency of use and test conditions. Therefore, calibration of pressure sensor is necessary before and after measurement. In addition, since calibration data has the greatest influence on measurement data, the importance of calibration is increasing day by day, while there is no abnormality of the sensor due to lack of a calibration system and calibration technique for calibrating piezoelectric low pressure sensors. Only calibration was done.

There has been continuous research on the needs of such a piezoelectric pressure sensor calibration system. Piezoelectric pressure sensors do not operate at a static pressure with a constant value in time, and only have rapid rise and fall characteristics. Dynamic pressure calibration was used because of its ability to respond only to dynamic pressure.

However, the conventional dynamic pressure calibrator uses a comparative calibration method using a reference pressure sensor receiving a standard retrofit as a standard pressure source, and there are many calibration error factors due to the manual operation of the control valve. As calibration time of more than 7 hours is required per sensor, calibration time is very long.

The present invention, in order to solve the problems of the prior art as described above, by developing an automatic dynamic pressure calibrator by creating an automatic mixing calibration method using an absolute calibration method and a comparative calibration method, the valve crusher and pressure leakage generated in the conventional manual operation The accuracy of the calibration is improved by eliminating the causal error factors caused by the sensor. In order to improve the calibration efficiency and improve the system performance and accuracy, the calibration time is shortened to about 10 minutes.

1 is an overall configuration diagram of a dynamic pressure calibration device of a piezoelectric pressure sensor according to the present invention.

2 is a visualized user interface initial screen and dynamic pressure calibration signal diagram of a dynamic pressure calibration apparatus according to the present invention.

3 is a block diagram of a piezoelectric type low pressure sensor calibration means of the dynamic pressure calibration apparatus according to the present invention.

Figure 4 is a functional flow chart of the piezoelectric pressure sensor calibration means of FIG.

Fig. 5 is a block diagram showing the configuration of a signal acquisition unit in the dynamic pressure calibration apparatus according to the present invention.

6 is a circuit diagram of a control interface in the dynamic pressure calibration apparatus according to the present invention.

Figure 7 is a circuit diagram of a foot switch of the dynamic pressure calibration device according to the present invention.

8A is an overall flowchart of an automatic calibration program of the dynamic pressure calibration device according to the present invention;

8B is a flowchart of an initialization step of initial variable setting and hardware calibration of an automatic calibration program of the dynamic pressure calibration apparatus according to the present invention;

8C is a flowchart of a first calibration step of calibrating a reference sensor in an automatic calibration program of the dynamic pressure calibration apparatus according to the present invention;

8d is a flowchart of a second calibration step of calibrating a reference sensor in an automatic calibration program of the dynamic pressure calibration apparatus according to the present invention;

9 is an operational flow diagram of an automatic pressure controller of the dynamic pressure calibration apparatus according to the present invention.

10 is a flowchart of a calibration step for constructing an error correction file in an automatic calibration program of the dynamic pressure calibration apparatus according to the present invention.

Fig. 11 is a block diagram of a calibration algorithm of an automatic calibration method of a dynamic pressure calibration apparatus according to the present invention.

12 is a block diagram of an error correction algorithm of the automatic calibration method of the dynamic pressure calibration apparatus according to the present invention.

Figure 13 is an error correction table created by the calibration and error correction algorithm of the automatic calibration method of the dynamic pressure calibration apparatus according to the present invention.

14 is a calibration report of the piezoelectric type low pressure sensor calibrated according to the automatic calibration method of the dynamic pressure calibration apparatus according to the present invention.

FIG. 15 is a graph illustrating a sensitivity (mV / psi) distribution chart of the calibration certificate of FIG. 14. FIG.

The present invention relates to a dynamic pressure calibrating device of a piezoelectric pressure sensor, and specifically, an automatic mixed calibration method using a standard dynamic pressure as a standard pressure according to the needs of the system and using an absolute calibration method and a comparative calibration method. To calibrate the low pressure sensor.

The absolute calibration method is a calibration method using a deadweight tester, which is a pressure source defined by the force acting on a unit area, as a standard pressure source, and the comparative calibration method is a calibration method using a standard retrofitted pressure sensor as a standard pressure source. . In the present invention, the reference pressure sensor used in the comparative calibration method by mixing the absolute calibration method and the comparative calibration method is directly calibrated in the calibrator using a deadweight tester and then the pressure offset for each section (the standard of the deadweight tester). Pressure-reference pressure sensor) is stored in a file and calibrated when calibrating the sensor to be calibrated to increase the accuracy of the reference pressure sensor and achieve automation of the system.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is an overall configuration diagram of a dynamic pressure calibration apparatus of a piezoelectric pressure sensor according to the present invention, the pressure sensor calibration means 10, the interface card 20, the control means 30, a general purpose interface bus (40) ), The signal acquisition means 50 and the voltage correction means 60. A detailed description of each component will be described below with reference to FIGS. 3 to 7.

FIG. 2 is a visualized user interface initial screen designed to control a system on a computer screen and simultaneously view a system status display and all calibration procedures, and includes dynamic pressure calibration signals obtained during calibration.

3 is a block diagram of the pressure sensor calibration means 10 according to the present invention. The low pressure sensor calibration means according to the present invention can be used not only for the piezoelectric pressure sensor but also for the gauge type low pressure sensor, the pressure source (for example, nitrogen tank 101), the pressure regulating device (for example, control valve A). , B, C, D, etc. 102), filter 103, pressure indicating pressure gauge 104, standard pressure generating device for generating calibration standard pressure (primary pressure standard 105), pressure volume regulator 106 A volume tank 107 that minimizes changes in pressure volume, solenoid valves 108, a sensor adapter 109 equipped with a sensor to be calibrated, a first reference sensor 110 equipped with a pressure indicator, It consists of the 2nd reference sensor 111 and the foot switch 112 with a pressure indicator.

Referring to the operation principle of the pressure sensor calibration means 10 according to the present invention, the pressure sensor calibration means 10 is divided into a first calibration step and a second calibration step to perform the calibration of the dynamic pressure. In the first calibration step, the standard pressure generating device 105 is used to calibrate the reference pressure sensors 110 and 111 used as the pressure reference during the automatic calibration, and store the offset value for each pressure section obtained in the file. . This file is called an offset correction file. In the second calibration step, the valves are controlled by the computer to produce the desired calibration pressure. When the optimum condition is reached, the pressure is applied to the sensor to be calibrated, and the signal generated from the sensor is processed. In the process of processing the calibration data, the calibration error stored in the first calibration step is read and then corrected for each calibration pressure section to eliminate calibration errors.

4 shows an operation sequence for each function of the calibration means in the time domain, and the operation procedure is divided into a first calibration step and a second calibration step. In the first calibration step, a standard weight is mounted on the piston to generate a standard pressure from the standard pressure generator 105, and then a pressure is applied to generate a standard pressure to calibrate the reference sensor to be used in the second calibration step. Here is a sequence of steps for getting the offset value from and saving it to a file. In the initial state, valves A, C, and D are closed, only valve B is opened, and when the standard pressure is applied to the reference sensor, the footswitch is used as a trigger signal to process the data by reading the sensor output value.

In the second calibration step, the system is operated by using the automatic pressure controller and error correction algorithm mentioned later as a mode for automatically calibrating the sensor to be calibrated. In the initial state, if the calibration parameters such as calibration range, calibration interval, calibration frequency, sensor model and calibrator name are entered, the control valve is automatically controlled until the set calibration pressure is reached. At this time, the on / off time of the valve is set differently according to the pressure value. When the calibration pressure value is reached, a stable time is given to remove the pressure wave, and the data is read at the same time as the pressure is applied.

In order to obtain the standard pressure for calibration, a pressure generator using the same principle as a deadweight tester was used.

Where W is the weight of the weight, M is the sum of the weights, g is the acceleration of gravity, P _a is the air density and P _M is the weight of the weight.

5 is a block diagram showing the configuration of the signal acquisition means 50, a piezoelectric type sensor to be calibrated 501, a gauge reference pressure sensor 502, a signal preprocessor 503, a pressure indicator 504, a data acquisition board 505 and digital oscilloscope 506.

Looking at each component of the signal acquisition means 50 by the operation sequence, if the pressure control by the control means satisfies the requirements, the generated correction pressure is applied to the calibration sensor 501 and the reference sensor 502 at the same time, The sensor generates an electrical signal proportional to the applied pressure. The signal is amplified by the signal processor and then converted into analog / digital (A / D) data from the data acquisition board 505 and sent to the control means 30 for processing. The digital oscilloscope 506 sends data to the controller 30 via the universal interface bus 40.

6 is a circuit diagram of an interface card 20 of the dynamic pressure calibration apparatus according to the present invention, and FIG. 7 is a circuit diagram of a foot switch of the dynamic pressure calibration apparatus according to the present invention. The interface card is responsible for relaying between the calibration means 10 and the control means 30, Figure 6 is a circuit diagram of the controller output for controlling the valves of the calibration means from the control means, Figure 7 is according to the present invention It is a circuit diagram of the input part of a control means in which a calibration means notifies a control means of a dynamic pressure calibration apparatus, and makes a control means control.

8A is an overall flowchart of a program for executing the automatic calibration method of the dynamic pressure calibration apparatus according to the present invention.

The overall program configuration of the dynamic pressure calibration system consists of an initial stage setting of the system and calibration of the hardware according to the operating function (S1), a first calibration step (S2) of calibrating the reference sensor and a second calibration of the calibration sensor. Divided into step S3, each step is shown in Figs. 8B to 8D.

Specifically, the initialization step (S1) is to specify the initial state of the control valve, the name of the calibration valve, the calibration date and time, the sensor model and serial number, the initial screen control and Display icon Initialization In the initial screen of the calibration system, the variable initialization step (S11), which sets initial values for initial variables required for sensor calibration, after initial values of initial variables are set, the initial value of the reference voltage calibrator is set. It consists of a hardware calibration step (S12) of setting and calibrating the input channels and gains of the signal acquisition devices (data acquisition board and digital oscilloscope) and storing the calibration results in a file. When calibrating the sensor, this file is read and used to remove offset values present in the acquisition device. After the initialization step S1, the mode is selected to proceed to the first calibration step S2 and the second calibration step S3.

As shown in FIG. 8C, the first calibration step S2 is a step of calibrating the reference sensors 110 and 111 using a deadweight tester, which is a standard pressure generating device 105. Conventional deadweight testers have high accuracy but are difficult to operate and are designed to be operated only manually. Therefore, a deadweight tester, which is a conventional calibration method, cannot be used to implement automation of a computerized calibration system. In the present invention, in order to solve such a problem, it is designed to be a fully automatic control calibration using a reference sensor. Before calibrating the sensor, calibrate the reference sensor using a deadweight tester, which is used as the standard for defining pressure, and save the calibration results in a file for use in the error correction algorithm.

Specifically, the first calibration step S2 inputs initial variables such as a calibration range, a calibration section, and the number of calibrations (S21), mounts a weight set on the piston to determine a calibration pressure (S22), and Check if the pressure is within ± 5% of the determined standard pressure (S23), if not within the range, repeat sequentially from step S22, if within the range, adjust the primary pressure by the automatic pressure controller (S24), and manual pressure Adjust the secondary calibration pressure by adjusting (S25), check whether the standard weight is floated for a certain time (for example, 5 seconds) (S26), if not plotted, repeat sequentially from step S25, If it is floated, it is determined whether the footswitch has been pushed (S27). If it is not pushed, it is repeated sequentially from step S25. If it is pushed, the pressure value of the reference sensor is read and compared with the standard pressure (S28). pressure If it is large determined in (S29), not greater again repeated in order from step S22, and the greater the offset value - ends the process proceeds to step (S210) to store (a standard pressure of the reference pressure) to a file. Here, the maximum pressure indicates the upper limit pressure value of the calibration pressure range.

As shown in FIG. 8D, the second calibration step S3 is a step of automatically calibrating the sensor to be calibrated. After the calibrating pressure is automatically generated by the calibrator, the calibration pressure is applied to the calibrated sensor and the pressure from the calibrated sensor is adjusted. Automatically obtain and process an electrical signal proportional to the computer and output a calibration certificate. When the calibration data is processed, the calibration error is eliminated by reading the hardware calibration file created before calibration and the offset calibration file of the reference sensor and correcting the calibration data.

Specifically, the second calibration step S3 inputs initial variables such as a calibration range, a calibration interval, and a calibration frequency (S31), adjusts the calibration pressure by an automatic pressure controller (S32), and monitors the current pressure. Read the pressure value of the reference sensor (S33), check if the current pressure is within ± 5% of the determined standard pressure (S34), and if it is not within the range, repeat sequentially from step S32, if within the range, the reference pressure and the measured pressure (S35), judging whether the current pressure is greater than the maximum pressure (S36), if it is not large, repeats sequentially from step S32 again, and if it is large, the data is processed by a calibration formula with an automatic pressure controller (S37) Proceed to step S38 of outputting and ends. Adjusting the calibration pressure by the automatic pressure controller (S32) is made by adjusting the valves shown in Figure 3, for example, to increase the pressure using the valve A and to reduce the pressure using the valves C and D Can be.

9 is an operation flowchart of the automatic pressure controller 30, the operation principle is as follows. The solenoid action time is determined according to the pressure value to be applied to the sensor to be calibrated, and the solenoid valves are controlled to fall within ± 5% of the input value. At this time, open the valve (A) to increase the pressure and close the valve (C, D), open the valve (C, D) to close the pressure (A). After the settling time for removing the pressure wave (for example, about 10 seconds), read the voltage from the reference sensor and convert it to the pressure. When the value is within ± 5% of the calibration pressure value, the control of the valve is terminated. .

10 is a flowchart of a calibration step for constructing an error correction file in an automatic calibration program of the dynamic pressure calibration apparatus according to the present invention. The calibration error of the calibration system occurs due to the pressure change caused by the valve crusher, the pressure leakage, and the nonlinearity of the signal acquisition device. FIG. 10 shows an error correction algorithm designed to eliminate such a calibration error. Calibration sensor for constructing the error correction file The calibration phase is obtained by comparing the pressure offset caused by the pressure change and pressure leakage of the calibrator valve clamper by comparing the deadweight tester, which is a standard pressure generator, with the reference sensor. Save to error correction file. If this is explained in the order of operation, put the standard weight corresponding to the calibration pressure value (the initial pressure plus the section pressure) on the piston, and send the trigger signal to the controller using the foot switch. Adjust the differential pressure within ± 5% of the calibration pressure. Secondary pressure regulation is done manually using a control volume regulator. At this time, if the weight maintains the floating state for a certain time (for example, 5 seconds), apply the standard pressure to the reference sensor using the foot switch to obtain the pressure offset value and save it in a file. If this value is the maximum pressure value, save it, and if it is not the maximum pressure value, repeat from the beginning.

11 shows a calibration algorithm in the automatic calibration program of the dynamic pressure calibration apparatus according to the present invention. The offset of the signal acquisition equipment is obtained by the work performed before calibration, and stored in the calibration file. The operation sequence is as follows. After selecting the calibration channel and calibration range of the signal acquisition means, the reference voltage calibrator is applied to each input terminal to be calibrated, and then the offset voltage, which is the difference between the reference voltage and the measured value, is calculated and stored in a file. The calibration algorithm takes the result of the first calibration of the signal acquisition device that acquires the signal from the pressure sensor and A / D conversion in the calibration system using the voltage calibrator, and corrects the result in the calibration data when the sensor is calibrated. By applying this algorithm to the calibration program, we eliminate the error caused by the nonlinearity and the input offset of the signal acquisition device.

12 is a block diagram of an error correction algorithm. After reading the error correction file and the calibration pressure file obtained before the sensor calibration, the calibration data is processed while correcting the offsets of the corresponding calibration pressure values while processing the calibration data during the sensor calibration. .

In order to increase the accuracy of calibration by eliminating the calibration error in the dynamic pressure sensor calibration system, the above-described calibration and error correction algorithm was devised and applied to the system.

13 is an error correction table created in a first calibration step by applying a calibration algorithm and an error correction algorithm to a calibration system.

As a result of applying the calibration and error correction algorithm to the calibration system, the error factor due to the pressure change in the valve press that caused the calibration error in the early stage of development was completely eliminated, and the calibration error due to the minute pressure leakage of the control valve was eliminated. This is removed by having the computer read both the reference sensor and the calibrated sensor at the same time, and after calibrating the signal acquisition device using the voltage reference, the resultant value is used as a correction value during calibration. There were correction error removal effects that minimize the correction error that occurs during the conversion process.

FIG. 14 is a calibration report calibrated using the developed low pressure sensor calibration system. In order to perform the sensor calibration, the 137A12 model of PCB, which is a low pressure sensor mainly used for pressure measurement, is used.

15 is a graph showing a sensitivity distribution with respect to the pressure of the calibration certificate of FIG. The sensor manufacturer's calibration report suggests only one average sensitivity across the sensor's span, so the exact sensitivity to the desired calibration point is not known. The developed low pressure sensor calibrator can be used to find the sensitivity of each desired calibration point over several sections. Since the sensitivity indicates a different sensitivity value for different calibration points with different pressure values, the sensitivity of the calibration point closest to the measured pressure value should be applied at the time of measurement.

The uncertainty of the dynamic pressure calibrator calculated by the standard deviation equation is as follows.

The reference pressure sensor error is a standard retrospective error and an error of the pressure sensor itself generated when the reference pressure sensor used as the reference pressure sensor in the calibration apparatus receives the standard pressure retrospectively from the standard pressure generator, which is a pressure standard device. Acquisition equipment error is the quantization error of the A / D converter (16 bits) of the signal acquisition equipment, and the measurement standard deviation is the standard deviation of the pressure values measured 10 times with 100 psi as a reference value.

N represents the number of repeated measurements, x_i is a repeated measurement, and x_m is an average value of the repeated measurements.

The correction errors that can occur during the control of the calibration device are eliminated through the system's automation and calibration algorithm, so they are excluded from the uncertainty calculation because they are small enough to not affect the system uncertainty.

The calibration method using the automatic mixing calibration method of the present invention improves the accuracy of the calibrator by using an absolute calibration method using a deadweight type pressure generator which is a pressure source defined by the magnitude of the force acting per unit area. By using a comparative calibration method using a reference sensor that can convert the amount of electricity into an electric quantity, it automates the entire process of manually operated calibration, and reduces calibration time due to automation and calibration reliability by eliminating personal error. In addition, by using the error correction algorithm, various types of calibration errors existing in the calibrator are obtained before calibration, and then corrected during calibration, thereby minimizing the calibration errors to increase the accuracy of the system.

Claims (8)

Low pressure sensor calibration means 10, the interface card 20, the control means 30, a general purpose interface bus (General Purpose Interface Bus, 40), the signal acquisition means 50 and the voltage calibration means 60 Dynamic pressure calibration device of the piezoelectric pressure sensor characterized in that. According to claim 1, wherein the low pressure sensor calibration means, pressure source, pressure regulator, filter, pressure indicator pressure gauge, standard pressure generator for generating a standard pressure for calibration, micro pressure regulator, minimizing changes in pressure volume A dynamic pressure calibration device of a piezoelectric pressure sensor comprising a volume tank, a solenoid valve, a sensor adapter equipped with a sensor to be calibrated, a first reference sensor, a second reference sensor, and a foot switch. The apparatus of claim 1, wherein the signal acquisition means comprises a piezoelectric type calibration sensor, a gauge type reference pressure sensor, a signal preprocessor, a pressure indicator, a data acquisition board, and a digital oscilloscope. . An initialization step S1 of initializing variables and calibrating hardware in sensor calibration; A first calibration step S2 of generating a standard pressure to calibrate the reference pressure sensor; The second calibration step (S2) of applying the standard dynamic pressure to the sensor to be calibrated and at the same time receiving and processing the signal generated from the sensor, is a method of calibrating the dynamic pressure of the piezoelectric pressure sensor using the absolute calibration method and the comparative calibration method simultaneously. . The method of claim 4, wherein the first calibration step (S2) is a step of inputting an initial variable such as a calibration range, a calibration interval, a calibration frequency (S21), and mounting a standard weight to the piston to determine the calibration pressure (S22). Checking whether the current pressure is within a range of ± 5% of the determined standard pressure (S23), if not within the range, repeats sequentially from step S22, and if within the range, adjusting the primary pressure by the automatic pressure controller (S24). ), Adjusting the secondary calibration pressure by manual pressure control (S25), checking whether the standard weight has been floated (S26), if not floated, repeats sequentially from step S25, and if it is a footswitch Determining whether or not to push (S27), if not pushed sequentially from step S25, and if pushed to read the pressure value of the reference sensor and comparing with the standard pressure (S28), the current pressure is Determining whether the pressure is greater than the large pressure (S29), if it is not large repeats sequentially from step S22 and, if large, the step of storing the offset value (standard pressure-reference pressure) to a file (S210) How to calibrate the dynamic pressure of piezoelectric pressure sensor. The method of claim 4, wherein the second calibration step (S3), the step of inputting an initial variable such as the calibration range, the calibration interval, the number of calibration (S31), the step of adjusting the calibration pressure by the automatic pressure controller (S32), To read the pressure value of the reference sensor in order to monitor the current pressure (S33), to check whether the current pressure is within the range of ± 5% of the determined standard pressure (S34), if not within the range iterate sequentially from step S32 If the range is within the range of obtaining the reference pressure and the measured pressure (S35), determining whether the current pressure is greater than the maximum pressure (S36), if it is not large, repeats sequentially from step S32 again and if it is large, the automatic pressure controller is calibrated. Process of the data by the formula (S34), the step of outputting a calibration certificate (S35) comprising a method for calibrating the dynamic pressure of the piezoelectric pressure sensor. 5. The method of claim 4, further comprising: correcting the result value in the calibration data when the sensor is calibrated with a result obtained by firstly calibrating a signal acquisition device that obtains a signal from the pressure sensor and converts A / D using a voltage calibrator. Method for correcting the dynamic pressure of the piezoelectric pressure sensor, characterized in that it further comprises. 5. The method of claim 4, further comprising: reading out the error correction file and the calibration pressure file obtained before the sensor calibration and processing the calibration data during the sensor calibration and simultaneously correcting offsets of the corresponding calibration pressure values. How to calibrate the dynamic pressure of piezoelectric pressure sensor.