Based on PPC4 pressure controller/controller, VB.NET is used as the development environment to compile software, cooperate with database and report software, realize automatic verification/calibration of pressure sensor, and validate it through reasonable experimental scheme. The system realizes the functions of automatic verification/calibration of pressure sensors, automatic creation and generation of certificates and records. To a great extent, it improves the efficiency and accuracy of pressure sensor verification and calibration, simplifies the work flow, reduces the work intensity, and ensures the smooth progress of scientific research and production tasks. Pressure sensor is one of the most commonly used sensors in industrial practice. Pressure sensor is a device or device that can sense pressure and convert pressure into available output signal (usually electrical signal) according to certain rules. It is usually composed of pressure sensor and conversion element. It can be used to monitor pressure parameters of equipment or environment. With the rapid development of China’s aviation industry in recent years, pressure sensors are more and more appearing in various test and production links of aviation manufacturing industry. As a signal conversion device, the performance parameters of the pressure sensor determine the accuracy of the output signal reflecting the actual situation. The calibration of pressure sensor is to test the performance index of pressure sensor by experiment in accordance with the unified standard procedure to see whether it meets the technical requirements. The traditional verification process of pressure sensor is to set the pressure point manually by the operator, and then record the output value of the sensor under the pressure point.
After completing all the operations, the verification results are given after complex operations. This manual detection method is not only inefficient, but also prone to errors, affecting the accuracy of measurement. In order to improve the verification efficiency and eliminate human errors, we have designed and completed an automatic verification/calibration system for pressure sensors.
Select m verification points, the verification process according to the verification point pressure, pressure relief. According to the calibration point, from the lower limit of the measurement, the pressure of the calibration point selected according to the regulations will rise steadily point by point to the upper limit of the pressure sensor, and the output values corresponding to each calibration point will be recorded. Then, the upper limit of the measurement is operated in reverse order according to the verification points, and the output values corresponding to each verification point are recorded in turn. The calibration curve of the pressure sensor can be obtained by mathematical processing of the data recorded in the verification process. The linear error, basic error, return error, repeatability error and working straight line of the pressure sensor can be obtained. The calculation process is as follows. The determination of calibration curve. According to the hardware configuration of PPC4 pressure controller, it can be controlled remotely.
The whole system is mainly composed of PPC4 pressure standard device, DC voltage regulator, data collector, RS232 communication cable, pressure connection platform, computer and printer. The system composition is shown in Figure 1.
The computer connects with PPC4 pressure controller and Keithley 2000 data collector through RS232 interface. The computer sends out control commands to control PPC4 pressure controller to produce standard pressure, which acts on the pressure sensor tested on the pressure connecting platform. The DC voltage regulator supply excitation voltage to the pressure sensor.
The Keithley 2000 data collector collects data. The electrical signals from the tested sensors under standard pressure are uploaded to the computer, which stores and processes the data, and gives the measurement results. In order to realize the simultaneous automatic measurement of multiple sensors, thermostatic element and considering the carrying capacity of PPC4 and the control ability of PPC4, the tooling of Figure 2 below is designed, which can automatically calibrate or calibrate four pressure sensors at the same time, and the working efficiency is greatly improved. The system software is developed on the platform of Microsoft visual studio and written in the environment of VB.NET. Microsoft Access is used as the database system. Certificates and record templates are made by Grid Report software. The system software can automatically collect and store pressure data, automatically determine whether the pressure sensor is qualified, automatically generate and print verification certificates and original records. The software is mainly composed of initialization module, pressure control module, data acquisition module and data storage and processing module. Its flow chart is shown in Figure 3. Initialization module. This module is mainly used to configure the communication serial port at the beginning of the system, and prompts the user to set the name, model specifications, manufacturers and other basic information of pressure sensor; to set the information of standard device and verification environment; to set the verification point information. Figure 4 shows the basic information interface of the pressure sensor being tested.
Pressure control module. According to the remote operation instructions provided by PPC4 technical agreement, PPC4 is controlled by RS232 serial port.
According to the verification process required in the verification rules, pressure verification points are set in the software to pressurize and relieve pressure, which provides standard pressure values for the whole verification process. Data acquisition module. The data acquisition module collects the electric signal value of the pressure sensor through the data collector Keithley 2000, and uploads the collected signal value to the computer through RS232 serial port. Data processing module. The software automatically calculates the basic errors, linear errors, repeatability errors, return errors and work according to the signal values collected and stored at each verification point of the detected sensor, and uses the algorithm embedded in the program to display directly printed certificates and records by calling the report software.
A pressure sensor with a range of 0-0.5 MPa and accuracy level of 0.2% is verified as an example. The results of two verification/calibration are compared through manual verification by the calibrator and automatic verification by the system. Manual verification. Automatic verification of pressure sensor verification system. The detected sensor is connected to the pressure connection stage, the sensor is connected to the data acquisition device and the DC voltage stabilized power supply. After the initialization of the software is completed, it enters. The results of automatic verification/calibration system of pressure sensor are consistent with those of manual verification. The automatic calibration/calibration system of pressure sensor based on PPC4 pressure controller has changed the previous working mode of setting pressure verification point manually, copying manually, transcribing and processing calculation data, changed the cumbersome mode that operators must work hand-eye in the whole process of calibration, and reduced the labor intensity of calibrators. It greatly improves the automation of pressure sensor verification. The software developed based on VB.NET has friendly interface and simple operation. The whole program adopts modular design, which is conducive to debugging and subsequent upgrading. It provides ideas for building a test and control system with higher automation and integration. Because of the immobilization and unification of the whole verification process, the automatic verification/calibration system of pressure sensor greatly reduces the errors caused by human factors in the traditional verification process, improves the accuracy and stability of the verification process, guarantees the accuracy and reliability of pressure measurement data in scientific research and production, and makes the whole verification possible. The fixed process is more standardized and systematic, which improves the quality of measurement.