0 Introduction
In the 21st century, smart sensors are the most influential and promising high-tech, and all countries attach great importance to them and have introduced a variety of encouraging policies and industry regulations in order to promote the development of related industries. With the development of industrial intelligent automation in recent years, the demand for sensors is also increasing at a rate of 5 times per year, and the future sensor industry will be the most emerging and most promising industry in China. With the continuous expansion of China’s industrial production automation scale, traditional sensors have been unable to meet the needs of industrial automation, industrial automation has a strong demand for high-quality, high-precision sensor products. In this environment, the automatic pressure calibration system is of great significance for the improvement of the quality and productivity of the sensor.
1 High precision automatic pressure calibration system
1.1 System Overview
The high precision automatic pressure calibration system is an automatic control system for high and low temperature, high and low pressure, aging, screening and testing. It is automatically controlled by the computer to generate the required high-precision standard pressure, which is transmitted to the standardized equipment or working chamber through the special tool interface. The data acquisition unit automatically collects the response data of the calibrated equipment, realizes the automatic detection of the pressure equipment, and automatically records, stores and calculates the calibration data. Print original records or verification (calibration) certificates according to instructions. See Figure 1 for the system work flow chart.
1.2 By Standard
According to JJG 860–2015 “Pressure sensor” verification regulations; JJG 882–2004 “Pressure Transmitter” verification regulations; JJG 875–2005 “Digital pressure gauge” verification regulations; JJG 1107–2015 “Automatic standard pressure generator” verification regulation.
1.3 Hardware Requirements
The main functions of the high precision automatic pressure verification system are: automatically set the temperature point and rise time (such as the thermostat has this function); Automatic setting of pressure control points; It has a good and simple man-machine operation Chinese interface; The test bench as a whole is mobile (except gas cylinders and printers), all equipment are fixed on the test bench, beautiful appearance, to achieve the system integration of each component, to achieve the internal connection of the circuit and gas; As shown in Figure 2.
Figure 2 Customized cabinet (System)
1) Data acquisition unit
The digital multimeter is the core component of the data acquisition unit, which is used to collect the output signal of the calibrated pressure sensor/pressure transmitter and send it to the computer for data processing. In order to ensure the sampling accuracy, the selected parameters of the digital multimeter are: the measurement accuracy is ± (0.003 5% indication value + 0.000 5% range); Features: 3-day AH with built-in 6-half-digit multimeter and 8 kinds of switch and control plug-in module, can measure and convert 11 different input signals: temperature (thermocouple, RTD and thermistor); Dc/AC voltage; 2-wire / 4-wire resistance, frequency and period; Dc/AC current. The system can test the voltage signal of up to 60 pressure sensors (transmitters) and the automatic test of the special short-circuiting mode of temperature compensation resistance.
2) Medium and low voltage console (removable console)
In order to meet the needs of detection, the modular system integration structure is adopted, except for printers and gas cylinders, the system hardware equipment is all installed on the host console; All hardware including vacuum pump, 20-way collector, power supply, industrial computer, medium and low voltage calibrator fixed installation is more firm and reliable; Easy to use with adjustable power supply for transmitter and power control box; Stainless steel table top is easy to clean; With wheels for easy placement and movement; The adjustable direction adapter is convenient to use and avoids errors caused by unsuitable viewing Angle of the equipment under inspection; A high pressure gas filter is installed on the console.
3) diaphragm vacuum pump
Limit pressure <200 Pa, suction speed >33 L/min; Oil-free low noise diaphragm vacuum pump from Germany can be installed directly in the cabinet. The advantages are small size, light weight, stable vacuum and easy to control. Technical indicators: suction speed 2.3 m3/h; Final pressure <7 500 Pa; Power supply 220 V.
4) Custom tooling (installation of sensor under test)
Considering the quick installation and sealing of the equipment, customized tooling and joints are used according to the actual situation. Multi-way tooling design, modular, easy to combine, but also can realize multi-way free combination. The reliability of the test is improved by using multi-way custom tooling. After multi-module design, the working test of the system will not be affected by the failure of one tooling module. Multiple custom tooling is also used to improve the safety of the test. When doing the test, take the design of a 20-way sealing chamber as an example, such as sealing gaskets, if the size is too long, it will lead to air leakage and other phenomena, and the use of multi-modular design will greatly reduce the probability of air leakage and improve the safety performance of the test.
2 High precision automatic pressure calibration software requirements
High precision automatic pressure control software, is through RS232 interface or Ethernet port to pressure calibrator, high and low temperature environment box (temperature box needs to provide interface protocol standards or message format) automatic control, in the given pressure and temperature range according to the national verification regulations for 1–20 pressure sensors or transmitters at the same time automatic detection. With data collection, data processing, data storage, according to the specified format print test report and test curve display function; There are pressure control data entry error warning and protection functions.
1) Pressure source automatic control: to meet the requirements, that is, after the user selects the pressure range, the system will automatically pressurize and depressurize the sensor/transmitter according to the requirements of the national verification regulations.
2) Data acquisition: Automatic acquisition, automatic storage and automatic processing of test data for the output of 1–20 sensors/transmitters.
3) Data storage: The test data and the information of the detected sensor/transmitter can be stored in text format.
4) Data processing: The test data can be automatically processed according to the relevant requirements of the national verification regulations or calibration specifications.
5) Data printing: The verification/calibration results can be printed in the format required by the user.
6) Test curve display: the verification/calibration results and process can be visually displayed online on the computer screen in the form of curves.
7) The software can provide protection functions including: can automatically determine whether the system pressure is stable, and has a display function.
3 Advantages of high precision fully automatic pressure calibration system
The whole system is based on the concept of “Industry 4.0 and intelligent measurement”, high-precision automatic pressure calibration system to achieve mechanical automatic production and calibration, compared with the domestic calibration system, to achieve the advantage of high precision (0.01 level), improve the performance of the product factory (automatic correction system, Industry 4.0), calibration accuracy (intelligent measurement); Compared with foreign fully automated systems, its advantage is cost-effective, the price is only half of foreign products; The application field is wide, foreign products can only apply their own pressure standard and can not achieve automatic inspection (calibration) in accordance with the requirements of China’s technical specifications. The fully automatic calibration system is suitable for all types of pressure standards and can even be extended to fully automatic calibration in other areas such as temperature and flow rate. Through efforts, more enterprises can realize automated production, and more measurement industries can realize automated calibration. Nowadays, according to the needs of users, the self-developed multi-channel gas switching system, custom tooling and supporting software for the high-precision automatic pressure calibration system have been successfully applied to the production of pressure instruments, pressure measurement verification and measurement calibration and other industries. This technology has been in the flow, temperature, liquid level and other measurement of professional applications, at present, has been successfully for some enterprises, colleges and universities and some large technical institutions made temperature, flow high-precision automatic calibration system, after trial, get a good response from users.
4 Conclusion
China’s instrumentation industry in the late start of the case, after more than 20 years of unremitting efforts, has become a commonly used instrumentation production country, research and development and production system is increasingly sound. At this stage, industrial intelligence is quietly leading the change of the instrumentation industry, in line with the development of the trend, as a sensor production enterprise service of the self-founded company, with a better calibration method to save more manpower and material resources, is the goal we have been fighting for.
At present, the fully automated pressure calibration system is mainly used in measurement, and on this basis, it is promoted and optimized. Later, relying on customized hardware and software, the fully automated calibration system will be developed to other areas of need.
reference
[1] National Technical Committee on Pressure Measurement. JJG 860–2015 Pressure sensor verification Regulation [S]. Beijing: China Quality Inspection Press, 2015.
[2] National Technical Committee on Pressure Measurement. JJG882–2004 Verification Regulation of Pressure Transmitter [S]. Beijing: China Metrology Press, 2004.
[3] National Technical Committee on Pressure Measurement. JJG 875–2005 Verification Regulation of Digital pressure gauges [S]. Beijing: China Metrology Press, 2005.
[4] National Technical Committee on Pressure Measurement. JJG 1107–2015 Automatic standard pressure generator verification regulation [S]. Beijing: China Quality Inspection Press, 2015.
[5] Mu Ahua, Zhang Lei, Zhang Jian. Design and implementation of Data Acquisition and Field Calibration System for Pressure Sensor [J]. Metrology Technology, 2011 (11) : 55–58.
[6] Xiang Sujun, Xie Qifeng. Design of Automatic Calibration device for Pressure Sensor [J]. Industrial Metrology, 2012 (s1) : 114–115.
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