Research on Temperature Compensation Method of High Precision Intelligent Pressure Transmitter

The high-precision intelligent pressure transmitter is the mainstream product of the pressure sensor market at home and abroad. The measurement accuracy is 004%~01%. It can not only output 4~20mA constant current signal, but also support international standard communication protocols, such as HART protocol. Wait. Digital data of the measured parameters can be obtained using a handheld communicator or communication software based on international standards. The signal processing and conversion circuit of the intelligent transmitter is based on the microprocessor and is equipped with a communication chip that conforms to international standards. The signal processing adopts digital technology, which can directly drive the digital display and conveniently support the data transmission of industrial processes. . These transmitters are highly resistant to internal electronic noise. The built-in microprocessor or microcontroller is powerful and flexible, supporting complex algorithms. Therefore, it is possible to accurately compensate for the effects of environmental temperature, humidity, etc., and to diagnose the system intelligently. In addition, intelligent pressure transmitters conforming to fieldbus standards (such as Profibus protocol) have been put into use recently. These products output all digital signals without 4~20mA current output, which is the mainstream direction of future process control development.

1.Temperature compensation system structure

1 temperature compensation system overall composition
In the temperature compensation system, in order to meet the automatic control of the industrial equipment in the system, to ensure the smooth progress of the compensation process, the system design uses Rs232 serial bus interface, GPIB bus interface and PCI bus interface to realize the system computer and test. Communication between devices.

As shown in the figure, the implementation of different bus interfaces and the completed transmission functions are respectively
1RS232 serial bus interface: the special RS232PPI multi-master cable is used to realize the connection between the industrial computer and the oven; the self-designed RS-232 interface is connected with the matrix switching circuit to realize the switching of the compensation gas path and the compensation station serial port.
2GPIB bus interface: use 82350 PCI GPIB bus interface card to realize the operation and control of temperature compensation software for compensation test equipment with GPIB bus interface
3PCI bus interface: Based on the matrix board of CH365 chip, realize the switching of the gas path and the switching of the compensation station serial port in the automatic temperature compensation process

2. Temperature compensation system software function

The main function of the pressure differential pressure transmitter automatic temperature compensation software is to assemble the metal capacitor sensor, data acquisition board, digital control board, chamber and housing into the whole machine transmitter meter and install it to the completely sealed On the gas pipeline, put in a high and low temperature oven. The program control oven keeps the metal capacitor sensor in a temperature stable state at different temperatures, and then controls the solenoid valve on the gas path through software control, so that the measured end of the metal capacitor sensor passes through the capillary channel and the pressure controller. The test end is turned on, and the control program controls the pressure controller according to the predetermined pressure calibration point. After the pressure control device is stabilized, the computer communicates with the transmitter's microcontroller according to the specified protocol to perform the sampling process under the current pressure. . During the entire temperature compensation process, the temperature points and pressure points are selected according to the established mathematical model, the original data is collected and the data is saved in the relevant file. The temperature-compensated metal capacitance sensor is linearly corrected according to the mathematical model, and the corrected correlation coefficient is written into the E2PROM of the controller. When the pressure transmitter is applied to the detection and transmission unit of the physical parameters such as pressure and differential pressure in the automatic control system, the real-time sampled value is substituted according to the correction coefficient after the temperature compensation, and the actual field is output according to the output formula in the mathematical model. The measured value is used to monitor the pressure status of the site in real time.
According to the temperature compensation process of the pressure/differential pressure automatic temperature compensation system software, six modules need to be designed in the software development stage. The basic functions are described as follows:
1 Test bench automatic detection module: detecting the sealing performance of the gas path of the transmitter to be compensated, compensating the communication status between the software and the test equipment and the transmitter to be compensated
2 Manual test bench detection module: Targeted detection of abnormal equipment and circuits, easy to maintain and repair on-site process personnel.
3 Zero-clamping station transmitter communication detection module: It detects the bit circuit of the transmitter to be compensated for communication abnormality.
4 compensation algorithm module: according to the linear differential correction principle of the differential pressure transmitter using the least squares method, complete the preparation of the relevant linear correction algorithm function
5 automatic temperature compensation module: complete the temperature compensation and pressure calibration of the transmitter.
6 File processing module for compensation data: Store and back up the sampled data during the temperature compensation and the current correction factor.
The above research on the high-precision intelligent pressure transmitter temperature compensation method, focusing on the overall structure of the temperature compensation system and the RS232 bus interface, PCI bus interface and GPIB bus interface adopted by the system to realize the automatic temperature compensation function and implementation mode, according to the automatic temperature compensation The process summarizes the main functions that the temperature compensation system software should have.

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