The Intelligent Pressure Transmitter's Research Based On The HART Protocol

With the development of Automation and the progress of the micro-electronics technology, and the maturity of Field Bus, automatic measuring technology is widely used in production process, so collection, transmission and data processing of field signal should meet higher requirements.In this case,field intelligent instruments should have higher stability, reliability and measuring precision.At the same time,HART Field Bus technology superimposes the digital signal to the present field control system successfully,which provides a riskless solution to improve the communications among intelligent instruments and deal with the non-linearity of field instrument system and temperature-excursion.So it is meaningful to study and develop the intelligent instruments based on HART protocol.The development of full-digital system in Field Bus is a general trend. However,4～20mA analog signal instruments also have a large application in industry,the HART communications protocol based on analog and digital—a traditional protocol during the transmission from analog system to full-digital system—emerges as the times require.Based on Bell202 communications standard,the HART protocol transfers digital signal with different frequency signal on 4~20mA analog signal.This paper mainly studies the intelligent instrument carries the timely transmission of the analog and digital signal based on HART communications protocol.,and also designs the MCU system and sensor system.The paper combines the MCU and the sensor into an intelligent pressure transmitter system.After the introduction of HART protocol, this paper introduces the design of hardware modules of the pressure transmitter system in detail, including the microprocessor module,the sensor module,the communications module and the A/D,D/A module. To overcome the output nonlinearity and temperature drift of pressure sensor, the paper proposes the pressure sensor and temperature sensor output as the variable to reconstruct pressure sensor outp- ut signal using bivariate polynomial,and the coefficients of curved surface formulation are decided by the least square method .Then the system can simply compute the measured pressure output after acquiring the output signal of pressure sensor and temperature sensor. The method not only benefts temperature compensation but also helps non-linear rectifying,which greatly improves the measuring precision of the system .Finally, this paper analyses and introduces the structures of the software.