The Research Of Intelligent Transmitter Based On HART Protocols

With the speed development of electronic technique, automation system is changing profoundly. From the micro perspective, the instrumentation of automation system go to intelligent direction; from the macro perspective, the automation system itself is changing from distributed control system to fieldbus control system. Intelligent instrument continuously improve the performance of itself, while changing the whole control system combined with the fieldbus technology. So the research of intelligent instrument based on fieldbus has important significance.The traditional based on 4 to 20mA analog signal equipment is still widely used, so the fieldbus technology compatible with analog and digital communication mode has huge demand, HART protocol was generated in this background. HART bus technology adds digital signal to the existing analog circuit, it is possible to make analog instrument digitally and intelligently. The automation system in China need the low cost solutions of upgrading analog instrument, so the research of intelligent transmitter based on HART protocol has the urgent practical significance.This paper design the intelligent transmitter in the core of C8051F410 according to the HART protocol standard, using 4-20mA analog signal transmit main variable and achieving digital communication through FSK signal. The low power consumption characteristic in C8051F410 processor solves the problem of transmitter low power consumption in hardware level. Digital communication sends commands to control the transmitter. On this basis, it is possible to achieve synchronization, gain adjustment, gain calculation, measure calibration functions and so on. Measure calibration function could store several standard fixed-point in Flash memory. Through these standard fixed-points, we could calculate the output current to realize the subsection nonlinear correction. This paper also introduces the hardware design of transmitter, consist of power unit, signal unit, communication unit and processing unit, especially the coupling way of HART modem and 4-20mA current loop. System software architecture is also discussed, especially the program realization of HART command layer and the nonlinear correction of output current. In addition, the hardware and software design of the HART/RS232 converter needed for debugging is also recommended.