Development Of HART Communication Interface For Intelligent Electric Pneumatic Positioner

Nowadays,fieldbus has already become hot spot in process control field in the world, which incorporates digital communication technique into field instruments, this leads to a revolution to industrial control systems. During the transition from conventional analog instruments to full-digital instruments,the HART communication protocol—a transitional protocol emerges as the times require. And it is now viewed as the standard of intelligent instruments. However,the supply of intelligent instruments in our own country is dominated by foreign companies. In order to meet the needs of field communication demand in our country, the paper made a useful attempt of HART protocol on application of intelligent instruments. And the HART communication interface for Intelligent Electric Pneumatic Positioner is developed.In this thesis, all the research and development are based on HART protocol. Firstly,HART protocol is illustrated. The relationship between HART protocol and OSI/ISO with seven functional layers is introduced. Through deep research on physical layer, data link layer and application layer of HART protocol,it makes clear that how HART protocol works.Secondly, being based upon HART protocol and the requirements of smart valve control systematic,a hardware design plan of HART communication interface is presented,including chip selecting and low power dissipation analysis of the system. In this thesis, hardware such as power generation circuit,HART modem module,interface of HT2015 and MCU,receive bandpass filter,output wave shaping filter, and clock generation circuit are emphasized and described in detail. Finally we completed the development of two hardware circuit board—the HART modem of PC and the HART interface card of positioner. In software of lower place machine,the command system is designed based on the function requirements of Intelligent Electric Pneumatic Positioner. Also the HART communication state transition diagram is discussed,and the software design of lower place machine is completed by using C programming language in MSP430 Single-Chip. At the same time,this thesis gives a brief introduction of the function requirements of PC special software and it's communication mechanism as a master device.In the end, the paper introduces the debugging work of the HART communication interface,including the application of HART475,the problems in debugging and how to overcome it. The test results proves that the HART communication interface is reliable and feasible. So it has a good value for engineering application.