Hart Fieldbus-based Intelligent Valve Control System

The bus line on-the-spot is a kind of open system , it is hot in computer local area network of present automation field. This paper first makes more overall comparison for the characteristic of various bus lines , then it introduces HART bus line in the application in valve control system.The bus line on-the-spot includes two partial groups: Main equipment and slave equipment. Main equipment delivers the instruction of user to the equipment on-the-spot , at the same time it gives user the information feedback of the equipment on-the-spot; Slave equipment is used to control the valve in scene . According to the agreement requirement of HART bus line , we have realized the control of personal computer and the slave equipment. Full text divides into 3 minutes totally:The first minute introduces the concept of the bus line on-the-spot and develops prospect The text is detailed to discuss the message rule of application layer, physical layer, link layer as well as the signal rule of HART bus line.Because computer system in early stage exists the defect that system encloses influence, the product of each big manufacturer can not link mutually, and different manufacturer is hard to realize exchange and operate mutual. Therefore it is difficulty with larger scope to share network systematic. The new control system on-the-spot of bus line have dealt with those problem by the requirement that different manufacturer make the automation equipment with the same agreement.The second is explained how HART bus line is designed. In this part, according to last one Zhang, it tells how to design the system. The digital signal that will be delivered through the HT2012, then we will get the signal of square wave; on the other hand AD421 exports current. When this signal of square wave passes through AD421, it will be overlayed on imitate and bedelivered to accepting equipment; Accepting equipment demodulates the accepted signal and carry out corresponding order according to the meaning of signal.The part of 3th explains from software how to communicate between main equipment and slave equipment. The program of personal computer accepts the instruction of user and delivers this instruction according to the communication standard of HART agreement to slave equipment. On the other hand, personal computer accepts the information of feedback from equipment and shows this information user. There are two functions in slave equipment: It monitors equipment on-the-spot and sends main equipment the state of the equipment on-the-spot; On the other hand, it accept the order of main equipment and do some adjustments for systematic control parameter.