Intelligent Valve Positioner Based-on HART Protocol

Field-bus is a new type industrial control system; it causes a great change in the field of industrial control and will be a main trend of industry process control in the future. Because of the essential difference between analog device and digital device, it will need a long time to be accepted by the market. HART communication protocol which belongs to transitional protocol introduced in this paper is rudiment of field bus, which permits transmitting digital signal on analog signal circuit. Nowadays, since analog instruments are already applied in a wide-range, developing and studying intelligent valve positioner based-on HART protocol has valuable applications as well as a brilliant prospect in market field.In this article, the design scheme of an intelligent electric-pneumatic valve positioner adopting the HART protocol is introduced. It is used in controlling pneumatic linear(rotary)actuators in order to orient the positioner of valve exactly. And it can not only communicate with other intelligent instruments or monitor computer bidirectionally but also provide the functions of setting up working parameters and working mode remotely and so on. Through the research, the following achievement has been made.1) Improved the hardware architecture using MSP430 micropower processor, including central control unit, HART protocol module, power module, I/P control circuit, protection circuit and valve position feedback module.2) Studied the characteristic of the valve positioner and used five step valve control algorithm, got the deviation between controlled quantity and feedback quantity firstly, then sorted the deviation and made subdivision control to make the system fix position quickly.Compared with the traditional positioners, the position has some advantages such as high control accuracy, low energy consumption, self-adjusting, fixing position quickly and wide application. At present, HART protocol instruments have wide market requirements. And it will play the leading role in the future.