Research And Development On Smart Electrical Valve Positioner Based On HART Protocol

Field-bus and intelligent instruments will be a main trend of industry processcontrol in the future. HART communication protocol introduced in this paper isrudiment of field bus, which permits transmitting digital signal on analog signalcircuit and belongs to transitional protocol. The cost invested for all standard filesabout this protocol is very low. And DCS control system maintains meters that usingHART protocol. So development of intelligent valve positioner based on HARTprotocol posses good applications and market foreground.In this article, the design scheme of an intelligent electric-pneumatic valvepositioner adopting the HART protocol is introduced. It is used in controllingpneumatic linear(rotary)actuators in order to orient the positioner of valve exactly.And it can not only communicate with other intelligent instruments or monitorcomputer bidirectionally but also provide the functions of setting up workingparameters and working mode remotely and so on. Through the research, thefollowing achievement has been made.1. The control system based on MSP430 single processor is constructed,including control panel with LCD and 3 pushbuttons, 4~20mA feedbackmodule, alarm module, springless pneumatic actuator module , valve drivingunit and HART communication module.2. Working characteristic about the valve positioner is studied in this paper.Automatic startup function and manual operation without additionalequipment is realized just using three keys and a LCD. The microcontrollercan antomatically determine the zero, full-scale value, direction of action andpositioning speed of the actuator during initialization. It uses aforementionedfunctions to determine the minimum pulse time and the dead zone, so as tooptimize the control.3. Designing of hardware circuit and system software package is optimized inthis paper so that the whole system runs well below 2mA of signal current.The problem of the low-power consumption requirement of two-wire smartvalve positioner is also solved.4. The system software package with modularity has been developed, whichincludes control, management and HART communication module. Controllingmodule is used to control linear or rotary actuators and push the actuator to avalve position corresponding to the setpoint. Managing program offers LCDdisplay, configuration parameter setting function , protection with power-off,advanced diagnostics for valve and actuator. HART communication moduleperforms the task of data link layer and commands of HART protocol.Compared with the traditional positioners, this has many advantages, such asproviding high control accuracy with low air consumption, low energy consumption,self-adjusting, wide application, the ability which can choose the flow characteristicand split range operation. Moreover, it has the function of displaying valve positionand sending alarm signal. At present, HART protocol instruments have wide marketrequirements. And it will play the leading role in the future.