Study of Two-wire Electropneumatic Valve Positioner’s Design Based on HART Protocol

The automatic control of the production process referred to as process control , plays an extremely important role in the national economy . Process Control Distributed Control System to mixed analog-digital from analog control system development , and the further development of the fieldbus control system . The quality depends largely on the process control process control instruments , including transmitters, regulators , actuators, and a variety of assistive devices . Pneumatic control valve which is very important in the process control actuator valve positioner pneumatic control valve attachments , you can improve the valve characteristics , improve control precision , speed , and increase the flexibility of control . Valve positioner to the development of intelligent , fieldbus instrumentation direction brought profound changes to the process control , represents the development direction of the pneumatic actuator technology . At present , some foreign companies have successively successfully developed smart valve positioner , some with HART protocol , PROFIBUS bus , FF fieldbus interface bus ; domestic research in this area is still in its infancy . 4 ~ 20mA current paper developed smart valve positioner , HART protocol can be configured to interface two-wire valve positioning system , the overall design to expand around the realization of low-power , research work and results are as follows : 1 for low power made a preliminary study for the control circuits , DC-DC conversion and other technical problems , proposed solutions accordingly ; 2 . constructed ADμC 812 microcontroller as the core of the control system , including the a / D sampling , data processing , D / A unit of output , valve position driver ; prepared based the system modularization package composed of two parts, control procedures and functional modules ; preliminary exploration HART protocol communication design , design and debug HART protocol communication circuit hardware and software systems ; 5 . construct a prototype of an intelligent two-wire valve positioner .