Study Of Two-wire Electropneumatic Valve Positioner's Design Based On HART Protocol

The process control is abbreviated from the automatic control of manufacture process, which is great important in the national economy and developed from analog control system to DCS, and forward to FCS. In the great degree, the quality of process control is decided by the instrumentations of process control that includes transmitters, controllers, actuator and various attachments.The pneumatic valve is one of the most important actuators in the process control. As a key attachment to the valve, the valve positioner significantly improves the performance of the valve in many aspects such as measurement precision, speed and flexibility. The valve positioner based on smart structure or on the Fieldbus is becoming an increasingly important technique and is promoting the industry process control dramatically, and now which represents the development direction in the pneumatic actuator.In the past few years, many plants abroad had investigated and successfully developed the smart valve positioner or digital valve positioner based on HART protocol, PROFIBUS or Foundation Fieldbus. However, the research on it is still an immature technique in china.In this thesis, the author studied mainly the method for smart valve positioner which based on 4~20mA current, which can be configured with HART protocol, and using two-wire system. The system design is about how to reduce power consumption. In the research, the following achievements have been made:1. A novel method for the low-power consumption control system and DC-DC conversion technique has been developed;2. The control system based on ADμC 812 single processor is constructed, including data acquisition and processing unit, D/A convert and valve driving unit;3. The system software package includes a monitoring program and a functional module with modularity has been developed;4. According to the HART protocol, a communication interface circuit and the communication software scheme have been designed;5. A prototype of a smart two-wire valve positioner has been designed and constructed.