The Development Of Digital Valve Controller Based On Fieldbus Technology

As a new development direction of the industrial process control, The application of Fieldbus Control System(FCS) has changed the structure of conventional process control system and shaped a new generation named integrated distribution control system. The development of FCS brings forward new requirements for slave actors. New fieldbus devices should have the capacities not only for measuring, but also for alternately communicating. Through master computers, they can be configured and diagnosed on line.Digital Valve Controller (DVC) is the new generation production of the smart pneumatic valve controllers. By adding the digital communication technique to the conventional controllers, the performance in many aspects such as measurement precision, speed and flexibility, has been significantly improved. With the intelligent structure, digital communication performance, and the capacity of connecting with fieldbus, the digital valve controller is becoming an increasingly important technique and promoting the industry automation control dramatically.The digital valve controller introduced in this paper is the two-wire system based on HART communications protocol.The focus problem is about how to fulfill the intrinsic safety peculiarity of the two-wire instruments and realize the HART communication system. In the research, the following achievements have been made.(1)To satisfy the demand for intrinsic safety peculiarity of the two-wire instruments, the ultra low-power system has been designed, including:1) Designed low-power current supply unit for the two-wire system; resolved the problem of low-power consumption.2) With the application of MSP430 single processor, the control system has been optimized and the consumed power has been decreased.3) Resolved the low-power consumption problem of data acquisition about current, air pressure, temperature, valve position by choosing the lower-power parts.4) Developed the system software package with modularity, which includes a functional module and a HART communication program, and made the power consumption lower.(2)Designed the HART process control loop, by which the digital controller can communicate with the master device under the control of MCU, including:5) Developed the hardware system which satisfied the HART FSK physical layer specification.6) Resolved the problem about separating or mixing digital signals and analog signals in the process loop.(3)Produced the demo of the digital controller using two-wire system based on HART protocol.