Research And Development Of Field Control Station Based On New DCS

DCS (Distributed Control System) is a decentralized control, centralized operations, graded management system, which is controlled with the constant development of industrial production and has been widely used in industrial fields. With the development of computer technology, fieldbus technology and industrial Ethernet technology, DCS presents a new structural model with the combination of these technologies. New DCS is developed based on the traditional DCS, resulting from the application of fieldbus and Ethernet. Typically, the data communication is using Ethernet technology between field control station and engineering station;the data transmission is using CAN fieldbus between master control card and intelligent measuring and controlling card.Field control station is the core unit of DCS, accomplishing directly the field I/O data acquisition, information exchange, control algorithms and logical control, and completing real-time control of industrial process. The design of field control station directly determines the reliability and stability of the entire DCS system. Field control station is made up of master control card, measuring and controlling card and field instruments.In the subject, the hardware platform of the master control card is based on 32-bit microcontroller STM32F107 of Cortex-M3 core, which is produced by STMicroelectronics, the software platform is based on real-time operating systemμC/OS-Ⅱ, by means of the application of the various tasks to complete data communication, configuration algorithm solution, control strategy implementation and data transmission to other stations and so on. The measuring and controlling card includes analog input card, analog output card, digital input card, digital output card, pulse input cars, thermocouple input card and RTD input card. This paper mainly introduces the hardware and software design of analog input card, analog output card, thermocouple input card and digital output card. The measuring and controlling card applies 32-bit microcontroller STM32F103 produced by STMicroelectronics, in order to improve the intelligence of cards, automatic fault diagnosis and health status indicator is increased on hardware design, isolation protection measures is applied from the consideration of reliability; software design is used for field signal acquisition, control output, fault detection and alarm and data communication to master control card through the CAN bus.MCU comes with Ethernet module, Ethernet hardware interface is accomplished with an external PHY chip, greatly simplifying the hardware design of master control card. The data communication is using Ethernet technology between master control card and PC; by embedding TCP/IP protocol stack LwIP into real-time operating systemμC/OS-Ⅱ. LwIP protocol stack includes ARP, IP, ICMP, TCP and UDP protocols. MCU comes with CAN controller, CAN communication between master control card and measuring and controlling card can be achieved by increasing an external CAN transceiver. PC downloads CAN communicating commands by Ethernet, after the master control card receives the commands, which is transmitted to measuring and controlling card by CAN bus. Measuring and controlling card returns data under the CAN data frame format after receiving an order. Data transmission in field control station uses CAN bus, greatly improving the reliability of data transmission and real-time capability.