Design of Gas Mass Flow Controller Based on Bus

With the rapid growth of the number of decentralized structure designs in manufacturing automation and process automation, the application of fieldbus is becoming more and more extensive. Profibus is a standardized, open fieldbus standard developed by Siemens and other companies that does not depend on equipment manufacturers. It can be used in occasions with strict time requirements and high-speed data transmission, as well as in large-scale and complex communication occasions. . It is not only suitable for the application of discrete processing in industrial automation, but also suitable for the application of continuous and batch processing in process automation. It has been widely used in manufacturing automation, process industry automation, building automation, transportation, electric power and other automation fields. At present, many automation equipment manufacturers in the world provide Profibus interfaces for their equipment. According to different application characteristics and user needs, Profibus field bus includes three main specification subsets: Profibus-FMS, Profibus-DP and Profibus-PA[ 1]. Gas mass flow controller (Gas Mass Flow ntroller, referred to as MFC) is used for precise measurement and control of gas mass flow, in semiconductor integrated circuit technology, special material discipline, chemical industry, petroleum industry, medicine, environmental protection and vacuum, etc. It has important applications in scientific research and production in various fields. The CS200 Profibus MFC is based on the Profibus-DP protocol to realize its application in the Profibus-DP industrial control network. 2 Hardware circuit design structure As an open, manufacturer-independent, and non-intellectual property protection standard, the Profibus protocol can be implemented on any microprocessor in principle. This design uses“Microcontroller MCU+Profibus communication chip”The solution is that the protocol chip implements the data link layer protocol of Profibus-DP, the MCU basically initializes the protocol chip and performs subsequent data interaction, and the asynchronous serial communication interface completes the physical layer communication [2]. In terms of hardware design structure, MFC mainly includes: MCU control module, Profibus-DP intelligent slave station interface module, slave station address setting module, sensor module, solenoid valve module and power supply module, etc. The product hardware structure block diagram is shown in Figure 1 . Figure 1 Product hardware structure block diagram 2.1 MCU control module The microprocessor of MFC uses Microchip's 16-bit high-performance DSP chip dsPIC30F6012A, which has 8KB of SRAM and 4KB of EEPROM, which meets the requirements of data exchange during Profibus-DP and RS-485 communication The characteristic of relatively large quantity. 144KB Flash program memory with high reliability and stability, which meets the characteristic requirements of the flowmeter with multiple functions. Using low-power high-speed flash memory technology, the maximum working speed can reach 30MIPs. The chip has a complete interface type, supports SPI synchronous serial interface mode, and meets the requirements of fast communication between the microprocessor and the VPC3+S protocol chip. the

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