Research And Design Of Intelligent Measurement And Control Module Based On MODBUS RTU Field Bus Protocol

With the development of communications, microprocessors, micro-electronics, and other technologies, the computer control system has been widely used. Traditional control system has transited to a communications network, which is digital, two-way transmission and multi-branch structure between the intelligent field devices and automation system. Because of using a communications cable, so it reduces the massive signal cables compared to the past DCS. It simultaneously allows system's equipment to distribute in a big region. FCS has been formally used in the industrial scene and obtained successful as a better computer controlling plan. Intelligent control module based on MODBUS RTU fieldbus protocol is put forward and designed according to the demand of the underlying equipment of FCS. In the respective sections of the paper, gives a detailed discussion about hardware design and software design of the functional modules, MODBUS RTU protocol programming on the RS-485 serial communications, PC module functions software design. At the end, enumerates application example on this series intelligent module in industrial control scene.There are all kinds of front-end data acquisition and control modules in computer control system because of measuring and controlling varies of physical parameters (temperature, pressure, flow, levels, physical properties, displacement, etc.). Based on the market requests of new multi-function modules, we design eight kinds of general modules which include:1. 8 standard signal (AI) Acquisition Module, which provides 1-5 V or 4-20 mA input, current limiting and power distribution function.2. 8 standard signal input, 4-way switch input, 3-way switch output module.3. 6-way temperature signal (AI) Acquisition Module, which supports dual thermal resistance or thermal couple sensor. 4. 6-way pulse input acquisition module.5. Conditioning control (including AI, AO, DO) module can support two single-loop or one cascade regulation.6. 16 Switch Input Module.7. 8-way switch output module.8. Data communication control module.These modules can meet the needs of most measurement and control system. MCU uses MCS-51 and programming uses C51. Research and design, make this series of modules reach a relatively high technical target, which is focused on isolated RS-485 hardware driven circuits, high-performance DC 24V circuits, 220V AC input isolated switching power supply circuits and multifunction analog input circuits.Reliable and real-time communication between the functional modules or between modules and PC is the basis to ensure the normal operation of the system. In the design, we choice common MODBUS RTU communication protocol to program. Software includes two main functions:1. Data received adopt serial interrupt mode. At the same time, it uses a timer interrupt by one serial port controlled to judge data flow discontinuance, then makes Teport synchronous.2. This design uses a look-up table method to compute CRC. It is fast and effectively improve the reliability of data transmission.To meet the different requirements of parameters measurement and control in the industrial control scene, the system should be able to achieve a flexible configuration. Configuration software of lower-machine is programmed by DELPHI language to configure the module. Its functions include communication baud rate settings, module address settings, digital calibration, module adaptive parameter settings and so on.