Design Of Modular Data Acquisition And Communication System

With the rapid development of computer, control, communication and other technologies, the fieldbus technology has been gradually transformed from the distributed control system to the fieldbus control system. However, considering the cost, technology, maintenance, and other factors, numerous traditional devices will be retained while upgrading. This paper hence designs the modular data acquisition and communication system which achieves the needs of monitoring and control in the industrial field by using the traditional devices.Consisting of main controller, digital module and analog module, the system designed in this paper gathers data from field devices and updates their outputs.The eight RJ45 jacks based on Modbus RTU protocol of the main controller power all the modules cascaded via twisted pair. The main controller communicates with host computer via asynchronous serial interface, USB interface or Ethernet interface. It also features 32 digital input and output channels, respectively, as well as 8 analog input and output channels, respectively.The digital module has 16 digital input and output channels, respectively, as while as the analog module has 8 analog input and output channels, respectively. As the bus cascaded nodes, each module has two RJ45 jacks, one for connecting to the previous module or the main controller and the other for the next module. The modules are used to connect traditional digital and analog devices nearby in the industrial field.STM32F103ZET6 microcontrollers are chosen as the control cores in both the main controller and the modules. The main controller transplants RT-Thread real-time operating system (RTOS) as the runtime environment and implements the Modbus host protocol stack based on FreeModbus. The open source FreeModbus slave protocol stack is ported into the firmware programs of the modules.Finally, the results of bit error rate test, stability test and real-time performance test shows that the system runs stably and its performance meet the design requirements.With the low cost and flexible installation features, the modular data acquisition and communication system applies to the small industrial field with traditional digital and analog devices, and can be used as a transitional plan during upgrading to the fieldbus control system.