Research Of High Precision Collection Instrument For Analog Signals Based On Modbus Protocol

The paper takes a project as its application background.The project, named design of boiler control system for Guangxi Leiping sugar company, needs to design a real-time boiler control system based on fieldbus. The existing boiler control systems in Leiping suger company are worked out with DDZ-â… ,DDZ-â…¡electro-motion assembled instruments. Several problems exist in this general instrument control technique, such as lower precision, higher fluctuation of the system, larger amount of measuring instruments, higher cost of maintenance, et. So, it requires a new kind of collection instruments to realize the design of this system. In this paper, a high precision collection instrument, based on Modbus communication protocol, is designed to measure analog signals. The instrument can reduce the amount of used instruments and increase the precision of the instrument by adopting a 24-bit high precision A/D transformer, which can convert 8 routes analog input signals simultaneously. At the same time, it takes use of WGM12864B LCD display module which shows collected data and run- curves dynamically. The watchdog circuits promote the stability and anti-jamming ability of the instrument; furthermore, it can check and restart the whole system automatically when powered on. Besides, a RS-485 serial communication interface is integrated on the instrument, which can upload analog data such as spot temperature and valve opening of the boiler to the monitor computer and receive downloaded data and control signals from the host computer. The communication speed could be selected manually by a dial switch. This new instrument, based on standard industrial bus, realizes the communication between lower equipment networks and advances the intelligentized and network level of the control system.In a summary, the instrument designed in the paper has advantages as the following: better real-time character,high precision, wide use, and high quality. It achieves the function of data-collection required by control systems, satisfies the needs of system design and can be used to industrial area.