Design Of Intelligent Transmitter Based On RS-485 Bus

With global warming, environmental problems have become prominent increasingly. It also raises higher and higher requirement in monitoring of hydrology and other environmental information. This requires the function of the instruments that used for field testing more completely. And now the rapid development of the field-bus technology brings new development direction to water-level monitoring. Because the RS-485 bus has mature technology, low development costs and other advantages, so it is widely used in some small monitoring system. RS-485 bus can easily form a network with different instrumentation equipment which made by different manufacturers. So, we can centralize monitoring and management some information. But the most important thing is that the equipment must have a unified interface of RS-485.This paper is about the transformation and upgrade of the inductive digital water-level sensor which is researched and developed by Taiyuan University of Technology institute of measurement and control technology independently. The sensor is designed for the project of Shanxi Wan Jiazhai Yellow River Diversion specially.Although it fully meet the long tunnel, closed and long distance communications requirements, but the sensor is not good in versatility.In order to make the sensor compatible with other systems. Consulting a large number of the relevant literature, according to the development needs of modern instruments, and combining with the current research on hydrology monitoring systems at home and abroad. This paper puts forward a set of design scheme about intelligent transmitter which is based on RS-485 bus. And it gives the detail design of the software program and hardware circuit. This paper mainly research contents include:(1) Analysis of the detection technology and instrument used in the common areas and the principle of communication technologies, compare their advantages and disadvantages, and to establish the bus using the RS-485 communication.(2) In order to reduce the costing and the number of instruments and chips.C8051F021 microcontroller is selected as the master controller of the hardware circuit which is produced by GYNAL. It's a mixed-signal processing MCU with high-speed and high performance. C8051F021 can gather 16 analog signals at the same time because it has 16 ports of ADC input. Also, operating speed which is up to 25MIPS system can meet the needs of real-time.(3) To prevent the hydrological information loss caused by power outages or other reason, the subject chooses ferroelectric memory FM24C256 as extended external storage. The memory can store data more than 40 years without power, and it's using the low power design. So, it is widely used in the instrumentation industry.(4) The subject provides a variety of low-power approach and anti-jamming processing measures in hardware design to improve the stability of the system.(5) After studying the bus protocols and signal transmission timing of the RS-485, design the system software program.It's including:ADCO collection procedures, data processing and storage, communication code and so on.The experiment and debug show that the RS-485 intelligent transmitter improve the part of performance of the original water-level sensor. It makes the sensor's output signal digital to standardization, so we can form a network conveniently.