The Design Of PLC Data Acquisition Module

In the field of industrial process control,system is frequently collectting the currentsignals, voltage signals and temperature signals and so on analog signal from the scene.Especially in the complex control system of industrial automation, such as Steel RollingEngineering， Petroleum Engineering， Chemical Engineering， Electrical PowerEngineering， the reason of the complexity technological requirements， the dataacquisition of the scene is particularly important. In the industrial control,programmablelogic controller (PLC) served widely as the actuators. PLC is small volume, powerful,flexible assembly, reliability, simple programming, support diversify communicationmode, and working for a long time in the various severe conditions of industrial field,won the highly praise from users. But the variety of PLC producers,then make differentproducts and the analog acquisition module between each other is can’t swap, becauseless the unit and higher the price, the control cost increased to some extent. This topicdesign the data acquisition module can collect8channel PT100signal,8channel4~20mA current signal,8channels of0~5V voltage signal,completing a variety of analogquantity acquisition,at the same time，both save the PLC of the port resources andeffectively reduce control cost with a higher control precision.The CPU processor of acquisition module is MCU AT89SC52, selection of analogsignal source by dial the code switch set to complete, each analog signal through thesignal conditioning circuit and multiplex switch CD4051, putting them into multi-channel A/D converter CS5224, data is stored in the register of the MCU after filtering.In order to reduce the error of linear system,the four piecewise curve fitting algorithm isadopted to complete calibration of temperature data, using MATLAB software to getfour least squares curve fitting, and through the comparison of data forms，obtainingthe optimized control precision.This paper chooses omron manufacturer’s CPM2AH PLC to communicate withacquisition module,two communication modes is provided that is serial and parallel,putdate that is in the register of the MCU into PLC.Parallel communication is set up by fiveswitches of quantity sequence change,through the PLC program written the data from the MCU registers into omron PLC CPM2AH DM data storage registers.In the serial interface, designed RS485interface, through the converter that converts RS485to RS232,the module communicates with CPM2AH PLC through HostLink in serial communication,put date into PLC DM data storage registers. In order to reflect more brightly the analog data that is collected,by kingview software of BEIJING YAKONG company producers into Upper machine configuration display with the part of the collected analog datas. The design of the data acquisition module has reliable generality, and save the control cost, has the strong practical significance.