In the industrial production process, there are many of the continuous change, such as temperature, pressure, flow, level and speed are all analog. In order to deal with analog programmable controller must achieve A Analog (Analog) and Digital (Digital) between the A / D conversion and D / A conversion. PLC manufacturers are supporting the production of A / D and D / A converter module, the programmable logic controller for analog control. And in the actual IO module plc environment, the system often plc analog output modules weak current or voltage signal (mV or mA level), and generally with a load capacity is low. Direct implementation of the remote monitoring device is used, often because of the attenuation caused by long-distance transmission signal, distortion, and sometimes due to industrial automation plc external signal errors caused by signal interference, affecting the normal operation of the entire system. This requires that we ask for RTD, thermocouple temperature signal and the current and voltage signal acquisition, the digital output port via RS485 serial interface using standard communication protocols to transfer data to the PLC.
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