Function plc communication module, when the PLC communication port itself is not enough to use, because there may be more than one third-party PLC needs and communications instruments. Then you need to use the communication module plc, there are many types of communication module, a common serial module (RS232, RS485, RS422) and Ethernet communication module。
The analog input module is a remote site analog signal acquisition to the computer equipment, the use of RS-485 bus as a data communication line, provided to 485 analog functions, can simultaneously eight plc analog input module, and by RS-485 bus transfer to the computer. As a result of RS-485 interface as a communication interface, which is capable of transmitting a plurality of modules combination analog signal more large ones, and can be dispersed on a 485 line configuration, using the address code to distinguish, you can directly access the MODBUS RTU protocol configuration software.
programmable logic control plc because of its high reliability, simple programming, versatility, small size, compact structure, easy installation and maintenance, etc., and in industrial control has been widely used. PLC modules are generally divided into the following categories:digital output module, analog input modules, analog output modules. In industrial control especially in the field of process control analog acquisition and control needs a relatively large amount, so the PLC analog input and output modules require more, and analog input and output modules are more expensive, increasing the analog input, output modules increases the cost and reduces the cost of the entire system, limit the application of PLC. This paper presents a simulation based on the amount of communication of input and output expansion module method seeks to solve this problem.