PLC's common networking

PLC system has become a widely used control mode. Combining with the popular trend of computers, it also puts forward better requirements for PLC data interaction and networking functions. So what are the commonly used networking methods of PLC? Xiaobian introduces the commonly used PLC networking methods can be roughly summarized as based on the common serial port, based on the dedicated bus and Ethernet-based three, specifically see the following description.

1. The universal serial port module implements network connection based on the serial port communication module. The network structure is as shown in Fig. 1. It adopts the form of a computer link. The corresponding settings are made in the configuration software of the host computer. PLC communication, taking Mitsubishi's FX1S series of PLC as an example, RS232C/485 conversion adapter selection FX-485PC-IF, RS-485 communication board selection FXlN-485 a BD can be achieved, this method is more convenient to use, performance Also very good, the key is the relatively high cost of the serial communication module.

2. Based on the dedicated bus Currently, PLC manufacturers such as OMRON, Siemens, etc., have provided dedicated network systems for their PLC products, such as OMRON's ControllerLink network, DeviceNet network, etc. This network system is due to the exclusive nature of the manufacturer's products. , Different manufacturers of equipment can not communicate with each other, basically choose a manufacturer's PLC, other equipment and equipment must also be for the manufacturer, the cost is relatively high, so there are certain limitations when applied.

3, based on standard industrial Ethernet network based on standard industrial Ethernet network, the system is generally divided into three levels: the first layer is composed of IPC PC monitoring station; the second layer by the hub, twisted pair and send and receive Industrial Ethernet composed of devices, etc.; the third layer is the control station, TCP/IP is selected as the communication protocol, and the C/S mode is used to enable the control station and the monitoring station to realize connection-oriented communication.

In this way, the biggest advantage is that you can use the existing factory LAN, improve the overall utilization, and speed, Ethernet communication speed up to 100Mbps; If you use fiber transmission, the anti-interference ability is greatly enhanced, and transmission The distance is up to tens of kilometers. However, Ethernet cannot directly communicate with serial devices such as PLCs, and it needs to be equipped with related equipment to realize communication. This increases the cost. In general small and medium-sized control systems are rare.