The COM terminal is equivalent to the male terminal and connected to the negative pole of the power supply. In network technology, ports have several meanings. The ports of hubs, switches and routers refer to the interfaces connecting other network devices, such as RJ-45 port and serial port. The port mentioned here is not a physical port, but a port in TCP/IP protocol, which is a logical port.

The voltage of analog output is different from COM, for example, com=0V, and output A= 10V, so the output analog is 10V, and if COM=3V, the output analog is 7V.

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At present, the programmable logic controller used in industry is equivalent to or close to the host of a compact computer. Its advantages in expansibility and reliability make it widely used in various industrial control fields.

There are always a large number of PLC controllers in computer direct control system, centralized distributed control system DCS and field bus control system FCS. There are many manufacturers of PLC, such as Siemens, Schneider, Mitsubishi and Delta. Almost all manufacturers involved in industrial automation will provide their PLC products.

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