Understanding Source and Sink Wiring Methods for S7-1200 PLCs
Sink Wiring Method
– Definition: Also known as common cathode wiring, this method connects the common terminal “1M” of the S7-1200 to the negative terminal of the power supply. Current flows from the common terminal of the PLC into the input terminal.
– Example: When using a PNP type proximity switch, the brown wire connects to the positive terminal of the power supply, the blue wire connects to the negative terminal, and the black wire (output signal wire) outputs a high level to the PLC input terminal, which is classified as a sink wiring method. For the digital input module of the S7-1200, if the sink wiring method is used, one end of the load connects to the output signal terminal of the external device, and the other end connects to the PLC input point, while the common terminal “1M” of the PLC input point connects to the negative terminal of the power supply.
Source Wiring Method
– Definition: Also known as common anode wiring, this method connects the common terminal “1M” to the positive terminal of the power supply. Current flows from the input terminal of the PLC into the common terminal.
– Example: For an NPN type proximity switch, its output signal is low level. The brown wire connects to the positive terminal of the power supply, the blue wire connects to the negative terminal, and when the black wire connects to the PLC input terminal, the source wiring method must be used. For the digital input module of the S7-1200, when using the source wiring method, one end of the load connects to the output signal terminal of the external device, and the other end connects to the PLC input point, while the common terminal “1M” of the PLC input point connects to the positive terminal of the power supply.