Wiring and precautions for NPN and PNP sensors and PLC

This article shares the wiring and precautions of NPN and PNP types with PLC, and teaches you how to deal with confusion when choosing between NPN and PNP sensor types. It is a practical technical article worth collecting.

How to connect a PNP sensor to a PLC? What should I pay attention to?

Wiring method of type sensor and PLC

Figure 1. Wiring method of NPN sensor and PLC

When a signal is triggered, the signal output line is connected to the V0 line, which is equivalent to outputting 0V (5V/24V-). When an NPN sensor is connected to a PLC, only a leakage connection can be used.

Wiring method of type sensor and PLC

Figure 2 Wiring method of NPN sensor and PLC

When a signal is triggered, the signal output line of the sensor is connected to the VCC line, which is equivalent to outputting VCC (5V/24V). When a PNP sensor is connected to a PLC, it can only be connected in source mode.

How to understand source and sink connection?

Source type wiring: Source type input is valid at a high level, which means that current flows into the input point; Sink type connection: Sink type input is valid at a low level, which means that current flows out of the input point.

I am confused about the PNP sensor type selection. What should I do?

How to convert a PNP sensor to a PNP sensor: Connect a pull-up resistor between the positive power supply and the signal line. The output logic is opposite to the logic of the NPN output, that is, when the transistor is turned on (when the sensor is triggered by a signal), the PLC input is OFF, and when it is not turned on, the PLC input is ON. The resistance of the pull-up resistor is determined by the PLCON voltage and the internal resistance of the PLC input point. Formula: PLC ON voltage = sensor power supply voltage × [PLC input point internal resistance / (PLC input point internal resistance pull-up resistor)].