How to Connect a Three-wire DC Sensor to a PLC

An application calls for a three-wire DC sensor to report to a PLC. How should they be connected together?  Check the input card of the PLC and find the voltage rating. Does it operate on DC voltage? Also determine whether the input needs to be sinking (NPN) or sourcing (PNP.) Look at the sensor and make sure the voltage rating and PNP / NPN type is the same. If there is a mismatch, refer to the manufacturer's instructions for both devices to determine compatibility.

If the PLC's input card is rated for DC voltage and it is a sinking (NPN) type input and also if the sensor operates on DC voltage in the same range and its output is sinking (NPN), then the two should be compatible. Connect the PLC to the power supply, but do not turn the power supply ON yet. Then connect the sensor's positive source voltage wire, which is normally brown, to the positive terminal of the power supply. Connect the negative or neutral sensor wire, normally blue, to the power supply as well, but on the negative terminal. Then connect the sensor's signal wire, normally black, to the PLC input card at the number address that you will assign as the sensor in the PLC program. When the sensor is activated, it will connect the PLC output to neutral or ground, which the PLC will interpret as a "true" condition and respond as programmed.

If the PLC's input card is rated for DC voltage and it is a sourcing (PNP) type input and also if the sensor operates on DC voltage in the same range and its output is sourcing (PNP), then the two should be compatible. Connect the PLC to the power supply, but do not turn the power supply ON yet. Then connect the sensor's positive source voltage wire, which is normally brown to the positive terminal of the power supply. Connect the negative or neutral sensor wire, normally blue, to the power supply as well, but on the negative terminal. Then connect the sensor's signal wire, normally black, to the PLC input card at the number address that you will assign as the sensor in the PLC program. When the sensor is activated, it will connect the PLC output to the positive terminal of the power supply, which the PLC will interpret as a "true" condition and respond as programmed.

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