Wiring diagram

The figure shows the state of no measured object and the sensor has no output. When the measured object is within the sensing range, the sensor outputs. In the figure, Z refers to the position of a typical load resistance; Uz refers to the voltage received by the load resistance. If Uz = high (≈ +Vs), there is current; if Uz = low (≈ 0 V), there is no current in the load resistance. The load resistance between the output and +Vs is a pull-up resistor, and the load resistance between the output and 0 V is a pull-down resistor.

PNP or NPN output

The sensor with PNP or NPN output is a 3-wire system (+Vs, output and 0 V), and the working current is direct current (DC). The load resistance of the PNP sensor is between the output and 0 V (pull-down resistor), and the load resistance of the NPN sensor is between +Vs and the output (pull-up resistor). Therefore, during switching, the PNP output is connected to the positive voltage (positive switching Output), while the NPN output is connected to a negative voltage (negative switch output). 

Normally open contacts and/or normally closed contacts determine the switching function. The normally open contact is called normally open (NO), and the normally closed contact is called normally closed (NC). When the measured object is within the measurement range, the sensor with the normally open function establishes a contact connection (Uz = high), and the sensor with the normally closed function disconnects (Uz = low).