How to distinguish PNP and NPN sensors using a multimeter
PNP and NPN sensors work by utilizing the saturation and cutoff states of the transistor, and therefore both belong to switch quantity sensors. The commonly used ones are PNP proximity switches and NPN proximity switches. PNP sensors belong to high-level output sensors, while NPN sensors belong to low-level output sensors. Therefore, attention should be paid to the actual wiring of the two sensors. This type of switch sensor generally has three lead wires, namely the power VCC, 0V line, and output signal line.
Distinguishing between these two sensors with a multimeter is actually quite simple. The PNP sensor operates when the signal output line is connected to the VCC power supply, while the NPN sensor operates when the signal output line is connected to the 0V line.
For example, for a 24VDC power switch sensor, supply 24VDC power to PNP or NPN sensors and set the multimeter to the DC voltage range. It can be determined whether it is a PNP sensor or an NPN sensor, and also whether it is a normally open or normally closed switch type sensor.
Do not trigger the signal for them yet. Use a multimeter to connect one probe to the signal output line without moving it, and connect the other probe to the VCC and 0V lines respectively. If there is a 24VDC voltage between the output signal line and the VCC power line, it can be determined that this switch type sensor is an NPN normally closed sensor. If there is a 24VDC voltage between the output signal line and the 0V line, it is a PNP normally closed sensor.
Give it a trigger signal, and the multimeter measurement method is the same. There is a 24VDC voltage measured between the output signal line and VCC. This switch type sensor is an NPN normally open sensor. There is a 24VDC voltage measured between the output signal line and the 0V line. This sensor is a PNP normally open sensor. It is quite easy to determine what type of switch type sensors they belong to, as long as there is a multimeter, many doubts can be solved.
