Distinguishing between PNP and NPN sensors with a multimeter
PNP-type sensors and NPN-type sensors utilize the saturation and cutoff states of the transistor, and therefore are switching sensors. Commonly used are PNP type proximity switches and NPN type proximity switches, PNP type sensors are high level output sensors, while NPN type sensors are low level output sensors. Therefore, two kinds of sensors in the actual wiring is to pay attention to. Such switching sensors generally have three lead wires, respectively, the power supply VCC, 0V line, the output signal line.
With a multimeter to distinguish between these two types of sensors is actually very simple. Signal output line with the power supply VCC conduction and work is a PNP-type sensors, signal output line with the 0V line conduction and work is a NPN-type sensors.
For example, a 24VDC power supply switching sensors, PNP-type or NPN-type sensors to send 24VDC power supply, the multimeter to DC voltage gear. You can judge whether it is a PNP-type sensor or NPN-type sensors can also determine whether it is a normally open or normally closed to switch-type sensors.
First do not give them a trigger signal, with a multimeter pen to the signal output line does not move, another pen were connected to the VCC line and 0V line. If the output signal line with the VCC power line between the 24VDC voltage, you can judge this switching sensor for the NPN normally closed sensor, if the fruit with the 0V line between the 24VDC voltage, is a PNP normally closed sensor.
Give it a trigger signal, multimeter measurement method is the same. If there is 24VDC voltage between the output signal line and VCC, this switching sensor is NPN normally open sensor, and if there is 24VDC voltage between the output signal line and 0V line, this sensor is PNP normally open sensor. It is quite easy to determine what type of switching sensor they belong to, as long as you have a multimeter you can solve a lot of doubts.
