The difference between NPN and PNP and how to use a multimeter to measure the difference
For industrial sensors, the wire colors are defined as: brown wire is VCC, blue wire is GND, and black wire is output.
In order to meet the needs of different customers and different applications, we will design NPN and PNP models. The difference between the two is that the internal output circuit is different
NPN output circuit
The internal circuit is an NPN transistor, and the load needs to be connected to the brown and black wires. When the sensor is working, it can drive the load to work.
PNP output circuit
The internal circuit is a PNP transistor, and the load should be connected to the black and blue wires. When the sensor is working, it can drive the load to work.
After understanding the above differences between NPN and PNP, you will know how to use a multimeter to measure the difference.
method one:
Turn the multimeter to the diode measurement setting, connect the red wire of the multimeter to the black wire of the sensor, and connect the black wire of the multimeter to the black wire of the sensor. If the multimeter shows almost 0.7V, then this is a PNP sensor.
The red wire of the multimeter is connected to the blue wire of the sensor, and the black wire of the multimeter is connected to the black wire of the sensor. If the multimeter shows almost 0.7V, then this is an NPN sensor.
If there is no protection diode inside the sensor, this method cannot detect it.
Method Two:
Turn the multimeter to the diode measurement setting, connect the red wire of the multimeter to the black wire of the sensor, and the black wire of the multimeter to the blue wire of the sensor. If the multimeter can be turned on and shows a voltage drop, then this is a PNP sensor.
The red wire of the multimeter is connected to the brown wire of the sensor, and the black wire of the multimeter is connected to the black wire of the sensor. If the multimeter can be turned on and shows a voltage drop, then this is a PNP sensor.
But if the sensor has an open-drain output, no pull-up resistor, or no anti-reverse connection circuit, this method cannot detect it.
Method three:
Turn on the power for measurement. The brown wire of the sensor is connected to the 12V positive pole and the blue wire is connected to the negative pole. Set the multimeter to DC mode and test the voltage of the black wire. If the sensor is high level when it is not working and low level when it is working, then it is NPN, otherwise it is PNP.
If the sensor has an open-drain output (no internal pull-up or pull-down resistor), you can connect it to an external 10K resistor and then test it. NPN is the resistor connected between the brown wire and the black wire, PNP is the resistor connected between the blue wire and the black wire
