The difference between NPN and PNP and how to use a multimeter to measure and distinguish
For industrial sensors, the wire color is defined as: brown wire is VCC, blue is GND, and black 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 should be connected to the brown and black wires. When the sensor works, 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 line and the blue line. When the sensor works, it can drive the load to work.
method one:
Turn the multimeter to the diode measurement position, 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.
Connect the red wire of the multimeter to the blue 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 an NPN sensor.
If there is no protection diode inside the sensor, this method will not be able to detect
Method Two:
Turn the multimeter to the diode measurement position, connect the red wire of the multimeter to the black wire of the sensor, and connect the black wire of the multimeter to the blue wire of the sensor. If the multimeter can be turned on and there is a voltage drop, then this is a PNP sensor.
Connect the red wire of the multimeter to the brown wire of the sensor, and connect the black wire of the multimeter to the black wire of the sensor. If the multimeter can conduct and show a voltage drop, then this is a PNP sensor
But if the sensor is an open-drain output, there is no pull-up resistor, or there is no anti-reverse connection circuit, this method cannot be tested.
Method three:
Power on for measurement, the brown wire of the sensor is connected to the positive pole of 12V, and the blue wire is connected to the negative pole. Turn the multimeter to the DC gear and test the voltage of the black wire. If the sensor is at a high level when it is not working and is at a low level when it is working, then it is NPN, otherwise it is PNP.
If the sensor is an open-drain output (without internal pull-up or pull-down resistors), you can connect it with a 10K resistor externally and test again. NPN is the indirect resistance between the brown wire and the black wire, and PNP is the indirect resistance between the blue wire and the black wire
