NPN vs. PNP and how to measure the difference with a multimeter
For industrial sensors, the wire colours are defined as: brown wire for VCC, blue for GND, black for the output
In order to respond to different customer needs 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 and blue wires. The load can be driven when the sensor works.
Method one:
Hit the multimeter to the diode measurement file, the multimeter red line connects to the sensor black line, the multimeter black line connects to the sensor black line, if the multimeter shows almost 0.7V, then this is a PNP sensor.
The red line of the multimeter connects to the blue line of the sensor, the black line of the multimeter connects to the black line of the sensor, if the multimeter shows almost 0.7V, then this is an NPN sensor.
Method two:
Play the multimeter to the diode measurement file, the multimeter red line connected to the sensor black line, the multimeter black line connected to the sensor blue line, if the multimeter can conduct, showing a voltage drop, then this is a PNP sensor.
The red line of the multimeter connects to the brown line of the sensor, and the black line of the multimeter connects to the black line of the sensor. If the multimeter conducts and shows a voltage drop, then this is a PNP sensor.
However, if the sensor is open-drain output, there is no pull-up resistor, or there is no anti-reverse connection circuit placed, this method will not be able to measure it
Method three:
Power on for measurement, the brown wire of the sensor is connected to the 12V positive terminal, and the blue wire is connected to the negative terminal. Multimeter to DC gear, test the voltage of the black line, if the sensor does not work is high, work is low, then it is NPN, and vice versa is PNP.
If the sensor is open-drain output (no internal pull-up or pull-down resistor), you can help it externally connected to a 10K resistor and then test the NPN is the brown line and the black line between the resistor, PNP is the blue line and the black line between the resistor!
