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PNP and NPN refer to the classification of the polarity of transistors. In proximity switches or sensors, different output logics can be implemented using PNP and NPN type transistors.
PNP type sensors usually output a high level (positive level) between the positive power supply and the negative power supply. When the sensor detects a target, the output changes to low level (negative level). This type of sensor is usually compatible with the PLC's drain input interface.
NPN type sensors usually output a low level (negative level) between the positive power supply and the common terminal. When the sensor detects a target, the output changes to high level (positive level). This type of sensor is usually compatible with the PLC's source input interface.
There are many ways to distinguish between PNP and NPN sensors. One way is to look at the sensor's data sheet to determine its output type. Another method is to use a multimeter to test. Connect the sensor to the appropriate power supply and load circuit, and measure the sensor output voltage. Based on the voltage value, the type of sensor can be determined.
It should be noted that sensors of different manufacturers and models may have different details and special requirements. Please consult the corresponding product documentation or consult the manufacturer for accurate information before use.
