PNP and NPN are terms commonly associated with sensors, particularly in the context of industrial automation and electronics. They refer to the type of output circuitry employed in a sensor.
PNP Sensor (Positive-Negative-Positive):
- In a PNP sensor, the output transistor conducts current when the sensor is activated or triggered.
- PNP sensors are referred to as "sourcing" sensors because they output a positive voltage (+V) when active.
- In simple terms, when the sensor detects an object or reaches a certain threshold, it will output a positive voltage signal relative to the sensor's ground.
- PNP sensors are commonly used in applications where the load is connected between the sensor output and the positive supply voltage.
NPN Sensor (Negative-Positive-Negative):
- In an NPN sensor, the output transistor conducts current to ground when the sensor is activated.
- NPN sensors are referred to as "sinking" sensors because they output a negative voltage (-V) when active, relative to the sensor's ground.
- When the sensor detects an object or reaches a certain threshold, it will connect the output to ground, effectively completing the circuit.
- NPN sensors are commonly used in applications where the load is connected between the sensor output and the negative supply voltage or ground.
Key Differences:
- PNP and NPN sensors differ primarily in the polarity of their output signal. PNP sensors provide a positive output, while NPN sensors provide a negative output concerning their ground reference.
- PNP sensors are compatible with positive logic systems, where a high voltage signifies an active state, while NPN sensors are compatible with negative logic systems, where a low voltage signifies an active state.
- The choice between PNP and NPN sensors depends on the requirements of the specific application and the compatibility with the existing control system.
