The full form of PNP NO in a proximity sensor is “Positive-Negative-Positive Normally Open.” Here, “PNP” refers to the type of transistor output used inside the sensor, and “NO” stands for Normally Open, which describes how the output behaves before and after detection.
In a PNP proximity sensor, the output transistor is built in a Positive-Negative-Positive structure. This means when the sensor detects an object, it sends out a positive voltage through its output wire. The sensor is known as a sourcing type, because it “sources” current from the positive supply and delivers it to the connected device such as a PLC input, relay, or indicator lamp. The wiring is simple: the brown wire goes to the positive supply, the blue wire goes to ground (0V), and the black wire is the output signal.
Now, the “NO” part — Normally Open — tells you what happens to the output when the sensor is not detecting anything. In a PNP Normally Open sensor, the output stays OFF (no voltage) when no object is present. The moment an object comes close to the sensing face, the output switches ON and delivers a positive voltage to the output wire. Think of it like a switch that stays open until something comes near the sensor, then closes to complete the circuit.
This combination — PNP NO — is the most common and preferred type in modern automation systems. It works perfectly with PLCs and control circuits that expect a positive signal when a sensor detects something. For example, in a conveyor system, a PNP NO proximity sensor can turn on an indicator light or stop the motor only when a metal object passes in front of it.
PNP NO means Positive-Negative-Positive Normally Open. It is a sourcing-type proximity sensor that sends a positive voltage to the output when an object is detected, and stays off when nothing is detected. This type is widely used because it’s easy to wire, safe to operate, and fully compatible with most PLC input systems.