But, in the NPN sensor wiring, the load is always connected to Positive, and the Negative is switched when an object is detected. The Positive is switched when the proximity sensor detects an object. In the PNP sensor wiring, the load is always connected to Negative. Therefore, they must always be connected to a 24V power source to function. To easily remember the wiring of a 3-wire DC proximity sensor, we can use the following analogy: A Way to Remember NPN and PNP Sensor Wiring PNP proximity sensors are also known as ‘ sourcing’ sensors. When connected to a PLC input, it detects this as a logic HIGH signal. When an object enters the detecting range of the sensor, the output of the sensor is connected with +24V. PNP proximity sensors provide an active HIGH output. This type of sensor is also known as ‘ sinking’ sensor. This means that when an object enters the detecting range of the sensor, the output of the sensor is connected with the ground. NPN proximity sensors provide an active LOW output. This article aims to provide an outline of the two main output types and a guide on how to connect a proximity sensor to a PLC. Selecting the correct type of proximity sensor for a particular application can ensure the correct operation of a system. There are two main types of proximity sensors based on their output type: NPN and PNP. There are 2-wire and 3-wire proximity sensors, and 3-wire proximity sensors are more popular. Proximity sensors are used to detect objects without making physical contact.
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