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Pnp switch12/2/2023 ![]() ![]() The SIMATIC S7-1200, Digital Input SB 1221 is such a sourcing-type input card. If the input is fed to the PLC through an input card, it must be a sourcing type input card, or else a configurable one. This means that the PLC will ‘source current’ out of the input, and the NPN sensor will ‘sink current’ when it detects an object. On a Siemens S7-200 PLC, this can be done by connecting input 1M to +24V. Wiring an NPN type 3-wire proximity sensor to a PLCīefore connecting the sensor to the PLC, make sure that the PLC is configured to the ‘sourcing’ type. If your sensor’s wires are differently colored or unsure about the color code, please refer to its manufacturer’s datasheet. On a 3-wire sensor, the wiring color code is as follows: (Brown: +24V, Blue: 0V, Black: output) Identifying the color code of a 3-wire proximity sensor Warning! Before attempting any wiring, make sure that the system is powered off to prevent electric shock. How to Connect NPN/PNP Proximity Sensor to PLC Regardless, the sensor is connected to +24 and 0V to supply power to it. But in the NPN type wiring, the relay is always connected to +24V and the sensor switches the 0V connection. The difference between the two wirings is that in the PNP type wiring, the relay is always connected to 0V, and +24V is switched by the sensor. Let’s have a look at a relay-type circuit, where a relay is operated directly by a proximity sensor. a PNP sensor can be either N/O or N/C as can an NPN be either N/O or N/C) This is dependent only on the application. Two of the wires are used to provide the sensor with power to operate, while the other wire is the output from the sensor.Īt this point, t’s worth mentioning that being a PNP or NPN type sensor, does not imply if the sensor output is normally open (N/O) or normally closed (N/C). They use PNP or NPN type transistors to switch the output when an object is detected. The most popular type of proximity sensor is the 3-wire type. PNP vs NPN for 3 wire connection of a sensorĪlmost all the industrial proximity sensors are solid-state devices, meaning that they do not have moving parts inside. 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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