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Is NPN normally closed?
An NPN output is commonly called a “sinking” output. When the sensor senses an object it will connect the output to the negative supply. NPN, PNP, and Configurable type sensors come in a Normally Closed and Normally Open configurations.
How does NPN transistor work?
The NPN transistor is designed to pass electrons from the emitter to the collector (so conventional current flows from collector to emitter). The emitter “emits” electrons into the base, which controls the number of electrons the emitter emits. The transistor is kind of like an electron valve.
What’s the difference between a PNP and NPN transistor?
Above a certain point a transistor reaches saturation, allowing electrons to flow freely. PNP transistors (sometimes called “sourcing sensors”) performs the same job, but is set up so that a negative voltage must be applied to the base pin to allow current to flow from the emitter to the collector lead.
The switching logic PNP or NPN are not related to the supply voltage of the sensor or the operating voltage of the input. Referring to the NPN wiring diagram above, note that the sensor supply voltage and the high side of the load are connected to the same point and are therefore at the same voltage.
Can a PNP sensor be mixed with a NPN sensor?
In most PLC’s it’s possible to configure cards as PNP or NPN. Another thing to note, is that NPN and PNP sensors should never be mixed on a PLC input card. Furthermore, if you have a specific type of PLC input card that’s NPN or PNP, It’s important to make sure that you choose sensors that match.
Why are PNP sensors sometimes called sinking sensors?
PNP sensors are sometimes called “sourcing sensors” because they source positive power to the output. NPN sensors are sometime called “ sinking sensors” because they sink ground to the output.