NPN vs PNP sensors

How to wire PNP and NPN sensors? What’s the difference and why should anyone care? If you’re confused by the terms PNP and NPN, then hopefully this post will shed some light on the differences between the two.  In the context of this post, they refer to the construction of a sensor’s transistor and whether it has a p-type or n-type semiconductor. The “N” stands for “Negative” and the “P” stands for “Positive”.  With respect to sensors, an NPN device is one that can switch the negative side of the circuit while a PNP device switches the positive side. The […]

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Testing a PNP or NPN sensor

How to Test Whether a Sensor has a PNP or NPN Type Output Using a Multi meter? If you are replacing a 3 wire sensor which operates on DC voltage, it is important to know whether the sensor’s output is a PNP or NPN type. Often this information is printed on the sensor itself, but it is not uncommon for it to be scratched off over a long period of time. Set the multi meter to DC voltage. This is indicated by either the letters “VDC” or “DCV” or by a symbol which looks like 3 dashed lines over a […]

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What is the difference between PNP and NPN when describing 3 wire connection of a sensor?

Most industrial proximity sensors  (inductive, capacitive, ultrasonic and photo electric) are solid state. The term solid state refers to the type of components used within the sensor. Solid state electronic components such as transistors are used to switch the output of the sensor upon detection of an object. Two specific types of 3 wire sensors are available; PNP and NPN. The difference is a result of the internal circuit design and type of transistors used. A key point to observe is that PNP and NPN has nothing to do with whether the sensor is normally open (N/O) or normally closed (N/C), i.e. a PNP sensor may be either N/O […]

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