Many modern PLC input cards can be configured and wired to be either 'sinking' or 'sourcing' although it will usually necessitate all inputs on a particular input card being configured the same. Can't find what you are looking for? Reach out to our Customer Care team to receive information on technical support, assistance for complaints and more. Contact Support. Leave a Reply Cancel reply Comment.
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Search for:. So early solid-state sensors were more likely to use NPN transistors in their switched outputs, so they were load-sinking. The machine bed was connected to ground. When a metal part, such as a piece of sheet steel or a stamped metal part, made contact with the whisker wire, the circuit became grounded and the relay pulled in.
This was a load-sinking connection. NPN control circuits. With PNP, if a load wire shorts to ground, the short can be found relatively easily because there may be visible damage due to the higher-than-normal current that would flow in the absence of a load impedance. An unprotected, unfused sensor may also have its output blown. If the PNP sensor has integrated thermal, latching, or pulsing short-circuit protection, the existence of a short circuit condition on the load wire will be apparent at the sensor.
In the case of a short to ground in an NPN circuit, there is no abnormal current flow; the load is simply pulled in regardless of the sensor state.
This could prove to be somewhat difficult to detect, because if the sensor associated with the grounded load wire is examined, it will be found to have no fault. In the modern industrial world, NPN is considered more common and popular in the Asia-Pacific region simply because of legacy practice and the desire for backward-compatibility. Nice website and good explanaition, however I still dont know in which situation should I use each other.
They have diferences, but why should I use one instead of the other? What do I gain using one or the other? Which one is best?
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