Poximity Switches of P&F Make

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If it isn't magnetic then it's either inductive or capacitive.

P&F say this.

Perform more independent research and come back with a specific query for clarification if you are still struggling.

It's most likely of a capacitance type. Basically your prox is basically one side of the capacitor and the object that the prox is detecting forms the other side of the capacitor and the air gap is essentially the di-electric (insulator). The closer the object is to the prox, the less capacitance. Sorry, I know it's a pretty basic explanation, but I hope it's helped.