Proximity switch NPN or PNP

[m_c]

NPN is usually the easier to inteface to most BOBs, but there's not that much difference in terms of prox switches.

A basic summary is NPN will switch a load to ground i.e. it switches the ground/negative side, whereas a PNP switches the positive side to power i.e. it switches the power/positive side.
It's just a case of how they're wired in, and keeping within their operating voltages. Some PNP need over 12V to operate, and that's the voltage they'll output, which would then need some kind of voltage divider/regulator if you're connecting to an input that can only handle 5V, so it's usually easier to go for NPN as then operating voltages are kept seperate with only grounds being connected.


In practical use for limit switches, Prox sensors can't be daisychained. For limit switches which all feed back to the one input (which should be as part of the E-stop circuit), it's easier to use mechanical switches, as you can daisy chain them together easily.
To use prox switches for the same job, you'd really need to have each one control a relay that then have their outputs daisychained together.

[Matt81]

Thanks for the answer. It helped much.

[JAZZCNC]

In practical use for limit switches, Prox sensors can't be daisychained.

Yes they can be daisy chained you just loose reaction time of each switch. In practice for Limts this is not a problem as the delay is in milli secs which is more than acceptable. I wouldn't daisy chain them and share for Home switches because you want the fastest reaction time you can for repeatabilty but for Limts they are fine chained together.

One thing I do for limits to save on switches is to use traveling switches and just have them triggered by a Target at each end of travel, less wiring and things to go wrong.