[laserpilot]

Hi guys,
I am about to start a new machine build and want to fit proximity sensors rather than the old click style switches. I want to use Normally closed as they are safer with regards to wiring breakages etc. This supplier offers them in both NPN and PNP versions. I am not sure which is the correct type to get. Here is the link to the items:

https://www.aliexpress.com/item/32343901022.html

would any one be so kind as to take a look and tell me which type to buy please. If you scroll down he lists all the different types

thanks in advance.

[wizard]

It will depend upon what you are booking the switches up to. Frankly this can be a bit confusing! Here is one explanation: https://www.google.com/amp/s/instrum...g-and-sourcing. This one might be a bit better: https://library.automationdirect.com...cing-concepts/.

So you can’t do much until you know what sort of devices you are hooking up to. Also it isn’t uncommon to need both PNP and NPN devices in a control system. Sometimes though you can save yourself some grief by designing around one or the other input device.

For example in the plant I work in the engineering department designed around devices that for the most part used PNP devices. This greatly reduces the issue of not having the right device on hand. Also those older input devices are often just as good as the solid state ones. For example snap action switches are often a better choice in metal working machines if the switch can’t be shielded from swarf. Magnetic reed switches are also pretty reliable in the right situations, both of these don’t care about sinking or sourcing. So I don’t think one can say that electronic prox switches are always the right solution.

By the way, you are right to be concerned about reliability as for the most part I don’t replace a lot of switches for a failed switch mechanism. It happens of course but far more switches get replaced because of the wiring to them failing. Often this is the result of being run through drag chains, getting snagged or destructive operators. The problem from the stand point of reliability though is that the cables can both short and go open so a NC switch isn’t a great increase in reliability. Actually the most often occurrence is a slight intermittent cable that drives you nuts until you find it.

[joeavaerage]

Hi,
if you intend to use these as limit switches be aware that you cannot hook them all in series like you can microswitches.

Craig