bin2work

I suppose there a number of different issues surrounding this but ive always used the NPN option mainly when it comes to commisioning a piece of plant you can have a small cable permenatly attached to ground this can then be touched on each point of all your output cards to prove the wiring etc from the control panel all the way through to the device ie valve,relay without having any code installed. This can be left in the panel for example on a pernament basis ( in a safe place that is) and it can then be used for fault finding etc. I suppose its just a matter of preference.

regards

Taggy

bin2work
I would generally say the more common logic is PNP in Europe. Siemens has the largest market share in Europe and PNP is the method typically used.

PNP seems to be standard among machine-tool manufacturers. It has advantages.

The "Test with a grounded wire" NPN advantage is exactly the opposite; a single ground fault activates a circuit with (sometimes) disastrous results.

The PNP output just dies (or is inactivated) when a ground fault occurs. That's why the PNP method is prescribed in many industry branches.

Gunnar Englund
www.gke.org

Apologies it should of said PNP on that post, my only excuse is that it was extremely early in the morning here! We have stuck with omron for many years and they have been extremely reliable!

Taggy

PNP seems to be the most common type of switching in Europe.

Mitsubishi Electric PLCs, both Modular and compact type PLCs allow both types of switching so the options are always open to you.

In their compact PLC the sink and source are selectable