PNP vs NPN output on sensors 1

[DReimer]

Hi,

I'm with an oem and we use several inductive and photoelectric sensors on our equipment. We have been using NPN type sensors since the dawn of time, dating back to the days we used printed circuit boards for machine control.

In the course of trying to find a photo sensor to solve a challenging application, one of my vendors has mentioned that they sell far more PNP type sensors than NPN. I've also noticed, anecdotally, that there seem to be more PLC modules and other input devices that are designed to work with a source output.

Does anyone here have any information about the market for these sensors? Any hard data about North American preference for either? I am contemplating a switch, but it is a fairly substantial logistical issue for us and I'd like some evidence on my side before I embroil my company in what will surely (given our past record) become a minor nightmare.

In the absence of hard data, just the gut-feel of you guys would be nice.

Thanks,
Dean

 

[Skogsgurra]

Well, I'm not in Nort America (and not in South America either). Here, in Europe, there are standards saying that machine-tool control and process control shall be done using PNP sourcing outputs and P level (+24 V) active inputs. This is mostly to improve safety (more easy to make an active circuit failsafe than one where a broken or loose wire could start a machine). I used to have an old standard in the shelf but can't find it. Be back soon with an EN number - or something...

Gunnar Englund

http://www.gke.org

 

[VEBill]

If a broken wire starts your machine, then the pull-up resistor should be relocated to the receiving end of the cable.