OUTPUTS - PNP or NPN in Europe

[bin2work]

Could anyone tell me which is the better option or most widely used in Europe regarding Transistor output cards? I have used both in many of my control systems but I want to know if there is a more preferred one used in Europe. I have some machines from Japan which are NPN switching but I have a new one which is PNP switching

[BobLfoot]

PNP Switching or NPN Switching I assume you are talking DC inputs and outputs. I get confused by the terms AB uses here in America namely DC Sink or DC Source. Most of the 1990's Japanese systems pulled outputs down to 0V for True or Logic 1 and expected Inuts to be 0V for a logic 1. When I switched to AB I found Outputs were pulled up to 24V for Logic 1 or true and Inputs pulled to 24V for logic 1. Hope this in target.

[TERdON]

We always use PNP unless we have to interface with some weird stuff that haven't been adapted for the european market yet. Hope this answers your question well. :)

[forqnc]

I prefer this method also, since I feel it's easier to troubleshoot when you can check for Voltage. Especially when Inputs can be in series and you are not sure which sensor/switch is a fault.

[TimWilborne]

The problem I have with taking an Input or an Output to ground is what happens if the wires get smashed in the conduit or something? It signals the that the input is made or even more dangerous is that it can turn on an output. Yes with a PNP you are going to go through a few boxes of fuses trying to hunt down the damaged wires but which is worse, spending money on fuses or turning on Inputs and Outputs when they are not suppose to?

[IO_Rack]

Realizing this leads into another disscussion...... What you state above is one good reason to isolate your power supply from ground. There is a ton of disscussion on this somewhere on these boards.

[BobLfoot]

Your statement TW is correct in most I'll call them American systems where 0V DC is also ground. But in the systems I worked with 0V is not grounded and neither is 24V. Thus a shorted conduit does not turn on outputs.

[TimWilborne]

Very true Bob, non grounded systems do not have this problem

[Snerkel]

PNP all the way. Non-grounded versus grounded. Unless a good reason otherwise always grounded. Big problem with non-grounded is that you still have the potential for two faults to then cause big problems. If you get a ground fault, eg the positive gets shorted accidently to ground... then an output cable gets shorted to ground you then have an output that appears to be on. A properly grounded system shouldn't have this sort of problem as either fault should take out a fuse.

[Sleepy Wombat]

Since you oringially asked for for output cards i would say that it can be either... Generally, outputs will be localised therefore i am not aware of a particular preference in Europe for outputs....And generally speaking outputs a more common to be relays or driving relays..... However, i believe that the inputs preferred method would be PNP or if you like switch the active into the card... To be honest, i hate all of the terminology of Sink, Source, PNP, NPN.....why not just keep it simple...Is the input card positive or negative switching or HI/LO switching... In AB, Sink/Source refers to the PLC card.....this can be confusing for the guy then needs to a Sourcing Sensor..because he then has to connect to a Sink card....

[JesperMP]

It is almost 100% PNP over here. The last time I had to deal with an NPN was more than 10 years ago.

[BobLfoot]

Thanks Sleepy -- Nice to Know I am not alone in the dislike of Sink / Source and eetc.