Sink/Source input definition warning

[xyzz]

Attention everybody.
The Mitsubishi definition of Sink/Source input is directly opposite to the Allen-Bradley's.
Mitsubishi defines input by being sinked or sourced by the sensor or contact.
AB defines input by being itself sinking or sourcing for connected external device.
As a result, our company just built a machine with sensors opposite to customers specification.
Our standard is Mitsubishi but this one was built on AB by cutomer's request.
Conclusion: always ask to specify NPN/PNP, not Sink/Source inputs.
By the way, Omron and Aromat do exactly this.

 

[cesarfranca]

Dear ZYZZ!

Why choose between NPN and PNP input technically speaking?

 

[xnuke]

xyzz,

"Conclusion: always ask to specify NPN/PNP, not Sink/Source inputs."

I develop a different conclusion. Learn about the parts you're integrating into your system. A bad assumption was made that is getting your company in trouble, all because somebody didn't read the equipment datasheets and manuals. Don't use the excuse that the spec should've read NPN/PNP instead of sinking/sourcing; a designer should be able to work with whatever brands are specified. I make a special effort to get to know the parts I'm using, especially when they're different than what I've used regularly. Even then, some products change over time without notice to people who've used them before, so always check out the manufacturer's information that comes with the part, even when you've used that part a thousand times.

Besides, some companies offer inputs that accept both sinking and sourcing. I found that out when I started to work with GE Fanuc.

Better luck next time.

xnuke

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[xyzz]

Xnuke, I am capable myself to learn on own mistakes, but your conclusion only looks correct.
We are talking here about using exactly the same words by two different companies for definition of exactly opposite things.
Everybody may pretend to understand black vs white without clarifying the definitions with authors each time.
Imagine buying manual transmission car instead of automatic, because such is this manufacturers definition.
And imagine your reaction on a following advise to read manuals before buying.
By my opinion, Mitsubishi definition is correct, this is another reason of why I simply could not imagine opposite.

Cesarfranca, the signal source is PNP or NPN, mot the PLC input.

 

[cesarfranca]

Dear xyzz!

I think I must clarify my question a litle bit more.
Let's forget about the plc type or manufacturer.
Let's think about the customer point of view only regarding about the field device, if you can agree with me. Then in this case, why choose between an NPN or PNP imput technicaly speaking?

Best Regards!

cesarfranca

 

[plcsavvy]

Lighten up a little guys, he made a mistake. It's not the end of the world, but a learning experience. Live and learn

Best regards, PLCSAVVY

 

[xyzz]

To Cesarfranca.
NPN open collector output is historically more conventional in electronics.
Today PNP and NPN devices are practically identical by price and capabilities.
So, choosing one is more a question of company standards and stocking policy, customer request, etc.
Still, some devices exist in NPN output version only, and very seldom vice versa.
From my experiense, this includes barcode readers, light curtains and some very special sensors.
Some another considerations may have place.
I sometimes simulate timer interrupt, lacking in many inexpensive PLCs, by connecting a high-speed pulse train from output to input of the PLC. This determines the inputs polarity.
The same in a case of a simple handshaking between two PLCs by direct I/O connections.

From the hardware point of view, NPN output may be safely shorted with zero (logic ground) and PNP with power.
For some reasons I believe the first is more likely to happen, so NPN sensors based system is more damage proof.
This is, however, my own opinion.
Inputs of most PLCs are sink/source configurable, but all at once (we are talking of single-unit PLCs here).
Extension modules may be configured differently.

 

[cesarfranca]

Dear zyzz!

I apreciate too much your answer and I will use your comments to help me in future projects, also I will study this subject deeply to as soon as possible bring to this Thread more information and examples.

Thank you for your help!

Cesar.

 

[xnuke]

plcsavvy,
My comment wasn't meant to slam anyone for making a mistake, but rather to try to correct what I saw as an erroneous conclusion learned from the mistake. I've made many mistakes (and I'm sure more are ahead), but to draw wrong conclusions from them wouldn't help me learn anything.

xyzz,
I'm sorry if you took my comments personally. They weren't intended to focus on the mistake, but rather the conlusion you reached. I only have two words in regards to your design problem (and your transmission analogy): Caveat emptor.

xnuke

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[BluBryMan]

You may want to make your NPN, PNP decision based on whether you will ship product to Europe and want to attain a CE mark and declare compliance with the machinery directive. In this case all outputs should be active high. You never want a shorted cable to be able to activate a sequence that could harm the user, machine or product.