Does any relation between Sinking/Sourcing PLC inputs and NPN/PNP sensors?

Tofo

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May 2013
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For example, I need to choose PNP sensor for a Sink PLC input.

Also do Sinking/Sourcing PLC inputs relay to the PLC reading? e.g. PNP sensor for a Sinking PLC input is 'High' in PLC when PNP sensor is ON , but PNP sensor for a Sourcing PLC input is 'High' in PLC when PNP sensor is ON.

Thanks
 
An NPN (Negative-Positive-Negative) output from a device is used with sinking inputs. It makes a connection negative (-).
A PNP (Positive-Negative-Positive) output for a device is used with sourcing inputs.It makes a connection to the positive terminal (+).
 
An NPN (Negative-Positive-Negative) output from a device is used with sinking inputs. It makes a connection negative (-).
A PNP (Positive-Negative-Positive) output for a device is used with sourcing inputs.It makes a connection to the positive terminal (+).
To expand...

Think of them as working in a complimentary fashion. You need one thing as PNP and one thing as NPN to mak it work.

NPN=sinking
PNP=sourcing

If you have a sinking input, it's NPN. You need it's compliment to source the current to the input: PNP

If you have a sourcing input, it's PNP. You need it's compliment to sink the current from the input: NPN

Automation direct has a pretty fair document on it.
http://www.automationdirect.com/static/specs/sinksource.pdf
 
You can throw out, in my opinion, the terms sinking and sourcing because it has not been used consistently throughout the industry and can be considered both ways depending on what point of view you are taking.

That said, It also has to be pointed out that strictly speaking, PNP is not necessarily only positive logic and NPN is not necessarily negative logic. There are reasons why one is used over the other depending on the type of logic you are using, and that has been covered in previous threads.
 
You can't throw it out, because if, for example, the card says "sinking input" or "sourcing output" then it forces you to think about it. In fact, I submit the inconsistency exists precicely because the information isn't disseminated enough.

End mini-rant.:D
 
When I see 'sourcing' or 'sinking' I turn skeptical until I see an electrical schematic or at least an 'equivalent' diagram of the input or output circuitry on the card. Those I understand.
 
OK. Now I want to make sure that I understand correctly.
From what I understand from the replies, if I have a Sourcing Input PLC, I will need to connect a NPN sensor.
If that is correct, will my PLC detect Hi or Low when my NPN sensor detect something?
 
The answer, of course, is "it depends".

Traditionally speaking, if the sensor "turns on" when it detect something, then the input will also "turn on"/"go high"/ "set to one"/"whatever-else-one-wants-to-call-it".

In reality, the design of the sensor comes into play. Some are designed to "turn off" when sensing an object.

What sensor are you using? If you give us a make/model we nay be able to be more specific in what to expect.

EDIT: Bernie beat me to it. My fingers just don't fly over my phone... ;)
 
The answer, of course, is "it depends".

Traditionally speaking, if the sensor "turns on" when it detect something, then the input will also "turn on"/"go high"/ "set to one"/"whatever-else-one-wants-to-call-it".

In reality, the design of the sensor comes into play. Some are designed to "turn off" when sensing an object.

What sensor are you using? If you give us a make/model we nay be able to be more specific in what to expect.

EDIT: Bernie beat me to it. My fingers just don't fly over my phone... ;)


Ok. I have a Sourcing Input PLC and I need to connect a palm sensor to the input

http://info.bannerengineering.com/xpedio/groups/public/documents/literature/33109.pdf

The sensor has 'NO' and 'NC' relay available. Should I consider that I need a NPN sensor? OR This type of relay sensor does not apply of what explain here
 
OK. Now I want to make sure that I understand correctly.
From what I understand from the replies, if I have a Sourcing Input PLC, I will need to connect a NPN sensor.
If that is correct, will my PLC detect Hi or Low when my NPN sensor detect something?
Nope! You need PNP output from your sensors.
 
Nope! You need PNP output from your sensors.

I thought sourcing PLC input should connection to NPN

From JordenCClark (the 2nd reply), "If you have a sourcing input, it's PNP. You need it's compliment to sink the current from the input: NPN"
 

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