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Old November 5th, 2017, 11:31 AM   #1
sabledanny
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A simple PNP/NPN QnA

Hi All,

Currently I have a PNP output device A connected towards an NPN input PLC.

Basically, there's 2 output terminals from device A called "Out1+" and "Out1-"
Just wanted to verify if my connection is correct below?

+24v supply (from PLC) ----> Out1+ (Device A)
Out1- (Device A) ----> PLC input 1

Looking forward to your replies.

Regards,
Danny
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Old November 5th, 2017, 12:01 PM   #2
bernie_carlton
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You might get more certain answers if you supply precisely the part numbers for the device and the place input or links to documentation for each (which you should have already reviewed anyway.)
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Last edited by bernie_carlton; November 5th, 2017 at 12:03 PM.
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Old November 5th, 2017, 06:17 PM   #3
Brandon_K
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What Bernie said. Without knowing the sensor, we can only grasp at guesses.

You say it's a PNP device which implies it doesn't have a sinking output. If that's the case, is it possible that Out 1 is a NO output and Out 2 is a NC output? If not, it's possible you have a NPN/PNP sensor which can go either way.

If you have a truly PNP only device, you would have to use a relay to invert the output signal to be able to be compatible with your NPN input.
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Old November 6th, 2017, 11:09 AM   #4
CapinWinky
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PNP is sinking inputs (you apply 24VDC to the input terminal and it turns on the input) and sourcing outputs (turning on an output supplies 24VDC to the output terminal).

NPN is sourcing inputs (you apply common to the input terminal and it turns on the input) and sinking outputs (turning on an output supplies common to the output terminal).

PNP/NPN has nothing to do with Normally Open and Normally Closed; there are two completely separate concepts.

To connect a PNP device to NPN IO or vice versa requires a relay. If your Device A has a relay output, that could work, you supply common to one pin and connect the other pin to your NPN input. However, the much more likely senario is that your Device A has both a NO and a NC output, and you will need to use one of those to fire a relay that supplies common to your NPN input.
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Old November 6th, 2017, 01:02 PM   #5
kalabdel
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Hello CapinWinky, may I suggest you rephrase your reply so that it's more accessible to the poster.
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Old November 6th, 2017, 01:11 PM   #6
gclshortt
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http://accautomation.ca/wiring-interposing-relays/

The above link will go through wiring interposing relays. There is also references for wiring NPN, PNP and relays.

Regards,
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Old November 6th, 2017, 01:12 PM   #7
dwoodlock
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The easiest thing to remember is that to make a NPN sourcing input card true, you must supply it a path to ground.

Your PNP sensor is the opposite, It supply's a voltage and the input card allows a path to ground.

Or something like that. Focus on the relationships between devices and its easy to remember.

You'll need an interface relay to convert, or an NPN sensor.
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Old November 6th, 2017, 03:05 PM   #8
bernie_carlton
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Note that the OP didn't say he had a two wire device. He said it had two outputs. Still waiting on part numbers for this device and his PLC input to give a knowledgeable answer.
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