PNP sensor PLC input to NPN PLC input

Discussion in 'General Electronics Chat' started by derekpaul, Dec 30, 2010.

  1. derekpaul

    Thread Starter New Member

    Dec 30, 2010
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    HI all
    I am trying to use a PNP proximity sensor 15-30 Vdc into a plc expecting an NPN type sensor as a quick fix. I cannot change the common rail as all the others sensors are NPN, and do not have a small relay available. Any ideas?
     
  2. The Wraith

    New Member

    Jun 19, 2010
    3
    1
    I think you might be able to use a pull down resistor to hold your input low until the sensor is triggered and a n.c. contact in your ladder logic. Care to give more details? What plc are you using? I assume you are working with 24vdc. Is that correct?
     
  3. derekpaul

    Thread Starter New Member

    Dec 30, 2010
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    the "PLC" is actually not your standard type, it uses +15Vdc/0Vdc as the supply to NPN sensors. 0Vdc is the HIGH when sensors are ON, so off course using a PNP sensor, 15Vdc is switched as being ON, thus the "PLC" thinks the sensor is OFF. So I need to pull the input HIGH, then when my PNP sensor switch's ON with 15Vdc, somehow pull the input LOW.
    Does this clarify it better
     
  4. derekpaul

    Thread Starter New Member

    Dec 30, 2010
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    0
    added to the above, I have no means of accessing the logic. Very old Industrial Washing Machine
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    OK, this should work. If you can't get 2N3904, almost any general purpose NPN will work.

    EDIT: I forgot to draw the grounds for the sensor and the PLC. All grounds should be connected together.
     
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