N/O NPN sensor

Discussion in 'General Electronics Chat' started by mic2182, Nov 12, 2013.

  1. mic2182

    Thread Starter New Member

    Nov 12, 2013
    1
    0
    Hi, I need to replace a sensor on a machine at work, Ive checked the other sensors (fibre optic) on the machine and they are all NPN, so ive got a photoelectric sensor to go in its place which is also NPN, so it should just be a straight swap, but I’m not getting the required output from the photoelectric sensor. The sensor looks to be working fine I’m just having trouble getting the right signal. Both sensors (fibre & photoelectric) are 24VDC, 3 wire (Brown, Blue & Black), NPN, open logic on the PLC.
    When I test the other fibre optic sensors, I test between the output from the sensor and the –vdc, so I get a resistance through (0.000) when I MAKE the sensor, which means I’m completing the circuit at the PLC which gives me 1 count (the sensor is for a counter) but when I do the same with the photoelectric sensor I don’t get the same, I get -0.747.
    Basically I need the same out-put as from the fibre optic senser to get the counter to operate. Can anybody help me understand why I can get the photoelectric sensor to work.

    SICK - WTB4-3N3162 -
    1028089

    Photoelectric proximity sensor

    And

    OMRON INDUSTRIAL AUTOMATION - E3X-A11 - SENSOR, FIRBRE OPTIC, NPN

     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,524
    2,369
    This is an open collector NPN so if testing separately from the PLC then you need to provide a load resistor, also the reading will be from output to 24v+ve.
    When connecting to the PLC you require a sourcing input, as the NPN is a sinking device.
    Max.
     
    mic2182 likes this.
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