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NPN & PNP sensors

Discussion in 'Electronic Basics' started by b, Apr 4, 2006.

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  1. b

    b Guest

    Hello. Can anyone explain the difference between npn & pnp sensors as
    used in industrial controls systems. How they work and why you would
    choose one type over the other.
  2. NPN outputs pull down to the negative supply rail and drive loads that
    are connected between the output and a positive supply. PNP outputs
    pull up to the positive rail, and drive loads connected between the
    output and the negative supply rail. If you have a lot of loads (like
    a PLC input card) hat has all its inputs commoned to the negative
    rail, you use PNP outputs. If the loads are all commoned to the
    positive supply rail, you use NPN outputs.
  3. Siong Boon

    Siong Boon Guest

    You can also think of it as a normally open or close configuration. Normally
    logic 0 or 1, active low or high. Depending on how you interface your
    There many other ways of looking at this.
    The NPN PNP terms basically come from the transistor
    that is at the output of the sensor, acting like a switch.
    For further information, you may like to search for topic relating to using
    transistor as a switch.

    Best Regards,
    Lim Siong Boon
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