Output Current vs Max Current - PLC I/O Cards

Discussion in 'General Electronics Chat' started by abu1985, Oct 18, 2015.

  1. abu1985

    Thread Starter New Member

    Oct 18, 2015
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    I'll look up current ratings for devices to make sure I do not overload the device. On National Instruments data sheets they use the term "output current" instead of maximum current. Now I always use relay output cards but this case I have to use a Sourcing Output card.

    Is "Current Output" the same meaning as "Max Current"? Or am I missing some detail on Sinking/Sourcing Output cards?

    Note: I could call NI and ask them for the details, but I have been coming to allaboutcircuits for years, and wanted to use this as an ice breaker to get started on the forums.

    Thanks!
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
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    You can essentially use the Output current to mean the maximum.
    Are these AC or DC output cards?
    Max.
     
  3. abu1985

    Thread Starter New Member

    Oct 18, 2015
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    It's a DC output card. It has an output current of .75A. I don't see a Max current rating so I'm assuming that output cannot exceed 750mA.
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Correct.
    Single output or multi outputs ?
     
  5. abu1985

    Thread Starter New Member

    Oct 18, 2015
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    8 Ch output card (.75mA per output). The current is sufficient for an LED stack light but if the end user wants to use one of the spares, they'll most likely have to fire a relay first.
     
  6. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    Can you supply a link to the datasheet?

    I've used NI products and they tend not to show all relevant needed info.
     
  7. abu1985

    Thread Starter New Member

    Oct 18, 2015
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  8. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    You kinda have to read INTO the datasheet. Short circuit trip time, the short circuit behavior table and the output Z tell you a lot about the behavior. It does tell you, that 13 A over 10 uS is permissible. The table has some other values. You do know the continuous ratings, the absolute maximum ratings and some in between stuff.

    Short circuit conditions are going to be dependent on the voltage you use and the output Z. Simply V / 0.07.
    It also suggest that at 1A, the module is not likely damaged.

    If your really concerned, you can select a fuse based on the blow time and expected short circuit conditions. e.g 0.750 A continuously and blow between 0.75 and 1 A quickly.

    I yipped at them to provide the equivalent I/O circuit of whatevr is hooked to the outside world many years ago. It must have fell on deaf ears.
     
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