Need help figuring this out.

Discussion in 'General Electronics Chat' started by whygumby, Aug 3, 2011.

  1. whygumby

    Thread Starter New Member

    Aug 3, 2011
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    I need help wiring up a wiring senario. What I am building is a test fixture that the customer will plug into their plc cabinet. I have digital inputs digital outputs and analog inputs to test. The issue I have is some of their analog inputs are 4-20ma and some are 0-5vdc I would like to set up a toggle switch inline to change the pot switch to control either signal depending on what the controler signal is needing. I know this cannot be that complicated but I think I am making a mountain out of a mole hill overthinking it. I have a 24vdc power supply in the panel that I will be getting voltage from for power in the loop. Thanks ahead of time for any help you can give me.
     
  2. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    Can you just explain more, for technical help.............
     
  3. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Will this test fixture test the plc itself, or their plc program. In other words, are you going to supply a test program where all the inputs/outputs are at the same address. Are all the plc's set up the same, with the different type cards in the same address location.
     
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    I'm wondering what the intent of such an exercise would be. I'd think that the integrity of the field devices would be of more importance than simulation, unless your evaluating the PLC prog, which would probably be better served by an emmulator.
     
  5. whygumby

    Thread Starter New Member

    Aug 3, 2011
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    It will be testing the wiring going all the way out to the plug on the outside of the enclosure. The plc already has program loaded into it with what the analog input value should read. I am building this to use on multiple cabinets of theirs with 8 analog inputs each, which will change to be a 4-20ma scale or a 0-5vdc scale.
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    A simple 250 ohm resistor will convert a 4-20mA output to a 1 to 5V signal so the same A2D can sense both types.
     
  7. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    wouldn't then a simple ohm reading from connector to terminal suffice. Software scaling should include the field device and for that matter, the process it's measuring.
     
  8. whygumby

    Thread Starter New Member

    Aug 3, 2011
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    It takes to long to ohm out all the pins when we have alot of panels to check out. If we can just plug into it with our fixture and give each pot a few spins and watch the touch screen we dont even have to get the drawing out for check out. They will final setup scale in the field when mounting it to the scales cabinet.
     
  9. GetDeviceInfo

    Senior Member

    Jun 7, 2009
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    then a din mounted signal converter should suffice. Sounds like a single pot (reference) is all that's needed.
     
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