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Decimal point with 4-20mA loop

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  • Decimal point with 4-20mA loop

    Hi, i'm new here.

    Didn't find what I need by searching, so here is my question:

    I have a 4-20mA loop for temperature reading. I will create somekind of thermostat with it by comparing its register with one I will write in data with a HMI.

    How can I make sure when I set it up that I will have at least 1 digit after the decimal? (ex. 18.7 Celsius) Do I have to use DF registers for my loop and my setpoint? Does the HMI will understand the decimal point or will I have to configure it also?

    Thanks for any help, info, direction to tutorials...

    Sylvain


  • #2
    As you get into this application you will find that the Click and pretty much any hmi have the flexibility to accommodate your decimal point needs. When you have the specific Click and hmi please repost with the details. I'm sure you will receive specific help.
    thePLCguy

    Bernie

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    • #3
      I do not have the PLC in hand to try, but i am already writing my project. Should I use DF or DS registers for decimal point?

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      • #4
        If you are setting up the scaling in the analog module then either will work. If you use a DS then allow for an implied decimal point - e.g. 1234 = 123.4 degrees. You should be able to display it properly on the hmi and provide for a similarly formatted entry. The DF may be more intuitive while viewing the program.
        thePLCguy

        Bernie

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        • #5
          I'm a little late to the party, but the CLICK analog uses DF by default so I'd tend to just stay with that. If one was communicating with some very simple device that didn't understand floating point, then an integer with an implied decimal point would also work. The CLICK has very little problem converting types (even conversions that don't seem to make sense) so you can copy the DF the analog input gives you to a DS without problem. As Bernie implied you'll want to do the implied decimal point in the "automagic" scaling setup for the analog input since copying to a DS will remove any fractional part (I'm not entirely clear if it rounds or truncates, but I think it rounds)

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