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simple differential temperature control

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  • simple differential temperature control

    Click PLC; C0-04THM. I am an absolute Newbie. I need to control a circulator for a solar hot water project. The circulator relay will turn on when a temperature difference of ten degrees F is reached between the two K type thermocouples.The program will not include the safety mechanisms built into the system. Safety is independently controlled. I need a few rungs which will detect when a differential temperature is reached between two floating temperatures and latch the circulator on for, say ten minutes. Thanks for your time. GREG


  • #2
    Here is a simple program implementing what you asked for. I picked the first Click model and added a power supply. Obviously you can modify as needed.
    Attached Files
    thePLCguy

    Bernie

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    • #3
      Possible modifications come to mind such as:

      Continue circulator until the difference is less than 10.0 or possibly continue until the difference is less than a lower amount.
      thePLCguy

      Bernie

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      • #4
        df1, df2 registers hold the temperature readings. df5 holds the difference. y1 turns on for 10 min
        the compare instruction should be >10, not =10. other than that, make sure you choose the sensors such as the difference gets +10 rather than -10.
        you should try the program with output disconnected just to make sure it cycles the way you want. do not just connect everything and expect too work, make sure you do the testing prior.
        Attached Files
        Last edited by Alexandru; 12-09-2018, 12:53 AM.

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        • #5
          Alexandra's using DF5 for the difference is good if you decide to use the other two inputs from the analog module.

          I did the two tests in the first two rungs because the Click doesn't have the 'absolute' function. Another way around this is to just do a single subtraction without the comparison but then immediately after test if the result was negative. If so just just subtract the result from zero.
          thePLCguy

          Bernie

          Comment



          • #6
            Iíve assumed one sensor is always hotter, so no need for absolute value.
            Program is not for use as is, just a pointer. In case of liability, please remember the responsibility lies with the one who implements the program, not the one who had a suggestion.
            there are flaws in that program. The purpose was never to do someone elseís work, but only to make a suggestion. sorry for repeating myself, to me is important that this aspect is very clear.

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