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  • RTD calibration issues

    I have one temp input that keeps drifting off 10 to 20 degrees of after I have done a non linear scale on the 4-20ma signal I get from a Universal Prosense temp transmitter. It was a 20 point calibration that I did, it was accurate to within .2 degrees. I have replaced the $500 custom rtd probe, it was great for 2 weeks now its back again with the drift. I am replacing the temp transmitter, the only thing is the wire to replace. I have 10 others that have the same configuration as this that all just work great. Am I just missing something here?
    Thanks In Advance
    Mike George
    Golden City Brewery

  • #2
    hydromike, please describe your setup a bit.
    From your other post, we know that you have a P2K CPU. Is this the same CPU?

    I may be asking dumb questions and you may have already checked these things, but:
    What part number is the RTD input module (I will assume P2-06RTD since PxK families only have one model each).
    If you can get to it, what is the full serial number from the label on the module. That number on the label may have important FW rev info.
    Spring clamp/screw clamp P2-RTB?
    Have you tied any/all unused RTD inputs to COMMON?

    2-wire, 3-wire, 4-wire?
    Is (all) grounding adequate?
    Is shielding?
    Any extension cabling?

    Are all CPU firmware revs the same?

    Comment


    • #3
      kewaki, I think hydromike is using a 4-20ma input.

      Comment


      • #4
        Originally posted by bsinkovich View Post
        kewaki, I think hydromike is using a 4-20ma input.
        Yeah, I don't have much experience with RTDs. I have a basic understanding. I totally failed to acknowledge the temp transmitter, too! thx
        My temperature monitoring/controlling needs are usually met with type j or type k thermocouples.

        Comment


        • #5
          Yes PK2, 3-wire grounded properly with shield, no extension cable. This goes into a 4-20 input. This worked for over 1 year then this started happening. We did have some tig welding done on this tank, but it was all powered down.Click image for larger version

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          Comment


          • #6
            The Left Zip link is the the input for the kettle.

            Comment


            • #7
              Hi Hydromike,
              I would check the power supply to the system. Ensure it is outputting the power required.
              Also, check the terminal connections on the wire to ensure they are tight.
              Ensure that the wire is run by itself. Running in the same conduit with power cables or VFD wires could cause drift.

              Just a couple of thoughts.
              Regards,
              Garry
              _________________________________________________
              Garry
              ACC Automation
              https://www.accautomation.ca
              Connect with us on Facebook: facebook.com/accautomation/

              Comment


              • #8
                The RTD was made by FTI Sensors International, a LTS-CA-3000. All of the latest firmware on the PLC and on the C-more display.

                Comment


                • #9
                  Garry, Yes the voltage is all correct, everything is tight. This is mind boggling to me. All of the runs out of the box are all low voltage, all vfds are in a separate conduit.

                  Thanks for the input on this issue.

                  Comment


                  • #10
                    You are not running the RTDs thru fuses are you?

                    Comment


                    • #11
                      Originally posted by hydromike View Post
                      I have one temp input that keeps drifting off 10 to 20 degrees of after I have done a non linear scale on the 4-20ma signal I get from a Universal Prosense temp transmitter. It was a 20 point calibration that I did, it was accurate to within .2 degrees. I have replaced the $500 custom rtd probe, it was great for 2 weeks now its back again with the drift. I am replacing the temp transmitter, the only thing is the wire to replace. I have 10 others that have the same configuration as this that all just work great. Am I just missing something here?
                      Thanks In Advance
                      Mike George
                      Golden City Brewery
                      I'm curious, what is the span of the temp transmitter (or more relevant, what percentage of full range is the 10 to 20 degree drift you are seeing)?
                      One theoretically nice thing about current loop is that they can be relatively easily monitored with another piece of equipment. I think I'd first check that the values getting to to the PLC where about right first, if "10 to 20 degrees" is a significant fraction of the total span that should be fairly east, maybe not so easy if it is a tiny fraction, but I'd still try to check.
                      While I can't justify the price, if you are working on a system with 10, $500 probes (+ transmitters etc.) the $1500 for a Fluke 773 or similar might not be totally crazy.

                      you say you "are" replacing the temp transmitter, not "did" replace, I think that would have been the first thing I did, unless the probe was obviously open or shorted an RTD would be low on my list of suspects, especially at the temperatures a brewer would use, a foundry might be a different matter.

                      Comment


                      • #12
                        Where are the Universal Prosense temp transmitters?

                        Are you running the 4-20 signal wires thru fuses?

                        Comment


                        • #13
                          Does it always drift the same direction? Higher could mean resistance is increasing somewhere in the transmitter input. Can you measure the RTD resistance with a good meter when the drift occurs and compare it to an appropriate chart?
                          ADEN ENGINEERING
                          Automation & Electronic Controls

                          Design, Build, Repair, Training

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                          • #14
                            So after reading the responses, we ordered a new RTD transmitter, I can't find the Universal ones that we currently have. The company that made the rtd sensor for us is sending us a new one just for shipping charge too. The drift varies, we have turned off and on loads that are close to any of the conduit and there is no change. Once I get the new parts in I will update the thread.
                            Mike George
                            Golden City Brewery

                            Comment


                            • #15
                              Are you running the 4-20 signal wires thru fuses? Sure are a lot of them in the pictures

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