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RTD calibration issues

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  • #16
    Personally, I'd eliminate the temperature transducers, and go with P2K RTD modules. I've done 5 glue melters with that setup without ANY temperature issues.
    Why worry? If you've done the best you can, worrying won't make it any better

    - Walt Disney


    • #17
      One advantage to using fuses is that a current measurement device can be applied to both sides then the fuse opened to place the meter in the circuit without disconnecting any wires.



      • #18
        Todd - There is no way that we are re wiring our sensors, there is over 2000' of wire runs it is all in conduit, but not happening.

        Yes the 4-20ma loops are all fused to protect the PLC. We are in a wash down environment and have tanks that move so disconnection of m12 connector can blow a fuse vs the PLC. This system was installed and WORKED perfectly for 1 year before I started. I am just the one that fixes and adds more sensors to the system. This is the first of three panels. We are getting a new brew house in the fall, we have 100 more inputs to add to this setup, 50 more outputs too. This does not count the 30 R-485 slaves that we also have planned. That is what is frustrating is that this is my ONLY messed up input.


        • #19
          It pretty much has to be the probe or induced noise.

          The following is based on the assumption that the RTD has the 4-20ma built in.

          To start I'd disconnect the wiring at the RTD and stick a 1.5V battery on the wires. Take a look at your readings and log them for an hour or so. should be rock solid with possibly a low donward drift due to battery discharge. This should eliminate the wiring and the module as the culprits.

          If this doesn't do it, then I'd start looking at tank grounding/bonding along with checking any other wiring that goes to the tank or connecting tanks to see if something is inducing voltage into the ground plane that you should have on each tank. The tanks are bonded to ground right???
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          • #20
            do you own a good multimeter?
            I would start by reading the ma value into the module. Does it match value reported by the module closely? Does it make sense? Next measure ohm across rtd with rtd disconnected from transmitter. Convert ohm to temp and check the value.

            daignose then replace faulty parts. Dont just replace parts until issue goes away.


            • #21
              Well so far so good, three days of solid temps, so it was the temp transmitter that was suspect. Time will tell all though. Can I silicone the temp connection head shut on the threads. I think that steam from the kettle is making it's way in. It is vertically mounted on the top of the copper kettle. Thank you to all that have given so much advice.
              g.mccormick -- I do have a decent one. We ordered what we needed, I won't have a scheduled down time for 1 month. This does not impair our operations. We just switch back to using hand held temp probes from REOTEMP. So yes we just order parts until it goes away. The PLC is a Luxury item that my boss likes to have.