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Mounting a thermocouple in a drum roaster.

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  • Mounting a thermocouple in a drum roaster.

    I have tested the meter and software and like the setup. I have been using a Fluke 54-11 which came with my 5kg Toper roaster but without any logging software. I tested the CS meter to compare temperature readings and found that the CS meter gave readings of about 40-60 degrees higher at various temperature levels (this was with an empty chamber, stabilizing temperature and then swapping the probes and meters). The CS probe is significantly longer than the one with the Fluke. I am guessing this could be the reason although I am surprised at the magnitude of the difference but perhaps someone more knowledgeable could confirm. I am attaching a photo showing the location of the probe.


  • #2
    Re: Mounting a thermocouple in a drum roaster.

    Id reckon the longer probe would be much more reliable in this situation as it might be possible to shunt some heat through to the front plate of the roaster and reduce the temperature being reported with the shorter probe.

    Have you tried the CS DMM Probe in the Fluke or are the connectors too different?

    Mal.

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    • #3
      Re: Mounting a thermocouple in a drum roaster.

      Yes, you guessed it Mal, the connectors are different. I will try a roast with it soon and make the same heat and airflow adjustments I usually do in terms of approximate timing and see how it turns out.

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      • #4
        Re: Mounting a thermocouple in a drum roaster.

        You might be better off just trying the two different setups in a cup of hot water?

        The CS meter should be accurate, if not it can be adjusted. If you are seeing a big difference then I would wonder if the Fluke is expecting a J-type not a K-type thermocouple?

        You are also pretty close to the axle of the drum and might not have a lot of beans there. Given the choice I prefer the probe just under the sight-glass as this is where the maximum bean mass is and the beans are at their lowest velocity. You might be able to remove one of the screws in the sightglass or get it drilled-out.

        The other "gotcha" is how the probes are mounted, if the outside of the probe is touching the roaster then the temperature of the face drum will hold the temp higher, for longer than if it is insulated. Wrap some paper around the probe or use a teflon plug to isolate it.

        Interested to hear how your testing goes.

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        • #5
          Re: Mounting a thermocouple in a drum roaster.

          thanks Andy I will give it a try and report back. The testing I did previously was with no beans in the drum, so I am not sure whether that makes a difference. I also noticed that the fluke temperature reading stabilzed far quicker than the CS meter which kept creeping up for much longer before "flattening out".

          Anyway the hot water test should reveal where the issue is.

          Not sure what you mean by the "outside of the probe"...does that mean the exterior of the probe for the whole of its length?

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          • #6
            Re: Mounting a thermocouple in a drum roaster.

            Originally posted by 797C737364751D0 link=1236075603/6#6 date=1290662067
            Not sure what you mean by the "outside of the probe".
            If the probe is in contact with the drum (ie: tight fit through a small hole) then the heat via conduction of the drum face plate will heat the probe and create a false reading or a slower reaction. Ergo my suggestion of isolating or insulating the probe mounting point so you are only reading the probe.

            The hot water test will remove the drum mounting variable during testing.

            At the end of the day, the actual numbers on the roast monitor are not that important, what is important is you are logging the readings and seeing the trend differences that are not obvious when watching a meter tick over.

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            • #7
              Re: Mounting a thermocouple in a drum roaster.

              The cup of water test showed almost identicle readings on the Fluke and CS meter. I turned on the roaster and inserted the CS probe about half way instead of fully as I had in the past. The reading was then far more similar to that of the Fluke. I will isolate the mounting point as you suggested Andy. I understand that the numbers themselves are not so important but its nice to get familiar readings in terms of temperature.

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              • #8
                Re: Mounting a thermocouple in a drum roaster.

                [movedhere] Home Roasting - Tips, Tricks etc [move by] Andy Freeman.

                Ok, so same readings then its not a calibration problem... just a mounting problem so Ive split the discussion off from the software/meter thread.

                You should be able to fix it without too much grief.

                8-)

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                • #9
                  Sorry for reviving an old thread can dannyh or anyone who's got experience in installing a probe and the meter in a Toper tell me where's the best position to have it in? Pic will be much appreciated.

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