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  1. #1

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    Thermometer Calibration/Jobo Processor

    I am wondering whether the temperature read out on my Jobo CPP processor is accurate and if there is a way to check it's calibration. There is a difference of .6C between the Jobo and my tried & true Kodak Process thermometer. I don't know which to believe. It doesn't matter for B&W but the temp. tolerance for E-6 is .3C. Any suggestions?

  2. #2
    rwyoung's Avatar
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    So leave your Kodak thermometer in the water bath and tweak the Jobo temperature knob until you are happy.

    It will take some time for the temperature to stabilize. Maybe put in a tank and let it roll to swish things about. And also watch to see how much hysteresis the Jobo controller allows.

    I've only ever done B&W with mine. I don't worry much about the absolute temperature since I'm going to be testing for personal EI and developing time anyway. Just always set it to 20C and wait to start a run until I hear the relay cycle a few times.
    Don't sweat the petty things and don't pet the sweaty things! http://rwyoung.wordpress.com

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    I wouldn't trust the JOBO display. On my CPP-2 that I bought brand new just a few months ago, I need to set the temperature to 21.9 to get 20.0 according to my calibrated Greisinger electronic thermometer, which in turn matches my fever thermometer to 0.1C.

  4. #4

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    Hi !
    Yes, I've a suggestion !
    E6 processing is at quite the same temperature than the human body. One can find very precise (because checked) thermometers centered toward this temperature at the pharmacy (drugstore).
    In France where I live, I've bought a set of 3 for less than 20 USD. Each one has a little marking at 36.5 c (I supose that this is the calibration point) and the metal scale running along the tube is of different length on the 3. They give surprisingly identical results when placed on the same bucket, and can be read AFTER pulled out of the water as they hold the reading. Last but not least they do not use mercury at all but a different metal but I don't know which one.
    Try it, and you'll be satisfied, I think....
    Oh, after bathing them in E6 chemistry, don't use them for medical usage ;-)
    BTW, when the water bath is at 38.5 C, the knob said 42 on my CPE2 ...

  5. #5
    rwyoung's Avatar
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    Quote Originally Posted by rwyoung View Post
    So leave your Kodak thermometer in the water bath and tweak the Jobo temperature knob until you are happy.

    It will take some time for the temperature to stabilize. Maybe put in a tank and let it roll to swish things about. And also watch to see how much hysteresis the Jobo controller allows.

    I've only ever done B&W with mine. I don't worry much about the absolute temperature since I'm going to be testing for personal EI and developing time anyway. Just always set it to 20C and wait to start a run until I hear the relay cycle a few times.
    Should have mentioned, that on my unit, the dial is quite reasonable for absolute temp, within 0.5C based on two different lab grade glass thermometers. And also very good about repeatability. The thermostat seems to allow about -1C drop before it kicks in. Haven't specifically tested this, just anicdotal evidence for the hysteresis.
    Don't sweat the petty things and don't pet the sweaty things! http://rwyoung.wordpress.com

  6. #6
    hal9000's Avatar
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    My JOBO CPP-2 is extremely precise - I calibrated it when I first bought it and check the temperature every now and then and have never found more than even 0.1C difference. But it is not very accurate - as I said, mine requires a setting of 21.9 to obtain 20.0C. In any case since precision (reproducibility) is more important than accuracy in photography (at least in b/w), especially if you test your materials, the JOBO processor does the job extremely well. And if you calibrate against a trusted thermometer then you should achieve high accuracy as well.

  7. #7
    hka
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    Here the same. I trimmed the temperature of the CPP2 exactly at 20C. By doing that the high temperatures for E6 or C41 settings (38 or 35C) are much higher than read on the display. These are at least 3C to low. Reproducibility is no point if you know what to do. I develop E6 at 35.4C and C41 at 32.4C).
    harry

    Release, the best you can do...

  8. #8

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    I have a CPP2 and a Kodak process thermometer. I find that for 68 F, I have to set the JOBO to 20.8 C. For 75 F I have to set the JOBO to about 25C. However, I find that once I set the temp, the JOBO holds it within a half a degree F all day. The Kodak thermometer is extremely accurate, highly responsive, and completely analogue, so I trust it as my standard.

  9. #9

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    Thanks to all for your thoughtful suggestions. I thought Georges Giralt's suggestion to use a medical thermometer as a calibration standard was a good one and I will try it. It is good to know that others have experienced the same calibration issues as I have. This was my first post on APUG and it is gratifying to see responses from all over the world! Thanks to all.

  10. #10

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    I have both a CPE2+ and a CPA2 and to get 38 C in the chemistry, I must set the JOBO's to 37 C.
    To add to the confusion, try measuring the temperature of the JOBO water bath on different places...

    Harry, you live like a risky man. Bring some of your slides on the next meeting, will you? I'll bring mine.

    G

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