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  1. #21

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    OK, I'm not sure of the differences between these two...

    pH-2 (HI98103 Checker-1)

    HI99104

    the price difference is $1

    As far as I can tell, the new one (99104) has automatic temperature compensation...but it doesn't say if the "Checker" does or not
    Last edited by DarkroomExperimente; 12-14-2007 at 12:56 PM. Click to view previous post history.

  2. #22

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    and how important is temperature compensation if I'm not doing anything critical & test in a narrow temp range anyway??

  3. #23
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    That is a hard one to answer.

    When making emulsions, the pH is measured from 20 C to 40 C, but standardization is at 20 C. When processing, regardless of process temp, again over the same range, or emulsion making, standard temp is considered to be 20 C.

    PE

  4. #24

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    I'll just be using it to test pH of my homemade developers

  5. #25
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    Use 20C.

    I did in the lab all the time.

    PE

  6. #26
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    From memory:

    At 20C, the ideal glass pH electrode would have, according to Herr Nernst, a slope of 58.2mV/pH and an intercept of 0mV at pH 7.

    The ideal slope drops to something like 54mV/pH at 0C and increases to something near 64mV/pH at 50C AT 40C I'd guess it is around 62mV/pH.

    What it all works out to is something like -0.2 mV/C to adjust the slope.

    This all assumes a perfect probe which will never be the case. Your best bet for a meter without ATC, is to calibrate at or near the temperature of interest and if you can, using the charts that come with the buffer solutions, enter the corrected pH for the buffer temperature.

    If you are using an IsFET or Iridium oxide probe, the idea is the same but the slope and intercepts are different.
    Don't sweat the petty things and don't pet the sweaty things! http://rwyoung.wordpress.com

  7. #27
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    Without checking the Nernst values, I would say I could agree.

    OTOH, if you calibrate at 20C all the time, then the error is at least constant and reduces the complexity of the calibration process. You will therefore see all Kodak solution pH values reported at 20C regardless of the temperature at which they are used.

    PE

  8. #28

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    Thanks

    can't wait to get my new toy

  9. #29
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    My personal experience with these meters is; the best model is the one which will do what you require and is waterproof, as opposed to water resistant.

    I have had pH meters which require the solution to be at 20C for correct measurements, but after having a meter with inbuilt temperature compensation, for times when I couldn't get the temperature down to 20C, I'm sold on the idea.

    Sort of a bit like a pH meter auto-focus I suppose.

    However I really think whatever you get, ensure it's waterproof, these little meters are so easy to slip into a solution.

    Mick.

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