Author Topic: Calibrating a pH meter  (Read 391 times)

Offline BrewBama

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Calibrating a pH meter
« on: August 03, 2021, 08:21:16 pm »
I have an analog Milwaukee pH meter that requires me to turn potentiometers with a jeweler’s screwdriver to adjust the readout to the calibration solution (one for 4/10 and one for 7). My question is how anal are y’all in hitting the exact readout?

Those potentiometers are touchy and I have no way of really knowing if my test solutions are exactly 4.00 or 7.00. They could be 4.XX/7.XX.

Do y’all keep fiddling with those potentiometers until you’re dead nuts on 4.00 or 7.00? I figure if I am within .0X I am close enough.



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Offline dmtaylor

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Re: Calibrating a pH meter
« Reply #1 on: August 03, 2021, 08:31:05 pm »
I'd be happy with anything within like 0.04-ish.  I doubt they're that accurate anyway.  User-error in itself is probably 0.1x -- i.e., you test it, I test it, both with the same gauge, but still somehow come out with slightly different numbers.  Carbon dioxide is a wild-card as well, it's constantly dissolving itself in there so the numbers will tend to bounce a little bit no matter how careful and consistent you try to be.

And then, of course, ask yourself... does it REALLY matter if your pH is 5.23 or 5.27??  Doubtful!!
« Last Edit: August 03, 2021, 08:32:39 pm by dmtaylor »
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Offline BrewBama

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Re: Calibrating a pH meter
« Reply #2 on: August 03, 2021, 08:33:38 pm »
That’s what I’m thinking.



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Offline Richard

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Re: Calibrating a pH meter
« Reply #3 on: August 03, 2021, 09:18:50 pm »
I know this won't help you directly answer your question, but my meter is fully digital. To calibrate it I put it in the solution and hold the power button down for a bit. It knows which solution it is in and it knows the temperature of the solution and it does the calibration itself. I was puzzled at first because calibrating with the 7.0 solution would finish with a reading of 7.01 or 7.02, but eventually I realized (by reading the label on the bottle) that the solution is only 7.00 at 25 C (77 F) and I usually use it colder, so 7.01 or 7.02 is correct. Even then, the calibration solutions that I have say they are +/- 0.02. Bottom line for me is that I'm not going to get better than +/- 0.02 accuracy no matter what, so there is really no point in worrying too much about that last decimal place.
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Offline BrewBama

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Re: Calibrating a pH meter
« Reply #4 on: August 03, 2021, 11:31:34 pm »
Actually, that helps a lot. Knowing there is tolerance stacking on top of user error makes close enough good enough. (My mantra)



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Offline goose

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Re: Calibrating a pH meter
« Reply #5 on: August 04, 2021, 09:52:40 pm »
I also rinse the probe with a small amount of 7.0 buffer before calibrating in that solution.  I then remove the probe when it calibrates in the first buffer, shake it a bit, then rinse it with the 4.0 buffer before putting it in the 4.0 solution.  You have maybe 30 seconds or so to do this before the probe registers an error bit that is plenty of time.

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Offline BrewBama

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Re: Calibrating a pH meter
« Reply #6 on: August 06, 2021, 02:24:56 pm »
I sat and took some time with the calibration. It’s touchy but I got it dialed in. This might be a night before brewday task and if it drifts overnight oh well. I can’t see myself taking this much time to do this on brewday.



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