pH Meter - MW102 or Hach Pocket Pro+

[TrickyDick]

"The bitterness of poor quality remains long after the sweetness of low price is forgotten."

I am going to be using this quote frequently, I just love it!



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[TrickyDick]

I use the mw102 for the past year. I have not performed the tests as outlined in the sticky, but will soon. I use the recommended method for calibration in the manual with the 7.01 and 4.01 solutions. I use the Bru'n water spreadsheet for planning my brewing water, built up from RO as my tap water is poorly suited to brewing. For the last two brew days, I suspected my meter wasn't keeping cal. I had to recalibrate between each measurement. I'm wondering if its a bad battery, or probe needs replacing, or the calibration solutions are no longer good/fresh. They are about a year old, all stored at room temps. Probe is stored in the probe storage solution when not being used. I calibrate the probe on every brew day usually just before taking my first measurement.
I see that there is a replacement probe on amazon for 30 something dollars. The picture gives a different model number than what is on the probe I have now. I will point out that the bru'n water sheet is very very close to the probe readings in the dozen or so brews I've done since buying the probe. I have heard that the probes do need replacing over time. I have been mostly careful to cool the liquid to room temp before taking a reading, however there may have been a couple times I forgot to do this early on in my use of the the meter.

TD


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[ajdelange]

The electrodes don't last forever but with a modern meter we hope for more than a year.

The calibration solutions should be freshly prepared or, if from stock, freshly removed from unexpired stock and should never, after use, be returned to stock. If the buffers are off that will, of course, add error to pH readings but will not have an effect on stability. Stability simply means the meter reads the pH of the buffer as being the same each time the buffer is read.

 

[CyclingCraig]

I received my new meter on Friday 8/29 along with bottles of 7.01 and 4.01 ref solutions just in time for my brew day yesterday 8/31. I spent Sat running a stability test as outlined in ajdelange's sticky (see attached jpg file for my time series). Following calibration I did 2 min readings up to t+20 min then went to 20 min readings for total time of t+2 hours. Between 2 min readings I left probe in 4.01 solution. Between 20 min readings I rinsed in DI water and stored in storage solution. Prior to each reading I rinsed probe in DI water and blotted dry with paper towel. The 2 min interval readings appear consistent with all but one reading within the 0.01 accuracy rating of the meter. The 20 min interval readings slipped 0.03 points below calibration point. Gotta wonder if I would have stayed closer to 4.01 cal point if I'd left probe in 4.01 solution instead of returning to storage solution. Returning to storage solution between readings would reflect reality of probe usage day to day.

On brew day, yesterday, prior to testing my first mash sample I checked calibration in the 7.01 solution to see how well it held from previous day's calibration. It was reading 7.06, so, did another 7.01/4.01 calibration.

These are similar to my results: MW102 Stability thread.

One thing to note, is the temperature of the sample. For example @65F your calibration buffer should (Maybe depending on brand) would be 4.00 NOT 4.01.

So make sure you check the package for the temp/pH values when evaluating your results. You might be a WHOLE .01 pH closer than you thought :cross:

 

[ajdelange]

I've put the temperature dependencies for these technical buffers at https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/. The meter's ATC program has these formulas, or their equivalents programmed in. As these buffers have standard formulations they should all exhibit the same temperature dependence regardless of the manufacturer subject to the proviso that the manufacturer uses the standard formulation.

Note that I got the formulas posted by fitting the given polynomial to the data on Hach buffer packaging. There may be more 'official' formulae posted elsewhere.

It is particularly important to note that these buffers are specified as being at their given pH values ± 0.02 pH (in most cases but ±0.01 products are available too).