Do pH probes 'go off'?

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guypettigrew
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Do pH probes 'go off'?

Post by guypettigrew » Fri Jul 12, 2019 6:50 pm

About 18 months ago I bought a Voltcraft PH-100ATC Ph meter.

A couple of days ago was brewday. During the first 15 minutes of the mash I calibrated (or tried to) the pH meter using pH 4 and pH 7 buffers. New ones, by the way.

The pH 7 point was wandering all over the place every time the probe was put back into it. By anything up to +0.6 -0.3. This meant the slope from the pH 4 had to be constantly altered. I must have gone back and forth between the two buffers about 8 times.

Eventually I was happy with the readings at 4 and 7. Dropped the probe into some cooled wort and got 5.2. No idea if this was real or not!!

Some details;
  • the probe is stored in 'Growth Technology' storage solution
  • The buffers are 'Growth Technology
  • The probe is washed in reverse osmosis water between readings
Any thoughts, please?

Guy

WalesAles
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Re: Do pH probes 'go off'?

Post by WalesAles » Fri Jul 12, 2019 7:57 pm

guypettigrew wrote:
Fri Jul 12, 2019 6:50 pm
Any thoughts, please?
Guy
Guy,
I thought it was lovely sitting in the garden drinking copious amounts of Beer today! :D

WA

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Robwalkeragain
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Re: Do pH probes 'go off'?

Post by Robwalkeragain » Sat Jul 13, 2019 8:15 am

Might need a new probe if they’re not expensive? Contact the company for spares...

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Re: Do pH probes 'go off'?

Post by Heron1952 » Sat Jul 13, 2019 10:20 am

aka Rhys

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Eric
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Re: Do pH probes 'go off'?

Post by Eric » Sat Jul 13, 2019 10:46 am

They don't last for ever. My first probe didn't last long, but wasn't giving erratic readings, instead it just continued to drift.

For readings to be practical and meaningful they should be taken with the sample and probe at very similar temperatures, close to 20C and constant. For our purpose perfect precision isn't essential, but we should avoid taking potentially misleading readings. The following is my procedure. The probe is rinsed in DI water before and after every stage and excess surplus DI water gently shaken off the probe.

With DI water, probe and sample at the same and right temperature, the sample is gently stirred using the probe. The probe is left in the sample and allowed to settle while the reading observed. This is repeated until the reading stabilises quicky and remain constant for about a minute, then recorded. The rate at which this happens depends upon the buffering power of the medium being measured. Buffers used to calibrate the meter will settle to a constant reading more quickly than will, for example, low gravity wort runnings from a thin mash created using RO liquor. DI water itself has virtually no buffering power and therefore a large range of potential pH.

My first probe was replaced when the pH reading began stabilising, but continued to rise very slowly for many minutes. I replaced it with one of these, although maybe not this particular supplier. I found this better than the original in that it has lasted much longer and used for vastly more readings. It also can be opened to allow the calibration fluid to flow into the membrane and be topped up using the syringe supplied, something I was unable to do with the original.

As your readings were erratic Guy, I wonder if there might be an intermittent contact in the wiring. Also, as no doubt you have found, any reading can be disturbed if the body is moved when taking a reading. You can get pH probe cleaning fluid, but it will likely cost more than the probe above.
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mozza
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Re: Do pH probes 'go off'?

Post by mozza » Sat Jul 13, 2019 3:37 pm

I had a similar situation with my rather expensive Milwaukee ph meter ( a good £60-£80 I think) worked fine for a couple years, always cleaned and stored the probe in storage solution. It wouldn’t calibrate at all and a new probe was more than a new one!

So I bought one of these Image and it’s brilliant. Best part is when it dies I’ve only lost £10
Cheers and gone,

Mozza

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Eric
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Re: Do pH probes 'go off'?

Post by Eric » Sat Jul 13, 2019 4:37 pm

mozza wrote:
Sat Jul 13, 2019 3:37 pm
I had a similar situation with my rather expensive Milwaukee ph meter ( a good £60-£80 I think) worked fine for a couple years, always cleaned and stored the probe in storage solution. It wouldn’t calibrate at all and a new probe was more than a new one!

So I bought one of these Image and it’s brilliant. Best part is when it dies I’ve only lost £10
I've often wondered about buying a cheaper one, particularly since finding the cheap probe to be at least equal to the much more expensive one. How frequently do you calibrate yours and well does it hold calibration?
Without patience, life becomes difficult and the sooner it's finished, the better.

guypettigrew
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Re: Do pH probes 'go off'?

Post by guypettigrew » Sun Jul 14, 2019 8:57 am

Thanks. When I first got the meter it calibrated easily without having to go back and forth between the buffers. I've got another probe in the drawer. A fairly cheap one from ebay. Sounds like it might be worth trying it out.

Guy

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mozza
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Re: Do pH probes 'go off'?

Post by mozza » Sun Jul 14, 2019 12:03 pm

Eric wrote:
mozza wrote:
Sat Jul 13, 2019 3:37 pm
I had a similar situation with my rather expensive Milwaukee ph meter ( a good £60-£80 I think) worked fine for a couple years, always cleaned and stored the probe in storage solution. It wouldn’t calibrate at all and a new probe was more than a new one!

So I bought one of these Image and it’s brilliant. Best part is when it dies I’ve only lost £10
I've often wondered about buying a cheaper one, particularly since finding the cheap probe to be at least equal to the much more expensive one. How frequently do you calibrate yours and well does it hold calibration?
I don’t brew that regularly so I always calibrate it, but to be honest it only needs a slight tweak every now and then. I’m really impressed by the accuracy of it
Cheers and gone,

Mozza

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Re: Do pH probes 'go off'?

Post by aamcle » Mon Jul 15, 2019 9:30 am

Probes do go off, something you might try is soaking your probe in a warm solution of Biological detergent (for the washing machine). The enzymes may remove any proteins that are blocking the poures in the glass membrane.

It works sometimes.


Atb. Aamcle

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mozza
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Re: Do pH probes 'go off'?

Post by mozza » Tue Jul 16, 2019 11:31 am

Eric wrote:
I've often wondered about buying a cheaper one, particularly since finding the cheap probe to be at least equal to the much more expensive one. How frequently do you calibrate yours and well does it hold calibration?
Image

First time out the box in a couple of months and virtually no calibration needed.
Image

Well worth a tenner even if it’s there as a spare
Cheers and gone,

Mozza

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Eric
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Re: Do pH probes 'go off'?

Post by Eric » Tue Jul 16, 2019 2:00 pm

mozza wrote:
Tue Jul 16, 2019 11:31 am

Well worth a tenner even if it’s there as a spare
That seems to be so. It would be interesting to compare the linearity between and outside the calibration points for both machines.

Mine tends to be used in flourishes. Often I won't bother when time is short or for a basic brew, but it gets a bashing on occasions when several readings are taken during mash and sparge, plus start and finish of the boil. Measuring pH of other peoples beer is sometimes interesting, gets used when making invert sugars and is invaluable when diluting acids to particular strengths.

Busy working on the house at present and the garage, where I brew, is a right mess. As one doesn't take up much space I'll order one soon.
Without patience, life becomes difficult and the sooner it's finished, the better.

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