Author Topic: pH Meter Calibration  (Read 1663 times)

Offline metron-brewer

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pH Meter Calibration
« on: May 13, 2015, 04:33:06 PM »
I use a Milwaukee pH-56 meter and use (2) point calibration (7 and 4), at the start of each brew day. I've noticed lately that on the second point I initially get a "Wrong" reading, but then it will calibrate. I'm wondering if maybe an issue with the meter, or my process or the calibration fluids? The meter itself has not always displayed this characteristic. It seems to have started over the last 3-4 months. The issue has continued to show up after I have opened a new bottle of calibration solution.

I rinse meter in plain tap water and gently blow off, then first reading. After it registers I again rinse in tap water and blow off, then into second solution. The meter is about 3 years old, and the tip itself was replaced just over one year ago. It is cleaned using cleaning solution after each brew day and stored in storage solution until the next brew day.
Ron B.
White Bear Lake, MN

Offline brewinhard

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Re: pH Meter Calibration
« Reply #1 on: May 13, 2015, 04:37:06 PM »
As I understand it, rinsing in distilled water is best instead of tap water.  Could the battery be getting low?

Offline metron-brewer

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Re: pH Meter Calibration
« Reply #2 on: May 13, 2015, 04:44:14 PM »
As I understand it, rinsing in distilled water is best instead of tap water.  Could the battery be getting low?

I have heard that I should be using distilled for rinsing, I'll change that part of my process. I looked into the battery aspect but according to the instructions it has a low battery indicator which I have not seen light up. Also according to the instructions: "The meter is also provided with BEPS (Battery Error Prevention System), which avoids any erroneous readings due to low battery level by automatically switching the meter off."
Ron B.
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Offline Wort-H.O.G.

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Re: pH Meter Calibration
« Reply #3 on: May 13, 2015, 05:38:43 PM »
if the meter shows signs of erratic or slow stabilization, its usually a good time to use the very acidic cleaning solution on the probe (think its 2.0 or less). if you still have issues, could be probe needs replaced.
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Offline metron-brewer

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Re: pH Meter Calibration
« Reply #4 on: May 13, 2015, 05:48:51 PM »
if the meter shows signs of erratic or slow stabilization, its usually a good time to use the very acidic cleaning solution on the probe (think its 2.0 or less). if you still have issues, could be probe needs replaced.

I do use the MA9016 Cleaning Solution after every brew day. According to the MSDS it's pH is ~1.7. I was thinking it may be the probe as well. I'll probably just let it go for a bit until it becomes a real PIA, then replace it. I have a spare on hand.
Thanks.
Ron B.
White Bear Lake, MN

Offline pfabsits

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Re: pH Meter Calibration
« Reply #5 on: June 30, 2015, 04:32:59 PM »
There can be mulitple reasons as why the pH meter is not holding its calibration. They include:
Coating on glass electrode: Any coating that forms on the electrode will change the value the meter displays when in the pH buffer. Typically, the change would affect all buffers, so a change that is observed in pH 4 would also be observed in pH 7. This type of change is known as an offset error.

Contaminated buffer:The calibration of a pH meter is as only as good as the buffer. If a pH buffer value changes then the value displayed will change. Typically a contaminated buffer will affect only one calibration point. This will change the slope of the electrode. This should not be a problem as long as the buffers are fresh (less than 6 months old) and changed frequently. For example place buffer in a small baby food jar for daily calibration and change out at least once/week.

After using a cleaning solution it is important to place the probe in storage solution for 2-3 hours before performing a calibration.

Rinse the probe with purified water (distilled, reverse osmosis, deionized) water when moving the probe from one solution to another. For example I have my probe in storage solution then I would rinse and then place in a calibration buffer. If performing a two point calibration then rinse between buffers. After calibration rinse. After taking a reading rinse before placing back in storage solution.

Always store the probe in a solution. It is important to maintain the hydrated layer on the glass and keep the junction hydrated as well. If you do not use storage solution then use pH4. If you do not have pH 4 then use pH 7. Storage solution has microbial inhibitors to keep stuff from growing on the glass. pH 4 is the next recommendation since bacteria do not grow well at lower pH's. For this reason pH 4 is recommended over pH 7. NEVER store in purified water.

pH probes do not last forever. They have a life of 1-2 years. If you have a pH meter with a mV mode the offset/slope can be checked. As long as the offset/slope is acceptable then the probe can be used indefinitely.

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Offline metron-brewer

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Re: pH Meter Calibration
« Reply #6 on: June 30, 2015, 04:49:30 PM »
There can be mulitple reasons as why the pH meter is not holding its calibration. They include:
Coating on glass electrode: Any coating that forms on the electrode will change the value the meter displays when in the pH buffer. Typically, the change would affect all buffers, so a change that is observed in pH 4 would also be observed in pH 7. This type of change is known as an offset error.

Contaminated buffer:The calibration of a pH meter is as only as good as the buffer. If a pH buffer value changes then the value displayed will change. Typically a contaminated buffer will affect only one calibration point. This will change the slope of the electrode. This should not be a problem as long as the buffers are fresh (less than 6 months old) and changed frequently. For example place buffer in a small baby food jar for daily calibration and change out at least once/week.

After using a cleaning solution it is important to place the probe in storage solution for 2-3 hours before performing a calibration.

Rinse the probe with purified water (distilled, reverse osmosis, deionized) water when moving the probe from one solution to another. For example I have my probe in storage solution then I would rinse and then place in a calibration buffer. If performing a two point calibration then rinse between buffers. After calibration rinse. After taking a reading rinse before placing back in storage solution.

Always store the probe in a solution. It is important to maintain the hydrated layer on the glass and keep the junction hydrated as well. If you do not use storage solution then use pH4. If you do not have pH 4 then use pH 7. Storage solution has microbial inhibitors to keep stuff from growing on the glass. pH 4 is the next recommendation since bacteria do not grow well at lower pH's. For this reason pH 4 is recommended over pH 7. NEVER store in purified water.

pH probes do not last forever. They have a life of 1-2 years. If you have a pH meter with a mV mode the offset/slope can be checked. As long as the offset/slope is acceptable then the probe can be used indefinitely.

Thanks for your response. I've pretty much determined that either the electrode is going bad or I have a bad bottle of calibration fluid. The only item that I wasn't doing correctly per your post was using tap water instead of purified water to rinse with. I've since adjusted that part of my process and still have the issue during second point calibration. It seems to be working ok and it will calibrate so I'm going to continue using it as is. I'll be switching to new bottles of calibration fluid here soon, if it continues I think I can narrow it down to a failing electrode and I'll switch that out.
Ron B.
White Bear Lake, MN

Offline ScottBeh

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Re: pH Meter Calibration
« Reply #7 on: June 30, 2015, 04:59:21 PM »
I had the same problem when using the pH56.  Try shaking it 2-3 times hard like your trying to shake off all liquid from the probe after the 7 and before the 4 calibration.  Worked for me.    No idea why.

Offline metron-brewer

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Re: pH Meter Calibration
« Reply #8 on: June 30, 2015, 05:11:30 PM »
I had the same problem when using the pH56.  Try shaking it 2-3 times hard like your trying to shake off all liquid from the probe after the 7 and before the 4 calibration.  Worked for me.    No idea why.

In between solutions I rinse in distilled, wipe the outside of the meter with paper towel and give it a light shake and blow the excess water off. Next time I'll try giving it a good shake in between.
Ron B.
White Bear Lake, MN

Offline brewinhard

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Re: pH Meter Calibration
« Reply #9 on: June 30, 2015, 06:33:21 PM »
I had the same problem when using the pH56.  Try shaking it 2-3 times hard like your trying to shake off all liquid from the probe after the 7 and before the 4 calibration.  Worked for me.    No idea why.
Next time I'll try giving it a good shake in between.

Sure is better than letting it drip dry all over your pants!

Offline metron-brewer

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Re: pH Meter Calibration
« Reply #10 on: June 30, 2015, 06:39:20 PM »
I had the same problem when using the pH56.  Try shaking it 2-3 times hard like your trying to shake off all liquid from the probe after the 7 and before the 4 calibration.  Worked for me.    No idea why.
Next time I'll try giving it a good shake in between.

Sure is better than letting it drip dry all over your pants!

DOH! Walked into that one!  :o
Ron B.
White Bear Lake, MN

Offline pfabsits

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Re: pH Meter Calibration
« Reply #11 on: June 30, 2015, 07:52:43 PM »
Never wipe the glass probe. The static generated will shorten the life of it.

The reason that the shaking might have fixed your problem is that the internal reference is gel filled on a tested. If there is an air bubble that acts as a barrier from the reference junction to the internal reference then it will block the electrical pathway.

In every pH electrode there are two wires. One that is in the glass indicating bulb and the other in the internal reference. The junction allows electrical continuity between these two wire. If the junction gets clogged or if there is something in the way, like a trapped air bubble, then there will not be a good reference potential.

Not sure if this will work but there should be an image below showing two different types of pH electrodes and their components.

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Offline mabrungard

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Re: pH Meter Calibration
« Reply #12 on: June 30, 2015, 08:20:49 PM »

Always store the probe in a solution. It is important to maintain the hydrated layer on the glass and keep the junction hydrated as well. If you do not use storage solution then use pH4. If you do not have pH 4 then use pH 7. Storage solution has microbial inhibitors to keep stuff from growing on the glass. pH 4 is the next recommendation since bacteria do not grow well at lower pH's. For this reason pH 4 is recommended over pH 7. NEVER store in purified water.


Storage solution is far better than calibration solutions since calibration solution has a low ionic strength and can leach ions out of the probe's internal solution. Storage solution is often a 1 to 3 molar solution of potassium chloride in water. Calibration solutions are only slightly better than distilled, RO, or deionized water. 

There are cases when you might use pure water or calibration solutions to keep a bulb moist. If your probe comes with a sealed cover that fits over the bulb, then it is OK to use a drop or two of those fluids to help create a humid atmosphere around the bulb. Some manufacturers recommend this approach. Just remember, you only want a drop or two since those fluids can leach the ionic content out of the probe if they come in contact with the bulb for a long storage period.

I agree that touching the bulb is not a good idea. I prefer to rinse my probe with distilled or RO water and then blow off any droplets from the bulb. I don't blot or touch the bulb with anything.

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Offline metron-brewer

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Re: pH Meter Calibration
« Reply #13 on: June 30, 2015, 08:35:13 PM »
Thanks pfabsits and Martin. I never actually wipe the bulb but usually blot the end of the probe so it's possible that it touches the paper towel, no more blotting. I'll also re-look at the probe info on the Bru'n Water Facebook page.
Ron B.
White Bear Lake, MN

Offline ScottBeh

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Re: pH Meter Calibration
« Reply #14 on: June 30, 2015, 09:48:03 PM »
To tell the truth, I despised that pH56, I must of had to call them a dozen times, mine was so unstable out of the box.  They replaced it twice and still a problem.  The last of 3 probes I bought in a year was the only one that worked to any degree.  I tried the MW101 or 102 cant remember which, but they needed more counterspace and hands than I can spare on brewday, the leads kept knocking stuff over and mine didn't stabilize much faster than the 56.  A nice pen style is the Hach PocketPro+.  Stabilizes in seconds, easy to calibrate and read.  It has a icon to let you know when it thinks it needs calibrated.  If you ever tire of your 56.