pH Meter Calibration

CornyKegs 728
Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
ajdelange said:
Two seem to have emerged: the Hach Pocket Pro + and the Milwaukee MW 102. This does not mean that there may not be others equally as good. Omega has a relatively new pen style meter that one or two people have tried and seemed pleased with. The Hach and the Milwaukee get the best marks from the HBT Consumers Union because several users have done the stability checks described at https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/ and had favorable results.

The Hach meter is a pen type and it does, IIRC, allow calibration with buffers of arbitrary pH whereas the MW102 has a separate electrode.
Click to expand...


Which Pocket Pro+? There seem to be multiple models.

Thanks in advance.

-BD
 
Any that have the 0.01 resolution. As it is unlikely that you will want to do conductivity or ORP you probably should not pay for a model that does that. That leaves only 1 - pH to 0.01 res.
 
BrunDog said:
Which Pocket Pro+? There seem to be multiple models.

Thanks in advance.

-BD
Click to expand...

There's the Pocket Pro, and the Pocket Pro Plus. The Pocket Pro Plus has a replaceable sensor whereas the Pocket Pro does not. The Pocket Pro has 3 point auto calibration whereas the Pocket Pro Plus has that, plus customizable calibration points if you're into that kind of thing. The Pocket Pro has a 6-month warranty whereas the Pocket Pro Plus has a 1-year warranty and 6-month warranty for replacement sensors (manufacturer defects only).

Resolution: Pocket Pro is ±0.1 pH, Plus is ±.01 pH
Accuracy: Pocket Pro is ±0.1 pH, Plus is ±.01 pH

So yeah, you'll definitely want the Plus. I have one and I love it. I keep checking to re-calibrate it but it hasn't needed it in the past ten brew days.
 
Just purchased this one on Amazon:

Hach 9532000 Pocket Pro+ pH Tester with Replaceable Sensor

$115 plus $17.79 shipping.
 
Thought I would post this to help anyone thinking about pH meters. I bought the Hach Pro+ Christmas before last. I had problems with the first one that I posted here https://www.homebrewtalk.com/showthread.php?t=464632 but the company itself was very helpful. They sent me free buffers, cleaners, a new sensor and finally a whole new unit. I have used it about 15 times this past year and decided to run a stability check on it today for 75 minutes with fresh buffers. The temperature ranged from 74.7 to 75.4 and the meter initially read 4.01 in the 4.01 buffer for about 15 minutes then for the next 60 minutes it read a constant 4.02. I'm thinking that is pretty good. Hoping to get another year or more out of the sensor.
Also, just for fun, I rechecked the 4.01 buffer today which is about 22 hours later. Same buffer I mixed up yesterday and it read 4.00 at 75.2 F.
 
I have a big problem. I tried to calibrate my pH meter with the two calibration buffer solutions that were provided with the pH meter but it didn't work. I did something wrong maybe but I didn't catch what happened. I had put tap water 250 ml and poured 7.01 buffer and the meter was reading around 6.80 constantly changing around that pH. Now I have no buffer calibration solutions and I would like to know what should I do to calibrate this type of meter? What calibration solutions should I buy?

View attachment 1447526139782.jpg
 
Finlandbrews said:
I had put tap water 250 ml and poured 7.01 buffer and the meter was reading around 6.80 constantly
Click to expand...

If you make buffer solution it has got to be made with distilled water. Tap water is no good for this task I'm afraid.

ETA: If this is the meter you have I would suggest you'd be better off without it.
 
Last edited by a moderator:
You are probably reaping the rewards of that low price you paid for the meter. I wouldn't expect that this unit will serve very well or be very accurate. You can read my recommendations for what to consider when buying a pH meter on the Bru'n Water Facebook page.

Regarding the calibration solution, assuming this solution was supposed to be prepared by mixing with water, you should use distilled water and not tap water. Do purchase small bottles of 4 and 7 calibration solutions (250 to 500 ml bottles). Do pour a dose of each solution into separate containers and rinse the probe with RO or distilled water between its trip into the solutions and blow off the excess rinse water and blot off the exterior. Discard the used solution after calibration and don't return solution to the original bottles.
 
mabrungard said:
You are probably reaping the rewards of that low price you paid for the meter. I wouldn't expect that this unit will serve very well or be very accurate. You can read my recommendations for what to consider when buying a pH meter on the Bru'n Water Facebook page.

Regarding the calibration solution, assuming this solution was supposed to be prepared by mixing with water, you should use distilled water and not tap water. Do purchase small bottles of 4 and 7 calibration solutions (250 to 500 ml bottles). Do pour a dose of each solution into separate containers and rinse the probe with RO or distilled water between its trip into the solutions and blow off the excess rinse water and blot off the exterior. Discard the used solution after calibration and don't return solution to the original bottles.
Click to expand...

Thanks. Just why is that pH not good. I bought it based on many positive reviews and accuracy is 0.01 they say. But maybe I got screwed... Can anybody link some good models that are not overly expensive just so I can get a better idea what to look for. Cheers
 
Finlandbrews said:
Can anybody link some good models that are not overly expensive just so I can get a better idea what to look for. Cheers
Click to expand...

the Hach Pocket Pro+ has been mentioned/reviewed by many homebrewers as an accurate inexpensive meter. I use it and am happy with the results.
 
Is there any reason to not use copper as a sample container for testing ph?
Was thinking about making a small test tube out of 3/4" copper to hold the wort sample. This would allow the sample to chill faster in ice water or cold water. Would the copper mess up the probe in any way?
 
I hope not. I've taken thousands of readiings in stainless steel beakers. The only caveat I can think of is to be sure the beaker is at ground potential as the job of the meter is to measure small (millivolt) potentials.
 
Thank you for the reply.
But I have to ask: what is ground potential and how do I achieve it?
 
That essentially means that the beaker and the meter should be electrically connected together. Setting the beaker on a metal sheet which is connected to the pH meter or on a sheet which is connected to the outlet into which the pH meter is plugged would put both at ground potential. If it's a hand held meter putting it on a piece of metal which you touch with your left hand while inserting the meter with your right should do. What you should not do is wear thick rubber soles, slide along a fluffy rug and pet the cat with your left hand while lowering the meter/probe into the beaker with your right on a crisp winter's day.
 
biestie said:
What are the increments on the temperature compensation knob? It goes 0-50C with a mark at 25.
Click to expand...

Good question. I just leave the knob in the middle and calibrate and measure at a temperature between 20C and 25C. Its useless in my opinion. It doesn't even seem to alter the reading much when turned.
 
That control needs to apply additional gain of (K1/K2) where K1 and K2 are the reference and sample temperatures. If calibrated at 273.15 + 20 (room temperature in Kelvins) and the reading is made at 273.15 + 50 (mash temperature) the correction for the meter response only is then
(273.15 + 50)/(273.15 + 20) = 10% but that's 10% of the amount subtracted from 7 to get the displayed pH. See #1. For example at pH 5 the displayed value is 7 - 2 = 5 at room temperature. At 50 m the meter would produce a voltage 10% greater than at room temperature and calculate and display 7 = 1.1*2 = 7 - 2.2 = 4.8. For 5° temperature difference the error is less dramatic amounting to 1.7% and at pH 5 we'd have 7 - 1.017*2 = 4.97. For 6° temperature offset the reading would be 4.96 so that it is apparent that each degree error in setting the control introduces about 0.01 pH (it is actually 0.0084). But then if you wanted precision measurements you would have bought the MW102.
 
Well precision was the wrong word. Yes, it is precise enough but not, apparently accurate enough if you try to use the compensation. Set it and leave it, calibrate it and measure at the same exact temperature and, barring drift from the analogue components it should be accurate enough. Do the stability check and see.

BTW I don't recommend putting much reliance on ATC in the digital instruments either. If the isoelectric pH of the electrode is off that too will induce error.
 
Seems that DI water is hard to find. I'm only seeing it at chemical supply stores. Is distilled water not pure enough?
 
Dougal said:
Seems that DI water is hard to find. I'm only seeing it at chemical supply stores. Is distilled water not pure enough?
Click to expand...

Also could use grocery store RO water, I've checked those machines hardness levels are in the ppb range and conductivity <5 mmhos. Assuming the machines are the same process and managed well. Distilled water should be similar.
 
They are buffers, after all. The water can be reasonably 'dirty' as long as it has no buffering capacity (bicarbonate). The purer it is, however, the less we worry about such things. I've used RO water in a pinch.
 
Ok, great. I bought the premixed buffer solutions and so will only need to use the distilled water for rinsing and storage (I have the pocket pro +). Thanks.
 
Dougal said:
Ok, great. I bought the premixed buffer solutions and so will only need to use the distilled water for rinsing and storage (I have the pocket pro +). Thanks.
Click to expand...

Do not use distilled water for storage, it will kill the probe almost as fast as letting it dry out. Tapwater is better but not good. You need "storage solution", which you can make yourself with RO water and potassium chloride (salt substitute or low-sodium water softener salt) I'm not sure how many grams per liter. I think 15 grams in 100ml of water will give approximately a 2M solution, but I don't know if they take a 2M or 3M solution for storage -- either will be much better than tapwater or distilled water.
 
Those comments are applicable to pH meters in general but for the Hach Pocket Pro + they are not. Either tap water or RO/DI are fine for storage but only put a couple of drops in the cap and store the meter upright. The idea is to keep the humidity inside the cap up. If you forget to do this and things dry out it is not much of a problem. The original manuals for this meter instructed one to store it dry. You just rehydrate. It just bothered me to store it dry so I started putting the water in the cap and eventually Hach came around to the same position.

Distilled water won't destroy many regular electrodes either. What it does do is work its way into the reference cell diluting the electrolyte. Just replace the electrolyte (can't do this if the electrode is not refillable, of course so distilled water will ruin a gel filled electrode).

Storage solution for most electrodes is saturated KCl. That is, I believe, just about 3 M.
 
The important thing to recognize is that the RO/DI water is not in contact with the actual bulb. It is just humidifying the environment around the bulb when the sealed cap is applied. That prevents the electrolyte from leaching and keeps the glass moisturized.
 
Wouldn't hurt to let it touch the bulb but if it is in a position where it can touch the bulb it can touch the reference junction and that is what you want to keep water (other than a solution of the filler electrolyte) away from.
 
Aj and Martin, thanks for using your brains and taking the time to explain all this. Even with a degree in biochemistry, I feel like this thread helped me.
 
I believe that this particular meter has a precision of 0.1 which is generally not terribly useful in brewing as the quantizing noise (0.03 pH) alone is pretty large. If I'm wrong and it has precision of 0.01 then run the stability test on it. If it passes then my opinion doesn't matter!
 
The accuracy for my model is 0.05, the other two are 0.1.
The resolution is 0.01 pH.

I'll make the stability tests and let you guys know what I found.
 
So,

I have had my MW102 for just under 2 years. Been working flawlessly, and love having accurate pH readings.

Just recently I noticed some long calibration times and very slow response times.

So I did a little test.

  1. Fresh Calibration solution
  2. Calibrate pH meter.

Then I test some tap water...
I get a reading of 5.6 !!! (I tested the tap water with my pool test kit and get about 7.1, so I KNOW it's not 5.6)

Check pH meter in Calibration solutions again..
I get 7.00 and 4.00 in each... But takes a LONG time to get to the 4.

I did this twice to make sure I didn't contaminate the tap water some how and got similar readings.

In addition if I leave the probe in the 7.00 calibration solution, I can slowly watch it climb until... maybe .01 every 2 minutes but levels off at like 7.05 - 7.06

Is this an indication of my pH probe reaching end of life?
 
CyclingCraig said:
Is this an indication of my pH probe reaching end of life?
Click to expand...

Yes, sounds like it. Check the manual and see if they have any 'rejuvenation' procedures listed and try those if they do. Try soaking the probe in a solution of Zymit or a similar enzyme based cleaner. Try blasting the junction with a stream of water from a squirt bottle. No promises with any of them but most problems are related to a blocked junction. No matter what you do eventually they do go TU.
 

Similar threads

micraftbeer
Using pH Meter Continually While Adding Alkaline Cleaner
Replies
0
Views
338
micraftbeer
micraftbeer
R
Ph meter calibration time
Replies
21
Views
1K
tracer bullet
tracer bullet
wsmith1625
1st Time Using PH Meter
Replies
23
Views
3K
Brian66
Brian66
hilljack13
Bottled water only option for now
Replies
28
Views
1K
hotbeer
hotbeer
johnnycordner
Ph meter help
Replies
4
Views
1K
rushpapers
rushpapers
Williams Brewing 300

Latest posts

Back
Top