PH meter with cabled probe, for titrations and brewday?

[Gadjobrinus]

Hey all,

Outside of limited lab experience, I've always used a pH meter with the integral or enclosed electrode, of the Pocket Pro (or, in my case, Extech pH 110) type.

I have a buret at home, along with an accumulating amount of glassware, and I'd like to do alkalinity titrations using a pH meter and cabled (name?) probe, rather than a bromcresol indicator. I'd like it to do double duty, put to use on brewdays as well.

I don't have the budget to go in deep; I'd like to keep it to about $125, much like the above meters. I saw a Milwaukee pH/temp meter, but have no idea of its quality as I've never used it, nor Milwaukee generally.

Any thoughts, anyone?

Thanks.

ps: I will also use the Salifert kits, probably more regularly. I thought I saw somewhere on here their working accuracy, but can't recall how close that was. Perhaps it was precision and not accuracy. Brewers, do you use the Salifert for alkalinity testing? How close can we count on them getting?

 

[day_trippr]

If you're referring to the MW102, it sports essentially the same accuracy/stability as the Hach PP+ but with the encumbrance of a heavy cabled probe.
They use the same enclosure and probe assembly (with different guts, of course) for their MW600 DO meter.
The probe is an uber clunky pita, imo. My money voted for the Hach...

Cheers!

 

[Gadjobrinus]

Thanks trippr, yep, it is the MW102. That's helpful feedback.

I've never used a cabled probe meter, but I'd like to implement AJ's titration and can't see a way doing that without a cabled probe. Although as I write this, I guess a beaker on a stir plate would work, with something like the HACH fixed on the buret stand and dipped into the sample?

I've been intrigued ever since making friends with a genius (everything) cheesemaker (and goat farmer, when he's not being sought globally for security software concerns), he had a very sophisticated (and pricey) bench meter for his dedicated home lab, and we talked about the remote probe. Seems pretty nice when doing something as AJ outlines on his measuring alkalinity page, using an erlenmeyer. That's what sparked it, probably a poor reason to switch up (meaning, used in a limited way only).

 

[day_trippr]

With the right size beaker you could use the Hach's belt hook.

I'm sure you could rig something up. I have small spring clamps with rubber grips that I've used to hold various meters/probes inside open vessels, clamping them to the sidewall.
At least the PP+ has flats that avail themselves to this technique, while the MW102 probe is round...

Cheers!

 

[Gadjobrinus]

Good ideas, thanks Trippr. I think I'll be obtaining the Hach. I was just curious if any have used a cabled probe like this, and your experience with the Milwaukee is telling.

Much appreciated.

 

[ajdelange]

The choice of pen style vs benchtop style meter is one of personal preference. If planning on doing any 'lab' work, however, serious consideration should be given to a benchtop style meter. While one can, I am sure, kluge something with pen style meters it is going to be a lot easier to set up and do a titration with cabled electrode. If using a conventional buret you will need a stand for that and an extra clamp on that stand conveniently holds the electrode. You can let the RTD probe, if separate, just rest on the bottom of the flask or fleaker but most modern electrodes have the RTD built in.

 

[day_trippr]

I would agree with the basic premise save for the heavy, large probe housing that Milwaukee seems to have standardized.
I mean the thing is freaky heavy - feels like cast pot metal or perhaps zinc.
Sure, one could likely obtain and adapt a sturdy stand clamp but otoh clipping a Hach to a beaker seems dead simple...

Cheers!

 

[ajdelange]

I didn't specifically suggest a Milwaukee meter though those who use them seem pleased. I was unaware that they use an unusually bulky electrode. In the pics they look like a normal gel filled epoxy body design.

Personal preference will be the driver. I've done titrations both ways and the benchtop configuration has been, for me, more convenient.

An exception would be the Hanna offering with titanium body. It is as slender as a normal electrode and can be conveniently used for titration especially as the pH values are recorded and graphed on your iPhone.

 

[Gadjobrinus]

OK thanks guys, some things to chew on. At this stage it would have to be a choice between the two styles, just a budgetary thing. I was hoping to find one that could adequately serve both lab and "field" needs well enough, with the balance of the use tipped heavily to brewday uses. At the same time, as I've never used any kind of cabled probe, much less a dedicated lab meter, it's something that sticks in my mind.

AJ, lol, it occurred to me last night, as I looked at my buret and stand (glassware is currently, weirdly, in our bedroom), that in fact I do have a pen-style clamp on the stand - I use to run total acidity titrations for my cheesemaking. Don't have much memory of it to be honest, so can't say whether I found it to be a PITA then, but it is kind of funny. Thanks for the specific note on the titanium probe, too. Is this a universal probe, or only one universal to Hanna meters (sorry if I missed that).

Thank you, AJ. Your suggestions carry considerable weight with me. Once this thing is put together, meaning, the system is all built out and each room has its purpose (storage-milling-lab, etc.), I hope to return to the science of it all, and in turn repay the generosity of people who've given some thoughts but have yet to get my reply. So looking forward to reading your material with focus.

Trippr, thank you as well, of course. The experience points on the Milwaukee is gold. The idea of simply attaching to a beaker sidewall is appealing in its simplicity, as you say. That, and this double-service notion.

 

[ajdelange]

The Hanna meter I was referring to looks like a lollipop. It uses Bluetooth to send data to your smart phone and the app in the phone does all the calculation. They make it in several flavors with one intended especially for brewers. Recognizing that it is probably going to be subject to some rough treatment in a brewery they made the electrode body out of titanium. As far as size and handling are concerned it is like a cabled electrode without the cable (a normal one, that is - not like the apparently weird one used by Milwaukee). The lollipop part is pretty small and no bigger than the cable interface part of, for example, a Hach intelligent electrode. It also passes the HBT stability test and so is deemed suitable (by us at HBT) for use in brewing.

 

[mabrungard]

If you're referring to the MW102, it sports essentially the same accuracy/stability as the Hach PP+ but with the encumbrance of a heavy cabled probe.
They use the same enclosure and probe assembly (with different guts, of course) for their MW600 DO meter.
The probe is an uber clunky pita, imo.

The SE220 pH probe that Milwaukee uses on the MW-101 and 102 meters is very light and small. What is it that you are referring to? It appears you are somehow mistaken.

 

[Gadjobrinus]

The Hanna meter I was referring to looks like a lollipop. It uses Bluetooth to send data to your smart phone and the app in the phone does all the calculation. They make it in several flavors with one intended especially for brewers. Recognizing that it is probably going to be subject to some rough treatment in a brewery they made the electrode body out of titanium. As far as size and handling are concerned it is like a cabled electrode without the cable (a normal one, that is - not like the apparently weird one used by Milwaukee). The lollipop part is pretty small and no bigger than the cable interface part of, for example, a Hach intelligent electrode. It also passes the HBT stability test and so is deemed suitable (by us at HBT) for use in brewing.

Wow, sounds great, honestly. Now comes one of many embarrassing revelations. I'm a luddite, almost delusionally romanticist in outlook and....I don't have or use a cell phone, much less a smart phone. I wonder, though, if I saw this in an issue of BYO, as the smartphone app rings a bell. My son, the modernist, has a smartphone. Papa may be appropriating certain electronics on certain days....

Thanks, AJ.

 

[Gadjobrinus]

The SE220 pH probe that Milwaukee uses on the MW-101 and 102 meters is very light and small. What is it that you are referring to? It appears you are somehow mistaken.

Martin, I know these are dangerous waters (Ha! No pun intended), but do you have any overall opinion on the meter, for the purposes above?

 

[ajdelange]

The SE220 pH probe that Milwaukee uses on the MW-101 and 102 meters is very light and small.

Always nice to know, at this stage of my life, that I have not lost all my marbles - yet.

 

[mabrungard]

Martin, I know these are dangerous waters (Ha! No pun intended), but do you have any overall opinion on the meter, for the purposes above?

Those cabled meters from Milwaukee seem to be reliable. I've had a MW-101 for over 5 years and the meter and probe are still going strong and calibrating well. I can tell via the shunting test that the probe is getting near the end of its life. At around $40 for a new SE220 probe, I'd say that its cost/benefit ratio has been good. The 101 uses all analog electronics and potentiometers and a digital display, so it may not be as precise as digital equipment. But it seems to be more durable than the digitals.

I too have a Hanna Halo pH meter and have to say its a very nice unit...even better than my old 101. But that niceness comes at a price. It is more expensive and you essentially throw it away when the probe is exhausted. I'm guessing that it will otherwise be long-lived, but I've only had it in use for about 8 months. The phone app makes it easy to use and calibrate.

 

[day_trippr]

Ok, somewhere along the line I had conflated the heavy probe supplied with the MW600 DO meter with the probe supplied with the MW102.
Could've sworn I saw the same probe with that meter somewhere but now I can see they are completely different - like a pen compared to a baseball bat.
Sorry, my bad

 

[Gadjobrinus]

Always nice to know, at this stage of my life, that I have not lost all my marbles - yet.

I have 2. You may have 1. I'd give both but I enjoy the reverb.

 

[Gadjobrinus]

Those cabled meters from Milwaukee seem to be reliable. I've had a MW-101 for over 5 years and the meter and probe are still going strong and calibrating well. I can tell via the shunting test that the probe is getting near the end of its life. At around $40 for a new SE220 probe, I'd say that its cost/benefit ratio has been good. The 101 uses all analog electronics and potentiometers and a digital display, so it may not be as precise as digital equipment. But it seems to be more durable than the digitals.

I too have a Hanna Halo pH meter and have to say its a very nice unit...even better than my old 101. But that niceness comes at a price. It is more expensive and you essentially throw it away when the probe is exhausted. I'm guessing that it will otherwise be long-lived, but I've only had it in use for about 8 months. The phone app makes it easy to use and calibrate.

Fantastic information, many thanks Martin. I never needed to refill my Extech electrode so I don't recall how much it cost, but it worked well enough. Very glad to hear of your experience with the 101, as I am intrigued by a probe like this.

Thanks again!

 

[Gadjobrinus]

Ok, somewhere along the line I had conflated the heavy probe supplied with the MW600 DO meter with the probe supplied with the MW102.
Could've sworn I saw the same probe with that meter somewhere but now I can see they are completely different - like a pen compared to a baseball bat.
Sorry, my bad

All I can say is you're forgiven, providing the beer was good.

 

[ajdelange]

I can tell via the shunting test that the probe is getting near the end of its life.

I always thought the shunt test involved shunting (shorting) the BNC center pin to ground as a check on the electronics (using the shorting cap that is often furnished with meters with BNC input to protect the sensitive electronics during storage). As this would tell you nothing about the electrode clearly I am wrong on this. So what is the shunt test?

 

[mabrungard]

The shunting test provides an indirect measure of the probe’s condition. When shunted, the meter should read 7.00. The actual shunted reading is compared to 7.00.

For analog meters, you’re shifting the 7.00 ‘zero’ setting via one of the potentiometers. I’m not sure that this works with an automatically-calibrating meter.

 

[helibrewer]

All I can say is you're forgiven, providing the beer was good.

I use an MW102 and it is the meter we use on the brewdeck at work for all of our brew day checks. The temp probe is separate which isn't ideal but the unit works very well, calibration is simple, and probe replacement is pretty cheap. I recommend it.

 

[Gadjobrinus]

I use an MW102 and it is the meter we use on the brewdeck at work for all of our brew day checks. The temp probe is separate which isn't ideal but the unit works very well, calibration is simple, and probe replacement is pretty cheap. I recommend it.

Perfect. I'm not very concerned with the temp probe as I have a million analog and digital thermos I trust, so thanks on that note as well. Great info, many thanks helibrewer.

I salute your avatar. Corpsman, late '70's.

 

[ajdelange]

The shunting test provides an indirect measure of the probe’s condition. When shunted, the meter should read 7.00. The actual shunted reading is compared to 7.00.

For analog meters, you’re shifting the 7.00 ‘zero’ setting via one of the potentiometers.

O.K. I think I get the intention. With the shunt in place the meter reads the meter's offset (divided by T/R*F as it is displaying pH units). Thus if you have calibrated your electrode to 7 buffer, removed the electrode and installed the shunt the meter will read 1/57th of the sum of the electrode's and electronic's offsets. But the fact that the offset pot is not at 0 after the calibration tells you the same thing i.e.that either the meter or the electrode or both have non 0 offset.

I’m not sure that this works with an automatically-calibrating meter.

Yes, it does but most digital meters tell you what the offset and slope are after each calibration and many time tag and record this information.

Offset is not the major concern with the health of an electrode though it may drift. The more relevant indicators of end of life are decrease in the slope (to less than T/R*F mV/pH) and slowed response time. Decline in slope is indicated by the fact that you have to advance the gain (slope) knob on an analogue meter to make the pH 4 calibration. As noted, digital meters report and often keep a history of slope.

If I had an analogue meter I think I would make marks on the offset and slope pot scales when calibrating a new electrode. This way I would see right away the extent of aging.

 

[ajdelange]

I'm not very concerned with the temp probe as I have a million analog and digital thermos I trust,

I'm afraid you are. The temperature probe is not there just to serve as a handy extra thermometer. The meter needs to know the temperature in order to calibrate itself and to convert mV reading to pH. In No. 24 I noted that the slope of a perfect electrode is T/R*F. T is the temperature, R is the gas constant and F the Faraday constant. Besides that, the 4 and 7 buffers have pH's of exactly 4 and 7 only at, respectively, 15 and 25 °C. Thus the meter needs to know the temperatures of the buffers to be able to calculate ph7(T) - pH4(T) which it then multiplies by T/R*F to get the voltage difference that a perfect electrode would observe in going between these buffers. It compares that voltage difference to the observed voltage difference to obtain its slope correction factor (number less than 1 usually). When calibration and sample measurement are done at different temperatures it uses the ratio of the measurement and calibration temperatures (in Kelvins) to adjust the slope factor so that the sample pH will be correctly computed.

 

[Gadjobrinus]

I'm afraid you are. The temperature probe is not there just to serve as a handy extra thermometer. The meter needs to know the temperature in order to calibrate itself and to convert mV reading to pH. In No. 24 I noted that the slope of a perfect electrode is T/R*F. T is the temperature, R is the gas constant and F the Faraday constant. Besides that, the 4 and 7 buffers have pH's of exactly 4 and 7 only at, respectively, 15 and 25 °C. Thus the meter needs to know the temperatures of the buffers to be able to calculate ph7(T) - pH4(T) which it then multiplies by T/R*F to get the voltage difference that a perfect electrode would observe in going between these buffers. It compares that voltage difference to the observed voltage difference to obtain its slope correction factor (number less than 1 usually). When calibration and sample measurement are done at different temperatures it uses the ratio of the measurement and calibration temperatures (in Kelvins) to adjust the slope factor so that the sample pH will be correctly computed.

Oh, OK, thanks, AJ. Yes, I'd not connected the two, thanks for the explanation. I've always used the Extech to good effect (my measure was that my cheeses were very high quality, and pH control was done effectively), and so never put 2 and 2 together per your paragraph above. Can I ask for a comment, then, if the temp probe is seen to be of lesser quality, thoughts on this MW 102?

Have you seen the Extech? Like I said, lousy QC but once the company sent me, 3 I think it was, we got a ringer that lasted me the rest of my cheesemaking days. Refillable electrode. Great for measuring hard curds or sampled finished cheeses due to its squared off end. But I also found it worked well for brewing. Then again, I always want to learn more, and how to use more.

 

[ajdelange]

To my way of thinking the most important things for a pH meter are that it passes the stability test and can be expected to last a couple of years at least. The MW 102, according to those here that own them, meets both those requirements. It would be nice if the temperature sensor were incorporated into the electrode as it is is so many modern electrodes but it is not really that big of a problem to fumble with the extra probe.

I have not seen the Extech to which you linked so I can offer no opinion. We'd all love it if you bought one and did the test so that we would be able to either include it or exclude it from the HBT Vetted pH Meter list.

 

[Gadjobrinus]

AJ, I wasn't aware of this list - is this a formal thing, or just kind of known in the community? I'm comfortable returning to the meter, provided I either get sent "the right one" or they've not changed their policy on sending a replacement "until I get the right one." Once they did, as I said, it performed very well for my needs and I'd be happy to use it again.

Though I will say, it's in my nature, to always look over the hill as I'm sure there's a better solution I'm not using. That's why I got so geeked about the MW102.

I just realized, too, after reading your above post, I misread helibrewer's comment with respect to the temp probe. I'd thought he meant it's a poor probe, not that it's a bit less than optimal to have a separate probe. Apologies for a rather inane side-track, all.

 

[ajdelange]

- is this a formal thing, or just kind of known in the community?

Probably more of the latter than the former. The MW 102, the Hach Pro+, a similar offering from Omega (whose model number I can never remember) and the Hanna lollipop have all been checked by at least one person here and have passed the stability test. These are all meters that sell for a bit over $100. Obviously most, if not all, lab grade meters would too but we don't concern ourselves with them since most brewers won't shell out $1000 + for a pH meter.

 

[Gadjobrinus]

Probably more of the latter than the former. The MW 102, the Hach Pro+, a similar offering from Omega (whose model number I can never remember) and the Hanna lollipop have all been checked by at least one person here and have passed the stability test. These are all meters that sell for a bit over $100. Obviously most, if not all, lab grade meters would too but we don't concern ourselves with them since most brewers won't shell out $1000 + for a pH meter.

OK, thanks, AJ. I will take that into heart, bringing in the Extech. This may be dumb, but is there a formal criterion for the stability test?

 

[ajdelange]

No, not really.I have deduced that the meters accuracy spec is the rms stability over a period of an hour or two after calibration as that is what Hach says accuracy means in the data on the pH pro + but I have never seen any other manufacturer say what it means. Also this seems practical. If a meter stays within ±0.02 of its calibration for as long as it takes us to conduct a mash clearly it is sufficiently stable for use in brewing. If it wanders off 0.05 pH in 15 minutes clearly it isn't.

There may be an ISO or ASTM or DIN standard for measuring pH meter accuracy but if there is I can't find it.

 

[Gadjobrinus]

No, not really.I have deduced that the meters accuracy spec is the rms stability over a period of an hour or two after calibration as that is what Hach says accuracy means in the data on the pH pro + but I have never seen any other manufacturer say what it means. Also this seems practical. If a meter stays within ±0.02 of its calibration for as long as it takes us to conduct a mash clearly it is sufficiently stable for use in brewing. If it wanders off 0.05 pH in 15 minutes clearly it isn't.

There may be an ISO or ASTM or DIN standard for measuring pH meter accuracy but if there is I can't find it.

OK, perfect, thanks AJ. If we're talking what I know of as drift (?), I can already tell you from memory that I wasn't the happiest with the meter in that I felt I was constantly calibrating it during any cheesemaking day. Now, that may be an issue with the meter, or my neurotic perfectionism gone wild, can't recall. I'm sorry I don't know the term or have forgotten the term rms stability (slope?), but want to investigate it.

 

[ajdelange]

OK, perfect, thanks AJ. If we're talking what I know of as drift (?), I can already tell you from memory that I wasn't the happiest with the meter in that I felt I was constantly calibrating it during any cheesemaking day.

That suggests that it wasn't very stable.

Now, that may be an issue with the meter, or my neurotic perfectionism gone wild, can't recall. I'm sorry I don't know the term or have forgotten the term rms stability (slope?), but want to investigate it.

They say a picture is worth a thousand words so here's a picture of what a series of pH readings of the pH 4 buffer might look post calibration. I emphasize "might" because this is phony data cooked up by me to illustrate the two types of error at play here.

The open circles in the bottom half represent pH readings taken one time unit apart after calibration. Calibration adjusts the gain and offset of the meter electronics to force it to read 4.00 when in 4 buffer. Thus we would expect, just after calibration, that it will read 4 or very close to it. Over time, though, the reading will wander off. The errors contain a noise like component (the open circles in the upper part of the graph) and a trend (represented by the straight sloped line). If there is no trend the actual readings will look like the upper trace. If there is a trend the actual readings are the sum of the upper trace errors plus the trend line.

RMS error is the 'root mean square' error computed by taking each of the errors, squaring it, adding to an accumulator which, after all errors have been considered, contains the sum of the squared errors. Now we divide this by the number of measurements which gives us the average squared error (mean square error) and finally we take the square root to get the root mean square error. This is sort of like and effective constant error magnitude (it can't be negative).

Finally, with respect to the earlier question as to how a stability test is interpreted we note that if the time units in the graph are hours we'd say we had a pretty good meter. Even though there is clearly some instability including a trend (drift) the expected readings stay within + 0.02 pH (not ± 0.02 note) for 12 hours. Most brewers would be happy with that level of accuracy over the course of a 12 hour brew day. OTOH if the time units are minutes the meter does not look so good. After 15 minutes it's off by + 0.04 an clearly drifting appreciably in a quarter of an hour. It is possible, of course, to use such a meter but we would want to recalibrate every 15 minutes or so.

 

[Gadjobrinus]

AJ, thank you for so patiently and so helpfully bringing this out. I've lamented alot, I know - when the world of even history went quantitative and I went back to U of M over a summer to take stats and some quant. history courses, I got it then but that's long gone. This really helps to walk me in some, in a way even I can understand. Thank you.

I see now the Extech was poor, and I think, too, I transgressed the primary ethic - if data is dependable, go with it, and not what you want it to be. Don't know if that makes any sense but looking back on its use in my cheesemaking days, I'm almost certain I was doing just that, the latter.

Very much appreciate it, AJ.