pH Meter - Milwaukee MW101 vs MW102

[ResumeMan]

Yes, another pH meter thread. Sorry all, I couldn't find quite what I was looking for by searching the forum.

In looking at the MW101 vs the MW102, it appears that the difference between the two is:

- MW101 doesn't have a thermometer and requires manual temperature correction; the MW102 has a temp probe and does auto temp correction

- MW101 is manually calibrated, MW102 has auto-calibration

Is that right? Are there other differences? Are the electronics the same?

And if so, do those two features provide sufficient value in actual use to be worth the extra cost? In his pH meter buying guide, Kai actually said he prefers manual calibration to automatic.

What are folks' experiences with these two units? Santa's trying to beat the Christmas shopping rush ;-)

 

[mtnagel]

I'm a chemist and if I'm understanding manual vs automatic calibration, I wouldn't let that sway your decision at all. Instead of the meter guessing exactly which buffer you are using, you just have to type in the number (usually by scrolling with arrow keys). If I'm assuming wrong, someone correct me. That said, all our meters at work have auto cal and that's what we use, but if it's more than a few bucks more, I wouldn't spend my personal money on it

As for the temp correction, everything I've read, which admittedly isn't all that much, but you should be cooling your sample down anyway so that feature isn't necessary.

And now that I looked both prices up on Amazon, I wouldn't spend the extra $45 on those features, but hopefully a real expert will chime in too.

 

[ajdelange]

See https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/

The main reason for wanting ATC is not to get ATC so much as it is to get the digital electronics which the presence of ATC implies. ATC is useful though, of course, it is most useful when doing fine work. If you are willing to regulate the temperatures of sample and buffers you don't need it. If you don't care about high accuracy you don't need it but there is a reason why most meters except the real cheapies have it.

Automatic buffer recognition and Automatic Temperature Compensation are two different things. Both are available on most digital meters.

OP should look into the reported reliability and stability of any unit he is considering buying. The bitterness of poor quality remains long after the sweetness of low price is forgotten.

 

[revansCAAD8]

Order mine back in August from Kats Safety and have been very happy with it:

Milwaukee MW101
Milwaukee MA6370 - Hard Carrying Case for MW Portable Meters
Milwaukee Instruments - MA9004 - pH 4.01 PH Buffer Solution 220ml
Milwaukee Instruments - MA9007 - pH 7.01 Buffer Solution 220ml
Milwaukee Instruments - MA9015 - Storage Solution in 220ml bottle
Milwaukee Instruments - MA9016 - Cleaning Solution (220ml)
Milwaukee SE220 - Double Junction pH Electrode - (bought as an extra/backup/spare)

*all dropped shipped fast and directly from Milwaukee

Robert

 

[grathan]

You can kinda tell by the price that there isn't any major difference between the two. Same replacement probe. I've had the 101 for a few months now and would say it is all you need for brewing. It doesn't need calibration and the temperture dial doesn't do much anyways (you can crank it from one extreme to the other and your talking hundredths of a ph point. If you need hundredths accuracy you would be spending $500 on a probe I would imagine and using it for more than just brewing beer.

 

[ResumeMan]

Thanks for the thoughts. When you say "it doesn't need calibration" do you mean you aren't calibrating it at all?

 

[ajdelange]

You can kinda tell by the price that there isn't any major difference between the two.

There are major differences between the two. One is clearly an analogue design (with a digital voltmeter - the pots and manual temp. dial tell us this). The other is clearly a digital design (the absence of the pots, ability to do auto buffer recognition and ATC tell us this).

Same replacement probe.

That is true.

I've had the 101 for a few months now and would say it is all you need for brewing.

That depends on what you are trying to do. If you want to see the effects of an addition of, say, calcium chloride on the pH of a mash you will need a meter which can read pH accurately down to a couple of hundredths. You can get that kind of performance out of these inexpensive meters if
1) Your unit is temporally stable
2) It is calibrated frequently

It doesn't need calibration

It certainly does! There is no pH meter made that doesn't require calibration. I have been working a lot with an electrode that costs about three time what your meter does in the last few days. It's slope has changed 2% and its offset by 3 mV.

and the temperture dial doesn't do much anyways (you can crank it from one extreme to the other and your talking hundredths of a ph point.

. That depends on the pH. If you do that in 7 buffer you should see no change in reading. If you do it at pH 5 (closer to mash pH) you should see a change of about 0.034 pH for every 5 degrees you dial in. That's appreciable for fine work.

If you need hundredths accuracy you would be spending $500 on a probe I would imagine

Your imagination is very vivid. I have electrodes costing a lot less than that that give accuracy to hundredths and even one pen meter for a little over $100 that does that.

..and using it for more than just brewing beer.

Beer brewing is the most demanding application that I have though I do use pH meters for other things. In brewing we do chase changes of a couple of hundredths on a fairly regular basis.

Perhaps the most compelling reason for considering the 102 vs the 101 is it fares better in user satisfaction reports (though the data is thin). I have seen no complaints about 102s here though I have seen several about 101's and the Amazon reviews seem to echo this.

 

[ResumeMan]

There are major differences between the two. One is clearly an analogue design (with a digital voltmeter - the pots and manual temp. dial tell us this). The other is clearly a digital design (the absence of the pots, ability to do auto buffer recognition and ATC tell us this).

Wait, what? The MW101 is analog? If that's the case then it's a pretty easy decision...

What are "the pots"? I don't recall that term discussed before.

 

[ajdelange]

'Pot' is slang for 'potentiometer' which is a grandiose name for what used to be called a 'volume control' back in the days when analogue reigned supreme and the idea of digital processing was a dream. It's a band of resistive material arranged in an arc with a wiper which can be positioned anywhere along the length of the arc. It's called a potentiometer because if you apply a potential between the two ends of the resistor you can pick off any fraction of that potential you want from the wiper by positioning it at the proper angle. The two calibration adjustments and the temperature compensation adjustment are 'pots'.

 

[ResumeMan]

Ok well digi vs. analog is a much bigger difference between the two than I thought. Not that digital is always the be-all and end-all, but the stuff I've read from several respected sources (yourself and Kai among others) make it clear that for a pH meter I would prefer to go digital, and the price difference isn't that large.

Thanks

 

[grathan]

Thanks for the thoughts. When you say "it doesn't need calibration" do you mean you aren't calibrating it at all?

I mean that after many uses and months when I stick it in calibration solutions, it doesn't need adjustment. Calibration is the only time I pay attention to hundredths.

 

[Wynne-R]

I’d like to push back against the ‘digital is better idea’. I enjoy my digital calculator way better than my old slide rule. However when I was in Radio Shack and they tried to sell me a “digital antenna” I wanted to slap the salesperson. There’s no such thing as a digital antenna.

Re pH, we are measuring an analog representation (voltage) of an analog quantity (pH). With the MW 101 and the MW 102, they both have digital readout. It’s probably the same op-amp. The only difference is in the calibration.

If you want to juggle two probes and pay an extra $40, have a good time.

Personally, I trust the two pots (analog adjustments) more than I trust the software Fudge-o-Matic. AJ seems to think the pots drift. In my experience, it’s everything else. The pots are there to compensate, otherwise they would have used fixed resistors.

 

[LuckyBeagleBrewing]

I will have to side with the digital on this. having something that reads the temp and compensates is going to be more accurate imo. It takes the "Human Factor" out of the equation. Less knobs to turn.

 

[ajdelange]

Re pH, we are measuring an analog representation (voltage) of an analog quantity (pH).

Then you would prefer that they return to the even more primitive meters that used a galvanometer?

Is temperature an analogue quantity? How about weight? Or density? Or pressure? Or sound? Or light intensity? I have 'instruments' (with the one for light intensity called a camera) that measures all of these. None of them use analogue circuitry beyond that necessary to impedance match and drive an A/D converter. The phone company just came in and ripped out my analogue telephone service. The advantages of digital are simply too great to be ignored if it is economically feasible to have them (and it is today). How would pH meters different?

With the MW 101 and the MW 102, they both have digital readout. It’s probably the same op-amp.

Probably the same instrumentation amp but the 101 would probably have an additional op amp with adjustable gain (slope and temp.) and offset pots.

The only difference is in the calibration.

Viva la differance!

Personally, I trust the two pots (analog adjustments) more than I trust the software Fudge-o-Matic.

Three. That's because you don't understand the way in which a pH electrode functions nor, apparently, have comparative experiences with analog and digital equipments that are designed to perform the same function. You are probably also convinced that analogue phonograph records have better sound than 16 bit 88 ksps audio (lots of people still believe that). Your use of the term 'Fudge-o-Matic' advertises lack of understanding. pH electrode response is accurately modeled by a simple mathematical equation. Determination of slope and offset parameters requires solution of a pair of equations. The designer of a meter, be it analogue or digital must implement these equations. They are easily solved in a computer (microprocessor) to machine precision and the factors then substituted into the pH equation which can be calculated to machine precision. The designer of an analogue meter can't do this and so has to fudge a solution by setting the gains of op-amps and supplying them with a physical offset voltage (note that drift in this supply is another source of analogue meter drift). There was a day before computers when lots of problems had to be done this way using 'analog computers' which consisted of op-amps configured as gain stages, differentiators and integrators. Those devices are only found in museums now and the analogue pH meter is headed that way.

Perhaps you fail to appreciate the power of 'signal processing' which is easy to implement in software/firmware and hard to implement with accuracy in analogue circuitry. The signal processing in pH measurement isn't extensive but includes ATC, solution of the calibration equations, determination as to when the reading is stable, auto buffer recognition, averaging of readings for better accuracy and other bells and whistles found in more expensive meters. One very important feature of a digital meter that hasn't been mentioned so far is that a digital meter knows what the pH of your buffers are. They vary somewhat with temperature. With a manual meter you have to look up the pH in a table on the package (and not all packages give this data). pH 7 buffer has pH 7 at 25 °C but at 19 °C it is 7.02

AJ seems to think the pots drift. In my experience, it’s everything else.

As noted above that is because you don't have the relevant experience. They do drift. The example that comes to mind is lying on my back behind a relay rack on a Greek Navy base trying to produce a single sideband signal with quadrature balanced mixers and fiddling with gain and offset pots (in a $20K instrument) trying get rid of the unwanted sideband. Getting it right was difficult enough because of backlash (and these were 10-turn pots) and then when I finally did get it the pots would drift enough by the time I crawled out that the unwanted sideband was back. In a modern digital system where one programmed the math and stuffed the numbers into a D/A converter - no unwanted sideband and no drift.

The pots are there to compensate, otherwise they would have used fixed resistors.

The pots are there to try to fudge the mathematical equations into analog circuitry. If you don't understand that digital circuitry is at a tremendous advantage over analogue circuitry there isn't much point in me trying to explain it but you might ask yourself the question as to why analogue circuitry has been replaced by digital in almost every piece of electronics equipment you buy (I gave several examples above). Other than these toy meters there are really no analogue pH meters out there on the market (which is a pity because I think they could be good teaching tools - I'd really like to have one with an actual D'Arsenval movement on it).

If you want to juggle two probes and pay an extra $40, have a good time.

Do pay the extra $40. It's definitely worth it but spend it on a meter that has the temperature probe built into the pH electrode.

The equations that must be solved are at

http://wetnewf.org/pdfs/ph-meter-calibration.html

 

[mabrungard]

While I agree that digital electronics can be better in many situations, in a pH meter they are interfacing a truly analog sensor. That introduces a conundrum. However, we know that many analog and digital meters are fairly stable in their operation. Digital should be better, but it's no guarantee.

 

[TrickyDick]

While we are at it, might be a good time to ask about calibration and temperature. It appear the OP may be getting a probe soon, and will probably wonder, as do I about a couple basic questions.

With the calibration solutions, can these be re-used, or should the decanted portion used for calibration be disposed of after calibration?

I calibrate my meter on brewing days immediately before I measure my mash pH for the first time. I haven't been into the habit of measuring the pH nor the wort at multiple time points, but I may begin to do that. It is my understanding that I would probably need to calibrate the meter once for these measurements performed over a period of a 2-3 hours typically. Would recalibrate on be necessary over this short of a time frame?

I understand the reading the pH of hot liquids will shorten the lifespan of the probe. What is an acceptably safe temperature to measure at?

I have the mw102 and find it to be relatively easy to operate and calibrate for its price. I also have been using the bru'n water spreadsheets and find those extremely useful (look for my donation soon). The measured pH is highly concordant with the predicted values I have found. I am considering buying or building some type of holder for the probes to keep the sample containers from falling over during use as they can tip the sample containers if you are not cautious. The smaller containers permit less waste of the calibration solutions.

Lastly, when storing the probe, it is my understanding that it should be stored wet, in order to preserve longevity of the probe. Is this correct?

Thanks!

TD

 

[mtnagel]

At my work, we calibrate daily.

Bru'n Water sheet says room temp, so I'd cool to around the upper 60s.

Yes, they should be stored wet. (sounds dirty )

 

[TrickyDick]

Thanks!

Saw another thread discussed the cal solution and capsules mixed with DI water. Less $$ so I won't be so stingy with the solutions anymore.

Hey here in FL room temp is 75°!

TD

 

[ajdelange]

There is no conundrum here. The mechanisms are well (if not completely) understood and the workings of a pH meter are typical of the solution to the general measurement problem. Given that you have a parameter whose value you wish to determine you find a transducer which translates the level of the parameter to something you can measure using a rule you know. In virtually every case today the engineers look for a parameter-to-voltage transducer because there really isn't any convenient, robust, inexpensive, reliable signal alternative available. A voltage signal is easy to convert, by means of an A/D converter, to a stream of numbers which can be processed in a virtually limitless number of ways in a computer. Clearly at a minimum this processing must 'invert' the rule i.e. the transducer converts the parameter to a voltage and the processor must convert that voltage back to its best estimate of the value of the parameter most likely responsible for the observed voltage. The rule used to do this is often known in general form but often involves some parameters which may change over time as the transducer is subjected to different measurement conditions and as its inherent properties change with age. Thus another major responsibility of the processing is to determine those parameters by measurement of calibration standards - samples for which the value of the parameter being measured is known.

In a pH meter the parameter is the activity of the hydrogen ion (actually the negative logarithm of that) and the transducer is a thin membrane of specially doped glass. In a barometer or other pressure measuring device it is a piezo electric crystal. In a scale it is a piece of wire whose resistance changes with strain. In a thermometer it is a resistor whose resistance changes with temperature (as the resistance of all resistors do). In a microphone it is a capacitor, a coil over a magnet, or a piezoelectric crystal. In a hygrometer it is a capacitor whose dielectric constant changes with humidity. In an analytical balance it is a resistor through which current, also flowing through an electromagnet and of sufficient magnitude to produce force which balances the force of gravity acting on the mass, flows. In an anemometer it is the voltage across a wire through which a known current flows. These transducers are all 'truly analog', are all linear or near linear and are all governed by the same basic equations. In explaining how a pH meter works I often start with how a balance works as the concept of mass is more concrete than pH to most people and the math turns out to be exactly the same. The only cases where there is no transducer is where the thing to be measured is a voltage itself and example of instruments that are designed to measure voltage are voltmeters, EKGs, EEG's, ORP meters etc.

There is usually some analog conditioning of the transducer signal required to get its level well up above the self noise of the A/D converter, to provide a proper impedance match to the transducer and to reject common mode signals and noise picked up from the environment (power line hum, noise from motors...). This analogue conditioning is subject to all the ills analogue circuitry is heir to and so is kept to the minimum necessary to interface the transducer to the A/D.

Yes, it is possible to have analogue instrumentation that works. A lot of science was done with analogue instruments prior to the digital revolution. But it was a revolution and it revolutionized measurement and many other aspects of modern life too. There is no way I could do the experiments I do on malt titration with an anlogue meter. I realize that most people here have no desire to do that kind of work but as fully digital meters are now available at comparable prices I think it is a disservice to suggest that analogue ones are as good or better. I used to meet this sort of Luddism in the early days when digital processing was becoming a reality but I haven't experience it in years. Perhaps that's why I give such a violent knee jerk response to it. If you guys are getting adequate performance out of the meters you have then that's great but I don't think its proper to suggest that the older technologies are somehow superior.

Note: I did find an old style pH meter with a d'Arsenval movement but they want $300 for it. Too much!

 

[ajdelange]

While we are at it, might be a good time to ask about calibration and temperature. It appear the OP may be getting a probe soon, and will probably wonder, as do I about a couple basic questions.

See https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/. It should answer your questions.

 

[Wynne-R]

Digital vs Analog is ridiculous. To say digital is better is just as dumb as saying analog is better. Most systems these days are hybrids.

I thought the question was MW101 vs MW102. As I said in post 12, “If you want to juggle two probes and pay an extra $40, have a good time.” The 102 accuracy is rated at .01 , while the 101 is rated a still impressive .02. I prefer the simpler design of the 101 compared to the added cost and complexity of the 102.

For the record, I have considerable experience with measurement systems both analog and digital. I understand how they work. I am not a Luddite. Other than that I agree with most of what AJ said.

 

[ajdelange]

For fun lets design 2 pH meters: one digital and one analogue

Digital meter:

(2) LMC6001 op amps ($8 each) in instrumentation-amp config for > E14 Ω input impedance (1 gives E12)
(1) Atmel AT168 microcontroller ($4)
(1) Suitable LCD display
(1) Power supply
(2) Pushbuttons for mode control, buffer selection...
(1) Op amp for RTD (XTR105 $6 - this is for 4-20 loops but there is probably a similar part with voltage output)

Analog meter:

(2) LMC6001 op amps ($8 each) in instrumentation-amp config for > E14 Ω input impedance (1 gives E12)
(1) Atmel AT168 microcontroller ($4)
(1) Suitable LCD display
(1) Power supply
(3) Potentiometers (gain, offset, temp compensation)
(1) Op amp for gain control
(1) Reference voltage source for offset.

So you can see where the additional complexity lies.

Keep in mind that the firmware for the analog meter is much simpler than the firmware for the digital one.

Though it should go without saying I have not done a complete design here nor breadboarded nor tested either of these. This is what I was able to come up with in about 15 minutes looking at chip makers' web sites.

 

[fethdarman]

Order mine back in August from Kats Safety and have been very happy with it:

Milwaukee MW101


Robert

Robert, how often should a pH Calibration be done?
And would this be ok to use?https://www.amazon.com/dp/B0063MVU5S/?tag=skimlinks_replacement-20

 

[ajdelange]

A pH meter should be calibrated before each brew day and more frequently if its stability requires it. See the Sticky on pH meter calibration.

 

[fethdarman]

A pH meter should be calibrated before each brew day and more frequently if its stability requires it. See the Sticky on pH meter calibration.

Thank you Sir! I was worried that the solutions cost a lot. I checked and the cost is cheap.

 

[juggabrew]

I finally, after two years of debating if a PH meter is worth it I broke down and bought the MW101. Im now looking at PH buffers and found these on amazon. Would any of these be okay to use? My thought is as long as its NIST rated should be fine?

https://www.amazon.com/dp/B01F7OXRG2/?tag=skimlinks_replacement-20

https://www.amazon.com/dp/B007X5KAV4/?tag=skimlinks_replacement-20

https://www.amazon.com/dp/B017H73794/?tag=skimlinks_replacement-20

 

[Sourz4life]

Biopharm is the best in my opinion. I currently use it in our lab for both media buffer solutions and pH meter calibration.

 

[ajdelange]

I'm sure that any of them will serve but I will mention that many of us here like the buffers that are sold as powders sealed in little plastic 'pillows'. When one is ready to measure pH he clips the end off the pillow and dumps its contents into 50 mL of DI water. This insures that you have a freshly prepared buffer each time you calibrate.

You would think that these would have a much longer shelf life than the bottled stuff but they do have listed shelf lives and they are not that much longer than that of the bottled buffers. The main reason for them is convenience and absolute assurance that your buffers are not contaminated or different from their design values from dilution or evaporation.

Even more convenient are pre-made buffers which come sealed in little plastic envelopes like those used for ketchup. They are prohibitively expensive however.

Most of us use the Hach pillows.

 

[rustygates]

I finally, after two years of debating if a PH meter is worth it I broke down and bought the MW101. Im now looking at PH buffers and found these on amazon.

Sorry to revive this ancient thread but just curious to see how you are liking the MW101 after a year. Any regrets not getting the 102?

Have you had any issues with non-Milwaukee brand pH buffers or storage solution?

Have you had to replace the electrode yet?

 

[juggabrew]

The 101 is great and hasn’t given me any issues so far. I️ do calibrate before every brew but never really budges from the 4 buffer. Small tweaks if that.

I️ chose the 101 over the 102 because I️ can chill my sample quickly with a cocktail shaker and ice so I️ don’t need or want to waste my money on the extra cost of the temp probe.

Honestly, now that I’ve used it I️m starting to use it less and less and trusting what brewnwater estimates the mash at. It’s pretty damn accurate IME. I’m glad I️ have the 101, but I️ would’ve been just as happy going with a cheaper pen style. I️ do get annoyed with the cord on the probe ...

As far as the buffers, they’re great. Happy brewing

 

[mabrungard]

I’m glad I️ have the 101, but I️ would’ve been just as happy going with a cheaper pen style. I️ do get annoyed with the cord on the probe ...

I know your frustration. I've got a little nook in my brewery that I can set the sample and probe in and everything is fine. But it would be better to have a pH probe support instead. The problem is that those specialized supports are EXPENSIVE!!!!

A far less expensive option would be to get a Laboratory Support Stand with a clamp. That way you can keep the probe and cord from getting in the way or falling over.