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Old 11-02-2012, 11:47 PM   #31
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I need to order a meter soon. Is anyone aware of a sticky comparing ph meters?

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Old 11-02-2012, 11:48 PM   #32
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I need to order a meter soon. Is anyone aware of a sticky comparing ph meters?
Kai had a thread on it. I don't remember the name of the thread though.
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Old 11-03-2012, 12:13 AM   #33
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Kai has an article at brewkaiser but it recommends against ATC saying it is not necessary. I think that's bad advice. At the marginal cost of ATC in modern meters I'd say it is well worth having as it allows you to read buffers and samples at different temperatures without having to measure temperatures and dial them in via a temperature compensation pot. It is automatic - that is what's great about it. One should not stress the ATC algorithm however unless he knows that the isoelectric pH of his electrode is 7.00 (which is what the ATC algorithm assumes).

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Old 11-03-2012, 02:59 PM   #34
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Here’s Kai’s article: http://braukaiser.com/wiki/index.php...r_Buying_Guide

I think the thing about precision is important. A digital meter’s accuracy is always ± x% or ±1 digit, whichever is bigger. So an indication of 5.3 actually means 5.2-5.4.

I disagree with AJ about ATC. I have the MW101, the updated version of the one Kai has. It has a manual temperature comp, it doesn’t do much. I just leave it on 25C. AJ is probably looking for more precision than I am.

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Old 11-03-2012, 03:38 PM   #35
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Wynne, I'm on board with you. I don't see ATC doing much for me either. AJ's comment has some validity since the cost of a meter with ATC keeps coming down. I'm just not sure its really worth it though.

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Old 11-03-2012, 04:12 PM   #36
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There are many factors that contribute to pH meter error. The limiting factor for the typical ± 0.02 NIST technical buffers is the buffers themselves if all measurements are taken at the same temperature. At midrange between the pH's of the two buffers (i.e. right around where mash pH falls) the uncertainties in the individual buffers 'averages down' and accuracy of a bit better than 0.02 (i.e. the accuracy of each buffer) is attainable. If, OTOH, the temperatures of the individual buffers and/or the sample are not the same the algorithm that calculates the slope and offset must know those temperatures quite accurately. In a meter that is capable of reading voltage to ±0.5 mV which has been calibrated at 20 °C reads a sample at 30 °C it is still capable of accuracy dominated by the buffers but a bit worse than 0.02 provided that the temperature is measured to ± 0.5°C (and, used properly by the algorithm). It also requires that the uncertainty in the isolectric pH of the electrode be ± 0.3 pH.

It seems to me that we would want the limitations on the accuracy of our pH readings to be set by the buffers, not by the electronics. It's sort of like buying a Hi-Fi. The speakers are the limiting factor in the performance of a Hi-Fi. Would we buy an amplifier that limits the performance further especially when we can buy one for only marginally less that removes the amplifier from the equation?

I do chase accuracy more than most - no question about it but that's because of my engineering background. Error analysis may be a strange hobby but it can be interesting to see how error's propagate. In an inexpensive pH meter it is doubtless the instability (which means that the voltage error amounts to mV rather than a fraction of mV) that dominates ultimate meter accuracy but that can be 'calibrated out' if you are fast enough. ATC just makes all that much easier. Seems silly not to blow the extra $10 and get ATC. Advising people that they don't need it is, IMO, bad advice.

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Old 11-03-2012, 07:18 PM   #37
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Sorry AJ, you haven’t convinced me that I need ATC, or even that I want it. You might consider it a worthwhile feature, but it’s far from being a necessity.

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ATC just makes all that much easier. Seems silly not to blow the extra $10 and get ATC. Advising people that they don't need it is, IMO, bad advice.
It’s more like $25. I like simple, mine has a power switch and two adjustment pots.

How did easier turn into need it ? I measure all my samples at room temperature, that’s just good practice. At room temperature ATC does nothing.
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Old 11-03-2012, 10:37 PM   #38
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Sorry AJ, you haven’t convinced me that I need ATC, or even that I want it.
No need to apologize. No loss to me. I'm not trying to convince you in particular that you should or should not have ATC. But I do need to make sure other readers are aware of the value of it. Were there none the manufacturers would not offer it because people wouldn't pay the 'premium' for it. It's not quite the same as Apple convincing people they need the new iPhone. pH meters are used by engineers and scientists capable of making informed decisions (for the most part). It is perhaps true that in a meter that uses analogue circuitry (potentiometers) for calibration gain and offset that ATC isn't justified because of the inherent inaccuracies/instabilities introduced by the use of analogue techniques but I don't suggest that people buy analogue meters either. There is a reason they have long been supplanted by digital.

If you don't appreciate the value of ATC I suggest that you refrain from buying meters equipped with it.

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You might consider it a worthwhile feature, but it’s far from being a necessity.
I definitely do but then I've done error propagation analysis on pH measurement.


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Originally Posted by Wynne-R View Post
It’s more like $25. I like simple, mine has a power switch and two adjustment pots.
You do need the power switch but you don't really need the adjustment pots. Just a high impedance voltmeter will do. In fact that's how I use my lab pH meter. All it does is send millivolt and temperature readings to the computer. Of course the computer does ATC on the calibration and readings. I really can't imagine what sort of code I could write that didn't incorporate ATC. It's an intrinsic part of pH measurement.

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How did easier turn into need it ?
Well a lot of people measure pH for a lot of reasons and as most modern meters are equipped with ATC I guess a lot of meter buyers think they need it. As noted above, if they didn't then the meter manufacturers would not be able to use it as a sales promoting feature. But then again as also implied modern meters use digital circuitry after a fixed gain instrumentation amp. The numbers from the A/D get inserted into microprocessor algorithms identical to the ones in my lab computer. ATC is an inherent part of this.

Beyond that I have lots and lots of thing I don't need in my brewery. It is those things by and large that make the difference between a day of drudgery and an enjoyable brewing experience.


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Originally Posted by Wynne-R View Post
I measure all my samples at room temperature, that’s just good practice. At room temperature ATC does nothing.
That's not so. Temperature compensation is being done whether you are aware of it or not. The meter has to know the temperature difference between the buffers (if any) and the temperature difference between the buffers and samples. The only case where no temperature compensation is required is where both buffers and sample are at exactly the same temperature. If I calibrate without ATC using an analog meter then I need to insure that the buffers are at the same temperature. That should be easy enough to do as I can just put them in a water bath. But then I (or the meter) must know the temperature of any sample I measure because the slope is directly proportional to temperature. If I'm using an old analogue meter I have to measure that temperature and dial it in with another potentiometer or bring the sample to very close to the buffer temps. If I'm using a modern meter it's done automatically (including the temperature measurement and I can focus on brewing - not correcting pH readings. I don't have to worry that one buffer was a little warmer than the other nor do I have to get the sample temperature exactly or very close to the buffer temp. Without temp. compensation 5 °C means 0.017 pH error. With ATC 10°C or more is close enough (subject to isoelectric pH being close to 7 and because of possible pHi variation one doesn't want to be too far from the buffer temperature - not to mention physical stress on the electrode). I like to take lots of pH measurements and, with ATC, I can do that with ease and have confidence in the numbers that go in my log.

In an analogue meter you control the gain and offset of operational amplifiers to set slope and offset and trim the gain by (Tsamp/Tbuff) to compensate for temperature. In a digital meter you solve a pair of linear equations (which may contain different buffer temperatures) and then simply multiply the slope by the ratio of buffer to sample temperature. Since you have to implement the equations anyway that is why all digital meters have ATC capability - it's automatically built in. I suppose you could figure out some way to 'cripple' the ATC so you can charge $25 to un-cripple it but as I've seen ATC equipped meters for under $80 I doubt anyone is doing that.

Looking at what I've just written perhaps the best reason to insist on ATC, then, is to be sure you have a meter than does calibration and interpretation of electrode signals digitally.
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Old 12-21-2012, 06:10 PM   #39
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Wow. I know what I'm getting for Christmas. MW102!

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Old 01-05-2013, 03:29 AM   #40
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Well I completed my first attempt using a ph meter as well as using acidified malt and adding Calcium Sulfate and Calcium Carbonate to the mash. As you can see from my fist and original post my water ph read 8.0 (tested from wards labs). Not until after I mashed I decided to investigate why my ph was lower than my target (target 5.45, measured 5.29). I'm convinced this had much to do with my starting pH which was later measured to be 7.0. What other carbonate and/or bicarbonates are effected in my water report due to have a measured pH of 7.0 water than 8.0 for this instance. If this information is known I need to make the corrections to my water profile for that day. Looks like on brew day I need to calibrate and measure tap water pH instead of assuming the water report pH is up to date.

Another challenge I seemed to face was determining what value to record when using the Ph meter. The display just didn't seems to settle. When I say this it wasn't jumpy rather shifting 0.05 within 10 minutes. Is this unusual with a meter that has a resolution to 0.01? By thy the way I'm using the MW102 from Milwaukee. I need to prepare myself for next time. See attached is my water profile before and after. Take a look and share your comments about the ions added with respect the the DIPA beer style that was brewed. I'm not sure why the CaC03 read -98 and the RA at -160. Can this be possible?

Thanks,

~Justin

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