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-   -   Hannah Checker PH meter reading are all over the place. (http://www.homebrewtalk.com/f128/hannah-checker-ph-meter-reading-all-over-place-317948/)

swerner 04-02-2012 02:42 AM

Hannah Checker PH meter reading are all over the place.
 
I purchased The Hannah checker from my LHBS and I have to say I'm disappointed in its performance. I treated and calibrated according to the directions. First off the calibration is a manual calibration were you have to use a small screw driver to calibrate the 4.01 and the 7.01 range. This is where my problem begins. After calibrating, I'll clean off the bulb with distilled water and when I stick it back in the 4.01 buffer again it will be off by .1. I've used it on my last two brews and the meter never seems to stabilize. I used AJ's R/O primer and I'm trying to get fairly accurate readings but I just don't trust what I'm reading. Today My first reading @ 5min. was 5.31. The next reading @ 10min jumped up to 6.1. I let the samples cool to room temperature on every reading(about 72F). The rest of the reading flucuated between 5.3 and 5.4. I could never get any of the readings to stabilize where I was confident in any of the readings I got. Does any one else have this meter. I've read the sticky on meter calibration and I can't think of anything I'm doing wrong. Am I just expecting too much from an inexpensive meter. :confused:

ajdelange 04-02-2012 05:23 AM

It's normal for pH readings to climb in a mash for an hour or more but I'm not sure it is normal for them to climb that much. The question is indeed one of the stability of the meter. I would suggest leaving the meter in each buffer for at least 5 minutes before making the adjustments. Then after the calibration is complete stay in the 4 buffer and record readings over time. Obviously, the reading should hang in there right around 4. If it steadily but slowly climbs or descends then the meter is drifting but if the readings are erratic i.e. sometimes higher, sometimes lower then there is a problem with the meter (not that drift isn't but I think you have to expect some drift with an inexpensive meter). There are 2 possible solutions to slow drift. One is wait long enough that the drift has stabilized before twiddling the offset and slope pots and the other is to correct the drifted readings. If it comes to that I'll post the formulas for doing this.

If this is a meter with a removable electrode you might try pulling the electrode off and putting it back on (the idea being that the removal and replacement will polish the contacts some). Also make sure that your cell phone is off or well removed from the area (or any other transmitting device such as a wireless router - I was once working with an electronic barometer that gave erratic readings but only when one of the dogs was nearby. They wear collars which transpond their GPS locations).

I'd say that if it is new and readings in buffer are erratic you should take the thing back to the dealer and get a replacement unit.

mabrungard 04-02-2012 12:45 PM

Not storing the probe in pH storage solution could create that problem. The potential drying of the liquid-filled bulb or leaching of potassium from the bulb might be a cause.

PistolsAtDawn 04-02-2012 03:05 PM

If this was made by Hannah Instruments, then I'm not surprised. I bought and immediately returned one of their "high accuracy" thermometers because it looked like a dollar store kid's toy. The screws on the battery door stripped with no force at all.

swerner 04-02-2012 09:46 PM

There definitely is some drift. I re-calibrated the meter using AJ's suggestions and then I let it sit in the 4.01 solution for an hour. It drifted to a reading of 3.92. I'm thinking I may want to spend a little extra and get a more stable meter. If I'm making adjustments with lactic acid and lime, I want to be confident that my meter is working properly. I really do enjoy these forums and appreciate everyone's help.

iverasp 04-07-2012 03:03 PM

I have this model from Hanna and it works just fine. I calibrated it in the lab and always store it in 4M KCl solution. This was after many years of being stored dry.

feffer 09-11-2012 11:47 PM

This post is a bit old, but I have been using a Hanna Checker for 6 months and think it works pretty well, but there are a few things to watch for. One of them is temperature. All pH meters work similarly: a current is generated through the electrode and its intensity is reflected as the pH reading. This pH reading will vary with the temperature. Since this model does NOT automatically compensate for temperature differences, the electrode and the solution being measured must come to the same temperature. If your beer or wine is much different than room temperature, two things happen. First, the electrode warms up (or cools down) until it reaches equilibrium with the solution it's in. That's why the reading moves rapidly and then settles down to a stable point. This should be an accurate reading if the unit is calibrated correctly.

However, if the liquid is far from room temperature, it will begin to cool (or heat) until it reaches equilibrium with the room. This is a slower process, and if the pH meter is in the liquid during this time, the reading will gradually drift as the liquid's temperature changes. That's the theory, and I've noticed this behaviour in practice. If I measure a solution that is near room temp, the reading stabilizes fairly quickly. On the other hand, if I try to measure a solution that I've just taken out of the fridge, it will drift continually making an accurate reading impossible.

What I do now is take a sample of something I want to check and put it in a small covered glass, and let this glass sit while I do other things. When I'm sure it has reached room temp, I check the pH. This seems to work well, and I don't get "drift."

Finally, this is a useful meter, but it is only designed to be accurate to .2 (plus or minus) at least according to Hanna's specs. However, measuring the same solution weeks or months apart gave me very similar readings. So I think this unit IS useful for beer or wine-making.

ajdelange 09-12-2012 02:40 AM

The electrode and solution must be in thermal equilibrium whether the meter is equipped with ATC or not. Since the thermal masses of the electrode is small this usually happens pretty fast.

The electrode produces a voltage which varies with pH. pH electrodes are very high impedance devices with resistances of around 1E12 Ω. Though a current must flow in order for a measurement to be made it is in fact the voltage which the meter measures. The voltage is
E = Eo +s*(T/To)*(pHi - pH)

Eo is the voltage the electrode produces when immersed in a solution at pH equal to pHi. pHi is the pH at which the response of the meter does not depend on temperature. T is the temperature in K and To is a reference temperature (also in K). s is the 'slope' of the electrode at To, typically something around 58 mV/pH. It depends on the temperature and the age of the electrode. To use the meter one must have values for the calibration constants Eo and s. Clearly the response depends on T. If the meter's circuitry can insert the (T/To) factor into its calculation then the meter is 'temperature compensated' (ATC equipped) and measurements can be taken at any temperature but one has, when calibrating at temperatures other than room temperature, to take into account that the calibrating buffer's pH's vary somewhat with temperature. An ATC equipped meter does this automatically. In a non ATC meter it must be done by the operator. It is quite possible to do but a little involved. It is, thus, when the meter is not ATC equipped, very important to make sure that the buffers and sample are all at the same temperature.

craigevo 09-14-2012 08:22 AM

I have used this meter for about a year now. I had to get a second probe after only a month. The first probe worked very consistently for a few batches, then went haywire with crazy readings. I got a new probe and things appear to be fine now. Its always pretty much bang on when I calibrate with 4 and 7 solution - only ever .02 off at most. And my mash ph's are pretty much always the same for the same receipes with same salt additions, so Im pretty confident at least its consistent.

I did notice one gotcha, I once got erratic readings and tracked it down to a piece of grain in between the probe and the outer plastic shell. I now pour my samples through a small sieve to get just the liquid. Also as mentioned by a previous poster - this thing is really sensitive to temp. I now always calibrate and measure samples at about 25-27 C. When I think about it now, maybe my first probe was OK after all but I was measuring at different temps.

In summary, I may have been unlucky with the quality control on my first probe, otherwise this is a good meter once you get used to it. I have never done much pH reading work before and so this learning curve may have been the case if I had started with another model of meter.

lastly, one thing it wont measure very easily is water. eg sparge water - it goes from 5.5 to 6.0+ over a minute or two, stir the water and it goes down again then creeps up again. I have to take an average and leave it at that. I normally do another reading once I have collected the entire kettle volume and assume my sparge water ph was fine as long as the ph of the kettle wort is not much different to the mash ph eg 5.4 to 5.5. I am not sure if this derivation is reasonable or not.

Kaiser 09-14-2012 04:33 PM

Quote:

Originally Posted by craigevo (Post 4412291)
lastly, one thing it wont measure very easily is water. eg sparge water - it goes from 5.5 to 6.0+ over a minute or two, stir the water and it goes down again then creeps up again. I have to take an average and leave it at that. I normally do another reading once I have collected the entire kettle volume and assume my sparge water ph was fine as long as the ph of the kettle wort is not much different to the mash ph eg 5.4 to 5.5. I am not sure if this derivation is reasonable or not.

This is because your water is weakly buffered. The pH probe actually consumes a tiny amount H+ and thus works like a base which drives up the pH of the liquid close to the membrane if it is weakly buffered. When you move it around the measured pH drops b/c you even out the H+ concentration.

The good thing is that if your water is weakly buffered it canít have a strong effect on mash or sparge pH and its actual pH also matters very little.

Kai


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