Thermoworks 8689 pH meter?

[ajdelange]

ajdelange: You said, "See the Sticky on pH meter calibration for tips." I don't see anything like that; is this posted somewhere else?

It's at the top of this page https://www.homebrewtalk.com/showthread.php?t=302256

 

[Hophappy]

Thanks, great write-up! There's a lot of info in there to digest.

 

[rhys333]

BREW DAY UPDATE:
I'm pleased to report all went well today. Auto-calibration worked perfectly for both the 7.0 and 4.0 solutions. Took about 15 seconds to provide a stable temp-adjusted reading. Same for the wort sample. Bru'n predicted 5.33 at RT and the sample was 5.31 at 26C (78F).

Happy customer!

 

[rhys333]

So it looks like a couple of us here asked a question on the Thermoworks website about auto-calibration on 8689 and if we need to manually adjust the pH readout to match the buffer value at a particular temperature. Someone from Thermoworks answered that YES, we need to manually adjust.

I followed up with a phone call and it seems this answer is likely incorrect. With ATC, the 8689 should display the correct pH for a given temperature without you needing to make manual adjustments. The only time you would need to adjust the pH readout is if it does not match what the buffer pH is supposed to be at a certain temp. Those temp-corrected values are shown in a table on the solution bottle.

 

[ajdelange]

Of course that answer was wrong. Fire that man or send him back to pH U. The table on the bottle should be in the meter. If it is then it should do autocal and autocorrect without any intervention from you. If it isn't that is a very compelling reason for looking for another meter.

If the pH of a buffer differs over temperature from what is on the bottle lable that's an indication that the pHi (isoelectric pH) of the meter is not 7. In that case you cannot calibrate the meter effectively unless both buffers are at the same temperature and all samples are at that temperature too.

 

[rhys333]

QUESTION ABOUT MANUALLY CALIBRATING pH READOUT:

So last brew day the the pH readout on both 7.0 and 4.0 buffers were 0.01 below where they should have been for the temperature. According to the instructions, I'm supposed to manually correct this with the up/down buttons. Pushing these buttons doesn't change the pH readout though.

8689 owners, how do get the up/down calibration buttons to respond when I need to adjust readout values?

 

[JonM]

I think you have to hold the arrow buttons down.

 

[rhys333]

I think you have to hold the arrow buttons down.

Thanks, I'll try that. Hopefully it doesn't just reentrer full calibration mode.

 

[JonM]

In my experience (and it took a while for me to figure this out) is that calibration takes a long time with this meter. I put it in the buffer, move it around a bit then let it sit until it recognizes the buffer. It takes a minute or two for each one.

 

[rhys333]

In my experience (and it took a while for me to figure this out) is that calibration takes a long time with this meter. I put it in the buffer, move it around a bit then let it sit until it recognizes the buffer. It takes a minute or two for each one.

Similar results here... maybe 30-45 seconds. I didn't need to manually calibrate today as it was spot on. Tried holding the buttons though just to attempt a recalibtation. Did not work.

 

[sweetcell]

sooooo... any more updates from the field, now that it's been in use for a while?

 

[rhys333]

sooooo... any more updates from the field, now that it's been in use for a while?

Mine is still working fine, as far as I can tell. It gets a stable reading in 20-30 seconds, and nails calibration within 0.02 at a given temp. I still haven't figured out how to toggle the readout up or down to match cal solutions at a given temp (e.g.: to change a 4.00 readout to 4.01). I think there's a step missing in the written instructions.

 

[JDL]

I have used mine on two batches now. I calibrate it each time as it gets off pretty fast but each calibration has been fast and agree with above post, gets a stable reading in about 20 seconds.

I currently use these from amazon to hold testing item and calibration fluid. https://www.amazon.com/gp/product/B00BJPGIPQ/?tag=skimlinks_replacement-20

I use 4 of them, one has RO water for rinsing and then two more for calibration fluid and one with the beer sample. The cylinders work great because you can set it in and walk away and it holds it up nicely and keeps it submerged.

 

[rhys333]

I have used mine on two batches now. I calibrate it each time as it gets off pretty fast but each calibration has been fast and agree with above post, gets a stable reading in about 20 seconds.

I currently use these from amazon to hold testing item and calibration fluid. https://www.amazon.com/gp/product/B00BJPGIPQ/?tag=skimlinks_replacement-20

I use 4 of them, one has RO water for rinsing and then two more for calibration fluid and one with the beer sample. The cylinders work great because you can set it in and walk away and it holds it up nicely and keeps it submerged.

Have you figured out how to toggle the readout up or down while in CAL mode? Instructions say to press up or down, but when I do that nothing happens.

 

[Bottoms_Up]

The calibration instructions for the 8689 are confusing (just purchased one). The instructions say to match the chart by looking at the temperature. The pH reading should be adjusted to the reading opposite the temperature. Thus, for the 7.0 pH buffer solution at 20 C, the reading should be adjusted to 6.88. Is this understanding correct?

But, it says that the pH buffer solution should be 6.86 to start with. The buffer solution that comes with the kit says 7.0. Why this discrepancy between 6.86 and 7.0? Is the buffer solution actually 7.0 or 6.86? Others talk about 7.01. What's the point of 6.86 when we are trying to calibrate for 7.0? Or are buffer solutions slightly different, ranging between 6.86 and 7.01?

Very confusing.

 

[mongoose33]

Have you figured out how to toggle the readout up or down while in CAL mode? Instructions say to press up or down, but when I do that nothing happens.

I've ordered one of these so I'm quite interested in the conversation here.

Rhys, have you tried pressing and holding for 3-4 seconds? On my Inkbird controller, to reset parameters you have to hold the set button for more than 3 seconds for it to kick into reset mode, then have to hold it again for more than 3 seconds to save the changes.

Not sure that would be the problem here, just an idea.

 

[ajdelange]

Why this discrepancy between 6.86 and 7.0? Is the buffer solution actually 7.0 or 6.86? Others talk about 7.01. What's the point of 6.86 when we are trying to calibrate for 7.0? Or are buffer solutions slightly different, ranging between 6.86 and 7.01?

The pH of a buffer depends in its temperature. This is a basic fact of the chemistry. The meter's calibration procedure has to take the temperature of the buffer into account when it calibrates and has to, similarly, consider the temperature of the sample when it estimates the pH from the electrode voltage. Good modern meters have the table (or formulas) of buffer pH vs temperature built in and it should not, therefore, be necessary to make adjustment for temperature during calibration. I do not know anything about this particular meter.

 

[Bottoms_Up]

The pH of a buffer depends in its temperature. This is a basic fact of the chemistry. The meter's calibration procedure has to take the temperature of the buffer into account when it calibrates and has to, similarly, consider the temperature of the sample when it estimates the pH from the electrode voltage. Good modern meters have the table (or formulas) of buffer pH vs temperature built in and it should not, therefore, be necessary to make adjustment for temperature during calibration. I do not know anything about this particular meter.

Thank you. However, the difficulty is in understanding what pH this buffer actually is. In the charts, the basic pH rating is for 25 C, but they are 4.01, 6.86, and 9.18. The buffer solutions I purchased are for 4.0, 7.0 and 10.0, within 0.01 accuracy. If I assume these values are also at 25 C, they obviously differ significantly (especially the 10.0 buffer). The odd thing is that these buffer solutions come from the same manufacturer. In fact, in their table, under the 10.0 buffer, no temperature even comes close to the 10.0 value. The closest is at 0 C, which is 9.47.

 

[ajdelange]

The chart is for NIST standard buffers and the ones you bought are 'operational' buffers, derived from the NIST buffers and traceable to them but at more convenient values of pH. The vast majority of the meters in this price range are set to use the operational buffers but some do recognize the NIST buffers as well. Given that you have the operational buffers the temperature chart for the NIST buffers is of no use to you.

The pH values for the operational buffers can be calculated from simple formulas which are given at https://www.homebrewtalk.com/showthread.php?t=302256. As I noted, you should not, with an ATC equipped meter, have to do anything about buffer temperature. To check that this is the case you can calibrate and then warm or cool one of the buffers. Measuring it with the recently calibrated meter should give the pH calculated by the appropriate formula at the temperature of the buffer at which the measurement was made.

 

[Bottoms_Up]

Thank you. However, the difficulty is in understanding what pH this buffer actually is. In the charts, the basic pH rating is for 25 C, but they are 4.01, 6.86, and 9.18. The buffer solutions I purchased are for 4.0, 7.0 and 10.0, within 0.01 accuracy. If I assume these values are also at 25 C, they obviously differ significantly (especially the 10.0 buffer). The odd thing is that these buffer solutions come from the same manufacturer. In fact, in their table, under the 10.0 buffer, no temperature even comes close to the 10.0 value. The closest is at 0 C, which is 9.47.

I just heard back from the company that sells this device. The confusion lies in the chart in their Operation Manual, which they say should be used for calibration purposes. In fact, this is not correct. The chart does not match the buffer bottles that they sell. There are charts on the bottles themselves, that should be used, not the charts in the Operation Manual. Apparently, the chart in the Manual is simply a "guideline". I wish they had explained that in their Manual, and that the chart on the bottles should be used instead.

 

[rhys333]

I've ordered one of these so I'm quite interested in the conversation here.

Rhys, have you tried pressing and holding for 3-4 seconds? On my Inkbird controller, to reset parameters you have to hold the set button for more than 3 seconds for it to kick into reset mode, then have to hold it again for more than 3 seconds to save the changes.

Not sure that would be the problem here, just an idea.

Thanks for your reply. I am able to calibrate by holding the CAL button 2 plus seconds, so no issues there. It's when I want to try adjusting the digital readout up or down to match the buffer solution at a given temp. I've tried holding the up/down buttons while already in CAL mode to do this, but nothing happens. The device itself seems to be working perfectly, but what I'm experiencing is a combination of user error, vague instruction manual and Thermoworks product support staff that aren't up to speed on product specs. Other than that, the 8689 seems to be an excellent meter. It nails the buffer pH just about bang on. On two occacasions it was 0.01 off (which is how I encountered the issue with adjusting the readout).

 

[ajdelange]

An error of .01 on a cal check does not require correction.

 

[rhys333]

An error of .01 on a cal check does not require correction.

Thanks, I figured as much. Again, really happy with this unit and I do recommend it.

 

[Bottoms_Up]

The pH of the mash is usually measured at room temperature. However, the actual pH of the mash at mash temperature is different than the measured pH of that mash when it cools to room temperature. When a recipe suggests a certain mash pH, do they mean the pH measured at mash temperature, or the pH of that same mash, but measured when it cools down to room temperature?

 

[ajdelange]

That is entirely at the whim of the writer of the recipe. I don't think I have ever seen a recipe that specifies pH but I have seen the broad guidelines in Kunze that indicate that lagers tend to mashed at slightly higher pH than ales. But if you do see specific values assume that they are at room temperature unless specifically indicated that mash temperature is intended. Most writers adhere to this unwritten convention but there are exceptions. Gordon Strong, IIRC, uses mash temperature in all his writings.

In the literature authors often don't say which they have used with the exception of DeClerck who in his classic two volume tome specifically mentions that all pH values are at lab temp. Often you can tell by he pH range itself. If values are 5.4 - 5.6 it is likely that room temperature is applicable. If 5.1 - 5.4 mash temp is probably meant.

 

[Bottoms_Up]

Just a few questions about the buffer solutions.

1. What volume would be considered adequate enough for each calibration use? About 20 ml?
2. Can these smaller volumes be used more than once, if stored in a separate small bottle? Just wondering, because these buffer solutions are fairly expensive.
3. For the 8689 pH Meter, is it necessary to calibrate all 3 buffer solutions each time, especially if the upper range is not used? (i.e is there really any need to calibrate the 10.0 buffer?).

 

[rhys333]

Just a few questions about the buffer solutions.

1. What volume would be considered adequate enough for each calibration use? About 20 ml?
2. Can these smaller volumes be used more than once, if stored in a separate small bottle? Just wondering, because these buffer solutions are fairly expensive.
3. For the 8689 pH Meter, is it necessary to calibrate all 3 buffer solutions each time, especially if the upper range is not used? (i.e is there really any need to calibrate the 10.0 buffer?).

I use just the two buffer solutions that were recommended to me (7 and 4), and pour just enough into a shot glass to cover the probe and still allow for free movement of fluid. I also use regular distilled water for both rinsing and storage. The first company rep I spoke with back in March seemed to really know his stuff and recommended I go this route. I use so little of the buffer solutions (10 ml max) that I expect them to last quite a while.

 

[ajdelange]

1. What volume would be considered adequate enough for each calibration use? About 20 ml?

Enough to cover the sense bulb and the reference junction is sufficient but keep in mind that the electrode will have (unless you blot in with a paper towel and the blotting includes bulb and junction) some of the DI rinse water adhering to it. This dilutes the buffer and shifts its pH slightly. From this POV more buffer solution is desirable than the bare minimum.

2. Can these smaller volumes be used more than once, if stored in a separate small bottle? Just wondering, because these buffer solutions are fairly expensive.

Because a small volume is more easily contaminated relative to a large one I'd say no. Unless you buy buffers in the individual ketchup/mustard/mayonaise/soysauce packaging they aren't that expensive.

3. For the 8689 pH Meter, is it necessary to calibrate all 3 buffer solutions each time, especially if the upper range is not used? (i.e is there really any need to calibrate the 10.0 buffer?).

The meter assumes the pH is a linear function of the voltage produced by the electrode. In calibrating with a pair of buffers it determines the slope and offset of the calibration 'curve' between the pH's of the two buffers. Those values are not applicable to measurements taken outside the range spanned by the two buffers. So if your measurements are restricted to the range 4 - 7 pH then a two point cal with 4 and 7 buffers will suffice. You can accurately measure with a 4 - 7 cal a little outside the 4 - 7 range, say up to 8, but for best results you should use a 7 - 10 calibration for anything with 7 < pH < 10.

 

[Bottoms_Up]

Thank you, rhys33 and ajdelange! That is very helpful.

 

[rhys333]

Thank you, rhys33 and ajdelange! That is very helpful.

I'm just some schmo bumbling through the process, but AJ is the expert here on this.