Official Luthiers Forum!

Hi Folks,
Just wanted to pass on some information. I probably have more experience with the Caliber III's than most. I recently started including them with my guitars and have purchased dozens at this point.

I use Lab grade Anhydrous Potassium Carbonate to calibrate my 2 shop hygrometers twice a year. This establishes a known RH of 43.1. I have read that it can be difficult to establish a truly exact RH level with these saturated solutions but apparently the deviance is not significant in terms of real world performance. I have a nice little setup that I use and I give plenty of time to perform the calibration (about 20 hours).

All of the Caliber III's in the past year (about 12) have been within 3% accuracy upon opening. Nine out of ten are about 1% off.

I always keep two of these in my wood storage room. 1 year ago, one of these was 2% high and it has drifted 3 points lower. The other has remained the same.

I also have a digital RadioShack hygrometer for my workshop that I have had for years. It is about 3% to 4% high.

Overall, I have had very good luck with them. It still is good insurance to verify the readings but I think the folks who calibrate the Caliber III tend to do a very good job. Just thought I would pass on this information.

There only (mostly) reliable in the 42% - 48% range. Below or above is a mess (in most cases).

Because the meter is digital, doesn't mean it's correct. The (cheap) sensors which are used by most of these units are not linear but logarithmic in there readings. Changes between the 20-40% and 50 -90% scale are hard to detect, let alone convert correct by a cheap A/D converter.

The overview picture has a meter on the right which is calibrated (within +/- 2% range!).

The other pictures are from a new RH meter (with a humain hair). This meter got good test results and is cheap. Right out of the box it showed a RH which was 15% higher as it shoud be (around 65%). All RH meters with a hair should be regenerated when you take them out of the box (and every 2 to 3 weeks). This can be done with a wet towel.

After 1 hour it showed a RH of 110%. The meter can be adjusted with the little screw.

Best regards,


Edzard

MMV on Caliber III! (My Mileage Varies)

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Mine varies a lot!

My only accurate digital I have is a cheapie from Radio Shack. It's consistently within 3 percentage points of my wet/dry bulb psychrometer.


Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

I'm happy with my Caliber III.

I expect my guitars to be able to survive some swings in humidity, so I don't get very excited about =/- 5% RH.
I'm lucky to live in a very moderate climate, so RH is not the problem here that it is in many places.

Cheers
John

Looking at the tables for the wet/dry psychrometers shows that at 20 deg C (room temp), each degree difference in wet bulb depression corresponds to a seven percent difference in RH.
(ie 6 deg=51%RH, 7deg=44%RH, 8deg=37%RH)
So you need to be very confident in those temperature readings.

Cheers
John

Great idea!!!!!!!!!!

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Thanks Woody. I started doing this when one of my Ameritage case hygrometers was fairly off (it was 6% high).

Just to clarify - I am not saying that the Caliber III is always going to be accurate -- just that I have a lot of experience with them and they have been very accurate for me. For those who build regularly, it is essential to know for certain that your hygrometer is calibrated correctly. I feel like the salt test with Potassium Carbonate is pretty foolproof. I had a buddy that worked in the lab with me years ago and he had some trouble getting consistent readings with a sling psychrometer. When I run out of Potassium Carbonate, I might just buy a really nice hygrometer and pay annually to have it calibrated. Peace of mind when it comes to humidity control and lutherie is crucial.

Simon my hats off to you for going to the trouble and expense to include a Caliber III with your guitars. If nothing else it adds a physical reminder to the owners that RH is important.

However..... my mileage has varied too....

I did a study of the Caliber III's and posted my results here: http://www.anzlf.com/viewtopic.php?t=2116&highlight=caliber

Mine were around 9 - 10% off in the range that we work in and not always consistently off to this degree. Sometimes they were more off and sometimes less off. My standard was a calibrated Abbeon and of course several real-time wet bulb tests.

Although I agree that a Caliber III will show that the RH has changed and I also agree that one could with experience note the discrepancies and factor accordingly I don't agree that a Caliber III is accurate enough to use as the only reference to build by.

Earlier this afternoon when I first read this thread I set my phone on the wall to show the time and date and took a picture of what my Caliber III (I have three of them and they are all consistently off to the same degree....) said. As you can see today it's about 6% off.

Mind you I don't care about several percent but I do care when we approach 10%....

I used to recommend Caliber III's on the forums but can't do that anymore. I do understand that you have skin in the game so-to-speak with this company and device so I understand the importance to you of having anything that you include with your very fine guitars be of superior quality. And maybe yours are functioning better than mine. Mine are now several years old, batteries have been replaced, and I did not subject any of mine to any chemical testing in as much as the warranty that comes with the device explicitly says not to do this that it will damage the hygrometer.... Do I believe that? Don't know but I felt that a wet bulb test repeated several times and with different thermometers would be a better way to go.



Regarding the Abbeons I know the guy who was responsible for keeping 4 of them calibrated at Elderly Instruments. Calibration was done 4 times a year and my friend observed drift in accuracy of over 5% in just 3 months time..... They were calibrated just as I do mine with several repeated wet bulb tests.

Heck, Hesh, 6 to 7 points out of 44 is nearly 15% variant to actual. That's a lot. I know mine is often off by as much as 20 to 25% based on my tests.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Right you are Waddy - it's too far off for me to use them for anything other than an indicator of change.

I'm baffled a bit by all this....
What sort of thermometers are you folks using for your wet/dry bulb measurements?
Are these high-precision mercury thermometers that can read to a fraction of a degree?
Or just basic alcohol-filled thermometers?
Since a very small error in temperature depression measurements can result in quite a big difference in calculated RH, accurate temp readings are essential if you are using this as your 'calibration standard'.
Leaving aside the price/confidence issue for a minute...
If you have several hygrometers, and one gives a different reading from the others, and that one has been reported to 'drift' in calibration over a few months....the conclusion is that the one that is different from the rest is the correct one, and that the others are all defective?

Just curious about the reasoning here....though I do appreciate that you are checking the hygrometers against the wet/dry device.

Cheers
John

Just to add to the data pool I did the potassium carbonate test on 2 radio shack hygrometers and 1 system III and all checked out at within 2-3 degrees of 43%. They also were consistent (and have been for a couple years) when all placed next to each other but a difference of a few feet away could change the readings. My shop is not vapor barriered or anything etc.... Interestingly I have never heard anyone say anything bad about the radio shack ones, they seem to be pretty quality.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

Further clarification, I have no invested interest in the Caliber III. I just wanted to relate my experience because it has been overwhelmingly positive and consistent. Also, a saturated salt solution calibration CANNOT damage a hygrometer - the ions do not "evaporate".

My advice is also to "test" rather than go based on reputation alone.

Hesh,
If you are interested, I can send you some Potassium Carbonate and you can verify your Abbeon. The reason I like the salt test is that it isn't dependent on the calibration of another instrument (thermometer, etc...) but relies strictly on the known and very repeatable properties of an easy-made solution. I would be curious to see how your calibrated Abbeon is reading. The more data we can gather the better.

Kind Regards,
Simon

John and Simon you have overlapping questions that I can answer with one answer - the thermometers if you read my link above I purchased 4 and selected two that read identically for my tests. It's certainly possible that the two that I selected were off but all four read very close to each other without more than 1 degree of error IIRC. Sure I could purchase 10 more and keep going but where does it stop and when do you start believing what you learned?

I'm not the only one here in this thread reporting that Caliber III's are not accurate....

Simon the Abbeon is not being used as a standard/control in the original post above. The wet bulb test is the standard and a repeated standard at that.

I'm not interested in any testing of hygrometers beyond a wet bulb type test because I understand this kind of test. I don't understand the salt test beyond the theory. I've done salt testing before but with table salt and the 75% target.

No need to send me anything Simon but I would recommend to you that you conduct wet bulb testing and let us know what you find out? You are making the claim that Caliber III's are accurate to 1% nine out of ten times and my claim is that these hygrometers are not accurate. Perhaps future purchasers will let us know what they find out and how they came to the conclusions that they arrived at.

My shop is as insulated as can be, vapor barrier and all. North side is always drier than the south side by a few % points, except in the middle of the day when the sun is at its apex, then the south side -where the most light and heat come in- is drier, still by no more than 5%. It surprised me at first, until I put my hygrometers side to side.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Another datapoint here--my Caliber III reads 9% under the actual RH as measured by wet bulb test. It is very consistent, though.

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Evan McCartney

Another thing that is a good idea is to keep fans running in the shop all the time. I keep one oscillating fan and another in a little anti-room where the hot water heater is. I don't believer there is a spot in my shop with no air flow.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Hesh buddy, no offense intended here - but you keep putting words in my mouth. I am not making the claim that they are accurate 9 times out of ten. I am just saying that the ones I have received have been very accurate -- there is a huge difference between those 2 statements. One reflects one person's experience with a relatively small sample size (but still more experience with this one brand than most) and the other is an absolute statement regarding accuracy.

Also, if someone who has a calibrated hygrometer is up for it (Hesh, maybe) - I can send someone a Caliber III that is reading correctly and they can verify the reading - should only cost us both a couple dollars in shipping and would be a good way to compare calibration techniques. I myself might try out a couple different calibration techniques as well. The reason this is a good idea is that people introduce errors -- I have seen relatively easy and reliable calibrations yield different results for different people yet give consistent results for the individual. With something as finicky as RH, it is a good idea to pool our collective knowledge. Please call me at 386/690/2567 if anyone is interested in doing this.

Kind Regards,
Simon

Hi Simon - no offense taken my friend.

I want to get this thing right too so I asked David Collins to help. David has agreed to lend an independent voice to our discussion and test your Caliber III hygrometer.

I work with David so I will be there but no worries again I want to get this thing right regardless of the outcome. I'll PM you with an address that you can send a Caliber III to. I'll also test one of my CIII's at the time too. Perhaps my batch and your batch have different results.

David plans on using a rather cool psychrometer that is from the University of Michigan surplus. Here are some pics. You can see it's a powered wet bulb test with an electric fan to draw air over the wet bulbs. David has two of these so we may try them both:





Also David sent me this link which contains some interesting information about calibrating hygrometers, salt tests, etc. http://www.conservationphysics.org/satslt/satsol.php

I'll also pry my Abbeon off the wall and include it on testing day too but again it's only pictured to show it's different readings in my tests it was not used as a control.

Hopefully this will shed some light on how the Caliber III's do for accuracy.

Thanks again Simon - PM on the way.

I sure appreciate everyones input on this subject!

I like both the wet bulb test and the salt test. I don't have Potassium Carbonate so haven't used that test but I think it would be a good one for testing accuracy in the low 40% range; however, it doesn't tell you much about the accuracy at other humidity levels. Maybe testing with Potassium Carbonate in the low 40% range and then testing with table salt in the 70% range would give a good indication of the accuracy in the mid-range humidity levels......but not at extremes.

This was mentioned earlier, but the wet bulb test is only as good as the accuracy of the thermometer.......assuming good test procedures are used. It was noted earlier that 1deg F off in the reading can cause an inaccuracy in the humidity of 7%. If you read one degree high on one reading and one degree low on the other reading, the humidity from the look-up table could be off by 14% which would be very misleading. As far test procedures affecting the outcome of the wet bulb test, if you test near your body and it influences the temp by 1 deg (which could easily be done since your body temp is near 100deg and ambient air might be in the high 60s), then your humidity reading would be off by 7%.

So to summarize, if a digital hygrometer is reading +/- 7%, it may be as accurate as the wet bulb test with a cheap thermometer........or as accurate as the wet bulb test if carefull attention to procedures aren't followed. If you use a good thermometer and if your procedure is good, the wet bulb vs dry bulb differential is as accurate as any across the entire humidity range.

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Formerly known as Adaboy.......

I have two Abbeons and a Caliber III. The Caliber III consistently reads within 2 or 3 % of the Abbeons.