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Good morning, all.

I have been searching for a reliable hygrometer for quite some time now. I ran into trouble with widely diverging (salt calibrated) units. Some digital, some analog. None top-shelf.

I have found and read with great interest the threads about calibrating and will manage to get some carbonate to be able to calibrate at 43% RH. I have also watched Mr. O'Brien's recent video with great interest.

Today I’m asking for your input on the subject : what are you using as your reliable instrument for everyday RH checking? What do you recommend as a reasonably-priced unit? Is the Stew-Mac unit any good, for instance? I believe its display cannot be calibrated but this can be accounted for after testing, right?

Thanks a lot for your input, as always. You are the greatest bunch of people.


Pierre
www.torvisse.com

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Pierre Castonguay

I rely on a used Abbeon wall hygrometer, calibrated with a used psychrometer. You can also use a potassium carbonate solution to calibrate a hygrometer.

The key is to buy a good one, and calibrate it using a good method.

I see several used Abbeons on eBay. Apart from needing calibration, do those go bad over time or is the working principle reliable enough that I can buy a used one and have a reasonably good chance of ending up with a fully-working unit?


Pierre
www.torvisse.com

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Pierre Castonguay

I would not get one that cannot be calibrated. Well, I do have a cheapo unit as a backup that I used a red Sharpie on to mark the ideal settings after calibrating. I got one from a retired violin maker called an Air Guide and it's reasonably accurate. But at least twice a year I use a Psychro-Dyne wet bulb psychrometer to calibrate it.

I have three of these in the three main areas of the woodshop - AcuRite 01083 Indoor Thermometer & Hygrometer with Humidity Gauge & Pro Accuracy Calibration, White https://www.amazon.com/dp/B01HDW58GS/re ... 7Cb5CF90MB

I have an Abbeon in the wood storage room. Mostly because it looks more official.

All the cheapies calibrated within a couple percent. I check them every so often to make sure they haven’t gone sideways.

I don’t know what it is about my basement shop, but I have very little problem keeping it under control. Some others have had horror stories. I have two Home Depot self pumping dehumidifiers running. One in the woodshop and one in the wood storage room. I blow them out occasionally and they’ve been running fine for a couple years.


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I use an abeon and use these that are alternates around the shop. They calibrated easily with the salt method and are within a few points of the abeon. I will never use a digital I found them to be too unreliable. I had never got a digital one to stay reliable to the abeon.
https://www.amazon.com/Cigar-Oasis-Hygr ... 143&sr=8-6

The abeon is hard to beat. Remember holding to a point is one thing controlling the rh swings is most important.
I use a dehumidifier and humidifier set in the shop
Dehumidifier is set at 55% humidifier is set for 45%
my shop is about 1800 sq ft . It holds very stable. I am also 6 in insulation with vapor barrier and sealed concrete floor.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I have 2 not particularly expensive digital ones. The make is probably not relevant since I am in the UK. They have been fine for several years and pretty much agree with the one on my dehumidifier.

Having two does give me confidence and is well worth it in case one packs up.

Dave

I use a couple of Hygroset II digital hygrometers https://www.amazon.com/Hygrometer-10-Second-Tempeture-Quality-Importers-x/dp/B000H6CZQE. (Available also at Amazon.ca, Amazon.co.uk and many other suppliers, often on sale). There's good reason to be dubious about the accuracy of any hygrometer, digital or analog, so calibration once a year with potassium carbonate is essential.

The Hygroset in my wood room lives beside the sensor for my programable humidity controller, built around an industrial panel mounted unit, so one is verification of the other. The controller is programmed to fire up the humidifier at 40% and the dehumidifier at 44%.

Two Lufft units (marketed by Abbeon in the US, but made by Lufft) and an Extech 445815. One of the Lufft units - one old enough to be labelled as West German - was full disassembled and refurbished, while the other was a relatively new unit purchased at auction for a few dollars. All were calibrated with salt solutions and checked with Boveda humidity control & calibration packs. The Extech unit reads high, but between 32% and 58%, that error is +4%, +/- 1%, so very useful.



We did have both of Mr. Morelli's Cole-Parmer-branded Lufft units in, as well as several others (Boston and a no-name) from area builders for our calibration fest in December and January . Other than an aging Accurite indoor/outdoor unit that refused to yield anything close to a consistent value on RH, all were calibrated to reasonable usefulness for RH values we see in the Central Atlantic states.

What I learned from buying and mixing various salts up for calibration: just buy the Boveda packs...same accuracy and much less mess and bother. We use the 49% packets for a center point, then check the high and low ends of the range with the 32% and 58% packs.

Boveda sells a 32%/75% calibration kit, but IMO, the 75% table salt test is so far out of the useful range that it makes little sense to bother with it, as in every case we checked, a hygrometer that was calibrated for accurate measurement at 75% had 7% or more error in the desired 40%-50% RH range.

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For the times they are a changin'

- Bob Dylan

The "fit the right range" issue is why I use potassium carbonate to calibrate, if not using the psychrometer. A potassium carbonate solution creates RH of 43.13%, right where we want it. Table salt creates a RH so far outside the range we want that you might as well not calibrate.

Potassium carbonate is easily purchased on eBay for next to nuthin'.

I use a sling psychrometer to calibrate my meters. They are quick and easy.

A photo of my calibration box — a plastic freezer food storage box, with a sealed hole to pass the cable for my RH controller sensor. There’s enough room to also place my Hygrosets in the box at the same time. The white dish contains the moist K2CO3.




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Thanks for all the useful input on calibrating and the absolute need for it folks, but let's not forget I'm asking for what model hygrometer you are using and if you're recommending this particular unit.


Pierre
www.torvisse.com

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Pierre Castonguay

I have two digital hygrometers in use. One is an old Planet Waves hygrometer intended to be used in guitar cases and the other is an AcuRite hygrometer: https://www.amazon.com/gp/product/B01HDW58GS/ref=ppx_yo_dt_b_asin_title_o01_s01?ie=UTF8&psc=1

I check them about every 6 months with the potassium carbonate equilibration test and both of them always read 44% at equilibrium when they should read 43%. Pretty darn close and consistent. The AcuRite unit has magnets on the back so I have it mounted on the face of a metal shelf where it is easy to see. The unit is small but the humidity readout numbers are large enough that I can read them from about 15 feet away.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Sorry to be that guy, but I would hate for someone to buy the wrong stuff. Potassium carbonate is what you want to use, not potassium chloride. Potassium carbonate solution yields RH of around 43.13%, whereas potassium chloride solution yields RH of around 88.62%. Different stuff.

A BestAir HG050 Hygrometer, an Ikea analogue (hair) one, and an inexpensive digital -?
All calibrated in a snap lid box with potassium carbonate periodically.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Thanks for being "that guy". It's a very important distinction. My mistake. I do use potassium carbonate not potassium chloride. Corrected my post above.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

Just a quick tip if you are using salts to calibrate. You want a saturated solution - not damp salt. You need to see water or you aren't performing the test correctly. For those of you who ever took a chemistry course or have a background in chemistry, you'll recognize the term slurry. That is pretty much what you are looking for. In our case, we want an aqueous solution that is saturated with salt - meaning no more salt will dissolve. I do a Potassium Carbonate calibration and it takes quite a few hours for the container I do it in to equilibrate. In practice, I set up and then check the readings the next day.



So the above scenario will give you what you want as will a saturated solution that has a lot more water in it and that looks like the image below.



To recap, just make sure you can see a both water and salt and you'll be fine.


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Regarding hygromoters, I use the Caliber V - incredibly accurate right out of the box but they drift over time. Calibrate once a year and then throw away after about 4 years. At $25 a pop, they are worth it. I have an Abbeon as well but it responds much slower to changes and I feel that the Caliber V is actually a bit more user friendly.

Abbeon and a sling psychrometer for me. I have had the Abbeon over 10 years and it has been very close to the psychrometer without recalibration. Every digital one I have seen reads low by 5-10%. I have never had one read high.

I was just in a guitar shop today and every guitar I looked at was probably half to a full step sharp. They were relying on a digital hygrometer and I think it was way too humid.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Thanks a lot. Are you referring to the Caliber IV? Can't find the V...


Pierre
www.torvisse.com

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Pierre Castonguay

My mistake --- I meant the Caliber IV. This is the hygrometer that I recommend.

There are some great threads if you search the archives. You will learn that nearly all of them suck especially the digitals and many of them can be 15% off which can crack a guitar top.

We've tested them all over the years and offer calibration services to our clients so long as Hesh here doesn't have to go to the post office and you can bring it to us with maybe lunch too...

Some summarized things that we have learned. YMMV and I don't care.

1). Digitals suck and if it can't be calibrated don't buy it.

2). Digitals rely on an electro chemical reaction meaning that if by chance you find a digital that is acceptable for now check it in three, five, etc. years it can be 20% off and there is nothing that you can do about it.

3). There is an issue of "range." By range I mean that a hygrometer may be accurate in a specific range of say 45%. So for 45% it may be plus or minus say 4% which is usable. But for 55% it may be plus or minus 10% which is getting not usable.

Methods of calibration using chemicals provide the stated results at the RH of calibration, say 75% but when you consider the issue of range the thing may be 15% off in the range that we care about which is basically 40 - 50%.

The jury is still out on this one since we never verified this but some chemicals may damage the chemicals in the digital hygrometer rendering it either inaccurate or providing the manufacturer with a scapegoat when you learn that the thing that you just purchased for $40 is a POS.

The makers of the Caliber hygrometers used to say their warranty is null and void if you do the chemical testing. Of course this is said in the small print on the instructions in the box not on the outside of the package.

4). Some mechanical hygrometers can be way off too and need calibration so a mechanical hygrometer is not in and of itself an answer.

So.... WTH does a Loothier do?

This:

1). Purchase a mechanical hygrometer that can be calibrated such as the Abbeon which is on my wall in my lounge and I'm looking at it right now. I've had this one from Elderly Instruments for 15 years now and it's been great the entire time. It gets checked annually and I've only had to increment it no more than several percent to calibrate it and some years not at all.

PS: Nothing is more important to a proper guitar building shop (repair too) than accurate RH readings and keeping the shop in the proper range. Ignore this and your creations will surely fall apart or crack all to heck in time and no I am not calling you Shirley.

2). Purchase the stuff to do a "wet bulb" test and learn how to do one. There are many different ways to do a wet bulb test, some of the threads in the archives here have my take on how to proceed with the testing and calibration. I'd find it for you but I'm old and hung over.... today. I'll be old tomorrow too but I digress.

3). Perform a wet bulb test (can you hum a few bars...) with the mechanical hygrometer very close in proximity to the test. Simply breathing on stuff can skew things so being dead already provides better test results. Where is a White Walker when you need one. Winter is coming....

4). Note difference, calibrate the hygrometer, repeat and check yourself (for accuracy on the test not looking inside your depends). Once your hygrometer is within a few percent of the results of the wet bulb test you are good for a year. Repeat in a year. I would repeat in 6 months the first time with a known unknown new hygrometer attribution Rummy.

It's really very simple and easy but you can never trust a digital or a fart. Learning to do wet bulb tests is easy, fun and it's science too which sadly can be spelled sc*ence these days by some but who cares most of them can't tread water well anyway.

Good luck!

Just dug up some pics from the past here showing my current Abbeon and a couple variations of wet bulb testers along with other hygrometers.

The extracted data from Omega Engineering's Z-103 reference document covers the various salt solutions, and - more importantly - the dependency of the RH on temperature. Some saturated salt solutions provide a stable RH reading over a wide range of temperatures, and other vary quite a bit. Also note that salt mixes must be made up with pure water (distilled/deionized), and the usual recommendation is to allow the humidity sensor 24 hours in the chamber to allow both RH and sensor to fully stabilize. Our sole digital unit has a half meter long cable between unit and sensor, so just the sensor is exposed to the potentially corrosive atmosphere in the calibration box (a gasket-sealed clear poly-carbonate plastic gear box re-purposed from former duty as cigar storage container for overseas trips which never seem to be discussed in any meaningful detail).



Here are links to the Z-103 reference page and to the cited papers:

https://www.omega.co.uk/temperature/Z/pdf/z103.pdf

https://nvlpubs.nist.gov/nistpubs/jres/ ... 19_a1b.pdf

https://nvlpubs.nist.gov/nistpubs/jres/ ... 89_A1b.pdf

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For the times they are a changin'

- Bob Dylan

The small $20 digital hygrometers used for cigar humidors will work just fine so long as you 'calibrate' them. This can mean two different things: I suspect that most people mean mechanically adjusting the hygrometer so that it matches a known accurate standard. The other meaning of calibration is to determine the margin or percentage of error of the hygrometer and then factor that in when reading it. Either method will work well, provided the known standard is accurate and the hygrometer maintains a consistent margin of error, within a safe range.

I use a wet bulb system made by Psychro-Dyne to accurately calibrate all my hygrometers. Affordable, fast, and easy. http://www.iisusa.com/Psychro-Dyne-Batt ... nfo/22014/. I can open a case and play a guitar that hasn't been used for months and find that it doesn't need tuned because the RH in my shop is so stable. My small cigar hygrometers read a few percentages low consistently. When they read 42-43%, my shop is at 45-47%.

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It will probably be alright.