Case Hygrometers

[John Flynn]

I'm getting ready to add to my collection of digital hygrometers (yes, I have H-A-S!) to mount in a couple of my cases. I know there has been some information posted about this in the past, but I have also seen that there are some new models of small hygrometers out there that I haven't seen before. I was wondering if anyone has any experience with them.

There are a couple of different models by HygroSet and a couple of models under the "Super Accurate" brand. There is also an Oasis and a Caliber III. There may be others.

My requirements are:
1. Small enough to mount in a case with not much room
2. Either adjustable or so accurate out of the box that it passes a calibration test.
3. Has a memory function that shows the minimum and maximum RH since the last reset.

Any actual experiences with these devices would be appreciated.

[mandroid]

Anyone have a museum nearby to ask? wonder where they get their Hygrometer and climate control equipment from?

I expect accuracy as a criteria is more than a brand name when protecting the collections in the display cases is the requirement..

[liestman]

Hi John!

I use the Oasis hygrometer and humidifier in my various instrument cases. I really love the humidifiers, since they shrivel up like a prune when they need more water and they work really well at keeping the humidity in the 50-60% range (even in a large uilleann pipes case). The hygrometer I am very happy with as well. It is thin and flat, would tuck in nearly any case and is at least far more accurate than my wall mounted thing. No idea if it can be calibrated but I tend to think it is accurate to within AT LEAST a few % and I have no reason to be any more accurate. 30% is clearly too dry, so is 40%, and 50-60 is happy.

And yes it has the max / min memory since last reset function.

[John Flynn]

Anyone have a museum nearby to ask? wonder where they get their Hygrometer and climate control equipment from?

I expect accuracy as a criteria is more than a brand name when protecting the collections in the display cases is the requirement..

Interesting suggestion. I'll look into it, but I'm thinking museum display cases are a completely different application than an instrument case. For one thing, a musuem display case should have a lot more room to put a device and that device would not have to be battery operated, it could use hard-wired power. Also, museums have a much bigger budget for that than I have! But the merit of the suggestion might be more to find out what museums use in the cases that transport works of art and antiquities. If I find anything out along that line, I'll report back.

John L: Good to hear from you. I will definitely consider the Oasis.

[mandroid]

Museum ones more likely for like Lee's going away leaving several cases to keep from getting out of range, and putting them in a box.

I'm thinking the ones in cases have to cost like a dollar or 2 to make and cannot be more than a guess ..

I bought some moisture indicator cards from Porter camera , they, like litmus strips change color at their range [though indicate moisture rather than Ph] from pink to blue.
and may be as accurate as a dial gimmick put in a case .

I live with water on 3 sides on the pacific coast, and haven't concerned myself too much,
may dig out the cards from the photo bags, and see what they read these days.

have reusable desiccant bags to suck up excess moisture , silica bits with indicators with similar color shift.

[herbsandspices]

I use a Barigo model #777 hygrometer for my cases. Made in Germany, compact size, good build quality, and accurate - provided you calibrate every so often.
john

[liestman]

Out of curiosity, how do you calibrate a hygrometer (I mean what do you compare it to?) and how does one know it is accurate (do you calibrate it at several different humidity levels or ???) Not trying to argue or put anyone down, I genuinely want to know!

[John Flynn]

John:

The most accurate way is to compare it to a sling hygrometer, which you can either make, if you are handy, or buy for about $30. A company is also selling a calibration kit. Neither is necessary.

A reasonably accurate, and free, method is the "salt test" which you can do easily with just a large ziplock bag, a milk jug cap, a little salt and water. If you type "hygrometer salt test" into your browser, you will find several sites with instructions.
The jist is: Clean and dry the milk jug lid, fill with salt. Dampen the salt with a few drops of water. The salt should only be damp, not wet. The salt must not be dissolving. Put the cap full of damp salt and the hygromter into the ziplock bag and seal completely. Make sure there is enough air in the bag that the top of the bag does not lay on top of either object. The bag should be like an air pillow. Wait 8 hours. The RH in the bag will be 75%. Whatever the difference in the hygrometer reading is the error of the device. If the device is adjustable, adjust and repeat until it reads 75%. If it is not adjustable, you either mentally add/subtract the error from the reading or do like I do and make a label for it that says something like "Add 3% RH."

It is not perfect, but close enough. My personal opinion is that if the hygrometer is way outside its advertised tolerances, you should return it. I had to do that with a Planet Waves unit that was the most expensive unit I'd ever bought. It was 40% off and not adjustable.

[45ACP-GDLF5]

I've been using Planet Waves hygrometers for a few years now, and they are very accurate as long as the battery is replaced regularly. I have one in the headstock of my guitar case, and another one in a mandolin case. Both are velcro-ed down and stay in place. They show the temp. humidity, date, time (hr.min.sec.). You can also set the humidity level at a certain % that if the RH reaches that low level, it will show a water drop, indicating that you need to humidify.

[Michael Cameron]

Radio Shack used to have digital hygrometers that may meet your requirements(small,memory/Max. Min). I got one years ago;still using it.
Don't recall price;but,it wasn't expensive.

It reads within 5% of a larger one I have that was used in surgical suites(OR).

[earthsave]

There are also Boveda packs, that are preset a various humidty levels to cal or tag your hygrometer. Tag meaning if yours is high either mark it + or - that amount.

http://www.bovedapacks.com/

[John Flynn]

Scot:

I looked at those, but they are basically made for cigars, so the lowest tag level is 65%, which is too high for instruments. If they come out with 50% pack, they would open up a whole new market. I sent them an email on it. We'll see what they say.

[John Flynn]

Just heard back from Boveda. They teamed with Planet Waves to market the tecnhnolgy for musical instruments, but the product had to be recalled. They predict a mid-'09 re-launch and Planet Waves will announce it.

[acousticphd]

Interesting description of the "salt test".
I googled "hygrometer salt test" and EVERY hit that came up on the first two pages was from sites or discussion forums centered on cigar humidification. In at least half, it seemed pretty clear that the details of the test was being passed from forum to forum, without any sound reference for the test itself. Call me a fact-checker, (since the election campaign, I have developed fact-checker acquisition syndrome [FCAS]), but I'd be interested in locating at least one textbook-type, non-cigar-related reference, or "proof", as it were, for why one can be ~100% confident that this test generates 70% RH.

You'll notice that several of these same cigar sites recommend digital hygrometers, a la Radio Shack, as being very accurate and not needing calibration by the salt-test or other method (citing that these devices are factory-calibrated). This very 'fact' is one that has raised doubt here. I'm kind of interested to know since this is the type of hygrometer I use myself....

[acousticphd]

Well, I spent a few minutes putting my money where my fact-checking mouth is and found several sites documenting the above NaCl test, namely in FAQ sheets for re-calibrating or field testing honest-to-goodness weather-meter type humidity or dew-point instruments. Here's one:
http://www.randomuseless.info/weathe...ion/index.html

2 side notes:
1. The salt must be NaCl, for anyone who was considering using MgCl2 or LiCl!.
2. A Gibson guitar forum also cited the veracity of the 75% RH calibration test. Enough said.

The key is that one uses a "saturated" NaCl solution, ie, more salt than the water can dissolve (salt paste), and that it is sealed in a volume (eg, jar or bag) and allowed to equilibrate (1-12 hrs). Apparently, at a fixed temperature over a specific sat'd salt solution, there is a certain RH in the air over said solution. For NaCl, it is 75.3%. There doesn't seem to be a concern with exposing digital instruments to this test.

[John Flynn]

Jeff:

I don't know what you need for "proof," but a quick web search turned up a couple of somewhat more authoritative, non-cigar, non-instrument references. This from a site for a home inspector, talking about calibrating hygrometers used in his profession:

It is convenient for us that a solution of ordinary salt mixed with water (preferably distilled water) produces a predictable humidity over a wide range of temperatures. The humidity created, with ordinary salt (Sodium Chloride) and water, is 75.29% at an ideal temperature of 77 degrees Fahrenheit. The temperature of the room is not critical for our purposes. For example, the RH is quite stable even with large variations: Salt solution at 59 degrees Fahrenheit will produce 75.61% RH and at 86 degrees Fahrenheit the RH is 75.09%.

To calibrate the lower end, 33% humidity, Magnesium Chloride (a salt) and water is used again. At the ideal temperature of 77 degrees Fahrenheit, this solution will produce an RH of 32.78%. At 59 degrees Fahrenheit it will produce an RH of 33.30% and at 86 degrees Fahrenheit it will produce 32.44% RH. Once again, “room temperature” is not critical.

This is backed up by a site I found for National Safety Products, Inc. They sell calibration kits for $30 each, a "Reference 75% RH at 77º F saturated SODIUM CHLORIDE Solution" and a "Reference 33% RH at 77º F Saturated MAGNESIUM CHLORIDE Solution."

So if you really want to be sure, you need to buy one each of those and check your hygrometer's highs and lows. How exactly does this all work? I dunno, I slept through science class! But I figure if the salt test gets my hygrometers within a few points of 75% RH, and then I try to keep my instruments as close to a 50% reading as I can with those hygrometers, those instruments are in reality somewhere between the target 45% - 55%.