Humidity

[Jim Hilburn]

So our old outside wireless thermometer quit so we went to Lowes and got a new one. The new one shows in and out humidity. Years ago I got a fairly pricey hygrometer for the shop from Griz and it's made by Arbeon. The Lowes unit was $20.
So the new one shows 37% while the one in the shop is at 46%. They are in different rooms but not that far apart. Because of the shop reading at least 45% I've never fired up the humidifier there so far.
But it's snowy, cold and the furnace runs quite a bit. Holding that 45 seems a little hard to believe. I once went in Lowes and looked at a batch of cheap dial hygro's and none of them matched. How can I check these to see what's accurate? I go to Wikipedia and look up psycrometers and I go psycho and my eyes cross trying to grasp what they're talking about.
Any reliable way to check these?

[John Flynn]

http://www.kingofthehouse.com/hygrometer/

[Jim Hilburn]

Thanks, John.
I also found an About.com how to that just gives the simple how to without all that 'splainin'.

[sunburst]

The old, non-electronic, non-dial, wet and dry bulb thermometer is the standard by which all others are calibrated. A little arithmetic is involved, but you can post a table right next to it to avoid having to do the calculations. It is not instant 'gratification', can't be read at a glance, but it's as accurate as you can get, and once you compare the dial or digital types to it, you know how to read them, if they are working at all.

Another low tech yet very accurate hygrometer is a hair hygrometer. I've been meaning to make one for years but still haven't done it. A gooooooogle search will turn up instructions on how to make one.

[Paul Busman]

Why not just take both hygrometers into the same place and see if they match? Am I missing something in your question?
Put'em both in the shop and let them come to equilibrium. Then take them wherever else you want a reading and repeat. If they're off, you'll at least know by how much and have a general idea of what your readings mean.

[Bernie Daniel]

The old, non-electronic, non-dial, wet and dry bulb thermometer is the standard by which all others are calibrated. A little arithmetic is involved, but you can post a table right next to it to avoid having to do the calculations. It is not instant 'gratification', can't be read at a glance, but it's as accurate as you can get, and once you compare the dial or digital types to it, you know how to read them, if they are working at all.

Another low tech yet very accurate hygrometer is a hair hygrometer. I've been meaning to make one for years but still haven't done it. A gooooooogle search will turn up instructions on how to make one.

I think some of those more expensive digital hygrometers are based on a strand of human hair. The dominant protein in hair is keratin which of course has a lot of sulhydral linkages (freeing bonds via chemical reduction and then re-bonding (oxidation) of the sulfhydryl bonds of these cysteine-based cross linkages is the mechanism for women's -- or men's these days I suppose permanents -- but this is OT).

Anyway the tertiary structure of the hair is via non-covalent hydrogen bonds (bonding associations between the associated water molecules (i.e. HOH....HOH) in the hair shaft -- the number of these bonds is highly influenced by humidity (water in the air natch) so the hair shaft lengthens and contracts accordingly.

For $25 -50 you can buy some very good scientific hygometers that are quite accurate and (if you don't drop theme and break the hair in the process) quite accurate.

Here is a really good (http://www.thomassci.com/Instruments/Hygrometers/_/Thomas-Traceable-Dew-PointWet-BulbHumidityThermometer/?=) but expensive one. You can beat this in price and still get a decent unit.

The cheap ones you get at hardware stores are near worthless IMO - -you can usually pull the back off and rough calibrate them by twisting the dial (but don't break the hair!). They may work for a while that way but when you run them against a decent unit you find they are very inconsistent -- neither accurate NOR precise.

[Jim Hilburn]

So I followed the easy instructions in the About.com "How to calibrate a Hygrometer"
site which is in an exotic pets section and here is the result.
There's a half cup of salt and 1/4 cup of water in the cup and sealed in the bag for several hours you should get a 75% reading. So it appears my high dollar hygro reads high by about 4%, something I've always be suspicious of.

[Jim Hilburn]

And I see when I re-visit the site John F. linked to it was pretty much the same instructions.

[Bernie Daniel]

So I followed the easy instructions in the About.com "How to calibrate a Hygrometer"
site which is in an exotic pets section and here is the result.
There's a half cup of salt and 1/4 cup of water in the cup and sealed in the bag for several hours you should get a 75% reading. So it appears my high dollar hygro reads high by about 4%, something I've always be suspicious of.

That is a reliable method for calibrating a hygrometer. However, you do not need that much salt and water. I got this method years ago from a local tobacco store owner who does this calibration once a month. Just fill a small bottle cap (like from a bottle of spring water) with about 1 teaspoon of table salt -- then add about a 0.5 to 1 teaspoon of water on top of the salt and seal in a small sandwich baggie for 3 - 6 hours. As you note the hygrometer should stabilize at between 74.8 to 75.2% relative humidity.

[Jim Hilburn]

Well, I'm drying out the salt and will put it back in the shaker.

[Bernie Daniel]

Well, I'm drying out the salt and will put it back in the shaker.

Well now you see the beauty of it, by using only a teaspoon one can afford just to throw it out....

Getting back to the pic you posted what make of a hygrometer is that I can't quite make it out...but you said it was high dollar. I'm not so sure 4% "error" is so outrageous. Here (http://www.dwyer-inst.com/Product/TestEquipment/Thermo-Hygrometers/ModelTHI-10/Specs)for example is a $100 digital hygrometer that is only spected to +/-3% RH.

[Jim Hilburn]

I tried posting this earlier but it didn't take. It's an Abbeon I got from Griz and it's made in Germany. I looked it up and it said it was accurate to +/- 3% so that's acceptable. It was $185 at the site I found it on. I paid something like that quite a few years ago.

[Bernie Daniel]

I guess the rule of thumb is that mandolins and guitars should be kept at 40 -50% RH.

For those of us in winter climates it is pretty tough to maintain that. We have a modern geothermal furnace with a radiator type humidifier -- but even running water at 56 F (i.e., using water in thermal equilibrium with earth sub-surface temperature) over the exchanger I can only reliably maintain the marginal 40% through out the house in the winter cold months. So I use in-case humidifiers.

If one takes the tension off the strings are instruments safe from wood cracking for extended periods below 40% RH?

[sunburst]

If one takes the tension off the strings are instruments safe from wood cracking for extended periods below 40% RH?

No. Wood moves in response to changes in moisture content regardless.

[Rob Grant]

Sounds like a lot of "hair splitting" to me.<G>

Happy Christmas and a Merry New Year to all the gang here from humid, cyclonic Far Out North Queensland, Oz.

[AW Meyer]

The 12th Fret in Toronto sells these, and they're pretty darned accurate. They calibrate them and will re-calibrate them, when necessary. They also ship pretty well anywhere.
http://www.12fret.com/cleaning-maintenance-products-humidity-control-c-88_45_1450/barigo-dial-hygrometer-p-2637

[Bernie Daniel]

They look nice and the colored zones are a good idea -- but they seem on the pricey end -- the specs say 3 to 5% accuracy on RH with is "ordinary" performance. What they might have going for them is durability and if you happen to be local to Toronto the recalibration service is a handy feature.

[Steve Ostrander]

Bernie, you lost me at "keratin"... :)

[Bernie Daniel]

Bernie, you lost me at "keratin"... :)

I don't blame you. Not that you are missing out on anything relative to the topic at hand -- in truth the chemistry of hair curling does not have much to do with mandolins, humidity or hygrometers I guess .. But I have always been interested by the linkage for some reason...notwithstanding that the whole thing could have been much better written......... :))