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It reminds me of the time when I put a humidifier and a dehumidifier in the same room, closed the door and left them to fight it out...

guys, it may have gotten lost in all this high tech calibration stuff, but dave mentioned a sling psychrometer above and in my mind it is the best and most accurate method to let you know the actual humidity now. It takes a minute, not 24 hrs and they are cheap. But very acurate. The would be worth having just to use once a month to see if your digital monitors are working properly. Thats the way we did it a lab loaded with million dollar electronic equipment.. just sling away... but make sure you watch were you sling,,, they do break..
Mike

Here's a link to a pdf on calibrating hygrometers using salt solutions.

However, you will not achieve really accurate results if you use table salt in tap water. Table salt can have iodine added plus modifiers to improve flowability, these will have an impact on the humidity you acheive, as will the hardness of the water you use. That said, distilled water and table salt will probably be close enough for us.

It's interesting that the table (in the pdf) states that a saturated solution of potassium carbonate will give a RH of 43% at 25 degC. There is no reason this stuff couldn't be used to control the humidity in a work shop, provided you have a big enough exposed surface area on your salt bath(s) and maybe a fan moving air across it. I'm going to give this a try as soon as my new shop is built later in the year, I'll put some plastic trays on a couple of shelves mounted near the ceiling and mount a couple of small fans on the wall over them.

Humidifiers/dehumidifiers cost an arm and a leg over here, this sounds like a much cheaper alternative, and is probably how it was done in the days before electricity.PaulB38895.9012615741

[QUOTE=larkim] Brock you only need about a teaspoon of damp salt in a
seal-able Tupperware or other plastic container. Put the damp salt in a
drink bottle lid or what ever and place the salt filled lid and hygro in the
container( plastic bag is ok, just as long as you can take a reading
through the bag) and seal. Leave for 24hrs and check, if your hygro is
sweet, it will read 75% RH. If it is out, you can re-calibrate, or just allow
for the % difference. merchant.mvc?Store_Code=ch&Screen=howto_calibrate">HERE is a
link to check details.

Cheers

Kim[/QUOTE]

Kim,

Of course youre aware that we dont need fancy hygrometers here down
under. To check humidity you just whip out a ruler and measure how far
your Blue Heeler has his tongue hanging out

[QUOTE=Hesh1956] This may be worthy of another thread....or not....or
simply not worthy of any thing but I have a thought.

With this thought in mind if I know a guitar built in my area's average RH
will live in this area can I not exceed the 42-47% for something more in
line with my average like 48-54%?


[/QUOTE]

Hesh,

Im of the view that its better having wood swell a bit rather than shrink
and crack so I aim to keep my workshop humidity a bit lower than that of
the area the guitar will be living in. Target humidity in the workshop is
about 40%.

[QUOTE=Hesh1956]
With this thought in mind if I know a guitar built in my area's average RH will live in this area can I not exceed the 42-47% for something more in line with my average like 48-54%?
[/QUOTE]

Hesh,

I wouldn't worry about it. See my comment re: the chart in Hoadley's book in my earlier post. I think that the Yamaha folks, brilliant that they are (yes, I'm a BIG fan of Yamaha ), are probably taking things to unnecessary extremes.

Best,

MichaelMichael McBroom38895.919224537

_________________
Live to Play, Play to Live

Hesh, I'm going to build a room in my workshop where I'll control the humidity, probably twice the size of your bathroom. I was thinking two shallow plastic tubs maybe 4" deep x 14" x 25", or whatever size is available that's close to that. with a small fan blowing air over each one. I don't think it'd work all that well without the fan. If it doesn't give me good control, I'll add more tubs. I haven't done this yet myself, so it's a matter of 'suck it and see'.

The good thing is that you should never have to replace or top up the salt, the water will need topping up though, how often will depend on the temp. The humidity won't really change much with changes in temp, the table says 43 point something at a temp range of 0 - 30C for potassium carbonate.

The difficult thing is that it's fairly salt specific, different salt solutions will give different RH's. I don't know what the water softener salts are, we don't need that stuff here, you can test whatever salts you have around in your plastic bag calibration set up, see what you get.

*edit* you can buy potassium carbonate at the chemistrystore.com for under a buck fifty a pound.PaulB38895.9370601852

[QUOTE=PaulB] I was thinking two shallow plastic tubs maybe 4" deep x
14" x 25", or whatever size is available that's close to that. with a small
fan blowing air over each one. I don't think it'd work all that well without
the fan. If it doesn't give me good control, I'll add more tubs. I haven't
done this yet myself, so it's a matter of 'suck it and see'.

[/QUOTE]

Paul, probably easier just to get yourself a dehumidifier and a panel
heater like me. Dehumidifier runs year around and kicks in when humidity
gets above 40-45%. During winter I have a 400 watt ceramic wall heater
going around the clock which helps keep humidity down. During the
summer humidity outside outside can get down to 20% here in Adelaide
Hills but insulation and door seals means humidity in the shop never gets
to that level.

Mitsubishi make a good dehumidifer but its no longer available in
Australia. I got my unit from a crowd in Queensland for about $Aus1000.

Cheers

[QUOTE=kiwigeo]

Paul, probably easier just to get yourself a dehumidifier and a panel
heater like me. Dehumidifier runs year around and kicks in when humidity
gets above 40-45%. During winter I have a 400 watt ceramic wall heater
going around the clock which helps keep humidity down. During the
summer humidity outside outside can get down to 20% here in Adelaide
Hills but insulation and door seals means humidity in the shop never gets
to that level.

Mitsubishi make a good dehumidifer but its no longer available in
Australia. I got my unit from a crowd in Queensland for about $Aus1000.

Cheers [/QUOTE]

Easier yes, inexpensive? No. There's the cost of the unit plus the running costs.

I'm pretty sure I can do this for under fifty bucks, plus I'll have bugger-all running costs - a couple of 12V fans is all. Plus I won't have to worry about heating or its costs, unless I feel cold, and it doesn't get all that cold in Sydney. Neither myself nor the other scientists I work with can see a reason that this won't work. A geeky solution to a PITA problem

All I know is that I have two digital that give me diferent readings in the same spot. About a ten percent difference. I'm thinking that the digitals are not that good. I think i'm gonna look for an old fasion one like my grand mom had with a dial type of gauge. It was mounted on a plaque. It used to read the temp, humidity and barometer pressure.

Sling psychrometers are definately the way to go as they typically whats used to calibrate other units in labs. I don't have one, wish I did though and thought for years that I would buy one so I could know which of my digitals is right
My digitals agree pretty well around 40% at 70F, but if thing move too much off that mark they vary from each other.
Sling psychrometers to the rescue!

_________________
Jim Watts
http://jameswattsguitars.com

Nah, no good Martin. Had to have the bluie put down I'm afraid mate, little mongrel kept knock'in off the snags from the esky....sod of a thing, the green dream was too good for him.

Still I do miss his ability to spin a good yarn late at night when he would start talk'in, and also the fact that he would fetch me a coldie when required. Hmm, spose it's a good thing I got kids now aay, at least I don't have to licence them and the dog catcher leaves em alone.

Cheers

Kim

Yes Hesh, add 5 it is really that simple and really that accurate.

Cheers

Kim

I don't want to discourage experimentation, but I doubt that you will be able to practically control the humidity in any normal room with salt baths. In the lab we were only trying to stabilize small chambers of a couple cubic feet at most. The chambers have to be completely sealed air tight. After opening a chamber to place or retrieve samples, it would take some time for the humidity to re-stabilize.

Using saturated salt solutions in trays is messy too. If the solution is giving up water, the salt crystallizes on the sides of the tray and eventually will end up climbing over the edge! Plus think about all the dust and stuff that will collect in the tray. Another problem is that salt solutions are best used for raising humidity, but they don't work very well for lowering it.

[QUOTE=Michael Shaw] All I know is that I have two digital that give me diferent readings in the same spot. About a ten percent difference. I'm thinking that the digitals are not that good. I think i'm gonna look for an old fasion one like my grand mom had with a dial type of gauge. It was mounted on a plaque. It used to read the temp, humidity and barometer pressure. [/QUOTE]

Yeah, that is what I thought. That is how I ended up in this pickle.   

I am running the bag experiment now. So far it looks like the Abbeon is the one that is way off.

_________________
Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Don't worry about it Hesh, the salt bag will maintain a stable 75%RH indefinitely (with in reason), it just takes most hygros around 24hrs to stabilise to a set RH. 24, 48, 72 hours, it just won't matter. It is all about testing your instrument in a known environment. Salt damped to the consistency of wet beach sand and sealed in a small container gives you that know environment.

The secret here is to not make it to hard, and not to be swayed by what you think should be. IE no matter how much or how little you paid for your hygro, if it reads 75% after 24hrs in the bag, it perfectly accurate. If it does not, it needs to be calibrated or an allowance for the differential must be made, it is as simple as that.

If you really must test further, put your hygro back in the bag a second time for 24 hrs after 24hrs out in the shed (bathroom) and you should get the same reading as the first 24hr test. If not, get yourself another hygro because the bag did not change, it will be pretty much 75%RH in there no matter what, that is the point.

I have used just plain tap water and table salt with no problem for this test, if anti flow agents or water additives etc do make a difference, I have not noticed and besides, the difference would be a CONSTANT so all is still good.

I don't think being a bit high on RH or a bit low is here nor there, I feel it is all about getting a reading that will allow you to know there are fluctuations in RH occurring so you can do something about it, that would seem the main point of the tool.

Cheers

Kim

You can also make a wet dry thermometer and put a fan on it once a week to check. I include a digital thermometer from Home Hardware with all my guitars and test them all before they go out. Except for one that was out by 15% they have all been with in 5%, any that are more than 2% off I return to home hardware as defective.

Hesh, you can't really just subtract the difference from the known reading to
your hygrometer. Because the instrument may not be linear.


A proper calibration for this type of instrument would be to do a two point
calibaration, One low (zero) and one high (100%). You should be able to
move the dial or meter once the known value of zero is achieved and then
again at 100%. That will tell you how much the instrument is off at each end.

Having said all that. I just keep the Radio Shack meter on my shelf and take
the reading in account for what I am doing at the time. If I am bracing a bass
violin I will crank the dehumidifier and try for a low humidity state.
Otherwise I pretty much just take what I get.