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Just read Hesh's post. His experience confirms my experiences as well. As I mentioned in my previous post, the wet bulb or sling psychrometer is a very good way of checking your hygrometers. My method of using a standardized atmosphere just illustrates my chemistry bias.

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Randy Muth
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Interesting that some people have apparently had good luck with some of the digitals. I've had about five different ones and they were all wildly inaccurate. Maybe there's something about my personal energy field that interferes with their functioning...

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

They certainly aren't all accurate. Before my present Digital I bought one that was off by 10 points. I deemed that to be too far off and sent it back.

I was incorrect in my hesitance to use a chemical environment with potassium chromate. I wasn't aware of the difference in the environment it produced. I have been corrected, and rightly so!

That said, I have a Calabre III and it is awful. The thermometer is off by several degrees and the hygrometer is off by near 10%. However, it is pretty regular in it's offness, so I suppose I could extrapolate all the time. But why? Hesh is right. A pair of lab thermometers is pretty cheap, and making a set-up on a board is practically free. Much easier than making a jig for a step in guitar making!

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Waddy

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Sound Clips of most of my guitars

Waddy, sorry I have to correct you again. It's potassium carbonate, not potassium chromate. I wouldn't recommend just anyone working with chromium salts, they're very toxic. Potassium carbonate is pretty harmless. The impure form is known as potash, which used to be made from wood ashes. Sodium carbonate is known as washing soda and can be purchased in the grocery store, but it won't give the correct RH atmosphere.

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Randy Muth
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Waddy bro your description of how RH is dynamic and using a fan can help equalize various nooks and crannies of our shops is excellent.

RH can be very dynamic and as mentioned prior here by several posters it can change as often as we can measure time... So it's a moving target at times but fortunately this is why we tend to subscribe to the idea of an acceptable "range" and not nailing some specific number.

Randy my friend I just thought that it's worth a mention since you have not had the opportunity to play with these Caliber III's that in their instructions that say that subjecting the unit to a salt test or perhaps salt-like test, I don't remember, will damage the unit and void the warranty. I know this because I posted a lot of information about these units 3 years ago including the instructions that came with them.

If I recall correctly this moratorium imposed by Caliber III on this method of testing/calibration had more than one reader wondering if something was amiss here, claiming 1% accuracy but voiding the warranty if one tested this for themselves......

Randy do you know of any reason why subjecting a digital hygrometer to the testing that you use or the old salt test shooting for a read of 75% could in reality damage these units? Perhaps I see something that is not there in my suspicion about this moratorium on testing that Caliber imposes.

That's why I didn't do well in chemistry! I should have looked at your post to make sure I typed the right chemical! I have trouble with peoples names too!

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

Hesh, now I really have problems with this company. What BS. The salt is not in the atmosphere, only the moisture is. It's not like we're talking about the wind kicking up the ocean spray at the shore. I don't have a humidor, but I would assume that one way of keeping them at the proper RH would be to use a dish of saturated sodium chloride in the chamber. Wouldn't the hygrometer be in there as well.

Here's an experiment. Dissolve some salt in a bowl of water, stick you head over it and see if the air taste salty. Totally ridiculous.

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Randy Muth
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Thanks Randy - I thought so....

So now we know what happened to the Caliber I and Caliber II....

Thank you for the info everyone. I have 2 radio shack digitals and 1 caliber III and they are all within 2% of each other when placed together. But now I am doubting them. If anything I think they may be reading high. My guitars have been doing very well in low humidity but I notice a larger change in high humidity.

Randy,
Is there a best source for the potassium carbonate? Also, I apologize if I sound a little dense, but is a saturated solution just the carbonate in water?

Thanks

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

Hi Burton,

It may be available on the web at soap making supply houses, but I think the best way to get it would be at a local college. Just find the lab coordinator for the chemistry department and tell him/her what you are using it for. Tell him/her that you build guitars and they will think that is so cool! The stuff literally cost pennies and isn't controlled or harmful, so hopefully they will oblige by filling up a jar for you.

A saturated aqueous solution is one where as much solute (potassium carbonate) will dissolve in the water as possible at a given temperature. You want enough in there so that there is still some left sitting on the bottom of the dish, that way you know it's saturated. 112g of potassium carbonate dissolves in 100g of water at room temperature, close to 1:1 so you can gauge how much you will need. You only need to use a small dish in a bag chamber. This is pretty much fool proof and doesn't even require measuring. In fact I don't measure anything, I just keep adding the potassium carbonate with stirring until no more dissolves and some is left undissolved on the bottom. I use maybe 2-3 oz of water. Just don't spill any on your hygrometer. Also potassium carbonate, just like washing soda is caustic, so wash your hands if you get any on you.

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Randy Muth
RS Muth Guitars Website
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BTW, I (like a lot of people) tend to use the word "accurate" to mean both accurate and precise, which is not a precise use of the word, but, as long as I use it that way consistently, it is accurate!

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

Burton, if for some reason the lab coordinator is hesitant to help you, just find a friendly professor, they pull rank. Again, tell him/her you build guitars. Better yet, find a guitar playing professor.

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Randy Muth
RS Muth Guitars Website
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Very clever Todd!

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Randy Muth
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I thought that mentioning the Caliber III might stir up some debate. I can only report that it has worked well for me. My wood has been well behaved.

About three years ago, I had one of the larger digital hygrometers that StewMac sold and did not find it to be as accurate (or is that precise?). It was 4%-5% off, but seemed to be pretty consistent in its inaccuracy (or precision), so it worked with a little a mental adjustment. About a year ago, I knocked it off the top of a shelf and it stopped working. No big deal since it was pretty inexpensive and I wanted a better hygrometer anyway. I was going to order the Abbeon, but as a temporary solution, I ordered the Caliber III based on someone's recommendation. I've been pleased with how it worked out, so haven't gotten around to ordering the Abbeon. I may still order the Abbeon, but certainly don't feel compelled to do so.

With a digital hygrometer (I have the Caliber III), be sure to check the manufacturers advice before using the 'chemical in a bag' test method. I recall that 'Caliber' cautioned against this- saying it would damage the sensor- but my memory on this (as on many other things) may be faulty.

In my past life, I was a high-school science teacher and we used sling psychrometers on environmental sci field trips, and wet/dry bulb thermometers in the lab. The results the kids got were far from consistent - so a bit of double-checking is in order before using the wet/dry bulb (with cheap thermometers) as the 'gold standard'.

Anyway, let's not kid ourselves .... if +-5% rel humidity during construction results in a 'problem' with our instruments, they will not do very well out in the real world. As long as the shop environment is stable from day-to-day and in the right (40-50%) range, things should be fine, IMO.

Cheers
John

Here is a link with the ERH values of different materials at different temps if you want to calibrate at other than 43% of P Carbonate. I believe that we would all agree that it is useful to get many data points when calibrating an instrument.

I did this kind of Equilibrium Relative Humidity testing a lot at a lab (many years ago) where we were determining the effect of humidity on the shelf like of different food ingredients.

http://www.omega.com/temperature/z/pdf/z103.pdf

I just got one of these that Allen posted in the other discussion .
http://cgi.ebay.com.au/PSYCHROMETER-WOO ... 1362wt_941

Wow, the price isn't bad, but $30.50 for shipping?

Joe

It's only $7.95 in the US. At least that's what it says and what I paid.
Where are you at Joe?

John,

If you scroll up you can see my response to Hesh about the disclaimer the Caliber has on using a salt test. Unless you actually spill the salt solution on the hygrometer there is absolutely no scientific basis for why this should destroy the sensor.

Steve,

Thanks for providing that link for everyone. To be more thorough it would be good to test at different RH levels. However, most hygrometers that we are talking about here can only be calibrated to work well within a certain range and fortunately as builders we are only interested in one range. That is why for simplicity I test with potassium carbonate for 43% RH and make sure that the changes in reading are reasonable when moved into different environments. Having said that, a good test wood be to see if it reads 33% for magnesium chloride and 53% for magnesium nitrate at ambient temperature. I expect most people would chose to go with the wet/dry bulb method rather than sourcing all these chemicals.

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Randy Muth
RS Muth Guitars Website
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I'm afraid I have to disagree with you here, no offense intended.

The scientific basis is called vapour deposition. That's the reason why you can smell Chlorine when you sit out by the swimming pool. Water evaporates and becomes airborne but it does take things (ions) with it.

Salts will deposit on the sensor, which if they are not removed, will over time will cause corrosion and that will kill the sensor. Once or twice is probably ok, but if you keep on doing it you'll have to buy another hygrometer. Hence; the voided warranty.

You can Google it if you disagree with me. Telling people there's no reason to not calibrate in a standard salt solution that could ruin their electronic hygrometers and cost them money is why I responded, otherwise I, frankly, couldn't be bothered.

Oh, and if you're concerned about my credentials (I noticed you mentioned yours), I can tell you that most recently I've been teaching Chemical Engineering to post grads at the University of Sydney.

That said, I have no interest in debating this with you.

Paul,

Nice of you to discredit me and then state that you have no interest in debating me. Fact is you are in error.

In order for vapor deposition to occur the compound being deposited has to be volatile. Sodium chloride, sodium ion and chloride ion are not volatile unless you heat them to a couple of thousand degrees or maybe less under reduced pressure. Look up the vapor pressure of sodium chloride or potassium carbonate. The reason you can smell chlorine around a swimming pool is because sodium or calcium hypochlorite is added, i.e. bleach. Very different than sodium chloride. Sodium hypochlorite in solution is in equilibrium with free chlorine gas. This is actually what is doing the disinfecting. Yes, I also own a swimming pool. In fact sodium hypochlorite is made by bubbling chlorine gas into a sodium hydroxide solution. You can detect chlorine at very low levels by smell. You cannot smell chlorine when you dissolve sodium chloride (table salt) in water, unless your municipal water supply is chlorinated.

I suggest you talk to your colleagues in your chemistry department, not the engineering department.

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Randy Muth
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I just want to be clear. What you are smelling around a swimming pool is chlorine gas (Cl2) NOT chloride ions (Cl-).

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Randy Muth
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Look mate, I'm sorry if I came off a little harsh on you, or if you feel I've disrespected you. That was not my intention at all, which is why I don't want to get into an argument with you. I'm not denying you right of reply. Call me whatever names you like

My background has alway been in Chemistry, I just happen to have a fair bit of hands-on Engineering experience too and Chemical Engineering seems to have chosen me at the moment. I think that most Chemical Engineers can't find their ass with both hands, most but not all.

Now, There will always be ions in water unless it's been deionized. If you have a salt bath, as the water evaporates it WILL take ions with it too, otherwise distilled water would be just the same as deionized water, but it's not. Water is volatile - to an extent, even at ambient conditions, that's what we're trying to measure here. If that water vapour then deposits on a surface (such as a sensor) salt will deposit there as well. In fact if the salt builds up on the sensor, provided it stays moist, you'll only be reading what level of humidity a standard salt solution for that particular salt will give, right up until the sensor corrodes too much to be able to operate further. Hence the voided warranty.

Vapour deposition still occurs at ambient conditions, it just works a hell of a lot better at high temps, and throw in a vacuum if you like. But it still happens at ambient conditions.

Maybe we can agree to disagree?

*edit* Oh, and you are right about the Chlorine gas thing, bad example. Mea culpa.