Let's design and build a better hygrometer, once and for all..!

[Mario Proulx]

If you saw my handwriting......

I'm in the market for a cheap tablet, specifically to keep in the shop. I have a Blackberry phone, but it's too damned small for me to type anything into it without two pencils with new erasers... <sigh>, so I only use it to check e-mail during the day.

All told, the GIT method is only necessary once or twice a year, to check and recalibrate(if necessary) the shop's hygrometers, so walking back to the house with the dewpoint and air temps scribbled on a piece of scrap isn't a bother.

BTW, my wife, the soapmaker, has never heard of potassium carbonate. Thus, we have none...

[Mario Proulx]

Methinks this thread has run its course and very much served its purpose. In the next day or so, I'll take some step-by-step photos and non-confusing and clear instructions for doing the GIT RH test, and post it in a new thread, and ask that it gets "locked". We've tried it, tested it, and even found out that it wasn't a new method at all, so debating it or further commenting on it in the new thread will only make it confusing and such. As it is, this thread is now a mish-mash and even I am afraid to re-read it! <bg>

[David King]

Not to change the subject too much but I would love to get folks recommendations on decent, everyday hygrometers that can be calibrated. The $29 Radio Shack ones I have can not and they only seem to work for a few years before they go blank. That info might be useful as part of the permanent record.

[Mario Proulx]

Any mechanical hygrometer can easily be calibrated.

None of the digital ones can. At one time, the digital units had adjustable pots inside for calibrating, but none that I know of, today. Progress....

In my direct experience, all the inexpensive mechanical hygrometers use the same, or very similar, mechanism, and having just added a third different one in the shop(to replace the old adjustable digital unit that just died), once calibrated, they do a really nice job within the RH and temperature ranges we keep our shops at. Most of the time, if they begin to read differently, a good blast with the air gun will bring them all back. Dust buildup is the enemy.... In other words, just get 2 or 3 inexpensive($10-20) units, hang them on the side by side or on over the other, and call it done.

[Mario Proulx]

Here, like these for $10 each at Lee Valley....

http://www.leevalley.com/en/wood/page.a ... at=1,42405

[Simon Magennis]

Over on delcamp there is also a humidity discussion at the moment. Someone posted this link: http://www.kingofthehouse.com/hygrometer/
It's for the saturated solution method. What might be worth a look for those interested is a chart at the bottom of the page which lists numbers for 11 different salts which can be used. If one salt is more readily available than another it might worth a look.

[David King]

I did a little research and I see some of the humidor digital hygrometers are calibratable now. Amazon sells a Hygroset II for around $16.
http://www.amazon.com/Quality-Importers ... B000H6CZQE

[Jason Rodgers]

Read the reviews on that one before buying, David. I usually only read the 1- and 2-star reviews to find out where people had issues. This unit has a number of complaints about the ease (or even possibility) of calibration.

[Bob Hammond]

Perhaps this Temp/RH/Dewpoint datalogger might be a storebought solution. They can be ordered with NIST calibration certificates.

http://www.dataq.com/products/hardware/ ... ogger.html

[Bob Gramann]

I got a nice calibration certificate with an Abbeon hygrometer that I bought new a few years ago. When I tested it against a psychrometer, it was way off. You need the combination of a good instrument and the ability to accurately calibrate it locally. Even if you get lucky and the hygrometer you bought was correctly calibrated, it will drift over time. There have been three calibration methods discussed in this thread. None are difficult. I don't think you can purchase a long-lasting solution.

[Simon Magennis]

If you saw my handwriting......

... I have a Blackberry phone, but it's too damned small for me to type anything into it without two pencils with new erasers... <sigh>,

...

You can get keyboards and a little stand for Blackberrys. Have used one myself but I was thinking about it this morning and did a search. Could be a solution.

[Bob Hammond]

Bob, on the spec sheet for the datalogger, I see that the longterm stability of the device is typically 0.5%, and that at a sampling interval of 1 reading per 12 hours, that the device will store at least 2 years of data. Is that ok for you? Besides that, I've been using this company's A/D recording systems in a laboratory for about 25 years, and their equipment has been very reliable.

[Bob Gramann]

Okay. That's better than I would have expected. I haven't taken the step of buying scientific equipment. Your device doesn't cost any more than the hygrometers that I have bought. Maybe I'll do one of those the next time I have to buy one. The cheap electronic ones that I know about have a sensor that gets dirty over time and loses accuracy (not that they were ever very accurate). I took one apart and cleaned the sensor. It hasn't worked at all since then.

[Bob Hammond]

Bob,

you've raised an issue that I hadn't fully considered, i.e. dust contamination. Maybe a solution to that is to protect the hygrometer by placing in a box with a HEPA filter. I don't know if the readings would be affected by a reduction in airflow, but it would be possible to add a tiny computer fan too. Incidentally, I see on the DATAQ ordering literature that the calibration points should be specified at the time of ordering, probably to minimize errors.

[Mario Proulx]

Bob, you're slowly creating the Rube Goldberg hygrometer to end all Rube Goldberg hygrometers! And spending a ton in the process, too. And you still would only have one of them, and that one needs to be checked against a precise reference, and that's what we've come-up with here. For the cost of one(1!) thermometer....

besides, that unit is nothing more than a glorified digital hygrometer and thermometer. It then -calculates- the dewpoint from those readings. It is therefor no more precise than any other digital unit, though it would be more carefully calibrated from then factory. That won't keep it calibrated through the years, though....

Honestly, just get 2 or 3 of the $10 mechanical units in the link I posted, from LeeValley, check them against, and calibrate according to, the GIT test. Done! For $20 or $30! I've had one of the above mentioned hygrometers for about 8 or 10 years now, and it has always read well, and reads the same as the other units I have, and is no more prone to drifting than the others.

Another advantage that mechanical units have VS digital units is that they're slower to respond. How is that better, you ask? I found out, a long time ago, that when I'm working in the vicinity of my hygrometers that the digital unit would begin reading much higher, within minutes, especially if I was using hot hide glue, but the mechanical units generally weren't as "bothered" by my temporary presence.....

[David King]

Lee Valley has free shipping for the next two weeks.