Official Luthiers Forum!

Hi guys,
I built a wet bulb hydrometer, I used a 4" fan placed at 24" with the dry bulb upwind.
My readings are as follows,
Dry bulb 27*c, wet bulb 13*c, differance of 14*c
According to the chart Hesh posted my RH is 16%
I took 3 different readings, each reading I timed the "read" time at 10
minutes, the RH was the same all 3 times.
This was a very interesting test, I plan to take reading every day for months in my shop and
in my house where my guitars live, this should give me the info I need to determine when to work on my tops.
I plan to brace, voice, detail and glue on my tops at the very low end RH range.
I'd rather deal with the RH raising slightly then lowering.
Hesh, you were right, my Wal-mart digital hydrometers were so far off I felt they were useless,
they now reside in my shop trash can.

_________________
Gregg

HVAC and Lab technicians use a "Sling Psychrometer" which does the same thing. Here's one on e-bayhttp://cgi.ebay.com/SLING-PSYCHROMETER-BACHARACH-12-7013_W0QQitemZ350336036804QQcmdZViewItemQQptZLH_DefaultDomain_2?hash=item5191a7afc4 These have both wet and dry bulbs and a direct reading scale on the body of the instrument. Very accurate. Very inexpensive.
Cheers!
Art

Gregg-
How far off were your Wal-Mart instruments?
(BTW-those are partial immersion thermometers, but it probably doesn't make any difference.)

Cheers
John

Hi John,
The Wal-Mart digitals were both high, one by 8% the other by 6%,
Yes I am aware they are partial immersion thermometers,
However as long as the bulb is covered the reading should be correct.
Thanks

Gregg

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Gregg

Great job Gregg and now you know one way or the other. You also have a reliable way to test RH going forward too.

You might want to keep the digitals in as much as they can be a reliable indicator of change, just not how much change.... I use mine for that so that at a glance I can tell if everything jives with the calibrated Abbeon.

It's also interesting that in testing every digital that I encounter I find that they are more accurate in certain ranges than others. For example one of my digitals is 12% off at 45% and 19% off at 28%.....

Stay tuned because David Collins, Simon Fay and I are collaborating to test some Caliber III digitals and then post our results.

Glad this helped Gregg.

Couldn't have done it without your help Hesh,
Thanks !!

Gregg

_________________
Gregg

Awe shucks..... Thank YOU Gregg!

Deleted

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Keep in mind that even on a decent quality BACHARACH Wet/Dry Bulb Mercury Sling Psychrometer (similar to the one linked to above) they only claim an accuracy of +/- 5% for humidity.......so if your digital units are within 8%, that's not that bad. If your thermometer isn't accurate within 1 deg F, then you your humidty calculations could be off by 7%. If your thermometer is one deg off and you sometimes have an error of 1 deg reading the thermometer, then the humidity calculation could be off as much as 14%. If you aren't careful and let your body influence the temperature reading by 1 deg F, then your humidity calculation could be 7% off.

I guess my point is that just because you are doing a wet/dry bulb test doesn't mean it is perfectly accurate. You need an accurate thermometer, you need to read it accurately and consistently, and you need to pay close attention to test procedures. If you've done all that, then the wet/dry bulb test is a good one.

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Formerly known as Adaboy.......

Hey Darryl,
Thanks for the input,
It's funny you mention my body temp influencing the reading, I already
thought about that and believe it or not I hold my breath while taking readings.
As for reading the therometer I use 6x reading glasses so I can be as
accurate as possible.
I even purchased 4 therometers and set them side by side, allowed them to
stabilize for an hour and used the two that were reading exactly the same for my
hydrometer.
I follow the same routine each time I take a reading,
#1...Reservoir 2/3rds full,
#2...Wicking action completely wet,
#3...The same 4" fan on at 24" with dry bulb upstream,
#4...Reading time 10 minutes,
#5...Hold breath, take readings and calculate.
I think I've got it nailed to the best of my abilities.

_________________
Gregg

I notice that the pic shows the thermometers at floor level.
Do you read the thermometers at eye level?


Darryl's points are well taken.

Cheers
John

The pic was taken on the floor leaning aganist the couch,
However reading are taken in the house at approx 42" on a "bar top"
Readings are taken in my shop at 40" on my bench.

_________________
Gregg

Greg,

Did the mfg of your thermometers incude an accuracy with the documentation?

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Formerly known as Adaboy.......

"Did the mtg of your thermometers incude an accuracy with the documentation?"

Don't think so, I did receive some paperwork with the purchase, however I don't remember
any "documented accuracy"

_________________
Gregg

I followed this thread and after last summer and this winter with outrageous RH problems, I bought one of those Bacharachs. I have several of the Radio Shack(or, even more "hip," THE SHACK)digitals that were kind of decent in helping maintain a broad range of safe RH-safe in the most generous sense.

This winter I learned that the little vertical side braces do stop cracks from going past the location on a side-tailblock to first one on a walnut. As it has been, if I get +/- 5% I am worlds' better off.

I was further pushed, not only by you folks shaming my laxity, but also by the loving generosity of daughter and SIL who gave me an Amazon gift card--"Papa, you are always looking for some small gimmick there!<G>" Me, Big hugs and sheepish <G>.How lucky can a certifiably insane old man get-and I actually liked the SIL, Chad, from first meeting. My lovely daughter met me as I met him at the door-"not quite ready", but a genuine glowing beauty;her Mom's a looker--"Chad, this is my Papa; would you like to see his shotgun collection?" Nervous young man laugh. One of those couples where when you are in the room with them, you can literally sense the power of their love-got to be a gift from "You know where."

Sorry-you know how I ramble;always have a "back story." Grateful man and member, MT