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| Thermometer type for humidity check? http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=14673 |
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| Author: | Todd Rose [ Sat Nov 24, 2007 10:44 pm ] |
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Does it matter whether I use a "total immersion" or "partial immersion" thermometer for a "sling psychrometer" (I don't plan on actually slinging it, but holding it in the air stream of my dust collector, as suggested by Mario)? I don't know jack about thermometers. Thanks. |
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| Author: | Bill Bergman [ Sun Nov 25, 2007 1:34 am ] |
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If no one else chimes in, use the partial. The wet cover will only cover part of the thermometer. |
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| Author: | grumpy [ Sun Nov 25, 2007 2:29 am ] |
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Won't matter; just get a decent one. |
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| Author: | JohnAbercrombie [ Sun Nov 25, 2007 4:21 am ] |
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Todd- You're obviously not getting your thermometers at Wal-Mart- it might be as cheap (and simpler) to just buy a complete sling psychrometer. BTW, partial immersion thermometer is the way to go for this application, if you're buying a lab-grade thermometer. And (gasp!) mercury thermometers are 'way superior to alcohol-filled, though you do want to be careful- the better the quality, the thinner the glass bulb. I did notice that one supplier spec'd their sling psychrometer at +/- 5%, so you might be as far ahead with a Caliber II or other digital-type unit @$20. You may be planning to calibrate/check your digital unit with the sling psychrometer? When I had kids using sling psychrometers in science classes (yeah, I know, these days we'd need hard hats and full face shields to do that...) there was definitely 'operator error'. Also, if the 'sock' gets mineral deposits on it (you should use distilled water) it can affect the readings. Fun experiment, though. Cheers John |
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| Author: | grumpy [ Sun Nov 25, 2007 4:41 am ] |
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I use my dust collector to pull air past the bulbs, thus eliminating operator error. Tests are VERY repeatable, which should be considered very accurate. http://www.proulxguitars.com/test/shop_tips/rh.htm |
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| Author: | grumpy [ Sun Nov 25, 2007 4:44 am ] |
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If someone can make that link "live", muchly appreciated. Better yet, where's the new site? |
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| Author: | JohnAbercrombie [ Sun Nov 25, 2007 7:25 am ] |
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Mario's RH Measurement |
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| Author: | JohnAbercrombie [ Sun Nov 25, 2007 7:37 am ] |
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[QUOTE=grumpy] Tests are VERY repeatable, which should be considered very accurate. [/QUOTE] Though it probably doesn't apply in this situation, repeatability doesn't necessarily mean the results are accurate. Precision vs Accuracy Slick idea using the airflow into the dust collector for a 'standard breeze'...wish I'd thought of that. Cheers John |
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| Author: | Bill Bergman [ Sun Nov 25, 2007 8:02 am ] |
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Keeping in mind the difference in accuracy and precision, as noted above, an inaccurate thermometer can give very repaeatedable, but inaccurate results. So can a systematically flawed technique. For those of you who are sticklers on humidity, a source of error is simply that you move the air in your shop only when you test for humidity. At other times, the temperature and humidity can become very stratified and localized if you do not have a little fan always circulating the air. |
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| Author: | grumpy [ Sun Nov 25, 2007 8:20 am ] |
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Circulating fans are a must. Always. By repeatable, I mean that i can increase the flow, change the wick, longer time frame, etc... yet the readings no longer change. There was a point where i didn't have enough air flow, and that would be like the lazy kid in class who wasn't spinning the sling fast enough. And I can repeat these tests daily and they compare well with all my hygrometers. Again, at lower air flows, that wasn't the case, so now that I've arrived at this setup, I feel it's up to par. |
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| Author: | Todd Rose [ Sun Nov 25, 2007 10:51 pm ] |
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Thanks, Bill, Mario, and John. Much appreciated. I ordered a thermometer from McMaster-Carr. "Pocket Glass Thermometer with Case Plain, Red Organic-Liquid, -30 to 120 Degree F"... $26.23 I reckon this'll do the trick. |
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