ive always wondered. now i know.
thanks hesh.
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| Hygrometers - Digital vs Analog http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=14020 |
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| Author: | Heath Blair [ Fri Oct 12, 2007 10:03 am ] |
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ive always wondered. now i know. thanks hesh.
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| Author: | David Collins [ Fri Oct 12, 2007 10:42 am ] |
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I've never been a big fan of the salt test for calibration, because you will be calibrating the hygrometer in a range which you will hopefully not be needing much. There is never any reason to expect that by calibrating a hygrometer at a certain percentage that it will be consistent throughout it's entire range. In fact, most are rated for their consistency in the middle, but accuracy gets further off toward the extremes. If you calibrate perfectly at the 75% salt bath but the sensor/ribbon/hair doesn't have perfectly even response as it goes down, it could easily read 60% when it's really 50%, then 45% when it's down to 30%. That's the biggest risk I feel, is if the reaction of the sensor slows down as the humidity drops lower. All those hygrometers are great for quick reference, but I still hold the cheapest, easiest, and absolute most accurate way to calibrate them is with a simple wet/dry bulb setup. I've not been a big fan of the sling hygrometers, because I don't care to stand swinging something in circles for two minutes. A sling hygrometer is much better if you set it down and hook a small fan to draw air through it. Or just put two thermometers on a board, one with some wet gauze on the bulb, and put a fan to it. Just do your best to make sure the air flows over the wet bulb past or parallel to the dry bulb, just not in line before it. It's also common practice to put the fan past the bulbs to draw air across, rather than blowing. It's probably insignificant, but I suppose the heat of a fan motor could influence the results. |
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| Author: | David Collins [ Fri Oct 12, 2007 10:44 am ] |
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And I meant to end the italics after parallel.... |
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| Author: | Cecil [ Fri Oct 12, 2007 11:10 pm ] |
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I'm with you David, I was once a certified weather observer for the US Weather Service. We always used a fan blowing directly on the wet bulb. Cecil |
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| Author: | Steve Walden [ Sat Oct 13, 2007 2:53 am ] |
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Hesh - You may alter the relative humidty close to the wet bulb if you break wind close to it. 
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| Author: | TonyFrancis [ Sat Oct 13, 2007 9:04 pm ] |
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Is that the same one that LMI sells? |
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| Author: | TonyFrancis [ Sat Oct 13, 2007 9:07 pm ] |
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Never mind.... One must always think/research before asking (doh!)...
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