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ive always wondered. now i know.  thanks hesh.

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sweat the small stuff.

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.

And I meant to end the italics after parallel....

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

Hesh - You may alter the relative humidty close to the wet bulb if you break wind close to it.

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Steve Walden
Aspiring Builder,
Bartlesville, OK

 

Is that the same one that LMI sells?

Never mind....

One must always think/research before asking (doh!)...