Moisture Meters?

[Farrell]

----- Original Message ----- 
From:  Jim I


> My meter has 2 issues:
SNIP

Correct. There are no meters available that will accurately directly measure MC of a piece of wood at low MC.
 
> The RH tables are useful way to gauge EMC, and I have used them. But, how long it takes a sample to reach equilibrium is an open question in all of the hot boxes I've seen.
SNIP

Not true. Evaluating equilibrium is easy. When I place a panel in my hot box for drying, I push a small nail into the panel at one edge and place a pencil mark on the opposite edge where a line between the two would be perpendiclar to grain and near the widest part of the panel - usually around three feet. When I first place the panel in the box I measure the distance between the nail and the opposite edge at the pencil mark. Turn on the heat and monitor temp and RH. When you have the proper temp and RH for your desired MC (according to the chart), measure your panel width. Measure it again at 12 hour intervals. Within two or three days you will observe the panel width to stabilize at the target temp and RH of the box. Most panels will shrink several millimeters going from about 9 or 10% MC down to 6%. So it is real easy to accurately observe when equilibrium has been achieved.

> That brings another inaccuracy to mind.  How do we measure the RH in the box. My first unsuccessful attempts used digital meters. I quickly found that by putting 3 meters in the box I could get 3 different (sometimes significantly) different RH readings (hey that way I choose the one I like best). Further when I pushed the temp up past 110 degrees my meters lost their minds.

Just buy a good gauge. I bought one for maybe $200 (I forget exactly how much). It is calibrated at the factory and comes with certification that it is within some very small amount of error and is certified by some very impressive atmospheric/humidity/ weather/ whatever national association. Bottom line - you might want to go beyond Radio Shack and get a decent gauge - I'm quite sure it is more than accurate enough for our purposes.

> But my question here is very basic step 1 material.  When people are talking about their board EMC during construction whatever their construction choice, how are the EMC's being quantified...accurately.

I believe my methods described above will provide an EMC characterization more than accurate enough for our needs. If you have any more specific questions on any of my procedures or equipment, I'm happy to share.

Hope this helps.

Terry Farrell
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