help a beginner measure mc in wood with confidence

Gene Nelson nelsong at intune88.com
Sat Aug 16 09:53:44 MDT 2008


I have been using the technique Bruce Hoadley talks about - cut several samples of spruce (similar dimensions) to the same weight - 100g is easy to deal with - oven dry one of them to get a dry weight to compare the others with. Sounds straight forward enough.
Then I compare calculated mc using weighed samples with my hygrometer and the EMC charts and the disagreement begins.
If conditions are changing, certainly there is a lag time for equalization but the disagreement continues. Also the samples must be placed in the shop so they are representative - still the disagreement continues.
Probably it would pay to get a much more accurate hygrometer? 
Is the weighing technique really accurate? How would you determine if it was?
Would it be helpful to add a moisture meter to the lot?
I am curious how shop folks gain confidence in their technique to measure mc so that if the measurements are telling you the mc is 7% it really is 7% +/- an irrelevant amount?

I can give one example: I use my humidifier to get the rh up to 40% at 95 deg f - this should get my weighed samples up to about 7%rh but they insist on weighing in at 6.1%. Is this a typical discrepancy between cheap hygrometer and weighed samples?

Thanks for any comments. 
Gene Nelson
Thanks,
Gene Nelson
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