Hygrometer

[Greg Newell]

BTW Ron. I just love this word "compuationalizationating" !!!!

What's that smell? that smoke!?!?!?!  Egads i think it's coming from the 
spell checker <G>


Greg

At 07:39 PM 8/30/2002, you wrote:

>>Yes, I believe it is. That's why I am confused. It seems that the intent 
>>is to dry down the board to a specific moisture content. Since this is 
>>the case why is an instrument that measures the moisture content of the 
>>air being discussed? Again, respectfully, what am I missing?
>>
>>Greg Newell
>
>
>The connection Greg, the connection. If you know the temperature and 
>relative humidity, you can compute the equilibrium moisture content of a 
>piece of wood that has been in that temperature and humidity long enough 
>to reach equilibrium, moisturizationally. The rate at which the MC in a 
>piece of wood changes is relative to the difference in MC of the wood, and 
>in the surrounding air. The greater the difference, the faster the 
>moisture exchange between the two. Wood left in 70°F air at 40%RH will 
>eventually stabilize at about 7.7%MC. But you don't know at what rate. If 
>you are kiln drying and want an absolute minimum cycle time, you don't 
>have time to sit around with a yard full of green 16/4 wood waiting for 
>the stuff in the kiln to reach EMC, so you jack up the temperature to 
>provide a greater moisture potential differential and measure it directly 
>with a probe from time to time until it hits the target MC and pull it out 
>before it passes on to ultimate mummification. In a piano shop, drying out 
>an 8mm thick spruce panel, the drying time is considerably less and you 
>probably aren't processing 10,000 board feet at a time, so you can afford 
>another day for it to stabilize in it's own time in the box. That being 
>the case, if you'll keep an eye on the temperature and RH% in the box, and 
>compare the MC computation from those measurements with your target EMC, 
>you just have to leave the sucker alone and wait for the wood to get to 
>that MC all by itself. You can leave it in there for two weeks, 
>justifiably assuming that anything that thin that hasn't reached 
>equilibrium by then probably never will, or you can use your handy 
>homemade faux soundboard MC indicator instead of a probe to get an 
>adequate indication of the MC of the panel without poking holes in it with 
>a $200 instrument who's calibration is most likely in doubt anyway, most 
>especially at low MC levels.
>
>Didn't I send you a copy of my Excel MC compuationalizationating worksheet?
>
>Ron N

Greg Newell
mailto:gnewell@ameritech.net