ATC? moisture meters

[kelLOGg]

I have a Protimeter Timberlogger which I use to monitor the drying progress in my homemade DH kiln which is a big insulated box with a room de-humidfier in it. The meter is a pin type which is pounded in a test board and its output goes thru a port to the outside of the kiln which is the 2nd floor of my barn and gets toasty in the central NC afternoons.  The meter has automatic temp compensation but I'm not sure it works. I put air dried WO in the kiln at 17% MC and over a period of 2 weeks I saw it fall to 9.2%. During the kiln operation the temp varied from 115 - 125 degrees and I periodically vented it for 45 minutes every 4 hours.  I shut it down today to cool and took the lumber out. At 94 deg the MC was 7.9 % and  very few hours earlier before the shut down it was 9.2%. I had seen small variations in MC during operation: after the vent cycle the MC was always a little lower (~1/2 %) than before the vent. Now I'm convinced the MC reading is significantly temp dependent.

So, how do you guys who, unlike me ;D,  actually know what you are doing get a MC reading during the drying process. Is my meter suitable for kiln measurements?

Bob

[Den Socling]

A pin-type meter measures resistance to current. When wood is dry, the resistance goes up. When wood is hot, the resistance goes down (if I'm not mistaken). If you measure hot, readings will usually be a little lower when the wood cools. If you leave your pins in the kiln and the electronics are outside, then the temperature compensation can't work unless you have a remote temperature probe in the kiln.

BTW Most kilns are basically nothing more than big insulated boxes.

[kelLOGg]

If you measure hot, readings will usually be a little lower when the wood cools. If you leave your pins in the kiln and the electronics are outside, then the temperature compensation can't work unless you have a remote temperature probe in the kiln.

I observe just the opposite: that MC reading is lower with temp.

I failed to mention that the remote temp probe is in the kiln and the electronics outside.

[caver]

Harbor Freight in Columbia MO had those cheapo moisture meters on clearance for $8. The yellow case with LED's corresponding to a moisture % number.
Looks like they have a newer digital readout one in the catalog.

[red oaks lumber]

the quality of your kiln dried wood will only be as good as your m.c meter, spend the money on a good accurate meter.
they sell meters that have settings for species and temp, it helps take the guess work out.

[caver]

I was just throwing that out there VS starting a new thread. 
I guess by the same logic, my electrical work using a high dollar Fluke is better than the guy that uses the 3$ Harbor Fright  DVM?   ;D

[SwampDonkey]

Humidity was higher in the kiln than the outside air.

See the wood handbook table 3-4

[beenthere]

The pins driven into the wood will lose their good contact with the wood over time. I've heard in the past that leaving them in the wood in the kiln isn't a very accurate way to keep track of the mc of the wood. Removing samples from sample boards is the best way - from what I hear.

If the pins lose contact over time, the wood will show less resistance and thus lower mc % than actual mc %. Was this your observation? Also might be a reason for being erratic and change with temp.

[Larry]

The pins driven into the wood will lose their good contact with the wood over time. I've heard in the past that leaving them in the wood in the kiln isn't a very accurate way to keep track of the mc of the wood. Removing samples from sample boards is the best way - from what I hear.

If the pins lose contact over time, the wood will show less resistance and thus lower mc % than actual mc %. Was this your observation? Also might be a reason for being erratic and change with temp.

What he said.  A second problem I found was in my leads to the pins.  I used lamp cord, which absorbed moisture giving me false readings.

[kelLOGg]

Beenthere,
Losing contact over time sounds reasonable to me although that would cause a decreasing MC reading over time regardless of temp. My reading goes up with higher temp and down with lower temp.

Would a pinless meter be better? Does anyone know of a remote pinless?
Bob