500-72203-001 Rev. H Page 6 of 15
/Stack Probe combination will likely not be exactly the same as read by an in-line
system. An effective method to compensate for this is to establish a correction factor
based on the nominal readings obtained in the kiln and the desired (target) MC
reading as seen at the console. You should be looking for a correlation between
the stack probe readings and the in-line readings.
Example: I measured packs 3, 7, 10 and 12 of 2x4 Douglas Fir in Kiln #1 by taking
50 readings in each pack after 20 hours of drying. I obtained a hot check average of
18%. I know the MC of this lumber going through the planer 3 days from now will
have a 16.5% average.
Use the stack probe MC as a reference and adjust your correction factor as
necessary to obtain the desired target MC at the in-line console. Compile data from
previous kiln cycles to fine-tune your correction factor.
Consistency is the key! If your process changes, consider the impact to your
correction factor, but do everything possible to control the variables. Don’t
complicate the variables by measuring one way this time and another way the next.
If your consistent correction factor suddenly stops working ask yourself: What has
changed? Were the hot check readings taken the same way? Did the lumber have
more MC variability going into the kiln? Did the meter recently get calibrated? Did
the pack coming out of the kiln go through the planer sooner or later than usual?
Temperature can also have a small effect on the readings. We now know that high
lumber temperatures can cause the MC reading to increase by 2-3%. These
variances are far smaller than would be seen with a resistive pin meter. Some of this
temperature related measurement error could be attributed to the warm lumber losing
moisture as it cools.
Try to measure the lumber at approximately the same temperature from one cycle to
the next to maintain the best consistency in your readings. If possible, let the wood
cool for a couple of hours prior to measurement. The temperature effect is small, and
correlation is the real goal, but more accuracy can be obtained by letting the
temperature stabilize.
L722 MAINTENANCE
CLEANING
Maintenance of the probe consists of cleaning the probe assembly periodically with
mild detergent cleaning solution and a soft rag. Do not soak or submerge the probe
in liquid. Scrape excess pitch off with a flat bladed instrument such as a chisel or
putty knife, being careful not to dig into the probe. Never use solvent of any kind for
cleaning.
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