Moisture Meters: Correcting for Temperature

Understanding the effect of cold temperatures and freezing on moisture meter readings. October 1, 2009

Question
I have a couple of different moisture meters here where I work to check moisture before we ship to ensure moisture is low. I have recently had a problem and am finding that my meters are not accurate and are reading about 2.5 less then what the actual is when it comes out of the oven. We leave our lumber in an unheated storage barn and as we live in Canada it is very cold.

I asked a company in Holland that sells moisture meters if the weather has anything to do with why the meters are not working and the guy told me that the moisture inside the wood freezes and I will not get a correct reading. I funny thing is I have done this job for the past five years and have never had this kind of a problem (that I know of). Does anyone have any insight to this or know anything about this?

Forum Responses
(Sawing and Drying Forum)
From contributor R:
I’m not sure if this will help but my meter says you have to make allowances for ambient air temperature.

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From Gene Wengert, forum technical advisor:
I assume you are dealing with air-dried or kiln-dried lumber. The moisture in the wood does not freeze at this moisture level. However, there is a correction of about 1% MC for every 20 F above or below 70 F for pin meters. So, if the wood temperature is 30 F, then the meter will read about 2% lower than the true reading (that is, reading is 7% MC, the true value is 9% MC). Note that an incorrect oven test will almost always result in a lower MC than the true value.

Incidentally, it is the wood temperature and not the air temperature that matters. Of course, sometimes they are equal. Sometimes if the meter or wires are cold and the brought into a warmer and more humid room, moisture will condense in the wire or meter and give a false reading.