Using a multimeter to measure wood moisture level

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RobertNH

Member
Sep 25, 2014
144
New England
Great read! Great link!
Thank you for posting!

I now have a copy of the charts to use to check my expedited drying theories.
 

Babaganoosh

Minister of Fire
Nov 18, 2014
713
NJ
Getting annoyed at this. Drove some nails, pulled, inserted probes, couldn't get a stable reading. Then drove nails and tried to read off that. Not stable either. Just slowly climbs and climbs. Tried steady pressure, same result. Tried leaving them stuck in the wood same result.

Replaced battery, same result. Touched probes together and it immediately gives me a zero reading. I suppose it's not reading correctly but not likely. It's less than a year old and a decent auto ranging model. Klein tools. Not the 20 dollar jobber. I'm getting it to stay around 280 to 300 k ohms. But it's moving around within that range. If I remember from years ago that's 2 decimal places to mega. So around 2.85 on this maple.
 

Ashful

Minister of Fire
Mar 7, 2012
15,715
Philadelphia
You need to consider how your multimeter measures resistance. First, most output a constant current, and measure the voltage drop to calculate resistance. On older (manual ranging) DMM's, this current level would be set by the range selection, but on newer (auto-ranging) DMM's the current just varies by load to put the voltage reading in a reasonable accuracy (100+ mV) range. A good modern DMM like the Fluke 77 will output about 30 uA into 300 k-ohm, but nearly 1 mA into 200 ohms. Also, into very high resistance loads (>100 k-ohm), the combination of lower current and long leads on your meter sets up the perfect scenario for induced current (eg. AM radio pickup), which causes meter wandering.

Constant climbing is usually an issue of the current output by the meter causing some heating in the device being measured, albeit it small, it is multiplied to a large change by the high resistive value. Random wandering is usually caused by the long leads at a high resistance value.
 
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begreen

Mooderator
Staff member
Nov 18, 2005
85,009
South Puget Sound, WA
For those that just want a dedicated meter, there are many on the market. Lots of recommendations in the Gear forum if you search for Moisture Meter. And here is a quick poll:
 
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