Using a multimeter to measure wood moisture level

[RobertNH]

Great read! Great link!
Thank you for posting!

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

 

[lectraplayer]

What I need to know is how to make a multimeter out of my moisture level meter. ;-)

That sounds like a challenge to me! I'm gonna have to build me a moisture checker to check for this 3 megaohm resistance because I can.

 

[Babaganoosh]

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]

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.

 

[begreen]

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:

Moisture meter

hey guys and gals, hoping to get a recommendation on a moisture meter to check the wood. I’ve seen some for $30 and some for $450...hoping I don’t need a fancy expensive one like the latter. Any suggestions?

www.hearth.com