Moisture Meter Calibration

[fritz eng]

Can anyone tell me how to calibrate a moisture meter? Thanks

[John Pendery]

What type of moisture meter do you have?

[fritz eng]

What type of moisture meter do you have?

Recently purchased Wood Moisture Meter - Digital Moisture Detector Moisture Tester, Pin-Type by TavTool. Thanks

[Jim Becker]

I'm thinking that the process is going to be specific to the particular meter you acquired...did it not come with the details for the process of setting it up?

[John Pendery]

Im not familiar with that meter, but a quick search brought up the operating instructions which looked pretty straightforward. I don’t think you will be able to calibrate the meter, but could use it effectively as a relative measuring tool by checking a known dried wood to what you are buying or wanting to test (ideally they would be the same species). To get more accurate results a more expensive meter where you can set it to the specific gravity of a given species would be an option. The Wagner meters I’ve used with good results are in the $500 range I believe.

[Kevin Jenness]

It would be tedious, but you could oven dry a sample to 0% mc by weight, then allow it to regain moisture and correlate the weight/moisture % gain to your meter readings.

[John TenEyck]

A pin meter only reads as deep as the pins penetrate. To get an effective correlation I would cut a sample of wood that weighs around 100 gms to about 2X the thickness of the wood. Put it in an oven at 220F until it stops losing weight and shows a steady weight for a few hours. Now quickly weigh it on a scale with at least 0.1 gm accuracy. Then test it with your pin meter. It might not read 0% when the wood is fresh out of the oven, but I wouldn't worry about that because wood is never 0% at any other time. Leave the wood on suspended in the air and weigh it every few hours and take several readings with the pin meter (in different locations each time) to get an average. The actual % moisture is (Weight Now - Oven Dry Weight) / Oven Dry Weight X 100. As the wood gains weight you will see the correlation between the true moisture content vs. what your meter says. At some point the specimen will stop gaining weight depending upon the relative humidity where you are doing the testing. You can increase the RH to see how the meter correlates at higher moisture contents by putting it in a closed environment with a humidifier set at whatever RH that correlates with the moisture content of interest. Leave it in there for 24 hours, weight it and take readings, repeat as desired.

John

[roger wiegand]

Calibrating an instrument like that to yield a highly accurate result is hard, per John's instructions, adding that you'd need to repeat the process both across time and across wood species.

I'd argue that it's unlikely that, for woodworking purposes, you actually need high accuracy (if indeed that is possible with a device of this sort), and that what you care about is precision, the ability to reliably give the same reading for the same MC. I'd take the meter and test pieces of wood that have been in your house or shop for years or decades and determine whether they give a consistent reading, then declare whatever the device says that is, 6, 7, 8, 9%, to be the "fully equilibrated" dryness for your shop. A few newly cut pieces of wood will give you the "fully wet" value for comparison. Measuring both weight and meter reading for a few pieces as they dry will give you an idea of how linear the scale might be. I really only care whether a new piece of wood is equilibrated, or close to it, so comparing a new piece to a piece that's been in the shop for 10 years tells me what I need to know without worrying about ultimate accuracy.