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Moisture Meter Woes

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Forum topic by rolltopbox posted 674 days ago 1065 views 0 times favorited 5 replies Add to Favorites Watch
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rolltopbox

70 posts in 1597 days


674 days ago

When I bought my meter I read the following:

From the Manufacturer
The Extech MO280 Pinless Moisture Meter quickly indicates the moisture content of materials. The user can select from ten wood types and measurement ranges. This meter has an LCD display that shows the percent of moisture in the wood or whatever material is being tested. The measurement depth goes to 0.75 of an inch below the surface and it has an automatic internal tester and calibrator.

So I naturally took it to mean that I could use it to test the moisture content of my wood. It sure seemed to do that on kiln dried lumber purchased at known moisture contents.

Today I asked that company which wood group I might use to measure olivewood. I received the following answer.

“The MO280 does not measure % wood moisture.
It is as all pinless meters are, a relative moisture meter.

You measure a material of known moisture content and then you “compare” it to a unknown item of the SAME density.
Like 2 pieces of Olive wood, one of known dryness and one unknown.
When compared the piece with the higher reading indicates the presence of moisture.”

Did I mis-understand what my meter is supposed to do?

-- Bruce http://www.ovaltambour.com


5 replies so far

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WDHLT15

1079 posts in 1080 days


#1 posted 673 days ago

If you did misunderstand, it was because you were badly misled and deceived. The website says the meter measures % moisture.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT15 Sawmill. Nyle L53 Dehumidification Kiln

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HalDougherty

1820 posts in 1841 days


#2 posted 673 days ago

I’ve found the expensive meter aren’t any more accurate than the cheep ones. The most accurate way to measure moisture is the “oven dry” method. Here’s a pdf file that explains how to do the process.

http://woodlandinfo.org/publications/FEM/FEM_089.pdf

I speed up the process by first heating the sample in my microwave at full power for a minute or two to help break down the cell walls so bound moisture can easily pass from the cells. Then I use the cut weight I recorded to set my microwave to defrost that weight. The defrost setting on my microwave is 50% power for a time that’s calculated by weight. Each time I record the weight and let the sample cool to room temp before another heating. When it stops losing weight, I put it in the oven at 180 degrees and leave it overnight. That’s the oven dry weight and the original moisture content is an easy calculation.

-- Hal, Tennessee http://www.first285.com

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Tennessee

1447 posts in 1118 days


#3 posted 673 days ago

I used to use pin meters, not any more. I bought the Ryobi, with the big pads on the back. It measures moisture, or at least displays a moisture reading, off of a variety of substrates including softwood, hardwood, masonary, and drywall. You select one, (like hardwood), and measure by holding it tightly against the wood. You just have to have a flat surface. I have found it to be fairly accurate, easy to use, and matching within about 2% on known kiln dried that I tested it on. It is under $50.
I believe all of these meters use the same basic technology, where they measure the ability to pass a small current between pads or pins due to moisture and minerals in the moisture and display that as a percentage of moisture on a readout. Most people know that absolute pure water will not conduct electricity, so really what you are reading is the moisture with minerals in the water. The known fault on these is the fact that on tree wood cut very low to the ground, you will have more minerals in the wood that could be conductive, thereby skewing your results, but in my usage, if it says 9% or lower, I’m pretty safe to start cutting wood.

-- Paul, Tennessee, http://www.tsunamiguitars.com

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fernandoindia

1072 posts in 1547 days


#4 posted 672 days ago

Hi Bruce. Sounds funny.

As buying a clock which will tell you the exact and precise time difference to Greenwich.

-- Back home. Fernando

View WoodGoddess's profile

WoodGoddess

100 posts in 671 days


#5 posted 671 days ago

Just to add to what you said Hal…wood absorbs ambient water vapor from the air when its MC is lower and releases water vapor when it’s MC is higher than the ambient relative humidity (RH) of the surrounding air. It’s a balancing act: wood needs a certain amount of MC to retain its strength and durability over time (much like people) but too much or too little moisture can lead to other problems hence the reason we measure moisture in wood prior to working with it.

I’m new here and the world of wood! If I need to be corrected…let me know! :)

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