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moisture meter verse a multi-meter

Post in 'The Gear' started by struggle, Jan 16, 2008.

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  1. struggle

    struggle Minister of Fire

    Joined:
    Oct 24, 2006
    Messages:
    727
    Loc:
    NW Iowa
    For those that use a moisture meter has anyone ever tested it against a quality m ulti meter like say a Fluke on an Ohm setting. It seems to me the basic idea is the same.

    Maybe some one has or will check this out against a multi-meter. I am willing to guess that you get a reading that would be fairly predictable it would just be a matter of charting the readings for a multi-meter as to mositure content.

    What do you think or know about this?

    I do not have moisture meter so can someone verify this thought :p

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  2. JimmyMood

    JimmyMood New Member

    Joined:
    Jan 20, 2008
    Messages:
    43
    Loc:
    Southeast MA
    First time poster, long time lurker; here is my experience from late last year. Sorry if this all sounds like an advertisement for a meter, believe me I have no ulterior motive.

    After buying a cord from a local landscaper, trying to burn it, and finally suspecting I had been "had", I ended up buying an Extech M210. I tried to test the wood the way you describe. If you want to do that, the PowerPoint linked below will be helpful, it has a chart of moisture content vs. electrical resistance and wood species.

    http://www.vrac.iastate.edu/ethos/f...Hoffman ETHOS Conference - Moisture Meter.ppt

    I also attempted to measure with a multi-meter first, then an oven, then finally the moisture meter. Here is my experience with all 3 methods.

    1. The oven dry method yielded about 36% moisture, but it took to long to be practical for checking a cord of wood before delivery. I only ran the oven method for about 8 hours, the weight of the sample was still dropping at the end but the rate dropped off considerably from the start of the test.

    2. The multi meter was tougher to get a stable reading, maybe about 25 to 30%, but it was clumsy to measure the probe spacing, wrangle with the test leads and probes. The probes would not penetrate the wood well, and the reading would drift around considerably perhaps because the probes would not stick in far enough.

    3. The M210 read in the mid-30% on the outside and over 40% after splitting and checking the inside. The pins are sharp enough to penetrate the wood the recommended 2mm, the probe spacing is preset (no guessing or measuring) and it is a purpose built instrument. I had a feeling I was going to wreck my multimeter if I kept trying to jam the probes into red oak every year.

    If you read the resistance vs. moisture chart above, you will see there is a considerable difference between wood species. I'm not sure how Extech calibrated the meter, perhaps the difference is that the chart above indicates the measurements were taken parallel to the grain, the M210 measures across the grain. I was also considering that $20 meter from Amazon or EBay that seems to originate from some far-east company, but I coughed up the extra dough for the Extech because I use their other tools at work and they have been in the measurement business for a long time.

    I recently bought a 1/6 cord of wood from a small dealer and checked it with my moisture meter before loading it into my car. It mesured about 22% moisture content and is currently burning great in my stove.
  3. begreen

    begreen Mooderator Staff Member

    Joined:
    Nov 18, 2005
    Messages:
    46,003
    Loc:
    South Puget Sound, WA
    That was my thought. You'd need to buy an extra set of probes, sharpen them to a fine point. Then tape or better yet glue/weld them together so that the distance between the probes is fixed and consistent.

    Thanks for posting the resistance information link. It's good to hear that it works. I'm going to pull out my Fluke meter and give it a try.
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