How do I use a multimeter to check moisture?

marsfarmer Posted By marsfarmer, Sep 13, 2009 at 1:58 PM

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  1. marsfarmer

    New Member

    Sep 7, 2009
    I read something in one of the threads about using an ohmeter, I think, to check moisture as opposed to buying a special moisture meter. There was a Forest Service link that supposedly shows you how to perform this magic, but of course I couldn't open it. Now I'm itching to check on some sugar maple but I'm to cheap to buy a tool when there's a chance I can use something I already have. Anybody know how to do it, or how to get the info?
  2. kbrown

    Feeling the Heat

    Oct 19, 2008
    SE, Michigan
    Never heard of that but it makes sense since the higher the MC the less resistance there would be. Actually moisture meters don't have to be that expensive. It's just like a trying to figure which multimeter one should buy; it all depends upon what you will be using it for and how much. I just picked up a moisture meter from Harbor Freight a couple weeks ago and paid around $9 after using a 20% off coupon with the sale price. Many guys around here have the HF model and are very happy with it. I like it since it's very compact and can fit into a side pocket in a pair of cargo or work pants. You might want to check over in the gear forum for more info on this.
  3. RustyShackleford

    Minister of Fire

    Jan 6, 2009
    There is a link to a Forest Service PDF on one of the other threads - search
    for ones I've posted in - which has a massive table showing the resistance
    that should be measured for different moisture levels for many different

    The rub is that the resistance is spec'ed for two electrodes, spaced 1.25"
    apart, and penetrating to a depth of 5/16" (I think). Regular meter probes
    are not sharp enough, so you have to build some sort of jig of your own.

    Might be less trouble just to buy one of your cheaper meters ...
  4. ICY99

    New Member

    Sep 29, 2008
    What you need is a Megohm meter or a multimeter that can measure into the 10s and 100s of Mega Ohms (millions). Typically these megohm meters are quite expensive, so unless you already have one, it would be cheaper to buy a moisture meter (which is essentially a limited range Megohm meter).

    Here is a link to a site which shows some resistance vs. moisture values:
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