Hi Stanley,
I doubt that a normal ohm meter can read moisture levels
in timber reliably. There is more to it than just resistance. What you need
to do is sort out how much of the resistance is due to moisture, and how
much is due to the material and structure in the wood itself.

I don't know what principle the commercial moisture meters aer working on,
but an instrument that I have used to measure the moisture content in high
voltage busbar insulation is called dispersion meter. It was originally
developed to measure moisture content during sugar processing. It works on
the principle that some molecules polarise when placed in a DC electric
field, and some don't.

Moisture molecules do, and most other things in wood (which was one of the
main insulation structures in most of our 11,000 Volt busbars) doesn't. When
I say polarise, I simply mean that when the electric field is applied, they
all turn and line up in the same direction in the field. This turning around
and lining up takes time, and energy. When the field is removed, they go
back to where they were, but that takes time as well.

The way the dispersion meter worked, it applied the dc field to the sample
for a minute or so, then it shorted the sample out momentarily to discharge
it.It then removed the short, and applied the sample to a sensitive volt
meter so that you could see the voltage rising again. The voltage was rising
again because as the molecules returned to their normal state, they released
the energy that polarised them, causing the voltage to be generated. The
instrument would continue to short and measure until the voltage recovery
dropped away. The combination of how high the voltage rose and how long it
took to completely discharge was used to derive the moisture content.


Having said all that, the first response I saw to this thread of using the
microwave is an excellent one, provided the moisture is given time to fully
escape from the sample. In your situation, you can use a sample. We needed
the dispersion meter because we couldn't get a sample.

regards,

John


"stanley baer" wrote in message
...
I am in the market for a wood moisture meter to check the wood I have in
storage before I make them into furniture. The ones I have seen for sale
seem to be expensive for what they are. Could I make my own by making a
little handle that holds the two steel pins, and reading the moisture by
using an an ohm meter? I have access to a friend's moisture meter to
calibrate my homemade one with. I was thinking of making a rough table in
case the correlation between moisture and resistance is not linear.

What do you guys think about this plan (other than that I am too goddamn
cheap).