moisture detectors, wood speciaes, and ohm-meters

[marc rosen]

I have seen a few moisture detectors for lumber and was curious if I could use an ohm-meter to do the same? Do commercial made moisture meters have a selector switch for various wood species? Are there tables for interpreting the conductivity of one wood specie to another? (Or do I only need to standardize my ohm-meter to a "known" dry sample before I use it to test the lumber I plan to use?) Thanks in advance to those who reply(seriously or silly). Marc

[George]

Lots of resistance in wood, but yes, you can calibrate a megaohm range meter to read what is there.

[Doug Miller]

[dingbat]

Pin meters are a big disappointment. The problem is that you really have to measure conductance, not conductivity, and that needs a consistent arrangement of electrodes in the timber, not just a surface contact. The only way to get any really useful measurements from one are to use big pins and a slide-hammer to sink them repeatedly each time. With that and a few bucks worth of electronic front-end meter, then you're set. An FET front-end and moving-needle meter is easier to stick a calibration scale to than a digital meter.

If you want rapid NDT measurement, go for a loss factor bridge (still fairly easy to build, if you understand electronics at the "amateur radio" level).

On the whole though, measure air humidity and allow time for your timber to equilibriate. It's much more accurate (and useful) unless you expend serious effort on your moisture meter.