Moisture meters are essential in avoiding wood moisture problems such as shrinking, warping and cupping. Both, pin and pinless meters are available. It is not an easy choice between the two meter types, because both have advantages and disadvantages.
Pinless meters use electromagnetic wave technology, which measures the density in a three-dimensional field underneath the measuring pad. The average moisture in the measuring field is indicated. If the moisture varies within the measuring field, the pinless meter shows the average.
For accurate values, the measurements have to be corrected for different wood species. Advanced pinless meters have those corrections built-in and only a number needs to be selected. For all other meters a correction should be used to obtain accurate values. Wood temperatures do not affect measurements, therefore no correction for wood temperature is necessary.
Here are advantages for pinless meters:
• In a short time a large number of boards can be scanned and the measurements leave no visible marks – no pinholes.
• Even though pinless meters do not indicate differences between surface and core, the meters can detect water pockets and higher moisture levels across the board. (The Ligno-Scanner SD with the unique dual-depth feature (measures ¼” and ¾”) can indicate core and surface moisture.)
However, pinless meters require a somewhat flat and smooth surface. The measuring area should be at least as big as the measuring pad on the meter.
Also the measuring depth is crucial. Moisture values are too low for materials thinner than the measuring depth. And the pinless meters cannot read any deeper than the measuring depth indicates.
Pin Meters measure the electrical resistance between two pins. The electrical resistance changes with the moisture content of wood. If moisture varies within the small segment of the non-insulated part of the pins, the highest value is indicated. Wood species corrections are necessary to obtain accurate measurements.
Most pin meters have built in corrections for different wood species. If lumber is hot or cold the electrical resistance in the wood changes, therefore wood temperature corrections are necessary for hot or cold lumber.
For a thorough quality control, moisture should be measured down to the core. The slide-hammer electrode with Teflon coated pins is the ideal tool. As the pins are hammered towards the core, consecutive measurements indicate if the wood is dried to the core. Meters measure down into the board, even if the boards are several inches thick.