How to correct the readings of the moisture meter for different kinds of wood?
With pin and pinless moisture meters, the type of wood will affect the readings you get. For pin gauges, the difference in readings is due to the different inherent resistive properties of different species of wood. For pinless gauges, the specific gravity (SG) of the wood will affect the reading.
Each moisture meter is usually calibrated using a specific species of wood, such as Douglas fir or oak, which makes the meter accurate for that type of wood but less accurate for others.
In general, there are two ways to correct readings for a given species of wood:
Use the species correction table provided by the meter manufacturer.
Use a meter with built-in species correction.
Does temperature affect the accuracy of meter readings?
The short answer is yes, but usually to a very small extent in needle gauges. As the temperature of the wood increases, its electrical resistance decreases, resulting in an increase in the indicated %MC for this sample. For field conditions, if the temperature of the wood sample tested is between 50°F (10°C) and 90°F (32.2°C), there is no need to correct the temperature readings.
When measuring wood materials that exceed these temperature values, and the meter itself does not have a built-in temperature correction, you can use the temperature correction chart to find the correction (Delmhorst provides these with every hygrometer).
Needleless meter readings do not measure electrical resistance, so their readings are not affected by the temperature of the wood unless the sample is completely frozen.
How to determine the distribution of moisture in the circuit board?
To determine the distribution of moisture in the board, you'll need a pin type meter with insulated pins (non-insulated pins can be used, but insulated pins make this easier).
First, remove the meter's pins and gently push them into the material to be measured. Read the "shell" or outer layer of the board. After taking a reading, push the pin in 1/16 inch increments to take a new reading at any time. By recording moisture readings of the board at various depths, you can get a good indication of the distribution of moisture in the board.
Why not use a needleless meter? Because the pinless gauge can read the humidity of the entire area and the depth with a single digital scan, there is no way to isolate the depth at which moisture is present.
