How to determine the distribution of moisture in a circuit board?
To determine the distribution of moisture in a circuit board, you'll need to use a pin-type meter with insulated pins (non-insulated pins can be used, but insulated pins make this easier).
First, take the pins of the meter and gently push them into the material being measured. Read the "casing" or outer layer of the board. After taking a reading, push the pin in 1/16-inch increments, taking out new readings at any time. By recording moisture readings of the board at different depths, you can get a good indication of moisture distribution in the board.
Why not use a pinless meter? Because needleless meters can read the humidity of an entire area and the depth of a single digital scan, there is no way to isolate the depth at which moisture is present.
Does temperature affect the accuracy of meter readings?
Wood Moisture Meter FAQs with Figure 3 The short answer is yes, but usually to a very small extent in pin meters. As the temperature of wood increases, its electrical resistance decreases, causing the indicated %MC of this sample to increase. 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 reading results.
When measuring wood materials that exceed these temperature values, and the meter itself does not have a built-in temperature correction, you can use a temperature correction chart to find the correction (Delmhorst provides these corrections with every hygrometer).
Needleless meter readings do not measure resistance, so their readings are not affected by the temperature of the wood unless the sample is completely frozen.
How do I correct readings for different types of wood?
With both pin and pinless moisture meters, the type of wood will affect the readings you get. For pin meters, the difference in readings is due to different types of wood having different inherent resistance properties. For needleless meters, the specific gravity (SG) of the wood will affect the reading.
Each moisture meter is typically calibrated using a specific type of wood, such as Douglas fir or oak, which makes the meter accurate when measuring that type of wood, but less accurate for other woods.
Generally, there are two ways to correct readings for a given species of wood:
Use the species calibration table provided by the meter manufacturer.
Use a meter with built-in species correction.
Using a meter with built-in calibration is often easier and faster than referring to a manual and doing the math yourself.
