In many cases, it may be necessary to test the moisture content (%MC) of certain materials. And, when it comes to directly testing the moisture content of a material, there are two main options - pin-type moisture meters and pinless moisture meters are good times to use a pin-type moisture meter with Fig. 1 Minute meters and pinless moisture meters.

Pin Moisture Meters use the principle of electrical resistance to measure the moisture content in a variety of materials. Since water is a conductor and materials such as wood, cotton, gypsum and hay are resistors, the easier the current flows through the material, the wetter it will be. For accuracy, it's important to make sure that the needle meter is calibrated for the specific material being tested - as different materials have different inherent resistances to current.

Needle-free hygrometers, on the other hand, use electromagnetic radio frequency to "scan" a sample of material for the presence of water. Fluctuations in electromagnetic waves are used to measure the amount of water in the sample. The accuracy of a pinless moisture meter is affected by the specific gravity (SG) of the material being scanned, so the meter needs to be calibrated for the SG of that material. Specific gravity is a measure of the relative density of a material compared to another material, usually water.

Both needle and needleless moisture meters have unique advantages and disadvantages that may make them more or less useful for specific moisture testing situations. When should you use a pin-type moisture meter and when should you use a pinless moisture meter?

Pinless hygrometers are sometimes referred to as "non-invasive" or "non-destructive" hygrometers because they don't have to penetrate the surface of the material being tested in order to get an accurate moisture content measurement. That's why many flooring professionals ± use needleless hygrometers to test the moisture content of their hardwood floors. With a needleless meter, moisture content can be assessed without having to damage the hardwood floor.

Pin-type moisture meters - especially those that use insulated pins - are excellent at determining moisture distribution in circuit boards . With insulated pins, you can simply push the pins in a fraction of an inch, take a reading, push them in another inch, take another reading, and continue to repeat the process until the pins are fully inserted. The distribution of moisture in a board can be invaluable information to lumber dealers because it helps them determine how the wood is curing so they can adjust kiln conditions accordingly.