When to Use Needle Moisture Meters and Needle-Free Moisture Meters
In many cases it may be necessary to test certain substances for their moisture content (%MC). And, when it comes to directly testing the moisture content of materials, there are two main options - needle moisture meters and needle-free moisture meters.
Needle moisture meters use the principle of electrical resistance to measure the moisture content in various materials. Since water is a conductor and materials such as wood, cotton, plaster, and hay are resistors, the easier it is for electricity to flow through a material, the wetter it will be. For accuracy, it is important to ensure that the pin meter is calibrated for the specific material being tested - as different materials have different inherent resistances to current flow.
Pinless hygrometers, on the other hand, use electromagnetic radio frequencies to "scan" a sample of material for the presence of water. Fluctuations in electromagnetic waves are used to measure the amount of water in a 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 to the SG value of that material. Specific gravity is a measure of the relative density of a material compared to another material (usually water).
Both pin and pinless hygrometers have their own unique advantages and disadvantages that may make them more or less useful for specific humidity testing situations. When should I use a needle moisture meter and when should I use a needleless moisture meter? Here's a broad spectrum of situations where one hygrometer may be better than another.
