A good time to use needle moisture meters and needleless moisture meters
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?
Testing large, flat surfaces, such as entire floors
Pinless moisture meters specialise in testing large areas of a structure for moisture quickly and efficiently. Simply push the scanning plate into the floor, read it, lift it up and repeat the scanning in another position. The scanning plate checks large areas at a time and takes only a few seconds for each check. This allows the user to quickly scan very large areas of a structure with relative ease.
Pin hygrometers, on the other hand, can only check for moisture in small areas between contact pins. In addition, they need to go deep into the material being measured to get a full reading. This usually means that greater force is required to penetrate tougher materials, increasing the risk of strain and damage to the pins. Both the smaller test area and the extra effort contribute to the time and labour costs of measuring moisture over a large area.
Testing moisture in materials you don't want to damage
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.
Needle hygrometers, on the other hand, need to penetrate the surface of the material in order to perform a proper test. In applications where the surface condition of the final product needs to be protected, leaving pinholes, even small ones that can be easily filled or padded with epoxy, is usually less than flattering.
Determining Moisture Distribution Across the Board
When pinless moisture meters scan for moisture in a material, they provide an average reading of all the moisture in the area scanned. This means that if pockets of moisture are detected, you won't know how deep it is. Or, if a sample of material has a different shell and moisture content, you won't know the difference.
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.
