The two different types of moisture meter work in different ways. The pin meters rely on electrical current to measure moisture, whilst the pinless meters use electromagnetic waves.
On a pin-type moisture meter there are two pins that are set a small distance apart and are generally quite short, around 8mm (5/16“). They are tapered to a point, so they can be pushed into the source material.
For harder materials, like concrete, the pins cannot be pushed below the surface, unless they are on a separate attachment which can be hammered in or they can be placed in pre-drilled holes. A surface measurement may not be as precise but still gives a good idea of moisture levels.
There is a circuit inside the moisture meter which is completed by the test material, via the pins.
The resistance between the pins is how the moisture content is determined. The more water in the material, the less resistance there will be. The moisture content is worked out from this.
The moisture content reading reflects only the area between the two pins and so for a more accurate result, multiple readings will be required.
The depth measured by a pin-type moisture meter is limited to how far the pins reach, so the maximum depth for an average moisture meter is 8mm; the length of the pins.
As an electrical current will take the easiest path and this could be between any two points on the pins, you will often find that the pins are insulated, leaving only a small section at the tips exposed. This ensures more accurate results.
Pin-type moisture meters are considered invasive as they have to punch holes in the test substrate. This is intensified by the need to take multiple readings, therefore making multiple holes.
