Moisture Meter Technology
What’s the difference between pin vs pinless moisture meters?
Wood moisture meters use two primary methods of determining moisture content: Capacitance and resistance.
Resistance Meters (Pin Type Moisture Meters)
Commonly known as a pin moisture meter, this type used to be the most widely used meter throughout the world. Two or more pins are pushed directly into the wood in two different spots, and a direct current travels from one pin to the other. This process measures the resistance to the current between pins and correlates that resistance to wood moisture content.
Electromagnetic Field Technology, EMF (Pinless Moisture Meters)
Often called a pinless moisture meter, this type measures the moisture content of wood without piercing the wood with pins. An electrical wave is emitted through a sensor pressed against the wood. This creates an electromagnetic field (EMF) the size of the sensor to a depth of .75” to 1.0”, depending on which model is specified. The field behaves differently depending on the amount of moisture present in the wood.
Pinless moisture meters are based on the capacitance method, but a properly designed meter will take many more factors into consideration. These moisture meters measure the capacity of wood to store energy (capacitance), the amount of power the wood absorbs from the field (power loss), or the wood’s resistance to the field (impedance). Pinless meters translate this electrical information to a percentage of moisture content.
Here’s a short list of factors that affect each type of meter:
|EMW Meter||Pin Meter|
*Certain EMW moisture meters correct this either digitally or using a lookup table.
**Some pin moisture meters may correct this using a lookup table.
Some factors on this list may be familiar. Since EMW meters read a large 3D-volume average of wood MC, the orientation of the wood won’t affect their readings. Pin moisture meters are affected by wet pockets, even if the surrounding wood is significantly drier, and may give a higher MC reading due to the smaller path of the current traveling through it. Temperature can also affect the resistance of wood measured by pin meters.
From the above list, you may have already developed a healthy skepticism regarding the accuracy of pin meter readings. Although some woodworkers may rarely have to deal with chemicals, the factors affecting pin meters are the most difficult to assess.
Surface texture, density, and species may either be assessed visually or will already be known. Wet pockets, however, are impossible to correct with a pin meter. On the other hand, some EMW meters will read up to 1-2% lower on extremely rough surfaces as you begin to measure the air trapped there instead of the wood itself. On most boards, simply pressing the meter firmly against the wood negates this factor. But on extremely rough wood, you may want to add 1% to your reading.