When looking for accurate wood moisture measurements, you’ll immediately run into two different styles of meters: pin and pinless. Which is the better addition to your tool belt? There are some basic differences that you should understand before you buy.
Pin vs. Pinless Moisture Meters
Too obvious? Maybe. But let’s point it out anyway. Pin-style meters usually have two metal pins that must physically penetrate the wood’s surface in order to take a moisture reading. Pinless meters use a sensor pad that works in contact with the wood surface but does not physically break or damage the surface to take a reading.Let’s look at why that matters.
Sensor Size vs. Pin-point Accuracy
The true difference rests in the underlying technology of each type of meter. Pin meters work on a resistance principle that measures the flow of electricity between two pin tips and measures the moisture content (MC) of that very tiny path. Keep in mind that pin meters only measure the MC at the point in the wood between the two pins. Multiple readings are always necessary to get an overview of the MC.Pinless moisture meters use a larger sensor pad and emit electromagnetic signals to measure the MC of wood. This provides the unique ability to quickly and accurately “scan” larger areas in each wood piece, providing instant MC readings. This technology can scan many board feet in seconds without the time consuming effort of driving pins into the wood.
Holes vs. No Holes
As we’ve already mentioned, a pin meter will penetrate the wood’s surface to measure the MC. Therefore, each MC reading will make a pair of holes in the wood. For 2x4s or firewood, this might not be a problem. For wood flooring, fine furniture, cabinets or other fine woodworking projects, those holes become a series of blemishes in the surface of the wood. Pinless meters leave no damage to the surface.
Fixed-depth Readings vs. Variable-depth Readings
Pinless moisture meters generally operate at two standard reading depths: ¼” below the wood surface, and ¾” below the surface. For most woodworking projects, like wood flooring or cabinetry, these depths provide the necessary MC readings required.Because pin meters take readings between the two pins, they offer slightly more variability in reading depths. The MC reading will always be taken at the depth the pins are driven into the wood. (Of course, this also means that if the pins are not inserted properly, the MC reading may not be accurate.) Pins are generally replaceable and can be purchased in different lengths, or the meter itself can be attached to external hammer probes for deeper MC depth readings.
Breakage vs. Calibration
Because of the force necessary to insert a pin meter into wood, the longer the pins, the greater the risk of breakage during use. If you don’t have replacement pins on hand, the meter becomes unusable. Pinless meters are less prone to breakage during normal use, but must be properly calibrated (as both styles must) in order to provide accurate MC readings. Fortunately, a calibration check of most pinless meters can be quickly verified on the job site using a calibration verification block purchased directly from the manufacturer.
Naturally, the accuracy of both pin and pinless moisture meters depends on using them correctly according to the manufacturer’s instructions. Also, you must program the meter or use specific gravity (SG) adjustment tables for each wood species that you are measuring. Understanding the differences and the proper use of either pin or pinless meters ensures you’ve got the MC readings necessary to get your wood project completed for a lifetime of use and enjoyment.