“Accuracy” in wood moisture meters is an often misunderstood or misused term. Every moisture meter manufacturer will claim that their products are accurate. But in determining a wood moisture meter’s accuracy, there are a number of factors to consider.
So how can you gauge a wood moisture meter’s accuracy? By understanding the technology and test methods of determining “accuracy” in wood moisture meters. Over the past 15 years, Wagner Meters has commissioned four separate independent studies that compared a variety of moisture meter types to determine this matter of accuracy. And the results of those studies are as valid today as they were when first commissioned. Let’s examine why.
When comparing two products, it’s always good to know if you’re comparing apples to apples. But with pin-style and pinless meters, the reality is that you’re comparing two different types of apples. Both measure moisture content, but there are two significantly different technologies underlying the two types of meters.
Pin-style meters use electrical resistance to make their measure content readings in wood. After the two probes, or “pins”, are inserted into the wood, a small electrical current is passed between the points, and the amount of resistance is correlated into a moisture content reading. Because moisture is a good electrical conductor, the “wetter” the wood, the less resistance there would be to the current, and vice versa. Because of the type of technology used, pin meter accuracy is affected by variances in the naturally-occurring chemical composition of wood species, but not as impacted by density variability from one piece of wood to the other.
Electromagnetic Wave Technology
Pinless meters (also referred to as non-damaging meters because they do not have to penetrate the wood) use Electromagnetic Wave technology. The meter sends out electrical waves at a certain electromagnetic frequency that creates an electromagnetic field in the area under the sensor pad. The meter then produces a moisture content correlated to the signal it reads back. Pinless meters typically test a much larger area than pin-style meters and can “scan” the wood for a more complete moisture content picture. Again, this technology is not without some limitations and can be impacted by density variations.
While it’s understandable to be skeptical of “sales talk” – the claims that manufacturers make about their products – it’s equally important to read product reviews with an eye to what is being said and how the product was used before the review was offered. While a user review can be a handy indication of what to expect in terms of feature usability or feel, very few users have the ability to accurately assess accuracy. Because of the number of variables involved, any stand-alone test is going to be problematic in one way or another.
Base-line Moisture Content
The laboratory standard for determining the accuracy of wood moisture meters is an ASTM standard (D4442-07) that uses an oven-dry laboratory method to determine the true moisture content in wood samples, and then comparing these oven dry results to the measurement results (prior to oven drying) given by the meters on the wood samples. The difference in the two results quantifies the measurement error of each moisture meter tested. The true measure of a moisture meter’s accuracy, then, is its accuracy when used in a real-world setting and then comparison of these readings against the oven dry test.
Next, any real-world accuracy test or study that uses an inadequate number of wood samples cannot really produce a reliable assessment. Put into practical terms, each piece of lumber of the same species will vary depending on its geographical growth region, growth-ring counts, location (heartwood or outer layer), amount and type of naturally-occurring chemicals and density. Therefore, in order to get the best overall data regarding a meter’s accuracy, a larger sampling of side-by-side tests must be performed. Even “the best” meters will vary in their measurement accuracy from board to board, but compared to “the next best” will still be superior in overall accuracy of the total samples tested.
Moisture meter features vary from manufacturer to manufacturer and in order to assess accuracy, it is also essential that the meter being tested be set to the manufacturer’s specifications. All meters require species adjustment tables or the user-entry of the correct species setting (for programmable meters). Additionally, pin meters require that readings be compensated up or down depending on the temperature of the wood if the wood is substantially hotter or colder than approximately 70 degrees F. Each meter must be used in accordance with its design to give a reading that supplies assessable data.
With the number of variables that must be taken into account for any moisture meter technology, the underlying reality is that the technology used to assess moisture content has not changed significantly over the last two decades. While there have been some improvements in the “field features” – the features that make MC data easier to collect and use in the field – the basic science of moisture meter technology remains the same.
And because the technology is still fundamentally the same, the results of accuracy studies also will predictably be the same. And in the four independent studies commissioned by Wagner Meters (see links below), the end result was that their pinless wood moisture meters were consistently more reliable for accuracy in assessing wood moisture content than any of the meters they were tested against.
So when comparing wood moisture meters for features, it is important to know your use and your specific needs for measuring moisture content in wood. But when comparing wood moisture meters for accuracy, make sure you understand which apple you’ve placed in your cart. Wagner Meters have been proven to be the most accurate moisture meters available today.
Learn more about Wagner Pinless Wood Moisture Meters