Wood Moisture Meter Accuracy: Pinless vs Pin-type (Guide)
If you want your wood creations to enjoy a long life, you need to treat the wood right. That’s where moisture meters come in. As a hygroscopic material, the longevity of the wood’s physical integrity and aesthetic quality depends on your understanding of the wood’s moisture condition at the time you want to start working with it. Whether you’re constructing a building, laying down a floor, or crafting furniture – wood moisture levels matter.
Here is your master class on wood moisture meters so you can use them wisely and confidently on all your woodworking projects.
Are Moisture Meters Accurate?
A superior moisture meter can be accurate within 0.1% of the wood’s moisture content. Lower-grade moisture meters are very inaccurate as numbers are misleading and changing. Depending on the quality and brand of wood moisture meter being used a moisture meter can be very accurate.
The real question is: What qualifies as “accurate” as it pertains to a wood moisture measurement?
The most accurate moisture level test for wood is the “oven-dry test” because it weighs the wood. The more moisture wood holds, the heavier it is. That’s logical.
An accurate oven-dry test requires weighing the wood before going through a round of oven drying and weighing it again after. It keeps going back into the oven until the wood weighs the same after a drying session as it did before it went in.
The wood’s moisture level is expressed as a percentage of its total weight. The formula to calculate the moisture percentage is:
[(weight when before drying) – (weight after drying)]/ (weight after drying) = moisture %
If the wood weighed 20 pounds before the test and 18 pounds when the test was done, then its moisture content would be 11 percent. (20-18)/18 = 0.111 * 100 = 11%
Most woodworkers don’t dry their own wood, let alone have space and money to operate an oven, thus the need for a hand-held moisture meter. Hand-held moisture meters do not weigh wood to measure moisture content. That’s not feasible.
The accuracy of a hand-held meter is determined by comparing the hand-held meter’s moisture reading against the over-dry test results. The closer its reading is to the oven-dry test, the more accurate the hand-held meter is considered.
A digital moisture meter can be accurate within 0.1% depending on the quality and brand of moisture meter being used. A top-line handheld moisture meter provides highly accurate readings. It also scores high on repeatability, which gives the user confidence that the moisture content readings are spot-on. Lower-grade moisture meters aren’t very accurate as numbers are misleading and changing.
What Does a Moisture Meter Do?
Moisture meters indirectly measure the moisture content in a piece of wood by measuring certain electrical properties within the wood. Fortunately, there are wood moisture meters that work with great precision. So indirectly measuring moisture with a quality moisture meter provides a reading sufficiently accurate for you to make smart decisions about when and how to use the wood.
So how does a moisture meter take its measurements? There are two main technologies used: Pinless and Pin-Type.
What Is a Pinless Moisture Meter?
Pinless moisture meters work by using a sensor pad that works in contact with the wood surface but does not physically break or damage the surface to take a reading. Pinless moisture meters typically provide the capability to measure moisture content from the surface down to .25″ or deep depth measurements to .75″.
What Is a Pin-Type Moisture Meter?
Pin-type moisture meters usually have two metal pins that must physically penetrate the wood’s surface in order to take a moisture reading.
How Does a Pin-Type Moisture Meter Work?
Resistance Technology: Pin-type moisture meters work with resistance technologies using probes, or “pins,” inserted into the wood. Pin meters run an electric current between the two pins. The amount of resistance detected in the current as it moves between the pins is an indicator of the moisture condition of the wood. Because moisture conducts electricity well, the “wetter” the wood, the less resistance there is to the current flow. The drier the wood, the greater the electrical resistance is. The level of resistance found correlates to a moisture condition reading as a percentage. Meters using resistance technology are called “pin meters.” Pin meters’ accuracy can be affected by variations in the natural chemical composition of different wood species. A wood’s density doesn’t impact the flow of the current, but it can interfere with properly inserting the pins.
How Does a Pinless Moisture Meter Work?
Electromagnetic Wave Technology: Pinless wood moisture meters work with electromagnetic frequency technology using sensor pads that lay flat on the wood. Pinless moisture meters send out electrical waves at a certain electromagnetic frequency, which creates an electromagnetic field in the area under the sensor pad. The waves sent out by the sensor through the electromagnetic field trigger return waves the sensor detects.
As noted above, the amount of moisture in the wood impacts the movement of electrical impulses. Pinless meters use the changes in wave movement data to correlate to a moisture content percentage and provide accurate readings. Meters using this type of technology are called “pinless meters” since they don’t insert pins into the wood. They’re also referred to as “non-damaging meters” as avoiding the use of pins to penetrate the wood means the pinless meters don’t cause the damage to a piece of wood that a pin meter can. While pinless meters’ ability to read waves may be impacted by density variations in the wood, they are able to test a broader expanse of the wood and provide a more complete picture of its moisture condition.
Whether you’re using a pin or pinless moisture meter, you’ll get a percentage reading that reflects the wood’s moisture level.
Why Moisture Testing Matters
No one wants wood to continue changing shape after it has been used in a woodworking piece or is otherwise in service. Thus, it’s vital for the contractor, flooring professional, or woodworker to start working with wood only once it has reached an acceptable moisture percentage.
Because wood is hygroscopic, it never stops absorbing moisture from, and releasing moisture to the atmosphere around it. In other words, the wood is always trying to equalize to its environment. Any given piece of wood’s acceptable moisture percentage depends on the relative humidity and temperature conditions to which it will ultimately be exposed. Only when the moisture condition of the wood and the ambient conditions around it have equalized will the wood stop losing or gaining moisture in quantities large enough to affect its physical properties. Only an accurate reading of the wood’s moisture condition can tell you when a piece of wood is ready for use without risking future problems.
Let’s take a step back.
When green lumber goes through the drying process, it will lose all its free water first. Free water is the moisture that exists in the wood’s cavities. Bound water is the water that’s fused (or “bound”) with the wood’s cells. When a piece of wood loses or gains bound water, the size of its cells change. That’s what causes wood to expand, shrink, split, and crack.
Green lumber is said to reach its fiber saturation point (FSP) once it has lost all of its free water. Across all species, the FSP for wood translates to roughly 30% moisture content. There are slight variations for a few species, but on average, lumber at 30% moisture level has reached its FSP. All the drying that occurs after the FSP is reached is the drying that affects the shape of the wood.
The wood will continue to lose moisture until it reaches the point of equilibrium moisture content (EMC) with its surroundings. EMC occurs when the moisture level in the wood and in the air around it are roughly the same. At EMC, there’s no pressure moving moisture between the wood and the air.
The goal for a moisture meter is to collect the data needed in order to make decisions about what steps to take next. Does it need more drying or is it ready to be used for its intended purpose? No one can make a smart decision about when to start working with a piece of wood without knowing its moisture condition and whether it has reached its point of EMC. And you can’t know that without using a reliably accurate timber moisture meter.
How to Read Moisture Meters
Alright, so how do you understand what your moisture meter is telling you?
The primary data point any moisture meter provides is the moisture content percentage. Any handheld moisture meter provides this reading at the time you take the measurement. To be accurate, you need to be able to set the meter to read the species being measured.
More sophisticated handheld models, like Wagner Meter’s Orion® 950, also gather relevant data like air temperature and humidity and calculate EMC and dew point. As explained above, knowing the EMC is the vital data point you need to determine whether the wood is ready to be used.
There is no one particular moisture content percentage that is ideal for all cases. The end-use and intended location are the key factors determining the optimal MC percentage range for the wood you are measuring. The digital moisture meter will tell you the moisture content percentage, and some handheld meters can be programmed to alert you if the wood is reaching unacceptable high moisture levels.
Either way, the MC percentage reading is just one piece of data you need. Once you have that from the moisture meter, you need to use that data, along with other data points like air temperature and relative humidity (RH), to calculate what you really need to know: the EMC. There are EMC tables and calculators you can use to determine the MC percentage that meets the EMC if your meter doesn’t calculate it for you.
You Should Know Your Target EMC
The typical EMC to which wood will be exposed ranges from 7% to 19%. However, that’s too large a range to accept for a specific project.
Most wood flooring manufacturers dry the wood they use to between 6% to 9%. The EMC applicable to a specific location depends on temperature and RH variations throughout the year in that region and how controlled the environment will be in the immediate usage area (i.e., is this wood for indoor or outdoor installation).
Wood being used for construction has a higher EMC range of 9% to 14%. Again, this will vary by location and species and is just the typical range. If you’re building in a dry city like Las Vegas, the local EMC can drop as low as 4%.
Last, wood objects intended to spend their lives indoors, from violins to tables, have a more predictable target EMC range of 6% to 8%.
How to Assess a Meter’s Accuracy
Well, this is really the ballgame, isn’t it? No point in using a moisture meter that doesn’t give you accurate readings.
You can assess a moisture meter’s accuracy subjectively and objectively. Subjective assessments can include manufacturer claims and user product reviews. User product reviews are a valuable source of insight into a meter’s usability or feel. However, the average user is rarely in the position to evaluate a meter’s accuracy.
Manufacturer’s claims can be subjective, or they can be based on objective testing. (You’ll find links to a number of objective tests conducted with Wagner Meters wood moisture meters at the end of this article.) When looking at objective tests conducted or cited by the manufacturer, look at the sample size of the test. If a low number of wood samples were used, the test has limited utility. Each piece of lumber, even within the same species, varies based on its geographical growth region, growth-ring counts, location (heartwood or outer layer), amount and type of naturally occurring chemicals and density. Any test that purports to make a thorough assessment of a meter’s accuracy must cover a large sampling of wood with side-by-side tests.
Either way, user reviews and manufacturer claims are useful information sources, but not definitive as to a meter’s accuracy.
The objective laboratory standard for determining the accuracy of timber moisture meters is ASTM standard D4442-16 (Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Base Materials). This standard uses an oven-dry laboratory method to determine the true moisture content in wood samples. It then compares the oven-dry results to the measurements taken on the wood samples from the meters prior to oven drying.
The difference between 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 based on a comparison of its readings against the oven-dry test.
Which is better pin or pinless moisture meter?
One of the benefits of using a pin meter is that you can test at a wide variety of depths within the wood. Pins come in different lengths, so you can always swap out pins to measure at different depths. Measuring for moisture at multiple depths creates a broader picture of the overall MC of the wood. The accuracy challenge with pin meters is that accurate measurement depends on the pins being driven into the wood properly. It can take a fair amount of pressure to get the pins inserted properly, especially the longer the probe. The denser the wood species, the more pressure required to properly insert the pins. The accuracy of the pin meter can also be impacted by the wood’s temperature. If substantially hotter or colder than approximately 70 degrees F, pin meters require their readings be compensated up or down depending on the exact temperature.
Indeed, one of the factors driving inaccuracy in pin meters is the challenge they present to the user. Pin meters only measure the moisture content of the small area between the two probes, which means multiple tests must be conducted at different spots. And even more tests if you want to switch out pins to measure at multiple depths. At each test site, pins need to be inserted properly into the wood, which is a common cause of pin or meter breakage. The bottom line: The process of using a pin meter can be time-consuming, tedious and exert stress on the physical meter, which tends to result in taking short-cuts when measuring moisture. Short-cuts are never an accurate moisture measurement method.
One of the benefits of a pinless meter is that it’s easier and faster to use than a pin meter, which means that users are more likely to take enough readings to get a complete picture of the wood’s moisture level. First, a pinless meter measures a wide swath of wood with each test, necessitating fewer tests than is required if using a pin meter. You can also switch measurement depth faster with the pinless meter. Better pinless meters come with dual depth measurement options, typically at a quarter and three-quarter inch depths. Due to the challenges swapping out and driving in pins at different lengths, pin meters often have less utility at a practical level. The main concern to ensure accuracy with a pinless meter is to apply enough pressure so there aren’t large air gaps between the sensor and the wood’s surface.
The other main advantage pinless meters have over pin meters is that they don’t cause damage to the wood. Every measurement taken with a pin meter drives two holes into the wood. A pinless wood meter never breaches the surface.
Pin meters accuracy can be impacted by the wood’s temperature, can damage the wood, if the wood is dense it’ll be harder to drive the pins in, and you can often break pins. Pinless meters are more accurate, take faster readings, can take dual depth measurements, and don’t damage your wood. These are a few reasons why we believe pinless to be the best moisture meter.
Read more about the differences between a pin vs pinless meter.
Some issues affect meter accuracy regardless of the meter type.
Each wood species has its own properties that impact moisture and moisture measurement. Higher quality meters let you adjust the species setting before using the meter. Lower end meters require you to use species adjustment tables. Either way, make sure specifying the species is part of your measurement process.
Collecting enough data points:
No one point in a piece of wood will give you a complete and accurate reading of the wood’s overall moisture level. If you need to measure the moisture condition of a shipment, testing one piece of the batch isn’t going to cut it either. You need to conduct enough tests at various spots on each piece and among pieces in a batch to get an accurate picture of the moisture condition of the whole shipment. Using a sophisticated pinless moisture meter like the Orion® 950 that stores readings gives you a high, low and average statistics of the moisture readings taken.
Using a calibrated meter:
Both meter types need proper maintenance in order to take accurate readings. Over time, the meter may become uncalibrated. If it doesn’t get recalibrated, its readings aren’t reliable.
The first step is to check the calibration on your meter. Some meters have so-called ‘internal calibration checks’ that purport to tell you when the meter is uncalibrated, but this internal check should not heavily be relied upon over a true check with an ‘external’ and stable reference. Pin and pinless meters each have a different type of external tool you can use to test a meter’s calibration. You’d use a moisture content standard (MCS) to test whether a pin meter is calibrated. Place the pins against the MCS. Compare the meter reading to the MCS reading. If they’re the same, the meter is calibrated.
For pinless meters, you’ll place the meter on a calibration verification block. Place the pinless meter on the calibration block as you would a piece of wood you want to measure. If the reading comes back to match the calibration block spec, you know the meter remains within factory specifications.
It’s critical to understand that these internal and external calibration tests only tell you whether the meter is calibrated. None of them can recalibrate the meter so it can provide accurate readings again.
Most uncalibrated meters need to be sent back to the factory to get recalibrated. All digital moisture meter models in the Orion line come with an On-Demand Calibrator that lets you recalibrate your meter on-site.
How to Select the Best Wood Moisture Meter
Now we’re down to the brass tacks.
How can you select the best moisture meter for your work?
Many people prefer a pinless moisture meter because they don’t want the probes to ruin the wood. The more tests run with a pin meter, the more damage it does to the wood. Yet without running enough tests, you won’t get an accurate understanding of the wood’s moisture condition.
Using pin meters also takes more time to finish complete testing of a batch of wood and have more ways things can go wrong during testing. It’s not uncommon for pins to break during testing, especially when inserting them into the hardwood. There also is no model of pin meter that can be recalibrated onsite.
In truth, the technology used by both pin and pinless meters haven’t changed significantly over the last two decades. That’s why the objective tests of Wagner Meter moisture meters, linked below, from years ago remain valid today. All four of these independent studies, commissioned by Wagner Meters, found that Wagner Meter pinless wood moisture meters were consistently and reliably more accurate in assessing wood moisture content than any of the meters they were tested against.
The final area for comparison when selecting a moisture meter is the scope of “field features” you find valuable. Since the moisture measurement technology hasn’t fundamentally changed, the addition of high-value field features is how you can distinguish an advanced moisture reader from a simpler one.
Such features can include having an extended range of species settings, calculating EMC for you, storing large amounts of measurement data, and on-site calibration, among others. Determine the scope of your need for comprehensive wood moisture meter enhancements.
What Is the Best Moisture Meter?
Our choice for the best moisture meter is the Orion 950 pinless wood moisture meter. It all depends on what you’re looking for as far as meters go. There are many different articles out there with their lists of best moisture meters, but how can you tell if it’s the right one for you? Most people prefer a pinless moisture meter over a pin meter because they don’t want to put holes in the wood.
Do Moisture Meters Calculate EMC?
A wood moisture meter that can calculate EMC is a rare find, but they are available. How do we know? Because we sell them.
EMC is the moisture level where the wood neither gains nor loses moisture since it is at equilibrium with the relative humidity and temperature of the surrounding environment.
Calculating EMC involves a complex mathematical equation for precise results. The first-class, all-in-one Orion 950 Smart Pinless Wood Moisture Meter can calculate the moisture content that your wood needs to be at to reach equilibrium with the surrounding environmental conditions.
Mathematical formula for determining EMC
EMC = [ -ln (1 – ϕ) / 4.5 x 10-5 ( T + 460 ) ]0.638
ln = natural logarithm (a mathematical equation that calculates the time it takes to reach a specified point)
ϕ = relative humidity expressed as a decimal
T = temperature in Fahrenheit
The Eternal Allure of Wood
Having expertise in woodworking, whether in construction or goods, is some job security. People will always want gorgeous wood flooring, structures, and furniture. However, working with wood will always require you to manage potential moisture issues. Using the right moisture reader to conduct your moisture testing will help you create amazing living spaces, fittings, and furnishings to be enjoyed for centuries.
And now that you’ve read through our masterclass on wood moisture meters, you should have a solid foundation for a number of key issues. It starts with your new understanding of what moisture meters actually measure and how to read the information the meter provides you.
With your deeper understanding of how they work, and in particular, the differences in how pin and pinless moisture meters work, you’re better positioned to make decisions about what type of moisture meter makes the most sense for your purposes. Especially since you also now have the basic knowledge about how to assess a moisture meter’s accuracy and the importance of calibration.
You can also visit the sources listed below to learn more right now about the accuracy of Wagner pinless moisture meters.
As Sales Manager for Wagner Meters, Ron has more than 35 years of experience with instrumentation and measurement systems in different industries. In previous positions, he has served as Regional Sales Manager, Product and Projects Manager, and Sales Manager for manufacturers involved in measurement instrumentation.
Last updated on January 7th, 2021