When making lumber products it is very important for wood to have a certain moisture content. That is why any company engaged in woodworking has such a device as a moisture meter. Without it you can not do without it in everyday life if you like to make something out of wood.
Moisture is the amount of water in the wood material. It is measured as a percentage. You can determine the moisture content of wood at any time during the woodworking process. Such measurements are usually taken after the trunk has been sawn into boards or round timber. The higher the moisture content of wood, the lower its cost, because wet workpieces are not suitable for further processing and you will still need to spend time and money on its drying.
Wet wood is prone to rot. Under the influence of fungal infestations, it deteriorates very quickly. Also, remember that different types of wood have different densities. The possibility of choosing the type of wood, while working with a moisture meter for wood, allows you to make more accurate measurements.
The maximum moisture content of wood for processing is 20-22%, no more. Otherwise, drying out, the board “twists”, warps, it’s difficult to plan.
Thus, measuring the moisture content of wood before buying is the most important task.
What you need to know before choosing a moisture meter
First of all, you should accurately determine the range of work for which you plan to use the moisture meter. Remember that there is practically no universal moisture meter. Moisture meters with different structures and operating principles are selected for different tasks and different spheres of activity.
Moisture meters in wood have different technical characteristics, among which the most important:
- Moisture detection range. The measuring range is the ability of the device to determine the moisture index.
- Accuracy of measurement. Each instrument has an allowable error in measurement. The more accurate the moisture meter, the more expensive it is. Therefore, you need to know the peculiarities of your technological process and norms on possible deviations from the real moisture content. If you need extremely accurate readings according to regulatory instructions, you should not save money. In this case, go for the best meter in its class for accuracy. If accuracy is not particularly important, you can take the budget version, which gives an inaccuracy of measurement a little more.
- Conditions of use. Not every wood moisture meter has a high degree of protection from external factors (weather, temperature). That is, not all meters well tolerate frost, high temperatures, dusty rooms. All these factors can greatly distort the measurement values. Therefore, operating conditions of the moisture meter (place of use, technological process, duration of application) are also an important prerequisite. The more difficult these conditions are, the more attention should be paid to the presence of device protections when choosing.
Types of moisture meter models
The main difference between all wood moisture meters is in the type of sensors and the principle of measuring the moisture value.
Pinned moisture measures
The general characteristics of needle moisture meters:
- Moisture measurements are made only at plus temperatures. At 0 0C and below the error increases sharply.
- Accuracy of readings – ±0.2%.
- Limit (maximum) – 35%.
Pros of the conductive moisture meter are:
- High measurement accuracy (due to deep penetration into the inner layer of wood).
- The ability to measure moisture at multiple points simultaneously.
- Possible damage to the wood. As by sticking the spikes into the wood you are actually making a puncture in the wood. For high-end, premium quality timber it’s material damage, so non-contact moisture meters are a good option in this case.
Pin moisture meters can also be divided into several types:
The sensors in such moisture meters are short needles that plunge shallowly into the wood. Such devices are compact and easy to fit in a pocket. Given the depth of the sensors, the main purpose is to measure the moisture content of the board.
The dimensions of such moisture meters are larger, but they allow working with a wide range of wood samples – beam, log, a thick plank. Readings of the device give an accurate idea of the liquid content throughout the structure of the material. The only thing required is accuracy in use. Carelessness leads to breakage of the needle, which then gets out of the solid wood is unlikely to succeed.
Non-contact, pinless moisture measures
These moisture meters include sensors that are either attached to the surface of the wood or are built into the body of the device, and it is placed on the controlled sample. Such models – the only possible option for measuring the humidity of the parquet (a piece or in the form of a board), laminate, plywood, and other materials characterized by high density.
Yes, and to pierce with probes such samples is hardly advisable, knowing that after the measurements will be left indelible traces. Sensors are not immersed in the wood but are fixed on its surface without damaging the material.
Pros of non-contact moisture meters:
- Easy to use – no electrodes need to be inserted into the material.
- Do not damage the wood.
- Wide measurement range. The minimum moisture threshold, as well as the maximum, is always better with high-frequency non-contact moisture meters than with contact ones.
- High sensitivity. Electrode-free moisture meters are designed for any wood species. Their memory contains a large number of dielectric permittivity values of materials, not only wood species, but other materials as well.
- Can be used for different materials, parts and workpieces.
- Accuracy can be distorted if the moisture content of the top layer of the material is very different from the inner layers.
Additional moisture meter options
In some cases, individual functions can be very useful. What else can be measured?
- The average moisture value. If you have to check large volumes of wood, the device will give the final result itself. Therefore, you will not have to make several measurements, in different places, and engage in calculations.
- Environmental parameters – temperature, humidity. In the case of wood processing in the drying chamber, the organization of its long-term storage are very necessary options. They will help to control local conditions and regulate the process.
What to pay attention to when choosing a wood moisture meter?
First of all, it is necessary to determine the range of tasks for which the device will be used.
Conductometric devices of budget class are used to check the moisture content of surface layers of wood, which is necessary when checking the condition of wooden parts of building structures, working with wood of small thickness, general assessment of wood, and the like.
Top-class conductometric devices are used to check the moisture content of untreated wood, control the moisture content when shipping and receiving valuable wood, to determine the moisture gradient of wood during and as a result of drying, control the work of moisture meters of other types, etc.
Dielectric devices with sensors in the form of plates fixed on the body are usually used to determine the moisture content of treated wood and finished wood products.
Devices with sensors in the form of external metal elastic plates are universal devices. Their only disadvantage is lower accuracy compared to conductometric wood moisture meters.
The number of measurement groups for different types of wood is important for moisture meters. And it is very desirable to have a choice not only by wood type (for example, “pine”, “oak”, “aspen”), but also by wood density. Changing the density value allows you to adjust the moisture meter exactly to your wood, ensuring high accuracy of measurements. While the concept of “pine” or “oak” can be very different from manufacturer to manufacturer and from country to country.
When buying a dimensional moisture meter (non-contact) pay attention to such parameters as penetration depth (scanning). If you work with a board, for example, 40 mm, try to buy the device with the penetration depth of exactly 40 mm, but not less than half of the board thickness (it can be measured from both sides). We also draw your attention to the fact that on the market there are some models with 2 built-in sensors with different penetration depth
Please note that if the moisture meter has a flat sensor, it must be applied completely to the plane of the board. Moreover, if the board is untreated and there is a small gap between the sensor and the board, the readings will be inaccurate.
If you need to measure an untreated board with a moisture meter, we recommend choosing a device with a special spring sensor, which is more universal (it can measure both treated and untreated wood).
When buying a conductivity meter it is worth paying attention to the presence of thermal compensation, which is important for obtaining accurate measurement results. This is especially critical for measuring the moisture content of a hot board. And not just for the conductometric measurement method. Dielcometric moisture meters have a negligible dependence of the results on the sample temperature, which in most cases can be neglected.