Microwaves enable fast and reliable measurement of moisture content in stacked round timber. If the technology is further developed, the accuracy can be at least as high as today’s manual and labor-intensive methods.
Measuring the moisture content of wood is important in order to make the best use of the raw material. The moisture content determines, for example, whether a roundwood pile should be classified as fuel wood or pulpwood – a division that in turn has a major impact on everything from transport, planning and sorting to combustion and manufacturing processes. Despite this, there are currently no effective and reliable methods for measuring the moisture content of stacked round timber. Similar challenges also exist for wood chips, where existing measurement methods are time-consuming and require extensive manual sampling
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That’s a remarkable amount of work hours for a single machine, the Norcar 600 owned by Erkki Rinne is taken well care of, it even has the original Diesel engine.
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Timber hauliers need to encourage young blood in, and also look after the hauliers we have, we need make the sector a safe and positive place to work.
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Microwave transmission as a measurement method
In a project funded by the Swedish Energy Agency’s Bio+ research and innovation programme, the Forestry Research Institute of Sweden has investigated the possibility of determining the moisture content of stacked round timber through microwave transmission, also known as radio measurement – a technique that is already used in other areas. The project has also further developed methods for measuring moisture content in decomposed forest fuel using the same technique. The results show that microwave technology is promising, but that the signals are affected by noise and other disturbances, which leads to uncertainty in individual measurements.
Causes of uncertainty
There are several factors that contribute to this uncertainty:
- Reference sampling, i.e. the determination of the actual moisture content of the logs, is significantly more labor-intensive for round timber than for wood chips, for example. Samples from the end surfaces tend to underestimate the moisture content because the end surfaces dry faster than the rest of the wood. The most reliable method is to chip the entire stack and measure the moisture content using the oven method.
- The diameter of the logs is often of the same magnitude as the wavelength of the microwaves, which leads to complex scattering phenomena that make it difficult to interpret the signals.
- Timber stacks contain larger and more varied air pockets than decomposed forest fuel, which further complicates the interpretation of the signals.
All in all, this means that microwave measurement of round timber is significantly more complex than the corresponding measurement of wood chips. Despite these challenges, the project shows that the technology can reach accuracy that is on par with or higher than today’s manual and labor-intensive methods.
Hands forward
The next step is to collect more measurement data to improve the models, preferably from stacks where the entire volume is chipped to provide reliable reference values. There is also a need for a better understanding of how variations in compaction and freezing affect the
signals. In addition, it would be valuable to link weather data to the results to better predict the freezing of the material.
Source Skogsforsk
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