The influence of noise on the measurement of the dynamic modulus of elasticity using the timber grading device STIG was examined within this thesis. The results obtained with a laser vibrometer and a microphone were compared under various external noise conditions. Measurements were conducted in a closed, quiet environment, followed by outdoor measurments conducted near a road, with music playing, during the operation of a circular saw and at a small sawmill at different noise levels. During the measurements, the first natural frequency of the boards was measured. Based on this frequency, along with the specific density and measured moisture content of the wood, the dynamic modulus of elasticity is determined. The dynamic modulus of elasticity serves as an indicating property (IP) for classifying the measured piece of wood into a strength class. We have found that measurements taken with a microphone, regardless of the noise, deviate to some extent from the measurements taken with a vibrometer. Noise makes it difficult to detect the true natural frequency of the test subject. The measurements under different noise levels confirmed that strength grading can be performed under different noise conditions. The most important factors in the operation of the system in a noisy environment are sufficient proximity of the microphone, a sufficiently loud impact, and the correct choice of hammer.
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