| 摘要 |
The present invention concerns a procedure for measuring the length of a log passing a measuring point. The measuring equipment located at the measuring point 3 includes a transmitter S1 which directs ultrasonic waves onto the log surface 2. The direction and wavelength are selected and adjusted in such a way that the movement of the log surface 2 produces a Doppler shift in the ultrasonic waves scattered from the surface. The said scattered waves are received by a receiver S2 included as part of the measuring equipment, and on the basis of the difference between the transmitted waves and the scattered waves, the length of the log which has passed the measuring point is determined in such a way that, in the signal produced from the scattered ultrasonic waves, there is incorporated a signal, based on the frequency of the transmitted ultrasonic signal, for the production of a signal of lower frequency than the aforementioned signals. From this lower-frequency signal, the total value of the phase shift can be measured. <IMAGE>
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