Abstract: In order to monitor the dynamic load characteristic of rotating shaft of large-scale rotary machine, a new measured parameter—dynamic load fluctuation coefficient KID is presented. The mathematical model of KID measurement method is deduced by utilizing the principle of dynamics. Based on laser Doppler technology, a novel approach to KID measurement is proposed. Speed fluctuation values of rotating shaft segment and relative speed fluctuation values of between sections are obtained directly by measuring instantaneous rotational velocity of double sections in two successive times by designed optical measurement system, and then the values of KID are obtained by submitting the values of speed fluctuation into the measurement model. The feasibility is validated by experimentation. Experi-mental results indicate that dynamic load fluctuation coefficient KID reflects accurately the dynamic load fluctuation characteris-tic of rotating shaft. The technique provides a new means for monitoring dynamic load characteristic of large-scale rotating machine in engineering.

Key words: Dynamic load fluctuation coefficient KID, Laser measurement, Rotary machine, Rotating shaft, Torsional vibration