JPH0121888B

The disclosed torsional vibration monitoring apparatus estimates torsional vibration at arbitrary positions in a shaft system, such as in a turbine generator. Detectors detect torsional vibrations produced at fixed positions of the rotating shaft system and the detected vibrations are separated into modal vibrations so that subtractors and matrix operators can obtain up to n vibration mode components from the modal vibrations and the torsional vibrations detected. First modal vibration operators obtain modal vibrations higher than the (n+1)th modal vibrations at the arbitrary positions of the rotating shaft system from the detected torsional vibrations, second modal operators obtain up to the n-th modal vibrations at the arbitrary positions from the vibration mode components and adders add the respective modal vibrations obtained by the first and second modal operators.