Torsional vibration amplitude sensor and monitor

A device is disclosed for measuring torsional vibrations superimposed on rotating equipment such as a shaft. The device may be fastened to a rotating shaft by a collar and includes a sensor array comprising two or more accelerometers measuring the radial acceleration of the sensor array and the tangential acceleration of the sensor array. The gravitational component of the accelerometer signals is identified either by isolation in one of the signals, or by comparing two or more signals. From the tangential and radial acceleration signals, a torsional vibration amplitude is calculated from the ratio of the tangential acceleration and the radial acceleration. The radial acceleration is further used to determine the average velocity of the sensor array. The tangential acceleration may further be integrated to obtain the angular velocity of the sensor array, or further integrated to obtain the angle rotated through.