21414 Development of Absolute Displacement Vibrometer for measuring a Long Period and Large Amplitude of Vibrations,

This paper proposes a new type of absolute displacement sensor measuring a long period and large magnitude. When we measure one object's displacement, the sensor's natural frequency must be lower than the object's one. So it is difficult to measure a low frequency vibration below 1 Hz using conventional displacement sensors. In order to lower the natural frequency and enlarge the detectable amplitude, the sensor with the low natural frequency is realized by using feedback control. It has been demonstrated that a developed sensor has a detecting range from about 0.2 Hz to 10Hz for absolute displacement. In addition, the measurement displacement amplitude has been expanded to about 51dB (350 times).