Development of seismometer -type absolute displacement sensor aimed for detecting earthquake waves with large magnitude and long period

Abstract

This paper proposes a novel seismometer-type absolute displacement sensor aimed at detecting earthquake waves with a large magnitude and long period. However, since the measuring range of the conventional displacement sensor is higher than the natural frequency of itself, it is difficult to detect a low frequency vibration below 1Hz using conventional seismic-type displacement sensors. In order to provide an absolute displacement detection which is capable of lowering the natural frequency and enlarging the detectable amplitude without causing a structural defect, the relative signals of displacement, velocity, and acceleration between a detected object and the auxiliary mass of the sensor are fed back into the sensor. In addition, a phase lag compensation is inserted to adjust phase angles, which are below a frequency lower than 1Hz. Theoretically, this sensor is able to detect a lower frequency range from 0.2Hz to 10Hz and large amplitude with 100 times to the movable range of the sensor. It has been demonstrated by experiments that the developed sensor with a small size and lightweight has a detecting range from 0.2 Hz to 10Hz for absolute displacement and velocity. As an additional advantage, the measurement displacement amplitude has been expanded to about 40dB (100 times) for detecting earthquake waves with large magnitude and long period. As the typical application example of the developed absolute displacement sensor, a seismic wave based on Hachinohe wave is used with well observation results.

Keywords

• displacement sensor
• earthquake wave
• natural frequency
• large magnitude
• long period