OPTICALLY POWERED ELECTRICAL ACCELEROMETER AND ITS FIELD TESTING

This paper introduces an optically powered electrical accelerometer re cently developed by the author for measuring dynamic response of civil structures and describes a field test using its prototypes installed on a 310-m tall concrete TV tower, together with the results of system identification analysis based on the field measurement. This sensor e mploys an electric circuit, LC oscillator, in the sensor head. The res onant frequency of the LC oscillator is modulated by the movement of a pendulum installed inside the sensor head, indicating the acceleratio n of the pendulum support. The oscillatory electric voltage is transfo rmed to an optical signal and transmitted through an optical fiber. Th e LC circuit is optically powered as well. Therefore, there are no ele ctrical cables involved in this sensor, which brings many advantages t o the sensor, such as immunity to an electromagnetic field and signifi cantly less troublesome cabling problems. Prototype accelerometers wer e fabricated and installed on the TV tower to measure its ambient vibr ation. Based on the measurements, dynamic characteristics of this towe r, including the natural frequencies, damping ratios, and mode shapes, were successfully identified. They are essential for the assessment o f the dynamic response of the tower under wind and earthquake loads. T his field test has not only provided valuable information of the tower 's dynamic characteristics, but also demonstrated the excellent perfor mance and great potential of this optically powered sensor for civil s tructure applications.