DESIGN AND PERFORMANCE OF THE KFD--WIDEBAND, LARGE DYNAMIC RANGE FEEDBACK SEISMOMETER

A portable wideband feedback seismometer has been developed and compared with a conventional seismometer (Model Type 763) and force balance type wideband feedback seismometer system (STS-1V, STS-1H). Experiments of environmental disturbance and operating conditions have also been made, with satisfactory results.The seismometer has one vertical component and two horizontal components. Each employs an inertial pendulum of mass 0.8kg which has a natural period of 15 sec. The mechanical Q factor is about 50. Displacements of the mass are detected by a differential capacitive transducer and feedback is applied via an electromagnetic system to maintain the mass stationary with respect to its supports.The overall response, which is defined by the feedback, has a flat response to displacement over the passband. It is identical to that of the displacement sensor of an LP seismometer with a natural period 30 sec and a second order low pass filter with a cutoff at 0.03 sec. The instruments have a dynamic range of 100 dB and damp of 0.8.The main considerations in the design are portability, convenience of installation, efficient .shielding against environmental disturbance and low power consumption.