Broadening the Response of Short-Period Sensors: An Application to the Sprengnether S-7000 Seismometer

Abstract

In this study the application of active damping on a short-period Sprengnether S-7000 passive sensor is presented. This sensor uses a unique magnetic suspension mechanism that eliminates spring resonance effects and ensures improved thermal behavior. The resilient properties of the magnetic spring are devoid of nonlinearities seen in the metallic springs. Although the magnetic suspension is highly susceptible in external magnetic fields, the magnetic scheme applied on the S-7000 seismometer ensures reliable magnetic shielding and it can be considered as a stable suspension. The multiple frequency-dependent feedback, which is the dominant technique in the design of broadband sensors, modified the original velocity response envelop of the old instrument. The theoretical response obtained from the new transfer function, in accordance with the experimental response obtained from calibration data, characterizes the modified S-7000 seismometer as a flat velocity (0.011 to 20 Hz) sensor with top sensitivity 1046 V/m/sec. Amplitude and spectral analyses of datasets obtained from local ground noise, as well as from local, regional, and teleseismic earthquake activity, have been shown to be comparable with respective recordings of other standard broadband seismometers operated at the Athens (ATH) seismographic station vault.

Mood regulation in bipolar disorders viewed through the pendulum dynamics concept

“…The generalization of this approach has also been applied in the modeling of complex physical phenomena and in the understanding of correction procedures and manipulations in economic problems (Luenberger 1975 ; Sengupta 1997 ). For example, recent studies (Koutsoukos and Melis 2005 , 2007 ) in the field of ground motion (seismic) instrumentation have shown that novel seismic instrumentation topologies following the application feedback were extremely sensitive, linear, and stable enough to detect both strong and long period external disturbances. In both the abovementioned works, the pendula assemblies were ideal experimental paradigms to study the properties and the dynamics of feedback control on sensitive devices under observatory grade conditions.…”