Seismic alarm system

Communications: electrical – Condition responsive indicating system – Specific condition

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Details

33 1HH, 73594, 73652, 181122, 367135, 367181, G08B 2100, G01V 118

Patent

active

043001351

ABSTRACT:
An alarm system is provided for detecting a seismic tremor and for generating an audio and/or visual alarm signal which varies depending upon the magnitude of the seismic tremor. In the preferred form of the invention, the alarm system comprises a free running oscillator having a pair of terminals the capacitive value across which controls the frequency of the oscillator. A fixed oscillator plate is electrically connected to one terminal while a variable position oscillator plate is electrically connected to the other terminal and has an inertial mass secured to it. A spring positioned between the plates urges the variable position capacitor plate away from the fixed plate but still enables the variable position capacitor plate to move in response to a seismic tremor thus varying the capacitive value between the terminals and the frequency of the oscillator. The output from the oscillator is coupled through a phase locked loop circuit which tracks the oscillator output. The output from the phase loop lock circuit is fed to a signal conditioner which shapes the amplitude response and in addition provides continuous recalibration to a zero output level when the device is unperturbed. The output from the signal conditioner in turn is coupled to an event classifier which compares the output signal from the signal conditioner with at least two preset reference levels. When the signal from the signal conditioner exceeds a first preset reference level, the event classifier activates a first alarm signal. When the output signal from the signal conditioner exceeds a second preset reference signal, the event classifier activates a second alarm signal.

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