New Silica Compact Tiltmeter for Deformations Measurement

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Abstract
A cheap, sensitive, compact tiltmeter made of melted silica is developed for the measurement of small movements of civil engineering structures. Available surveying instruments are expensive, moderately sensitive, and they rarely give continuous records. For these reasons, a new instrument was designed, derived from a high sensitivity tiltmeter used for the measurement of terrestial tidal waves. It is a horizontal pendulum, operating in a vacuum, realized with two silica fibers and a silver mass. A photoelectic cell is used for the detection of the mass movement. The range and resolution depend on the prechosen natural period of the pendulum, which can be adjusted by the operator. The instrument is tested in the laboratory and the field. Results obtained in a volcanic survey reveal that this type of instrument gives precise information about the behavior of a volcano before and after eruption: the direction and the speed of the interior magma, the future opening position, and its inflation and deflation.