Browse Prior Art Database

Long Period Seismographic Sensor

IP.com Disclosure Number: IPCOM000074213D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Gaston, CA: AUTHOR

Abstract

The sensor comprises a vessel 10 containing a float 14 suspended in a fluid 12. The float 14 has a large submerged body portion 16 and small diameter mast portion 20 which is partially submerged. A weight 18 at the bottom of the body 16, keeps the float 14 upright. A horizontal mirror 22 forms the top of the mast 20. The mirror 22 permits interferometric measurement of the vertical position of the float. A vertical scale 24 on the mast 20 can also be used to determine the vertical position of the float 14.

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Long Period Seismographic Sensor

The sensor comprises a vessel 10 containing a float 14 suspended in a fluid
12. The float 14 has a large submerged body portion 16 and small diameter mast portion 20 which is partially submerged. A weight 18 at the bottom of the body 16, keeps the float 14 upright. A horizontal mirror 22 forms the top of the mast 20. The mirror 22 permits interferometric measurement of the vertical position of the float. A vertical scale 24 on the mast 20 can also be used to determine the vertical position of the float 14.

The natural period of the float 14 depends on the ratio of its inertia to the restoring force which is generated in response to the displacement of the float. The inertia is made high by providing a large-volume body portion 16, since the float unit 14 must have a mass equal to the mass of the fluid it displaces. Because of the small diameter of the mast 20, a small vertical movement of the float 14 produces a very small change in the amount of fluid displaced by the float and creates a very small restoring force.

To detect long-period seismic waves, vessel 10 is firmly attached to the earth, so the vessel 10 and the fluid 12 move with any vibrations in the earth. The movement of the fluid 12 will be transmitted to the float 14 through the small restoring force generated by vertical movement of the fluid relative to the float. Because of the float's long natural period, only long-period seismic waves will be effectively coupled...