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Digital Transducer for Petroleum Exploration

IP.com Disclosure Number: IPCOM000093509D
Original Publication Date: 1967-Oct-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Sanders, JW: AUTHOR

Abstract

In this highly accurate optical digital seismometer, the conventional potentiometer in a seismometer is replaced by a Kosters interferometer. A photocell is used to sense the shift of fringes which occurs as the length of the optical path is varied by moving the movable mirror attached to the mass. The output of the photocell can thus be converted into the actual distance which the movable mirror moves. This is because a fringe shift occurs each time the optical path is varied by one wavelength.

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Digital Transducer for Petroleum Exploration

In this highly accurate optical digital seismometer, the conventional potentiometer in a seismometer is replaced by a Kosters interferometer. A photocell is used to sense the shift of fringes which occurs as the length of the optical path is varied by moving the movable mirror attached to the mass. The output of the photocell can thus be converted into the actual distance which the movable mirror moves. This is because a fringe shift occurs each time the optical path is varied by one wavelength.

A hollow cone with the finished surface on the outside is used as the movable mirror to alleviate the problem of exact perpendicular movement. The cone is a 90 degree x 45 degree cone and is finished to an accuracy of 1/8th of a wavelength. One half of the fixed mirror is coated with a phase retarding layer which causes half the field to be shifted 90 degrees out-of-phase, which enables the determination of direction of movement.

The Kosters prism used for beam-splitting results in decreased susceptibility to problems caused by vibration and mirror malaligment. A low-pressure electrodeless mercury lamp and filter are utilized for the light source to produce a highly coherent beam suitable for obtaining interferences at the distances involved.

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