California Institute of Technology

Michael A Carr

James A Westphal

Apparatus is described for positioning a tilt meter (12) in a horizontal plane (14) and maintaining it horizontal despite temperature changes, with greater precision than heretofore. Leveling screws 25-27 which hold the upper surface (18) of a base member (16) precisely horizontal, are engaged with nuts (21-23) attached to the base member, where the nuts are made of the same material as the screws, to eliminate tilting of the base member with temperature changes, due to different nuts engaging a screw at a different height. The nuts are attached to the upper surface (18) of the base member, to further avoid imprecision. The curved glass bubble tubes (60) are mounted in V-grooves (80) in four point contact therewith.

Positioning device

A tilt meter comprises two tilt sensors (110 and 110S, see FIG. 7) in a housing (105). Each sensor acts as two variable resistors (R.sub.s), which together with two fixed resistors (R.sub.F) form a Wheatstone bridge (25), driven by a square wave signal from a drive source (30). The output of the bridge is fed to an electronic circuit (35) which includes a synchronized switch (43) to cut out the spikes (50), which the bridge outputs at the transitions of the square wave. The output of the electronic circuit is a DC signal, whose amplitude indicates tilt magnitude and polarity indicates direction of tilt. The housing (105) is supported on a support surface (102S) by means of 15 legs (116, 117) threaded into nuts of the same metal, and which has a very low thermal coefficient of expansion.

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La Crescenta, CA, United States of America

Michael A Carr