Two-axis differential capacitance inclinometer

• US 4,811,491 A
• Filed: 09/04/1987
• Issued: 03/14/1989
• Est. Priority Date: 09/04/1987
• Status: Expired due to Term

• Current Assignee: Tele Atlas North America (TomTom NV)
• Original Assignee: Etak, Inc. (TomTom NV)
• Inventors: O'Brien, Terence J., Phillips, Alan C.
• Primary Examiner(s): Martin, Jr., William D.
• Application Number:
  US07/093,017
• Time in Patent Office: 557 Days
• Field of Search: 33/366, 340/689, 364/559, 361/284
• US Class Current: 33/366.12
• CPC Class Codes: G01C 9/06 Electric or photoelectric indication or reading means
• CPC Class Codes: G01C 9/20 the indication being based on the inclination of the surface of a liquid relative to its container

Abstract

A two-axis inclinometer having a central electrically conductive member inserted within and spaced from the interior walls of a non-electrically conductive vessel. A plurality of four plates are mounted symmetrically on the exterior surface of the vessel. A dielectric fluid is provided in the gap between the center member and the interior wall of the vessel so as to provide a differential change in the capacitance between opposite plate members as the inclinometer is tilted about an axis perpendicular to its longitudinal axis.

Claims

1. A two-axis inclinometer comprising:

an electrically conductive member;

first, second, third and fourth electrically conductive plates;

means for mounting said first and said second plates adjacent to opposite surfaces of said member so as to provide a gap between said first and said second plates and said member;

means for mounting said third and fourth plates adjacent to opposite surfaces of said member so as to provide a gap between said third and fourth plates and said member, said first and said second plates being mounted orthogonal to said third and said fourth plates;

means for retaining a dielectric fluid in said gaps in such a manner that as said member and plates are inclined about a pair of orthogonal axes, the amount of said fluid in each of said gaps will change as a function of the angle of tilt of said member and said plates about said pair of orthogonal axes;

a pair of current sources for charging opposite ones of said plates relative to said member;

means for periodically switching said current sources between each of said opposite plates to compensate for variations in current from said sources;

means for periodically discharging said opposite plates relative to said member, said charging and said discharging producing a pair of sawtooth voltages; and

means for filtering and differentially amplifying said sawtooth voltages for providing an output signal which is proportional to the inverse of the differential capacitance between said opposite plates and said member as said member and said plates are tilted about said orthogonal axes.