FLUID ACCELEROMETER

• US 3,602,049 A
• Filed: 06/07/1968
• Issued: 08/31/1971
• Est. Priority Date: 06/07/1968
• Status: Expired due to Term

• Current Assignee: Kearfott Guidance and Navigation Corporation
• Original Assignee: William C. Albert
• Inventors: Albert, William C.
• Primary Examiner(s): Gill, James J.
• Assistant Examiner(s): Goldstein, Herbert
• Application Number:
  US04/735,260
• Time in Patent Office: 1,180 Days
• Field of Search: 73/516,517,503 200/61.45,47,53
• US Class Current: 73/503
• CPC Class Codes: G01P 15/02 by making use of inertia forces using solid seismic massesG01P15/14 takes precedence

Abstract

A fluid accelerometer in which a proofmass assembly containing a volume of inert gas is disposed in a passage containing a damping fluid, and translates in the passage in response to acceleration.

Claims

1. An accelerometer of the type capable of producing an output signal proportional to the time integral of the acceleration of its proofmass comprising:

an outer hollow housing member, an inner housing member having an interior bore and being disposed within said outer housing to provide an annular-shaped restricted clearance space between the outer wall of said inner housing and the inner wall of said outer housing, said clearance space communicating with the interior bore of said inner housing at either end thereof to define an endless passage, a proofmass assembly disposed within the interior bore of said inner housing for axial displacement therein in response to an applied acceleration, a dense liquid metal disposed in said endless passage and extending into the interior bore of said inner housing for surrounding said proofmass assembly, said proofmass assembly having a density less than that corresponding to said liquid metal whereupon axial displacement of said assembly in said inner member'"'"''"'"'s interior bore causes said liquid metal to flow through said restricted clearance space between said inner and outer housings, said flow being restricted by said clearance space to dampen the motion of said proofmass, and signal means responsive to a predetermined axial displacement of said proofmass assembly for producing an output signal, wherein said proofmass assembly comprises a pair of displaced piston elements axially displaceable within said bore, and means for resiliently coupling said piston elements together wherein the axial space between said piston elements may be decreased upon an increase in the density of said liquid metal acting on said piston elements and an inert gas disposed between said piston elements within said inner housing bore, said resilient coupling means normally maintaining said liquid metal at a pressure greater than said inert gas.

2. The apparatus of claim 1 wherein each of said piston elements includes a protruding portion extending into said liquid metal in opposite directions respectively, whereby the dispLaceable volume of said protruding portions is sufficient to provide a buoyant force equal to the mass of said proofmass assembly times the acceleration of gravity, said buoyant force acting perpendicular to the longitudinal direction of the axis of said inner housing bore.

3. The accelerometer of claim 2 wherein said outer housing includes a first electrical contact means extending into said outer housing and communicating with said endless passage and therefore said liquid metal, and second electrical contact means extending through said inner and outer housings and into the space between said piston elements occupied by said inert gas, said second contact means disposed within an insulating fill tube which latter serves the dual function of insulating said electrical contact means from the remainder of the apparatus and for providing an inlet means for said inert gas.

4. The apparatus of claim 3 wherein said inner housing is integrally connected to a radially extending flange portion at one end thereof, said flange portion having an axis of rotation and including means for threadedly engaging the inner wall of said outer hollow housing at one end thereof, wherein said annular clearance space is inclined at an angle to said axis, whereby the cross-sectional area of said annular clearance space may be varied by rotating said flange portion relative to said outer housing through said threaded engagement means.

5. The accelerometer of claim 4 wherein said flange portion includes a bore centrally disposed therein in substantially coaxial relation to the bore in said inner housing, plug means disposed within said central bore in sealing engagement therewith and adjustable latch means coupled to said plug means extending therefrom and in engagement with one of the protruding portions on one of said piston elements whereby said latch means may determine the initial position of said proofmass assembly.

6. The accelerometer of claim 5 wherein said latch means includes a magnet means coacting with said one protruding portion of said piston element whereby said proofmass assembly will be prevented from axial displacement within said bore of said inner housing until a predetermined acceleration force has been exceeded equal to the force applied by said magnetic means on said piston element protruding means.

7. The accelerometer of claim 1 including means for maintaining said damping constant despite changes in ambient temperature, wherein said last-mentioned means includes said inner housing being formed of a material having a first temperature coefficient of expansion and, said outer housing being formed of a dissimilar material with respect to said inner housing whereby said outer housing material has a coefficient of temperature expansion dissimilar to that associated with said inner housing material, and said last-mentioned means further includes a second inner housing member disposed adjacent said first-mentioned inner housing member but displaced therefrom and from the inner walls of said outer housing member to form a second restricted clearance space between its outer wall portion and the inner wall portion of said outer housing member, the second restrictive clearance space formed by said additional inner housing member communicating with said first-mentioned restricted clearance space, and said second inner housing being formed of a material dissimilar to either material corresponding to said first-mentioned inner housing member or said outer housing member whereby the temperature coefficient of expansion of the outer housing member is dissimilar to the temperature coefficient of expansion of either the first-mentioned or second-mentioned inner housing members respectively.

8. The accelerometer of claim 1 wherein each of said piston elements is of electrically conductive material and wherein said outer housing includes a first electrical contact means extending into said outer housing and communicating with said endless passage and therefore said liquiD, and a second insulated electrical contact means extending through said inner and outer housings into the space between said piston elements occupied by said inert gas, whereby predetermined axial displacement of said proofmass assembly in said inner housing bore closes an electrical circuit through said first and second contact means.