Capacitance accelerometer

• US 5,092,174 A
• Filed: 10/19/1989
• Issued: 03/03/1992
• Est. Priority Date: 10/19/1989
• Status: Expired due to Fees

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Kawate, Keith W., Reidemeister, Eric P.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Miller, Craig
• Application Number:
  US07/423,922
• Time in Patent Office: 866 Days
• Field of Search: 361/277, 361/278, 361/280, 361/290, 361/303, 361/304, 73/516 R, 73/517 R
• US Class Current: 73/514.32
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

A capacitive acceleration sensor using a common PWB as one of the plates of the capacitive transducer and the wiring connections thereto. An acceleration input moves a capacitor plate to produce a measurable change in capacitance. An electronic signal conditioner accurately converts the capacitance output to a voltage signal to provide an acceleration sensor featuring accurate DC performance. The transducer and electronics are disposed on a PWB making up a complete sensor package. In a first embodiment, the capacitor comprises a fixed electrode on the PWB and a movable acceleration responsive electrode secured to a support by a conductive resilient member, the support coupled to an electrically conductive region on the PWB spaced from the fixed electrode by a guard ring to minimize stray charge between the capacitor electrodes. In a second embodiment, the movable capacitor electrode is supported at its center by a pair of electrically conductive members, one coupled to an electrically conductive region on a substrate spaced from the movable electrode by a sealing spacer. The fixed capacitor electrode is disposed either on the same substrate or a separate substrate on the opposite side of the movable electrode spaced from the movable electrode by a sealing spacer and having the fixed capacitor electrode thereon. The movable capacitor electrode can be secured at its center or at an edge and can be produced by stamping and/or photoetching and provide a single element where plural elements were previously required.

Claims

1. A capacitive accelerometer comprising a first substrate, a second substrate having a metallization thereon defining a fixed capacitor plate, a conductive metal disc, a pair of conductive epoxy supports secured to central portions of the metal disc at respective opposite disc sides securing the disc to respective substrates to disposed the disc in selected spaced relation to the substrates and the fixed capacitor plate to mount a disc rim for movement relative to the fixed capacitor plate in response to acceleration, sealing ring means secured to the substrates around the disc rim for sealing the accelerometer, and electronic means connected to the fixed capacitor plate and to a conductive epoxy support so that the disc rim and plate form a capacitor, the disc rim moves in response to acceleration to provide a change in capacitance of the capacitor corresponding to the acceleration, and the electronic means provide an output signal corresponding to the change of capacitance.

2. An accelerometer according to claim 1 wherein the central portion of the disc is connected to the disc rim by a plurality of arms extending from the central disc portion in a plurality of directions.

3. An accelerometer according to claim 1 having three arms spaced around the periphery of the central disc portion connected to the disc rim.

4. A capacitive accelerometer unit comprising a mass formed of a sintered metal powder, a support of sintered metal powder surrounding the mass, a plurality of integral tabs interconnecting the mass and support to be substantially coplanar, and a spring metal beam secured to the mass and support ring by low-stress attachment means selected from the group consisting of solders, brazing materials, welds and adhesives to retain the mass substantially coplanar to be response to acceleration to move relative to the support, whereby the support is adapted to be secured in selected spaced relation to a fixed capacitor plate and to have the tabs removed to disposed the mass in selected spaced relation to the plate to form a capacitor and to permit movement of the mass in response to acceleration to produce a change in capacitance of the capacitor corresponding to the acceleration.