Secondary accelerometer pickoff

• US 5,092,173 A
• Filed: 12/29/1989
• Issued: 03/03/1992
• Est. Priority Date: 12/29/1989
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Aske, Vernon H.
• Primary Examiner(s): Chapman, John E.
• Application Number:
  US07/459,397
• Time in Patent Office: 795 Days
• Field of Search: 73/654, 73/517 B, 73/651, 73/517 R
• US Class Current: 73/514.21
• CPC Class Codes: G01P 15/123 by piezo-resistive elements, e.g. semiconductor strain gauges
• CPC Class Codes: G01P 15/132 with electromagnetic counterbalancing means

Abstract

An accelerometer apparatus capable of sensing accelerations ranging from steady state to at least 500 Hertz is described. The apparatus uses a piezo resistive pickoff for low frequency sensing and applies a potential to the accelerometer'"'"'s pendulum to excite a secondary pickoff for frequencies above 100 Hertz.

Claims

1. An accelerometer capable of measuring acceleration from steady state to at least 500 Hertz, said acceleration comprising:

a sensor capsule for sensing acceleration including a silicon sensor die and a top and bottom stop, said die having a pendulum made of layers of silicon with a layer adjacent to said top stop being held at a steady potential which serves as excitation for a secondary pickoff which detects acceleration above 100 Hertz, rebalancing means attached to said pendulum and four flexures which support said pendulum, two of said four flexures having piezo resistive elements implanted therein for measuring stress in said two flexures; and

a housing to which said sensor capsule is mounted by a mounting means.

2. The apparatus according to claim 1, wherein said rebalancing means includes rebalance coils mounted thereon to restore the pendulum to an original position.

3. The apparatus of claim 1 wherein the rebalancing means are electromagnetically driven.

4. The apparatus of claim 1 wherein the rebalancing means are electrostatically driven.

5. The apparatus as in claim 1 having four flexures, two of which have piezo resistive elements, said two flexures therein are offset form the remaining two flexures so as to provide compensation for cross axis acceleration.

6. An apparatus for detecting acceleration from steady state to at least 500 Hertz comprising:

a piezo resistive pickoff, including flexures having piezo resistive elements which support a pendulum member of a silicon sensor die, for detecting accelerations below 100 Hertz; and

a secondary pickoff for applying a steady potential to a silicon layer of said pendulum for detecting frequencies greater than 100 Hertz.

7. Apparatus for an accelerometer, said apparatus capable of sensing accelerations from steady state to at least 500 Hertz, said apparatus comprising:

a single pendulum member having a high frequency sensing means capable of sensing accelerations greater than 100 Hertz and low frequency sensing means capable of sensing accelerations up to 100 Hertz.

8. The apparatus as in claim 7 wherein said high frequency sensing means comprises:

a silicon layer of a pendulum member which is a part of a silicon sensor die of said accelerometer, said silicon layer serving to excite a secondary pickoff when a steady voltage is applied and functioning as one plate of a capacitor;

a top stop of a sensor capsule, said stop acting as a second plate of said capacitor; and

said capacitor having a time varying, frequency dependent capacitance caused by sinusoidal motion of said pendulum.

9. The apparatus as in claim 7 wherein said low frequency sensing means comprises piezo resistive elements mounted in flexures of a silicon sensor die of a sensor capsule of said accelerometer.