Charged mass thin film condenser accelerometer

• US 5,710,376 A
• Filed: 12/22/1995
• Issued: 01/20/1998
• Est. Priority Date: 12/22/1995
• Status: Expired due to Fees

• Current Assignee: Dow, Inc., International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Weber, Gerard Vincent Jr.
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US08/577,453
• Time in Patent Office: 760 Days
• Field of Search: 73/514.32, 73/514.38, 73/652, 73/654, 361/280
• US Class Current: 73/514.32
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

An accelerometer having a pair of spaced apart planar electrodes in a housing wherein one of the planar electrodes is made of a thin film and has a mass attached to one side such that acceleration causes the thin film to flex. A solid state amplifier is located in the housing attached to one of the planar electrodes to measure the change in capacitance caused by the flexing of the thin film. The solid state amplifier may be an NPN transistor. The mass may be a 4.5 mm steel airgun shot, and the thin film may be 1 mil polyester aluminized metallic film. The output of the accelerometer is connected to one input of a operational amplifier, and the other input of the operational amplifier is connected to a transducer measuring ambient noise such that the ambient noise is removed from the signal from the accelerometer.

Claims

1. A charged mass thin film condenser transducer comprising:

a housing;

spaced apart planar electrodes in said housing forming a condenser whose capacitance changes when a first one of the planar electrodes is flexed, said first electrode being a thin film;

a spherical mass located in said housing connected to and flexing said first planar electrode responsive to acceleration; and

an electrical amplifier having an input terminal connected to a second one of said planar electrodes for sensing changes of capacitance of said condenser, and an output terminal for providing an electrical output which changes according to the change of capacitance of said condenser.

2. The charged mass thin film condenser transducer of claim 1 wherein said mass is a 4.5 mm steel airgun shot.

3. The charged mass thin film condenser transducer of claim 1 wherein said mass is a sphere having a weight of about 5.5 grains.

4. The charged mass thin film condenser transducer of claim 1 wherein said first planar electrode is a thin film of 1 mil thick polyester aluminized metallic film.

5. The charged mass thin film condenser transducer of claim 1 wherein said electrical amplifier is an NPN transistor having a base connected to said second planar electrode, an emitter extending out of said housing for forming a first output lead, and a collector forming a second, grounding, output lead.

6. The charged mass thin film condenser transducer of claim 5 wherein said second planer electrode includes a slot therein for allowing air to pass therethrough as said first planar electrode flexes.

7. The charged mass thin film condenser transducer of claim 1 wherein said housing has a larger portion and a smaller portion, said spaced apart planar electrodes being located in said larger portion of said housing, and said mass being on one side of said condenser and extending into said smaller portion of said housing.

8. The charged mass thin film condenser transducer of claim 7 wherein said planar electrodes are spaced apart by a spacer ring formed of a dielectric material.

9. The charged mass thin film condenser transducer of claim 8 wherein said first planar electrode comprises a stiffening ring and a thin film of polyester aluminized metallic film spread over said stiffening ring, said mass is a metal sphere attached to the center of said thin film, and said spacer ring is of sufficient thickness to prevent contact between said planar electrodes when said thin film is flexed from said stiffening ring of said first planar electrode toward said second planar electrode.

10. The charged mass thin film condenser transducer of claim 9 wherein said first planar electrode is in said larger portion of said housing having one side against the smaller portion of said housing, and said second planar electrode is secured in said larger portion of said housing with said spacer ring between said planar electrodes for forming a condenser.

11. The charged mass thin film condenser transducer of claim 1 further comprising;

an operational amplifier having a first input connected to said output terminal of said electrical amplifier, a second input, offset null inputs and an output;

an ambient mechanical wave transducer for measuring ambient mechanical waves, said ambient mechanical wave transducer connected to said second input of said operational amplifier; and

a null circuit connected to the offset null inputs of said operational amplifier for providing on the output of said operational amplifier, an output signal which is the difference of a signal from the output terminal of said electrical amplifier and the signal from said ambient mechanical wave transducer.

12. The charged mass thin film condenser transducer of claim 11 further comprising a second operational amplifier connected to the output of said first mentioned operational amplifier, said second operational amplifier acting as an amplifier for a signal on the output of said first mentioned operational amplifier.