Pressure transducer with an invariable reference capacitor

• US 4,422,125 A
• Filed: 05/21/1982
• Issued: 12/20/1983
• Est. Priority Date: 05/21/1982
• Status: Expired due to Term

• Current Assignee: The Bendix Corporation (Honeywell International Inc.)
• Original Assignee: The Bendix Corporation (Honeywell International Inc.)
• Inventors: Ohnesorge, David H., Antonazzi, Frank J.
• Primary Examiner(s): Griffin, Donald A.
• Application Number:
  US06/380,647
• Time in Patent Office: 578 Days
• Field of Search: 361/283, 73/718
• US Class Current: 361/283.3
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass
• CPC Class Codes: G01L 9/0086 using variations in capacitance
• CPC Class Codes: H04R 19/016 for microphones

Abstract

A quartz capacitive pressure transducer including a sensing plate and a reference plate disposed on one quartz substrate which are opposed across a gap by a common plate on another quartz substrate to form capacitances. The substrates are maintained in their opposing relationship by an annular frit which seals a chamber between the substrates to a reference pressure. The reference plate is disposed in the area occupied by the frit annulus to provide a reference capacitance that has a zero pressure gradient.

Claims

1. A pressure transducer with an invariable reference capacitor comprising:

a first substrate of insulative material and a second substrate of insulative material;

wherein at least one substrate is flexible and will deform in response to a pressure change;

wherein said substrates are positioned to oppose each other across a gap;

an annular frit joining said substrates and forming a chamber between them by sealing said gap to a reference pressure, said annular frit comprising an insulative material with a dielectric constant in excess of one;

at least one sensing capacitor plate formed of a conductive material disposed on one of the substrates and located entirely within the area defined by said chamber;

at least one reference capacitor plate formed of a conductive material disposed on said one substrate and located entirely within the annular area defined by the frit;

at least one common plate formed of a conductive material disposed on said other substrate and opposing said sensing plate in the area defined by said chamber to provide a sensing capacitance between said one common plate and said sensing plate; and

another common plate formed of a conductive material disposed on said other substrate and opposing said reference plate in the area defined by the frit annulus to provide a reference capacitance between said other common plate and said reference plate.

2. A pressure transducer as defined in claim 1, wherein:

said one common plate and said other common plate form a contiguous conductive area located partially within the area defined by said chamber and partially within the area defined by said frit annulus.

3. A pressure transducer as defined in claim 2, wherein:

said sensing capacitor plate and said reference capacitor plate is separated by a conductive area forming a ground screen which is adapted to be electrically connected to the same potential as said common plate.

4. A pressure transducer as defined in claim 1 wherein:

at least one of said insulative substrates is formed of quartz.

5. A pressure transducer as defined in claim 4, wherein:

said frit is comprised of a material with a similar temperature expansion coefficient to that of at least one substrate.

6. A pressure transducer as defined in claims 2, 3, 5 or 3, wherein:

said reference capacitance is substantially equivalent to said sensing capacitance at a minimum pressure value.

7. A pressure transducer as defined in claims 2, 3, 5 or 3, wherein:

said reference capacitance is substantially equivalent to said sensing capacitance at a maximum pressure value.