Precision capacitance transducer

• US 4,329,732 A
• Filed: 03/17/1980
• Issued: 05/11/1982
• Est. Priority Date: 03/17/1980
• Status: Expired due to Term

• Current Assignee: Kavlico Corporation (Sensata Technologies Holding Plc)
• Original Assignee: Kavlico Corporation (Sensata Technologies Holding Plc)
• Inventors: Park, Kyong, Kavli, Fred, Affel, John J.
• Primary Examiner(s): Goldberg, Elliot A.
• Application Number:
  US06/130,695
• Time in Patent Office: 785 Days
• Field of Search: 361/283, 361/399, 73/718, 73/724
• US Class Current: 361/283.1
• CPC Class Codes: G01L 9/0086 using variations in capacitance
• CPC Class Codes: H04R 19/00 Electrostatic transducers

Abstract

Two square plates of ordinary inexpensive soda lime glass are spaced apart from one another, and are sealed together by a ring of glass frit, with the two plates overlying one another, but with the corners of the two plates displaced so that the corners of each of the two plates extend past the sides of the other plates. The plates may be spaced apart by a small distance, for example, from about 1/2 to several thousandths of an inch, and thin conductive layers on the two facing surfaces form a variable capacitor which changes in capacitance when pressure is applied to the outside of the two plates. Connections for the conductive plates extend out to the corners of the plates beyond the sides of the other plate to permit easy access. Electrical connections are made through the use of elongated conductive rubber elements. Silicone rubber gaskets and suitable plastic housing members including electrical shielding are employed to mount the capacitive transducer and its associated output hybrid electronic circuit which assembly may be mounted on a ceramic substrate.

Claims

1. A mechanically floated precision low cost pressure transducer comprising:

first and second thin non-circular plates of glass;

frit means for bonding said plates of glass together with said two plates being generally aligned but with exposed areas of each of said first and second plates extending past the edges of the other plate and said plates being spaced apart by a distance in the order of one-half to a few thousandths of an inch, said frit extending substantially around a central open area of said plates;

conductive coatings on the adjacent opposed surfaces of said respective plates of glass, forming a capacitor which is variable in accordance with pressure applied to the exterior surfaces of said plates, said conductive coating extending to exposed areas of said plates;

resilient means for mounting said first and second glass plates and for concurrently applying pressure from a medium of which the pressure is to be measured to the outer surfaces of both said first and second plates, whereby the capacitance of said capacitor varies in accordance with the variations in the applied pressure of said medium;

associated output electronic circuitry; and

resilient conductive elements interconnecting said output circuitry and conductive material on the exposed areas of said plates.

2. A transducer as defined in claim 1 including housing means for both mechanically supporting and also conductively shielding said pressure transducer.

3. A transducer as defined in claim 1 including inert, insulating resilient gaskets mounted on both sides of said bonded plates of glass.

4. A transducer as defined in claim 1 wherein said conductive elements extend through said insulating resilient gaskets, whereby the pressure of a conductive medium may be measured.

5. A transducer as defined in claim 1 wherein said resilient conductive elements are made of conductive rubber.

6. A transducer as defined in claim 1 wherein said resilient means includes a pair of O-rings.

7. A transducer as defined in claim 1 including paths of substantially equal length for applying pressure to said first and second glass plates.

8. A precision low cost pressure transducer comprising:

first and second thin square flat plates of glass;

frit means for bonding said plates of glass together with said two plates being substantially overlapping with the corners of each of said first and second plates being offset relative to one another to extend past the edges of the other, and said plates being spaced apart by in the order of one-half to a few thousandths of an inch, said frit extending substantially around the overlapping area of said plates;

conductive coatings on the adjacent opposed surfaces of the respective plates of glass, forming a capacitor which is variable in accordance with pressure applied to the exterior surfaces of said plates, said conductive coatings extending to exposed corners of said plates;

means for mounting and enclosing said first and second glass plates to concurrently apply pressure from a medium of which the pressure is to be measured to the outer surfaces of both said first and second plates, whereby changes in the capacitance of said capacitor accurately indicates the applied pressure of said medium;

a square output electronic substrate or assembly mounted in alignment with one of said plates of glass; and

resilient conductive elements interconnecting said electronic assembly and the conductive coating on the exposed corners of said plates.

9. A precision low cost pressure transducer comprising:

first and second thin square flat plates of glass;

frit means for bonding said plates of glass together with said two plates being substantially overlapping with the corners of each of said first and second plates being offset relative to one another to extend past the edges of the other, and said plates being spaced apart by in the order of one-half to a few thousandths of an inch, said frit extending substantially around the overlapping area of said plates;

conductive coatings on the adjacent opposed surfaces of the respective plates of glass, forming a capacitor which is variable in accordance with pressure applied to the exterior surfaces of said plates, said conductive coatings extending to exposed corners of said plates;

means for mounting and enclosing said first and second glass plates to concurrently apply pressure from a medium of which the pressure is to be measured to the outer surfaces of both said first and second plates, whereby changes in the capacitance of said capacitor accurately indicates the applied pressure of said medium; and

conductive rubber means engaging conductive material on the corners of each of said plates which extend past the edges of the other plate.

10. A precision low cost pressure transducer comprising:

first and second thin square flat plates of glass;

frit means for bonding said plates of glass together with said two plates being substantially overlapping with the corners of each of said first and second plates being offset relative to one another to extend past the edges of the other, and said plates being spaced apart by in the order of one-half to a few thousandths of an inch, said frit extending substantially around the overlapping area of said plates;

conductive coatings on the adjacent opposed surfaces of the respective plates of glass, forming a capacitor which is variable in accordance with pressure applied to the exterior surfaces of said plates, said conductive coatings extending to exposed corners of said plates;

means for mounting and enclosing said first and second glass plates to concurrently apply pressure from a medium of which the pressure is to be measured to the outer surfaces of both said first and second plates, whereby changes in the capacitance of said capacitor accurately indicates the applied pressure of said medium;

said glass frit being in the form of a ring, having a small break in its peripheral extent for evacuation and backfilling; and

means for sealing said break in the ring of frit to completely seal the space between said plates.

11. A precision low cost pressure transducer comprising:

first and second thin flat plates of inexpensive glass;

glass sealing means for bonding said plates of glass together with the edges of at least one of said plates extending past the other, and said plates being spaced apart by in the order of one-half to a few thousandths of an inch, said glass sealing means extending substantially around the overlapping area of said plates;

conductive coatings on the adjacent opposed surfaces of the respective plates of glass, forming a capacitor which is variable in accordance with pressure applied to the exterior surfaces of said plates, said conductive coatings extending to exposed surfaces of at least one of said plates extending beyond the other plate;

means including a pair of O-rings for resiliently mounting said first and second glass plates and for applying pressure from a medium of which the pressure is to be measured to the outer surfaces of at least one of said plates, whereby changes in the capacitance of said capacitor correspond to changes of the applied pressure of said medium;

an output electronic assembly mounted in substantial alignment with said plates of glass; and

nonmetallic resilient conductive elements interconnecting said assembly and conductive material on the exposed surfaces of said glass plates.