Capacitor transducer

• US 4,168,518 A
• Filed: 05/10/1977
• Issued: 09/18/1979
• Est. Priority Date: 05/10/1977
• Status: Expired due to Term

• Current Assignee: Shih Y. Lee
• Original Assignee: Shih Y. Lee
• Inventors: Lee, Shih Y.
• Primary Examiner(s): Goldberg, E. A.
• Application Number:
  US05/795,617
• Time in Patent Office: 861 Days
• Field of Search: 73/724, 73/718, 361/283
• US Class Current: 361/283.1
• CPC Class Codes: G01L 1/142 using capacitors
• 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

Abstract

A pressure sensing transducer and method of construction therefor. The device includes a pair of contoured dielectric plates joined together at their periphery and having a central portion with conductive film on opposed portions of the inner surfaces of the dielectric plates. One or more regions between the central portion and the periphery are of reduced thickness and pressure or force loading of the transducer causes deformation to occur in the dielectric elements to cause the spacing between the conductive films to vary in relationship to the applied pressure or force. The regions of reduced cross-section serve to reduce the stress setting up in the joint and to reduce the distortion of the central portion due to the application of pressure or force. The device further includes means for electrically coupling each of the conductive films to an associated terminal exterior of the transducer.

Claims

1. A pressure sensing transducer comprising two dielectric elements, each of said elements having a central planar portion with a conducting surface, said conducting surfaces serving to form a capacitor, at least one of said central portions being surrounded by an area wherein the thickness of the dielectric is reduced, each of said dielectric elements having a planar peripheral region in the same plane as its central planar portion, means free of clamping force and torque holding said peripheral regions in fixed spaced parallel relationship to form a single interior interconnected volume, whereby a difference in pressure between said interior volume and pressure exterior to at least one of said elements causes deflection of an element in the region of reduced thickness, the deflection causing a change in the spacing between said conducting surfaces and the capacitance of the capacitor related to said pressure difference, the bending deflection in said area of reduced cross section being substantially greater than that in a corresponding area of the central portion so that both the bending moment applied to the peripheral regions and the distortion of the central portions are reduced.

2. A transducer according to claim 1 wherein said area of reduced thickness serves to provide an increased internal volume without a corresponding increase in the spacing of the conducting capacitor surfaces.

3. A transducer according to claim 1 wherein said area of reduced thickness is of varying thickness in radial directions from the center to provide substantially uniform stress distribution in the radial direction.

4. Apparatus according to claim 1 wherein said transducer elements are fabricated of quartz.

5. Apparatus according to claim 1 wherein said transducer elements are fabricated of molded glass.

6. Apparatus according to claim 1 wherein said transducer elements are fabricated of molded ceramic.

7. A pressure transducer according to claim 1 having means to apply force to at least one of said central portions to provide a force sensing transducer.

8. Apparatus according to claim 1 wherein an electrically conducting lead is provided through said central portion from said conducting surface to an exterior surface.

9. A transducer according to claim 1 wherein said conducting surface is provided with an electrically conducting lead passing through the region in which said elements are joined together.

10. Apparatus according to claim 1 wherein the means for holding said elements together is fused glass.

11. A pressure sensing transducer comprising two dielectric elements, each of said elements having a central planar portion with a conducting surface, said conducting surfaces serving to form a capacitor, at least one of said central portions being surrounded by an area wherein the thickness of the dielectric is reduced, each of said dielectric elements having a planar peripheral region in the same plane as its central planar portion, means free of clamping force and torque holding said peripheral regions in fixed spaced parallel relationship to form a single interior interconnected volume, a first conducting film applied to a portion of the interior surface of the area of reduced thickness of one of said dielectric elements, said first conducting film being electrically connected with the conducting surface of said dielectric element, a second conducting film applied to a corresponding area on the outside of a portion of the area of reduced thickness of said dielectric element, said first and second conducting films with the dielectric element therebetween serving to provide a coupling capacitor for indicating the capacitance of the transducer capacitor in the absence of any lead passing through either dielectric element or through the region in which said dielectric elements are joined, whereby a difference in pressure between said interior volume and pressure exterior to at least one of said elements causes deflection of an element in the region of reduced thickness, the deflection causing a change in the spacing between said conducting surfaces and the capacitance of the capacitor related to said pressure difference, said central portions being of sufficient cross-section to be substantially rigid and undistorted by the application of pressure whereby only the spacing between the conducting surfaces is affected by applied operating pressure and hysteresis effects and non-linearity are minimized.