Multiple capacitor transducer

• US 4,458,292 A
• Filed: 07/22/1982
• Issued: 07/03/1984
• Est. Priority Date: 07/22/1982
• Status: Expired due to Fees

• Current Assignee: Tward 2001 Limited
• Original Assignee: Tward 2001 Limited
• Inventors: Tward, Emanuel, Junkins, Philip D.
• Primary Examiner(s): GRIFFIN, DONALD
• Application Number:
  US06/400,725
• Time in Patent Office: 712 Days
• Field of Search: 361/283, 73/724
• US Class Current: 361/283.2
• CPC Class Codes: G01D 5/2417 by varying separation
• 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 9/12 by making use of variations in capacitance , i.e. electric circuits therefor
• CPC Class Codes: H01G 7/00 Capacitors in which the capacitance is varied by non-mechanical means; Processes of their manufacture

Abstract

A capacitive type pressure, force or displacement sensing transducer comprised of a mating pair of spaced dielectric elements each carrying a pair of capacitive elements forming two like capacitors of variable capacitance value depending upon the variable spacing distance between the dielectric elements and two like capacitors of fixed capacitance value. The pair of variable value capacitors and pair of fixed value capacitors comprise all of the capacitance elements of a Wheatstone bridge circuit in a single structural unit in which such capacitive elements are all subjected to the same temperature and pressure environment and which is not sensitive to stray capacitances. Each pair of capacitors forms opposing sides of the Wheatstone bridge circuit. A source of alternating current of constant voltage and set frequency is applied across a first set of bridge terminals at opposite corners of the bridge and a current detection circuit is connected across a second set of bridge terminals independent of the first set of terminals and at opposite corners of the bridge. Detection and measurement of the current value of the bridge circuit is translated into a value of force, pressure or motion applied to the transducer unit in direct linear relationship with the current value as determined by the separation distance between the spaced dielectric elements of the transducer.

Claims

1. A capacitive type pressure or displacement sensing transducer comprising:

(a) two elongated transducer body elements formed of dielectric material and positioned in spaced parallel relationship, each of said body elements having a central portion and terminal end portions and at least one of said body elements being capable of deflection upon the application of an external pressure force to its central portion;

(b) four electrically conductive capacitor elements each formed to present two angularly disposed and electrically connected capacitive plates with two of said capacitor elements mounted in fixed spaced relationship from one another in the central portion of each of said transducer body elements and positioned therein so that each capacitive plate thereof defines with a capacitive plate of the next adjacent capacitor element a dielectric space therebetween whereby said mounted capacitor elements together form four dielectric spaces, a first pair of said dielectric spaces being comprised of the like dielectric space located within each central portion of each transducer body element between capacitive plates of the capacitor elements mounted therein and said first pair of like dielectric spaces containing the dielectric material of said transducer body elements thereby forming with their respective space defining capacitive plates two capacitors of like fixed electrical capacitive value; and

(c) means for holding the terminal end portions of said transducer body elements in fixed spaced relationship to establish and maintain the transducer body elements in their spaced parallel relationship whereby capacitive plates of the two capacitor elements in the central portion of one of said body elements define with capacitive plates of the two capacitor elements in the central portion of the other of said body elements a second pair of said dielectric spaces comprised of like open dielectric space located between said body elements, said second pair of like open dielectric spaces forming with their respective space defining capacitive plates two capacitors of like variable electrical capacitive value, the application of an external pressure force to the central portion of said transducer body elements causing deflection of at least one of said elements and a change in the spacing distance between the central portions of said body elements thereby varying the electrical capacitive value of said variable value capacitors in direct relationship to the force value of said pressure force.

2. A capacitive type pressure or displacement sensing transducer as defined in claim 1 wherein both of the elongated transducer body elements are capable of deflection upon application of equal and opposing external pressure forces to the central portions thereof.

3. A capacitive type pressure or displacement sensing transducer as defined in claim 1 wherein intermediate portions of the elongated transducer body element capable of deflection between the central portion and the terminal end portions thereof are of reduced thickness of dielectric material whereby application of an external pressure force to said central portion causes deflection of said intermediate portion(s) of said body element to a substantially greater degree than deflection of said central portion whereby distortion of the central portion of said body element is reduced.

4. A capacitive type pressure or displacement sensing transducer as defined in claim 1 wherein intermediate portions of the elongated transducer body elements between the central portions and the terminal end portions thereof are of reduced thickness of dielectric material whereby application of equal and opposing external pressure forces to said central portions causes deflections of said intermediate portions of said body elements to a substantially greater degree than the deflections of said central portions of said body elements whereby distortion of the central portions of said body elements is reduced.

5. A capacitive type pressure or displacement sensing transducer as defined in claim 1 wherein means are provided to apply force to at least one of said central portions of said transducer body elements to provide a force sensing transducer.

6. A capacitive type pressure or displacement sensing transducer as defined in claim 1 wherein means are provided to connect the two capacitors of like fixed electrical capacitive value and the two capacitors of like variable electrical capacitive value together to form the four capacitive sides of a Wheatstone bridge circuit, the pair of fixed value capacitors connected as two opposing sides of said bridge and the pair of variable value capacitors connected as the remaining two opposing sides of said bridge.

7. A capacitive type pressure or displacement sensing transducer as defined in claim 6 wherein a source of alternating current of constant voltage and set frequency is applied across said bridge circuit to a first set of bridge terminals at opposite corners of the bridge, each of said first terminals located between a fixed value capacitor and a variable value capacitor, and a detection circuit is connected across said bridge circuit to a second set of terminals independent of said first set of terminals and at opposite corners of the bridge, each of said second terminals located between a fixed value capacitor and a variable value capacitor, said detection circuit including current value measurement and current value indication circuitry.