Signal translating circuit for variable area capacitive pressure transducer

• US 4,104,595 A
• Filed: 12/27/1976
• Issued: 08/01/1978
• Est. Priority Date: 12/27/1976
• Status: Expired due to Term

• Current Assignee: Borg-Warner Automotive Electronic & Mechanical Systems Corporation
• Original Assignee: BorgWarner Incorporated
• Inventors: Overzet, John Kenneth
• Primary Examiner(s): Miller, Jr., Stanley D.
• Assistant Examiner(s): Davis, B. P.
• Application Number:
  US05/754,381
• Time in Patent Office: 582 Days
• Field of Search: 328/155, 307/308, 361/290, 361/292, 361/300, 361/321, 331/65, 340/258 C
• US Class Current: 327/517
• CPC Class Codes: G01D 5/2412 by varying overlap
• CPC Class Codes: G01D 5/2417 by varying separation
• CPC Class Codes: G01L 19/04 Means for compensating for effects of changes of temperature , i.e. other than electric compensation
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01L 9/12 by making use of variations in capacitance , i.e. electric circuits therefor

Abstract

An electrical circuit translates the capacitance change of a variable area capacitive transducer into a d-c voltage change. The transducer has two electrodes, and the surface of one electrode is anodized or otherwise provided with a dielectric layer. One of the two electrodes is nonlinear, having an apex point nearer the other electrode than the remainder of the electrode surface. As a force is applied to the deformable one of the two electrodes, there is a change in the effective contact area between the electrodes in accordance with the applied pressure, producing a resultant change in capacitance. The signal translating circuit produces a d-c output signal which varies as a function of the transducer capacitance change.

Claims

1. The combination of a variable area capacitive transducer of the type having two electrodes abutting each other, with a thin-film layer applied to one of the electrodes as a dielectric layer, and a signal translating circuit comprising:

an astable multivibrator circuit for providing a square-wave output signal;

a capacitor, connected in the multivibrator circuit to determine the duty cycle of the square-wave signal;

a first conductor coupled between one of the transducer electrodes and one plate of said capacitor, and a second conductor coupled between the other transducer electrode and the other plate of said capacitor, to modify the duty cycle of the output signal as a function of a change in the effective capacity of the transducer;

an integrating circuit connected to receive the square-wave signal and to provide a d-c signal which varies with the variations in the duty cycle of the received square-wave signal; and

a pair of output conductors connected to pass the d-c signal from the integrating circuit to associated equipment.

2. The combination claimed in claim 1, and further comprising a buffer amplifier stage coupled between the astable multivibrator and the integrating circuit.