US3886473A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Capacitive pressure and displacement transducers
Assignee: Individual
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Filing: 1974-06-13
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Granted: 1975-05-27
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Expires: 1994-06-13
Abstract
Abstract A capacitive transducer for converting a small displacement of a mechanical input member into an electrical signal directly proportional to the quantity being measured, even if the transfer-function between input quantity and output signal is non-linear, by use of a cylinder-and-piston capacitor with suitably shaped electrodes, and a plurality of adjustable vernier-capacitors. When used in an alternating-current bridgecircuit, an a.c. voltage proportional to said mechanical input quantity results. (Claim 1). To provide a digital output signal directly proportional to a mechanical input quantity being measured, a fixed high-frequency oscillator with an attached binary counter is combined with a second, substantially identical oscillator-and-counter circuit whose frequency is varied by said capacitor assembly. A third counter generates said digital output signal by a count proportional to the frequency difference of said two oscillators, thus substantially compensating for temperature-, supply-voltage, and ageing drifts which affect both oscillators equally. (Claim 2). The polarity of bi-directional displacements is determined by a digital priority detection circuit which generates a NEGATIVE INPUT bit whenever a negative input displacement occurs. (Claim 3).
Inventors
- 👤 Hans D Heyck
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 20:39
CPC Classifications
G; G01; G01L; G01L9/00; G01L9/12; G01L9/0082; G01L9/0086
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
252 words
In a capacitive transducer for converting a small mechanical displacement into a corresponding electrical signal, the improvement comprising: a. a displaced mechanical input member representing the quantity being measured; b. a variable capacitor comprising a metallic cylinder, freE to move axially and concentrically but insulated from a stationary piston; the surfaces of said cylinder and said piston being shaped to yield a predetermined nonlinear capacitance to displacement relationship; c. a means for connecting said mechanical input member axially to said capacitor-cylinder without requiring exact centering, comprising a flat surface perpendicular to said axis on one of said members, and a convex surface on the other member; d. an elastic member causing said capacitor-cylinder to press lightly against said mechanical input member; e. a plurality of magnetic members exerting forces upon each other which causes said capacitor-cylinder to remain in mechanical contact with said mechanical input member; f. a guide restraining said capacitor-cylinder rotationally; g. a plurality of stationary, individually adjustable vernier capacitor stators with edges facing an axially slanted metallic edge which is attached to the outer surface of said capacitorcylinder, thereby forming a plurality of adjustable verniercapacitors staggered along said displacement-path for trimming the transducer calibration curve in a plurality of locations; h. a threaded member for adjustment of the insertion depth of said stationary capacitor-piston into said capacitor-cylinder; i. a plurality of support members controlling the spacing between said mechanical input member and said capacitor-piston, having coefficients of thermal expansion chosen to compensate thermal expansion errors caused by other components.
Claim 2
Dependent Claim
252 words
In a capacitive transducer for converting a small mechanical displacement into a corresponding electrical signal, the improvement comprising: a. a displaced mechanical input member representing the quantity being measured; b. a variable capacitor comprising a metallic cylinder, freE to move axially and concentrically but insulated from a stationary piston; the surfaces of said cylinder and said piston being shaped to yield a predetermined nonlinear capacitance to displacement relationship; c. a means for connecting said mechanical input member axially to said capacitor-cylinder without requiring exact centering, comprising a flat surface perpendicular to said axis on one of said members, and a convex surface on the other member; d. an elastic member causing said capacitor-cylinder to press lightly against said mechanical input member; e. a plurality of magnetic members exerting forces upon each other which causes said capacitor-cylinder to remain in mechanical contact with said mechanical input member; f. a guide restraining said capacitor-cylinder rotationally; g. a plurality of stationary, individually adjustable vernier capacitor stators with edges facing an axially slanted metallic edge which is attached to the outer surface of said capacitorcylinder, thereby forming a plurality of adjustable verniercapacitors staggered along said displacement-path for trimming the transducer calibration curve in a plurality of locations; h. a threaded member for adjustment of the insertion depth of said stationary capacitor-piston into said capacitor-cylinder; i. a plurality of support members controlling the spacing between said mechanical input member and said capacitor-piston, having coefficients of thermal expansion chosen to compensate thermal expansion errors caused by other components.
Claim 3
Dependent Claim
213 words
In a capacitive transducer for converting a small mechanical displacement into a corresponding electrical signal, the improvement comprising: a. a variable capacitor assembly according to claim 1; b. a padding capacitor connected in series with the insulated terminal of said variable capacitor assembly, and limiting the effective capacitance variation of said variable capacitor assembly; c. an inductance coil having a plurality of metallic turns fused to an insulating form and being connected in parallel to the series connected said variable capacitor and said padding capacitor; d. a plurality of additional capacitors connected across said inductance coil, having capacitance values chosen to determine the range of resonance frequencies of said capacitor and inductor combination, and having temperature coefficients of capacitance chosen to minimize shifts of said resonance frequencies caused by temperature variations; e. an electronic amplifying device for exciting said resonant circuit into continuous oscillation, and connected across no more than one quarter of said resonant circuit reactance to minimize frequency pulling; f. an externally adjustable variable capacitor connected across said resonant circuit for introduction of predetermined frequency offsets; h. a single-conductor circuit for both carrying the direct-current supply voltage into said transducer, and exiting said high-frequency oscillator signal, comprising low-pass filters for the direct-current path, and high-pass filters for said said high-frequency signal.
Claim 4
Dependent Claim
218 words
In a capacitive transducer for converting a small mechanical displacement into a corresponding electrical signal, the improvement comprising: a. a variable high-frequency oscillator according to claim 2; b. a fixed high-frequency oscillator similar to said variable high-frequency oscillator, except that a fixed capacitor is used instead of said variable capacitor assembly of claim 1; c. a digital frequency counter A, starting upon a strobe signal to count cycles from said fixed-frequency oscillator until a filled-up signal appears at its most-significant bit output terminal; d. a digital frequency counter B, indentical to said digital frequency counter A, and simultaneously upon said strobe signal starting to count cycles from said variable-frequency oscillator until a filled-up signal appears at its most-significant-bit output terminal; e. a thirD digital frequency counter C which starts counting cycles from said fixed-frequency oscillator when the first of said two binary counters is filled up, and which stops counting when the other binary counter is filled up, thus storing a digital count proportional to the frequency difference between said fixed and variable high-frequency oscillators, and substantially immune to disturbances equally affecting both high-frequency oscillators; f. a bistable latching circuit, sensing which of said binary counters A and B was the first to fill up, and generating a negative-input signal whenever said binary counter B was first filled-up.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-05-26 | 1978-11-25 | 1979-05-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-05-26 | 1982-11-25 | 1983-05-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-05-26 | 1986-11-25 | 1987-05-27 | $7700.00 | Window Closed / Lapsed |