US4295091A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Circuit for measuring low capacitances
Assignee: Vaisala Oy
•
Filing: 1979-12-04
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Granted: 1981-10-13
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Expires: 1999-12-04
Abstract
Abstract A capacitance to be measured is connected between the input and output of an inverting amplifier. A bistable circuit has an input connected to the output of the inverting amplifier and an output impedance inversely proportional to the capacitance to be measured. A resistive feedback is connected from the output of the bistable circuit to the input of the inverting amplifier.
Inventors
- 👤 Jorma Ponkala
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-30 17:26
CPC Classifications
G; G01; G01R; G01R27/00; G01R27/02; G01R27/26; G01R27/2605
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
90 words
A circuit for measuring low capacitances with the elimination of the influence of stray capacitances, said circuit comprising an inverting amplifier having an input and an output; a capacitance to be measured connected between the input and the output of the inverting amplifier; a bistable circuit having an input connected to the output of said inverting amplifier, an output and an output frequency inversely proportional to the capacitance to be measured; and a resistive feedback connected from the output of the bistable circuit to the input of the inverting amplifier.
Claim 2
Dependent Claim
90 words
A circuit for measuring low capacitances with the elimination of the influence of stray capacitances, said circuit comprising an inverting amplifier having an input and an output; a capacitance to be measured connected between the input and the output of the inverting amplifier; a bistable circuit having an input connected to the output of said inverting amplifier, an output and an output frequency inversely proportional to the capacitance to be measured; and a resistive feedback connected from the output of the bistable circuit to the input of the inverting amplifier.
Claim 3
Dependent Claim
37 words
A circuit as claimed in claim 1, wherein the input of said amplifier functions as a low impedance generator having a low internal resistance and the output of said amplifier functions as a circuit measuring only current.
Claim 4
Dependent Claim
14 words
A circuit as claimed in claim 1, wherein bistable circuit comprises a bistable multivibrator.
Claim 5
Dependent Claim
15 words
A circuit as claimed in claim 1, wherein said bistable circuit comprises a Schmitt trigger.
Claim 6
Dependent Claim
47 words
A circuit as claimed in claim 1, wherein the capacitance to be measured is located remotely from said inverting amplifier and said bistable circuit and further comprising a pair of coaxial cables connecting said capacitance to be measured to the input and output of said inverting amplifier.
Claim 7
Dependent Claim
100 words
A circuit as claimed in claim 5, wherein said capacitance to be measured has a pair of spaced terminals and each of said coaxial cables has an inner conductor and an outer conductor, the outer conductor of each of said cables being connected to ground, the inner conductor of one of said cables connecting one of the terminals of said capacitance to be measured to the input of said inverting amplifier and the inner conductor of the other of said cables connecting the other of the terminals of said capacitance to be measured to the output of said inverting amplifier.
References Cited (Backward Citations)
US3716782A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1984-10-12 | 1985-04-13 | 1985-10-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1988-10-12 | 1989-04-13 | 1989-10-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1992-10-12 | 1993-04-13 | 1993-10-13 | $7700.00 | Window Closed / Lapsed |