US3775678A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Impedance comparing circuit with ground referenced readout and stray capacitance insensitivity
Assignee: ADE Corp
•
Filing: 1971-12-09
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Granted: 1973-11-27
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Expires: 1991-12-09
Abstract
Abstract An impedance comparing circuit for supplying excitation to equal or unequal reference and sensing impedances with a ground referenced output signal indicative of the difference between impedances. A diode matrix excites the reference and sensing impedances from an oscillator through first and second DC blocking impedances respectively during one polarity of current and in the reverse relationship during the opposite polarity of current. Low impedance values in the first and second impedances provide near equality in the voltage across the reference and sensing impedances and minimize the effect of capacitance between them. Tuning or increased diode matrix impedances will augment the sensitivity at a sacrifice in the elimination of the effect of capacitance between the reference and sensing impedances.
Inventors
- 👤 R Abbe
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 22:18
CPC Classifications
G; G01; G01R; G01R27/00; G01R27/02
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
135 words
An impedance comparing circuit for operating from a source of alternating electric excitation, said circuit comprising: a. DC blocking first and second impedances joined at a first terminal; b. a reference impedance; c. a sensing impedance joined at a second terminal to said reference impedance; d. means for conducting one polarity of excitation through said first and second impedances and serially through said reference and sensing impedances respectively and for conducting the other polarity of excitation through said first and second impedances and serially through said sensing and reference impedances respectively; and e. means for detecting at least one signal indicative of the difference between polarities in the excitation through at least one of said first and second impedances whereby an indication is given of the difference in impedance between said reference and sensing impedances.
Claim 2
Dependent Claim
135 words
An impedance comparing circuit for operating from a source of alternating electric excitation, said circuit comprising: a. DC blocking first and second impedances joined at a first terminal; b. a reference impedance; c. a sensing impedance joined at a second terminal to said reference impedance; d. means for conducting one polarity of excitation through said first and second impedances and serially through said reference and sensing impedances respectively and for conducting the other polarity of excitation through said first and second impedances and serially through said sensing and reference impedances respectively; and e. means for detecting at least one signal indicative of the difference between polarities in the excitation through at least one of said first and second impedances whereby an indication is given of the difference in impedance between said reference and sensing impedances.
Claim 3
Dependent Claim
16 words
The circuit of claim 1 further characterized by having said reference and sensing impedances capacitive impedances.
Claim 4
Dependent Claim
32 words
The circuit of claim 1 wherEin said means for detecting further includes: a. means for low-pass filtering of said signal; and b. means for metering said signal after it is low-pass filtered.
Claim 5
Dependent Claim
33 words
The circuit of claim 1 further characterized by having means for amplifying the difference in a pair of said detected signals indicative of the difference in excitation through said first and second impedances.
Claim 6
Dependent Claim
36 words
The circuit of claim 1 wherein said first and second impedances are substantially smaller in impedance than said reference and sensing impedances whereby the instantaneous electric potential across said reference and sensing impedances is approximately equal.
Claim 7
Dependent Claim
14 words
The circuit of claim 5 wherein said reference and sensing impedances are capacitive impedances.
Claim 8
Dependent Claim
26 words
The circuit of claim 1 wherein said first and second impedances are tuned with said reference snd sensing impedances to the excitation frequency of said source.
Claim 9
Dependent Claim
49 words
The circuit of claim 1 further characterized by having means for inducing an opposition to the excitation in said first impedance dependent on the excitation through said second impedance and for inducing an opposition to the excitation in said second impedance dependent on the excitation through said first impedance.
Claim 10
Dependent Claim
68 words
The circuit of claim 1 wherein said means for conducting includes a closed path of four serially joined, matched semiconductor diodes oriented for conduction in the same direction with said first and second impedances making respective electrical contacts at opposite junctions between diodes in said path and with said reference and sensing impedances making respective electrical contacts at the other two opposite junctions between diodes in said path.
Claim 11
Dependent Claim
27 words
The circuit of claim 9 wherein each diode in said path has impedance connected in series with it between junctions with the next diodes in said path.
Claim 12
Dependent Claim
15 words
The circuit of claim 1 further comprising means for guarding said sensing and reference impedances.
Claim 13
Dependent Claim
30 words
The circuit of claim 1 further characterized by having means for amplifying at least one of said signals indicative of the difference in excitation through said first and second impedances.
References Cited (Backward Citations)
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US3111845A
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US3424977A
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US3497801A
Cited
US3577072A
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US3639832A
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US3688190A
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-11-26 | 1977-05-28 | 1977-11-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-11-26 | 1981-05-28 | 1981-11-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-11-26 | 1985-05-28 | 1985-11-27 | $7700.00 | Window Closed / Lapsed |