US3862571A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Multielectrode capacitive liquid level sensing system
Assignee: AGRIDUSTRIAL ELECTRONICS Inc
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Filing: 1973-08-06
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Granted: 1975-01-28
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Expires: 1993-08-06
Abstract
Abstract A bridge circuit has in one branch a long capacitive probe and in the other branch a plurality of parallel capacitive probes of different lengths, the probes to be mounted in a storage tank. Inductors used across the respective probes function to subtract the values of capacitances equal to the value of the capacitances of the respective probes when no liquid is present in them, thereby to obtain capacitance readings indicative of only increased capacitances resulting from the presence of liquid. The outputs of the branches resulting from the presence of liquid are compared, and a control voltage is developed for application to a capacitive diode in the one branch of the bridge circuit to maintain the bridge circuit substantially balanced. The control voltage is measured to indicate the level of the liquid in the tank, and the use of a plurality of probes in the other branch extends the useable range of the curve for observable voltage changes. The effect of different densities of liquids is balanced out.
Inventors
- 👤 Ronald F Vogel
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 21:31
CPC Classifications
G; G01; G01F; G01F23/00; G01F23/22; G01F23/26; G01F23/263
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
252 words
A system for measuring level of a liquid comprising: a probe assembly having at least two elongated capacitive probes of uniform cross section, each of said probes having at least two electrodes with space therebetween to be filled with liquid as a dielectric to the same height as the height of the surface of the surrounding liquid, said probe assembly adapted to hold said probes vertically beside each other in a container for liquid, the lower ends of said probes extending to different predetermined depths, the increased capacitances of said probes caused by presence of liquid being different while the level of liquid in said container is intermediate the upper and lower ends of all of said probes, an electrical circuit including a voltage source and having first and second branches, each connected to an output circuit, said first branch connected to one probe havinG the longer length, and the second branch connected to at least one of the other of said probes, impedance means in each of said branches connected to said probes effective to balance out the effect of the capacitances of said probes while liquid is not present thereabout, and said electrical circuit operative to provide in said output circuit a difference signal indicative of the ratio of the increased capacitance of that portion of said probe assembly connected in said first branch resulting from presence of liquid to the increased capacitance of that portion of said probe assembly connected in said second branch resulting from presence of liquid.
Claim 2
Independent Claim
252 words
A system for measuring level of a liquid comprising: a probe assembly having at least two elongated capacitive probes of uniform cross section, each of said probes having at least two electrodes with space therebetween to be filled with liquid as a dielectric to the same height as the height of the surface of the surrounding liquid, said probe assembly adapted to hold said probes vertically beside each other in a container for liquid, the lower ends of said probes extending to different predetermined depths, the increased capacitances of said probes caused by presence of liquid being different while the level of liquid in said container is intermediate the upper and lower ends of all of said probes, an electrical circuit including a voltage source and having first and second branches, each connected to an output circuit, said first branch connected to one probe havinG the longer length, and the second branch connected to at least one of the other of said probes, impedance means in each of said branches connected to said probes effective to balance out the effect of the capacitances of said probes while liquid is not present thereabout, and said electrical circuit operative to provide in said output circuit a difference signal indicative of the ratio of the increased capacitance of that portion of said probe assembly connected in said first branch resulting from presence of liquid to the increased capacitance of that portion of said probe assembly connected in said second branch resulting from presence of liquid.
Claim 3
Dependent Claim
99 words
A system for measuring level of liquid as claimed in claim 1 wherein said second branch of said electrical circuit includes a plurality of probes connected in parallel, said probes in said seco d branch extending to different depths within said container such that at least one of said probes in said second branch extending below the surface of liquid in said container while the liquid is at a low level to be measured and at least an additional one of said probes in said second branch extends below the surface at a predetermined level above said low level.
Claim 4
Dependent Claim
100 words
A system as claimed in claim 1 wherein said electrical circuit voltage source includes an oscillator connected to said branches, said branches forming a bridge circuit, said oscillator applying high-frequency signal to said bridge circuit, said first branch including a capacitive diode connectedto said probe in sqid first branch, detecting circuit means connected to said probes in each of said branches, and a comparator circuit connected to said detecting circuit means to compare the voltage detected across said probes in each of said branches and to apply the difference thereof to said capacitive diode to balance substantially said bridge circuit.
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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) | 1978-01-27 | 1978-07-29 | 1979-01-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-01-27 | 1982-07-29 | 1983-01-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-01-27 | 1986-07-29 | 1987-01-28 | $7700.00 | Window Closed / Lapsed |