US3901079A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Two-mode capacitive liquid level sensing system
Assignee: AGRIDUSTRIAL ELECTRONICS Inc
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Filing: 1974-06-18
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Granted: 1975-08-26
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Expires: 1994-06-18
Abstract
Abstract A reference capacitive probe for sensing permittivity is substantially longer than the short reference probes positioned near the bottom of a tank in prior systems. Like former reference probes its lower end is spaced only far enough above the bottom of fuel tanks to avoid water, but its upper end may be at a substantial height above the bottom, such as one-fourth to onethird of the height of a tank. A main probe, used for measurement, has its lower end at a level far enough above the lower end of the reference probe to provide a substantial predetermined difference in increases of capacitances in the probes due to presence of liquid while the level of the liquid is intermediate the limits of overlapping capacitive portions of the probes. Voltage that is a function of this predetermined difference of capacitances is used as a reference in a permittivity-compensating circuit as long as the level of liquid is below the upper end of the capacitive portion of the reference probe, and a mode-switching means conditions the compensating circuits to use as a reference the voltage that is a function of only the capacitance of the reference probe while the level of liquid is high enough to fill the capacitive portion of the reference probe. Through two-mode operation along with the use of a longer reference probe to sense permittivity over greater differences in depth, two portions of output curves are selected to provide accurate, linear readings over a wide range of level of liquid.
Inventors
- 👤 Ronald F Vogel
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 18:02
CPC Classifications
G; G01; G01F; G01F23/00; G01F23/22; G01F23/26; G01F23/263
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
269 words
A capacitive probe assembly having first and second elongated capacitive portions adapted to be inserted vertically in a container, said first and second capacitive portions having first and sEcond capacitive electrodes respectively, the length of each of said capacitive electrodes being predetermined to define the effective length of said respective capacitive portion, each of the capacitive portions being the type that change capacitance and provide a respective output as a function of the change in proportional amount of said respective capacitive electrode that is surrounded by liquid in which it is inserted, said second capacitive electrode extending downwardly from a first level to a lower second level, said first and second levels defining a range through which levels are to be measured, said first capacitive electrode extending downwardly from a level intermediate said first and second levels in an overlapping relation to the lower portion of said second capacitive electrode and continuing far enough below said second level at which said second capacitive electrode is terminated to provide significant detectable change in capacitance of said first capacitive portion due to filling the space below said second level with liquid, capacitive measuring means connected to said second capacitive portion to provide a reading of level of liquid at any level within said range of levels, and compensating circuit means connected to both said first and second capacitive portions and to said capacitive measuring means, said compensating circuit means operative in response to receiving said outputs from both said first and second capacitive portions to compensate said reading for changes in permittivity of liquid into which said capacitive portions are inserted.
Claim 2
Dependent Claim
269 words
A capacitive probe assembly having first and second elongated capacitive portions adapted to be inserted vertically in a container, said first and second capacitive portions having first and sEcond capacitive electrodes respectively, the length of each of said capacitive electrodes being predetermined to define the effective length of said respective capacitive portion, each of the capacitive portions being the type that change capacitance and provide a respective output as a function of the change in proportional amount of said respective capacitive electrode that is surrounded by liquid in which it is inserted, said second capacitive electrode extending downwardly from a first level to a lower second level, said first and second levels defining a range through which levels are to be measured, said first capacitive electrode extending downwardly from a level intermediate said first and second levels in an overlapping relation to the lower portion of said second capacitive electrode and continuing far enough below said second level at which said second capacitive electrode is terminated to provide significant detectable change in capacitance of said first capacitive portion due to filling the space below said second level with liquid, capacitive measuring means connected to said second capacitive portion to provide a reading of level of liquid at any level within said range of levels, and compensating circuit means connected to both said first and second capacitive portions and to said capacitive measuring means, said compensating circuit means operative in response to receiving said outputs from both said first and second capacitive portions to compensate said reading for changes in permittivity of liquid into which said capacitive portions are inserted.
Claim 3
Dependent Claim
81 words
A capacitive probe assembly as claimed in claim 1 wherein said first and second capacitive portions have first and second rigid tubular outer conductors and first and second insulated cylindrical inner conductors respectively, said first and second inner conductors being said first and second capacitive electrodes respectively and being mounted coaxially within said first and second outer conductors respectively, the extent of said inner conductors within their respective outer conductors being the extent of said respective first and second capacitive electrodes.
Claim 4
Dependent Claim
114 words
A capacitive probe assembly as claimed in claim 2 wherein said first outer conductor extends higher than said first inner conductor at least to said first level, a seal in said first outer conductor about said first inner conductor at said intermediate level to prevent liquid from flowing upwardly into that portion of the first outer conductor above said seal, a conductive wire for connection to said first capacitive portion connected to said first inner conductor at said intermediate level and extending coaxially upwardly within said first outer conductor, said conductive wire being insulated from said outer conductor and having small diameter and low distributed capacitance compared with those of said first inner conductor.
Claim 5
Independent Claim
526 words
A system for measuring level of liquid comprising: first and second channels providing voltages corresponding to levels of liquid, first and second capacitive measuring circuits connected in said first and second channels respectively, a measuring probe assembly having first and second elongated capacitive portions connected to said first and second capacitive measuring circuits respectively, each of said capacitive measuring circuits being adjusted to provide output voltage proportional to the increased amount of capacitance of the respective one of said capacitive portions due to presence of liquid, said capacitive portions having similar uniform capacitive characteristics over equal lengths thereof and being adapted to be positioned vertically in a container in which level of liquid is to be measured, said second capacitive portion being of such length to extend downwardly from a first level in a container to a lower second level, said first and second levels defining a range through which levels are to be measured, said first capacitive portion being of such length and positioned With respect to said second capacitive portion to extend downwardly from a level intermediate said first and second levels in an overlapping relation to the lower portion of said second capacitive portion and continuing far enough below said second level at which said second capacitive portion is terminated to provide significant detectable change in capacitance of said first capacitive portion due to filling the space below said second level with liquid, an output metering circuit connected to said second channel to respond to said output voltage of said second capacitive measuring circuit for providing reading for the level of liquid within said range, a compensating circuit operable to compensate said reading for differences in permittivity of liquid, said compensating circuit including switching means for conditioning said compensating circuit for first and second modes of operation, first and second inputs connected to said first and second channels respectively to receive output voltage from said respective capacitive measuring circuits, and an output of said compensating circuit connected to said second channel for controlling the amplitude of its output for compensating said reading, said switching means having control means connected to at least one of said channels to receive voltage derived from said respective capacitive measuring circuit, said switching means operable between a first state and a second state in response to the voltage applied to said control means from said channel to which it is connected passing through a value for said intermediate level of liquid substantially even with the upper end of said first capacitive portion, said switching means being in said first state while the level of liquid is between said intermediate and second levels where said capacitive portions are overlapped to cause said compensating circuit to be in its first mode of operation to respond to the difference in voltages derived from said first and second channels, and said switching means being in said second state while level of liquid is higher than said intermediate level to exclude from said compensating circuit voltage from said second channel and to cause said compensating circuit to be in its second mode of operation to respond to voltage from only said first channel.
Claim 6
Independent Claim
526 words
A system for measuring level of liquid comprising: first and second channels providing voltages corresponding to levels of liquid, first and second capacitive measuring circuits connected in said first and second channels respectively, a measuring probe assembly having first and second elongated capacitive portions connected to said first and second capacitive measuring circuits respectively, each of said capacitive measuring circuits being adjusted to provide output voltage proportional to the increased amount of capacitance of the respective one of said capacitive portions due to presence of liquid, said capacitive portions having similar uniform capacitive characteristics over equal lengths thereof and being adapted to be positioned vertically in a container in which level of liquid is to be measured, said second capacitive portion being of such length to extend downwardly from a first level in a container to a lower second level, said first and second levels defining a range through which levels are to be measured, said first capacitive portion being of such length and positioned With respect to said second capacitive portion to extend downwardly from a level intermediate said first and second levels in an overlapping relation to the lower portion of said second capacitive portion and continuing far enough below said second level at which said second capacitive portion is terminated to provide significant detectable change in capacitance of said first capacitive portion due to filling the space below said second level with liquid, an output metering circuit connected to said second channel to respond to said output voltage of said second capacitive measuring circuit for providing reading for the level of liquid within said range, a compensating circuit operable to compensate said reading for differences in permittivity of liquid, said compensating circuit including switching means for conditioning said compensating circuit for first and second modes of operation, first and second inputs connected to said first and second channels respectively to receive output voltage from said respective capacitive measuring circuits, and an output of said compensating circuit connected to said second channel for controlling the amplitude of its output for compensating said reading, said switching means having control means connected to at least one of said channels to receive voltage derived from said respective capacitive measuring circuit, said switching means operable between a first state and a second state in response to the voltage applied to said control means from said channel to which it is connected passing through a value for said intermediate level of liquid substantially even with the upper end of said first capacitive portion, said switching means being in said first state while the level of liquid is between said intermediate and second levels where said capacitive portions are overlapped to cause said compensating circuit to be in its first mode of operation to respond to the difference in voltages derived from said first and second channels, and said switching means being in said second state while level of liquid is higher than said intermediate level to exclude from said compensating circuit voltage from said second channel and to cause said compensating circuit to be in its second mode of operation to respond to voltage from only said first channel.
Claim 7
Dependent Claim
74 words
A measuring system as claimed in claim 4 having a controlled source of a-c signal, said controlled source of a-c signal having an output and a control input, said output of said source of a-c signal connected to each of said capacitive measuring circuits, and said output of said compensating circuit that is connected to said second channel for controlling its amplitude being connected to said control input of said source of a-c signal.
Claim 8
Dependent Claim
194 words
A measuring system as claimed in claim 4 wherein each of said capacitive measuring circuits comprises an amplifier with first and second input terminals, first and second capacitors, and a voltage divider, a source of a-c signal having first and second output terminals connected to said voltage divider to apply signal thereacross, an intermediate tap of said voltage divider being connected to said first input terminal of said amplifier, said first capacitor being connected between said first output terminal of said source of a-c signal and said second input terminal of said amplifier, said second capacitor connected between the output of said amplifier and said second input terminal, the respective one of said capacitive portions to be measured connected between said second input terminal of said amplifier and said second output terminal of said source of a-c signal, and the output of said amplifier in each of said capacitive measuring circuits connected to said respective compensating circuit, each of said voltage dividers providing at its tap the required voltage to provide in the output of said respective amplifier a predetermined voltage corresponding to the capacitance of said respective capacitive portion while it is empty.
Claim 9
Dependent Claim
215 words
A measuring system as claImed in claim 4 wherein said measuring probe assembly comprises first and second parallel rigid tubular outer conductors adapted to extend vertically in a container, said first tubular outer conductor extending at least from said first level downwardly below said second level at least to the level at which said first capacitive portion is terminated, said second tubular outer conductor extending at least between said first and second levels, said first and second capacitive portions comprising first and second inner conductors mounted coaxially in said first and second outer conductors respectively, the vertical extents of said first and second inner conductors being the respective vertical extents of said first and second capacitive portions, a seal in said first outer conductor about the upper end of said first inner conductor at said intermediate level to prevent liquid from flowing into that portion of said first outer conductor above said first inner conductor, a conductive wire mounted coaxially within that portion of said first outer conductor extending upwardly above said intermediate level, said wire insulated from said first outer conductor and connected between said first inner conductor and said first capacitive measuring circuit, the diameter of said wire and its distributed capacitance being relatively small compared with those of said first inner conductor.
Claim 10
Dependent Claim
129 words
A measuring system as claimed in claim 4 wherein said compensating circuit comprises a divider having two inputs and an output, said switching means and its control means comprising a differential amplifier and a pair of diodes, said first capacitive measuring circuit connected through one of said diodes to one of said inputs of said divider, both said first and second capacitive measuring circuits connected to respective inputs of said differential amplifier, the output of the differential amplifier connected through the other one of said diodes also to said one input of said divider, said second capacitive measuring circuit connected to the other of said inputs of said divider, and said output metering circuit being connected to said second channel by being connected to said output of said divider.
Claim 11
Independent Claim
413 words
A system for measuring level of liquid comprising: a probe assembly having first and second elongated capacitive portions, said capacitive portions having similar capacitances per unit of length, said probe assembly being adapted to position said capacitive portions vertically to predetermined different depths in a container for liquids, said second capacitive portion extending downwardly from a first level to a lower second level, said first and second levels defining a range through which levels are to be measured, said first capacitive portion extending downwardly from said first level and continuing far enough downwardly below said second level where said second capacitive portion is terminated to provide significant detectable change in capacitance of said first capacitive portion due to filling the space below said second level with liquid, each of said capacitive portions admitting liquid as a dielectric to a height of liquid in which they are inserted, a source of controlled alternating current having an output and a control input, the amplitude of the alternating-current voltage at said output being controlled by application of voltage to said control input, first and second capacitive measuring circuits including said first and second capacitive portions respectively, each of said capacitive measuring circuits connected to said source of alternating current for applying operating voltage thereto and each having an output for providing an a-c voltage that has an amplitude as a function of the capacitance of the respective one of said capacitive portions and of the operating voltage applied to said respective capacitive measuring circuit from said controlled source of alternating current, a difference circuit having first and second inputs connected to said outputs of said first and second capacitive measuring circuits respectively, detecting means, said difference circuit connected to said detecting means for applying thereto a-c voltage proportional to the difference in capacitances of said capacitive portions, said detecting means having an output connected to said control input of said source of controlled alternating current, said output of said source of controlled alternating current being controlled by said output of said detecting means to maintain the difference in the outputs of said capacitive measuring circuits substantially constant while level of liquid is between said first level and said second level to compensate for changes in permittivity of the liquid into which said capacitive portions are inserted, and an output metering circuit connected to said output of one of said capacitive measuring circuits to display the level of the liquid into which said capacitive portions are inserted.
Claim 12
Independent Claim
413 words
A system for measuring level of liquid comprising: a probe assembly having first and second elongated capacitive portions, said capacitive portions having similar capacitances per unit of length, said probe assembly being adapted to position said capacitive portions vertically to predetermined different depths in a container for liquids, said second capacitive portion extending downwardly from a first level to a lower second level, said first and second levels defining a range through which levels are to be measured, said first capacitive portion extending downwardly from said first level and continuing far enough downwardly below said second level where said second capacitive portion is terminated to provide significant detectable change in capacitance of said first capacitive portion due to filling the space below said second level with liquid, each of said capacitive portions admitting liquid as a dielectric to a height of liquid in which they are inserted, a source of controlled alternating current having an output and a control input, the amplitude of the alternating-current voltage at said output being controlled by application of voltage to said control input, first and second capacitive measuring circuits including said first and second capacitive portions respectively, each of said capacitive measuring circuits connected to said source of alternating current for applying operating voltage thereto and each having an output for providing an a-c voltage that has an amplitude as a function of the capacitance of the respective one of said capacitive portions and of the operating voltage applied to said respective capacitive measuring circuit from said controlled source of alternating current, a difference circuit having first and second inputs connected to said outputs of said first and second capacitive measuring circuits respectively, detecting means, said difference circuit connected to said detecting means for applying thereto a-c voltage proportional to the difference in capacitances of said capacitive portions, said detecting means having an output connected to said control input of said source of controlled alternating current, said output of said source of controlled alternating current being controlled by said output of said detecting means to maintain the difference in the outputs of said capacitive measuring circuits substantially constant while level of liquid is between said first level and said second level to compensate for changes in permittivity of the liquid into which said capacitive portions are inserted, and an output metering circuit connected to said output of one of said capacitive measuring circuits to display the level of the liquid into which said capacitive portions are inserted.
Claim 13
Dependent Claim
352 words
A system for measuring level of liquid as claimed in claim 9 wherein said second capacitive portion extends upwardly through said first level in the container in which said probe assembly is inserted at least to the highest level at which the liquid is to be measured, said second level and said highest level defining an extended range through which levels are to be measured, said output metering circuit being connected to said second capacitive measuring circuit, said first capacitive portion being short enough to be entirely submerged while the level of liquid is above said first level at a relatively low level in said container, switching means connected between the output of said second capacitive measuring circuit and said second input of said difference circuit, a mode control circuit connected between said second capacitive measuring circuit and said switching means, said switching means being operable between a closed state and an open state in response to voltage applied thereto from said mode control circuit passing through voltage for said first level at which said first capacitive portion becomes entirely submerged, the voltage applied from said mode control circuit being a function of the a-c voltage supplied from the output of said second capacitive measuring circuit, said switching means being in said closed state in response to the level of the liquid in the container being below said first level such that the amplitude of the output of said controlled alternating current is a funcof the difference in capacitances of said first and second capacitive portions, said switching means being in said open state in response to the level of the liquid being above said first level to disconnect said difference circuit from said second capacitive measuring circuit, said difference circuit while disconnected from said second capacitive measuring circuit responding to changes only from said first capacitive measuring circuit for controlling the output of said controlled alternating current to the extent required to maintain substantially constant the output of said first capacitive measuring circuit while said first capacitive portion is submerged and thereby to compensate the readings in said output metering circuit.
Claim 14
Independent Claim
430 words
A system for measuring level of liquid comprising: a probe assembly having first and second elongated capacitive portions, said capacitive portions having similar capacitances per unit of length, said probe assembly being adapted to position said capacitive portions vertically to predetermined different depths in a container for liquids, said second capacitive portion extending downwardly from a first level to a lower second level, said first and second levels defining a range through which levels are to be measured, said first capacitive portion extending downwardly from said first level and continuing downwardly through said second level where said second capacitive portion is terminated to provide significant detectable change in capacitance of said first capacitive portion due to filling the space below said second level with liquid, each of said capacitive portions admitting liquid as a dielectric to a height of liquid in which they are inserted, a source of controlled alternating current having an output and a control input, the amplitude of the alternating-current voltage at said output being controlled by application of voltage to said control input, first and second capacitive measuring circuits including said first and second capacitive portions respectively, each of said capacitive measuring circuits connected to said source of alternating current for applying operating voltage thereto and each having an output for providing an a-c voltage that has an amplitude as a function of the capacitance of the respective one of said capacitive portions and of the operating voltage applied to said respective capacitive measuring circuit from said controlled source of alternating current, first and second detecting means connected to said outputs of said first and second capacitive measuring circuits respectively, a difference circuit having first and second inputs connected to said first and second detecting means respectively, said first and second detecting means applying d-c voltage proportional to the difference in capacitances of said capacitive portions to said first and second inputs of said difference circuit, said difference circuit having an output connected to said control input of said source of controlled alternating current, said output of said source of said controlled alternating current being controlled by said output of said difference circuit to maintain the difference in the outputs of said capacitive measuring circuits substantially constant while level of liquid is between said first level and said second level to compensate for changes in density of the liquid into which said capacitive portions are inserted, and an output metering circuit connected to said output of one of said capacitive measuring circuits to display the level of the liquid into which said capacitive portions are inserted.
Claim 15
Independent Claim
430 words
A system for measuring level of liquid comprising: a probe assembly having first and second elongated capacitive portions, said capacitive portions having similar capacitances per unit of length, said probe assembly being adapted to position said capacitive portions vertically to predetermined different depths in a container for liquids, said second capacitive portion extending downwardly from a first level to a lower second level, said first and second levels defining a range through which levels are to be measured, said first capacitive portion extending downwardly from said first level and continuing downwardly through said second level where said second capacitive portion is terminated to provide significant detectable change in capacitance of said first capacitive portion due to filling the space below said second level with liquid, each of said capacitive portions admitting liquid as a dielectric to a height of liquid in which they are inserted, a source of controlled alternating current having an output and a control input, the amplitude of the alternating-current voltage at said output being controlled by application of voltage to said control input, first and second capacitive measuring circuits including said first and second capacitive portions respectively, each of said capacitive measuring circuits connected to said source of alternating current for applying operating voltage thereto and each having an output for providing an a-c voltage that has an amplitude as a function of the capacitance of the respective one of said capacitive portions and of the operating voltage applied to said respective capacitive measuring circuit from said controlled source of alternating current, first and second detecting means connected to said outputs of said first and second capacitive measuring circuits respectively, a difference circuit having first and second inputs connected to said first and second detecting means respectively, said first and second detecting means applying d-c voltage proportional to the difference in capacitances of said capacitive portions to said first and second inputs of said difference circuit, said difference circuit having an output connected to said control input of said source of controlled alternating current, said output of said source of said controlled alternating current being controlled by said output of said difference circuit to maintain the difference in the outputs of said capacitive measuring circuits substantially constant while level of liquid is between said first level and said second level to compensate for changes in density of the liquid into which said capacitive portions are inserted, and an output metering circuit connected to said output of one of said capacitive measuring circuits to display the level of the liquid into which said capacitive portions are inserted.
Claim 16
Dependent Claim
217 words
A system for measuring level of liquid as claimed in claim 11 wherein said second capacitive portion extends upwardly through said first level in the container in which said probe assembly is inserted at least to the highest level at which the liquid is to be measured, said second level and said highest level defining an extended range through which levels are to be measured, said output metering circuit being connected to said second capacitive measuring circuit, said first capacitive portion being short enough to be entirely submerged while the level of liquid is above said first level at a relatively low level in said container, a pair of diodes having similar electrodes connected to said control input of said source of controlled alternating current, the other electrode of one of said diodes being connected to the output of said difference circuit, and means for connecting the output of said first detecting means to the other electrode of the other of said diodes, said one diode being conductive and said other diode being non-conductive in response to the application of voltages thereto while level of liquid is between said first level and said second level, and said other diode being conductive and said one diode being non-conductive while level of liquid is higher than said first level.
References Cited (Backward Citations)
US2724273A
Cited
US3037165A
Cited
US3170479A
Cited
US3389602A
Cited
US3543046A
Cited
US3665209A
Cited
US3771548A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-08-25 | 1979-02-24 | 1979-08-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-08-25 | 1983-02-24 | 1983-08-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-08-25 | 1987-02-24 | 1987-08-26 | $7700.00 | Window Closed / Lapsed |