EP0101580A1
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Capacitance-type material level indicator
Assignee: Cessione bindicator Co
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Filing: 1983-07-29
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Granted: —
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Expires: 2003-07-29
Abstract
Abstract A system and probe for indicating the level of material (28) in a vessel (22) as a function of material capacitance comprising a resonant circuit (14) including a capacitance probe (20) adapted to be disposed in a vessel so as to be responsive to variations in capacitance as a function of material level. An rf oscillator (10) has an output coupled to the resonant circuit (14) and to a phase detector (32) for detecting variations in phase angle as a function of probe capacitance. Level detection circuitry (36, 38) is responsive to an output of the phase detector and to a reference signal indicative of a predetermined level of material for indicating material level as a function of a difference between capacitance at the probe and the reference signal. In the preferred embodiments of the invention disclosed, an automatic calibration circuit (34) adjusts the resonance characteristics of the parallel resonant circuit of the reference signal indicative of a predetermined reference material level. Also disclosed is a capacitance probe (20) and method of probe manufacture for material level sensing systems and like applications.
Inventors
- 👤 Ronald G. Brenton
- 👤 Robin B. Runck
- 👤 George H. Fathauer
- 👤 Charles F. Hood
- 👤 Phillip P. Fleckenstein
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 09:39
CPC Classifications
G; G01; G01F; G01F23/00; G01F23/22; G01F23/26; G01F23/263; G01F23/266; G01F23/268
Claims Analysis
Total Claims: 35
Claim 1
Independent Claim
145 words
A system for indicating the level of material (28) in a vessel (22) as a function of material capacitance comprising a resonant circuit (14,20) including a capacitance probe (20) adapted to be disposed in a vessel so as to be responsive to variations in capacitance as a function of material level in said vessel, oscillator means (10) coupled to said resonant circuit including said capacitance probe and phase detection means (32) responsive to variations in phase angle at said oscillator means as a function of probe capacitance, characterized by further comprising calibration means (34) for identifying a reference capacitance indicative of a predetermined level of material in said vessel, and means (36,38) responsive to said phase detection means and to said calibration means for indicating material level in said vessel as a function of a difference between capacitance at said probe and said reference capacitance.
Claim 2
Independent Claim
145 words
A system for indicating the level of material (28) in a vessel (22) as a function of material capacitance comprising a resonant circuit (14,20) including a capacitance probe (20) adapted to be disposed in a vessel so as to be responsive to variations in capacitance as a function of material level in said vessel, oscillator means (10) coupled to said resonant circuit including said capacitance probe and phase detection means (32) responsive to variations in phase angle at said oscillator means as a function of probe capacitance, characterized by further comprising calibration means (34) for identifying a reference capacitance indicative of a predetermined level of material in said vessel, and means (36,38) responsive to said phase detection means and to said calibration means for indicating material level in said vessel as a function of a difference between capacitance at said probe and said reference capacitance.
Claim 3
Dependent Claim
85 words
The system set forth in claim 1 characterized in that said calibration means (14) comprises comparison means (54) having a first input responsive to said phase detection means (32), a second input and an output responsive to a comparison between said first and second inputs, reference means (56) connected to said second input and indicative of said reference capacitance, and means (44-50 or 50,106 or 50, 106-114) for varying operating characteristics of said system to obtain a predetermined comparison between said first and second inputs.
Claim 4
Dependent Claim
31 words
The system set forth in claim 2 characterized in that the last-named means varies operating characteristics of said system to obtain said predetermined comparison substantially at resonance of said resonant circuit.
Claim 5
Dependent Claim
80 words
The system set forth in claim 2 characterized in that said calibration means comprises automatic calibration means including means (40) for initiating a calibration operation, means (50) responsive to said initiating means for continuously varying said operating characteristics of said system, and means responsive to said output of said comparison means for terminating said calibration operation when said output indicates said predetermined comparison between said first input from said phase detection means and said second input from said reference means.
Claim 6
Dependent Claim
84 words
The system set forth in claim 4 characterized in that said automatic calibration means comprises counter means (50) including means (52) responsive to said initiating means (40) for resetting said counter means, means responsive to said comparison means for enabling operation of said counter means during said calibration operation, and means (10) for varying the count in said counter means during said calibration operation, and means (44-48 or 106 or 106-114) responsive to the count in said counter means for varying said system characteristics.
Claim 7
Dependent Claim
30 words
The system set forth in claim 5 wherein said count-responsive means comprises means (44-48 or 106-114) for varying resonance characteristics of said resonant circuit as a function of said count.
Claim 8
Dependent Claim
46 words
The system set forth in claim 6 characterized in that said resonant circuit comprises capacitance means (46a-46f) and inductance means (44) connected in parallel with said capacitance probe (20), and in that said count responsive means includes means (48a-48f) for varying capacitance of said capacitance means.
Claim 9
Dependent Claim
46 words
The system set forth in claim 7 characterized in that said capacitance means comprises a plurality of capacitors (46a-46f), and in that said count-responsive means includes switch means (48a-48f) responsive to said counter means (50) for selectively connecting said plurality of capacitors into said resonant circuit.
Claim 10
Dependent Claim
80 words
The system set forth in claim 8 characterized in that said inductance means (44) comprises an inductor coil having a plurality of coil turns, and in that said plurality of capacitors (46a-46f) are connected at electrically spaced locations among said plurality of coil turns such that capacitance of said capacitance means varies in response to said switch / means (48a-48f) as a conjoint function of nominal capacitance of said capacitors and connection of said capacitors among said plurality of turns.
Claim 11
Dependent Claim
91 words
The system set forth in claim 9 characterized in that said counter means (50) comprises a digital counter having a plurality of outputs indicative of corresponding count bits in an order of numerical significance, in that said switch means (48a-48f) comprises a plurality of electronic switches each selectively controlled by a corresponding said counter output, and in that said plurality of capacitors (46a-48f) are connected to said switches and to said spaced locations so as to vary said capacitance as a direct function of numerical significance of the corresponding counter output.
Claim 12
Dependent Claim
46 words
The system set forth in claim 6 characterized in that said resonant circuit means comprises capacitance means (104) and inductance means (102) connected in parallel with said capacitance probe (20), and in that said count-responsive means includes means (106-114) for varying inductance at said inductance means.
Claim 13
Dependent Claim
32 words
The system set forth in claim 11 characterized in that said count-responsive means comprises means (106-114) for applying a variable direct current to said inductance means as a function of said count.
Claim 14
Dependent Claim
65 words
The system set forth in claim 12 characterized in that said counter means (50) comprises a digital counter, and in that said count-responsive means comprises a variable direct current source including a transistor (110) having primary electrodes operatively connecting said inductance means (102) to a source of d.c. potential, and a control electrode, and digj.tal-to-analog converter means (106) connecting said counter to said control electrode.
Claim 15
Dependent Claim
27 words
The system set forth in claim 13 characterized by further comprising means (12,112) for connecting said oscillator means (10) to said resonant circuit through said primary electrodes.
Claim 16
Dependent Claim
38 words
The system set forth in claim 5 characterized in that said count-responsive means comprises means (106) for varying said reference means (56) connected to said second input of said comparison means (54) as a function of said count.
Claim 17
Dependent Claim
65 words
The system set forth in claim 15 characterized in that said comparison means (54) comprises means responsive to a difference in voltage between said first input from said phase detection means (32) and said second input from said reference means (56), and in that said count responsive means (106) comprises means for varying the reference voltage applied to said second input by said reference means.
Claim 18
Dependent Claim
44 words
The system set forth in claim 16 characterized in that said counter means (50) includes a digital counter, and in that said count-responsive means (106) includes digital-to-analog converter means for applying an analog voltage to said second input as a function of said count.
Claim 19
Dependent Claim
39 words
The system set forth in any preceding claim 5-18 characterized by further comprising means including a battery (64) coupled to said counter means (50) for maintaining said calibration count in said counter means in the event of power failure.
Claim 20
Independent Claim
25 words
The system set forth in any preceding claim characterized in that said means (40) for initiating a calibration operation includes an operator-responsive manual push button.
Claim 21
Dependent Claim
34 words
The system set forth in claim 19 further comprising indicator means (60) and means (58) connecting said indicator means to said output of said comparison means (54) for indicating duration of a calibration operation.
Claim 22
Dependent Claim
65 words
The system set forth in claim 20 characterized in that said means (58) connecting said indicating means comprises a solid state switch having primary electrodes and a control electrode connected to said output of said comparison means, and in that said indicating means (60) comprises an LED connected in series with said primary electrodes and said push button (40) across a source of d.c. power.
Claim 23
Independent Claim
72 words
The system set forth in any preceding claim characterized in that said means (36,38) responsive to said phase detection means (32) and said calibration means (34) comprises comparison means (70) having a first input connected to said phase detection means, a second input connected to said calibration means, and an output which varies between first and second digital states as a function of a threshold difference between said first and second inputs.
Claim 24
Dependent Claim
19 words
The system set forth in claim 22 further characterized by means (62, 80-86) for selectively varying said threshold difference.
Claim 25
Dependent Claim
34 words
The system set forth in claim 23 characterized in that the last-named means comprises at least one resistor (80,82) and means (84,86) for selectively connecting said at least one resistor across said second input.
Claim 26
Dependent Claim
44 words
The system set forth in claim 22 characterized by further comprising means (75) connected between said phase detection means (32) and said comparison means (70) for delaying operation of said comparison means in response to said phase detection means for a selected delay time.
Claim 27
Dependent Claim
22 words
The system set forth in claim 25 characterized by further comprising means (72, 74, 76, 78) for selectively varying said delay time.
Claim 28
Dependent Claim
38 words
The system set forth in claim 26 wherein the last-named means comprises at least one capacitor (72,74) and means (76,78) for selectively connecting said at least one capacitor to said first input of said comparison means (70) .
Claim 29
Dependent Claim
36 words
The system set forth in any claim 22-27 characterized by further comprising fail safe means (90-94) for indicating a preselected level condition in the event of failure at said system and independently of actual material level.
Claim 30
Dependent Claim
55 words
The system set forth in claim 28 characterized in that said fail safe means comprises exclusive-or means (90) having a first input connected to said output of said comparison means (70) and a second input, and means (92,94) for selectively connecting said second input to either a high level or a low level digital signal.
Claim 31
Dependent Claim
27 words
The system set forth in claim 29 characterized by further comprising relay means (100,102) connected to said output of said exclusive-or means (90) for indicating material level.
Claim 32
Dependent Claim
133 words
A capacitance probe (20) for use in material level sensing applications or the like comprising an elongated probe element (18) having a central axis, a tubular guard (26) coaxially surrounding and radially spaced from said probe element, said probe element having a greater axial dimension than said guard and projecting from one end of said guards one-piece unitarily formed insulation means (126) surrounding said probe element and surrounding and radially overlapping axially spaced ends of said guard, a portion of said guard intermediate said ends and an end portion of said probe element being exposed through said one-piece insulation means, and means (124,130) capturing said insulation means and adapted for mounting said probe to a material vessel (140,142) with said exposed portion of said guard and probe element disposed internally of said vessel.
Claim 33
Dependent Claim
133 words
A capacitance probe (20) for use in material level sensing applications or the like comprising an elongated probe element (18) having a central axis, a tubular guard (26) coaxially surrounding and radially spaced from said probe element, said probe element having a greater axial dimension than said guard and projecting from one end of said guards one-piece unitarily formed insulation means (126) surrounding said probe element and surrounding and radially overlapping axially spaced ends of said guard, a portion of said guard intermediate said ends and an end portion of said probe element being exposed through said one-piece insulation means, and means (124,130) capturing said insulation means and adapted for mounting said probe to a material vessel (140,142) with said exposed portion of said guard and probe element disposed internally of said vessel.
Claim 34
Independent Claim
115 words
A method of constructing a capacitance probe for a level indicating system comprising the steps of: (a) pro-. viding a solid probe rod, (b) fixturing a hollow tubular guard telescopically surrounding and radially spaced from said probe rod and axially spaced from at least one end of said probe rod, (c) injection molding insulation material surrounding said probe rod between said probe rod and said guard and radially surrounding axially spaced ends of said guard, said one end of said probe rod and a portion of said guard intermediate said spaced ends being radially exposed through said insulation material, and (d) mounting the molded assembly within a nipple adapted for assembly to a material vessel.
Claim 35
Independent Claim
115 words
A method of constructing a capacitance probe for a level indicating system comprising the steps of: (a) pro-. viding a solid probe rod, (b) fixturing a hollow tubular guard telescopically surrounding and radially spaced from said probe rod and axially spaced from at least one end of said probe rod, (c) injection molding insulation material surrounding said probe rod between said probe rod and said guard and radially surrounding axially spaced ends of said guard, said one end of said probe rod and a portion of said guard intermediate said spaced ends being radially exposed through said insulation material, and (d) mounting the molded assembly within a nipple adapted for assembly to a material vessel.
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