US6073488A
Expired / Lapsed
US
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Capacitive liquid level sensor with integrated pollutant film detection
Assignee: ABB Research Ltd Switzerland
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Filing: 1998-12-10
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Granted: 2000-06-13
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Expires: 2018-12-10
Abstract
Abstract The subject matter of the present invention is a method and a device for capacitive liquid level measurement which are particularly suitable for determining liquid level between adhesive media 10, 11 of different conductivity. The known sensor principle is based on the fact that the environmentally dependent capacitance is measured between neighboring electrodes 13, 4; 4, 5; 5, 6 of a rod-shaped probe 1. According to the invention, the probe 1 has electrodes 4, 5, 6, 13 with covers 7 of different thicknesses d i . The effective thickness d s /ε s of an insulating pollutant film 14 can then be determined by capacitance measurements between at least two pairs of electrodes 4, 5, 6, 13. The influence of a conductive pollutant film 14 on the capacitance signal can be eliminated by selection of at least one suitable measuring frequency. Furthermore, by optimizing the electrode height h, a large capacitance jump is achieved for a digital liquid level display, and/or a largely continuous increase in capacitance is achieved for an analog liquid level display. The sensor is preferably used to determine the location of an interface 12 between water 10 and oil 11 in a separator tank.
Inventors
- 👤 Anghony Byatt
- 👤 Thomas Christen
- 👤 Thomas Kleiner
- 👤 Daniel Matter
- 👤 Walter Ruegg
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 11:11
CPC Classifications
G; G01; G01F; G01F23/00; G01F23/22; G01F23/26; G01F23/263; G01F23/266; G01B; G01B7/00; G01B7/02; G01B7/06; G01B7/08; G01B7/085; G01F23/268
Claims Analysis
Total Claims: 23
Claim 1
Independent Claim
131 words
A method for liquid level measurement with a liquid level measurement device, the liquid level measurement device including electrodes which are arranged along an axis of a rod-shaped probe and which are provided with corresponding electrically insulating covers, wherein at least two of the electrically insulating covers have thicknesses different from each other, the method for determining the effective thickness of the insulating pollutant comprising the steps of: determining an effective thickness of an insulating pollutant film on the liquid level measurement device by measuring capacitances between the electrodes; and calculating an effective thickness (d s /ε s ) of the insulating pollutant film based on the measured capacitances, where d s is a geometric thickness of the pollutant film and ε s is a dielectric constant of the pollutant film.
Claim 2
Independent Claim
131 words
A method for liquid level measurement with a liquid level measurement device, the liquid level measurement device including electrodes which are arranged along an axis of a rod-shaped probe and which are provided with corresponding electrically insulating covers, wherein at least two of the electrically insulating covers have thicknesses different from each other, the method for determining the effective thickness of the insulating pollutant comprising the steps of: determining an effective thickness of an insulating pollutant film on the liquid level measurement device by measuring capacitances between the electrodes; and calculating an effective thickness (d s /ε s ) of the insulating pollutant film based on the measured capacitances, where d s is a geometric thickness of the pollutant film and ε s is a dielectric constant of the pollutant film.
Claim 3
Dependent Claim
132 words
The method of claim 1, wherein a) a quotient of double-layer capacitances C DSi and C DSj of i-th and j-th ones of the electrodes is determined in accordance with the formula C.sub.DSj /C.sub.DSi =(C.sub.σij.sup.-1 +C.sub.σik.sup.-1 -C.sub.σjk.sup.-1)/(C.sub.σij.sup.-1 +C.sub.σjk.sup.-1 -C.sub.σik.sup.-1), where C.sub.σij, C.sub.σik, C.sub.σjk denote total capacitances which are measured between the i-th and j-th, the j-th and a k-th one of the electrodes, and the i-th and k-th electrodes respectively, and b) the effective thickness (d s /ε s ) is calculated in accordance with the formula ##EQU2## where ε e =dielectric constant of the electrically insulating covers, d i , d j =thicknesses of ones of the electrically insulating covers corresponding to the i-th and j-th electrodes, and A i , A j =capacitor surfaces of the i-th, j-th electrodes respectively.
Claim 4
Dependent Claim
142 words
The method of claim 1, where a) adjacent ones of the electrodes are of different thickness, and alternate ones of the electrodes are of the same thickness as corresponding ones of the electrically insulating covers, b) a quotient of double-layer capacitances C DSi and C DSj of i-th and j-th ones of the electrodes is determined in accordance with the formula C.sub.DSj /C.sub.DSi =C.sub.σj /C.sub.σi, where C.sub.σj, C.sub.σi denote total capacitances which are measured between alternate ones of the electrodes, c) the electrodes have the same capacitor surfaces, and d) the effective thickness (d s /ε s ) of the insulating pollutant film is calculated in accordance with the formula ##EQU3## where ε e =dielectric constant of the electrically insulating covers and d i , d j =thicknesses of the ones of the electrically insulating covers corresponding to the i-th, j-th electrodes.
Claim 5
Dependent Claim
145 words
A capacitive liquid level sensor for measuring a liquid level by determining an effective thickness of an insulating pollutant film, comprising: a rod-shaped probe; a plurality of electrodes which are arranged along an axis of the probe; electrically insulating covers corresponding to the electrodes; and electronic measuring system connected to the plurality of electrodes; wherein at least two of the electrically insulating covers are of different thicknesses, and the electronic measuring system comprises means for measuring capacitance between ones of the plurality of electrodes and for determining a quotient of double-layer capacitances C DSi and C DSj of i-th and j-th ones of the plurality of electrodes, and for calculating an effective thickness (d s /ε s ) of the insulating pollutant film where d s is a geometric thickness of the pollutant film and ε s is a dielectric constant of the pollutant film.
Claim 6
Dependent Claim
145 words
A capacitive liquid level sensor for measuring a liquid level by determining an effective thickness of an insulating pollutant film, comprising: a rod-shaped probe; a plurality of electrodes which are arranged along an axis of the probe; electrically insulating covers corresponding to the electrodes; and electronic measuring system connected to the plurality of electrodes; wherein at least two of the electrically insulating covers are of different thicknesses, and the electronic measuring system comprises means for measuring capacitance between ones of the plurality of electrodes and for determining a quotient of double-layer capacitances C DSi and C DSj of i-th and j-th ones of the plurality of electrodes, and for calculating an effective thickness (d s /ε s ) of the insulating pollutant film where d s is a geometric thickness of the pollutant film and ε s is a dielectric constant of the pollutant film.
Claim 7
Dependent Claim
52 words
The capacitive liquid level sensor as claimed in claim 4, wherein a) adjacent ones of the plurality of electrodes are of different thickness, and alternate ones of the plurality of electrodes are of the same thickness as corresponding ones of the electrically insulating covers, and b) the electrodes have equal capacitor surfaces.
Claim 8
Dependent Claim
48 words
The capacitive liquid level sensor as claimed in claim 4, wherein a) the thicknesses of the electrically insulating covers are smaller than a maximum value (d e ) of 2.5 millimeters, and b) the electrically insulating covers have a dielectric constant (ε e ) of less than 10.
Claim 9
Dependent Claim
83 words
The capacitive liquid level sensor as claimed in claim 4, wherein a) a pollutant film of resistivity ρ f is prescribed a maximum permissible thickness b c and an associated critical frequency f c =2•(ε e •ε 0 •ρ f ) -1 •(d e /h 2 )•b c , where h=electrode height extending along the probe axis, ε 0 =absolute permittivity, d e =a maximum thickness of the electrically insulating covers, and b) a first measuring frequency f b >f c is selected.
Claim 10
Dependent Claim
68 words
The capacitive liquid level sensor as claimed in claim 4, wherein the sensor is a sensor for determining a location of an interface between different media in a separator tank, the media separated by the interface have different cut-off frequencies corresponding to respective dielectric relaxations of the media, and at least one measuring frequency is selected in a frequency range bounded by the cut-off frequencies of the media.
Claim 11
Dependent Claim
62 words
The capacitive liquid level sensor as claimed in claim 4, wherein a) a ratio of a height of at least one of the plurality of electrodes along the probe axis to a spacing between adjacent ones of the plurality of electrodes is selected which is greater than 1, and b) the liquid level sensor is equipped for an analog and/or digital display.
Claim 12
Dependent Claim
41 words
The capacitive liquid level sensor as claimed in claim 4, wherein a) the probe comprises a cylindrical tube to whose lateral surface the plurality of electrodes is applied, and b) the tube interior is sealed against the exterior surrounding the probe.
Claim 13
Dependent Claim
48 words
The capacitive liquid level sensor as claimed in claim 10, wherein a) the tube consists of a dielectric that is at least one of plastic, glass and ceramic, and b) the electrically insulating covers consist of at least one of epoxy resin, glass, ceramic, mica and reinforcing fibers.
Claim 14
Dependent Claim
21 words
The capacitive liquid level sensor of claim 6, wherein the thicknesses of the electrically insulating covers are smaller than 1.5 millimeters.
Claim 15
Dependent Claim
21 words
The capacitive liquid level sensor of claim 6, wherein the thicknesses of the electrically insulating covers are smaller than 1.0 millimeters.
Claim 16
Dependent Claim
24 words
The capacitive liquid level sensor of claim 6, wherein the electrically insulating covers have a dielectric constant (ε e ) of less than 5.
Claim 17
Dependent Claim
19 words
The capacitive liquid level sensor of claim 7, wherein a second measuring frequency f a <f c is selected.
Claim 18
Dependent Claim
16 words
The capacitive liquid level sensor of claim 9, wherein the selected ratio is less than 6.
Claim 19
Dependent Claim
17 words
The capacitive liquid level sensor of claim 9, wherein the selected ratio is between 1.5 and 4.5.
Claim 20
Dependent Claim
14 words
The capacitive liquid level sensor of claim 9, wherein the selected ratio is 3.
Claim 21
Dependent Claim
32 words
The capacitive liquid level sensor of claim 10, wherein: the cylindrical tube is circular; the plurality of electrodes is annular and/or segmented; and each of the plurality electrodes has a rectangular cross-section.
Claim 22
Dependent Claim
23 words
The method of claim 1, wherein the liquid level measurement device is configured for determining a location of an interface between different media.
Claim 23
Dependent Claim
12 words
The method of claim 1, wherein the media comprise water and oil.
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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) | 2003-06-13 | 2003-12-13 | 2004-06-13 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2007-06-13 | 2007-12-13 | 2008-06-13 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2011-06-13 | 2011-12-13 | 2012-06-13 | $7700.00 | Window Closed / Lapsed |