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WO2008062146A1 - Détecteur de position - Google Patents

Détecteur de position Download PDF

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Publication number
WO2008062146A1
WO2008062146A1 PCT/GB2006/004384 GB2006004384W WO2008062146A1 WO 2008062146 A1 WO2008062146 A1 WO 2008062146A1 GB 2006004384 W GB2006004384 W GB 2006004384W WO 2008062146 A1 WO2008062146 A1 WO 2008062146A1
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WIPO (PCT)
Prior art keywords
electrodes
excitation
signal
electrode
operable
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PCT/GB2006/004384
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English (en)
Inventor
Victor Evgenievich Zhitomirsky
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Sagentia Ltd
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Sagentia Ltd
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Priority to PCT/GB2006/004384 priority Critical patent/WO2008062146A1/fr
Publication of WO2008062146A1 publication Critical patent/WO2008062146A1/fr
Anticipated expiration legal-status Critical
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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/26—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields
    • G01F23/263—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/26—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields
    • G01F23/263—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors
    • G01F23/266—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors measuring circuits therefor

Definitions

  • the present invention relates to capacitive position sensors and to parts thereof.
  • the invention has particular, although not exclusive relevance to capacitive position sensors that can be used to sense the level of a liquid within a container and to transducers for use in such sensors.
  • FIG. 1 schematically illustrates the form of electrodes used in this prior art type of sensor.
  • the sensor includes three electrodes 9, 11 and 12 which are connected to excitation and processing circuitry 22 via a connection interface 20.
  • the electrodes 9 and 12 provide the main sensor signal that will vary with the level of the liquid 103 in the container (not shown) and the electrode 11 is used to provide the reference capacitor.
  • the present invention aims to provide an alternative capacitive position sensor that can be used to sense the level of a liquid or that can be used to sense the presence of a dielectric or metallic object in the vicinity of the sensor.
  • Preferred embodiments of the sensor overcome or at least reduce the problems with the prior art sensor discussed above.
  • the present invention provides a capacitive position sensor comprising: first and second sets of electrodes; excitation circuitry operable to generate and to apply a first excitation signal to an excitation electrode of said first set of electrodes and a second excitation signal to an excitation electrode of said second set of electrodes; and detection circuitry operable: i) to receive a first detection signal from a reception electrode of said first set of electrodes which first detection signal varies with the position along said measurement path of an inhomogeneity which affects the capacitive coupling between the excitation and reception electrodes of the first set of electrodes; ii) to receive a second detection signal from a reception electrode of said second set of electrodes, which second detection signal varies with the position along said measurement path of said inhomogeneity which affects the capacitive coupling between the excitation and reception electrodes of the second set of electrodes; iii) to subtract the first detection signal from the second detection signal to generate a difference signal which varies with the position along said measurement path of said inhom
  • each set of electrodes are symmetrically disposed about an axis that is parallel to said measurement path, with the electrodes of the first set being disposed on one side of said axis and the electrodes of the second set being disposed on an opposite side of said axis.
  • the electrodes of the first set are symmetrically disposed about the measurement path relative to the electrodes of the second set, such that there is mirror like symmetry between the electrodes of the first and second sets.
  • the excitation electrode of the first set has mirror symmetry with the excitation electrode of the second set and the reception electrode of the first set has mirror like symmetry with the reception electrode of the second set.
  • each set extends into a dead zone of the sensor beyond a measurement range of the sensor, wherein each set of electrodes includes a second reception or excitation electrode positioned adjacent said excitation or reception electrode in said dead zone.
  • the electrodes of each set which extend into said dead zone are preferably elongate in a direction transverse to said axis, in order to minimise the size of the dead zone.
  • each set of electrodes comprises two pairs of electrodes, one pair of electrodes being provided for position measurement and one pair of electrodes being provided to correct for changes in permittivity surrounding the sensor.
  • the electrodes of each pair that are provided for position measurement can be substantially identical and the electrodes of each pair that are provided to correct for changes in permittivity may not be identical.
  • a reference capacitor is preferably associated with each pair that is provided to correct for changes in permittivity, to compensate for the electrodes of that pair not being identical.
  • the electrodes may be formed from conductive tracks on or in a non-conductive substrate and a groove may be provided in the substrate between Hie excitation electrode and the reception electrode of said first and second sets.
  • the groove is a through groove. In another embodiment the groove is a blind groove.
  • the detection circuitry determines an amplitude measure obtained using the difference signal and updates the position only if said amplitude measure is above a predetermined threshold value. Similarly, the detection circuitry preferably determines a phase measure using the determined difference signal and updates the determine position only if said phase measure is above a predetermined threshold value. In this way, errors caused when the amplitude or phase measurements are small can be avoided.
  • the surface area of the excitation electrodes and/or the reception electrodes are designed so that there is a linear relationship between the position of the inhomogeneity and a measurement parameter obtained the difference signal.
  • the invention provides a capacitive position sensor comprising: a first electrode that extends along a measurement path over a measurement range; first and second pairs of electrodes arranged along the measurement path adjacent said first electrode such that electrodes of each pair are interleaved along said measurement path with the electrodes of the other pair; excitation circuitry operable to generate and to apply first and second excitation signals of opposite polarity to one of said first electrode and said first and second pairs of electrodes; and detection circuitry operable: i) to receive signals from the other one of said first electrode and said first and second pairs of electrodes; ii) to process said signals to obtain a first detection signal that varies with the difference in capacitive coupling between said first electrode and the respective electrodes of said first pair and a second detection signal that varies with the difference in capacitive coupling
  • the invention provides a capacitive position sensor comprising: first and second subsets of electrodes, the electrodes of which extend along a measurement path of the sensor; excitation circuitry operable to generate and to apply an excitation signal to said first subset of said electrodes; and detection circuitry operable: i) to receive first and second signals from said second subset of said electrodes, which first and second signals vary with the position along said measurement path of an inhomogeneity which affects the capacitive coupling between the electrodes of the first and second subsets; and ii) to process said first and second signals to determine the position of said inhomogeneity along said measurement path; wherein said electrodes are formed on or in a non-conducting substrate and wherein a blind groove is provided between the electrodes of said first and second sub-sets.
  • the blind groove may be provided in the substrate on which the electrodes are mounted or by providing a through groove on the substrate and by providing a backing layer on the base of the substrate.
  • Figure 1 is a schematic diagram illustrating a set of electrodes forming part of a prior art liquid level sensor
  • Figure 2 is a schematic diagram illustrating a set of electrodes forming part of a liquid level sensor according to one embodiment of the present invention
  • Figure 3 schematically illustrates an electrical equivalent circuit illustrating one way to connect the electrodes shown in Figure 2 to excitation and detection circuitry used to detect the liquid level;
  • Figure 4A is a plot illustrating the way in which one signal obtained from the electrodes shown in Figure 2 varies with the liquid level;
  • Figure 4B is a plot illustrating the way in which another signal obtained from the electrodes shown in Figure 2 varies with the liquid level
  • Figure 4C is a plot illustrating the locus of points obtained by plotting the two signals obtained from the electrodes against each other for different liquid levels
  • Figure 5 is a block diagram illustrating the main components of exemplary excitation and detection circuitry that can be used with the sensor shown in Figure 2;
  • Figure 6 is a block diagram illustrating the main components of a ratiometric calculator forming part of the detection circuitry shown in Figure 5;
  • Figure 7A is a block diagram illustrating the main components of a phase detector forming part of the ratiometric calculator shown in Figure 6;
  • Figure 7B illustrates the form of a logic circuit for zero crossing detection forming part of the circuitry shown in Figure 7A
  • Figure 7C is a plot illustrating the way in which the pulse width of the PWM signal output by the circuitry shown in Figure 7B varies with the time delay between the detected zero crossings;
  • Figure 8 schematically illustrates an electrical equivalent circuit illustrating an alternative way to connect the electrodes shown in Figure 2 to excitation and detection circuitry used to detect the liquid level;
  • Figure 9 is an electrical equivalent circuit illustrating an alternative way of connecting the electrodes shown in Figure 2 to the excitation and detection circuitry in which the electrodes previously connected to the excitation circuitry are connected to the detection circuitry and the electrodes previously connected to the detection circuitry are connected to the excitation circuitry;
  • Figure 10 is a block diagram illustrating excitation and detection circuitry that can be used to drive the electrodes in the inverted manner illustrated in Figure 9;
  • Figure 11 is a block diagram illustrating an alternative arrangement of the excitation and detection circuitry that can be used to drive the electrodes shown in Figure 2 in the inverted manner illustrated in Figure 9;
  • Figure 12 is a block diagram illustrating the excitation and detection circuitry that can be used in a further alternative for driving the electrodes shown in Figure 2 in the inverted manner illustrated in Figure 9;
  • Figure 13 is a signal and circuit diagram illustrating in more detail the way in which the circuitry shown in Figure 12 operates to generate a signal whose phase varies with the position being measured;
  • Figure 14 is a block diagram illustrating the excitation and detection circuitry that can be used in a further alternative for driving the electrodes shown in Figure 2 in the inverted manner illustrated in Figure 9;
  • Figure 15 which comprises Figures 15A to 15D 5 illustrates the way in which the excitation pulse trains are generated by the excitation circuitry shown in Figure 14;
  • Figure 16 which comprises Figures 16A to 16H, illustrates the effects of offsets in the measurements on calculated phase angles and hence on detected positions
  • Figure 17 illustrates an alternative set of electrodes that can be used in place of the electrodes illustrated in Figure 2;
  • Figure 18 is an electrical equivalent circuit illustrating one way to connect the electrodes shown in Figure 17 to excitation and detection circuitry used to detect the liquid level;
  • Figure 19 is an electrical equivalent circuit illustrating an alternative way of connecting the electrodes shown in Figure 17 to the excitation and detection circuitry, in which the electrodes previously connected to the excitation circuitry are connected to the detection circuitry and the electrodes previously connected to the detection circuitry are connected to the excitation circuitry;
  • Figure 2OA is a plot illustrating the way in which one of the signals obtained from the electrodes shown in Figure 17 varies with the liquid level;
  • Figure 2OB is a plot illustrating the way in which a second one of the signals obtained from the electrodes shown in Figure 17 varies with the liquid level;
  • Figure 2OC is a plot illustrating the locus of points obtained by plotting the two signals obtained from the electrodes against each other for different liquid levels
  • Figure 21 which comprises Figures 21 A to 2 IH, illustrates the effects of offsets in the measurements obtained using the electrodes illustrated inn Figure 17 on calculated phase angles and hence on detected positions;
  • FIG 22A schematically illustrates the form of an alternative electrode assembly that can be used to sense position instead of the electrodes illustrated in Figure 17;
  • Figure 22B is a cross section along the line A-A of the electrode assembly illustrated in Figure 22A;
  • Figure 23 A is a plot illustrating the way in which one of the signals obtained from the electrodes shown in Figure 22 varies with the liquid level
  • Figure 23B is a plot illustrating the way in which a second one of the signals obtained from the electrodes shown in Figure 22 varies with the liquid level
  • Figure 23 C is a plot illustrating the locus of points obtained by plotting the two signals obtained from the electrodes shown in Figure 22 against each other for different liquid levels;
  • Figure 23D is an error plot between the measured phase and the corresponding liquid level, illustrating a non-linearity of the sensor
  • Figure 24A is a plot illustrating the locus of points obtained by plotting the two signals obtained from the electrodes shown in Figure 22 against each other for different liquid levels and for two liquids having different dielectric constants;
  • Figure 24B illustrates a phase difference plot obtained for the electrodes illustrated in Figure 22, when two different liquids having different dielectric constants surround the electrodes;
  • Figure 24C illustrates a phase difference plot obtained when a first offset is introduced into the sensor illustrated in Figure 22;
  • Figure 24D illustrates a phase difference plot obtained when a second offset is introduced into the sensor illustrated in Figure 22;
  • Figure 25A schematically illustrates an alternative sensor in which the electrodes shown in Figure 22 are mounted on a layer of plastic
  • Figure 25B is a cross section along the line A-A of the electrode assembly illustrated in Figure 25A;
  • Figure 26A is a plot illustrating the locus of points obtained by plotting the two signals obtained from the electrodes shown in Figure 25 against each other for different liquid levels and for two liquids having different dielectric constants;
  • Figure 26B is a plot illustrating the difference in the measured phase obtained over the measurement range for the two different liquids plotted in Figure 26A;
  • Figure 27A illustrates a further alternative sensor in which the electrodes illustrated in Figure 22 are embedded within a layer of plastic
  • Figure 27B is a cross section along the line A-A of the electrode assembly illustrated in Figure 27A;
  • Figure 28 schematically illustrates the form of an alternative set of electrodes that can be used to sense position instead of the electrodes illustrated in Figure 2;
  • Figure 29A is a plot illustrating the way in which one of the signals obtained from the electrodes shown in Figure 28 varies with the liquid level;
  • Figure 29B is a plot illustrating the way in which a second one of the signals obtained from the electrodes shown in Figure 28 varies with the liquid level;
  • Figure 29C is a plot illustrating how the measured phase obtained using the signals illustrated in Figures 27A and 27B varies with the liquid level;
  • Figure 3OA schematically illustrates the form of an alternative set of electrodes that can be used to sense position instead of the electrodes illustrated in Figure 2;
  • Figure 3OB is a cross section along the line A-A of the electrode assembly illustrated in Figure 3OA;
  • Figure 31 schematically illustrates the form of an alternative set of electrodes that can be used to sense position instead of the electrodes illustrated in Figure 2;
  • Figure 32 schematically illustrates one way in which the electrodes illustrated in Figure 31 may be connected to excitation circuitry and detection circuitry of the sensor.
  • the embodiments of the invention enable the detection of the spatial position of an inhomogeneity in the dielectric constant (permittivity) in the space around a sensor.
  • the sensor can be used to detect the position of the interface between a liquid (or other fiowable material such as grain or powder) and the air, the position and displacement of a dielectric or a metallic object adjacent to the sensor, the movement of an air bubble inside a liquid (e.g. in a level gauge), etc.
  • FIG 2 schematically illustrates a capacitive liquid level sensor head 101 that is based on the sensor shown in Figure 1, except it includes two symmetrically arranged (back to back) sets of electrodes that are used for sensing the level of the liquid 103 within the container (not shown).
  • the electrodes of the first set 21 are positioned to the left of a vertical axis of symmetry that lies parallel to the measurement path of the sensor and the second set 23 are positioned to the right of this axis of symmetry.
  • the first set of electrodes 21 includes three electrodes 9, 11 and 12 which are connected to the excitation and processing electronics 22 via terminals 1 * to 4* and A* on the connection interface 20.
  • the second set of electrodes 23 also includes three electrodes 10, 15 and 16 which are connected to the excitation and processing electronics 22 via terminals 5* to 8* and B* on the connection interface 20. Electrodes 9 and 10 extend over the entire depth of the container (defined between levels O and Q); electrodes 12 and 16 extend over an operating range of the sensor (defined between levels P and Q); and electrodes 11 and 15 extend over an inoperative range or dead zone (defined between levels O and P) of the sensor. Both electrodes 11 and 12 are positioned adjacent and form capacitors with electrode 9 and similarly electrodes 15 and 16 are positioned adjacent and form capacitors with electrode 10. As shown, the electrodes of the first set 21 are positioned to the left of a vertical axis of symmetry that lies parallel to a measurement path of the sensor and the electrodes of the second set 23 are positioned to the right of this axis of symmetry.
  • connection interface 20 includes a pair of reference capacitors C 11 and C 12 which are connected between terminals A* and 2* and 4* respectively.
  • reference capacitor C 11 is provided to (try to) nullify the dry capacitance (i.e. in the absence of any liquid in the container) of the capacitor formed by electrodes 9 and 11.
  • reference capacitor C 12 is provided to (try to) nullify the dry capacitance of the capacitor formed by the electrodes 9 and 12.
  • a similar pair of reference capacitors C 15 and C 16 is also provided on the connection interface 20 between terminals B* and 6* and 8* respectively.
  • Reference capacitor Ci 5 is provided to nullify the dry capacitance of the capacitor formed by electrodes 10 and 15 and reference capacitor C 16 is provided to nullify the dry capacitance of the capacitor formed by electrodes 10 and 16.
  • Figure 3 schematically illustrates the way in which the two sets of electrodes 21 and 23 are connected, in this embodiment, to excitation circuitry 24 and detection circuitry 26 within the excitation and processing electronics 22 via the connection interface 20.
  • the excitation circuitry 24 is operable to apply a positive excitation voltage (+V 1 ) to electrode 9 and to the two reference capacitors C 11 and C 12 ; and to apply a negative excitation voltage (-V 2 ) to electrode 10 and to the two reference capacitors C 15 and C 16 .
  • electrode 11 and reference capacitor C 11 are connected to a first differential amplifier circuit 68 "1 of the detection circuitry 26.
  • the capacitance of capacitor C 11 is chosen so that in the absence of any liquid in the container, the two signals input to the amplifier circuit 68 "1 will be the same and will therefore cancel each other out. However, in the presence of the liquid, the signal obtained from electrode 11 will be different to that obtained from reference capacitor C 11 and as a result a signal will be output from amplifier 68 ⁇ l .
  • electrode 12 and reference capacitor C 12 are connected to differential amplifier circuit 68 "2 ; electrode 15 and reference capacitor C 15 are connected to differential amplifier circuit 68 ⁇ 3 ; and electrode 16 and reference capacitor C 16 are connected to differential amplifier circuit 68 ⁇ 4 .
  • the output from amplifier circuit 68 '3 is subtracted from the output from amplifier circuit 68 '1 by differential amplifier circuit 68 "5 to generate a first output signal V 1 .
  • the first output signal (V 1 ) will therefore vary with the capacitive coupling between electrodes 11 and 9 and 15 and 10.
  • the excitation signal applied to electrode 9 is of opposite polarity to the excitation signal applied to electrode 10, this will mean that the first output signal
  • V 1 will represent the sum of the capacitive couplings between electrodes 11 and 9 and electrodes 15 and 10.
  • the output from amplifier circuit 68 A is subtracted from the output from amplifier circuit 68 '2 by differential amplifier circuit 68 ⁇ 6 to generate a second output signal V ⁇ .
  • the second output signal (V 11 ) will therefore represent the sum of the capacitive couplings between electrodes 12 and 9 and electrodes 16 and 10.
  • electrodes 11 and 15 and 12 and 16 are symmetrically arranged (with mirror symmetry) along the sensor, the signals obtained from these electrodes will vary in the same way as the level of the liquid 103 varies within the container. Therefore, twice the signal levels will be obtained compared to the signal levels obtained from the sensor design of Figure 1. Further, because of the differential combination of the signals obtained from the electrodes, any common mode signals will be removed such as might occur in a noisy environment.
  • FIGS 4A and 4B illustrate the way in which these two output signals V 1 and V ⁇ vary with the level (x) of the liquid 103 in the container.
  • the two output signals are at zero.
  • the capacitive coupling between electrodes 9 and 11 and electrodes 10 and 15 will increase approximately linearly whilst the capacitive coupling between electrodes 9 and 12 and electrodes 10 and 16 will remain constant. Therefore, as the level of liquid in the container increases between levels O and P the first output signal (V 1 ) will increase linearly and the second output signal (V 11 ) will remain at zero.
  • the capacitive coupling between electrodes 9 and 11 and electrodes 10 and 15 will remain constant whilst the capacitive coupling between electrodes 9 and 12 and electrodes 10 and 16 will vary linearly. Therefore, between levels P and Q, the first output signal (V 1 ) will remain constant and the second output signal will increase linearly.
  • the detection circuitry 26 can then determine the level of the liquid in the container using a ratiometric calculation of the first and second output signals.
  • a ratiometric calculation of the first and second output signals There are various different ratiometric calculations that can be performed, but in the preferred embodiments the value of a phase angle is determined between V 1 and V ⁇ that monotonically varies with the level of the liquid in the container between levels P and Q.
  • This phase angle is illustrated in Figure 4C, which is a plot of V 1 against V ⁇ . As illustrated in Figure 4C, the phase angle ( ⁇ ) varies from zero degrees when the level of the liquid is at level P to approximately sixty degrees when the level of the liquid is at level Q.
  • This phase angle can be determined from:
  • the determined phase angle is then mapped, using an appropriate lookup table, to the actual liquid level which is then displayed on the level signal display 44.
  • amplitude and phase thresholds are used so that no phase measure is output until the signal amplitude is above the amplitude threshold and the determined phase angle is above the phase threshold.
  • the amplitude threshold is illustrated in Figure 4C by the dotted circle 29 and the phase threshold is defined by the arc 28 labelled ⁇ *.
  • the sensor design described above allows simple and cheap excitation and processing electronics 22 to be used to excite the electrodes and to process the two output signals to determine the liquid level in the container.
  • FIG. 5 is a block diagram illustrating one form of the excitation circuitry 24 and the detection circuitiy 26 that can be used with the sensor head 101 shown in Figure 2.
  • the capacitive sensor can operate over a range of excitation frequencies.
  • mutual capacitances are rather small and so the impedance of the sets of electrodes connected to the connection interface 20 will be relatively large. It is therefore preferable to operate at frequencies above IMHz or even 1 OMHz, in order to decrease the value of the impedance associated with these mutual capacitances.
  • the excitation circuitry 24 can generate and apply AC excitation signals to electrodes 9 and 10. However, this is not the most preferable option as this requires the use of expensive electronics and especially expensive differential amplifier circuits 68.
  • a pulse generator 60 that generates square form pulses of excitation signal (having a pulse width of the order of several hundred nanoseconds) with sharp rising and falling fronts (having widths of the order of several nanoseconds).
  • Fast fronts of the excitation pulses correspond to the equivalent frequency of tens of MHz.
  • the pulses of the drive voltages can have amplitudes in the range 0.1 V to 10V.
  • the pulse repetition frequency that is used is less important as it only affects the overall signal levels that will be processed by the detection circuitry 26. Therefore, in order to minimise power consumption of the sensor, the pulse repetition frequency should be set to the minimum necessary to obtain the required level of signal to noise ratio for the measurements to be made.
  • the pulsed excitation signal 31 generated by the pulse generator 60 is applied to terminal A* of the connection interface 20 (and thus corresponds to +V 1 ) and is applied to an invertor 32 for generating an inverted version 33 of the pulsed excitation signal which is applied to terminal B* of the connection interface 20 (and thus corresponds to -V 2 ).
  • V 1 and V 2 it is not essential for V 1 and V 2 to have the same magnitude, and therefore an inexpensive invertor circuit 32 can be used.
  • the non-inverted pulsed excitation signal 31 (+Vi) is applied to electrode 9 and the inverted pulsed excitation signal 33 (-V 2 ) is applied to electrode 10.
  • FIG 5 shows the differential amplifier circuits 68 '1 to 68 "6 forming part of the detection circuitry 26.
  • the signals obtained from the terminals of the connection interface 20 are connected to the corresponding differential amplifier 68 through respective switches 62 "1 to 62 “8 which are all opened and closed in synchronism with the pulses of the excitation signal 31.
  • each of the differential amplifier circuits 68 includes a storage capacitor 64 (on which voltages from the corresponding terminals are accumulated which will vary slowly over time reflecting the movement of the liquid level along the length of the sensor head 101) and a differential amplifier 66.
  • the signals (V 1 and V ⁇ ) output from the differential amplifiers 68 "5 to 68 “6 are applied to a ratiometric calculator 40 which determines the position (x) of the liquid level using the above arctangent function.
  • This calculation may be performed using a microprocessor.
  • microprocessors are expensive and therefore, in this embodiment, the ratiometric calculator 40 uses analogue processing techniques to generate a value that continuously varies with the liquid level (x).
  • Figure 6 is a block diagram illustrating the way in which the ratiometric calculator 40 performs the calculation in this embodiment.
  • the ratiometric calculator 40 includes a low frequency generator 48 that generates a low frequency (of the order of a few kHz) periodic signal.
  • This low frequency periodic signal is applied directly to a first amplitude modulator 50 "1 and a 90 degree phase shifted version of the low frequency periodic signal is applied to a second amplitude modulator 50 "2 .
  • the 90 degree phase shift is obtained by passing the low frequency periodic signal though a 90 degree phase shifter 52.
  • the amplitude modulator 50 "1 amplitude modulates the received low frequency periodic signal with the first output signal (V 1 ) obtained from the differential amplifier circuit 68 '5 ; and the amplitude modulator 50 '2 amplitude modulates the phase shifted low frequency periodic signal with the second output signal (V 11 ) obtained from the differential amplifier circuit 68 '6 .
  • the two amplitude modulated signals output from the amplitude modulators 50 are then added together by an adder 54.
  • the output from the adder 54 can therefore be represented (approximated) by:
  • f is the frequency of the low frequency periodic signal generated by the generator 48, which can be rewritten as:
  • A is a normalised amplitude term defined by:
  • the output from the adder 54 includes a sinusoidal signal at the low frequency (f) whose phase is proportional to the ratiometric arctangent function defined in equation (1) given above. Therefore, in this embodiment, the ratiometric calculator 40 calculates equation (1) by using a phase detector 56 to detect the phase of this signal output from the adder 54 relative to the low frequency signal generated by the low frequency generator 48. The output of the phase detector 56 will therefore be a value that continuously changes with the level of the liquid within the container.
  • the peak amplitude (A) of the signal output from the adder 54 is compared with a threshold value by the amplitude threshold detector 55 and the signal obtained from the adder 54 is only passed to the phase detector (through switch 57) when the detector 55 determines that the peak amplitude (A) is above the threshold value.
  • the phase detector is arranged so that it does not output a phase measurement until the phase is greater than the phase threshold.
  • FIG. 7A is a block diagram illustrating the main components of the phase detector 56 used in this embodiment.
  • the AC signal 41 from the adder 54 is amplified by an amplifier 42 and then input to a first comparator 43 "1 where it is compared with a threshold voltage.
  • the AC signal 45 from the low frequency generator 48 is input to a phase shifter 58 which phase shifts the reference signal 45 by the above described phase threshold, to generate a phase shifted signal 59 which is input to a second comparator 43 "2 where it is also compared with the same threshold voltage.
  • the phase detector 56 will automatically apply the desired phase thresholding discussed above.
  • the square wave signals 46 "1 and 46 "2 output by the comparators 43 are shifted in time relative to each other by a value ⁇ t corresponding to the phase shift between AC signal 41 and AC signal 59.
  • the two square wave signals 46 are input to a logic circuit for zero crossing detection 47 which generates a pulse width modulated sequence of pulses 51 whose pulse width depends upon the time delay ⁇ .
  • this pulse width modulated signal 51 is input to a PWM/DC converter 53 which converts this pulse train into a DC value which monotonically varies with the value of ⁇ and hence with the phase shift between the AC signal 41 and the AC signal 45.
  • Figure 7B illustrates the logic circuit 47 used in this embodiment for the zero crossing detection.
  • the logic circuit 47 is formed from two AND gates 63 '1 and 63 "2 connected so that the output of each AND gate feeds into the input of the other.
  • FIG. 7C illustrates how the pulse duration of the PWM signal 51 output from the detection circuit varies with the time delay ⁇ . As shown, no PWM signal will be output until the time delay ( ⁇ ) reaches T ⁇ */2 ⁇ , which corresponds to the phase threshold ( ⁇ *). From this point, the pulse width of the PWM signal varies linearly with the time delay ( ⁇ ).
  • the logic circuit 47 automatically performs the desired phase thresholding. This will also be the case if the phase shift is applied to the measured signal instead of the reference signal 45. What is important is to introduce an appropriate relative phase shift between the phase of the reference signal 45 and the phase of the measured signal 39. This may be achieved through the use of the phase shifter 58 or by the provision of a suitable signal generator that can generate the suitably shifted reference signal 59.
  • phase measure determined by the phase detector 56 will vary monotonically with the level of the liquid in the container.
  • the phase measure is, as shown in Figure 5, applied to a lookup table 42 which is determined in advance during a calibration routine.
  • the thus determined liquid level is then input to the level signal display 44, which displays the determined level of the liquid 103 within the container.
  • the signal input to the positive terminal of amplifier circuit 68 '1 is the signal (VE 1 1 ) obtained from electrode 11 plus the signal (Vc 15 ) obtained from the reference capacitor C 15 ; and the signal input to the negative terminal of amplifier circuit 68 “1 is the signal (Vc ⁇ ) obtained from the reference capacitor C 11 plus the signal (VBIS) obtained from electrode 15. Therefore, the output from amplifier 68 "1 will be (VEII+V C I S MVCII+VEI S ). Rearranging this gives (VEI 1 -V C1 O-(VE 15 -VC 15 ), which is the same output obtained from amplifier circuit 68 "5 shown in Figure 3.
  • V 1 and V 2 have opposite polarity
  • VE ⁇ will have opposite polarity to Va 5 and Vc 11 will have opposite polarity to V E15 .
  • V E15 the addition of these signals results in a significant reduction of common mode signals before they are applied to the amplifier circuits 68.
  • the most reduction occurs when the magnitudes of V 1 and V 2 are the same. Therefore, in this embodiment as common mode signals are significantly reduced before being applied to the amplifier circuits 68, less expensive amplifier circuits 68 can be used.
  • the excitation signals (+V 1 and -V 2 ) were applied to electrodes 9 and 10 respectively and the signals obtained from the electrodes 11, 12, 15 and 16 were connected to the detection circuitry 26.
  • the roles of these electrodes can be exchanged so that the electrodes 11, 12, 15 and 16 are connected to the excitation circuitry 24 and the electrodes 9 and 10 are connected to the detection circuitry 26.
  • One way of doing this is illustrated schematically in the electrical equivalent circuit shown in Figure 9.
  • the excitation signal +V 1 is applied in a first period (I) to electrodes 11 and 15 and subsequently in a second period (II) to electrodes 12 and 16; and the excitation signal -V 2 is applied in the first period (I) to reference capacitors C 11 and C 15 and subsequently in a second period (II) to reference capacitors C 12 and C 16 .
  • the switching between the first and second periods is controlled by the switches 72 "1 to 72 "4 .
  • the two signals obtained from terminals A and B are then subtracted in the differential amplifier circuit 68 to obtain V 1 in the first period and V ⁇ in the second period.
  • the remaining processing can be the same as in the first embodiment and a further description will be omitted.
  • Figure 10 illustrates an alternative arrangement of the excitation and processing electronics 22 that can be used with the sensor shown in Figure 2 and when operated in the inverted manner discussed above.
  • the pulse generator 60 generates a train of voltage pulses 31 "1 , each pulse having a similar pulse shape and duration as the pulses generated by the pulse generator 60 described with reference to Figure 5.
  • the pulse train 31 "1 is also applied to an invertor 32 "1 to generate an inverted pulse train 33 '1 .
  • the pulse train 31 " Ms also applied to a time shifter 74 to generate a pulse train 31 "2 that is time shifted relative to the pulse train 31 "1 .
  • This time shifted pulse train 31 "2 is also applied to an invertor 32 "2 to generate the inverted pulse train 33 ⁇ 2 .
  • pulse train 31 "1 is applied to terminals 1* and 6* of the connection interface 20;
  • pulse train 33 "1 is applied to terminals 2* and 5* of the connection interface 20;
  • pulse train 31 "2 is applied to terminals 3* and 8* of the connection interface 20;
  • pulse train 33 '2 is applied to terminals 4* and 7* of the connection interface 20.
  • the pulses will be applied to the appropriate electrodes in the desired time multiplexed manner.
  • terminal A* of the connection interface 20 is connected to switch 62 "1 and to switch 62 “3 and terminal B* of the connection interface 20 is connected to switch 62 '2 and switch ⁇ 2 ⁇ .
  • Switches 62 "1 and 62 “2 are opened and closed in synchronism with the pulses of the pulse train 31 "1 and the switches 62 "3 and 62 “4 are opened and closed in synchronism with the pulses of the time shifted pulse train 31 "2 .
  • the voltage accumulated on storage capacitor 64 "1 will vary slowly over time reflecting the level of the liquid relative to electrodes 11 and 15, whilst the voltage accumulated on storage capacitor 64 "2 will vary slowly over time reflecting the level of the liquid relative to the sets of electrodes 12 and 16.
  • the voltages accumulated on the storage capacitors 64 are amplified by differential amplifiers 66 '1 and 66 ⁇ 2 to generate the above described output voltages V 1 and V ⁇ , which are applied to the ratiometric calculator 40 as before.
  • the remaining processing of the detection circuitry 26 is the same as the processing performed in the embodiment described with reference to Figure 5 and will not, therefore, be described again.
  • FIG 11 is a block diagram illustrating alternative excitation and the detection circuitry 22 that can be used when the electrodes shown in Figure 2 are connected in the inverted manner illustrated in Figure 9.
  • the excitation circuitry 24 includes a signal generator 30, which generates an AC excitation signal 31 "1 .
  • a first invertor 32 "1 is provided for providing an inverted excitation signal 33 '1 .
  • the excitation circuitry 24 also includes a 90 degree phase shifter 52, which applies a 90 degree phase shift to the excitation signal 31 " Mo generate a phase shifted excitation signal 31 "2 .
  • This phase shifted excitation signal 31 "2 is also applied to an invertor 32 "2 to generate an inverted and phase shifted excitation signal 33 " .
  • the excitation signal 31 "1 is applied to terminals 1* and 6* of the connection interface 20; the inverted excitation signal 33 “1 is applied to terminals 2* and 5* of the connection interface 20; the phase shifted excitation signal 31 "2 is applied to terminals 3* and 8* of the connection interface 20; and the inverted and phase shifted excitation signal 33 "2 is applied to terminals 4* and 7* of the connection interface 20.
  • the excitation circuitry 24 used in this embodiment is therefore equivalent to the excitation circuitry shown in Figure 10, except the pulsed excitation signals are replaced with suitably phase shifted AC excitation signals.
  • a differential amplifier 68 of the detection circuitry 26 is connected to terminals A* and B* of the connection interface 20.
  • the output from the differential amplifier 34 can be represented by equation (2) or (3) given above, where f is the frequency of the excitation signals.
  • the output from the differential amplifier 68 includes a sinusoidal signal whose phase varies with the ratiometric arctangent function given in equation (1) above.
  • the amplitude of the signal output from the differential amplifier 68 is compared against the amplitude threshold by the detector 55 and, provided its amplitude is above the threshold, it is applied to the phase detector 56, which measures the phase of this signal relative to the phase of the AC excitation signal 31 "1 .
  • the remaining processing carried out by the detection circuitry 26 is the same as in the other embodiments described above and will not, therefore, be described again.
  • FIG 12 is a block diagram illustrating a further example of the excitation and detection circuitry that can be used when the electrodes shown in Figure 2 are connected in the inverted manner illustrated in Figure 9.
  • pulse width modulated pulse trains are used as excitation signals.
  • the excitation circuitry 24 includes a pulse generator 60 that is arranged to generate a high frequency periodic pulse train 61, the pulses of which have relatively fast rising and falling fronts (of the order of several nanoseconds) and a relatively long pulse period (of the order of several hundred nanoseconds).
  • the excitation circuitry 24 also includes a low frequency generator 48 that is arranged to generate a low frequency modulation signal 49 having a frequency of the order of several kHz.
  • the pulse train 61 generated by the pulse generator 60 and the low frequency modulation signal 49 are applied to a modulator 82 "1 which uses the low frequency modulation signal 49 to pulse width modulate the pulse train 61, to generate a pulse width modulated pulse train 84.
  • the pulse width modulated pulse train 84 is applied to terminals 1* and 6* of the connection interface 20 and is also applied to an invertor 32 '1 .
  • the inverted pulse train generated by the invertor 32 '1 is then applied to terminals 2* and 5* of the connection interface 20.
  • the low frequency modulation signal 49 generated by the low frequency generator 48 is also applied to a 90 degree phase shifter 52 that applies a 90 degree phase shift to the modulation signal 49.
  • the 90 degree phase shifted version of the modulation signal 49 is then applied to a pulse width modulator 82 '2 where it is used to pulse width modulate pulse train 61 generated by the pulse generator 60.
  • Figure 12 illustrates the pulse width modulated signal 86 output from the modulator 82 "2 . As shown, the pulse width modulated signal 86 is applied to terminals 3* and 8* of the connection interface 20 and is also applied to a second invertor 32 "2 . The inverted version of the pulse width modulated signal 86 is then applied to terminals 4* and 7* of the connection interface 20.
  • both terminals A* and B* of the connection interface 20 are connected to the two switches 62 “1 and 62 “2 .
  • the position of the switches 62 are switched in synchronism with the rising and falling edges of the pulses in the pulse train 61 '1 obtained by phase shifting the pulse train 61 by 90 degrees using the phase shifter 52.
  • the signal obtained from terminal A* is passed through one of the switches 62 "1 and 62 “2 and the signal obtained from terminal B* is passed through the other one of the switches 62 "1 and 62 ⁇ 2 .
  • the signals from switches 62 '1 and 62 "2 are then filtered and differentially amplified by the amplifier and filter circuitry 71.
  • both terminals A* and B* are coupled to ground through capacitors 64 "1 , 64 "2 , 64 “3 and 64 “4 .
  • high frequency components of the currents I 1 and I 2 are shorted to ground through a small impedance.
  • low frequency variations of the currents I 1 and I 2 (such as caused by the low frequency modulation of the excitation signals by the low frequency modulation signal 49) marked as I and I on Figure 13, are further amplified and combined by the circuitry 71.
  • the output current (Z 1 ) 73 from the circuitry 71 will become proportional to the difference in the currents I ⁇ and I ⁇ with simultaneous rejection of any common mode signals.
  • the circuit 71 will also remove signals due to resistive coupling between the electrodes caused by the liquid being conductive. This is because the capacitively coupled signals will be 90 degrees out of phase with the excitation signal (and hence are in phase with the switching signal 61 "1 ) whereas the resistively coupled signals will be in phase with the excitation signal (and hence 90 out of phase with the switching signal 61 "1 ). Consequently, the resistive coupling signals obtained at terminals A* and B* will also be removed as the output signal is proportional to the difference in the currents I ⁇ and I .
  • the output from the filter and amplification circuitry 71 can therefore also be approximated by equation (3) above, with the frequency f corresponding to the frequency of the low frequency modulation signal 49.
  • the amplitude of this signal is above the amplitude threshold (as determined by the detector 55) then it is input to the phase detector 56 which measures the phase of this signal relative to the phase of the low frequency modulation signal 49 generated by the low frequency generator 48.
  • the rest of the detection circuitry 26 used in this embodiment is the same as used in the previous embodiments and therefore a further description will not be given.
  • Figure 14 is a block diagram illustrating a further example of the excitation and detection circuitry that can be used when the electrodes shown in Figure 2 are connected in the inverted manner illustrated in Figure 9.
  • the excitation circuitry 24 comprises a signal generator 65 (which may be a memory) which generates the desired excitation signals in response to being clocked by the clock 63.
  • the desired excitation signals have the same form as the low frequency modulated PWM signals 84 and 86 used in the embodiment described above with reference to Figure 12.
  • the signal generator 65 generates: the PWM signal 84 which it applies to resistor R 1 ; the inverse of PWM signal 84 which it applies to resistor R 3 ; the PWM signal 86 which it applies to resistor R 4 ; and the inverse of PWM signal 86 which it applies to resistor R 6 .
  • Figures 15A and 15B illustrate in more detail part of the signals applied across resistors R 1 and R 3 and the resulting voltages V 1 and V 2 that are applied to terminals 1* and 6* and 2* and 5* of the connection interface 20 respectively.
  • the signal applied to terminals 1* and 6* varies between voltages Vj 1 and Vi 2 and the signal applied to terminals 2* and 5* varies between voltages V 2 1 and V 2 2 .
  • the voltages applied to terminals 1*, 2*, 5* and 6* therefore always have a different magnitude from each other.
  • this is similarly true of the voltages V 3 1 , V 3 2 , V 4 1 and V 4 2 that are applied to terminals 3* and 8* and 4* and 7* respectively.
  • electrode 11 and capacitor C 15 will be energised by voltage V 1 ; electrode 15 and capacitor Cn will be energised by voltage V 2 ; electrodel2 and capacitor C 16 will be energised by voltage V 3 ; and electrode 16 and capacitor C 12 will be energised by voltage V 4 .
  • the effective excitation occurs when the pulses transition between from a low value to a high value (corresponding to a positive excitation) and when the pulses transition from a high value to a low value (corresponding to a negative excitation), with the amplitude of the excitation being defined by the size of the step change between the low and high values.
  • the signal that will be obtained at terminal A* by applying V 1 to terminal 1 * can be represented by:
  • AV 1 is the step change between levels V 1 1 and V 1 2 and E 11 represents the capacitive coupling between electrodes 11 and 9.
  • a positive signal will be obtained when the transition is from V 1 2 to V 1 1 and a negative signal will be obtained when V 1 transitions from V 1 1 to V 1 2 .
  • the signal that will be obtained at terminal B* by applying V 1 to terminal 6* can be represented by:
  • C 15 represents the capacitive coupling through reference capacitor C 15 .
  • ⁇ V 2 is the step change between levels V 2 1 and V 2 2 and C 11 represents the capacitive coupling through reference capacitor C 11 .
  • a positive signal will be obtained when the transition is from V 2 1 to V 2 2 and a negative signal will be obtained when V 2 transitions from V 2 2 to V 2 1 .
  • the signal that will be obtained at terminal B* by applying V 2 to terminal 5* can be represented by: ⁇ AV 2 E 15 (8)
  • E 15 represents the capacitive coupling between electrodes 10 and 15.
  • V 1 transitions from a high value to a low value
  • V 2 transitions from a low value to a high value and vice versa.
  • the signal output from the differential amplifier circuit 71 (due to V 1 and V 2 ) at the transitions of signals V 1 and V 2 can be represented by:
  • each of the terms in the brackets performs the desired dry value compensation, to leave a signal of the form:
  • the pulses of V 1 and V 2 are PWM modulated by a low frequency signal. Therefore, the signal obtained from circuit 71 as a result of applying voltages V 1 and V 2 can be represented by:
  • the total signal output from circuit 71 is therefore the sum of equations (11) and (12).
  • ⁇ V 12 ⁇ V 34 , the result is a signal in the form of equation (3) above.
  • ⁇ V 12 can be made to equal ⁇ V 34 by appropriate selection of the values of resistors R 1 to R 6 .
  • ⁇ V 12 is given by:
  • ⁇ Vi 2 can be made equal to ⁇ V 34 by making resistors R 2 and R 5 equal and by making (R ⁇ R 3 ) equal (R 4 H-R 6 ).
  • the amplitude of the signal output from the circuit 71 is compared with the amplitude threshold by the amplitude detector 55 and if it is above the threshold, the signal is passed through switch 57 to two phase detectors 56 "1 and 56 ⁇ 2 .
  • the phase of the PWM modulated signals Vi and V 2 is changed by 180 degrees during the measurement process.
  • phase measurements obtained from the two phase detectors 56 are then passed through low pass filters 69 "1 and 69 ⁇ 2 (which effectively act as memories) and subtracted from each other by the differential amplifier 66 "3 .
  • this subtraction results in the addition of the desired phase measures whilst removing common phase offsets introduced by the electronics.
  • the phase measure is then applied to the lookup table 42 as before to determine the corresponding liquid level which is displayed to the user on the display 44.
  • each measurement electrode (11, 12, 15 and 16) requires its own separate dry value reference capacitor.
  • These reference capacitors are mounted on the connection interface 20 and are formed using different manufacturing processes to the capacitors formed by the measurement electrodes. As a result of the different manufacturing processes, the reference capacitors will have different temperature characteristics than the capacitors formed by the measurement electrodes (11, 12, 15 and 16) and therefore, they will not make the desired dry capacitance cancellation in all operating conditions. This leads to phase offsets and hence errors in the measurement results. As will be described below, in some situations these phase offsets can lead to significant errors in the measurement results. A more detailed description of this offset problem will now be described with reference to Figure 16.
  • Figure 16A shows, the desired or expected locus plot 76 and the actual locus plot 77 obtained if the dry capacitance of reference capacitors Cu and/or Ci 5 do not cancel out with the dry capacitance of the capacitors formed by the electrodes 9 and 11 and 10 and 15 respectively, and as a result the first output signal V 1 is reduced by ⁇ V 1 .
  • Figure 16B illustrates the resulting phase error plot as the liquid level is varied from levels O to Q. As can be seen, as the liquid level rises up the container, no phase error ( ⁇ 0 ) is introduced until some unknown level Wi when the measured phase angle exceeds the phase threshold ( ⁇ *).
  • FIGs 16C and 16D illustrate the situation when the dry capacitance of reference capacitors C 11 and/or C 15 do not cancel out with the dry capacitance of the capacitors formed by the electrodes 9 and 11 and 10 and 15 respectively, and as a result the first output signal V 1 is increased by ⁇ V 1 .
  • no phase error ( ⁇ 0 ) is introduced until the level W 2 corresponding to the level when the phase angle is expected to exceed the phase threshold ( ⁇ *).
  • FIGs 16E and 16F illustrate the situation when the dry capacitance of reference capacitors C 12 and/or C 16 do not cancel out with the dry capacitance of the capacitors formed by the electrodes 9 and 12 and 10 and 16 respectively, and as a result the second output signal V ⁇ is reduced by ⁇ V ⁇ .
  • no phase error ( ⁇ 0 ) is introduced until the level W 2 corresponding to the level when the phase angle is expected to exceed the phase threshold ( ⁇ *).
  • FIGS 16G and 16H illustrate the situation when the dry capacitance of reference capacitors C 12 and/or C 16 do not cancel out with the dry capacitance of the capacitors formed by the electrodes 9 and 12 and 10 and 16 respectively, and as a result the second output signal V ⁇ is increased by ⁇ V ⁇ .
  • phase error As shown, in this situation, as the liquid level rises up the container beyond level O, no phase error ( ⁇ 0 ) is introduced until the amplitude of the measured signals exceed the amplitude threshold (V A° - as represented by the circle 29) at level Y. As shown in Figures 16G, at this level the measured phase jumps to a relatively large phase ( ⁇ e ⁇ - o r), corresponding to a phase error of ( ⁇ erro r- ⁇ *). As shown in Figure 16H, as the liquid level increases further towards level P, this phase error will reduce. As the liquid level increases beyond level P, however, the phase error will rise again until the level W 2 corresponding to the level when the phase angle is expected to exceed the phase threshold ( ⁇ *).
  • Figure 17 schematically illustrates an alternative capacitive liquid level sensor head 101 that is based on the sensor shown in Figure 2, except that the dry value reference capacitors for the main measurement electrodes (12 and 16) have been incorporated into the electrode structure.
  • the sensor includes two symmetrically arranged (back to back) sets of electrodes 21 and 23.
  • the first set of electrodes 21 includes five electrodes 9, 11, 12, 13 and 14 which are connected to the excitation and processing electronics 22 via terminals 1* to 4* and A* on the connection interface 20.
  • the second set of electrodes 23 also includes five electrodes 10, 15, 16, 17 and 18 which are connected to the excitation and processing electronics 22 via terminals 5* to 8* and B* on the connection interface 20.
  • electrodes 9 and 10 are 'L' shaped with the long side extending over the entire depth of the container (defined between levels O and S). Electrodes 12, 13 and 14 and electrodes 16, 17 and 18 extend over the operating range of the sensor (defined between levels P and S); and electrodes 11 and 15 extend transverse to the measurement direction adjacent the shorter side of electrodes 9 and 10 respectively.
  • the inoperative range or dead zone (defined between levels O and P) of the sensor is much smaller than that of the sensor illustrated in Figure 2.
  • Electrodes 11, 12, 13 and 14 are positioned adjacent and form capacitors with electrode 9 and similarly electrodes 15, 16, 17 and 18 are positioned adjacent and form capacitors with electrode 10.
  • electrode 9 is connected to terminal A*; electrode 10 is connected to terminal B*; electrode 11 is connected to terminal 1*; electrode 12 is connected to terminal 3*; electrode 13 is connected to terminal 2*; electrode 14 is connected to terminal 4*; electrode 15 is connected to terminal 5*; electrode 16 is connected to terminal 7*; electrode 17 is connected to terminal 6*; and electrode 18 is connected to terminal 8*.
  • electrodes 12 and 14 are identical and are connected to the processing electronics 22 in such a manner that they form a balanced pair of electrodes. In other words in the absence of any liquid in the container or when the container is full of liquid the signals obtained from electrodes 12 and 14 cancel each other out.
  • electrodes 16 and 18 are identical and are connected to the processing electronics 22 in such a manner that they also form a balanced pair of electrodes.
  • electrodes 11 and 13 are also paired, but they are not identical and so they are not balanced.
  • An additional dry value reference capacitor C 11 is therefore provided to balance this pair of electrodes.
  • electrodes 15 and 17 are also paired, but they are not identical and so they are not balanced.
  • An additional dry value reference capacitor Ci 5 is therefore provided to balance this pair of electrodes.
  • Figure 18 illustrates how the electrodes shown in Figure 17 may be connected to the excitation and processing electronics 22, such that electrodes 9 and 10 are connected to the excitation circuitry 24 and the other electrodes are connected to the detection circuitry 26.
  • Figure 19 illustrates the inverted connection where electrodes 9 and 10 are connected to the detection circuitry 26 and the other electrodes are connected to the excitation circuitry.
  • V 1 and V ⁇ will be generated.
  • these voltages do not vary in the same manner as V 1 and V ⁇ obtained with the sensor shown in Figure 2.
  • Figure 2OA illustrates the way in which the first output signal V 1 varies as the liquid level varies between level O and level S.
  • the first output voltage is at zero. This is because at this liquid level the capacitive coupling between electrodes 9 and 13 is cancelled out by the capacitive coupling between electrodes 9 and 11 in combination with the capacitive coupling through reference capacitor C 11 ; and because at this liquid level the capacitive coupling between electrodes 10 and 17 is cancelled out by the capacitive coupling between electrodes 10 and 15 in combination with the capacitive coupling through reference capacitor C 15 .
  • the liquid level rises past level O, this balance is disturbed and the first output signal V 1 starts to rise.
  • electrodes 11 and 15 When the liquid level reaches level P, electrodes 11 and 15 will be fully submerged and V 1 will have reached its maximum value. As the liquid level rises further between levels P and Q, electrodes 11 and 15 are still fully submerged and as the liquid has not yet reached electrodes 13 and 17, the first output voltage will remain constant. However, once the liquid level rises past level Q, the first output signal V 1 starts to reduce and continues reducing as the liquid level rises, until the electrodes 13 and 17 are fully submerged. In this embodiment, electrodes 13 and 17 have approximately twice the surface area of electrodes 11 and 15 and therefore, by the time the liquid level has reached level R, the first output voltage will be at a peak negative value which is approximately equal in magnitude to the peak positive value reached at level P. The first output voltage then remains at this level as the liquid level increases toward the full level S.
  • Figure 2OB illustrates the way in which the second output signal V 11 varies as the liquid level varies between level O and level S.
  • the second output signal is also zero. This is because, as discussed above, electrodes 12 and 14 and 16 and 18 form balanced pairs of electrodes. Thus in the absence of any liquid to upset this balance, no signal will be obtained from these electrodes. However, as the liquid level rises past level P, this balance is disturbed and the second output signal V ⁇ starts to rise. When the liquid level reaches level Q, electrodes 12 and 16 will be fully submerged and V ⁇ will have reached its maximum value.
  • Figure 2OC is a locus plot obtained by plotting output signal V 1 against output signal V ⁇ as the liquid level rises between level O and level S. As shown, the locus plot almost defines a closed square. Therefore, the measured phase angle, ⁇ , will vary from 0 degrees to 180 degrees as the liquid level rises from level O to level S. As a result of this greater range of phase angle variation, the measurements that are obtained will be more accurate as the rate of change of the measured phase angle with the level of the liquid is greater. Further, as will now be explained with reference to Figure 21, this sensor design is also less sensitive to the phase offset problem discussed above with reference to Figure 16. As shown in Figure 17, reference capacitors C 11 and C 15 are still provided in this embodiment. Therefore, V 1 may still vary by ⁇ V 1 .
  • Figure 21 A illustrates the desired or expected locus plot 76 and the actual locus plot 77 obtained if the reference capacitors Cn and/or C 15 do not provide the desired balance between electrodes 11 and 13 and electrodes 15 and 17 respectively, and as a result the first output signal V 1 is reduced by ⁇ V 1 .
  • Figure 21B illustrates the resulting phase error plot as the liquid level is varied from levels O to S. As can be seen, as the liquid level rises up the container, no phase error ( ⁇ 0 ) is introduced until some unknown level Wj when the measured phase angle exceeds the phase threshold ( ⁇ *).
  • FIGS 21 C and 2 ID illustrate the situation when the reference capacitors C 11 and/or C 15 do not provide the desired balance between electrodes 11 and 13 and electrodes 15 and 17 respectively, and as a result the first output signal V 1 is increased by ⁇ V 1 .
  • no phase error ( ⁇ 0 ) is introduced until the level W 2 corresponding to the level when the phase angle is expected to exceed the phase threshold ( ⁇ *).
  • FIGs 21E and 21 F illustrate the situation when a small offset ⁇ V ⁇ reduces the second output signal. As shown, in this situation, as the liquid level rises up the container, no phase error ( ⁇ 0 ) is introduced until the level W 2 corresponding to the level when the phase angle is expected to exceed the phase threshold ( ⁇ *).
  • phase error (because the measured phase lags the expected phase) will start to be introduced which will increase in magnitude linearly as the liquid level rises, until the measured phase angle exceeds the phase threshold ( ⁇ *). At this level the phase error will have reached its maximum negative value. As the liquid level increases further, the phase error reduces again to zero when the liquid is halfway between levels Q and R. A positive phase error will then be introduced which will increase linearly to a maximum value when the liquid level reaches level S.
  • FIGS 21 G and 2 IH illustrate the situation when a small offset ⁇ V ⁇ increases the second output signal V ⁇ .
  • ⁇ V ⁇ increases the second output signal V ⁇ .
  • FIGs 2 and 17 schematically illustrate two different sensor head designs.
  • the electrodes may be formed from suitably shaped conductor plates or the electrodes (and their connections to the connection interface 20) may be formed using the conductive layers of one or more printed circuit boards. Such an arrangement would facilitate the positioning of the electrodes in the symmetric (back to back) arrangement due to the inherent parallel layer arrangement of multilayer printed circuit boards.
  • the conductors may be formed from a conductive ink printed onto suitable substrates which are then assembled to position the electrodes in the manner illustrated in Figures 2 and 17.
  • the electrode designs described above may be formed from conductors that are mounted in the same plane. This is illustrated in Figure 22A for a design of electrodes that is equivalent to those shown in Figure 17.
  • the electrodes shown in Figure 22A have been labelled with the same reference numbers as their equivalent in the design shown in Figure 17.
  • the electrodes 9 to 18 are mounted on a planar substrate 19 and through holes 89 '1 and 89 "2 are provided between electrode 9 and electrodes 11, 12, 13 and 14 and between electrode 10 and electrodes 15, 16, 17 and 18, respectively.
  • This allows space for the liquid whose level is to be sensed to be positioned in the gap between the measurement electrodes and thus affect the mutual capacitance between these electrodes as the liquid level rises up the container.
  • electrodes 11 and 12 and electrodes 15 and 16 overlap each other along the measurement range of the sensor. This is because there is insufficient space at the base of the sensor to form electrodes of the required size (surface area) and therefore electrodes 11 and 15 have been extended up the sensor to overlap with electrodes 12 and 16.
  • Figure 23 A illustrates the way in which the first output signal V 1 varies as the liquid level increases from level O to level S and Figure 23 B illustrates the way in which the second output signal V 11 varies as the liquid level increases from level O to level S.
  • the plots are similar but not identical to those shown in Figures 2OA and 2OB.
  • Figure 23C illustrates the locus plot obtained by plotting the first output signal V 1 against the second output signal V ⁇ as the level of the liquid changes (and which is shown in Figure 23C) is not identical to the locus plot shown in Figure 2OC.
  • Figure 23D illustrates, for information, the "non-linearity" of the sensor which is corrected using the lookup table 42.
  • Figure 23D shows that with the design of electrodes illustrated in Figure 22, the relationship between the measured phase and the level of the liquid in the container is non-linear.
  • the plot illustrated in Figure 23D is obtained during a calibration routine and used to generate the above described lookup table 42 that maps the measured phase angle to the corresponding liquid level.
  • resistive coupling between the excitation electrodes and each detection electrode will be attenuated by the differential amplifier circuits 68. This is because resistive coupling is less dependent on the separation between the excitation electrodes and each detection electrode and will therefore appear as a common mode signal in the inputs to the differential amplifier circuits 68. Phase Offset Due To Dielectric Variations
  • FIG. 24 A illustrates the locus plot of V 1 against V 11 obtained for the sensor shown in Figure 22 A for diesel (plot 91) and a scaled down plot obtained for ethanol (plot 92).
  • the ethanol plot is scaled down as the signal levels obtained when ethanol is the liquid are far greater than those obtained from diesel. As can be seen from the two plots 91 and 92, they do not follow the same path.
  • the offset ⁇ V ⁇ can be introduced by adding an appropriate capacitor to the electrodes affecting V (ie electrodes 12, 14, 16 and 18) or more simply by altering the length of electrodes 14 and 18 so that they are not exactly identical to electrodes 12 and 16 and thus do not exactly balance with these electrodes.
  • the critical measurement is when the fuel tank is near or at empty. It does not matter if the measurement is less accurate when the tank is half full or full.
  • a similar offset can be introduced to the electrodes that will affect output signal V 1 .
  • the inventor has realised that by attaching a non-conductive layer (made for example of plastic) to the bottom of the substrate, it is possible to reduce the extent of these fringing fields in low dielectric liquids (such as diesel).
  • This non-conductive layer will have no effect when the liquid has a high dielectric constant and therefore the locus plots for the different liquids will become more similar (at least at the start of the measurement range).
  • Figures 25A and 25B illustrate the sensor head of Figure 22A having such a nonconducting layer 98 attached to the bottom of the substrate 19.
  • Figure 26A illustrates the locus plot 92 obtained for the high dielectric liquid (which is unchanged from that shown in Figure 24A) and the locus plot 93 obtained for the low dielectric liquid.
  • the two locus plots 92 and 93 are much more similar to each other than plots 91 and 92, especially at the start of the measurement range (between levels O and P2).
  • the phase offsets introduced with the sensor shown in Figure 25 due to different dielectric constants are much smaller.
  • Figure 26B illustrates how this phase offset ( ⁇ d) varies over the measurement range. As shown, the phase offset error is now more symmetric than the plots illustrated in Figure 24 and also has a smaller peak offset of about 1.2%.
  • the electrodes were mounted on a planar substrate 19.
  • the liquid may include contaminants that affect the operation of the sensor if the contaminants contact or become stuck to one or more of the electrodes.
  • the liquids are conductive, then significant levels of current may be drawn from the sensor.
  • This may be used, for example, to control effects caused by fringing electric fields and/or to control the locus plots so that they have a similar trajectory for liquids having different dielectric constants and/or to control the variation of any resistive coupling that is not filtered out by the detection circuitry, so that it varies in the same way as the capacitive coupling (and thus will not interfere with the measurements that are being taken).
  • FIG. 28 illustrates a set of electrodes that are designed so that there is a linear relationship between the measured phase and the corresponding liquid level, so that there is no need for the lookup table 42.
  • electrodes 12, 14, 16 and 18 are "D" shaped and electrodes 13 and 17 are "hour glass” shaped.
  • Figures 29A and 29B illustrate the way in which the two output signals V 1 and V vary as the liquid level rises up the container from level O to level S.
  • Figure 29C illustrates how the measured phase angle (minus the phase threshold) varies as the liquid level rises from level O to level S.
  • the phase angle remains at zero until the second dashed line corresponding to the level when the actual measured phase exceeds the phase threshold. At this point, the phase angle increases linearly with the level of the liquid in the container. Therefore, in this embodiment, the liquid level can be determined simply by scaling the measured phase angle and there is no need for the use of a lookup table 42.
  • Figures 3OA and 30B illustrate another sensor head which aims to emulate the sensor head shown in Figure 28 using planar electrodes. As shown, the surface areas of the electrodes are varied along the length of the sensor head. Where there is insufficient room on the substrate to achieve the desired rate of change of capacitance per unit length of the sensor, inter-digitised fingers of electrodes may be provided, such as in region 99.
  • sensor heads were provided that comprised two sets of electrodes arranged back to back in a symmetric manner along the measurement axis of the sensor.
  • Figure 31 illustrates an alternative embodiment, where only one set of electrodes 21 is provided and Figure 32 illustrates how these electrodes may be connected to the excitation circuitry 24 and the detection circuitry 26.
  • the length of electrode 14 has been made slightly different to the length of electrode 12, so as to introduce a deliberate offset into the second output signal V ⁇ .
  • the length of electrode 13 has been made slightly different to twice that of electrode 11, in order to deliberately introduce an offset into the first output signal V 1 .
  • the two excitation signals applied to the electrodes nominally have the same magnitude but different signs. This is to provide the desired balance (apart from the above offsets) between the paired electrodes - 11 and 13; and 12 and 14.
  • the desired offsets may be introduced by applying different magnitude excitation signals to the electrodes.
  • one or more differential amplifier circuits subtracted the signals from complementary sets of electrodes.
  • the signals may be subtracted by inverting one of the signals and then by adding it to the other signal.
  • Other subtraction circuits may also be used.
  • connection interface is illustrated as being separate from the sensor head.
  • connection interface may be integrally formed with the sensor head and may, for example, be defined by conductor tracks on the sensor head.
  • excitation and detection circuitry may also be mounted on the sensor head, so that the sensor is carried by a single substrate.
  • the detection circuitry determined the value of an amplitude measure and a phase measure of the received signals. If the amplitude measure was below the threshold, then the detection circuitry did not further process the signals to determine position. Similarly, if the phase measure was not above the phase threshold, then the detection circuitry would not use the signals to calculate a new position. As those skilled in the art will appreciate, this can be achieved either by preventing the detection circuitry from performing further calculations or simply by ignoring or not outputting any measurements obtained when the thresholds are not met. Additionally, in some embodiments, the detection circuitry may only compare the amplitude or the phase measurement with the corresponding threshold rather than both as in the above embodiments. In sensor head D a non-conductive backing layer was provided under the substrate 19. As those skilled in the art will appreciate, instead of providing a backing layer, grooves may be formed in the substrate to the required depth. The appended claims refer to the use of "blind grooves" for this feature. This language has been used to cover both the above possibilities.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Electromagnetism (AREA)
  • Thermal Sciences (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)

Abstract

L'invention concerne un détecteur de position capacitif qui comporte une pluralité d'électrodes espacées le long d'une trajectoire de mesure. L'invention concerne également un circuit d'excitation destiné à générer et à appliquer des signaux d'excitation sur certaines de ces électrodes et un circuit de détection destiné à recevoir et à traiter les signaux obtenus à partir des autres électrodes. Le circuit de détection inclut un circuit destiné à soustraire une partie des signaux de détection les uns des autres pour éliminer les signaux en mode commun.
PCT/GB2006/004384 2006-11-23 2006-11-23 Détecteur de position Ceased WO2008062146A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/GB2006/004384 WO2008062146A1 (fr) 2006-11-23 2006-11-23 Détecteur de position

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/GB2006/004384 WO2008062146A1 (fr) 2006-11-23 2006-11-23 Détecteur de position

Publications (1)

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WO2008062146A1 true WO2008062146A1 (fr) 2008-05-29

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8424721B2 (en) 2008-10-06 2013-04-23 Conopco, Inc. Device and method for monitoring consumer test compliance
CN105352565A (zh) * 2015-11-02 2016-02-24 智恒（厦门）微电子有限公司 差分电容料位传感器
WO2016041726A1 (fr) * 2014-09-19 2016-03-24 Endress+Hauser Gmbh+Co. Kg Dispositif et procédé permettant de surveiller une grandeur de processus d'un milieu
EP3012602A1 (fr) * 2014-10-22 2016-04-27 Dover Europe Sàrl Dispositif de mesure d'un niveau dans un réservoir
US10086618B2 (en) 2015-11-04 2018-10-02 Dover Europe Sarl Device for level measurement in a reservoir
WO2019092395A1 (fr) * 2017-11-10 2019-05-16 Aspen Pumps Limited Jaugeur
WO2019126841A1 (fr) * 2017-12-28 2019-07-04 Billi Australia Pty Ltd Capteur de niveau capacitif ayant une installation d'auto-étalonnage
DE102018123852A1 (de) * 2018-09-27 2020-04-02 Ifm Electronic Gmbh Kapazitiver Füllstandsensor und Wassertank für ein Kraftfahrzeug mit einem Füllstandsensor
CN119984443A (zh) * 2025-01-15 2025-05-13 杭州九阳净水系统有限公司 一种液体加热器的液位检测方法

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1992018856A1 (fr) * 1991-04-20 1992-10-29 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Dispositif integrable de mesure de la conductivite
FR2752053A1 (fr) * 1996-07-31 1998-02-06 Comm Composants Soc Ind Sonde de mesure capacitive du niveau de liquide dans un reservoir
US6178818B1 (en) * 1995-05-08 2001-01-30 Ploechinger Heinz Capacitive filling level sensor
US20020174719A1 (en) * 2001-04-21 2002-11-28 Sven Petzold Level sensor and method of registering a level in a container
WO2005111551A1 (fr) * 2004-05-14 2005-11-24 Scientific Generics Ltd. Capteur de position capacitif

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1992018856A1 (fr) * 1991-04-20 1992-10-29 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Dispositif integrable de mesure de la conductivite
US6178818B1 (en) * 1995-05-08 2001-01-30 Ploechinger Heinz Capacitive filling level sensor
FR2752053A1 (fr) * 1996-07-31 1998-02-06 Comm Composants Soc Ind Sonde de mesure capacitive du niveau de liquide dans un reservoir
US20020174719A1 (en) * 2001-04-21 2002-11-28 Sven Petzold Level sensor and method of registering a level in a container
WO2005111551A1 (fr) * 2004-05-14 2005-11-24 Scientific Generics Ltd. Capteur de position capacitif

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8424721B2 (en) 2008-10-06 2013-04-23 Conopco, Inc. Device and method for monitoring consumer test compliance
WO2016041726A1 (fr) * 2014-09-19 2016-03-24 Endress+Hauser Gmbh+Co. Kg Dispositif et procédé permettant de surveiller une grandeur de processus d'un milieu
EP3012602A1 (fr) * 2014-10-22 2016-04-27 Dover Europe Sàrl Dispositif de mesure d'un niveau dans un réservoir
FR3027669A1 (fr) * 2014-10-22 2016-04-29 Dover Europe Sarl Dispositif de mesure de niveau dans un reservoir
US9701128B2 (en) 2014-10-22 2017-07-11 Dover Europe Sàrl Device for measuring a level in a tank
CN105352565A (zh) * 2015-11-02 2016-02-24 智恒（厦门）微电子有限公司 差分电容料位传感器
CN105352565B (zh) * 2015-11-02 2024-05-07 智恒（厦门）微电子有限公司 差分电容料位传感器
US10086618B2 (en) 2015-11-04 2018-10-02 Dover Europe Sarl Device for level measurement in a reservoir
US11604003B2 (en) 2017-11-10 2023-03-14 Aspen Pumps Limited Liquid level sensor
WO2019092395A1 (fr) * 2017-11-10 2019-05-16 Aspen Pumps Limited Jaugeur
US11788750B2 (en) 2017-11-10 2023-10-17 Aspen Pumps Limited Liquid level sensor
WO2019126841A1 (fr) * 2017-12-28 2019-07-04 Billi Australia Pty Ltd Capteur de niveau capacitif ayant une installation d'auto-étalonnage
CN111771105B (zh) * 2017-12-28 2023-01-03 比利澳大利亚私人有限公司 具有自动校准装置的电容式料位传感器
GB2583268A (en) * 2017-12-28 2020-10-21 Billi Australia Pty Ltd Capacitive level sensor having autocalibration facility
GB2583268B (en) * 2017-12-28 2023-03-22 Billi Australia Pty Ltd Capacitive level sensor having autocalibration facility
CN111771105A (zh) * 2017-12-28 2020-10-13 比利澳大利亚私人有限公司 具有自动校准装置的电容式料位传感器
DE102018123852A1 (de) * 2018-09-27 2020-04-02 Ifm Electronic Gmbh Kapazitiver Füllstandsensor und Wassertank für ein Kraftfahrzeug mit einem Füllstandsensor
DE102018123852B4 (de) * 2018-09-27 2025-06-12 Ifm Electronic Gmbh Kapazitiver Füllstandsensor und Wassertank für ein Kraftfahrzeug mit einem Füllstandsensor
CN119984443A (zh) * 2025-01-15 2025-05-13 杭州九阳净水系统有限公司 一种液体加热器的液位检测方法

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