US20050087013A1 - Liquid level sensing assembly and method for measuring using same - Google Patents
Liquid level sensing assembly and method for measuring using same Download PDFInfo
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- US20050087013A1 US20050087013A1 US10/998,345 US99834504A US2005087013A1 US 20050087013 A1 US20050087013 A1 US 20050087013A1 US 99834504 A US99834504 A US 99834504A US 2005087013 A1 US2005087013 A1 US 2005087013A1
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- excitation
- receiving
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- 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
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- 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
Definitions
- the invention relates to fluid level sensing assemblies. More particularly, the invention relates to fluid level sensing assemblies capable of accurately determining the level of a fluid within a reservoir by analyzing output signals of the fluid level sensing assembly.
- liquids are an important feature of many mechanisms.
- proper delivery of liquids is essential for the functioning and maintenance of a motor vehicle.
- a motor vehicle will not function without fuel, typically liquid gasoline. That same motor vehicle will not function properly without the proper amount of oil stored in the internal combustion engine allowing it to lubricate and cool itself.
- These are just two fluids in a particular environment that require close observation to make sure its host mechanism, i.e., the motor vehicle, can operate properly.
- Fluid level measuring mechanisms include floating arm mechanisms, pressure sensors, capacitive sensors, and ultrasonic sensors.
- the most commonly used fluid level measuring system is the floating arm mechanism.
- the floating arm mechanism is an imperfect mechanism for several reasons.
- the floating arm mechanism requires moving parts inside a liquid-filled container. This requires increased time to install the floating arm mechanism and seal it and the container or reservoir. Resistive strips used by the floating arm mechanism are susceptible to contamination and can develop contact problems. The contamination and contact problems result in erroneous measurements.
- a sensing assembly senses a level of a liquid in a reservoir.
- the sensing assembly includes a first input port for receiving a first input voltage signal.
- the sensing assembly also includes a second input port for receiving a second input voltage signal.
- An excitation circuit is electrically connected to the first and second input ports for receiving the first and second input voltage signals and for generating a first excitation signal and a second excitation signal.
- a receiving circuit is disposed adjacent the excitation circuit and defines a variable capacitance with the excitation circuit. The receiving circuit produces an output voltage variable with the level of liquid in the reservoir due to capacitance changes between the excitation circuit and the receiving circuit. The capacitance changes are due to dielectric changes created by the presence of the liquid.
- FIG. 1 is a perspective view of a reservoir, partially cut away, showing one embodiment of the invention and a liquid stored therein;
- FIG. 2 is a cross-sectional side view, partially cut away, of a reservoir that is partially filled with liquid with an exploded side view of the invention mounted to the reservoir;
- FIG. 2A is a side view of the invention separated into halves
- FIG. 3 is a graphic representation of the input signal utilized by the invention.
- FIG. 4 is a graphic representation of an output of the invention used to determine the level of the liquid in the reservoir.
- FIG. 5 is a schematic diagram of an electrical circuit utilized by the invention.
- a sensing assembly is generally indicated at 10 .
- the sensing assembly 10 is mounted to a reservoir 12 having a bottom surface 14 , a top surface 16 connected together by a plurality of side walls 18 .
- An inlet 20 allow a liquid 22 to enter the reservoir 12 and be stored therein.
- the liquid 22 defines a level 24 that is to be sensed by the sensing assembly 10 .
- air 26 fills the portion of the reservoir 12 that is not occupied by the liquid 22 .
- the sensing assembly 10 is shown to have first 28 and second 30 substrates.
- the substrates 28 , 30 are used to mount circuitry (discussed subsequently) thereto. While only the first 28 and second 30 substrates are shown, it should be appreciated that other substrates may be incorporated into the design of the invention 10 . These substrates may extend between the first 28 and second 30 substrates should it be desired to further isolate the circuitry extending along each of the substrates 28 , 30 .
- the sensing assembly 10 includes a first input port 32 .
- the first input port 32 receives a first input voltage signal 34 ( FIG. 3 ).
- the first input port 32 extends through the substrates 28 , 30 allowing circuitry in each of these substrates 28 , 30 to receive the first input voltage signal 34 .
- the sensing assembly 10 also includes a second input port 36 that extends between the substrates 28 , 30 .
- the second input port 36 receives a second input voltage signal 38 ( FIG. 3 ).
- a portion of an excitation circuit, generally shown at 40 is electrically connected to the first 32 and second 36 input ports.
- the excitation circuit 40 receives both the first 34 and second 38 input voltage signals.
- the excitation circuit 40 generates two excitation signals. A complete discussion of the electrical circuit is set forth below.
- the excitation circuit 40 includes four excitation electrodes 42 , 44 , 46 , 48 .
- the first 42 and third 46 excitation electrodes receive a first excitation signal
- the second 44 and fourth 48 excitation electrodes receive a second excitation signal.
- the two excitation signals are generated by the electrodes 42 , 44 , 46 , 48 when they receive the first 34 and second 38 input voltage signals. More specifically, the first 42 and third 46 excitation electrodes create a first excitation signal generated through the receipt of the first input voltage signal 34 and the second 44 and fourth 48 excitation electrodes generate a second excitation signal from the receipt of the second input voltage signal 38 .
- the first 42 and second 44 excitation electrodes extend along the first substrate 28 .
- the third 46 and fourth 48 excitation electrodes extend along the second substrate 30 .
- the first 42 and third 46 excitation electrodes are electrically connected to the first input port 32 and the second 44 and fourth 48 excitation electrodes are electrically connected to the second input port 36 .
- the sensing assembly 10 also includes a receiving circuit, generally shown at 50 .
- the receiving circuit 50 is disposed adjacent the excitation circuit 40 and, together with the excitation circuit 40 , defines a variable capacitance for the sensing assembly 10 .
- the receiving circuit 50 produces an output voltage signal, generally shown at 52 in FIG. 4 .
- the output voltage signal identifies the level 24 of the liquid 22 in the reservoir 12 .
- the output voltage signal 52 varies with the level 24 of the liquid 22 in the reservoir 12 due to capacitance changes between the excitation circuit 40 and the receiving circuit 50 due to dielectric changes created by the presence or absence of the liquid 22 along portions of the sensing assembly 10 .
- the output voltage signal 52 will be discussed in greater detail.
- the receiving circuit 50 includes first 54 and second 56 receiving electrodes.
- the first receiving electrode 54 extends between the first 42 and second 44 excitation electrodes.
- the second receiving electrode 56 extends between the third 46 and fourth 48 excitation electrodes. Therefore, the first receiving electrode 54 extends along the first substrate 28 , whereas the second receiving electrode 56 extends along the second substrate 30 .
- the first receiving electrode 54 extends along a first non-linear path.
- the first non-linear path is sinusoidal.
- the second receiving electrode 56 extends along a second non-linear path.
- the second non-linear path differs from the first non-linear path.
- the second non-linear path is sinusoidal.
- the second non-linear path is out of phase with the first non-linear path.
- the second sinusoidal path is out of phase 90 degrees with the first sinusoidal path. Therefore, as is shown in the Figures, the first receiving electrode 54 may be considered to be extending through a sine wave path and the second receiving electrode 56 could be extending through a cosine path.
- the first receiving electrode 54 is electrically connected to a first output port 58 and the second receiving electrode 56 is electrically connected to a second output port 60 .
- the output voltage signal 52 is transmitted through the first 58 and second 60 output ports to a control circuit (not shown) for analysis to determine the level 24 of the liquid 22 .
- the receiving circuit 50 generates an output voltage signal 52 that has two components.
- the first component is a first output voltage signal 62 .
- the second component is a second output voltage signal 64 .
- the first receiving electrode 54 generates the first output voltage signal 62 which, in the preferred embodiment, is a shifted minus cosine signal.
- the second receiving electrode 56 generates the second output voltage signal 64 , which, in the preferred embodiment, is a sine signal.
- the control circuit receives each of the first 62 and second 64 output voltage signals, it can map the values of each of these signals 62 , 64 to determine the percentage of liquid 22 in the reservoir 12 to determine the level 24 of the liquid 22 therein. Two signals are required because a reading of one signal would produce two potential level readings because the each of the output signals repeat through a single cycle of measurements.
- the sensing assembly includes first 66 and second 68 traces.
- the first trace 66 extends along the first substrate 28 and separates the first receiving electrode 54 from the first 42 and second 44 excitation electrodes.
- the second trace 68 extends along the second substrate 30 between the second receiving electrode 56 and the third 46 and fourth 48 excitation electrodes.
- the traces 66 , 68 are connected to ground.
- the traces 66 , 68 reduce parasitic voltages that may be created from the sensing assembly 10 during operation thereof.
- the electrical circuit 70 includes the excitation circuit 40 and the receiver circuit 50 .
- the excitation circuit 40 is powered by a signal generator 72 , whereas the receiving circuit 50 , along with the signal condition circuit described subsequently, are powered from another power supply (not shown).
- the excitation circuit 40 includes the excitation electrodes 42 , 44 , 46 , 48 .
- the first 42 and third 46 excitation electrodes are electrically connected together (they are at the same electrical field potential), and the second 44 and fourth 48 excitation electrodes are electrically connected together (they are at the same electrical field potential).
- An inverter 74 is connected the signal generator 72 and the second and fourth excitation electrode 44 , 48 . It is the inverter 74 that creates the negative sinusoidal input identified as the second input voltage signal 38 .
- a bias capacitor 76 may be needed to avoid phase inverse.
- the bias capacitor 76 is electrically connected between signal generator 72 and the second output port 60 .
- the first output port 58 and the second output port 60 are connected to a switch 80 that is controlled by a micro-controller 96 .
- the switch 80 makes the signal condition circuit of the receiver circuit 50 have the capability to alternate receiving signals from the first output port 58 , the first receiving electrode 54 , and from the second output port 60 , the second receiving electrode 56 .
- the amplifier 84 and feedback impedance 88 form a current-to-voltage converter stage.
- the positive input terminal 86 of the amplifier 84 is connected to ground.
- the negative terminal 82 of amplifier 84 is connected to both the switch 80 and the one terminal of the feedback impedance 88 .
- the negative terminal 82 is forced to virtual ground.
- An unbalanced current caused by an unbalanced capacitance between the first receiving electrode 54 and the first 42 and second 44 excitation electrodes generates voltage output 90 .
- the alternated current (AC) voltage signal 90 is then fed into the alternating current (AC) signal to direct current (DC) signal converter 92 .
- This converter 92 converts the AC voltage signal to DC voltage signal.
- the DC voltage signal is then fed into a DC amplifier 94 to amplify the signal level.
- the amplified DC signal feeds into the micro-controller's analog-to-digital converter port and read by the micro-controller 96 .
- the micro-controller 96 can control the switch 80 to select one signal from receiving electrode 54 , input port 58 , with output signal 62 or from receiving electrode 56 , input port 60 , with output signal 64 .
- the method used for measuring the level 24 of the liquid 22 in the reservoir 12 includes the step of applying the first input voltage signal 34 to the first 42 and the third 46 excitation electrodes and applying the second input voltage 38 , that has the same frequency and amplitude as the first input voltage but with 180 degrees phase difference, to the third 44 and fourth 48 excitation electrodes.
- the micro-controller 96 connects the switch 80 to the input port 58 so the receiving electrode 54 can be selected. Because the terminal 82 is virtually grounded, and the first excitation electrode 42 and the second excitation electrode 44 have the same frequency and amplitude input voltage but with 180-degree phase difference, the capacitance difference between the first receiving electrode 54 to first excitation electrode 42 and the first receiving electrode 54 to second excitation electrode 44 generates the unbalanced current.
- the unbalanced current through the current-to-voltage converter becomes the voltage signal at the output 90 of the amplifier 84 .
- the voltage signal through signal conditional circuits 92 , 94 feeds into A/D port of micro-controller 96 and is converted to digital signal and read by the micro-controller 96 as S 1 . Then, the micro-controller 96 sets the switch 80 to port 60 , e.g., the second receiving electrode 56 .
- the unbalanced current caused by the capacitance difference between the second receiving electrode 56 to the third excitation electrode 46 and the second receiving electrode 56 to the fourth excitation electrode 48 is converted to voltage signal and through AC to DC converter 92 , DC amplifier 94 , and A/D port by micro-controller 96 as S 2 .
- the signal S 1 and S 2 are varied with level as shown in FIG. 4 .
- the first output voltage signal 62 is the S 1 vs. percentage of level 24 and the second output voltage signal 64 is the S 2 vs. percentage of level 24 .
- percentage level z(in degree)/360.
- zero degrees equals 0% full
- 90 degrees equals 25% full
- 180 degrees equals 50% full
- 270 degrees equals 75% full
- the signs of equations determine the quadrant of the angle z.
- the liquid dielectric is not a parameter in the final equations. This is because the dielectric of the liquid cause the curves in the amplitudes of the output voltage signals 62 , 64 . They change, however, at the same rate. In the equations, the ratio cancels the dielectric effects.
- third 46 excitation electrodes and applying the second input voltage 38 that has the same frequency and amplitude as the first input voltage but with 180 degrees phase difference, to the second third and fourth 48 excitation electrodes.
- the micro-controller 96 connects the switch 80 to the input port 58 so the receiving electrode 54 can be selected.
- the capacitance difference between the first receiving electrode 54 to first excitation electrode 42 and the first receiving electrode 54 to second excitation electrode 44 generates the unbalanced current.
- the unbalanced current through the current-to-voltage converter (amplifier 84 and feedback impedance 88 ) becomes the voltage signal at the output 90 of the amplifier 84 .
- the voltage signal through signal conditional circuits 92 , 94 feeds into A/D port of micro-controller 96 and is converted to digital signal and read by the micro-controller 96 as SI.
- the micro-controller 96 sets the switch 80 to port 60 , e.g., the second receiving electrode 56 .
- the unbalanced current caused by the capacitance difference between the second receiving electrode 56 to the third excitation electrode 46 and the second receiving electrode 56 to the fourth excitation electrode 48 is converted to voltage signal and through AC to DC converter 92 , DC amplifier 94 , and A/D port by micro-controller 96 as S 2 .
- the signal S 1 and S 2 are varied with level as shown in FIG. 4 .
- the first output voltage signal 62 is the S 1 vs. percentage of level 24 and the second output voltage signal 64 is the S 2 vs. percentage of level 24 .
- the first S 1 and second S 2 values are used in the following two equations to calculate the level 24 of liquid 22 :
Abstract
A sensing assembly (10) senses a level (24) of a liquid (22) in a reservoir (12). The sensing assembly (10) includes a first input port (32) for receiving a first input voltage signal. The sensing assembly (10) also includes a second (32) input port (36) for receiving a second input voltage signal. An excitation circuit (40) is electrically (36) connected to the first (32) and second (34) input ports for receiving the first (34) and second (38) input voltage signals and for generating a first excitation signal and a second excitation signal. A receiving circuit (50) is disposed adjacent the excitation circuit (40) and defines a variable capacitance with the excitation circuit (40). The receiving circuit (50) produces an output voltage variable with the level (24) of the liquid (22) in the reservoir (12) due to capacitance changes between the excitation circuit (40) and the receiving circuit (50). The receiving circuit (50) includes a first receiving electrode (54) extending through a sine wave form and a second receiving electrode (56) extending through a cosine wave form. The capacitance changes are due to dielectric changes created by the presence of the liquid (22) adjacent at least a portion of the sensing assembly (10).
Description
- 1. Field of the Invention
- The invention relates to fluid level sensing assemblies. More particularly, the invention relates to fluid level sensing assemblies capable of accurately determining the level of a fluid within a reservoir by analyzing output signals of the fluid level sensing assembly.
- 2. Description of the Related Art
- The storage and delivery of liquids is an important feature of many mechanisms. In an automotive environment, proper delivery of liquids is essential for the functioning and maintenance of a motor vehicle. By way of example, a motor vehicle will not function without fuel, typically liquid gasoline. That same motor vehicle will not function properly without the proper amount of oil stored in the internal combustion engine allowing it to lubricate and cool itself. These are just two fluids in a particular environment that require close observation to make sure its host mechanism, i.e., the motor vehicle, can operate properly.
- Currently, there are a number of ways in which a fluid level may be measured. The mechanisms used to measure the fluid level help determine if more fluid is required in order to continue the proper maintenance and operation of the host mechanism. Fluid level measuring mechanisms include floating arm mechanisms, pressure sensors, capacitive sensors, and ultrasonic sensors. The most commonly used fluid level measuring system is the floating arm mechanism.
- The floating arm mechanism is an imperfect mechanism for several reasons. First, the floating arm mechanism requires moving parts inside a liquid-filled container. This requires increased time to install the floating arm mechanism and seal it and the container or reservoir. Resistive strips used by the floating arm mechanism are susceptible to contamination and can develop contact problems. The contamination and contact problems result in erroneous measurements.
- A sensing assembly senses a level of a liquid in a reservoir. The sensing assembly includes a first input port for receiving a first input voltage signal. The sensing assembly also includes a second input port for receiving a second input voltage signal. An excitation circuit is electrically connected to the first and second input ports for receiving the first and second input voltage signals and for generating a first excitation signal and a second excitation signal. A receiving circuit is disposed adjacent the excitation circuit and defines a variable capacitance with the excitation circuit. The receiving circuit produces an output voltage variable with the level of liquid in the reservoir due to capacitance changes between the excitation circuit and the receiving circuit. The capacitance changes are due to dielectric changes created by the presence of the liquid.
- Advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
-
FIG. 1 is a perspective view of a reservoir, partially cut away, showing one embodiment of the invention and a liquid stored therein; -
FIG. 2 is a cross-sectional side view, partially cut away, of a reservoir that is partially filled with liquid with an exploded side view of the invention mounted to the reservoir; -
FIG. 2A is a side view of the invention separated into halves; -
FIG. 3 is a graphic representation of the input signal utilized by the invention; -
FIG. 4 is a graphic representation of an output of the invention used to determine the level of the liquid in the reservoir; and -
FIG. 5 is a schematic diagram of an electrical circuit utilized by the invention. - Referring to
FIG. 1 , the invention, a sensing assembly, is generally indicated at 10. Thesensing assembly 10 is mounted to areservoir 12 having abottom surface 14, atop surface 16 connected together by a plurality ofside walls 18. Aninlet 20 allow aliquid 22 to enter thereservoir 12 and be stored therein. Theliquid 22 defines alevel 24 that is to be sensed by thesensing assembly 10. Typically,air 26 fills the portion of thereservoir 12 that is not occupied by theliquid 22. - Referring to
FIGS. 2 and 2 A, thesensing assembly 10 is shown to have first 28 and second 30 substrates. Thesubstrates invention 10. These substrates may extend between the first 28 and second 30 substrates should it be desired to further isolate the circuitry extending along each of thesubstrates - The
sensing assembly 10 includes afirst input port 32. Thefirst input port 32 receives a first input voltage signal 34 (FIG. 3 ). Thefirst input port 32 extends through thesubstrates substrates input voltage signal 34. - The
sensing assembly 10 also includes asecond input port 36 that extends between thesubstrates second input port 36 receives a second input voltage signal 38 (FIG. 3 ). - A portion of an excitation circuit, generally shown at 40, is electrically connected to the first 32 and second 36 input ports. The
excitation circuit 40 receives both the first 34 and second 38 input voltage signals. - Theexcitation circuit 40 generates two excitation signals. A complete discussion of the electrical circuit is set forth below. - The
excitation circuit 40 includes fourexcitation electrodes electrodes input voltage signal 34 and the second 44 and fourth 48 excitation electrodes generate a second excitation signal from the receipt of the secondinput voltage signal 38. - The first 42 and second 44 excitation electrodes extend along the
first substrate 28. The third 46 and fourth 48 excitation electrodes extend along thesecond substrate 30. The first 42 and third 46 excitation electrodes are electrically connected to thefirst input port 32 and the second 44 and fourth 48 excitation electrodes are electrically connected to thesecond input port 36. - The
sensing assembly 10 also includes a receiving circuit, generally shown at 50. The receivingcircuit 50 is disposed adjacent theexcitation circuit 40 and, together with theexcitation circuit 40, defines a variable capacitance for thesensing assembly 10. The receivingcircuit 50 produces an output voltage signal, generally shown at 52 inFIG. 4 . The output voltage signal identifies thelevel 24 of the liquid 22 in thereservoir 12. Theoutput voltage signal 52 varies with thelevel 24 of the liquid 22 in thereservoir 12 due to capacitance changes between theexcitation circuit 40 and the receivingcircuit 50 due to dielectric changes created by the presence or absence of the liquid 22 along portions of thesensing assembly 10. Theoutput voltage signal 52 will be discussed in greater detail. - The receiving
circuit 50 includes first 54 and second 56 receiving electrodes. Thefirst receiving electrode 54 extends between the first 42 and second 44 excitation electrodes. Thesecond receiving electrode 56 extends between the third 46 and fourth 48 excitation electrodes. Therefore, the first receivingelectrode 54 extends along thefirst substrate 28, whereas thesecond receiving electrode 56 extends along thesecond substrate 30. - The
first receiving electrode 54 extends along a first non-linear path. In the embodiment shown, the first non-linear path is sinusoidal. Likewise, thesecond receiving electrode 56 extends along a second non-linear path. The second non-linear path differs from the first non-linear path. Again, in the embodiment shown, the second non-linear path is sinusoidal. In addition to being sinusoidal, the second non-linear path is out of phase with the first non-linear path. The second sinusoidal path is out ofphase 90 degrees with the first sinusoidal path. Therefore, as is shown in the Figures, the first receivingelectrode 54 may be considered to be extending through a sine wave path and thesecond receiving electrode 56 could be extending through a cosine path. Thefirst receiving electrode 54 is electrically connected to afirst output port 58 and thesecond receiving electrode 56 is electrically connected to asecond output port 60. Theoutput voltage signal 52 is transmitted through the first 58 and second 60 output ports to a control circuit (not shown) for analysis to determine thelevel 24 of the liquid 22. - The receiving
circuit 50 generates anoutput voltage signal 52 that has two components. The first component is a first output voltage signal 62. The second component is a secondoutput voltage signal 64. Thefirst receiving electrode 54 generates the first output voltage signal 62 which, in the preferred embodiment, is a shifted minus cosine signal. Thesecond receiving electrode 56 generates the secondoutput voltage signal 64, which, in the preferred embodiment, is a sine signal. When the control circuit receives each of the first 62 and second 64 output voltage signals, it can map the values of each of thesesignals 62, 64 to determine the percentage of liquid 22 in thereservoir 12 to determine thelevel 24 of the liquid 22 therein. Two signals are required because a reading of one signal would produce two potential level readings because the each of the output signals repeat through a single cycle of measurements. - The sensing assembly includes first 66 and second 68 traces. The
first trace 66 extends along thefirst substrate 28 and separates the first receivingelectrode 54 from the first 42 and second 44 excitation electrodes. Likewise, thesecond trace 68 extends along thesecond substrate 30 between thesecond receiving electrode 56 and the third 46 and fourth 48 excitation electrodes. Thetraces traces sensing assembly 10 during operation thereof. - Referring to
FIG. 5 , one embodiment of the electrical circuit controlling thesensing assembly 10 is generally indicated at 70. Theelectrical circuit 70 includes theexcitation circuit 40 and thereceiver circuit 50. Theexcitation circuit 40 is powered by asignal generator 72, whereas the receivingcircuit 50, along with the signal condition circuit described subsequently, are powered from another power supply (not shown). Theexcitation circuit 40 includes theexcitation electrodes inverter 74 is connected thesignal generator 72 and the second andfourth excitation electrode inverter 74 that creates the negative sinusoidal input identified as the secondinput voltage signal 38. Abias capacitor 76 may be needed to avoid phase inverse. Thebias capacitor 76 is electrically connected betweensignal generator 72 and thesecond output port 60. - The
first output port 58 and thesecond output port 60 are connected to aswitch 80 that is controlled by amicro-controller 96. Theswitch 80 makes the signal condition circuit of thereceiver circuit 50 have the capability to alternate receiving signals from thefirst output port 58, the first receivingelectrode 54, and from thesecond output port 60, thesecond receiving electrode 56. Theamplifier 84 andfeedback impedance 88 form a current-to-voltage converter stage. Thepositive input terminal 86 of theamplifier 84 is connected to ground. Thenegative terminal 82 ofamplifier 84 is connected to both theswitch 80 and the one terminal of thefeedback impedance 88. Thenegative terminal 82 is forced to virtual ground. An unbalanced current caused by an unbalanced capacitance between the first receivingelectrode 54 and the first 42 and second 44 excitation electrodes generatesvoltage output 90. The alternated current (AC)voltage signal 90 is then fed into the alternating current (AC) signal to direct current (DC)signal converter 92. Thisconverter 92 converts the AC voltage signal to DC voltage signal. The DC voltage signal is then fed into aDC amplifier 94 to amplify the signal level. Finally, the amplified DC signal feeds into the micro-controller's analog-to-digital converter port and read by themicro-controller 96. The micro-controller 96 can control theswitch 80 to select one signal from receivingelectrode 54,input port 58, with output signal 62 or from receivingelectrode 56,input port 60, withoutput signal 64. - In operation, the method used for measuring the
level 24 of the liquid 22 in thereservoir 12 includes the step of applying the firstinput voltage signal 34 to the first 42 and the third 46 excitation electrodes and applying thesecond input voltage 38, that has the same frequency and amplitude as the first input voltage but with 180 degrees phase difference, to the third 44 and fourth 48 excitation electrodes. Themicro-controller 96 connects theswitch 80 to theinput port 58 so the receivingelectrode 54 can be selected. Because the terminal 82 is virtually grounded, and thefirst excitation electrode 42 and thesecond excitation electrode 44 have the same frequency and amplitude input voltage but with 180-degree phase difference, the capacitance difference between the first receivingelectrode 54 tofirst excitation electrode 42 and the first receivingelectrode 54 tosecond excitation electrode 44 generates the unbalanced current. The unbalanced current through the current-to-voltage converter (amplifier 84 and feedback impedance 88) becomes the voltage signal at theoutput 90 of theamplifier 84. The voltage signal through signalconditional circuits micro-controller 96 and is converted to digital signal and read by themicro-controller 96 as S1. Then, themicro-controller 96 sets theswitch 80 toport 60, e.g., thesecond receiving electrode 56. This time, the unbalanced current caused by the capacitance difference between thesecond receiving electrode 56 to thethird excitation electrode 46 and thesecond receiving electrode 56 to thefourth excitation electrode 48 is converted to voltage signal and through AC toDC converter 92,DC amplifier 94, and A/D port bymicro-controller 96 as S2. The signal S1 and S2 are varied with level as shown inFIG. 4 . The first output voltage signal 62 is the S1 vs. percentage oflevel 24 and the secondoutput voltage signal 64 is the S2 vs. percentage oflevel 24. The first S1 and second S2 values are used in the following two equations to calculate thelevel 24 of liquid 22: - where, percentage level=z(in degree)/360. In this embodiment, zero degrees equals 0% full, 90 degrees equals 25% full, 180 degrees equals 50% full, 270 degrees equals 75% full, etc.. The signs of equations determine the quadrant of the angle z.
- In this invention, the liquid dielectric is not a parameter in the final equations. This is because the dielectric of the liquid cause the curves in the amplitudes of the output voltage signals 62, 64. They change, however, at the same rate. In the equations, the ratio cancels the dielectric effects.
- The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.
- Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described. third 46 excitation electrodes and applying the
second input voltage 38, that has the same frequency and amplitude as the first input voltage but with 180 degrees phase difference, to the second third and fourth 48 excitation electrodes. Themicro-controller 96 connects theswitch 80 to theinput port 58 so the receivingelectrode 54 can be selected. Because the terminal 82 is virtually grounded, and thefirst excitation electrode 42 and thesecond excitation electrode 44 have the same frequency and amplitude input voltage but with 180-degree phase difference, the capacitance difference between the first receivingelectrode 54 tofirst excitation electrode 42 and the first receivingelectrode 54 tosecond excitation electrode 44 generates the unbalanced current. The unbalanced current through the current-to-voltage converter (amplifier 84 and feedback impedance 88) becomes the voltage signal at theoutput 90 of theamplifier 84. The voltage signal through signalconditional circuits micro-controller 96 and is converted to digital signal and read by themicro-controller 96 as SI. Then, themicro-controller 96 sets theswitch 80 toport 60, e.g., thesecond receiving electrode 56. This time, the unbalanced current caused by the capacitance difference between thesecond receiving electrode 56 to thethird excitation electrode 46 and thesecond receiving electrode 56 to thefourth excitation electrode 48 is converted to voltage signal and through AC toDC converter 92,DC amplifier 94, and A/D port bymicro-controller 96 as S2. The signal S1 and S2 are varied with level as shown inFIG. 4 . The first output voltage signal 62 is the S1 vs. percentage oflevel 24 and the secondoutput voltage signal 64 is the S2 vs. percentage oflevel 24. The first S1 and second S2 values are used in the following two equations to calculate thelevel 24 of liquid 22:
Claims (7)
1. A sensing assembly for sensing a level of liquid in a reservoir, said sensing assembly comprising:
a first input port for receiving a first input voltage signal;
a second input port for receiving a second input voltage signal;
an excitation circuit electrically connected to said first and second input ports for receiving the first and second input voltage signals and for generating a first excitation signal and a second excitation signal, said excitation circuit includes first and second excitation electrodes extending along a portion of the reservoir, said first and second excitation electrodes disposed adjacent to and separated by said first receiving electrode; and
a receiving circuit disposed adjacent said excitation circuit defining a variable capacitance with said excitation circuit, wherein said receiving circuit includes first and second receiving electrodes extending along a portion of the reservoir and a first trace connected to ground and extending between said first receiving electrode and said first and second excitation electrodes, wherein said first receiving electrode extends along a first non-linear path and said second receiving electrode extends along a second non-linear path differing from said first non-linear path, said receiving circuit producing an output voltage signal variable with the level of liquid in the reservoir due to capacitance changes between said excitation circuit and said receiving circuit due to dielectric changes created by the liquid.
2. A sensing assembly as set forth in claim 1 wherein said first non-linear path extends along a sine wave shape.
3. A sensing assembly as set forth in claim 2 wherein said second non-linear path extends along a cosine wave shape.
4. (canceled).
5. A sensing assembly as set forth in claim wherein said excitation circuit includes third and fourth excitation electrodes extending along a portion of the reservoir, said third and fourth excitation electrodes disposed adjacent to and separated by said second receiving electrode.
6. (canceled).
7. A sensing assembly as set forth in claim 1 including a second trace extending between said second receiving electrode and said third and fourth excitation electrodes, said second trace connected to ground.
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US10/998,345 US20050087013A1 (en) | 2003-10-10 | 2004-11-23 | Liquid level sensing assembly and method for measuring using same |
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US10/683,742 US6823731B1 (en) | 2003-10-10 | 2003-10-10 | Liquid level sensing assembly and method for measuring using same |
US10/998,345 US20050087013A1 (en) | 2003-10-10 | 2004-11-23 | Liquid level sensing assembly and method for measuring using same |
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US20070240506A1 (en) * | 2006-04-13 | 2007-10-18 | Yingjie Lin | Capacitive liquid level sensor |
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US20120240675A1 (en) * | 2011-03-22 | 2012-09-27 | Rochester Gauges, Inc. | Self-Calibrating Capacitive Liquid Level Sensor Assembly and Method |
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US6164132A (en) * | 1997-06-12 | 2000-12-26 | G.D.M, Inc. | Capacitive liquid level indicator |
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- 2003-10-10 US US10/683,742 patent/US6823731B1/en not_active Expired - Fee Related
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2004
- 2004-11-23 US US10/998,345 patent/US20050087013A1/en not_active Abandoned
Patent Citations (1)
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US6164132A (en) * | 1997-06-12 | 2000-12-26 | G.D.M, Inc. | Capacitive liquid level indicator |
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US20120240675A1 (en) * | 2011-03-22 | 2012-09-27 | Rochester Gauges, Inc. | Self-Calibrating Capacitive Liquid Level Sensor Assembly and Method |
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