CA1128772A - Electrical measurement of fluid void fraction for fluid having capacitive and resistive conductive components - Google Patents
Electrical measurement of fluid void fraction for fluid having capacitive and resistive conductive componentsInfo
- Publication number
- CA1128772A CA1128772A CA374,209A CA374209A CA1128772A CA 1128772 A CA1128772 A CA 1128772A CA 374209 A CA374209 A CA 374209A CA 1128772 A CA1128772 A CA 1128772A
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- CA
- Canada
- Prior art keywords
- conductive
- current
- capacitive
- voltage
- component
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Abstract
ABSTRACT OF THE DISCLOSURE
Liquid with solid or gas phases mixed therein is measured as to liquid and non-liquid volume percent by application of an oscillating voltage to the liquid and separation of resultant conductive and capacitive currents to achieve valid and effective measurement of the latter, unmasked by the larger conductive currents obtainable in the mixed phase medium analyzed.
Liquid with solid or gas phases mixed therein is measured as to liquid and non-liquid volume percent by application of an oscillating voltage to the liquid and separation of resultant conductive and capacitive currents to achieve valid and effective measurement of the latter, unmasked by the larger conductive currents obtainable in the mixed phase medium analyzed.
Description
~Z~77;~
Prior U. S. patents 4,074,184 granted 2/14/78, 4,063,153 granted 12/13/77 and 4,082,994 granted 4/4/7~, all of common assignment with the application describe inventions for measuring respective fractions of mixed phased fluids, particularly gas and conductive liquid or solids entrained in liquids utilizing means partlcularly suited for flow which develops a conductance under a voltage field or alternatively utilizing capacitance techniques for non-conductive fluids.
However, there remains a need for means for measuring liquid content of a mixed stream of liquid and gas in situations when the liquid fraction of a stream may be very small (less than 10%) -- a condition occurring, for instance, in some steam flows, which may be measured.
It is therefore the object of the invention to provide commercially practical apparatus meeting such need reliably and economically.
In accordance with the present invention, the amount of liquid is measured by employing its dielectric characteristics. There are two distinct advantages of employing a dielectric capacitive measurement of the amount of water present as a means of establishing respective fractions of water and gas. First, the water does not have to form a conductive lattice between electrodes as is required in conductive or impedance techniques. Second, the dielectric constant of water is very high when compared with most other materials. When the direct measurement of the capacitive component of water is attempted, the rather large conductive component usually causes amplifier over-load. The practice of the present invention involves means to automatically cancel out the conductive component toprevent amplifier overloading.
In accordance with a particular embodiment, a method of measuring liquid content of mixed phase fluid in a container wherein a conductive liquid contains voids therein comprises: making a capacitive current measurement between two spaced (in cross-section of the fluld container) electrodes, and cancelling out a conductive (electrically) component of the current measurement through the fluid inherently picked up in making the capacitive measurement so that the capacitive measurement is not masked by the conductive measurement and wherein the measured current is produced by application of an oscillating voltage to the electrodes and the output capacitive current component ~or a voltage derivative thereof) is shifted into phase with the oscillating voltage.
From another aspect, and in accordance with the invention, an apparatus for practicing the method of the invention comprises: means for applying an oscillating voltage to a mixed phase medium including relatively con-ductive liquid and relatively non-conductive second phase, first means for detecting current produced by said voltage in the medium as a current signal with mixed and varying - conductive and capacitive components, second means apply-ing such current to a summing junction together with a valid transfer function derivative of the conductive component, third means for producing such valid transfer function, fourth means for converting a current output of the summing junction to a voltage and applying components thereof to separate means for indicating conductive and capacitive components of the original measured component.
1~2B772 Other objects, features and advantages of the invention will be apparent from the following detailed description of preferred embodiments thereof, taken in connection with the accompanying drawing, in which:
FIGURE 1 is a block diagram of a circuit to accomplish the automatic cance]lation of the conductive components;
FIGURES lA-lC are voltage vs. time traces taken for different points of the circuit of Figure 1, as mentioned below, and FIGURE 2 is a schematic of a variant embodiment of the invention, The Figure 1 circuit comprises a sinusoidal oscil-lator 20 w~ich drives one plate, e.g., 12 of a sensor 10 so that a current (IG + jB ), due to bo-th the conductive and capacitive components, appears at the opposed plate 14. The sensor 10 and electrical circuit components, unless stated otherwise herein, can be essentially described in the above cited U, S. patents.
The oscillator output also is fed to a comparator 22 to detect the axis crossing of the sensor excitation voltage (see Figure lC), Also, the oscillator is fed to one input of multipliers 23 and 36. The current from the sensor plate enters the summing junction (~) input of an amplifier 24 which translates the current to a voltage signal with some effective gain, A second voltage gain stage indicated at 26 further amplifies the signal. A
FET switch circuit 2~, driven by the comparator 22, (see Figure lA) commutates the said amplified voltage signal in synchronism with the oscillator into an integration circuit 30 ~rectification is also achieved)~ The output of the ~Z8772 averaging circuit taken off at point 32 of the circuit is proportional to the conductive current IG (in phase component) of the sensor current. The signal from the amplifier 26 is also fed to an integrator 34 which shifts the phase of the signal by 90, therefore, the capacitive (quadrature) currenk signal is shifted into phase with the output of the oscillator (see Figure lB).
The output of the integrator enters multiplier circuit 36 which feeds an averager 38. The output of the averager 38 taken at point 40 is a signal proportional to the capacitive current IB (quadrature current) of the sensor. Since the conductive current of the sensor usually far exceeds (in water) the capacitive current, the ampli-fiers would be driven into saturation unless some means of nulling the conductive current is employed. To accomplish this, the proportional conductive component output of signal available at 32 is fed back to the second input of the multiplier 23. The output of the multiplier is an inversion of the oscillator input to the multiplier, but varying in amplitude. The output of the multiplier is a current, and as such is fed directly into the summing junction (~) as a signal nearly nulling the conductive component of the sensor current~ The averaged output (at 32) is now an error signal proportional to the conductive component IG. The signal levels in the amplifiers are now reduced to non-saturation levels. Thus, it is possible to measure a relatively small value of capacitance in the presence of a rather large con-ductance.
After considerable experimentation, it became evident that unless the plates were bridged by water, the field would tend to locate in the gap, thus reducing the apparent capacitive output due to the presence of the water.
A logical output derived from the conductive output would allow an operator to provide further gain at the capacitive output.
A further refinement is to drive the sensor input to ground, eliminating one active plate, as shown in Figure
Prior U. S. patents 4,074,184 granted 2/14/78, 4,063,153 granted 12/13/77 and 4,082,994 granted 4/4/7~, all of common assignment with the application describe inventions for measuring respective fractions of mixed phased fluids, particularly gas and conductive liquid or solids entrained in liquids utilizing means partlcularly suited for flow which develops a conductance under a voltage field or alternatively utilizing capacitance techniques for non-conductive fluids.
However, there remains a need for means for measuring liquid content of a mixed stream of liquid and gas in situations when the liquid fraction of a stream may be very small (less than 10%) -- a condition occurring, for instance, in some steam flows, which may be measured.
It is therefore the object of the invention to provide commercially practical apparatus meeting such need reliably and economically.
In accordance with the present invention, the amount of liquid is measured by employing its dielectric characteristics. There are two distinct advantages of employing a dielectric capacitive measurement of the amount of water present as a means of establishing respective fractions of water and gas. First, the water does not have to form a conductive lattice between electrodes as is required in conductive or impedance techniques. Second, the dielectric constant of water is very high when compared with most other materials. When the direct measurement of the capacitive component of water is attempted, the rather large conductive component usually causes amplifier over-load. The practice of the present invention involves means to automatically cancel out the conductive component toprevent amplifier overloading.
In accordance with a particular embodiment, a method of measuring liquid content of mixed phase fluid in a container wherein a conductive liquid contains voids therein comprises: making a capacitive current measurement between two spaced (in cross-section of the fluld container) electrodes, and cancelling out a conductive (electrically) component of the current measurement through the fluid inherently picked up in making the capacitive measurement so that the capacitive measurement is not masked by the conductive measurement and wherein the measured current is produced by application of an oscillating voltage to the electrodes and the output capacitive current component ~or a voltage derivative thereof) is shifted into phase with the oscillating voltage.
From another aspect, and in accordance with the invention, an apparatus for practicing the method of the invention comprises: means for applying an oscillating voltage to a mixed phase medium including relatively con-ductive liquid and relatively non-conductive second phase, first means for detecting current produced by said voltage in the medium as a current signal with mixed and varying - conductive and capacitive components, second means apply-ing such current to a summing junction together with a valid transfer function derivative of the conductive component, third means for producing such valid transfer function, fourth means for converting a current output of the summing junction to a voltage and applying components thereof to separate means for indicating conductive and capacitive components of the original measured component.
1~2B772 Other objects, features and advantages of the invention will be apparent from the following detailed description of preferred embodiments thereof, taken in connection with the accompanying drawing, in which:
FIGURE 1 is a block diagram of a circuit to accomplish the automatic cance]lation of the conductive components;
FIGURES lA-lC are voltage vs. time traces taken for different points of the circuit of Figure 1, as mentioned below, and FIGURE 2 is a schematic of a variant embodiment of the invention, The Figure 1 circuit comprises a sinusoidal oscil-lator 20 w~ich drives one plate, e.g., 12 of a sensor 10 so that a current (IG + jB ), due to bo-th the conductive and capacitive components, appears at the opposed plate 14. The sensor 10 and electrical circuit components, unless stated otherwise herein, can be essentially described in the above cited U, S. patents.
The oscillator output also is fed to a comparator 22 to detect the axis crossing of the sensor excitation voltage (see Figure lC), Also, the oscillator is fed to one input of multipliers 23 and 36. The current from the sensor plate enters the summing junction (~) input of an amplifier 24 which translates the current to a voltage signal with some effective gain, A second voltage gain stage indicated at 26 further amplifies the signal. A
FET switch circuit 2~, driven by the comparator 22, (see Figure lA) commutates the said amplified voltage signal in synchronism with the oscillator into an integration circuit 30 ~rectification is also achieved)~ The output of the ~Z8772 averaging circuit taken off at point 32 of the circuit is proportional to the conductive current IG (in phase component) of the sensor current. The signal from the amplifier 26 is also fed to an integrator 34 which shifts the phase of the signal by 90, therefore, the capacitive (quadrature) currenk signal is shifted into phase with the output of the oscillator (see Figure lB).
The output of the integrator enters multiplier circuit 36 which feeds an averager 38. The output of the averager 38 taken at point 40 is a signal proportional to the capacitive current IB (quadrature current) of the sensor. Since the conductive current of the sensor usually far exceeds (in water) the capacitive current, the ampli-fiers would be driven into saturation unless some means of nulling the conductive current is employed. To accomplish this, the proportional conductive component output of signal available at 32 is fed back to the second input of the multiplier 23. The output of the multiplier is an inversion of the oscillator input to the multiplier, but varying in amplitude. The output of the multiplier is a current, and as such is fed directly into the summing junction (~) as a signal nearly nulling the conductive component of the sensor current~ The averaged output (at 32) is now an error signal proportional to the conductive component IG. The signal levels in the amplifiers are now reduced to non-saturation levels. Thus, it is possible to measure a relatively small value of capacitance in the presence of a rather large con-ductance.
After considerable experimentation, it became evident that unless the plates were bridged by water, the field would tend to locate in the gap, thus reducing the apparent capacitive output due to the presence of the water.
A logical output derived from the conductive output would allow an operator to provide further gain at the capacitive output.
A further refinement is to drive the sensor input to ground, eliminating one active plate, as shown in Figure
2 where a current transformer IXF extracts a measured current from a grounded sensing electrode GE for application to the summing junction ~ Also, a driven shield ~S is extended to form an electrode around the driven electrode DE to focus the sensing field SF.
It is evident that those skilled in the art, once given the benefit of the foregoing disclosure, may now make numerous other uses and modifications of, and departures from the specific embodiments described herein without de-parting from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in, or possessed by, the apparatus and techniques herein disclosed and limited solely by the scope and spirit of the appended claims.
It is evident that those skilled in the art, once given the benefit of the foregoing disclosure, may now make numerous other uses and modifications of, and departures from the specific embodiments described herein without de-parting from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in, or possessed by, the apparatus and techniques herein disclosed and limited solely by the scope and spirit of the appended claims.
Claims (5)
1. Method of measuring a liquid content of mixed phase fluid in a container wherein a conductive liquid contains voids therein comprising, making a capacitive current measurement between two spaced (in cross-section of the fluid container) electrodes, and cancelling out a conductive (electrically) component of the current measurement through the fluid inherently picked up in making the capacitive measurement so that the capacitive measurement is not masked by the conductive measurement and wherein the measured current is produced by application of an oscillating voltage to the electrodes and the output capacitive current component (or a voltage derivative there-of) is shifted into phase with the oscillating voltage.
2. Method in accordance with claim 1 wherein the conductive current component is attenuated, through feed-back, and amplified, without saturation of amplifier apparatus.
3. Apparatus for practice of the method of claim 1 comprising, means for applying an oscillating voltage to a mixed phase medium including relatively conductive liquid and relatively non-conductive second phase, first means for detecting current produced by said voltage in the medium as a current signal with mixed and varying conductive and capacitive components, second means applying such current to a summing junction together with a valid transfer function derivative of the conductive component, third means for producing such valid transfer function, fourth means for converting a current output of the summing junction to a voltage and applying components thereof to separate means for indicating conductive and capacitive components of the original measured component.
4. Apparatus for practice of the method of claim 2 comprising, means for applying an oscillating voltage to a mixed phase medium including relatively conductive liquid and relatively non-conductive second phase, first means for detecting current produced by said voltage in the medium as a current signal with mixed and varying conductive and capacitive components, second means applying such current to a summing junction together with a valid transfer function derivative of the conductive component, third means for producing such valid transfer function, fourth means for converting a current output of the summing junction to a voltage and applying components thereof to separate means for indicating conductive and capacitive components of the original measured component.
5. Apparatus in accordance with either one of claims 3 or 4 wherein said third means include a feedback loop with voltage derivative of conductive component of current applied together with the oscillating voltage to a multiplier which produces a current output as a negative sign transfer function of conductive component of measured current.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA374,209A CA1128772A (en) | 1981-03-30 | 1981-03-30 | Electrical measurement of fluid void fraction for fluid having capacitive and resistive conductive components |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA374,209A CA1128772A (en) | 1981-03-30 | 1981-03-30 | Electrical measurement of fluid void fraction for fluid having capacitive and resistive conductive components |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1128772A true CA1128772A (en) | 1982-08-03 |
Family
ID=4119582
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA374,209A Expired CA1128772A (en) | 1981-03-30 | 1981-03-30 | Electrical measurement of fluid void fraction for fluid having capacitive and resistive conductive components |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1128772A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9465001B2 (en) | 2014-09-15 | 2016-10-11 | Bourns, Inc. | Conductive liquid property measurement using variable phase mixing |
-
1981
- 1981-03-30 CA CA374,209A patent/CA1128772A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9465001B2 (en) | 2014-09-15 | 2016-10-11 | Bourns, Inc. | Conductive liquid property measurement using variable phase mixing |
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