Interactive and adaptive data acquisition system for use with electrical capacitance volume tomography

Abstract

A control system and data acquisition system for an electrical capacitance tomography sensor comprised of a sensor having a plurality of electrodes, where each electrode is further comprised of a plurality of capacitance segments. Each of the capacitance segments of each electrode can be individually addressed to focus the electric field intensity or sensitivity to desired regions of the electrodes and the sensor.

Claims

1. A system for generating a three-dimensional tomograph of a vessel interior or other object, the system comprising: a three-dimensional capacitance sensor device comprising a plurality of electrodes for placement around the vessel or the object, wherein the three-dimensional capacitance sensor device is adapted to provide electric field distribution and sensor sensitivity in three geometric dimensions, wherein the three-dimensional capacitance sensor device has an input and an output; a reference capacitor electrically connected to the input of the three-dimensional capacitance sensor device; data acquisition electronics in communication with the output of the three-dimensional capacitance sensor device for receiving input data from the three-dimensional capacitance sensor device and in communication with the reference capacitor for obtaining the capacitance measurement of the reference capacitor; a processing system in communication with the data acquisition electronics, the processing system programmed with instructions for executing on the processing system to: a.) use the capacitance measurement of the reference capacitor as a reference for calibration of the system; b.) calibrate the system based on the capacitance measurement of the reference capacitor and use the capacitance measurement of the reference capacitor to back calculate capacitance values or to set calibration parameters for the three-dimensional capacitance sensor device; and c.) reconstruct a three-dimensional volume-image from the input data collected by the data acquisition electronics.

2. A system according to claim 1, wherein the three-dimensional capacitance sensor device is an adaptive electrical capacitance volume tomography sensor device and wherein the plurality of electrodes are each comprised of a plurality of capacitance segments; and wherein the plurality of capacitance segments of at least one electrode are individually addressable with voltages.

3. A system according to claim 1, further comprising: a balance signal line electrically connected to the output of the three-dimensional sensor for providing a balance signal to the system to mitigate the effect of drift; a receiver amplifier having an input and output, wherein the input of the receiver amplifier is electrically connected with the output of the three-dimensional sensor and wherein the output of the receiver amplifier is in electrical communication with the data acquisition electronics.

4. A system according to claim 3, further comprising: a precision balance attenuator electrically connected to the balance signal line to provide interactive control of the system.

5. A system according to claim 4, further comprising: a first digital-to-analog converter in electrical communication with the input of the three-dimensional capacitance sensor device; a first analog-to-digital converter in electrical communication with the output of the three-dimensional sensor; a second digital-to-analog converter in electrical communication with the precision balance attenuator; and a common voltage reference electrically connected to the first and second digital-to-analog converter and the first analog-to-digital converter to eliminate the effect of drift.

6. A system according to any one of claim 4, further comprising: reference plates embedded into walls of the three-dimensional capacitance sensor device; and wherein the processing system is programmed with instructions for executing on the processing system to: a.) determine temperature characteristics based on changes in capacitance of the reference plates; and b.) tune the three-dimensional capacitance sensor device based on the temperature characteristics.

7. A system according to any one of claims 1 and 4, further comprising: an excitation attenuator in electrical communication with the input of the three-dimensional capacitance sensor device to provide control over the electronic signaling to the input of the three-dimensional capacitance sensor.

8. A system according to claim 7, wherein the excitation attenuator is controlled based on the dielectric constant of a material used with the system.

9. A system according to claim 1, wherein the processing system is programmed with instructions for executing on the processing system to: store measured capacitances between a first and second electrode of the three-dimensional capacitance sensor device, wherein a first stored measured capacitance is the capacitance with the first electrode as a sending electrode and the second electrode as a receiving electrode, wherein a second stored measured capacitance is the capacitance with the second electrode as the sending electrode and the first electrode as the receiving electrode; and determining a final capacitance as a weighted average of the first and second stored measured capacitances of the first and second electrodes.

10. A system according to claim 1, wherein the processing system is programmed with instructions for executing on the processing system to: calibrate the system using Bayesian statistical prediction.

11. A system according to claim 1, wherein the processing system is programmed with instructions for executing on the processing system to: a.) store data collected from the three-dimensional capacitance sensor device; b.) use the stored data to predict a varying component of a capacitance signal using Bayesian statistical modeling.

12. A system according to claim 11, wherein the processing system is programmed with instructions for executing on the processing system to: set a balance signal to eliminate fixed components of capacitance measurements from the three-dimensional capacitance sensor device.

13. A system according to claim 1, wherein the three-dimensional capacitance sensor device is an adaptive electrical capacitance volume tomography sensor device and wherein the plurality of electrodes are each comprised of a plurality of capacitance segments; wherein the plurality of capacitance segments of at least one electrode are individually addressable with voltages, the system further comprising: a plurality of analog and Direct Digital Synthesis (DDS) attenuators in electrical communication with the plurality of capacitance segments for controlling voltage on the capacitance segments.

14. A system according to claim 1, wherein the three-dimensional capacitance sensor device is an adaptive electrical capacitance volume tomography sensor device and wherein the plurality of electrodes are each comprised of a plurality of capacitance segments; wherein the plurality of capacitance segments of at least one electrode are individually addressable with voltages, the system further comprising: a plurality of analog and phase shifters in electrical communication with the plurality of capacitance segments for controlling voltage on the capacitance segments.

15. A system according to claim 1, wherein the three-dimensional capacitance sensor device is an adaptive electrical capacitance volume tomography sensor device and wherein the plurality of electrodes are each comprised of a plurality of capacitance segments; wherein the plurality of capacitance segments of at least one electrode are individually addressable with voltages, the system further comprising: a tunable band pass filter in electrical communication with the output of the three-dimensional capacitance sensor device; and wherein the processing system is programmed with instructions for executing on the processing system to identify a location of active electricity within the three-dimensional capacitance sensor device.

16. A system according to claim 15, further comprising: a phase shifter in electrical communication with the input of the three-dimensional capacitance sensor device for synchronizing with the active electricity; and an attenuator in electrical communication with the input of the three-dimensional capacitance sensor device for detecting an amplitude of active electricity.

17. A system according to claim 1, wherein the processing system is programmed with instructions for executing on the processing system to use the capacitance measurement from the reference capacitor to autocorrect online imaging.

18. A system for generating a three-dimensional tomograph of a vessel interior or other object, the system comprising: a three-dimensional capacitance sensor device comprising a plurality of electrodes for placement around the vessel or the object, wherein the three-dimensional capacitance sensor device is adapted to provide electric field distribution and sensor sensitivity in three geometric dimensions, wherein the three-dimensional capacitance sensor has an input and an output; data acquisition electronics in communication with the output of the three-dimensional capacitance sensor device for receiving input data from the three-dimensional capacitance sensor device; and a processing system in communication with the data acquisition electronics, the processing system programmed with instructions for executing on the processing system to reconstruct a three-dimensional volume-image from the input data collected by the data acquisition electronics; wherein the three-dimensional capacitance sensor device is an adaptive electrical capacitance volume tomography sensor device and wherein the plurality of electrodes are each comprised of a plurality of capacitance segments; wherein the plurality of capacitance segments of at least one electrode are individually addressable with voltages, the system further comprising: a tunable band pass filter in electrical communication with the output of the three-dimensional capacitance sensor device; a phase shifter in electrical communication with the input of the three-dimensional capacitance sensor device for synchronizing with the active electricity; an attenuator in electrical communication with the input of the three-dimensional capacitance sensor device detecting an amplitude of active electricity; and wherein the processing system is programmed with instructions for executing on the processing system to identify a location of active electricity within the three-dimensional capacitance sensor device.

19. A system according to claim 18, further comprising: a reference capacitor of a fixed predetermined value electrically connected to the input of the three-dimensional capacitance sensor device and wherein the data acquisition system is in electrical communication with the reference capacitor for obtaining the capacitance measurement of the reference capacitor; wherein the processing system is programmed with instructions for executing on the processing system to: a.) use the capacitance measurement of the reference capacitor as a reference for calibration of the system; and b.) calibrate the system based on the capacitance measurement of the reference capacitor and use the capacitance measurement of the reference capacitor to back calculate capacitance values or to set calibration parameters for the three-dimensional capacitance sensor device.

20. A system for generating a three-dimensional tomograph of a vessel interior or other object, the system comprising: a three-dimensional capacitance sensor device comprising a plurality of electrodes for placement around the vessel or the object, wherein the three-dimensional capacitance sensor device is adapted to provide electric field distribution and sensor sensitivity in three geometric dimensions, wherein the three-dimensional capacitance sensor device has an input and an output; a reference capacitor electrically connected to the input of the three-dimensional capacitance sensor device; data acquisition electronics in communication with the output of the three-dimensional capacitance sensor device for receiving input data from the three-dimensional capacitance sensor device and in communication with the reference capacitor for obtaining the capacitance measurement of the reference capacitor; a processing system in communication with the data acquisition electronics, the processing system programmed with instructions for executing on the processing system to: a.) use the capacitance measurement of the reference capacitor as a reference for calibration of the system; b.) calibrate the system based on the capacitance measurement of the reference capacitor; and c.) reconstruct a three-dimensional volume-image from the input data collected by the data acquisition electronics; a balance signal line electrically connected to the output of the three-dimensional sensor for providing a balance signal to the system to mitigate the effect of drift; and a receiver amplifier having an input and output, wherein the input of the receiver amplifier is electrically connected with the output of the three-dimensional sensor and wherein the output of the receiver amplifier is in electrical communication with the data acquisition electronics.

21. A system for generating a three-dimensional tomograph of a vessel interior or other object, the system comprising: a three-dimensional capacitance sensor device comprising a plurality of electrodes for placement around the vessel or the object, wherein the three-dimensional capacitance sensor device is adapted to provide electric field distribution and sensor sensitivity in three geometric dimensions, wherein the three-dimensional capacitance sensor has an input and an output; data acquisition electronics in communication with the output of the three-dimensional capacitance sensor device for receiving input data from the three-dimensional capacitance sensor device; and a processing system in communication with the data acquisition electronics, the processing system programmed with instructions for executing on the processing system to reconstruct a three-dimensional volume-image from the input data collected by the data acquisition electronics; wherein the three-dimensional capacitance sensor device is an adaptive electrical capacitance volume tomography sensor device and wherein the plurality of electrodes are each comprised of a plurality of capacitance segments; wherein the plurality of capacitance segments of at least one electrode are individually addressable with voltages, the system further comprising: a tunable band pass filter in electrical communication with the output of the three-dimensional capacitance sensor device; a reference capacitor of a fixed predetermined value electrically connected to the input of the three-dimensional capacitance sensor device and wherein the data acquisition electronics is in electrical communication with the reference capacitor for obtaining the capacitance measurement of the reference capacitor; wherein the processing system is programmed with instructions for executing on the processing system to: a.) use the capacitance measurement of the reference capacitor as a reference for calibration of the system; and b.) calibrate the system based on the capacitance measurement of the reference capacitor and use the capacitance measurement of the reference capacitor to back calculate capacitance values or to set calibration parameters for the three-dimensional capacitance sensor device; and wherein the processing system is programmed with instructions for executing on the processing system to identify a location of active electricity within the three-dimensional capacitance sensor device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following detailed description of the example embodiments refers to the accompanying figures that form a part thereof. The detailed description provides explanations by way of exemplary embodiments. It is to be understood that other embodiments may be used having mechanical and electrical changes that incorporate the scope of the present invention without departing from the spirit of the invention.

(2) In addition to the features mentioned above, other aspects of the present invention will be readily apparent from the following descriptions of the drawings and exemplary embodiments, wherein like reference numerals across the several views refer to identical or equivalent features, and wherein:

(3) FIG. 1 depicts an example of a real-time image of voids in a bed of particles using a CT scan and an Electrical Capacitance Volume Tomography (ECVT) sensor.

(4) FIG. 2 illustrates one embodiment of the present invention having a sensor with up to 24 plates.

(5) FIG. 3 illustrates an exemplary circuit embodiment for single excitation and receiver channels to measure the capacitance of adaptive sensor segments for single capacitance measurements.

(6) FIG. 4 illustrates an exemplary circuit embodiment for single excitation and receiver channels for measuring the capacitance of adaptive sensor segments for single capacitance measurements.

(7) FIG. 5 illustrates one embodiment circuit for single excitation and receiver channels for measuring the capacitance of adaptive sensor segments for single capacitance measurements.

(8) FIG. 6 illustrates an exemplary circuit is for single excitation and receiver channels for measuring the capacitance of ECVT sensors for single capacitance measurements.

(9) FIG. 7 illustrates an exemplary circuit for single excitation and receiver channels for measuring capacitance of adaptive sensor segments for single capacitance measurements.

(10) FIG. 8 is a 3D depiction of exemplary capacitance sensors for temperature measurements.

(11) FIG. 9 is an exemplary embodiment for single excitation and receiver channels for measuring capacitance of active electricity for single capacitance measurements.

(12) FIG. 10 illustrates an exemplary embodiment for single excitation and receiver channels for measuring capacitance of adaptive sensor segments for single capacitance measurements.

(13) FIG. 11 illustrates an exemplary embodiment for single excitation and receiver channels to measure capacitance of adaptive sensor segments for single capacitance measurements.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

(14) FIG. 1 depicts an example of a real-time image of voids in a bed of particles using a CT scan and an Electrical Capacitance Volume Tomography (ECVT) sensor. Both CT scan image and ECVT imaging of the same structure were obtained for direct comparison. The image shows discrepancy of resolution between both imaging technologies. The left column illustrates reconstruction using ECVT of a packed bed with ping pong balls to simulate voids placed at different locations. The right column illustrates a CT scan of the ECVT system including particles, voids, column and sensors.

(15) FIG. 2 illustrates one embodiment of the present invention having a sensor with up to 24 plates. More plates can be accommodated by adding more excitation and receiver groups. The embodiment of FIG. 2 is comprised of:

(16) 1) a self-calibration (or reference) capacitor (10) connected to the multiplexer input. The self-calibration capacitor can be used to test the instrument, perform automatic calibration without user involvement, compensate for long term drift and temperature variation, and provide data of virtual flows.

(17) 2) low frequency interference blocking through high pass capacitors (12) to eliminate power line frequency interference.

(18) 3) excitation attenuators (14) at excitation channels: The attenuators are preferably used to control the drive signal amplitude for materials with different dielectric constants and for simulating low capacitance values from a reference capacitor.

(19) 4) a balance signal injection point (18) at the front to maintain stability.

(20) 5) precision balance attenuators (20) preferably compatible with a wide range of dielectric constants to provide interactive control of the acquisition system.

(21) 6) a common voltage reference signal supplying excitation and balance to Digital-to-Analog Converters (DAC) (shown at (22 A, B)), and Analog-to-Digital Converters (ADC) (shown at (22C)). This makes all measurements ratiometric, cancelling out temperature drift of the reference. The common voltage reference that supplies the excitation DAC (Digital-to-Analog Converter at (22A)), the Balance DAC (at (22B)) and the ADC's (Analog-to-Digital Converter at (22C)) improves temperature stability.

(22) The interactive design of the present invention enables self calibration by including an internal reference capacitor with a known value. The internal capacitor acts as a reference through which any capacitance measurement can be back calculated by comparing PGA, balance, phase shifts, and excitation parameters to those of the reference capacitance measurement parameters. Self calibration of a capacitance sensor can be achieved by simulating the capacitance signal of an empty sensor and adjusting parameters of data acquisition using the reference capacitor. In prior art systems, a capacitor is used to empty charges from and into a reference capacitor to compensate for parasitic capacitance. This prior art technique is different than the present invention in at least two ways: 1) it is designed for a charge/discharge acquisition system whereas present invention is AC based and 2) it uses a reference capacitor to empty or withdraw charges to compensate for parasitic capacitance whereas the present invention measures parameters of a reference capacitor through an FPGA and uses those parameters as a reference for parameters of other measured capacitances. Parameters are used to back calculate capacitance values or to set calibration parameters for a particular sensor.

(23) The electronic multiplexer (15) can be considered a switch that connects the drive signal to each electrode (or plate) of the sensor as each electrode is selected. Accordingly, the driving signal is considered the input to the sensor in the present invention. Similarly, the multiplexer (17) at the backend is a switch that connects to another one of the selected electrodes on the sensor so that a capacitance reading can be obtained between the selected electrodes. Accordingly, in FIG. 2, the output of the backend multiplexer can be considered the output of the sensor.

(24) The reference capacitor is connected to the output of the sensor through the same path which receiver signal comes from different channels (the output of the sensor is also referred to as the receiver signal because it is received by the data acquisition portion of the system that collects the capacitance data and reconstructs the image for the area within the sensor). The output of the reference capacitor of FIG. 2 replaces the capacitance coming from a sensor channel with a static value.

(25) The output of the sensor is also where the balance signal is connected (18). Accordingly, the balance signal connects to every channel output signal as they are selected by the multiplexer. As the reference capacitor is connected to act as a capacitance channel, it is also connected to the sensor output through the multiplexer. The self-calibration capacitor provides a static reference. The static capacitance of the reference capacitor can be used as a reference when measuring the drift or change in signal for testing of the instrument, when performing automatic calibration without user involvement, when compensating for long term drift and temperature variation, and when providing data of virtual flows.

(26) For example, the reference capacitor can be used in the following ways:

(27) 1measure the static capacitance and store calibration parameters. Then perform the same thing again after a period of time. The difference between both measurements would be attributed to drift in system electronics.

(28) 2use excitation attenuators with the static capacitor to simulate different capacitance values.

(29) 3store actual flow patterns by representing each measured capacitance value by different level of excitation to reference capacitor. The collection of all stored excitation for capacitance values in a frame represents data for reconstruction of flow image of the stored flow.

(30) The balance signal at the front end, and before the receiver amplifier, is used to eliminate drift in the signal due to temperature variation of the amplifier.

(31) The present invention preferably uses a common voltage reference for supplying excitation and balance of the DAC, and ADC's. This allows for ratiometric measurements, cancelling out temperature drift of the reference. The common voltage reference is supplied to items marked as (22) in FIG. 2. ADC and DAC devices convert analog signals to digital ones and digital signals to analog ones, respectively. Reference voltage is supplied to the ADC and DAC and is used to set the voltage level. The reference voltage is used to set how much voltage is from one digital step to another in the process of converting it to or from analog. The reference voltage is the maximum value that an ADC/DAC can convert. This voltage range is divided by the DAC/ADC resolution, or steps. If two DAC or ADC are used with a different voltage reference, the step size will be different, and the same digital number would be converted to a different analog value or vice versa.

(32) Having all ADC and DAC connected to the same reference voltage eliminates the effect of drift in the reference voltage. Since digital steps in all ADC or DAC are impacted the same because of a voltage drift, the net result is that they will be cancelled. For example, a drift in ADC will impact the digital step, when converting it back to analog, the DAC will be impacted by the same reference drift and it will cancel the total effect, thus preserving the signal.

(33) The balance signal is added to the receiver signal before receiver amplifier (or in other words to it is added to the output of the sensor at (18) to maintain stability). Accordingly, the drift in the receiver amplifier will affect both signals, mitigating its effect on the combined signal. In the past, the balance was injected after the receiver amplifier. In such arrangements, if a drift occurs after the cell is calibrated; a drift in the amplifier will yield a non-zero balance as it only affects the output of the sensor and not the balance signal. The balance signal function cancels the empty cell output. So a drift in the receiver amplifier would affect the receiver plate signal but not the balance.

(34) In the preferred embodiment, excitation attenuators are connected to the sensor input. The excitation attenuators at excitation channels control the drive signal for materials with different dielectric constants. The electronics can saturate if a material with high dielectric constant is used. They are brought back to the required dynamic range that matches the ADC by reducing the excitation signal using the attenuators.

(35) Precision balance attenuators are preferably used with the present invention that are compatible with wide range of dielectric constants to provide interactive control of acquisition system. The balance attenuator is implemented in two ways: 1through a multiplexer of voltage dividers in block 20 of FIG. 2, and 2digitally in the DDS. Similarly, the balance also preferably needs to be attenuated with precision to match the receiver signal and cancel out the empty cell output (e.g., empty column signal).

(36) FIG. 3 illustrates an exemplary circuit embodiment for single excitation and receiver channels to measure the capacitance of adaptive sensor segments for single capacitance measurements. In the following figures, the parallel lines labeled Exc(n) and Rec(n) represent capacitance segments of the sensors of the present invention. A segment in a plate is a small element that can be excited with different levels of voltage and degrees of phase. An adaptive plate is composed of a number of segments, each excited independently. Collective response of segments at the receiver end represent an adaptive receiver plate. This building block can be used with other circuit components like FIG. 2 to form a full system to measure multiple capacitance values of an AECVT sensor. Special features of this circuit are: 1) an attenuator (24) is used with each segment to provide control over voltage level; 2) signals are added (26) after the receiver (28) from each receiving segment; 3) signals (30) are preferably processed as a single capacitance value.

(37) FIG. 4 illustrates an exemplary circuit embodiment for single excitation and receiver channels for measuring the capacitance of adaptive sensor segments for single capacitance measurements. This building block can be used with other circuit components like FIG. 2 to form a full system to measure multiple capacitance values of an AECVT sensor. This building block features:

(38) 1) time division to isolate cross-excitation segment capacitance contribution to the total added capacitance signal.

(39) 2) activating each segment in a different time slot and storing its receiver value in a delay for later retrieval (when a segment is excited, all other sending segments are grounded and one receiver signal is activated at a time).

(40) 3) adding all receiver signals after all excitation segments are addressed.

(41) 4) since each receiver signal is measured independently at a different time, the added receiver signal represents the weight of each independent capacitance measurement at different time slots.

(42) FIG. 5 illustrates one embodiment circuit for single excitation and receiver channels for measuring the capacitance of adaptive sensor segments for single capacitance measurements. This building block can be used with other circuit components like FIG. 2 to form a full system to measure multiple capacitance values of an AECVT sensor. This building block features:

(43) 1) each segment is activated with multiple frequencies independently.

(44) 2) band pass filters (32) determine each receiver's excitation channel. (Receiver signals are added (34) after demodulation to isolate frequency factors for different capacitors).

(45) 3) each receiver channel reacts to all excitation channels for that specific frequency. This is different than the prior art as signals from different frequencies here are meant to implement adaptive signals by adding all receiver channels together. In the prior art, each frequency addresses a combination of excitation and receiver plates independently. In the present invention, collective responses from all segments are added to together.

(46) FIG. 6 illustrates an exemplary circuit is for single excitation and receiver channels for measuring the capacitance of ECVT sensors for single capacitance measurements. This building block can be used with other circuit components like FIG. 2 to form a full system to measure multiple capacitance values of an AECVT sensor. This building block features:

(47) 1) an excitation signal is activated with multiple frequencies simultaneously and received from one receiver plate to multiple receiver channels through BPF's (36).

(48) 2) this allows a degree of freedom in measured data related to capacitance change at different frequencies. Materials have different dielectric constant at different frequencies and temperatures.

(49) FIG. 7 illustrates an exemplary circuit for single excitation and receiver channels for measuring capacitance of adaptive sensor segments for single capacitance measurements. This building block can be used with other circuit components like FIG. 2 to form a full system to measure multiple capacitance values of an AECVT sensor. This building block features:

(50) 1) providing different phase shifts for different excitation signals.

(51) 2) phase shifts can be used to steer equivalent electric field distribution to steer a sensitivity matrix distribution. This feature enables focus and zooming in an AECVT sensor.

(52) FIG. 8 is a 3D depiction of exemplary capacitance sensors for temperature measurements. As sensor plate shapes (38) and orientation may affect temperature response in measured capacitance, different temperature sensing plates may be employed to mimic shape and orientation of ECVT sensor plates for better mapping of temperature effect. Sensors (40) are used to establish a temperature profile for each plate combination in the capacitance sensor. Temperature measurements may be collected by:

(53) 1) establishing a lookup table or graph for capacitance change of empty column to temperature for each sensor plate combination embedded in a column wall (42).

(54) 2) embedding a temperature sensor in the wall to measure temperature and changing balance signal to account for static change (allowing interactive control).

(55) 3) using multiple plates embedded in the column wall to measure temperature in the wall by comparing their capacitance to a reference capacitance. A lookup table is preferably used to lookup capacitance change associated with measured temperature and compensate through balance signal.

(56) 4) compensating for effect of temperature on capacitance change due to plate expansion/deformation from that due to flow variation (because the effect of flow variation and that of temperature change in the sensor material are embedded in the same capacitance measurements, it is of interest to isolate the portion of the measured capacitance that is due to flow changes from that which is caused by the sensor plates or from the refractory material changing temperature). This can be established by measuring capacitance variation of an empty sensor at different temperatures. The lookup table can then be used to estimate temperature and capacitance change of an empty sensor. This estimation is used to compensate for changes in capacitance measurement that are due to temperature change in the sensor itself, thus the new compensated capacitance measurement will only represent change in the flow (not sensor temperature) so flow can be imaged accurately. This process isolates capacitance change of temperature variation due to flow from that due to the sensor.

(57) The capacitance measurement from the reference capacitor can also be used to autocorrect online imaging. In online imaging, volume images are directly provided to the user by embedding the reconstruction algorithm in the FPGA. The system applies previously recorded parameters of static objects to reference capacitors to emulate a static object online. Discrepancies in reconstruction of emulated capacitance and images of static objects are then used to recalibrate the data acquisition system.

(58) FIG. 9 is an exemplary embodiment for single excitation and receiver channels for measuring capacitance of active electricity for single capacitance measurements. This building block can be used with other circuit components like FIG. 2 to form a full system to measure multiple capacitance values of an ECVT sensor. This building block features:

(59) 1) multiple frequency excitation or sweep excitation of plates, attenuator (44) for control of excitation amplitude and phase shifter (46) for control of excitation phase.

(60) 2) tunable Band Pass Filters (BPF) (48) to identify frequency of active electricity in imaging domain. The phase shifter in excitation channels is used to synchronize with active electricity for maximum signal output.

(61) 3) the attenuator is used to measure active electricity amplitude.

(62) 4) sweep frequency and tunable BPF are to identify frequency range of active electricity in the imaging domain.

(63) 5) collective measurements from ECVT sensor plates are to be used to reconstruct location of active electricity in the imaging domain.

(64) FIG. 10 illustrates an exemplary embodiment for single excitation and receiver channels for measuring capacitance of adaptive sensor segments for single capacitance measurements. This building block can be used with other circuit components like FIG. 2 to form a full system to measure multiple capacitance values of an AECVT sensor. This building block features:

(65) 1) current attenuator (50) located after receiver segments for assigning different weights to currents from different receiver segments.

(66) 2) the current attenuators are used to shape the sensitivity of the adaptive sensor by combing receiver segments with different weights.

(67) FIG. 11 illustrates an exemplary embodiment for single excitation and receiver channels to measure capacitance of adaptive sensor segments for single capacitance measurements. This building block can be used with other circuit components like FIG. 2 to form a full system to measure multiple capacitance values of an AECVT sensor. This building block features:

(68) 1) on-phase and quadrature parallel detectors followed by a root-sum-square magnitude summation (54). A 90 degree phase shifter (52) provides the reference signal for the quadrature detector.

(69) 2) the phase of the detected signal is the arctangent of the in-phase and quadrature components.

(70) 3) detected signal phase is used to represent dielectric and conductive material properties in a dual-modality mode. Phase of the detected signal in dual-modality is compared to phase of a calibrated signal to decouple material in the imaging domain from its conductive and dielectric properties.

(71) In an exemplary embodiment of the invention, synchronous detection of the signal after the receiver amplifier is provided using a detector reference and its 90 degree phase shifted complement. The detector reference and its 90 degrees phase shifted complement are multiplied separately with the signal from receiver amplifier. The magnitude of the signal is the root-sum-square summation of the in-phase and 90 degree quadrature components. The phase of the signal is the arctangent of the in-phase and quadrature components. The synchronous detector is used during imaging operation and is also used during the calibration process of the data acquisition system.

(72) The present invention also preferably includes a redundant plate measurement technique. Typically in capacitance measuring devices, the capacitance between two plates is considered to be the same regardless which of the two plates is considered a sender and which is considered a receiver. In the present invention a distinction is established and a capacitance between two pair of plates is calibrated and measured with each plate acting as a receiver and the other plate as sender in one arrangement, and vise versa in another arrangement. The final capacitance is a weighted average of the two measured capacitance values for the same pair of plates. A determination if the two redundant values are weighted equally or not is determined depending on sensor design.

(73) While certain embodiments of the present invention are described in detail above, the scope of the invention is not to be considered limited by such disclosure, and modifications are possible without departing from the spirit of the invention as evidenced by the following claims.