Systems and methods for flow sensing in a conduit

Systems and methods for flow sensing in a conduit are provided. One system includes a flow disturber disposed in a flow conduit and configured to impart a flow disturbance to the fluid flow. The system further includes a plurality of flow sensors disposed in the flow conduit and responsive to flow characteristics in the flow conduit. The system also includes a frequency resolver configured to determine frequency information related to the fluid flow based on the flow characteristics. The frequency resolver uses one or more time sample windows to select data samples for use in determining the frequency information, wherein a length of one or more of the time sample windows is based at least in part on the flow characteristics. The system additionally includes a processor configured to determine a flow rate of the fluid flow in the flow conduit using the frequency information.

BACKGROUND

Flow sensing may be used in a variety of different applications, such as to determine flow velocity of a fluid, such as gas (e.g., air) or liquid, through a pipe or tube. For example, flow sensing may be used in ventilation and respiration machines to detect and control the level of air flow. As another example, flow sensing may be used in gas metering systems, such as for residential applications.

The determination of the fluid flow may be affected by many different factors, such as temperature, moisture variations, or the type or density of fluid, among others. Some conventional systems are not satisfactorily responsive to these different factors. As a result, the outputs of these systems may drift and cause readings that are not accurate. Additionally, the robustness of these systems suffer.

In a medical setting, when using ventilation and respiration machines such as continuous positive airway pressure (CPAP) machine and a variable positive airway pressure (VPAP) machine, it is important to be able to determine accurately the flow rate of ventilation and/or respiration. For example, the air supply pressure from these machines is varied based on whether the person is breathing in or out, such as during inspiration and expiration phases of the respiratory system. By properly controlling the air flow during different phases of breathing, a more comfortable process results. The more comfortable the ventilation and/or respiratory machine is to a person during use, the more likely the person is to continue to use the ventilation and/or respiratory machine. Users of ventilation and/or respiratory machines may unilaterally decide to cease use of the machine as a result of the machine being uncomfortable during operation, such as when an appropriate air pressure is not supplied. However, due to the complex nature of breathing and the change in direction and speed of air flow during breathing (as well as other factors), it is very difficult to determine flow rates.

BRIEF DESCRIPTION

In accordance with various embodiments, a flow sensor assembly is provided that includes a flow conduit configured to allow fluid flow therethrough and a flow disturber disposed in the flow conduit, wherein the flow disturber is configured to impart a flow disturbance to the fluid flow. The flow sensor assembly further includes a plurality of flow sensors disposed in the flow conduit, wherein the plurality of flow sensors is responsive to flow characteristics in the flow conduit. The flow sensor assembly also includes a frequency resolver coupled to the plurality of flow sensors, wherein the frequency resolver is configured to determine frequency information related to the fluid flow based on the flow characteristics. The frequency resolver uses one or more time sample windows to select data samples from the plurality of flow sensors for use in determining the frequency information, wherein a length of one or more of the time sample windows is based at least in part on the flow characteristics. The flow sensor assembly additionally includes a processor coupled to the plurality of flows sensors and the frequency resolver, wherein the processor is configured to determine a flow rate of the fluid flow in the flow conduit using the frequency information.

In accordance with other various embodiments, a method for determining flow rate in a conduit is provided. The method includes positioning within a flow conduit a flow disturber configured to impart a flow disturbance to the fluid flow and disposing a plurality of flow sensors in the flow conduit, wherein the plurality of flow sensors are responsive to flow characteristics in the flow conduit. The method also includes coupling at least one frequency resolver to the plurality of flow sensors, wherein the frequency resolver uses one or more time sample windows to select data samples from the plurality of flow sensors for use in determining frequency information. Additionally, a length of one or more time sample windows is based at least in part on the flow characteristics. The method further includes coupling a processor to the plurality of flows sensors and the frequency resolver, wherein the processor is configured to determine a flow rate of the fluid flow in the flow conduit using the frequency information.

In accordance with other various embodiments, a method for determining flow rate in a conduit is provided. The method includes acquiring measurements from a plurality of flow sensors in a flow conduit having disturbances imparted therein, wherein the measurements correspond to flow characteristic information. The method also includes determining frequency information from the measurements within one or more time sample windows, wherein the one or more time sample windows define a plurality of data samples from the plurality of flow sensors for use in determining the frequency information. Additionally, a length of one or more time sample windows is based at least in part on the flow characteristics. The method further includes determining a flow rate of the fluid flow in the flow conduit using the determined frequency information.

DETAILED DESCRIPTION

Although the various embodiments may be described herein within a particular operating environment, it should be appreciated that one or more embodiments are equally applicable for use with other configurations and systems. Thus, for example, the various embodiments may be used in connection with a ventilation and/or respiratory machine, as well as in different medical and non-medical applications.

Various embodiments provide systems and methods for flow sensing or detection using one or more flow sensors. For example, various embodiments use flow sensors to provide volumetric flow sensing. In some embodiments, a plurality of sensors are used for time based sensing and optimization for fast time response volumetric flow sensing. The flow rate determination may be used, for example, in ventilation and/or respiratory machines, such as continuous positive airway pressure (CPAP) machines and variable positive airway pressure (VPAP) machines. However, various embodiments may be used in other systems and applications, for example, natural (or other) gas metering applications, residential gas metering applications, etc.

At least one technical effect of various embodiments is increased accuracy of flow sensing without drift and with a higher degree of robustness with respect to fluid density, mixture, temperature, and/or moisture variations. At least one technical effect of various embodiments is a more robust lower cost flow sensor. At least one technical effect of various embodiments is a simpler package design for a flow sensor with reduced constraints on design parameters.

FIG. 1illustrates schematically a flow sensor assembly110in accordance with an embodiment that may be used, for example, with a CPAP or VPAP machine to determine and control the flow of air to a user, such as to provide varying levels of positive airway pressure to a user when sleeping. However, as described herein, the flow sensor assembly110may be used in other applications. The flow sensor assembly110may be used to provide improved or optimized characterization and sensing of timing characteristics of volumetric flow sensing to obtain faster response flow measurements.

In general, the flow sensor assembly110includes a plurality of sensors, illustrated as the sensors114and116(which in various embodiments are flow sensors) that are disposed within a flow conduit112and are responsive to flow characteristics in the flow conduit. In some embodiments, the sensors114,116are configured (e.g., positioned within the flow conduit112and with respect to each other) to have a geometrical and functional relationship with the flow conduit112and one or more flow disturbers118(or flow disrupter), where one flow disturber118is shown in the illustrated embodiment. For example, the sensors114,116are responsive to flow characteristics within the flow conduit112as described in more detail herein. At least one additional sensor (not shown), such as a thermistor or thermopile device, which in various embodiments is a temperature sensor, may also be disposed within the flow conduit112and configured (e.g., positioned within the flow conduit112and with respect to each other) to have a geometrical and functional relationship with the sensors114,116. In various embodiments, the additional sensor may be responsive to different characteristics, such as temperature characteristics in vicinity or proximity to the sensors114,116.

The sensors114,116in various embodiments are configured to generate signals characteristic of disturbances within the flow conduit112. For example, the disturbances may include a disturbance of the fluid flow, pressure fluctuations in a flow conduit112, acoustic waves (e.g., audible sound waves or ultrasonic acoustic waves), and acoustic energy, among others. Accordingly, a disruption in a fluid flow creates certain characteristics, which may include vortices or pressure/flow pulses that can be sensed and analyzed. In particular, fluid flow will have a certain direction, velocity, pressure, and temperature associated therewith. By placing a disruption in the fluid stream (such as using the flow disturber118), the velocity is altered, as are the pressure and/or temperature. These changes can be detected and analyzed to determine a flow rate of the fluid flow in the flow conduit112, for example, using one or more frequency resolvers120(one is illustrated inFIG. 1). The frequency resolver120may implement, for example, one or more fast Fourier transform (FFT) methods or schemes to process raw waveform data output from the sensors114,116to determine frequency information for the detected flow within the flow conduit112. The determined frequency information then may be used to determine a flow rate of the fluid flow in the flow conduit112as described in more detail herein.

For example, the frequency resolver120may use an FFT algorithm in the art to compute the discrete Fourier transform (DFT) and the inverse of the waveforms. The Fourier transform converts time (or space) to frequency and vice versa. It should be noted that different Fourier transform methods may be used as desired or needed. Additionally, other types of frequency resolving methods may be used, for example, phase-locked loops or heterodyne devices, among others. Moreover, with respect to the frequency resolving, different methods may be used to determine, for example, peak values as described herein, such as thresholding, zero-crossing detection, and/or derivative changes, among others. Thus, the frequency resolver120may be configured, for example, as at least one of a frequency separator. FFT device, zero-flow component resolver, a phase locked loop resolver, a zero crossing resolver and/or a frequency-resolved demodulator.

The sensors114,116, as well as the frequency resolver120are also coupled to a processor122. For example, the sensors114,116may be operatively coupled to the processor124such that the output signals from the sensors114,116are responsive to the flow characteristics in the flow conduit112and are input to the processor122. Thus, the processor122is operably coupled to the sensors114,116and the frequency resolver120to receive measurement data and frequency resolved (e.g., frequency filtered) data. The processor122is configured to determine a flow rate of the fluid flow in the flow conduit112, wherein the processor122may also use the output of the frequency resolver120to select a processing method to determine the flow rate in the flow conduit112.

With respect particularly to the flow sensor assembly110that includes the pair of sensors114,116, which may be different types of sensing elements as described in more detail herein, each of the sensors114,116is positioned within the flow conduit112that has an upstream opening124and a downstream opening126. It should be understood that the terms “upstream” and “downstream” are relative terms that are related to the direction of flow, such as the flow of gas (e.g., air). Thus, in some embodiments, if the direction of flow extends from element126to element124, then element126is the upstream opening and element124is the downstream element. For ease of description, the upstream side of the flow sensor assembly110will be the side closest to the opening124and the downstream side of the assembly will be the side closest to the opening126.

In various embodiments, the flow disturber118is positioned within the conduit112, which in the illustrated embodiment is equidistant between the sensors114,116. However, the sensors114,116may be positioned at different distances from the flow disturber118. In one embodiment, the sensors114,116may be coupled or mounted to a printed circuit board (PCB) or other output interface and/or support member.

In operation, the flow disturber118is configured to form turbulence within the flow stream, such as, for example, waves or eddies, or vortices, where the flow is mostly a spinning motion about an axis (e.g., an imaginary axis), which may be straight or curved. Additionally, vortex shedding, for example, occurs as an unsteady oscillating flow that takes place when a fluid such as air flows past a blunt body such as the flow disturber118at certain velocities, depending to the size and shape of the body. The flow disturber118may be a passive (non-moving) or active device (moving, such as translating or rotating).

Thus, the flow disturber118causes the formation of turbulence within the flow conduit112, such as vortices that travel downstream within the flow conduit112. This turbulence is measured by the sensors114,116that are responsive to the flow characteristics in the flow conduit112.

In various embodiments, the sensors114,116are configured to acquire measurements and send signals to one or more signal conditioners124as illustrated inFIG. 2(showing one signal conditioner124coupled to both of the sensors114,116). The signal conditioner124conditions the signals by, for example, filtering or amplifying the received signals, prior to sending the signals to, for example, anti-aliasing filters, and the processor122for analysis. For example, the signals generated by the sensors114,116are communicated to the processor122that is configured to determine a flow rate within the flow conduit112, which may use a cross-correlation of the signals from the sensors114,116and frequency resolved information from the frequency resolver120.

It should be noted that the shape of the flow disturber118, the positioning of the flow disturber118relative to the sensors114,116and within the conduit112, and in general the size and positioning of the various components may be varied as desired or needed to generate particular disturbances within the conduit112and to allow measurement of the disturbances, such as the frequency and/or phase of the disturbances. For example, one or both of the sensors114,116are positioned a defined distance from the flow disturber118to allow detection of the turbulent vortices or pressure/flow pulses caused by the flow disturber118, in particular, within a distance where the disturbances have been formed, but not decayed to the point of being undetectable. These disturbances can be largely turbulent in nature. Thus, there are regions located at a distance from the flow disturber118, at which the sensors114,116are positioned and which have a geometrical relationship, wherein the error in the sensor reading is reduced or minimized. In one embodiment, the sensors114,116are located equidistant from the flow disturber118as described herein. It should be noted that although only one flow disturber118is shown inFIG. 1, two or more flow disturbers118may be utilized within the conduit112.

In operation, the characteristics, such as the vortices or disturbances in the form of pulses, of flow that can be determined are, for example, flow speed, flow direction, the pressure of the flow, the temperature of the flow, the change in velocity of the flow, the change in pressure of the flow, and the heat transfer of the flow. Thus, the sensors114,116can be any type of sensor capable of sensing any one or more of these disturbances. For example, the sensors114,116may be configured to determine pressure, temperature, change in pressure, change in temperature, or change in flow rate. In one embodiment, the sensors114,116are pressure sensors. In another embodiment, the sensors114,116are heaters. In yet another embodiment, the sensors114,116are microelectromechanical (MEMS) devices.

In some embodiments, such as wherein the flow sensor assembly110forms part of a CPAP or VPAP machine, a fan (and control motor), not shown, are in fluid connection with the flow conduit112to generate a flow of fluid, in this embodiment, air, through the flow conduit112. A mask (not shown) is in fluid connection with the conduit112, which may be configured as or form part of a flexible tube that is fluid connection with the fan. The fan is also communicatively coupled to the processor122to allow control of the fan. For example, the processor122uses signals received from the sensors114,116to control the operation of the fan, such as to vary the level of the speed of the fan or turn the fan on or off, which controls a flow of air to a the mask that may be worn by a person.

It should be noted that variations and modifications are contemplated. For example, different types of sensors114,116may be used. Additionally, different types of flow disturbers118may be used, such as passive actuators or active actuators that are configured to impart a disturbance to the flow within the flow conduit112. For example, the flow disturber118may include two parts separated from each other (e.g., each being half-cylindrical in shape) by a flow separator, such as to form a channel or gap therebetween. The first and second parts in one embodiment are blunt flow disturbers. The first and second parts may be separate pieces or may be opposite sides of a single flow disturber that has a flow separator formed in a middle portion thereof. Additionally, the flow disturber118may be positioned orthogonal to the fluid flow direction through the flow conduit112, such as coupled on opposing sides of the flow conduit112or is other transverse positions.

In operation, the direction of flow in the flow conduit112can be determined based on an amount of flow disruption. In particular, the flow disturber118will create, as a result of being in the fluid path, a higher flow downstream than is upstream. Thus, the upstream sensor will measure a lower flow rate than the downstream sensor. It should be noted that the disturbances may be, for example, periodic, aperiodic, random, or otherwise present or generated.

In some embodiments, separate receiving and/or processing components for receiving the signals from the sensors114,116may be provided. For example, in one embodiment, as shown inFIG. 3, the signal conditioners124a,124bare coupled to the sensors114,116, respectively, as well as to the processor122. Further, the frequency resolvers140a,140b, are coupled to the signal conditioners124a,124b, respectively, as well as to the processor122. Accordingly, a separate frequency resolving operation may be performed for measurement received from each of the sensors114,116. However, in some embodiments, two frequency resolvers140may be coupled to each of the sensors114,116. As should be appreciated, these and other variations are contemplated herein.

In some embodiments, dual frequency resolving, such as dual-FFT based sensing may be provided as described in more detail below. In various embodiments, for example, a plurality of FFTs, such as two FFTs in parallel may be operated concurrently. Using multiple frequency resolvers140(or processing units) allows for defining different time periods for use in performing the Fourier transform frequency analysis. The time periods may be, for example, shifted in time or have different time sampling ranges. In these time periods, the Fourier transform frequency analysis transforms the measured signals over time, defined as a function f(t), into a new function, defined by frequency with units of cycles/s (hertz) or radians per second. The new function is known as the Fourier transform and/or the frequency spectrum of the function f. Thus, the Fourier transform relates the function's time domain to the function's frequency domain. The component frequencies are spread across the frequency spectrum and are represented as peaks in the frequency domain. Thus, using a frequency calculation of the detected vortices at one of more of the sensors114,116, such as a FFT calculation, the speed of the flow may be determined, as frequency is related to time (T): 1/T. It should be noted that in vortex shedding, the speed of flow is related to the vortex shedding frequency as follows: St=f*L/V, where St is a Strouhal number, f is the vortex shedding frequency, L is the characteristic length, and V is the fluid velocity.

In various embodiments, the sampling time periods for the frequency resolvers120may be different and used, for example, based on a flow rate within the flow conduit112. In some embodiments, a threshold value may be defined and a particular frequency resolver120selected for analyzing the measurement data from the sensors114,116based on the threshold value (e.g., whether the flow rate is lower, higher, or equal to the threshold value). For example, a larger number of samples, such as resulting from a longer sampling time period, results in a better resolution for the Fourier analysis. However, as described herein, it may be preferred or desired to use a shorter time period, such as when the flow rate is high (and the frequency of the detected disturbances within the flow are also correspondingly high). For example, if the frequency is about 1000 Hz, then a 10 Hz resolution may be acceptable. However, if the frequency is 15 Hz, a 10 Hz resolution may perform unsatisfactorily. In various embodiments, as described in more detail herein, at least one of a threshold detector, a cross-calibrator, a mass flow calculator, a FFT module and/or an inverse FFT module may be provided.

In other embodiments, multiple frequency resolvers120may be implemented or a single frequency resolver120that uses a sliding or moving time sample window (e.g., shifting in time). For example, as data is acquired by the sensors114,116a moving time sampling window may be used that is shifted in time, such as shown inFIG. 4. It should be noted that a frequency resolver120may include one or more processors or modules that implement, for example, FFT operations in parallel, such as concurrently as data is acquired. In other embodiments, the processing of the acquired data may be performed at least partially sequentially or entirely sequentially. Thus, different configurations and arrangements of frequency resolvers140may be provided. For example, a functional relationship between a plurality of frequency resolvers140may be defined, such as plurality of parallel frequency resolvers140or a plurality of meshed frequency resolvers140.

As used herein, the terms “system,” “unit,” or “module” may include a hardware and/or software system that operates to perform one or more functions. For example, a module, unit, or system may include a computer processor, controller, or other logic-based device that performs operations based on instructions stored on a tangible and non-transitory computer readable storage medium, such as a computer memory. Alternatively, a module, unit, or system may include a hard-wired device that performs operations based on hard-wired logic of the device. Various modules or units shown in the attached figures may represent the hardware that operates based on software or hardwired instructions, the software that directs hardware to perform the operations, or a combination thereof.

“Systems.” “units,” or “modules” may include or represent hardware and associated instructions (e.g., software stored on a tangible and non-transitory computer readable storage medium, such as a computer hard drive, ROM, RAM, or the like) that perform one or more operations described herein. The hardware may include electronic circuits that include and/or are connected to one or more logic-based devices, such as microprocessors, processors, controllers, or the like. These devices may be off-the-shelf devices that are appropriately programmed or instructed to perform operations described herein from the instructions described above. Additionally or alternatively, one or more of these devices may be hard-wired with logic circuits to perform these operations.

For example,FIG. 4illustrates two time sample windows140and142that may be used by the frequency resolver120. The processing associated with each of the time sample windows may be performed using one processor or module or multiple processors or modules. In one embodiment, a separate frequency resolver120is coupled to each of the sensors114,116, which may facilitate operations described herein particularly when the direction of flow within the flow conduit112(shown inFIGS. 1-3) is not known. As can be seen, each of the time sample windows140and142includes a same number of data samples144(illustrated as 19 data samples), which may corresponds to different measurements acquired by the sensors114,116. For example, the sensors114,116may acquire discrete measurements at defined intervals (e.g., every 10 milliseconds). However, in other embodiments, the sensors114,116may acquire data continuously or substantially continuously, such that the data samples144correspond to time periods for the data acquisition (e.g., sub-divided time windows within the larger time sample windows140and142that correspond to sub-sets of the acquired data).

It should be noted that the data samples144may be different types of data and information as described herein and as acquired by the sensors114,116. Additionally, it should be noted that the data samples144aare data samples acquired and already processed within a previous time sample window. However, for ease of illustration, only the two time sample windows140and142are shown. Thus, in various embodiments, some of the data samples144may be used in multiple frequency resolving operations, for example, in separate FFT calculations. In other embodiments, the entire time sample window may be shifted such that there is no repetition in the data samples144used in the different calculations.

In the illustrated embodiment, the time sample window140includes a data sample144bthat is not used in the time sample window142. Instead, as the time windows are shifted, the time sample window142includes the data sample144c, which was not included in the time sample window140. For example, the data sample144cmay have been acquired after the time sample window140was processed, or exceeded the defined time limit of data samples for the time sample window140(which may be varied as desired or needed and as described herein). Thus, the time sample windows140and142process a same number of data samples144, but which include one or more different samples144. As another example, the shift in time of the time sample windows140and142may result in two, three, or more data samples being included in one of the time sample windows140and142and not the other time sample windows140and142. Accordingly, in various embodiments, a time shift value may be defined based on an amount of overlap of data samples in the time sample windows140and142that is desired or needed. It should be noted that the time sample windows140and142may be different windows or may be the same window that is shifted in time.

The time sample windows140and142defines or identifies the data that is used by the frequency resolver120to perform frequency resolving, such as FFT calculations or analysis as described herein. Accordingly, by varying the amount of data used for the calculations or analysis, the amount of time and resolution or accuracy of the frequency resolving may be changed. For example, as the amount of data used is increased (such as when a longer time sample window is used), the resolution increases, but the time period for the calculations also increases. Thus, a number of factors may be used to select or define the length of the time sample windows140and142, such as a desired or required: resolution, calculation time period, and/or flow rate within the flow conduit112, among others. Additionally, one or more different processing methods or schemes may be used for determining the flow rate based on these different factors, or a previous output value from the frequency resolver120. In some embodiments, the processing method, for example, may be based on a plurality of flow regimes as described herein.

Variations and modifications are contemplated. For example,FIG. 5illustrates the frequency resolver120configured to use a plurality of time sample windows150and152(two are shown for ease of illustration). In this embodiment, the time sample windows150and152have different lengths such that the time period and/or number of data samples154encompassed within each are different. Thus, the length of the time sample windows150and152is different. In the illustrated embodiment, the data samples154within the time sample window150are a subset of the data samples154within the time sample window152. For example, in this embodiment, all of the data samples154are also within the time sample window154, which includes additional data samples154that were acquired or exist before, after or before and after the data samples154within the time sample window152. It should be noted that the time sample window150may positioned at different locations within the time sample window152. For example, the time sample window150may be positioned generally in the middle, at the beginning of, or at the end of the time sample window152. However, it should be appreciated that the time sample window150may be positioned along any portion of the time sample window152. Additionally, the length of the time sample window150may be varied as desired or needed, such as based on the factors described herein and/or the size or length of the time sample window152. Additionally, the time samples windows150and152may be shifted in time as more samples are acquired and as discussed in connection withFIG. 4.

In the various embodiments, the time shifting for each of the time sample windows150and152may different, such that the amount each of the time sample windows150and152is shifted may be different. However, in various embodiments, the time shift for the time sample windows150and152may be the same. Additionally, the description above in connection with the time samples windows150and152is also applicable to the time samples windows140and142.

Moreover, although only a single time sample window150is shown within the time sample window152, multiple time sample windows150may be provided within a single time sample window152. It should be noted that each of the time samples windows150and152may correspond to or be the input to a single frequency resolver120, multiple frequency resolvers120, multiple FFTs or other frequency resolvers, and/or one or more processors, among others. Thus, while the time sample windows illustrated in various embodiments are shown within a single frequency resolver120, multiple frequency resolvers120may receive different inputs. In other embodiments, and for example, the frequency resolver120may include a one or more processors, modules, FFTs (or other frequency resolvers). Thus, in some embodiments, the data from different time sample windows may be processed by different processing units or components, such as multiple or plural processors and/or FFTs within the frequency resolver120.

Additionally, the time period defined by one or more of the time sample windows (e.g., time sample windows140,142,150,152) and the time shift for the time sample windows may be predetermined or defined (e.g., based on a user input or adjustment from a default value), as well as static or dynamic. For example, once initially set, the size or length of the time sample windows and/or time shift thereof may not change, unless, for example, adjusted by a user. However, in some embodiments, the size or length of the time sample windows and/or time shift thereof may change dynamically, such as based on one or more factors described herein. Thus, the size or length of the time sample windows and/or time shift thereof (as well as other variables) may be adjusted continuously or periodically to optimize or improve the processing (e.g., processing time or resolution) to provide a more robust determination of the flow rate.

FIG. 6illustrates a graph160of exemplary outputs from the frequency resolver120, where the horizontal axis corresponds to frequency and the vertical axis corresponds to amplitude (or the horizontal axis corresponds to the reciprocal of time and the vertical axis corresponds to amplitude). In the illustrated example, the curve162is the output from the frequency resolver120(such as shown inFIG. 5) corresponding to the frequency resolving calculations (e.g., FFT calculations) for the time sample window150. Additionally, the curve164is the output from the frequency resolver120corresponding to the frequency resolving calculations (e.g., FFT calculations) for the time sample window152. As discussed herein in more detail, the number of data samples154(or overall amount of data) processed within each of the time sample windows150,152is different. As can be seen, using the data samples154within the shooter time sample window150a coarser frequency resolving calculation may be performed, resulting in the curve162being wider than the curve164(such that a coarser resolution is provided). However, because less data samples154are processed, the frequency resolving calculation time is faster than the frequency resolving calculation time for the data samples154in the time sample window152.

As further can be seen, the curve164is narrower providing a finer resolution as illustrated by the narrower curve. However, the time to determine the curve164is longer than the curve162because more samples are processed as part of the frequency resolving calculation (assuming the same flow rate). In various embodiments, a combination approach is used to obtain or preserve a good response time, as well as a good resolution. For example, the size or length of the time sample windows150and152may be adjusted to encompass a number of data samples154or range of data samples154(e.g., based on a variable rate of the flow within the flow conduit112) to adjust the response time and/or resolution as desired or needed.

In one embodiment, an initial frequency resolving calculation is performed using the time sample window150to determine a coarse position of a peak166corresponding to the frequency for the frequency resolving calculation. For example, in some embodiments, using the reduced set of data samples154in the shorter time sample window150, a subsequent search range (S) may be determined for a finer frequency resolving calculation using additional data samples154within the time sample window152. Thus, the output from an initial frequency resolving calculation performed using the time sample window150may be leveraged to reduce the search range for determining the peak166using the data samples154within the time sample window152(which also includes some or all of the data samples154from the time sample window150). For example, the frequency resolving calculation may be performed in a shorter time period, but maintaining a resolution similar to using the data samples152in the longer time period of the time sample window152.

In various embodiments, using the coarser frequency resolving calculation, an approximate location of the peak166may be determined, such as within the search range (S). It should be noted that the range for the approximate location of the peak166may be varied, such as based on the different factors described herein, as well as, for example, the number of data samples in each of the time sample windows150,152. In some embodiments, the data samples154outside of the search range (S) are padded, for example, set to zero values. Thus, in various embodiments, improved or increased resolution in a same or shorter time period may be provided. Accordingly, in this embodiment, a meshed type of frequency resolver may be provided instead of a parallel type of frequency resolver as described herein (e.g., using samples from shifted time sample windows and not combined or leveraged).

In some embodiments, only one of the time sample windows150,152may be selected or used. For example, if the frequency is high, such as when a higher flow rate exists in the flow conduit112, a shorter frequency resolver may be used for performing FFT calculations using a shorter time sample window that includes a larger number of data samples154when the flow within the flow conduit112is faster. If the flow rate within the flow conduit112slows or is slower, then a longer time sample window, such as the time sample window152may be used. However, it should be appreciated that the selection of whether to use one or more of the time sample windows, and whether to perform, parallel, sequential and/or meshed frequency resolving calculations, may be determined based on various factors as described herein, and/or as desired or needed. Thus, in some embodiments, the frequency resolver120may comprise or provide at least one of meshed short-sample FFT and long-sample FFT based sensing.

The output of the frequency resolver120may then be used to determine the flow rate within the flow conduit112as the frequency of the disturbances is related to the flow rate.

Additionally, measurements from different flow regimes may be used for calibrations. In some embodiments, different flow thresholds may be selected based on when vortices are formed within the flow conduit112and calculations performed, such that an overlap region may be used to interpolate a linear relationship in the different regimes by using amplitude characteristics of the measured signals. This information may be used to calibrate the sensors below the threshold where vortices are not formed such that the flow rate may be calculated using calibrated flow information, such as described in co-pending patent application Ser. No. 13/247,107 filed on Sep. 28, 2011, entitled “FLOW SENSOR WITH MEMS SENSING DEVICE AND METHOD FOR USING SAME”. However, it should be noted that other suitable methods, such as known in the art, may be used to calculate the flow rate from the determined frequency, such as based on the identified peak166shown inFIG. 6. In some embodiments, for example, the frequency resolver120is configured with at least one of amplitude aided biasing or amplitude and frequency aided biasing.

Methods for determining a flow rate through a flow conduit are also provided. The methods, for example, may employ structures or aspects of various embodiments (e.g., systems and/or methods) discussed herein. In various embodiments, certain steps may be omitted or added, certain steps may be combined, certain steps may be performed simultaneously, certain steps may be performed concurrently, certain steps may be split into multiple steps, certain steps may be performed in a different order, or certain steps or series of steps may be re-performed in an iterative fashion. In various embodiments, portions, aspects, and/or variations of the methods may be able to be used as one or more algorithms to direct hardware to perform operations described herein.

A method170as shown inFIG. 7includes positioning within a flow conduit a flow disturber configured to impart a flow disturbance to the fluid flow at172. For example, the flow disturber118may be positioned within the flow conduit112as described herein. The method170also includes at174disposing a plurality of flow sensors in the flow conduit to have a geometrical and functional relationship with the flow conduit and the flow disturber as described herein, wherein the plurality of flow sensors are responsive to flow characteristics in the flow conduit. The flow sensors may be, for example, the sensors114,116. The method additionally includes at176coupling at least one frequency resolver (e.g., the frequency resolver120) to the plurality of flow sensors, wherein the one or more frequency resolvers are configured to generate an output signal based on at least one of the flow characteristics, which may include, for example, an FFT peak frequency determination as described in more detail herein. Additionally, as described in more detail herein, one or more time sample windows are used to select the data samples for use in one or more frequency resolving calculations.

The method170also includes at178coupling a processor to the plurality of flows sensors. The processor may be the processor122that is configured to determine a flow rate of the fluid flow in the flow conduit and optionally use the output signal from the frequency resolver to select a processing method for determining the flow rate in the flow conduit as described herein. The processing may include using frequency resolving calculation outputs that are generated from parallel, sequential and/or meshed operations.

In another method180shown inFIG. 8, measurements from a plurality of sensors in a flow conduit are acquired at182, such as the sensors114,116. The measurements may correspond to flow characteristic information for a fluid flow within the flow conduit as described herein (that includes disturbances from a flow disturber). The method180also includes at184determining frequency information from the measurements within one or more time sample windows. For example, different size or lengths of time sample windows may be used, which may be processed using different methods as described herein. The method180additionally includes at186determining a flow rate of the fluid flow in the flow conduit using the determined frequency information, which may be performed by the processor122. It should be noted that one or more time sample windows may have a length based at least in part on one or more flow characteristics, such as the rate of flow. It also should be noted that the rate of flow may be derived from the frequency of the flow disturbance in some embodiments and/or the amplitude of the flow disturbance in some embodiments. Additionally, various embodiments may use the frequency information and/or amplitude information to select a processing method for determining the flow rate in the flow conduit as described in more detail herein.

Thus, various embodiments use flow sensors, such as in a flow sensor assembly for flow sensing using frequency information from one or more time sample windows.