Robust flow sensor, controller, and method

Abstract

To provide a flow meter and a flow sensor controller that determine fluid flow rates, levels and conditions using ultrasonic transducers, where reliability is enhanced while reducing maintenance costs.SOLUTION: A sensor controller comprises: a transmitter configured to provide a drive signal to an ultrasonic sending transducer to generate an acoustic burst; a receiver configured to receive a response signal from an ultrasonic receiving transducer; a time-of-flight circuit configured to detect an arrival of the acoustic burst in the response signal and to measure a first time of flight associated with that arrival; and a phase shift circuit configured to measure a phase shift of the acoustic burst in the response signal and to determine a second time of flight corresponding to the phase shift.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Application No. 63 / 551,338, filed February 8, 2024, entitled "Ultrasonic flow / level meter with high level of functional safety and online calibration function" by inventor Marek Hustava, which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE INVENTION The present disclosure relates to the field of ultrasonic sensing technology. More particularly, the present invention relates to flow meters, flow sensor controllers, and related methods for utilizing ultrasonic transducers to determine fluid flow, level, and condition in various environments. [Background technology]

[0003] Flow meters are widely used in industrial processes, environmental monitoring, and fluid management systems to verify fluid flow rate, level, and condition. Despite their increasing popularity and established functionality, flow meters continue to face challenges with respect to measurement accuracy, reliability, and functional safety. These factors can affect the overall accuracy of readings and require maintenance, redundancy, and frequent recalibration, thereby increasing operational costs and downtime.

[0004] Furthermore, the integration of online calibration functions and redundant safety checks is becoming increasingly important in applications requiring high functional safety standards. Modern systems not only need accurate measurement capabilities, but also need to be able to diagnose and alert operators to any operational faults, thereby contributing to improved safety and reduced risk of malfunction. Summary of the Invention

[0005] In light of these challenges, the present disclosure explores systems, methods, and sensors that can address the deficiencies associated with existing flow meter technology and provide increased reliability while reducing component, system, and maintenance costs.

[0006] One illustrative sensor controller includes a transmitter, a receiver, a time-of-flight circuit, and a phase-shift circuit. The transmitter is configured to provide a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst. The receiver is configured to receive a response signal from the ultrasonic receiving transducer. The time-of-flight circuit is configured to detect the arrival of the acoustic burst in the response signal and measure a first time-of-flight associated with the arrival. The phase-shift circuit is configured to measure a phase shift of the acoustic burst in the response signal and determine a second time-of-flight corresponding to the phase shift.

[0007] One illustrative sensing method includes providing a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst, receiving a response signal from an ultrasonic receiving transducer, detecting the arrival of the acoustic burst in the response signal using a time-of-flight circuit and measuring a first time-of-flight associated with the arrival, and measuring a phase shift of the acoustic burst in the response signal using a phase shift circuit and determining a second time-of-flight corresponding to the phase shift.

[0008] One illustrative flow sensor includes a first ultrasonic transducer positionable to emit a signal in a first direction of propagation through a fluid flow, a second ultrasonic transducer positionable to emit a signal in an opposite direction of propagation through the fluid flow, and a sensor controller having a transmitter, a receiver, a time-of-flight circuit, a phase-shift circuit, and control logic. The transmitter is configured to provide a drive signal to the ultrasonic transmit transducer to generate an acoustic burst. The receiver is configured to receive a response signal from the ultrasonic receive transducer, the ultrasonic receive transducer being a selectable one of the first ultrasonic transducer and the second ultrasonic transducer, and the ultrasonic transmit transducer being the other of the first ultrasonic transducer and the second ultrasonic transducer. The time-of-flight circuit is configured to detect the arrival of the acoustic burst in the response signal and measure a first time-of-flight associated with the arrival. The phase-shift circuit is configured to measure a phase shift of the acoustic burst in the response signal and determine a second time-of-flight corresponding to the phase shift. The control logic is configured to swap the ultrasonic transmitting transducer and the ultrasonic receiving transducer to obtain a first time-of-flight and a second time-of-flight for each of a first propagation direction and an opposite propagation direction, and is configured to determine a first time-of-flight difference between the directions and a second time-of-flight difference between the directions.

[0009] Another exemplary sensor controller includes a transmitter, a first receiver, a second receiver, a propagation velocity circuit, and a level circuit. The transmitter is configured to provide a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst. The first receiver is configured to receive a first response signal from the first ultrasonic receiving transducer. The second receiver is configured to receive a second response signal from a second ultrasonic receiving transducer at a predetermined distance from the ultrasonic transmitting transducer. The propagation velocity circuit is configured to detect a direct arrival of the acoustic burst in the second response signal and measure a corresponding propagation velocity. The level circuit is configured to detect a reflected arrival of the acoustic burst in the first response signal and measure a corresponding time of flight, and is configured to derive a fluid level based on the time of flight and the propagation velocity.

[0010] Another illustrative sensing method includes providing a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst, receiving a first response signal from a first ultrasonic receiving transducer, receiving a second response signal from a second ultrasonic receiving transducer at a predetermined distance from the ultrasonic transmitting transducer, measuring a propagation velocity based on the direct arrival of the acoustic burst in the second response signal, measuring a time of flight for the reflected arrival of the acoustic burst in the first response signal, and deriving a fluid level based on the time of flight and the propagation velocity.

[0011] Yet another illustrative sensor controller includes a transmitter, a first receiver, a second receiver, and signal processing circuitry. The transmitter is configured to provide a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst. The first receiver is configured to receive a first response signal from the ultrasonic receiving transducer. The second receiver is configured to receive a second response signal from the MEMS transducer. The signal processing circuitry is coupled to the first receiver and configured to measure a first time-of-flight associated with the arrival of the acoustic burst in the first response signal, and is further coupled to the second receiver and further configured to measure at least one of leakage noise intensity, acoustic burst intensity, and a second time-of-flight associated with the arrival of the acoustic burst in the second response signal.

[0012] Yet another illustrative sensing method includes providing a drive signal to an ultrasonic transmit transducer to generate an acoustic burst; receiving a first response signal from the ultrasonic receive transducer; receiving a second response signal from the MEMS transducer; and using signal processing circuitry to measure a first time-of-flight associated with the arrival of the acoustic burst in the first response signal and measure at least one of a leakage noise intensity in the second response signal, an acoustic burst intensity in the second response signal, and a second time-of-flight associated with the arrival of the acoustic burst in the second response signal.

[0013] Yet another illustrative sensor controller includes a transmitter, a receiver, and signal processing circuitry. The transmitter is configured to provide a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst. The receiver is configured to receive a response signal from the ultrasonic receiving transducer. The signal processing circuitry is configured to measure a time of flight for the acoustic burst in the response signal. The transmitter is further configured to measure an impedance of the ultrasonic transmitting transducer.

[0014] Yet another illustrative sensing method includes providing a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst, receiving a response signal from an ultrasonic receiving transducer, measuring the time of flight for the acoustic burst in the response signal, and monitoring the impedance of the ultrasonic transmitting transducer.

[0015] Yet another illustrative sensor controller includes a transmitter, a receiver, signal processing circuitry, and control logic. The transmitter is configured to provide a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst. The receiver is configured to receive a response signal from the ultrasonic receiving transducer. The signal processing circuitry is configured to measure a time of flight for the acoustic burst in the response signal. The control logic is configured to modulate the drive signal to generate a near-field communication signal.

[0016] Yet another illustrative sensing method includes providing a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst, receiving a response signal from an ultrasonic receiving transducer, measuring a time of flight for the acoustic burst in the response signal, and modulating the drive signal to generate a near-field communication signal.

[0017] Each of the foregoing illustrative implementations may be embodied, individually or jointly, in any suitable combination, with one or more of the following optional features: 1. Control logic configured to determine a flow rate based on both a first time-of-flight and a second time-of-flight. 2. Control logic configured to compare the first time-of-flight with the second time-of-flight. 3. Control logic configured to compare a first flow rate derived from the first time-of-flight with a second flow rate derived from the second time-of-flight. 4. The controller is configured to assert a fault signal if the comparison indicates a persistent discrepancy. 5. The ultrasonic receive transducer is a separate transducer different from the ultrasonic transmit transducer. 6. Control logic configured to swap the ultrasonic transmit and receive transducers to obtain a first time-of-flight and a second time-of-flight for each burst propagation direction. 7. The control logic determines a first time-of-flight difference between directions and a second time-of-flight difference between directions. 8. The control logic is configured to determine the flow rate based on both the first time-of-flight difference and the second time-of-flight difference. 9. The control logic is configured to compare the first time-of-flight difference with the second time-of-flight difference. 10. The control logic is configured to compare the first flow rate derived from the first time-of-flight difference with the second flow rate derived from the second time-of-flight difference. 11. A second receiver configured to receive a reflected signal from the ultrasonic transmit transducer. 12. A Doppler shift circuit configured to detect an echo of an acoustic burst in the reflected signal and measure a velocity associated with the echo. 13. The control logic is configured to determine the flow rate based on the velocity when the echo has a magnitude above a threshold. 14. The control logic is configured to determine the flow rate based on the fluid level. 15. The first ultrasonic receive transducer is also an ultrasonic transmit transducer. 16. The second ultrasonic receive transducer is a MEMS transducer. 17. The control logic is configured to assert a leak detection signal when the leak noise intensity exceeds a predetermined threshold. 18. Control logic configured to assert a fault signal when the acoustic burst intensity falls below a given threshold.19. Control logic configured to initiate a cleaning cycle if the second response signal indicates loading of the ultrasonic transmitter / receiver. 20. The signal processing circuit is configured to derive a propagation velocity from the second time of flight. 21. Control logic configured to assert a fault signal if the impedance is outside a predetermined range. 22. Control logic configured to initiate a cleaning cycle if the impedance exceeds a predetermined threshold. 23. Control logic configured to monitor impedance as a function of frequency. 24. Based on the impedance as a function of frequency, the control logic is configured to adjust the carrier frequency of the drive signal to match the resonant frequency of the ultrasonic transmitter transducer. 25. A built-in self-test (BIST) circuit and control logic configured to assert a fault signal if the BIST circuit indicates a fault in the transmitter, receiver, signal processing circuit, or control logic. 26. The control logic is configured to operate the BIST circuit before generating each acoustic burst. 27. Control logic configured to compare the acoustic burst in the response signal with a standard waveform. 28. The control logic is configured to assert a fault signal if there is a mismatch between the acoustic burst in the response signal and a standard waveform. 29. The control logic is further configured to initiate a cleaning cycle if there is a mismatch between the acoustic burst in the response signal and a standard waveform. 30. The ultrasonic transmit transducer is also an ultrasonic receive transducer. 31. The signal processing circuit is configured to demodulate the response signal to receive a near-field communication response. 32. A second receiver coupled to the second ultrasonic receive transducer to receive the near-field communication response. 33. The control logic is configured to determine an open channel flow rate based at least in part on time of flight. 34. The control logic is configured to determine a closed channel flow rate based at least in part on time of flight difference. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a plan view of an illustrative flow meter configuration for closed channel flow. [Figure 2] 1 is a perspective view of an illustrative flow meter configuration for open channel flow; FIG. [Figure 3] FIG. 1 is a block diagram of an illustrative sensor controller with supporting components for ultrasonic transmission and reception. [Figure 4A] FIG. 2 is a block diagram of exemplary signal processing and diagnostic circuitry within the sensor controller. [Figure 4B] FIG. 10 is a block diagram of an exemplary phase calculation circuit that may be used in the sensor controller. [Figure 4C] 10 is a graph illustrating cosine and sine function values ​​that may be stored in a lookup table for low-power phase calculations. [Figure 5] FIG. 1 is a schematic diagram of a direct drive circuit for a piezoelectric transducer. [Figure 6] 10 is a graph illustrating various switch signal timings and resulting voltage levels for transducer activation. [Figure 7] 1 is a flow diagram of an illustrative flow sensing method using multiple independent measurements for robust sensing. [Figure 8] 10 is a flow diagram of an illustrative flow sensing method using a second receiving transducer for propagation velocity measurement, leak detection, and / or fault monitoring. [Figure 9] 1 is a flow diagram of an illustrative flow sensing method using impedance monitoring and fault detection to enhance reliability. [Figure 10] 1 is a flow diagram of an illustrative short-range communication method for an interrogator device. [Figure 11] 1 is a flow diagram of an illustrative short-range communication method for a responder device. DETAILED DESCRIPTION OF THE INVENTION

[0019] It is to be understood that the drawings and the following description are not intended to limit the disclosure, but rather to provide one of ordinary skill in the art with a basis for understanding all modifications, equivalents, and alternatives falling within the language of the claims.

[0020] To aid in understanding, Figures 1 and 2 show illustrative situations in which the described sensor controller and method may be used. Figure 1 shows a closed-channel fluid measurement system having a pipe 102 through which a completely enclosed fluid stream 104 is routed. The fluid may be of any flowable composition, including a liquid, a gas, or a heterogeneous mixture with suspended solids. The pipe 102 may be configured to provide a reasonably uniform, laminar flow stream having a predetermined cross-sectional flow area A and a mean flow velocity v along the longitudinal axis of the pipe.

[0021] A sensor controller 106 is connected to the system and controls the operation of the ultrasonic transducers 108, 112. The ultrasonic transmit transducer 108 is positioned on one side of the pipe 102 and emits an acoustic burst or other acoustic signal along a propagation path 110 spanning the diameter of the pipe that intersects the longitudinal axis at an angle θ. On the opposite side θ, an ultrasonic receive transducer 112 is located to capture the acoustic signal transmitted by the transmit transducer 108. The transmit transducer 108 may be further configured to receive reflections of the acoustic burst from, for example, bubbles, droplets, or particles entrained in the fluid flow. The sensor controller 106 processes these signals to evaluate parameters such as time of flight and phase shift, as described further below.

[0022] The sensor controller 106 periodically swaps the roles of the ultrasonic transducers so that transducer 112 can be the ultrasonic transmitting transducer and transducer 108 can be the ultrasonic receiving transducer, allowing the sensor controller 106 to determine parameters for opposite propagation directions along path 110. The downstream time-of-flight is shortened by an amount determined by the fluid flow velocity, and the upstream time-of-flight is similarly lengthened. By combining the upstream and downstream measurements (e.g., by determining the difference between their reciprocals), the sensor controller can measure the fluid flow velocity, v, in combination with other geometric parameters (such as pipe diameter and intersection angle, θ). The fluid flow velocity, when combined with the pipe cross-section, allows the sensor controller to determine and monitor the volumetric flow rate. If the fluid density is known or independently measured, the volumetric flow rate can be easily converted to mass flow rate. Given the close and well-understood correlation between fluid flow velocity, volumetric flow rate, and mass flow rate, each is contemplated herein as encompassed by the general term “fluid flow rate.”

[0023] Certain enhancements to this configuration provide increased reliability and robustness without unduly increasing implementation costs. Such enhancements may include an integrated microphone 120 to potentially enhance sound capture capabilities for additional analysis or communication purposes. Configuring such components allows for accurate measurement and monitoring of parameters associated with the fluid flow 104.

[0024] 2 shows an open channel 200 in which a fluid flow 204 is directed over a weir 202 or other obstacle. As is well understood in the civil engineering field, the geometry of the channel and obstacles causes the depth of the fluid flow to vary monotonically as a function of the fluid flow rate. Thus, by monitoring the fluid level, a suitably programmed sensor controller can determine the flow depth and thereby monitor the fluid flow rate and cumulative volumetric flow rate.

[0025] 2 further shows a level sensor 206 positioned above the fluid stream 204 to monitor the liquid level. The illustrated level sensor 206 uses an ultrasonic transmit transducer to emit an acoustic burst 208 and an ultrasonic receive transducer (which may be the same as the transmit transducer) to detect the reflection of the acoustic burst 208 from the surface of the fluid. (In an alternative configuration, the level sensor 206 is positioned below the surface of the fluid and pointed upward. The level sensor 206 includes a sensor controller for measuring the time of flight and the associated distance to the surface of the fluid stream 204. At this distance, the sensor controller can use stored geometric parameters, mathematical formulas, and / or look-up tables to determine the depth of the fluid stream and the associated fluid flow rate, from which the cumulative volumetric flow rate can be readily derived.)

[0026] As a potential enhancement, the illustrated configuration includes a second ultrasonic receiving transducer 210 positioned a predetermined distance from the ultrasonic transmitting transducer of the liquid level sensor 206. This transducer 210 is designed to receive the acoustic burst 208 along the direct propagation path, allowing the sensor controller to determine the propagation velocity of the acoustic burst. Because the speed of sound in air depends on temperature, pressure, and humidity, measuring the propagation velocity in this manner allows for a more accurate measurement of the distance to the liquid level. Adjustments and modifications to the positions of the liquid level sensor 206 and the ultrasonic receiving transducer 210 can be made to accommodate various fluid flow conditions, providing versatility in different operating environments.

[0027] 3 shows an illustrative sensor controller 300 that may be implemented as a monolithic integrated circuit chip with an arrangement of interconnected components designed to handle ultrasonic signal processing and communication tasks. At the center of the system, control logic 326 coordinates signal flow and processing via internal bus 324. Transmitter components, including transmitters 302, 304, and 306, are configured to deliver various drive signals to ultrasonic transmit transducers 352, 354, and (via transformer 356) 357 to generate acoustic bursts that emanate from these transducers. To provide configuration flexibility, transmitters 302, 304 may be direct-drive transmitters using voltage drivers as described further below, or transmitter 306 may be a current driver configured to provide drive current to transformer 356, enabling the transformer to provide a high-voltage signal to transducer 357.

[0028] The transmitter 306 may further provide the sensed voltage to an analog-to-digital converter (ADC) 318, allowing the sensor controller 300 to monitor the voltage response of the ultrasonic transmit transducer 357 during activation and / or post-activation reverberation. As described further below, the transmitters 302, 304 may be configured to monitor current or impedance, allowing the sensor controller 300 to monitor the impedance of the ultrasonic transmit transducers 352, 354 during activation. Although three transmit transducers are shown in FIG. 3, most contemplated sensor configurations will use only one or two ultrasonic transmit transducers.

[0029] Sensor controller 300 further includes receiver 308, receiver 310, and receiver 312 coupled to ultrasonic receiving transducer 358, ultrasonic receiving transducer 360, and microphone 362, respectively. Transducers 358, 360, and 362 are all shown for completeness; in practice, one or more of them may be omitted. While ultrasonic receiving transducers 358 and 360 are shown and may be implemented as individual elements, it is contemplated that each receiving transducer may also function as one of ultrasonic transmitting transducers 352, 354, and 357. For example, a sensor may have a single transducer that is driven by one of the transmitters to generate an acoustic burst before being used by one of the receivers to detect reflections of the acoustic burst. As another example, a sensor may have a transducer used to generate an acoustic burst and a second transducer used to receive a response. In this case, the second transducer may be used to generate a subsequent acoustic burst and the first transducer may be used to receive the subsequent response. The ultrasonic transmit and receive transducers may be piezoelectric (PZ) elements with optional separate support components. The microphone 362 may also be a piezoelectric element, although a micro-electromechanical system (MEMS) transducer may be preferred for greater sensitivity.

[0030] A demultiplexer 314 routes the digital transmit signal from the transmit signal generator 316 to a selected one of the transmitters 302-306 to drive a corresponding ultrasonic transmit transducer to generate an acoustic burst. A configuration of multiplexers 320, 322 selectively couples the analog receive signals from the receivers 308, 310, 312 to ADCs 321 and 323, which digitize the receive signals. A control logic 326 coordinates the operation of the components 302-323 to deliver the digital receive signals to a digital signal processor (DSP) 328, a microcontroller 330, a memory 332, and / or an application specific integrated circuit (ASIC) module within the control logic 326. In addition to providing software or firmware instructions and programmable parameters for the signal processing components, memory 332 may provide buffering of the digital received signal, intermediate signal streams, and measurement signals, but may also provide non-volatile storage for a log of measurement results, which may be stored for later retrieval or delivered in real time to other components or systems.

[0031] Signal processing tasks may be allocated in various manners among the microcontroller unit (MCU) 330, the DSP 328, and the control logic 326, which may be distinguished primarily with respect to their balance between software and hardware implementation of their desired functions. While Figure 3 shows the phase shift measurement circuit 334 as being implemented primarily within the digital signal processor 328, the disclosed modules may be distributed in other manners, with some functions implemented by ASIC modules and other functions implemented by software within the microcontroller.

[0032] 3 further shows a multiplexer 336 that routes a selected analog receive signal from the receivers 308, 310 to a time-of-flight measurement circuit 344. The time-of-flight measurement circuit 344 includes a pulse generator 338, a comparator 340, and a time-to-digital converter TDC 342. When the transmit signal generator 316 operates to generate an acoustic burst, it provides an asserted start signal to the pulse generator 338. The pulse generator 338 asserts its output signal until a stop signal from the comparator 340 is asserted. The comparator 340 determines whether the selected analog receive signal exceeds a predetermined threshold voltage V T and asserts a stop signal when the selected received signal exceeds a threshold voltage, indicating the arrival of an acoustic burst in the selected received signal. In some alternative implementations, the pulse generator 338 incorporates a zero-crossing detector for increased accuracy. The pulse generator 338 deasserts its output (1) after the envelope of the received signal exceeds a threshold voltage and (2) after the zero-crossing detector detects a subsequent zero crossing in the received signal. The TDC 342 converts the width of the pulse output by the pulse generator into a digital value indicating its duration. A suitable implementation may include (1) a high-frequency clock counter and (2) an integrator coupled to an analog-to-digital converter.

[0033] The sensor controller 300 may further include support components such as a built-in self-test (BIST) circuit 346, a general-purpose input / output (GPIO) interface module 347, a power supply 348, an oscillator 349, and a temperature sensor circuit 350. The BIST circuit 346 may be configured to test the functionality of various other components, including the transmitter, receiver, signal processing circuitry, and control logic. The GPIO interface 347 may be configured to provide digital input / output signaling capabilities for commands, control signals, and data. Various digital I / O and serial communication protocols may be supported, including, for example, UART, SPI, I2C, and 5V IO.

[0034] The power supply 348 provides power regulation using one or more bandgap (BG) references, voltage monitoring (VM) circuits, and a power-on reset (POR) module to perform power-on operations. One or more oscillators 349 may use crystals to generate various on-chip clock signals for synchronizing the operation of various other components. The temperature sensor circuit 350 may be coupled to an external thermocouple or other temperature sensor to monitor environmental conditions.

[0035] An additional feature that may be provided by the sensor controller 300 is near-field communication with a smart device 370, such as a smartphone or similar device, that has a microphone capable of sensing and a speaker capable of transmitting ultrasonic signals. As described further below, the sensor controller 300 and smart device 370 can modulate and demodulate ultrasonic signals to send and receive commands and responses to carry data between the sensor and the portable device, facilitating sensor configuration, sensor performance monitoring, and sensor data retrieval.

[0036] 4A shows a signal processing circuit 400 incorporating various components for processing ultrasonic signals. The various components may be implemented as control logic hardware or firmware modules implemented by the DSP 328 or microcontroller 330. An oscillator 349 provides a carrier signal to a transmit signal generator 316, which generates a digital transmit signal TXD to generate acoustic bursts for flow sensing. (Optionally, the transmit signal generator 316 may be further configured to modulate the digital transmit signal to generate a modulated ultrasonic signal for short-range communication with a smart device.) The carrier signal from the oscillator 349 is also provided to a digital quadrature mixer 402, which downconverts the digital receive signal from a given ADC to a baseband “zero intermediate frequency” ZIF signal 404 having an in-phase component and a quadrature-phase component.

[0037] Lowpass filter 406 processes ZIF signal 404 to remove noise that is out of the signal band associated with the acoustic bursts and to prevent aliasing when filtered baseband signal 410 is provided for decimation by decimator 412. Lowpass filter 406 may further combine the quadrature components of the filtered baseband signal to determine a phase shift measurement signal 408 that measures the digitized received signal phase relative to the carrier signal from oscillator 349, and may further determine a frequency measurement signal 409 that represents the frequency offset between the digitized received signal and the carrier signal. Frequency measurement signal 409 may be a derivative of phase shift measurement signal 408, which may be determined from a trigonometric relationship between the quadrature components.

[0038] The decimator 412 reduces the sample rate of the filtered baseband signal 410 to reduce the processing requirements for subsequent modules. The correlator 414 may use a correlation filter to convert the decimated baseband signal into a correlation signal, indicating when the digitized received signal contains an acoustic burst matching an expected waveform. The noise detection and suppression module 416 operates on the correlation signal, applying attenuation compensation to amplify peaks representing echoes and applying a nonlinear function to suppress noise. The magnitude determination module 418 converts the quadrature signal components into a magnitude signal, which may be processed by the time-of-flight measurement module 420 to determine the timing of peaks indicating the travel time of the acoustic burst. Data logging and integration with external systems is facilitated by the logging and I / O module 422, which manages data storage and interfaces.

[0039] Additional diagnostic and noise analysis functions are provided by a diagnostic module 424, a reverberation module 426, and a wideband noise measurement module 428. The wideband noise measurement module 428 evaluates noise characteristics across the entire spectrum of the digitized received signal. The reverberation module 426 optionally measures the frequency and duration of the transducer's reverberation after transmitting an acoustic burst. The diagnostic module 424, alone or in combination with modules 426, 428, analyzes the digitized response signal to detect and diagnose any transducer fault conditions. Some fault conditions may be indicated, for example, by an excessively short reverberation period (which may be due to a disconnected or defective transducer, suppressed vibration, etc.), while other fault conditions may be indicated by an excessively long reverberation period (faulty mounting, insufficient damping resistor, etc.). The diagnostic module 424 can detect and classify multiple such transducer fault conditions and store appropriate fault codes in internal registers, from which the fault codes can be communicated to the control logic.

[0040] It should be noted that modules 412-424 may be reordered or otherwise rearranged as needed to provide the desired signal processing, and in at least some implementations, these modules may be at least intermittently disabled to reduce processing requirements and associated power consumption.

[0041] FIG. 4B shows additional details of an illustrative low-power circuit for determining the phase-shifted measurement signal 408 and the frequency measurement signal 409. In this implementation, the oscillator 349 generates a clock signal at eight times the transmit carrier frequency, allowing eight-fold oversampling by the ADC 321. The divider / counter 432 uses the clock signal to cycle through eight output values ​​for the lookup table 434. As shown in FIG. 4C, the outputs of the lookup table correspond to cosine and sine functions. The sine function value is shifted two table positions from the cosine function value. In some contemplated implementations, the lookup table is replaced with logic that provides three output magnitudes of 0, 0.71, and 1 with appropriate sign inversions.

[0042] Multipliers 435 and 436 produce the product of the digitized received signal with cosine and sine function values ​​corresponding to the in-phase (I) and quadrature-phase (Q) components of the received signal, respectively. Low pass filters 437 and 438 remove noise that is out of the signal band associated with the acoustic burst and prevent aliasing when filtered component 410 is decimated.

[0043] The phase calculation module 440 may calculate the received signal phase as the arctangent of the ratio between the quadrature and in-phase components. When the in-phase component is zero (or much smaller than the quadrature component), the module 440 may determine that the phase is 90 degrees. A low-pass filter 442 may be used to smooth the phase measurement.

[0044] Note that the phase calculation is only meaningful when the received signal is valid, i.e., when an acoustic burst is being received. Thus, the magnitude calculation module 444 may combine the in-phase and quadrature-phase components to determine the magnitude of the received signal. The comparator 446 provides an output for disabling the phase calculation module 440 or the filter 442 when the magnitude of the received signal is below a predetermined threshold. In some implementations, the magnitude calculation is filtered or otherwise accumulated to ensure that the magnitude exceeds the threshold for at least a minimum time before allowing the module 440 or 442 to provide a non-zero output.

[0045] A differentiator circuit 448 may operate on the phase measurement output 408 to provide a frequency measurement output 409. The phase measurement output may be converted to a second order time-of-flight measurement.

[0046] 5 shows an illustrative implementation of a direct-drive transmitter 302, 304, which has three switches SW1, SW2, SW3 that respectively couple a positive supply voltage V1, a negative supply voltage 502, and an intermediate "ground" voltage to a piezoelectric ultrasonic transmit transducer PZ. When all three switches are off, the driver is in a high impedance state. A current sensor or small sense resistor R is provided in series with the transducer to allow sensing of current flow to the transducer.

[0047] The switches may be operated according to the control signal timing shown in the first three curves of Figure 6. Switches SW1, SW2, and SW3 conduct when their respective control signals are asserted (high) and are isolated when their respective control signals are deasserted (low). When SW3 conducts, the transmit transducer is connected to a voltage curve V PZ The voltage curve V is then coupled to ground. Switch SW3 is then opened and switch SW1 is closed, momentarily applying the positive supply voltage to the transmitting transducer. PZconverges rapidly to the positive supply voltage, even as the deformation of the piezoelectric element gains momentum. When the control signal has a periodicity close to that of the transducer's resonant frequency, momentum continues after switch SW1 is opened, and the voltage curve V PZ During the other half of the excitation cycle, switch SW3 couples the transducer to ground before switch SW2 momentarily applies the negative supply voltage.

[0048] Voltage curve V R shows the voltage across the sense resistor, which is proportional to the current in the transducer. The voltage curve shows clear peaks corresponding to the charging and discharging of the transmitting transducer. The charging peaks occur when the ground switch SW3 is open and either switch SW1 or SW2 is closed. These peaks are consistent over a wide frequency range. However, the discharging peak 602, which is generated when the ground switch SW3 is closed, is a strong function of frequency and reaches a minimum size when the control signal has a frequency that matches the resonant frequency of the transducer. Thus, the voltage curve V R A rectified and filtered version of can serve as an indicator of whether such resonant frequency matching has been achieved, thereby allowing the control logic to adapt the control signal as necessary to account for resonant frequency variations due to aging and changing environmental conditions.

[0049] 7 is a flow diagram of an illustrative flow sensing method using multiple independent measurements for robust sensing. Beginning at block 702, a trigger is checked to determine whether the sensor should enter near-field communication mode 704, as discussed further below. The trigger may be, for example, a button press, detection of a beacon signal, or the expiration of a periodic timer. Detection of the trigger causes the sensor to enter near-field communication mode 704. Exiting near-field communication mode 704 returns the method to the beginning.

[0050] If the short-range communication mode 704 is not entered, the sensor generates an acoustic burst using an ultrasonic transmit transducer in block 706 and receives a response signal using an ultrasonic receive transducer in block 708. In block 710, the sensor processes the response signal to detect the arrival of the acoustic burst and determine an associated time of flight (TOF). This may be accomplished, for example, using the time-of-flight measurement circuitry 344 (FIG. 3). In block 712, the sensor processes the response signal to determine a phase shift of the received acoustic burst relative to the carrier frequency. This phase shift may be determined using the mixer 402 and low-pass filter 406. As discussed above, this phase shift corresponds to the travel time of the acoustic burst and may be easily converted to a time-of-flight measurement independent of the measurement made in block 710.

[0051] Block 714 represents an optional measurement of Doppler shift, which may be obtained using mixer 402 and low pass filter 406. In the sensor configuration of Figure 1, the flow stream may contain bubbles, solids, or other sources of acoustic impedance variation that induce reflections of acoustic bursts back to the ultrasonic transmitting transducer. The frequency shift is essentially proportional to the flow stream velocity.

[0052] Block 716 represents a repetition of blocks 706-714 with the roles of the ultrasonic transmitting and receiving transducers swapped. In the sensor configuration of Figure 1, this repetition allows time-of-flight measurements to be obtained using acoustic bursts that propagate in the opposite direction to the original measurements. These measurements in the opposite propagation direction are combined with measurements in the original direction to obtain a TOF difference that is proportional to the fluid flow velocity.

[0053] In block 718, an independent measurement of fluid flow velocity is determined using the time-of-flight measurements of blocks 710 and 712 or the TOF difference obtained using the measurements in block 716. Optionally, in blocks 714 and 716, a fluid flow velocity measurement may also be obtained from the Doppler shift measurements.

[0054] At block 720, the independent measurements are compared. If any persistent discrepancy is detected, the sensor asserts a fault signal at block 722, which may be communicated to a user to indicate that maintenance or repair is required. At block 724, the sensor may combine the independent measurements to obtain a combined flow measurement. This combination process may be a selection of the measurement determined to be the most accurate or consistent, or may be a weighted sum configured to enhance measurement accuracy. The sensor may communicate the combined flow measurement to a logging service or monitoring system and / or store the combined flow measurement for later retrieval.

[0055] 8 is a flow diagram of an illustrative flow sensing method using a second receiving transducer for propagation velocity measurement, leak detection, and / or fault monitoring. Similar to the method of FIG. 7, the illustrative sensing method begins at block 802 by checking a trigger to determine whether the sensor should enter a near-field communication mode 804. If not, the sensor generates an acoustic burst using the ultrasonic transmitting transducer at block 806 and receives a first response signal using the first ultrasonic receiving transducer at block 808. At block 810, the sensor also receives a second response signal using the second ultrasonic receiving transducer. The second ultrasonic receiving transducer may be a piezoelectric transducer or, alternatively, may be a microphone having a microelectromechanical systems (MEMS) element.

[0056] In block 812, the sensor uses the first response signal to determine a first time-of-flight, which is dependent on the fluid flow rate. The flowchart of FIG. 8 then provides three parallel paths to illustrate different ways of using the second response signal. In block 814, the sensor uses the second response signal to determine a second time-of-flight, which is indicative of the propagation velocity of the acoustic burst (i.e., the speed of sound) but is independent of the fluid flow rate. To provide this measurement in an open-channel system, a microphone or ultrasonic receiving transducer is positioned a known distance from the ultrasonic transmitting transducer in a direction that can be reached without entering the fluid flow. In block 816, the sensor determines the propagation velocity of the acoustic burst, allowing for more accurate determination of the fluid flow level. In block 818, the sensor determines a flow rate measurement and transmits the measurement to a logging service or system monitor and / or stores the measurement for later retrieval.

[0057] The sensor processes the second response to detect the broadband "hiss" typically associated with a fluid leak from a pipe in block 820. In block 822, the sensor determines whether the level of the broadband noise exceeds a predetermined threshold, and if so, in block 824, asserts a leak detection signal or some other form of alarm signal to notify a user.

[0058] In block 830, the sensor processes the second response to determine the amplitude or intensity of the acoustic burst. In block 832, the sensor determines whether the amplitude or intensity is below a predetermined threshold, which indicates stress or weakening of the ultrasonic transmitting transducer. If below the predetermined threshold, in block 834, the sensor initiates a transducer cleaning operation and / or asserts a fault signal to notify a user that maintenance or repair is required. In some contemplated implementations, the cleaning operation may be performed by driving the ultrasonic transmitting transducer with an increased power drive signal to remove material from the surface of the transducer.

[0059] 9 is a flow diagram of an illustrative flow sensing method using impedance monitoring and fault detection to enhance reliability. The method begins at block 902 with running built-in self-test (BIST) diagnostics on the sensor's transmitter, receiver, and signal processing components. At block 904, the sensor determines whether the BIST results indicate a fault, and if so, at block 906, the sensor asserts a fault signal to notify a user that maintenance or repair is required. The sensor may then cease operation.

[0060] If not, in block 908, the sensor generates an acoustic burst using an ultrasonic transmit transducer. In block 910, the sensor measures the impedance of the transmit transducer, for example, by monitoring current flow during acoustic burst generation using a voltage-based driver or by monitoring voltage during acoustic burst generation using a current-based driver. In block 912, the sensor determines whether the impedance exceeds a predetermined threshold, and if so, in block 914, the sensor initiates a cleaning operation to remove debris from the transducer surface. If the cleaning operation is unsuccessful or if the impedance is determined to be outside a predetermined range in block 916, the method may proceed to block 906. Otherwise, in block 918, the sensor adjusts the carrier frequency, allowing multiple iterations to determine the frequency dependence of the impedance and find the carrier frequency that minimizes the transducer impedance.

[0061] In block 920, the sensor receives a response to the acoustic burst using an ultrasonic receiving transducer. In block 922, the sensor compares the response signal to an expected waveform to verify that the receiving transducer is operating as expected. If a discrepancy is identified, the sensor returns to block 906. Otherwise, in block 924, the sensor detects the arrival of the acoustic burst and measures the time of flight. In optional block 926, the sensor may repeat the operations of blocks 908-924 to determine a time-of-flight measurement for the opposite propagation direction. In block 928, the sensor determines a flow measurement and communicates the measurement to a logging service or system monitor and / or stores the measurement for later retrieval.

[0062] 10 is a flow diagram of an illustrative near-field communication method for an interrogator device, such as a smartphone or other portable smart device 370. At block 1002, the device determines whether a connection should be attempted. The trigger for the connection attempt may be, for example, receiving an acoustic beacon signal from a sensor, a determination by a navigation or location tracking system that a user has entered the vicinity of a vehicle, opening or launching an app on the device, a physical tap or shake of the device, or a voice command from the user. The device continues at block 1002 until a trigger is detected. Once the trigger is detected, the device generates an acoustic signal containing a connection request at block 1004.

[0063] The device checks for an acoustic signal containing a response message in block 1006. If a valid response message is not detected within a predetermined time window, the device checks whether the connection attempt timer has elapsed in block 1008. If so, the process returns to block 1002 to wait for another trigger. If not, another connection request message is sent in block 1004. If a valid response message is received in block 1006, the device proceeds to block 1010.

[0064] In block 1010, the device may select a command to be sent to the sensor in block 1012. In block 1012, the device transmits the command as an acoustic signal. In block 1014, the device checks the acoustic signal for a response message. If a valid response message is not detected within a predetermined time window, the device checks whether the command timer has elapsed in block 1016. If so, the process returns to block 1002 to wait for another trigger. If not, the command message is retransmitted in block 1012. If a valid response message is received in block 1014, the device proceeds to block 1018 to determine whether a further command should be sent. If so, the device returns to block 1010. If not, the device returns to block 1002.

[0065] The sequence of commands may vary, but may include, for example, diagnostic commands to obtain sensor identification and status, download commands to retrieve any stored measurement data, and configuration commands to set any available configuration parameters for the operation of the sensor.

[0066] 11 is a flow diagram of an illustrative near-field communication method for a sensor or other responder device. In block 1102, the sensor determines whether a connection should be attempted. The trigger for the connection attempt may be, for example, detection of nearby motion, detection of footsteps or other sounds, activation of a sensor button or control mechanism, detection of a physical knock (or kick or vibration) on the sensor, detection of a voice command, or detection of a connection request. The sensor continues in block 1102 until a trigger is detected. When a trigger is detected, the sensor generates an acoustic signal that includes a beacon in block 1104.

[0067] The sensor checks for an acoustic signal containing a connection request message in block 1106. If a valid request message is not detected within a predetermined time window, the sensor checks whether a connection attempt timer has elapsed in block 1108. If so, the process returns to block 1102 to wait for another trigger. If not, another beacon message is sent in block 1104. If a valid request message is received in block 1106, the sensor proceeds to block 1110.

[0068] At block 1110, the sensor may send a response message to the device. The response message may include the results of a previously sent command or other information. For example, the response message may include sensor status information such as whether the sensor is active, identification information, current configuration information, number of stored measurements, available storage memory, current flow measurements, downloads of stored flow measurements, fault alerts, etc. Such information may be provided by default settings or in response to an information request command.

[0069] After the sensor sends the response message in block 1110, it may check for an acoustic signal containing another command message in block 1112. If a valid command message is received, the sensor may attempt to execute the command in block 1114, after which the process moves to block 1110 to acknowledge the command and communicate a response message communicating the result, e.g., whether the command was executed successfully. If a valid command message is not detected within a predetermined time window, the sensor checks in block 1116 whether the command timer has elapsed. If so, the process returns to block 1102 to wait for another trigger. If not, the previous response message is retransmitted in block 1110.

[0070] Numerous modifications, equivalents, and alternatives will become apparent to those skilled in the art once the above disclosure is fully appreciated, and it is intended that the following claims be interpreted to include all such modifications, equivalents, and alternatives, as applicable.

Claims

1. a sensor controller, a transmitter configured to provide a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst; a receiver configured to receive a response signal from the ultrasonic receiving transducer; a time-of-flight circuit configured to detect the arrival of the acoustic burst in the response signal and measure a first time-of-flight associated with the arrival; and a phase shift circuit configured to measure a phase shift of the acoustic burst in the response signal and determine a second time-of-flight corresponding to the phase shift.

2. The sensor controller of claim 1 , further comprising control logic configured to determine a flow rate based on both the first time-of-flight and the second time-of-flight.

3. 2. The sensor controller of claim 1, further comprising control logic configured to compare the first time-of-flight with the second time-of-flight or to compare a first flow rate derived from the first time-of-flight with a second flow rate derived from the second time-of-flight, wherein the controller is configured to assert a fault signal if the comparison indicates a persistent discrepancy.

4. The sensor controller of claim 1 , wherein the ultrasonic receiving transducer is a separate transducer that is different from the ultrasonic transmitting transducer.

5. 5. The sensor controller of claim 4, further comprising control logic configured to swap the ultrasonic transmit transducer and the ultrasonic receive transducer to obtain a first time-of-flight and a second time-of-flight for each burst propagation direction, the control logic determining a first time-of-flight difference between directions and a second time-of-flight difference between directions.

6. The sensor controller of claim 5 , wherein the control logic is further configured to determine a flow rate based on both the first time-of-flight difference and the second time-of-flight difference.

7. 6. The sensor controller of claim 5, wherein the control logic is further configured to compare the first time-of-flight difference to the second time-of-flight difference or compare a first flow rate derived from the first time-of-flight difference to a second flow rate derived from the second time-of-flight difference, and assert a fault signal if the comparison indicates a persistent discrepancy.

8. a second receiver configured to receive a reflected signal from the ultrasonic transmitting transducer; a Doppler shift circuit configured to detect echoes of the acoustic burst in the reflected signal and measure velocities associated with the echoes; The sensor controller of claim 5 , wherein the control logic is configured to determine a flow rate based on the velocity when the echo has a magnitude above a threshold.

9. A sensing method comprising: providing a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst; receiving a response signal from the ultrasonic receiving transducer; using a time-of-flight circuit to detect the arrival of the acoustic burst in the response signal and measure a first time-of-flight associated with that arrival; and measuring a phase shift of the acoustic burst in the response signal using a phase shift circuit and determining a second time of flight corresponding to the phase shift.

10. The method of claim 9 , further comprising determining a flow rate based on both the first time-of-flight and the second time-of-flight.

11. comparing the first time of flight with the second time of flight, or comparing a first flow rate derived from the first time of flight with a second flow rate derived from the second time of flight; 10. The method of claim 9, further comprising: asserting a fault signal if the comparing indicates a persistent mismatch.

12. The method of claim 9 , wherein the ultrasonic receiving transducer is a separate transducer that is different from the ultrasonic transmitting transducer.

13. swapping the ultrasonic transmitting transducer and the ultrasonic receiving transducer to obtain a first time-of-flight and a second time-of-flight for each burst propagation direction; 13. The method of claim 12, further comprising determining a first time-of-flight difference between the directions and a second time-of-flight difference between the directions.

14. The method of claim 13 , further comprising determining a flow rate based on both the first time-of-flight difference and the second time-of-flight difference.

15. comparing the first time-of-flight difference to the second time-of-flight difference, or comparing a first flow rate derived from the first time-of-flight difference to a second flow rate derived from the second time-of-flight difference; 14. The method of claim 13, further comprising: asserting a fault signal if the comparing indicates a persistent mismatch.

16. receiving a reflected signal from the ultrasonic transmitting transducer; detecting an echo of the acoustic burst in the reflected signal; measuring a Doppler shift velocity associated with said echo; The method of claim 13 , further comprising: determining a flow rate based on the Doppler shift rate when the echo has a magnitude above a threshold.

17. 1. A flow sensor comprising: a first ultrasonic transducer positionable to emit in a first direction of propagation through the fluid flow; a second ultrasonic transducer positionable to emit in an opposite direction of propagation through the fluid flow; a sensor controller, wherein the sensor controller a transmitter configured to provide a drive signal to an ultrasonic transmitting transducer to generate an acoustic burst; a receiver configured to receive a response signal from an ultrasonic receiving transducer, the ultrasonic receiving transducer being a selectable one of the first ultrasonic transducer and the second ultrasonic transducer, and the ultrasonic transmitting transducer being the other of the first ultrasonic transducer and the second ultrasonic transducer; a time-of-flight circuit configured to detect the arrival of the acoustic burst in the response signal and measure a first time-of-flight associated with the arrival; a phase shift circuit configured to measure a phase shift of the acoustic burst in the response signal and determine a second time-of-flight corresponding to the phase shift; and control logic configured to swap the ultrasonic transmitting transducer and the ultrasonic receiving transducer to obtain a first time-of-flight and a second time-of-flight for each of the first propagation direction and the opposite propagation direction, and to determine a first time-of-flight difference between directions and a second time-of-flight difference between directions.

18. 18. The flow sensor of claim 17, wherein the control logic is further configured to determine a flow rate based on both the first time-of-flight difference and the second time-of-flight difference.

19. 18. The flow sensor of claim 17, wherein the control logic is further configured to compare the first time-of-flight difference with the second time-of-flight difference or compare a first flow rate derived from the first time-of-flight difference with a second flow rate derived from the second time-of-flight difference, and assert a fault signal if the comparison indicates a persistent discrepancy.

20. The sensor controller a second receiver configured to receive a reflected signal from the ultrasonic transmitting transducer; a Doppler shift circuit configured to detect echoes of the acoustic burst in the reflected signal and measure velocities associated with the echoes; 18. The flow sensor of claim 17, wherein the control logic is configured to determine a flow rate based on the velocity when the echo has a magnitude above a threshold.

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