Ultrasonic time-of-flight measurement method, circuit, flow metering method and device

Abstract

The application discloses an ultrasonic time-of-flight measurement method, circuit, flow metering method and device. The method acquires an ultrasonic transmission signal and an ultrasonic echo signal; performs first-wave detection on the ultrasonic echo signal and outputs a first-wave detection signal; samples the ultrasonic echo signal after a time corresponding to the first-wave detection signal and performs zero-crossing point detection to obtain echo sampling data and a first zero-crossing point detection signal after the first wave; performs time-to-digital conversion on the ultrasonic transmission signal and the first zero-crossing point detection signal and outputs a zero-crossing point time-of-flight; performs cross-correlation operation on the echo sampling data, reference wave data and a local delay search range with a time reference of a time corresponding to the first zero-crossing point detection signal and outputs a relative time deviation; corrects the zero-crossing point time-of-flight based on the relative time deviation and outputs the corrected zero-crossing point time-of-flight as an ultrasonic time-of-flight. The application can consider time deviation correction and reduce data volume and computing power consumption.

Description

Technical Field

[0001] This application relates to the field of ultrasonic measurement technology, and in particular to an ultrasonic time-of-flight measurement method, circuit, flow metering method and device. Background Technology

[0002] Ultrasonic flow meters typically calculate fluid velocity or flow rate by measuring the time difference between the propagation of ultrasonic waves in the fluid along and against the flow. Compared to mechanical flow meters, ultrasonic flow meters have advantages such as no moving parts, low pressure loss, wide measuring range, and applicability to various fluid media, making them widely used in water meters, gas meters, and industrial process metering applications.

[0003] In ultrasonic flow measurement based on the time-of-flight method, the ultrasonic flight time is typically obtained through initial wave detection, zero-crossing detection, and timing circuitry. This type of measurement method features simple circuit implementation, low computational complexity, and low power consumption, making it suitable for battery-powered or low-power applications. However, ultrasonic echo signals are easily affected by noise, interference, ambient temperature, transducer aging, transducer contamination, and changes in echo amplitude or envelope during actual propagation and reception. These factors can cause the zero-crossing position after the initial wave to drift, resulting in deviations in the flight time obtained based on zero-crossing detection.

[0004] Cross-correlation can determine the time offset between waveforms by comparing the similarity between the received waveform and the reference waveform, thus providing good noise immunity and waveform matching capability. However, if cross-correlation is directly used to search for the time of flight over a long sampling data range, it requires a long data acquisition time and a large amount of computation, which can easily increase the workload of analog-to-digital converters, storage units, and processing circuits, leading to increased power consumption and hindering the long-term operation of ultrasonic metering equipment powered by small-capacity batteries.

[0005] Existing solutions include adjusting the amplification gain based on the echo amplitude, adjusting the first-wave threshold based on the correlation between the echo and the reference wave, or updating the reference wave data. These solutions can improve the adaptability of the first-wave threshold and reference wave data settings to some extent, but their focus is usually on adjusting signal processing parameters or reference wave data, and they still cannot directly address the timing error caused by zero-crossing drift in the zero-crossing time of flight itself. Therefore, a solution is needed for ultrasonic time-of-flight measurement that combines the advantages of low power consumption in zero-crossing timing with the advantages of anti-interference capabilities from cross-correlation, in order to improve the accuracy and reliability of ultrasonic time-of-flight measurement with lower power consumption. Summary of the Invention

[0006] This application provides an ultrasonic time-of-flight measurement method, circuit, flow metering method, and device to solve the problem that existing ultrasonic time-of-flight measurements cannot simultaneously address timing deviation correction and reduce data volume and computational power consumption.

[0007] This application provides a method for measuring ultrasonic time-of-flight in a first aspect, comprising: acquiring an ultrasonic emission signal and an ultrasonic echo signal; performing first-wave detection on the ultrasonic echo signal and outputting a first-wave detection signal; sampling the ultrasonic echo signal after the time corresponding to the first-wave detection signal and outputting echo sampling data; performing zero-crossing detection on the ultrasonic echo signal after the time corresponding to the first-wave detection signal and outputting a first zero-crossing detection signal after the first wave; performing time-to-digital conversion on the ultrasonic emission signal and the first zero-crossing detection signal and outputting the zero-crossing flight time; performing cross-correlation calculation based on the echo sampling data, reference wave data, and a local delay search range and outputting the relative time deviation between the echo sampling data and the reference wave data; correcting the zero-crossing flight time based on the relative time deviation and outputting the corrected zero-crossing flight time as the ultrasonic time of flight; wherein, the cross-correlation value corresponding to the relative time deviation is the maximum value among the cross-correlation values ​​corresponding to the local delay search range, and the local delay search range is based on the time corresponding to the first zero-crossing detection signal.

[0008] Furthermore, the ultrasonic echo signal is subjected to first wave detection, and the first wave detection signal is output, including: comparing the ultrasonic echo signal with the first wave threshold, and outputting the first wave detection signal when the ultrasonic echo signal reaches the first wave threshold.

[0009] Furthermore, zero-crossing detection is performed on the ultrasonic echo signal after the time corresponding to the first wave detection signal, and the first zero-crossing detection signal after the first wave is output. This includes: after the first wave detection signal is generated, the detection reference is switched to the zero-crossing threshold, and the first positive zero-crossing detection signal or the first negative zero-crossing detection signal after the first wave is output based on the comparison result between the ultrasonic echo signal and the zero-crossing threshold.

[0010] Furthermore, the ultrasonic echo signal after the time corresponding to the first detection signal is sampled, and the echo sampling data is output, including: using the first detection signal as the sampling start signal to sample the ultrasonic echo signal, and ending the sampling when the preset sampling end condition is met; the preset sampling end condition includes at least one of reaching the preset number of sampling points, reaching the preset sampling duration, or reaching the preset number of zero crossings.

[0011] Furthermore, the time span of the local delay search range is less than or equal to one ultrasonic cycle.

[0012] Furthermore, cross-correlation calculations are performed based on the echo sampled data, the reference wave data, and the local delay search range to output the relative time deviation between the echo sampled data and the reference wave data. This includes: setting multiple candidate delay values ​​within the local delay search range; calculating the cross-correlation value between the echo sampled data and the reference wave data corresponding to each candidate delay value; and determining the candidate delay value corresponding to the maximum cross-correlation value in the calculation results as the relative time deviation.

[0013] Furthermore, the relative time deviation characterizes the amount of advance or lag of the echo sampling data relative to the reference wave data; the zero-crossing flight time is corrected based on the relative time deviation, including: increasing the zero-crossing flight time when the relative time deviation characterizes the echo sampling data as lagging behind the reference wave data; and decreasing the zero-crossing flight time when the relative time deviation characterizes the echo sampling data as advancing behind the reference wave data.

[0014] Furthermore, the reference wave data is pre-obtained reference waveform data or reference waveform characteristic data, which is obtained based on actual tests and used to characterize the oscillation characteristics of the piezoelectric conversion process when the transducer receives the echo.

[0015] Furthermore, in multiple ultrasonic time-of-flight measurement cycles, the corrected measurement cycle and the non-corrected measurement cycle are determined according to the preset correction enable condition; in the corrected measurement cycle, sampling, cross-correlation calculation and time-of-flight correction are performed; in the non-corrected measurement cycle, the zero-crossing time of flight is output as the ultrasonic time of flight.

[0016] Furthermore, based on the relative time deviation in at least one corrected measurement cycle, the zero-crossing drift characteristic is determined; when the zero-crossing drift characteristic meets the preset drift condition, the preset correction enable condition in the subsequent ultrasonic time-of-flight measurement cycle is adjusted to increase the occurrence frequency of the corrected measurement cycle; when the zero-crossing drift characteristic does not meet the preset drift condition, the occurrence frequency of the corrected measurement cycle in the subsequent ultrasonic time-of-flight measurement cycle is maintained or reduced.

[0017] Furthermore, it also includes error detection of the first wave detection result; error detection includes: extending the sampling time of the ultrasonic echo signal to obtain extended echo sampling data; performing cross-correlation calculation based on the extended echo sampling data, the reference wave data, and the extended delay search range; and determining whether an error occurred in the first wave detection based on the candidate delay amount corresponding to the maximum cross-correlation value within the extended delay search range; wherein, the time span of the extended delay search range is greater than one ultrasonic cycle.

[0018] This application provides an ultrasonic time-of-flight measurement circuit in a second aspect, comprising a transmit signal input terminal, an echo signal input terminal, a first-wave detection circuit, an analog-to-digital converter (ADC), a zero-crossing detection circuit, a time-to-digital converter (TD-DC converter), a reference wave data terminal, a cross-correlation processing circuit, and a time-of-flight correction circuit. The transmit signal input terminal receives an ultrasonic transmit signal; the echo signal input terminal receives an ultrasonic echo signal; the first-wave detection circuit is coupled to the echo signal input terminal and outputs a first-wave detection signal; the ADC is coupled to the echo signal input terminal and the first-wave detection circuit, receives the first-wave detection signal, samples the ultrasonic echo signal after the time corresponding to the first-wave detection signal, and outputs echo sampling data; the zero-crossing detection circuit is coupled to the echo signal input terminal and the first-wave detection circuit, receives the first-wave detection signal, performs zero-crossing detection on the ultrasonic echo signal after the time corresponding to the first-wave detection signal, and outputs the first zero-crossing detection signal after the first wave; the time-to-digital converter is coupled to the transmit signal input terminal. The input terminal and zero-crossing detection circuit perform time-to-digital conversion on the ultrasonic emission signal and the first zero-crossing detection signal, and output the zero-crossing flight time. The reference wave data terminal provides reference wave data. The input terminal of the cross-correlation operation processing circuit is coupled to the output terminal of the analog-to-digital converter, the reference wave data terminal, and the output terminal of the zero-crossing detection circuit. It performs cross-correlation operation based on the echo sampling data, the reference wave data, and the local delay search range, and outputs the relative time deviation between the echo sampling data and the reference wave data. The input terminal of the flight time correction circuit is coupled to the output terminal of the time-to-digital converter and the output terminal of the cross-correlation operation processing circuit. It corrects the zero-crossing flight time based on the relative time deviation and outputs the corrected zero-crossing flight time as the ultrasonic flight time. The cross-correlation value corresponding to the relative time deviation is the maximum value among the cross-correlation values ​​corresponding to the local delay search range, and the local delay search range uses the time corresponding to the first zero-crossing detection signal as the time reference.

[0019] Furthermore, the ultrasonic time-of-flight measurement circuit also includes a timing control circuit; the timing control circuit is coupled to the analog-to-digital converter, the cross-correlation operation processing circuit, and the time-of-flight correction circuit respectively; the timing control circuit enables the analog-to-digital converter, the cross-correlation operation processing circuit, and the time-of-flight correction circuit to enter the correction working state or the non-correction working state according to the correction enable signal; in the non-correction working state, the ultrasonic time-of-flight measurement circuit outputs the zero-crossing time as the ultrasonic time of flight.

[0020] This application provides an ultrasonic flow measurement method in a third aspect, comprising: performing the aforementioned ultrasonic time-of-flight measurement method in a first propagation direction to obtain a first ultrasonic time of flight; performing the aforementioned ultrasonic time-of-flight measurement method in a second propagation direction to obtain a second ultrasonic time of flight; and calculating the fluid velocity or fluid flow rate based on the time difference between the first ultrasonic time of flight and the second ultrasonic time of flight.

[0021] This application provides an ultrasonic flow metering device in a fourth aspect, comprising a first transducer, a second transducer, a flow calculation circuit, and the aforementioned ultrasonic time-of-flight measurement circuit; in a first propagation direction, the first transducer emits ultrasonic waves, the second transducer receives the ultrasonic waves propagating through the fluid and generates a first ultrasonic echo signal, and the ultrasonic time-of-flight measurement circuit outputs a first ultrasonic time of flight based on the ultrasonic emission signal and the first ultrasonic echo signal corresponding to the first propagation direction; in a second propagation direction, the second transducer emits ultrasonic waves, the first transducer receives the ultrasonic waves propagating through the fluid and generates a second ultrasonic echo signal, and the ultrasonic time-of-flight measurement circuit outputs a second ultrasonic time of flight based on the ultrasonic emission signal and the second ultrasonic echo signal corresponding to the second propagation direction; the flow calculation circuit is coupled to the ultrasonic time-of-flight measurement circuit and outputs the fluid velocity or fluid flow rate based on the time difference between the first and second ultrasonic time of flight.

[0022] This application has at least the following beneficial effects: by performing echo sampling and zero-crossing detection after the first wave detection, the zero-crossing flight time is determined by the ultrasonic emission signal and the first zero-crossing detection signal after the first wave. Within a local delay search range with the time corresponding to the zero-crossing detection signal as the time reference, cross-correlation calculation is performed on the echo sampling data and the reference wave data to obtain the relative time deviation used to correct the zero-crossing flight time. While retaining the advantages of low data volume and low computational volume in zero-crossing time measurement, the cross-correlation calculation is used to correct the time deviation caused by the change in echo waveform, thereby reducing the impact of zero-crossing drift caused by factors such as noise, interference, transducer aging or contamination on the flight time measurement results, and improving the accuracy and reliability of ultrasonic time-of-flight measurement.

[0023] This application also has the following advantages: by setting the first wave threshold and the zero-crossing threshold, the first wave detection and the zero-crossing detection after the first wave can be processed in stages; by setting the sampling end condition, the amount of echo sampling data can be controlled; by limiting the time span of the local delay search range to less than or equal to one ultrasonic cycle, and determining the candidate delay amount corresponding to the maximum cross-correlation value within this range, the number of candidate searches for cross-correlation calculations can be reduced; by making the relative time deviation characterize the advance or lag of the echo sampling data relative to the reference wave data, the zero-crossing flight time can be corrected bidirectionally; by setting the corrected measurement cycle and the non-corrected measurement cycle, and determining the zero-crossing drift characteristics based on the relative time deviation in the already executed corrected measurement cycle to adjust the subsequent correction frequency, a trade-off can be achieved between measurement accuracy and power consumption; by extending the sampling duration and the delay search range for error wave judgment, the measurement reliability under abnormal first wave detection scenarios can be improved. Attached Figure Description

[0024] Figure 1 A schematic diagram of the ultrasonic time-of-flight measurement method provided in this application; Figure 2 A schematic diagram of the ultrasonic time-of-flight measurement circuit provided in this application; Figure 3 A schematic diagram of a measurement circuit framework with correction enable provided for this application; Figure 4 A schematic diagram illustrating the principle of cross-correlation calculation provided in this application; Figure 5 A schematic diagram of the flow metering method provided in this application. Detailed Implementation

[0025] The content of this application will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are used to illustrate the technical solution of this application and are not intended to limit the scope of protection of this application.

[0026] It should be noted that the terms "first," "second," etc., used in this application are used to distinguish similar objects and are not used to limit a specific order, sequence, importance, or quantity. For example, "first propagation direction" and "second propagation direction" are used to distinguish two different ultrasonic wave propagation directions, and the first and second propagation directions can be interchanged where appropriate; "first transducer" and "second transducer" are used to distinguish two different transducers, and the first and second transducers can serve as the transmitting side or the receiving side, respectively, in different measurement stages. The terms "comprising," "including," "having," and their variations indicate non-exclusive inclusion, encompassing a method, circuit, apparatus, or device that includes a series of steps, components, circuits, or modules, and are not limited to the steps, components, circuits, or modules that have been expressly listed, but may also include other steps, components, circuits, or modules that are not expressly listed but are related to the method, circuit, apparatus, or device.

[0027] It should be understood that, in this application, "circuit" can refer to a functional structure formed by one or more electronic components, logic units, sub-circuits, processing units, or combinations thereof through electrical connections, signal connections, logical connections, or electromagnetic coupling. A circuit can be implemented by discrete components or by at least one of integrated circuits, application-specific integrated circuits, programmable logic devices, processors, and their peripheral circuits. When describing a circuit or port as "coupled" to another circuit or port, it can indicate a direct connection between the two or an indirect connection through one or more intermediate components, circuits, signal channels, or logic processing units; this coupling relationship can be a physical connection, a signal connection, a logical connection, or a combination thereof. Unless otherwise expressly stated, "coupled" should not be construed as limited to direct electrical connections.

[0028] It should also be noted that the port names such as "input terminal," "output terminal," and "data terminal" in this application are used to describe the transmission relationship of signals, data, or processing results, and are not limited to independently set physical pins. They can also be internal nodes of the circuit, logic interfaces, register interfaces, bus interfaces, or data interaction interfaces implemented in a software / hardware collaborative manner. The processing actions such as "acquisition," "output," "determine," "calculate," and "correct" described in this application can be executed by hardware circuits, processors, logic control units, programmable devices, or combinations thereof. Without affecting the implementation of the technical solution, each step can be executed in the order shown in the figure, or in parallel, in an interleaved manner, or according to a preset timing sequence.

[0029] In this application, "ultrasonic emission signal" refers to the start time signal corresponding to the ultrasonic emission action, which can be output by a transmission control circuit, a timing circuit, or other synchronization signal generation circuit. "Ultrasonic echo signal," as commonly understood in the field of ultrasonic flow metering, can represent the ultrasonic signal received at the receiving side, or an electrical signal converted from the ultrasonic signal at the receiving side. "Ultrasonic time of flight" can represent the time it takes for the ultrasonic wave to travel from the transmitting side to the receiving side. "Corrected measurement period" can represent the measurement period in which sampling, cross-correlation calculation, and time of flight correction are performed; "uncorrected measurement period" can represent the measurement period in which the zero-crossing time of flight is output as the ultrasonic time of flight without performing cross-correlation correction. "First wave" can represent the waveform portion of the ultrasonic echo signal that first reaches the preset detection condition. "Cross-correlation calculation," as commonly understood in the field of signal processing, can represent the calculation process used to measure the similarity of two signals at different relative time offsets; a larger cross-correlation value generally indicates a higher degree of matching between the two signals at the corresponding time offset.

[0030] Figure 1 This is a schematic diagram of the ultrasonic time-of-flight measurement method provided in this application. Figure 1 As shown, the ultrasonic time-of-flight measurement method provided in this embodiment may include steps S1 to S7.

[0031] In step S1, the ultrasonic transmission signal and ultrasonic echo signal are acquired. The ultrasonic transmission signal can be used as the start time signal for time-of-flight measurement, and the ultrasonic echo signal can be used for first-wave detection, sampling, and zero-crossing detection. In one embodiment, the ultrasonic transmission signal can be generated by transmission control logic, transmission drive circuit, or timing start circuit, and the ultrasonic echo signal can be formed by receiving ultrasonic waves through a transducer on the receiving side and then undergoing piezoelectric conversion. It can then be further amplified and filtered by the receiving circuit before being input into subsequent processing circuits.

[0032] In step S2, the ultrasonic echo signal undergoes first-wave detection, and a first-wave detection signal is output. Specifically, the ultrasonic echo signal can be compared with a first-wave threshold, and the first-wave detection signal is output when the ultrasonic echo signal reaches the first-wave threshold. The first-wave threshold can be preset based on the amplitude range of the ultrasonic echo signal, noise level, transducer characteristics, or the application scenario of the flow metering device. The first-wave detection signal can serve as a trigger signal for subsequent sampling and zero-crossing detection processes, ensuring that subsequent processing begins after the echo arrives.

[0033] In step S3, the ultrasonic echo signal after the time corresponding to the first detection signal is sampled, and the echo sampling data is output. Specifically, the first detection signal can be used as the sampling start signal, so that the analog-to-digital conversion process starts sampling the ultrasonic echo signal after the first detection signal is generated. The sampling process can end when a preset sampling end condition is met. The preset sampling end condition may include at least one of reaching a preset number of sampling points, reaching a preset sampling duration, or reaching a preset number of zero-crossing points. By starting sampling after the first detection signal is generated, invalid sampling data before the echo arrives can be reduced, thereby reducing the amount of sampling data and the data processing load of the analog-to-digital conversion process.

[0034] In step S4, zero-crossing detection is performed on the ultrasonic echo signal after the time corresponding to the first wave detection signal, and the first zero-crossing detection signal after the first wave is output. Specifically, after the first wave detection signal is generated, the detection reference of the ultrasonic echo signal can be switched from the first wave threshold to the zero-crossing threshold, and the ultrasonic echo signal is compared or judged based on the zero-crossing threshold to output the first positive zero-crossing detection signal or the first negative zero-crossing detection signal after the first wave. The detection reference can refer to the reference level, reference threshold, or reference value used by the comparator, sampling and judgment unit, or digital judgment program when judging whether the ultrasonic echo signal meets the detection conditions. The detection reference switching can be implemented by hardware circuitry or by program control. For example, in the hardware implementation, the reference input terminal of the comparator can be switched from the first wave threshold terminal to the zero-crossing threshold terminal by a switching circuit, multiplexer, or threshold selection circuit; in the program implementation, after the first wave detection signal is output, the comparison parameter used to judge the ultrasonic echo signal can be updated from the first wave threshold to the zero-crossing threshold, and zero-crossing detection can be performed according to the updated comparison parameter. A positive zero-crossing point corresponds to the moment when the ultrasonic echo signal changes from below the zero-crossing threshold to above the zero-crossing threshold, while a negative zero-crossing point corresponds to the moment when the ultrasonic echo signal changes from above the zero-crossing threshold to below the zero-crossing threshold.

[0035] It should be noted that, Figure 1Steps S3 and S4 are shown in sequence to facilitate understanding of the main processing flow of the ultrasonic time-of-flight measurement method. In actual circuit implementation, both the sampling process and the zero-crossing detection process can be triggered by the first wave detection signal. They can be executed in parallel or sequentially according to a preset timing sequence; this application does not impose any restrictions on this. As long as the sampling process can output echo sampling data for cross-correlation calculations, and the zero-crossing detection process can output the first zero-crossing detection signal after the first wave, subsequent time-of-flight correction can be achieved.

[0036] In step S5, the ultrasonic emission signal and the first zero-crossing detection signal are converted from time to digital, and the zero-crossing flight time is output. Specifically, the ultrasonic emission signal can be used as the start timing signal, and the first zero-crossing detection signal can be used as the stop timing signal. The time between the ultrasonic emission moment and the first zero-crossing moment after the first wave is obtained through time-to-digital conversion. This zero-crossing flight time can be denoted as td. For the first propagation direction, the zero-crossing flight time can be denoted as td12; for the second propagation direction, the zero-crossing flight time can be denoted as td21.

[0037] In step S6, a cross-correlation calculation is performed based on the echo sampling data, the reference wave data, and the local delay search range to output the relative time deviation between the echo sampling data and the reference wave data. The reference wave data can be pre-obtained reference waveform data or reference waveform characteristic data, which can be obtained from actual testing and used to characterize the piezoelectric conversion process start-up characteristics when the transducer receives the echo. The cross-correlation calculation can set multiple candidate delay values ​​within the local delay search range, calculate the cross-correlation value between the echo sampling data and the reference wave data corresponding to each candidate delay value, and determine the candidate delay value corresponding to the largest cross-correlation value in the calculation results as the relative time deviation. This relative time deviation can be denoted as δt. The relative time deviation in the first propagation direction can be denoted as δt12, and the relative time deviation in the second propagation direction can be denoted as δt21.

[0038] In step S7, the zero-crossing flight time is corrected based on the relative time deviation, and the corrected zero-crossing flight time is output as the ultrasonic flight time. Specifically, the relative time deviation δt can be used to algebraically correct the zero-crossing flight time td to obtain the ultrasonic flight time t. This relationship can be expressed as: t = td + δt. The relative time deviation δt can characterize the advance or lag of the echo sampling data relative to the reference wave data. When the relative time deviation δt indicates that the echo sampling data lags behind the reference wave data, the zero-crossing flight time td can be increased; when the relative time deviation δt indicates that the echo sampling data advances relative to the reference wave data, the zero-crossing flight time td can be decreased. Therefore, t = td + δt indicates an algebraic correction of the zero-crossing flight time td, rather than a correction only in the direction of increasing flight time. The sign of δt can be determined according to the definition of candidate delay in cross-correlation calculation. In this embodiment, as long as the relative time deviation δt can be substituted into t=td+δt to reflect the advance or lag correction of the echo sampling data relative to the reference wave data, the zero-crossing flight time td can be corrected.

[0039] Through the above steps, a low-data-volume, low-computational-volume zero-crossing time can be obtained by first-wave detection, zero-crossing detection, and time-to-digital conversion. Then, the relative time deviation is obtained by cross-correlation calculation within the local delay search range, and this relative time deviation is used to correct the zero-crossing time. Therefore, without excessively increasing the amount of data acquired and computational power consumption, zero-crossing drift caused by factors such as noise, interference, transducer aging, or contamination can be corrected, improving the accuracy and reliability of ultrasonic time-of-flight measurement.

[0040] Figure 2 This is a schematic diagram of the ultrasonic time-of-flight measurement circuit framework provided in this application. Figure 2 As shown, the ultrasonic time-of-flight measurement circuit may include a transmit signal input terminal 101, an echo signal input terminal 102, a first wave detection circuit 103, an analog-to-digital converter 104, a zero-crossing detection circuit 105, a time-to-digital converter 106, a reference wave data terminal 107, a cross-correlation operation processing circuit 108, a time-of-flight correction circuit 109, and an ultrasonic time-of-flight output terminal 110.

[0041] Transmit signal input terminal 101 receives ultrasonic transmitted signals. Echo signal input terminal 102 receives ultrasonic echo signals. First wave detection circuit 103 is coupled to echo signal input terminal 102 and performs first wave detection on the ultrasonic echo signal, outputting a first wave detection signal. Analog-to-digital converter 104 is coupled to echo signal input terminal 102 and first wave detection circuit 103, and after receiving the first wave detection signal, samples the ultrasonic echo signal after the time corresponding to the first wave detection signal, outputting echo sampling data. Zero-crossing detection circuit 105 is coupled to echo signal input terminal 102 and first wave detection circuit 103, and after receiving the first wave detection signal, performs zero-crossing detection on the ultrasonic echo signal after the time corresponding to the first wave detection signal, outputting the first zero-crossing detection signal after the first wave.

[0042] A time-to-digital converter 106 is coupled to the transmit signal input terminal 101 and the zero-crossing detection circuit 105, and performs time-to-digital conversion on the ultrasonic transmit signal and the first zero-crossing detection signal, outputting the zero-crossing time of flight. A reference wave data terminal 107 provides reference wave data. The input terminal of a cross-correlation processing circuit 108 is coupled to the output terminal of an analog-to-digital converter 104, the reference wave data terminal 107, and the output terminal of the zero-crossing detection circuit 105, and performs cross-correlation calculations based on the echo sampling data, the reference wave data, and the local delay search range, outputting the relative time deviation between the echo sampling data and the reference wave data. The input terminal of a time-of-flight correction circuit 109 is coupled to the output terminal of the time-to-digital converter 106 and the output terminal of the cross-correlation processing circuit 108, and corrects the zero-crossing time of flight based on the relative time deviation, outputting the corrected zero-crossing time of flight as the ultrasonic time of flight. The ultrasonic time of flight output terminal 110 outputs this ultrasonic time of flight.

[0043] It should be noted that, Figure 2 The arrows in the diagram are used to indicate the transmission direction of different signals or data between circuits, and do not limit the physical routing of each signal line in the actual chip, circuit board or wiring structure. Figure 2 If there is an intersection between different arrows or lines, unless a connection node is explicitly set at the intersection or the text clearly states that there is a coupling relationship, it does not mean that there is an electrical or signal connection between the two intersecting lines. Figure 2In the process, the ultrasonic wave emission signal is transmitted to the time-to-digital converter 106, and the ultrasonic wave echo signal is transmitted to the first wave detection circuit 103, the analog-to-digital converter 104, and the zero-crossing detection circuit 105, respectively. The first wave detection signal output by the first wave detection circuit 103 triggers the analog-to-digital converter 104 and the zero-crossing detection circuit 105, respectively. The first zero-crossing detection signal output by the zero-crossing detection circuit 105 is transmitted to the time-to-digital converter 106 and used as the time reference for the cross-correlation operation processing circuit 108 to determine the local delay search range. The echo sampling data output by the analog-to-digital converter 104 and the reference wave data provided by the reference wave data terminal 107 are input to the cross-correlation operation processing circuit 108. The cross-correlation operation processing circuit 108 outputs the relative time deviation to the flight time correction circuit 109. The time-to-digital converter 106 outputs the zero-crossing flight time to the flight time correction circuit 109. The flight time correction circuit 109 outputs the ultrasonic wave flight time based on the zero-crossing flight time and the relative time deviation.

[0044] Figure 3 A schematic diagram of a measurement circuit framework with correction enable provided for this application. (See attached diagram.) Figure 3 As shown, in Figure 2 Based on the ultrasonic time-of-flight measurement circuit shown, the ultrasonic time-of-flight measurement circuit may further include a timing control circuit 111 and a correction enable signal input terminal 112. The correction enable signal input terminal 112 receives the correction enable signal and transmits it to the timing control circuit 111. The timing control circuit 111 is coupled to the analog-to-digital converter 104, the cross-correlation operation processing circuit 108, and the time-of-flight correction circuit 109, and outputs a sampling enable signal, an operation enable signal, and a correction enable signal according to the correction enable signal, so as to control the analog-to-digital converter 104, the cross-correlation operation processing circuit 108, and the time-of-flight correction circuit 109 to enter the correction working state or the non-correction working state.

[0045] In the corrected operating state, the analog-to-digital converter 104 responds to the sampling enable signal, samples the ultrasonic echo signal after the time corresponding to the first detection signal, and outputs the echo sampling data; the cross-correlation operation processing circuit 108 responds to the operation enable signal, performs cross-correlation operation based on the echo sampling data, the reference wave data, and the local delay search range with the time corresponding to the first zero-crossing detection signal as the time reference, and outputs the relative time deviation; the time-of-flight correction circuit 109 responds to the correction enable signal, corrects the zero-crossing time of flight output by the time-to-digital converter 106 based on the relative time deviation, and outputs the corrected zero-crossing time of flight as the ultrasonic time of flight.

[0046] In non-correction operation mode, one or more of the following circuits can be turned off or disabled: analog-to-digital converter 104, cross-correlation processing circuit 108, and time-of-flight correction circuit 109. The zero-crossing time of flight output by time-to-digital converter 106 is then output as ultrasonic time of flight or directly via cross-correlation processing circuit 108. Figure 3 (Not shown) The output is the ultrasonic time of flight. Therefore, cross-correlation correction can be performed based on accuracy and power consumption requirements.

[0047] It should be noted that, Figure 3 Solid arrows can indicate the transmission direction of measurement-related information such as measurement signals, sampled data, reference wave data, zero-crossing flight time, and relative time deviation. Dashed arrows can indicate the output path of correction enable signals, sampling enable signals, operation enable signals, correction enable signals, or non-correction operating states. Figure 3 If there are intersections between different arrows or lines, unless a connection node is clearly set at the intersection or the coupling relationship is clearly stated in the text of the image, it does not mean that there is an electrical or signal connection between the two intersecting lines. Figure 3 In the process, the correction enable signal input terminal 112 provides a correction enable signal to the timing control circuit 111. The timing control circuit 111 outputs corresponding enable control signals to the analog-to-digital converter 104, the cross-correlation operation processing circuit 108, and the time-of-flight correction circuit 109 according to the correction enable signal. In the correction working state, the analog-to-digital converter 104 outputs echo sampling data, the cross-correlation operation processing circuit 108 outputs the relative time deviation, and the time-of-flight correction circuit 109 outputs the ultrasonic flight time after correcting the zero-crossing flight time based on the relative time deviation. In the non-correction working state, the ultrasonic time-of-flight measurement circuit can output the zero-crossing flight time output by the time-to-digital converter 106 as the ultrasonic flight time without cross-correlation correction. Figure 3 The modified and unmodified operating state paths shown are used to illustrate the signal flow under different operating states and do not limit the actual circuit to using the physical wiring paths shown.

[0048] In some implementations, a corrected measurement period and a non-corrected measurement period can be determined based on preset correction enable conditions within multiple ultrasonic time-of-flight measurement cycles. During the corrected measurement cycle, sampling, cross-correlation calculations, and time-of-flight correction are performed; during the non-corrected measurement cycle, the zero-crossing time of flight is output as the ultrasonic time of flight. The preset correction enable conditions can be determined based on at least one of the following: the number of measurement cycles, a preset time interval, the degree of flow rate variation, battery level, measurement accuracy requirements, historical relative time deviation, or external control commands.

[0049] In some implementations, the zero-crossing drift characteristic can be determined based on the relative time deviation in at least one corrected measurement cycle. The zero-crossing drift characteristic characterizes the deviation of the zero-crossing time of flight relative to the cross-correlation correction result. The zero-crossing drift characteristic can include at least one of the magnitude, direction, trend, or fluctuation range of the relative time deviation. When the zero-crossing drift characteristic meets a preset drift condition, the preset correction enable condition in subsequent ultrasonic time-of-flight measurement cycles can be adjusted to increase the frequency of corrected measurement cycles; when the zero-crossing drift characteristic does not meet the preset drift condition, the frequency of corrected measurement cycles in subsequent ultrasonic time-of-flight measurement cycles can be maintained or reduced. The preset drift condition can include at least one of the following: the absolute value of the relative time deviation is greater than a preset deviation threshold, the relative time deviation changes continuously in the same direction in multiple corrected measurement cycles, or the fluctuation range of the relative time deviation is greater than a preset fluctuation threshold. This allows for a trade-off between measurement accuracy and power consumption.

[0050] Figure 4 A schematic diagram illustrating the principle of cross-correlation calculation provided in this application. For example... Figure 4 As shown, the reference wave y(t) and the received wave x(t) can have similar waveform characteristics. When the received wave x(t) reaches the first wave threshold Vfirst, sampling of the received wave x(t) can begin, and the zero-crossing flight time td is obtained at the first zero-crossing point after the first wave. Cross-correlation can be used to calculate the similarity between the received wave x(t) and the reference wave y(t) under different candidate delay amounts τ, resulting in the cross-correlation function Rxy(τ).

[0051] In one implementation, the cross-correlation function can be expressed as:

[0052] Where x(t) represents the received wave corresponding to the echo sampling data, y(t) represents the reference wave corresponding to the reference wave data, τ represents the candidate delay amount or delay factor, and Rxy(τ) represents the cross-correlation value when the candidate delay amount is τ.

[0053] like Figure 4As shown, when τ takes a certain candidate value, the corresponding cross-correlation value Rxy(τ) can be calculated. When the candidate delay τ makes the received wave x(t) and the reference wave y(t) reach the optimal alignment on the time axis, the contribution of the same phase portion of the two waves to the cumulative cross-correlation value is the greatest, and the cross-correlation value reaches its maximum value. Therefore, the candidate delay corresponding to the maximum cross-correlation value can be determined as the relative time deviation δt between the echo sampled data and the reference wave data. The local delay search range can be based on the time corresponding to the first zero-crossing detection signal, and multiple candidate delay values ​​can be set around this time reference. When the time corresponding to the first zero-crossing detection signal is used as the time reference, the candidate delay value corresponding to this time reference can be recorded as 0, and multiple candidate delay values ​​can be set before and after this candidate delay value. Figure 4 The horizontal coordinate corresponding to the cross-correlation function Rxy(τ) is used to represent the value of the candidate delay τ, which represents the tentative time offset between the echo sampled data and the reference wave data. Since the zero-crossing flight time td already provides a coarse location result of the echo arrival position, the cross-correlation operation can be performed within the local delay search range without needing to re-search for the flight time within the full echo range. In some implementations, the time span of the local delay search range can be less than or equal to one ultrasonic cycle. One ultrasonic cycle can be the time interval between adjacent in-phase points in the ultrasonic echo signal, such as the time interval between adjacent positive zero-crossing points, or the time interval between adjacent wave crests.

[0054] In some implementations, error detection can also be performed on the initial detection results. Error detection can include: extending the sampling time of the ultrasonic echo signal to obtain extended echo sampling data; performing cross-correlation calculations based on the extended echo sampling data, the reference wave data, and the extended delay search range; and determining whether an error has occurred in the initial detection based on the candidate delay amount corresponding to the maximum cross-correlation value within the extended delay search range. The time span of the extended delay search range is greater than one ultrasonic cycle. If the candidate delay amount corresponding to the maximum cross-correlation value within the extended delay search range shows a cross-cycle shift relative to the conventional local delay search range, it can be determined that an error may have occurred in the initial detection. This method can identify potential error phenomena during the initial threshold detection process, improving the reliability of time-of-flight measurement in abnormal scenarios.

[0055] Figure 5 A schematic diagram of the flow metering method provided in this application. Figure 5As shown, during flow measurement, transducer transmit / receive switching settings and circuit initialization can be performed first. Transducer transmit / receive switching settings are used to determine the current propagation direction. Circuit initialization may include at least one of the following: clearing the timing circuit, setting the first wave threshold, setting the zero-crossing threshold, resetting the cross-correlation processing circuit, and correcting the enable state settings. Subsequently, the transmitting transducer emits ultrasonic waves, and the receiving transducer receives the ultrasonic waves propagating through the fluid and generates ultrasonic echo signals. The first wave detection, echo signal sampling, zero-crossing detection, cross-correlation calculation with the reference wave, and time-of-flight correction within the dashed box correspond to the aforementioned ultrasonic time-of-flight measurement method.

[0056] In the first propagation direction, an ultrasonic wave can be emitted by a first transducer, and received by a second transducer after propagation through the fluid, generating a first ultrasonic echo signal. The first ultrasonic flight time t12 is obtained using the aforementioned ultrasonic flight time measurement method. The zero-crossing flight time in the first propagation direction can be denoted as td12, and the relative time deviation can be denoted as δt12. The first ultrasonic flight time can be expressed as: t12 = td12 + δt12.

[0057] In the second propagation direction, an ultrasonic wave can be emitted by a second transducer, and received by a first transducer after propagation through the fluid, generating a second ultrasonic echo signal. The second ultrasonic flight time t21 is obtained using the aforementioned ultrasonic flight time measurement method. The zero-crossing flight time in the second propagation direction can be denoted as td21, and the relative time deviation can be denoted as δt21. The second ultrasonic flight time can be expressed as: t21 = td21 + δt21.

[0058] After obtaining the first ultrasonic flight time t12 and the second ultrasonic flight time t21, the fluid velocity or flow rate can be calculated based on the time difference between them. Specifically, if the straight-line distance between the first and second transducers is L, the angle between the line connecting their centers and the fluid flow direction is θ, the cross-sectional area of ​​the flow channel is S, the calibration coefficient is K, the fluid velocity is v, and the fluid flow rate is Q, then it can be calculated using the following formula: Q=K·S·v=K·S·L·Δt / (2·t12·t21·cosθ) Where Δt = t12 - t21. The above flow rate calculation formula is only an example. In actual implementation, other equivalent calculation methods can be used depending on the flow channel structure, transducer installation method, and calibration parameters.

[0059] This embodiment also provides an ultrasonic flow metering device. The ultrasonic flow metering device may include a first transducer, a second transducer, a flow calculation circuit, and the aforementioned ultrasonic time-of-flight measurement circuit. In a first propagation direction, the first transducer emits ultrasonic waves, and the second transducer receives the ultrasonic waves propagating through the fluid and generates a first ultrasonic echo signal. The ultrasonic time-of-flight measurement circuit outputs a first ultrasonic time of flight based on the ultrasonic emission signal and the first ultrasonic echo signal corresponding to the first propagation direction. In a second propagation direction, the second transducer emits ultrasonic waves, and the first transducer receives the ultrasonic waves propagating through the fluid and generates a second ultrasonic echo signal. The ultrasonic time-of-flight measurement circuit outputs a second ultrasonic time of flight based on the ultrasonic emission signal and the second ultrasonic echo signal corresponding to the second propagation direction. The flow calculation circuit is coupled to the ultrasonic time-of-flight measurement circuit and outputs the fluid velocity or fluid flow rate based on the time difference between the first and second ultrasonic times of flight. The aforementioned ultrasonic time-of-flight measurement circuit can be implemented by multiple discrete devices or integrated into a dedicated integrated circuit to adapt to low-power, small-size flow metering devices.

[0060] In summary, this application's embodiments obtain the arrival trigger information of the ultrasonic echo signal through first-wave detection, and perform echo sampling and zero-crossing detection after the first-wave detection signal is generated. This allows the time-to-digital conversion process to obtain the zero-crossing flight time based on the ultrasonic transmission signal and the first zero-crossing detection signal after the first wave. Simultaneously, the cross-correlation calculation process can obtain the relative time deviation based on the echo sampling data and the reference wave data. Since the local delay search range uses the time corresponding to the first zero-crossing detection signal as the time reference, the cross-correlation calculation does not need to re-search for the flight time within the entire echo range, but can perform local corrections around the position corresponding to the zero-crossing flight time. Therefore, this application can correct the timing deviation caused by zero-crossing detection while reducing data acquisition volume and computational power consumption, improving the reliability of ultrasonic flight time measurement and the flow measurement results based on this flight time.

[0061] The above embodiments are merely illustrative of the technical concept and features of this application, intended to enable those skilled in the art to understand the content of this application and implement it accordingly, and should not be construed as limiting the scope of protection of this application. It is obvious to those skilled in the art that this application is not limited to the details of the above exemplary embodiments, and that this application can be implemented in other specific forms without departing from the spirit or essential characteristics of this application. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of this application is defined by the appended claims rather than the foregoing description, and thus all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within this application.

Claims

1. A method for measuring ultrasonic time of flight, characterized in that, include: Acquire ultrasonic transmission signals and ultrasonic echo signals; The ultrasonic echo signal is subjected to first wave detection, and the first wave detection signal is output. The ultrasonic echo signal after the time corresponding to the first wave detection signal is sampled, and the echo sampling data is output. Zero-crossing detection is performed on the ultrasonic echo signal after the time corresponding to the first wave detection signal, and the first zero-crossing detection signal after the first wave is output. The ultrasonic emission signal and the first zero-crossing detection signal are converted from time to digital, and the zero-crossing flight time is output. Based on the echo sampling data, reference wave data, and local delay search range, cross-correlation calculation is performed to output the relative time deviation between the echo sampling data and the reference wave data. This includes: setting multiple candidate delay values ​​within the local delay search range, calculating the cross-correlation value between the echo sampling data and the reference wave data corresponding to each candidate delay value, and determining the candidate delay value corresponding to the maximum cross-correlation value in the calculation results as the relative time deviation. The zero-crossing flight time is corrected based on the relative time deviation, and the corrected zero-crossing flight time is output as the ultrasonic flight time. in, The reference wave data is pre-obtained reference waveform data or reference waveform feature data; The local delay search range is based on the time corresponding to the first zero-crossing detection signal.

2. The ultrasonic time-of-flight measurement method according to claim 1, characterized in that, The ultrasonic echo signal is subjected to first-wave detection, and the first-wave detection signal is output, including: The ultrasonic echo signal is compared with the first wave threshold, and the first wave detection signal is output when the ultrasonic echo signal reaches the first wave threshold.

3. The ultrasonic time-of-flight measurement method according to claim 1, characterized in that, Zero-crossing detection is performed on the ultrasonic echo signal after the time corresponding to the first wave detection signal, and the first zero-crossing detection signal after the first wave is output, including: After the first wave detection signal is generated, the detection reference is switched to the zero-crossing threshold, and the first positive zero-crossing detection signal or the first negative zero-crossing detection signal after the first wave is output according to the comparison result between the ultrasonic echo signal and the zero-crossing threshold.

4. The ultrasonic time-of-flight measurement method according to claim 1, characterized in that, The ultrasonic echo signal after the time corresponding to the first detection signal is sampled, and the echo sampling data is output, including: The ultrasonic echo signal is sampled using the first detection signal as the sampling start signal, and sampling ends when the preset sampling end condition is met. The preset sampling termination condition includes at least one of reaching a preset number of sampling points, reaching a preset sampling duration, or reaching a preset number of zero-crossing points.

5. The ultrasonic time-of-flight measurement method according to claim 1, characterized in that, The time span of the local delay search range is less than or equal to one ultrasonic cycle.

6. The ultrasonic time-of-flight measurement method according to claim 1, characterized in that, The relative time deviation represents the amount of advance or lag of the echo sampling data relative to the reference wave data; Correcting the zero-crossing flight time based on the relative time deviation includes: When the relative time deviation indicates that the echo sampling data lags behind the reference wave data, the zero-crossing flight time is increased; When the relative time deviation indicates that the echo sampling data is ahead of the reference wave data, the zero-crossing flight time is reduced.

7. The ultrasonic time-of-flight measurement method according to claim 1, characterized in that, The reference waveform data or the reference waveform characteristic data are obtained based on actual tests and are used to characterize the oscillation characteristics of the piezoelectric conversion process when the transducer receives the echo.

8. The ultrasonic time-of-flight measurement method according to claim 1, characterized in that, In multiple ultrasonic time-of-flight measurement cycles, the corrected measurement cycle and the non-corrected measurement cycle are determined according to preset correction enable conditions. During the corrected measurement period, sampling, cross-correlation calculations, and time-of-flight corrections are performed. During the uncorrected measurement period, the zero-crossing time of flight is output as the ultrasonic time of flight.

9. The ultrasonic time-of-flight measurement method according to claim 8, characterized in that, The zero-crossing drift characteristics are determined based on the relative time deviation in at least one corrective measurement cycle that has been performed. When the zero-crossing drift characteristic meets the preset drift condition, the preset correction enable condition in the subsequent ultrasonic time-of-flight measurement cycle is adjusted to increase the frequency of the correction measurement cycle. When the zero-crossing drift characteristic does not meet the preset drift condition, the frequency of the correction measurement cycle in the subsequent ultrasonic time-of-flight measurement cycle is maintained or reduced.

10. The ultrasonic time-of-flight measurement method according to claim 1, characterized in that, This also includes determining the error rate of the initial detection results; The fault wave determination includes: Extend the sampling time of the ultrasonic echo signal to obtain extended echo sampling data; Cross-correlation calculations are performed based on the extended echo sampling data, the reference wave data, and the extended delay search range; Based on the candidate delay amount corresponding to the maximum cross-correlation value within the extended delay search range, determine whether the first wave detection has a wrong wave; The time span of the extended delay search range is greater than one ultrasonic cycle.

11. An ultrasonic time-of-flight measurement circuit, characterized in that, include: The signal input terminal receives ultrasonic transmission signals. The echo signal input terminal receives ultrasonic echo signals. The first wave detection circuit is coupled to the echo signal input terminal and outputs the first wave detection signal; An analog-to-digital converter is coupled to the echo signal input terminal and the first wave detection circuit. After receiving the first wave detection signal, it samples the ultrasonic echo signal after the time corresponding to the first wave detection signal and outputs the echo sampling data. The zero-crossing detection circuit is coupled to the echo signal input terminal and the first wave detection circuit. After receiving the first wave detection signal, it performs zero-crossing detection on the ultrasonic echo signal after the time corresponding to the first wave detection signal and outputs the first zero-crossing detection signal after the first wave. A time-to-digital converter, coupled to the transmission signal input terminal and the zero-crossing detection circuit, performs time-to-digital conversion on the ultrasonic transmission signal and the first zero-crossing detection signal, and outputs the zero-crossing flight time; The reference wave data terminal provides reference wave data, which is pre-obtained reference waveform data or reference waveform characteristic data. A cross-correlation processing circuit, whose input terminal is coupled to the output terminal of the analog-to-digital converter, the reference wave data terminal, and the output terminal of the zero-crossing detection circuit, performs cross-correlation calculations based on the echo sampled data, the reference wave data, and the local delay search range, and outputs the relative time deviation between the echo sampled data and the reference wave data. This includes: setting multiple candidate delay values ​​within the local delay search range, calculating the cross-correlation value between the echo sampled data and the reference wave data corresponding to each candidate delay value, and determining the candidate delay value corresponding to the maximum cross-correlation value in the calculation results as the relative time deviation. The time-of-flight correction circuit has its input terminal coupled to the output terminal of the time-to-digital converter and the output terminal of the cross-correlation operation processing circuit. It corrects the zero-crossing flight time based on the relative time deviation and outputs the corrected zero-crossing flight time as the ultrasonic flight time. The local delay search range is based on the time corresponding to the first zero-crossing detection signal.

12. The ultrasonic time-of-flight measurement circuit according to claim 11, characterized in that, The ultrasonic time-of-flight measurement circuit also includes a timing control circuit; The timing control circuit is respectively coupled to the analog-to-digital converter, the cross-correlation operation processing circuit and the time-of-flight correction circuit; The timing control circuit enables the analog-to-digital converter, the cross-correlation operation processing circuit, and the time-of-flight correction circuit to enter either a correction working state or a non-correction working state based on the correction enable signal. In the non-corrected operating state, the ultrasonic time-of-flight measurement circuit outputs the zero-crossing time of flight as the ultrasonic time of flight.

13. An ultrasonic flow measurement method, characterized in that, include: The ultrasonic time-of-flight measurement method according to any one of claims 1 to 10 is performed in the first propagation direction to obtain the first ultrasonic time of flight. Perform the ultrasonic time-of-flight measurement method according to any one of claims 1 to 10 in the second propagation direction to obtain the second ultrasonic time of flight; The fluid velocity or fluid flow rate is calculated based on the time difference between the first ultrasonic flight time and the second ultrasonic flight time.

14. An ultrasonic flow metering device, characterized in that, include: The system comprises a first transducer, a second transducer, a flow calculation circuit, and an ultrasonic time-of-flight measurement circuit as described in claim 11 or 12. In the first propagation direction, the first transducer emits ultrasonic waves, the second transducer receives the ultrasonic waves after propagation through the fluid and generates a first ultrasonic echo signal, and the ultrasonic time-of-flight measurement circuit outputs the first ultrasonic time of flight based on the ultrasonic emission signal and the first ultrasonic echo signal corresponding to the first propagation direction. In the second propagation direction, the second transducer emits ultrasonic waves, the first transducer receives ultrasonic waves propagated through the fluid and generates a second ultrasonic echo signal, and the ultrasonic time-of-flight measurement circuit outputs the second ultrasonic time of flight based on the ultrasonic emission signal corresponding to the second propagation direction and the second ultrasonic echo signal. The flow calculation circuit is coupled to the ultrasonic time-of-flight measurement circuit and outputs the fluid velocity or fluid flow rate based on the time difference between the first ultrasonic time of flight and the second ultrasonic time of flight.

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