Ultrasonic flowmeter and flow velocity measurement method
By converting ultrasonic signals to digital form and applying DFT or FFT to determine the phase, the method addresses SNR limitations, enabling precise fluid velocity measurement in ultrasonic flowmeters.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- FUJI ELECTRIC CO LTD
- Filing Date
- 2024-12-27
- Publication Date
- 2026-07-09
Smart Images
Figure 2026115359000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to an ultrasonic flowmeter and a flow velocity measurement method, and for example, relates to a method for measuring the propagation time required for flow velocity calculation.
Background Art
[0002] Generally, ultrasonic flowmeters include a trigger method using a comparator and a calculation method using an AD (Analog / Digital) converter.
[0003] FIG. 3 shows an example of a trigger method using a comparator. In this method, in order to measure the propagation time of ultrasonic waves, after the transmission timing of the transmitted wave, it is detected as a trigger that the amplitude of the received wave has reached a specific level. After the detection of the trigger, the timing of the first zero crossing is detected by a comparator. The time difference from the start of transmission of the transmitted wave to this zero crossing is measured by a TDC (Time to Digital Converter) circuit or the like, and the flow velocity of the fluid is calculated using the measured time difference. An example of such a method is described in Patent Document 1.
[0004] Also, in the calculation method using an AD converter, the received wave is AD-converted at high speed to obtain a digital signal of a waveform sequence. Then, the propagation time of ultrasonic waves is calculated based on this waveform sequence. For example, there are methods for estimating a specific zero crossing position based on the waveform sequence, and methods for performing a correlation operation between the waveform sequence and a reference waveform to accurately obtain the propagation time of ultrasonic waves.
Prior Art Documents
Patent Documents
[0005]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0006] However, conventional technology had the challenge of making it difficult to improve measurement accuracy.
[0007] To achieve high accuracy with ultrasonic flowmeters, one approach is to improve the signal-to-noise ratio (SNR) of the received signal, but this has its limitations. Therefore, the challenge lies in developing a method for accurately measuring propagation time even with a low SNR.
[0008] In triggering methods using comparators, the time jitter of the comparator is related to the signal-to-noise ratio (SNR). Therefore, one method is to acquire many comparator signals with jitter, average them, and effectively reduce the comparator jitter. Examples of this method include the sing-around method and the high-speed transmission and reception method described in Patent Document 1. However, this method has the drawbacks of having an upper limit on the operating speed determined by the switching time between transmission and reception directions, and the need for increased costs due to high-speed processing.
[0009] In calculation methods using AD converters, high-resolution time measurement is possible depending on the calculation method. However, methods that estimate the zero-crossing time from AD values before and after the zero-crossing have the challenge of requiring improvements to the AD sampling interval and resolution. In addition, methods that determine the propagation time of ultrasound using correlation calculation with a reference waveform have the challenge of requiring a considerable amount of time for the correlation calculation.
[0010] This invention was made to solve these problems and aims to provide an ultrasonic anemometer and a flow velocity measurement method that can more easily improve measurement accuracy. [Means for solving the problem]
[0011] An example of an ultrasonic flowmeter according to the present invention is: In an ultrasonic flowmeter, which measures the velocity of a fluid using ultrasound, The ultrasonic flowmeter described above is A first frequency of ultrasound is transmitted from either the first ultrasonic transducer or the second ultrasonic transducer. The ultrasonic waves that have passed through the fluid are received by the other of the first ultrasonic transducer and the second ultrasonic transducer. The received ultrasonic waveform signal is converted to digital by AD conversion to obtain a digital signal. The phase of the first frequency component included in the digital signal is obtained. Based on the acquired phase, the fluid velocity is obtained.
[0012] An example of a flow velocity measurement method according to the present invention is: In a fluid velocity measurement method that uses ultrasound to measure the fluid velocity, The aforementioned method, Transmitting ultrasonic waves of a first frequency from either the first ultrasonic transducer or the second ultrasonic transducer, The ultrasonic waves that have passed through the fluid are received by the other of the first ultrasonic transducer and the second ultrasonic transducer. The process involves obtaining a digital signal by performing an AD conversion on the signal representing the waveform of the received ultrasound, To obtain the phase of the first frequency component included in the digital signal, Based on the acquired phase, the fluid velocity is obtained, Includes. [Effects of the Invention]
[0013] The ultrasonic flow meter and flow velocity measurement method according to the present invention use AD conversion to acquire flow velocity based on the phase of the ultrasonic vibration frequency component, thereby making it easier to improve the accuracy of flow velocity measurement.
[0014] Other effects are described by the embodiments and modifications shown in this specification and in the drawings. [Brief explanation of the drawing]
[0015] [Figure 1] An example of the configuration of an ultrasonic flowmeter 100 according to Embodiment 1 of the present invention. [Figure 2] Examples of operating timing diagrams for ultrasonic flowmeter 100. [Figure 3]Example of a trigger method using a comparator in the prior art.
Mode for Carrying Out the Invention
[0016] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. [Embodiment 1] FIG. 1 shows a configuration example of an ultrasonic flowmeter 100 according to Embodiment 1 of the present invention. The ultrasonic flowmeter 100 measures the flow velocity of a fluid using ultrasonic waves and calculates the flow rate based on the flow velocity. Therefore, it can be said that the ultrasonic flowmeter 100 is a kind of ultrasonic flow velocity meter. As another example of an ultrasonic flow velocity meter, a configuration that does not calculate the flow rate but outputs the measured flow velocity as it is is also possible.
[0017] The ultrasonic flowmeter 100 includes a pipe 10 or is arranged with respect to the pipe 10. The fluid to be measured flows inside the pipe 10. The ultrasonic flowmeter 100 includes a pair of ultrasonic transducers. In the present embodiment, it includes a first ultrasonic transducer 21 and a second ultrasonic transducer 22. Both the first ultrasonic transducer 21 and the second ultrasonic transducer 22 can transmit and receive ultrasonic waves. The first ultrasonic transducer 21 and the second ultrasonic transducer 22 can be configured as transducers including, for example, piezoelectric elements.
[0018] The ultrasonic flowmeter 100 includes a control unit 30 that controls the operation of the entire ultrasonic flowmeter 100. The control unit 30 includes a transmission pulse circuit 31, a transmission / reception switch circuit 32, an amplification circuit 33, an AD conversion circuit 34, a DFT calculation unit 35, a flow rate calculation unit 36, and a reference clock circuit 37.
[0019] The reference clock circuit 37 generates a reference clock signal that serves as a reference for the operation timing of the ultrasonic flowmeter 100. Specific operations according to the reference clock signal will be described later with reference to FIG. 2.
[0020] The first ultrasonic transducer 21 and the second ultrasonic transducer 22 are positioned at different locations relative to each other in the direction of motion of the fluid to be measured. In this embodiment, they are positioned at different locations along the piping 10, i.e., along the direction of motion of the fluid, with the second ultrasonic transducer 22 positioned relatively upstream and the first ultrasonic transducer 21 positioned relatively downstream.
[0021] The first ultrasonic transducer 21 and the second ultrasonic transducer 22 are preferably positioned on opposite sides of the fluid flow path to be measured. In this embodiment, the second ultrasonic transducer 22 is positioned on the left side of the flow path and the first ultrasonic transducer 21 is positioned on the right side of the flow path, as viewed from the direction of fluid flow.
[0022] The first ultrasonic transducer 21 and the second ultrasonic transducer 22 operate so that at a given point in time, one transmits the ultrasonic waves 40 and the other receives them. The transmit / receive switch circuit 32 switches which of the first ultrasonic transducer 21 and the second ultrasonic transducer 22 becomes the transmitter (and therefore which becomes the receiver) based on a reference clock signal. The timing of the switch will be described later. In the state shown in Figure 1, the first ultrasonic transducer 21 is the transmitter and the second ultrasonic transducer 22 is the receiver.
[0023] The above configuration is merely an example, and the configuration of the piping 10 and the precise placement of each ultrasonic transducer in the piping 10 can be the same as any known ultrasonic flow meter.
[0024] The transmitting pulse circuit 31 generates a pulse signal (transmitting pulse) that represents the transmission waveform of the ultrasonic wave 40 based on a reference clock signal. The transmitting pulse is, for example, a high-voltage pulse. The transmitting pulse circuit 31 transmits the generated transmitting pulse to the transmitting ultrasonic transducer via the transmitting / receiving switch circuit 32.
[0025] The transmitting ultrasonic transducer (first ultrasonic transducer 21 in the state shown in Figure 1) vibrates in response to the transmission pulse, thereby generating ultrasonic waves 40. In this way, ultrasonic waves 40 are transmitted from the first ultrasonic transducer 21. The vibration frequency (first frequency) of the ultrasonic waves 40 is a frequency corresponding to the frequency of the transmission pulse. Here, it is preferable to match the frequency of the transmission pulse with the resonant frequency of the ultrasonic transducer in order to efficiently generate ultrasonic waves 40.
[0026] The receiving ultrasonic transducer (the second ultrasonic transducer 22 in the state shown in Figure 1) vibrates upon receiving ultrasonic waves, thereby generating a signal (received signal) that represents the waveform of the received ultrasonic waves. The ultrasonic waves received here are, for example, the ultrasonic waves 40 transmitted from the transmitting ultrasonic transducer, that is, the ultrasonic waves that have passed through the fluid being measured. The receiving ultrasonic transducer transmits the generated signal to the amplification circuit 33 via the transmit / receive switch circuit 32.
[0027] The amplification circuit 33 is a circuit that amplifies voltage. The amplification circuit 33 amplifies the signal received from the receiving ultrasonic transducer (received signal) and transmits it to the AD conversion circuit 34. The AD conversion circuit 34 performs AD conversion on the received signal amplified by the amplification circuit 33 (i.e., the signal representing the waveform of the received ultrasonic wave), and as a result obtains a digital signal. The AD conversion circuit 34 transmits the obtained digital signal to the DFT calculation unit 35.
[0028] The DFT calculation unit 35 performs a Discrete Fourier Transform (DFT) operation on the digital signal received from the AD conversion circuit 34 to obtain the frequency representation of the digital signal. The frequency representation of the digital signal includes information representing the phase of the frequency component corresponding to the frequency of the transmitted pulse. The specific calculation content of the DFT operation can be appropriately designed by those skilled in the art, but for example, using an FFT (Fast Fourier Transform) operation is preferable because it allows for faster calculation. The principles of DFT and FFT operations are well known to those skilled in the art, so a detailed explanation is omitted.
[0029] In this manner, the DFT calculation unit 35 uses DFT or FFT calculation to acquire the phase of the vibration frequency component of the ultrasonic wave 40 among the frequency components included in the digital signal. The DFT calculation unit 35 transmits the acquired phase of the vibration frequency component of the ultrasonic wave 40 to the flow rate calculation unit 36.
[0030] The flow rate calculation unit 36 calculates the fluid flow rate based on the acquired phase. The time it takes for the ultrasonic waves 40 to travel from the transmitting ultrasonic transducer to the receiving ultrasonic transducer (propagation time) varies according to the fluid velocity in the piping 10. This change in time is expressed as a change in phase in the vibration frequency component of the ultrasonic waves 40 included in the digital signal related to the received signal. Therefore, by measuring the change in phase, the propagation time of the ultrasonic waves 40 can be calculated, and the fluid velocity can be obtained based on the propagation time.
[0031] A specific method for calculating the flow velocity based on propagation time can be appropriately designed by a person skilled in the art based on known technologies, etc. For example, the propagation time reciprocal difference method can be used to determine the flow velocity with high accuracy, but other methods may also be used. The flow rate calculation unit 36 then calculates the fluid flow rate based on the fluid velocity and outputs information representing the fluid flow rate.
[0032] The DFT calculation unit 35 and the flow rate calculation unit 36 may be configured using a computer. In that case, both the DFT calculation unit 35 and the flow rate calculation unit 36 may include calculation means, storage means, and input / output means. The calculation means may include, for example, a processor. The processor can be manufactured using an integrated circuit, ASIC, FPGA, etc. The storage means may include, for example, a storage medium such as a semiconductor memory device and a magnetic disk device. Some or all of the storage medium may be a non-transitory storage medium. The input / output means may include, for example, an interface such as an input / output circuit.
[0033] Figure 2 shows an example of the operating timing diagram of the ultrasonic flowmeter 100. Figure 2 relates to the operation, including the transmission and reception of a single ultrasonic wave in a specific propagation direction.
[0034] A specific propagation direction is, for example, a propagation direction in which the first ultrasonic transducer 21 is the transmitter and the second ultrasonic transducer 22 is the receiver. In order to obtain the flow velocity, the propagation direction is switched by the transmit / receive switch circuit 32, and the process shown in Figure 2 is performed for each different propagation direction (i.e., round trip). The ultrasonic flowmeter 100 transmits ultrasonic waves 40 from one of the first ultrasonic transducer 21 and the second ultrasonic transducer 22, and receives the ultrasonic waves 40 that have passed through the fluid with the other of the first ultrasonic transducer 21 and the second ultrasonic transducer 22.
[0035] To improve accuracy, ultrasound may be transmitted and received multiple times. For example, the process shown in Figure 2 may be repeated three times with the first ultrasonic transducer 21 as the transmitter, and then repeated three more times with the second ultrasonic transducer 22 as the transmitter.
[0036] In this embodiment, the ultrasonic flowmeter 100 accurately determines the phase of the ultrasonic waves 40 at their vibration frequency using DFT calculation, and obtains the propagation time of the ultrasonic waves 40 based on this phase.
[0037] In Figure 2, the horizontal axis of the graph representing the signal waveform is time, and the vertical axis is the signal value (e.g., amplitude or voltage). The reference clock signal S1 is the clock signal that serves as the operating reference for the entire ultrasonic flowmeter 100, and in this embodiment it is 64 MHz. The transmit pulse circuit 31 divides the reference clock signal S1 to generate the transmit pulse S2. In the example in Figure 2, the reference clock signal S1 has a period of 16 times (2 4 The frequency is divided so that it is doubled, meaning the frequency of the transmitted pulse S2 is 4 MHz. The first ultrasonic transducer 21 and the second ultrasonic transducer 22 are used, each having a resonant frequency of 4 MHz.
[0038] In the following explanation, we will describe a propagation direction in which the first ultrasonic transducer 21 is the transmitter and the second ultrasonic transducer 22 is the receiver as an example. The transmission pulse S2 (or the transmitted pulse S2 may be an amplified signal) is transmitted to the first ultrasonic transducer 21, thereby exciting the first ultrasonic transducer 21. In the example in Figure 2, the number of pulses involved in one ultrasonic transmission is two, but this number can be arbitrarily designed as long as it is one or more. The number of pulses is preferably selected so that a stable sine wave appears in the received signal, as this reduces errors when calculating the phase.
[0039] In this way, the first ultrasonic transducer 21 transmits ultrasonic waves 40. In the example in Figure 2, the transmission start time is time T0. Subsequent times (for example, times T1 to T4 described later) can be expressed with respect to time T0.
[0040] The transmitted ultrasonic wave 40 passes through the fluid to be measured and reaches the second ultrasonic transducer 22. The second ultrasonic transducer 22 receives the received signal S3. Here, the propagation time of the ultrasonic wave 40 is affected by the fluid velocity. The AD conversion circuit 34 starts sampling the received signal S3 at time T1, which is a predetermined delay time Ta after the transmission start time (time T0). Sampling is performed in synchronization with, for example, a reference clock signal S1, i.e., sampling is performed at an interval of 64 MHz (64 Msps). Sampling ends at time T4, which is the time when a predetermined sampling time Tb has elapsed from time T1. Note that the received signal S3 shown in Figure 2 has different frequencies, etc., from the actual ones for the sake of explanation.
[0041] The delay time Ta and sampling time Tb can be any value that is an integer multiple of the reference clock signal. The delay time Ta and sampling time Tb do not need to be precisely calculated times. For example, the delay time Ta is preferably set to the propagation time of the ultrasonic wave 40 corresponding to the average or standard flow velocity measured by the ultrasonic flowmeter 100, or a time close to that length. In this case, the received signal S3 corresponding to the ultrasonic wave 40 will start at time T1 or a time around that time. The sampling time Tb is preferably set to the duration of the received signal S3 corresponding to the ultrasonic wave 40, or a time close to that length. In this case, the received signal S3 corresponding to the ultrasonic wave 40 will end at time T4 or a time around that time.
[0042] Here, the start time of the digital signal (sampled data) acquired by the AD conversion circuit 34 is time T1. That is, the phase in the frequency representation of the digital signal is expressed with reference to this time T1. In this way, the ultrasonic flowmeter 100 acquires the phase of the vibration frequency components of the ultrasonic wave 40 by sampling the signal representing the waveform of the received ultrasonic wave 40 in synchronization with a reference clock signal.
[0043] The DFT calculation unit 35 performs a DFT calculation (in particular, an FFT calculation) on the digital signal. Here, the DFT calculation unit 35 may use the entire digital signal for the DFT calculation, or it may use only a part of the digital signal for the DFT calculation, as shown in Figure 2.
[0044] In the example shown in Figure 2, the DFT calculation unit 35 uses only the digital signal from time T2 to time T3 (conversion time zone Tc). The conversion time zone Tc is preferably set to a time period when the received signal S3 is stable, as this improves the accuracy of the DFT calculation (including the accuracy of phase calculation). Examples of a time period when the received signal S3 is stable include a time period when the waveform is stable, a time period when the amplitude is stable, etc.
[0045] The conversion time zone Tc may differ depending on the propagation direction of the ultrasonic waves 40. That is, the conversion time zone Tc (i.e., time T2 and / or T3) may differ between the case of a first propagation direction (for example, a propagation direction in which the first ultrasonic transducer 21 is the transmitter and the second ultrasonic transducer 22 is the receiver) and the case of a second propagation direction opposite to the first (i.e., a propagation direction in which the second ultrasonic transducer 22 is the transmitter and the first ultrasonic transducer 21 is the receiver).
[0046] Furthermore, it is preferable that the conversion time period Tc be designed to reduce the influence of noise caused by reflection and leakage of the ultrasonic waves 40. For example, considering the materials of the piping 10, the arrangement of each ultrasonic transducer, the diffraction and reflection of the ultrasonic waves 40, the measurement range of the flow velocity, etc., it is preferable to predetermine the start time (time T2) and end time (time T3) of the conversion time period Tc as a time period corresponding only to ultrasonic waves 40 propagating in a straight line between each ultrasonic transducer. For example, the conversion time period Tc can be a time period in the receiving ultrasonic transducer where only the waveform of linearly propagating ultrasonic waves 40 appears.
[0047] In other words, the conversion time period Tc can be set as a time period in which no signals from the diffraction of the ultrasonic waves 40 or signals from the reflection of the ultrasonic waves 40 appear. The DFT calculation unit 35 is preferably configured to acquire the phase of the vibration frequency component of the ultrasonic waves 40 based on the digital signal included in such a conversion time period Tc. In particular, the end time of the conversion time period Tc (time T3) is preferably a time after the linearly propagating ultrasonic waves 40 have reached the receiving ultrasonic transducer, and before the diffracted and reflected ultrasonic waves 40 have reached it. The conversion time period Tc may be dynamically determined according to the content of the digital signal, etc.
[0048] Furthermore, window functions may be used in DFT calculations. For example, window functions such as the Hamming window, Hanning window, Gaussian window, Blackman window, and Kaiser window can be used. Using an appropriate window function improves the accuracy and stability of DFT calculations.
[0049] The DFT calculation unit 35 obtains the phase of the vibration frequency component of the ultrasonic wave 40 included in the digital signal by performing a DFT calculation, and transmits the obtained phase to the flow rate calculation unit 36.
[0050] The flow rate calculation unit 36 calculates the propagation time of the ultrasonic waves 40 based on the phase acquired by the DFT calculation unit 35. The propagation time can be calculated by adding the time corresponding to the phase to the time from the start time of transmission (time T0) to the start time of the conversion time period Tc (time T2) that is the target of the DFT calculation (base time Td). Here, the case where the sign of the phase is negative may be included, in which case the propagation time may be calculated by subtracting the absolute value of the time corresponding to the phase from the base time Td. In this way, the time corresponding to the phase can be calculated based on the vibration frequency of the ultrasonic waves 40, etc.
[0051] Furthermore, in order to eliminate the 360-degree ambiguity in phase, it is preferable to determine the vibration frequency of the ultrasonic wave 40 based on the range of flow velocity to be measured (i.e., the range of propagation time to be measured).
[0052] For example, suppose the upper limit of the measurement range (first range) for the propagation time of ultrasonic waves 40 by the ultrasonic flow meter 100 is fa [seconds] and the lower limit is fb [seconds]. That is, the ultrasonic flow meter 100 is capable of measuring the propagation time of ultrasonic waves 40 in the first range having a changing upper limit fa and lower limit fb of propagation time. Here, the signs of the upper and lower limits may be different. That is, the ultrasonic flow meter 100 may be capable of measuring the flow rate including the direction of fluid flow.
[0053] In this case, it is preferable to design the relationship between the measurement range and the vibration frequency of the ultrasonic wave 40 such that the absolute value of the difference between the upper limit fa and the lower limit fb, |fa-fb|, is less than half of the period corresponding to the vibration frequency of the ultrasonic wave 40. In this embodiment, since the vibration frequency is 4 MHz, it is preferable to design the difference between the upper limit fa and the lower limit fb of the propagation time to be within ±125 ns (excluding the boundary). In this way, the propagation time can be uniquely determined within a range with a width of 360 degrees (for example, within the range of -180 degrees to +180 degrees, or within the range of 0 degrees to 360 degrees) according to the phase obtained as a result of the DFT calculation.
[0054] In this way, the flow rate calculation unit 36 obtains the propagation time of the ultrasonic waves 40 based on the phase of the vibration frequency component of the ultrasonic waves 40 included in the digital signal. Then, the flow rate calculation unit 36 obtains the fluid velocity based on the obtained propagation time. For example, it is possible to calculate the fluid velocity based on the propagation time in the first propagation direction and the propagation time in the opposite second propagation direction. Such a method for calculating the fluid velocity based on the propagation time for each direction can be appropriately designed by those skilled in the art, but as an example, the propagation time reciprocal difference method may be used.
[0055] In this manner, the flow rate calculation unit 36 calculates the fluid velocity based on the phase of the ultrasonic waves transmitted by the first ultrasonic transducer 21 and received by the second ultrasonic transducer 22, and the phase of the ultrasonic waves transmitted by the second ultrasonic transducer 22 and received by the first ultrasonic transducer 21. Furthermore, the flow rate calculation unit 36 calculates the flow rate based on the calculated flow velocity and outputs this flow rate as a measured value.
[0056] The above-described embodiment 1 can be modified as follows.
[0057] Although Embodiment 1 described an ultrasonic flowmeter 100, it is also possible to configure an ultrasonic flow velocity meter as a modified example. In that case, a flow velocity calculation unit may be provided instead of the flow rate calculation unit 36. The flow velocity calculation unit may output information representing the fluid velocity, in which case the process of calculating the flow rate based on the velocity can be omitted.
[0058] In Embodiment 1, the ultrasonic flowmeter 100 efficiently acquires the phase of the vibration frequency component by using DFT or FFT calculations. However, as a modification, it may be configured to acquire the phase component of the vibration frequency without using DFT or FFT calculations.
[0059] In Embodiment 1, the ultrasonic flowmeter 100 divides the reference clock signal by a frequency division ratio of 16 to generate a transmission pulse. However, the frequency division ratio of the transmission pulse is not limited to 16. The ultrasonic flowmeter divides the reference clock signal by 2 M By dividing the frequency by a division ratio (where M is an integer greater than or equal to 2), ultrasonic waves of a desired vibration frequency (first frequency) can be generated.
[0060] In Embodiment 1, the ultrasonic flowmeter 100 acquires the propagation time of the ultrasonic waves 40 based on the phase acquired by the DFT calculation unit 35 for each of the first and second propagation directions, and further acquires the flow velocity based on the propagation time for each propagation direction. In modified examples, the acquisition of propagation time may be omitted. For example, it is possible to acquire the flow velocity based on the phase without explicitly calculating the propagation time. For example, the flow velocity may be directly acquired based on the difference between the phase acquired for the first propagation direction and the phase acquired for the second propagation direction. The correspondence between the phase difference and the flow velocity can be appropriately defined by a table or function, etc. [Explanation of symbols]
[0061] 10...Piping, 21...First ultrasonic transducer, 22...Second ultrasonic transducer, 30...Control unit, 31...Transmit pulse circuit, 32...Transmit / receive switch circuit, 33...Amplification circuit, 34...AD conversion circuit, 35...DFT calculation unit, 36...Flow rate calculation unit, 37...Reference clock circuit, 40...Ultrasound, 100...Ultrasonic flow meter (ultrasonic flow velocity meter), S1...Reference clock signal, S2...Transmit pulse, S3...Received signal, Ta...Delay time, Tb...Sampling time, Tc...Conversion time zone, Td...Base time, fa...Upper limit, fb...Lower limit.
Claims
1. In an ultrasonic flowmeter, which measures the velocity of a fluid using ultrasound, The ultrasonic flowmeter described above is Ultrasound of a first frequency is transmitted from either the first ultrasonic transducer or the second ultrasonic transducer. The ultrasonic waves that have passed through the fluid are received by the other of the first ultrasonic transducer and the second ultrasonic transducer. The received ultrasonic waveform signal is converted to digital by A / D conversion to obtain a digital signal. The phase of the first frequency component included in the digital signal is obtained. Based on the acquired phase, the fluid velocity is obtained. An ultrasonic flow meter characterized by the following features.
2. In the ultrasonic flowmeter according to claim 1, The ultrasonic flowmeter is capable of measuring the propagation time of the ultrasonic waves in a first range having upper and lower limits for the propagation time, The absolute value of the difference between the upper limit and the lower limit is less than half of the period corresponding to the first frequency. An ultrasonic flow meter characterized by the following features.
3. In the ultrasonic flowmeter according to claim 1, The first ultrasonic transducer and the second ultrasonic transducer are positioned at different locations relative to each other in the direction of fluid motion. The ultrasonic flowmeter acquires the fluid velocity based on the phase of the ultrasonic waves transmitted by the first ultrasonic transducer and received by the second ultrasonic transducer, and the phase of the ultrasonic waves transmitted by the second ultrasonic transducer and received by the first ultrasonic transducer. An ultrasonic flow meter characterized by the following features.
4. In the ultrasonic flowmeter according to claim 1, The ultrasonic flowmeter acquires the phase of the first frequency component using DFT calculation or FFT calculation. An ultrasonic flow meter characterized by the following features.
5. In the ultrasonic flowmeter according to claim 1, The ultrasonic flowmeter described above is The reference clock signal, 2 Ｍ The first frequency ultrasound is generated by dividing the frequency by a frequency division ratio (where M is an integer of 2 or more), The phase of the first frequency component is obtained by sampling the signal representing the waveform of the received ultrasonic wave in synchronization with the reference clock signal. An ultrasonic flow meter characterized by the following features.
6. In the ultrasonic flowmeter according to claim 1, The ultrasonic flowmeter described above is Based on the phase of the first frequency component included in the digital signal, the propagation time of the ultrasonic wave is obtained. Based on the acquired propagation time, the fluid velocity is obtained. An ultrasonic flow meter characterized by the following features.
7. In a fluid velocity measurement method that uses ultrasound to measure the fluid velocity, The aforementioned method, Transmitting ultrasonic waves of a first frequency from either the first ultrasonic transducer or the second ultrasonic transducer, The ultrasonic waves that have passed through the fluid are received by the other of the first ultrasonic transducer and the second ultrasonic transducer. The process involves obtaining a digital signal by performing an A / D conversion on the signal representing the waveform of the received ultrasound, To obtain the phase of the first frequency component included in the digital signal, Based on the acquired phase, the fluid velocity is obtained, A method for measuring flow velocity, characterized by including the following: