Ultrasonic flow meter

Abstract

Provided is a technique capable of measuring a flowrate more easily and more accurately without carrying out real flow correction in an ultrasonic flow meter. An ultrasonic flow meter 1 according to an embodiment of the present invention comprises: a measurement pipe 2 which is provided in a linearly extending manner and through which a fluid to be measured flows; an ultrasonic vibrator 3 attached to the outer surface of the measurement pipe 2; an ultrasonic vibrator 4 attached to the outer surface of the measurement pipe 2 so as to be, when viewed from the ultrasonic vibrator 3, separated in an X-axis direction in which the measurement pipe 2 extends; and an ultrasonic vibrator 5 attached to the outer surface of the measurement pipe 2 so as to face the ultrasonic vibrator 3 when viewed from the same in a Z-axis direction perpendicular to the X-axis direction.

Description

[Technical field]

[0001] The present disclosure relates to ultrasonic flow meters. [Background technology]

[0002] 2. Description of the Related Art Conventionally, ultrasonic flowmeters that use a thin measuring tube to measure (calculate) the flow rate of a fluid to be measured by a transit time difference method are known (see, for example, Patent Document 1).

[0003] In Patent Document 1, two annular ultrasonic transducers are attached to the outer surface of a straight, thin measuring tube, spaced apart in the direction the measuring tube extends, and the propagation time of ultrasonic waves in the downstream direction and the upstream direction are measured, from which the flow velocity and flow rate are calculated using the transit time difference method.In Patent Document 1, the sound speed of the measured fluid is calculated from a theoretical formula using the physical properties of the measured fluid and the physical properties of the measuring tube, and the flow velocity and flow rate are calculated based on the calculated sound speed using the transit time difference method.

[0004] Usually, in the case of a thin measurement pipe, the effect of the vibration of the measurement pipe due to the ultrasonic waves transmitted from the ultrasonic transducer cannot be ignored, and measurement is performed while accumulating data when the temperature and pressure change by actual flow calibration and correcting for these changes. In contrast, Patent Document 1 makes it possible to measure the flow rate accurately without performing actual flow calibration. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4851936 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in Patent Document 1, the density of the fluid to be measured is required to obtain the sound speed of the fluid to be measured. Therefore, for example, if a fixed value is used as the density, the density changes depending on the temperature of the fluid to be measured, and therefore the measurement accuracy of the flow rate may decrease depending on the temperature of the fluid to be measured.

[0007] On the other hand, for example, the density value used in the theoretical formula can be changed according to the correlation between the temperature and density of the measured fluid, but it is necessary to measure or estimate the temperature of the measured fluid. Also, for example, if the type of the measured fluid is not determined, it may be necessary to prepare data on the correlation between temperature and density in advance according to the expected type of measured fluid, or it may be impossible to measure the flow rate of the measured fluid for which no data is prepared.

[0008] In view of the above problems, an object of the present invention is to provide a technique for measuring flow rate more simply and accurately in an ultrasonic flowmeter without performing actual flow calibration. [Means for solving the problem]

[0009] In order to achieve the above object, in one embodiment of the present disclosure, a measurement tube extending linearly and through which a fluid to be measured flows; A first ultrasonic transducer attached to an outer surface of the measuring tube; a second ultrasonic transducer attached to an outer surface of the measuring pipe so as to be spaced apart from the first ultrasonic transducer along a first direction in which the measuring pipe extends, as viewed from the first ultrasonic transducer; a third ultrasonic transducer attached to the outer surface of the measuring pipe so as to face the first ultrasonic transducer in a second direction perpendicular to the first direction; A transmitting unit that outputs a signal for transmitting an ultrasonic wave; a transmission switching unit that switches between the transmission unit and either one of the first ultrasonic transducer and the second ultrasonic transducer, or between the transmission unit and either one of the first ultrasonic transducer, the second ultrasonic transducer, and the third ultrasonic transducer; a receiving unit to which a received ultrasonic signal is input; a reception switching unit that switches between the reception unit and one of the first ultrasonic transducer, the second ultrasonic transducer, and the third ultrasonic transducer, or between the reception unit and one of the first ultrasonic transducer and the second ultrasonic transducer; A control unit that controls transmission and reception of ultrasonic waves from the first ultrasonic transducer, the second ultrasonic transducer, and the third ultrasonic transducer; a flow rate calculation unit that calculates a flow rate of the fluid to be measured; Equipped with、 The control unit executes a first process of controlling the transmission switching unit and the reception switching unit so that ultrasonic waves transmitted from either one of the first ultrasonic transducer and the second ultrasonic transducer are received by the other one, and executes a second process of controlling the transmission switching unit and the reception switching unit so that ultrasonic waves transmitted from either one of the first ultrasonic transducer and the third ultrasonic transducer are received by the other one, separately from the first process; The flow rate calculation unit calculates a flow rate of the fluid to be measured based on ultrasonic waves transmitted and received by each of the first process and the second process. R, An ultrasonic flow meter is provided. Effect of the Invention

[0010] According to the above-described embodiment, in the ultrasonic flowmeter, it is possible to more simply and more accurately measure the flow rate without performing actual flow calibration. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is an exploded perspective view illustrating an example of an ultrasonic flowmeter. [Diagram 2] FIG. 1 is a perspective view showing the appearance of an example of an ultrasonic flowmeter. [Diagram 3] FIG. 1 is a cross-sectional view showing an example of an ultrasonic flowmeter. [Figure 4] FIG. 1 is a block diagram showing a first example of the configuration of an ultrasonic flowmeter. [Diagram 5] FIG. 11 is a block diagram showing a second example of the configuration of an ultrasonic flowmeter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment will be described with reference to the drawings.

[0013] [Ultrasonic flowmeter overview] An overview of an ultrasonic flowmeter 1 according to this embodiment will be described with reference to FIGS. 1 to 5.

[0014] Hereinafter, for convenience, the arrangement of the components of the ultrasonic flowmeter 1 and the direction of the flow of the fluid to be measured may be described using an orthogonal coordinate system of the X-axis, Y-axis, and Z-axis in Figures 1 to 3. In addition, the positive X-axis direction and the negative X-axis direction may be collectively referred to as the X-axis direction, and the positive Z-axis direction and the negative Z-axis direction may be collectively referred to as the "Z-axis direction." In addition, for convenience, the radial direction and the circumferential direction as viewed from the measuring tube 2 may be simply referred to as the "radial direction" and the "circumferential direction."

[0015] FIG. 1 is an exploded perspective view that typically illustrates an example of an ultrasonic flowmeter 1. FIG. 2 is a perspective view that illustrates the appearance of the example of the ultrasonic flowmeter 1. FIG. 3 is a cross-sectional view that illustrates the example of the ultrasonic flowmeter 1. FIG. 4 is a diagram illustrating a first example of the configuration of the ultrasonic flowmeter 1. FIG. 5 is a diagram illustrating a second example of the configuration of the ultrasonic flowmeter 1.

[0016] Since the structure of the holding portion 7 is common to each of the ultrasonic transducers 3 to 5, only the cross section of the holding portion 7 corresponding to the ultrasonic transducer 3 is depicted in Fig. 3. Also, in Fig. 3, the portion of the acoustic coupling material 6 that contacts the ultrasonic transducer 3 is crushed and is substantially invisible.

[0017] As shown in FIGS. 1 to 5, the ultrasonic flowmeter 1 includes a measuring tube 2, ultrasonic transducers 3 to 5, an acoustic coupling material 6, a holding unit 7, a transmission / reception processing unit 8, and a measurement processing unit 9.

[0018] The ultrasonic flowmeter 1 measures (calculates) and outputs the flow rate of a fluid to be measured flowing through a measuring tube 2.

[0019] The ultrasonic flowmeter 1 is used, for example, in the field of semiconductor manufacturing. Specifically, the ultrasonic flowmeter 1 is used, for example, for flow control of a fluid to be measured, such as pure water for a plant, a polishing agent for silicon wafers, a cleaning liquid, etc. The ultrasonic flowmeter 1 may also be used in the medical field. Specifically, the ultrasonic flowmeter 1 may be used for flow measurement of a fluid to be measured, such as an artificial dialysis fluid, etc.

[0020] The measurement tube 2 is a tube through which the fluid to be measured flows. The measurement tube 2 is made of, for example, a fluororesin such as PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer) resin, which has excellent corrosion resistance.

[0021] As shown in Figs. 1 and 2, the measurement tube 2 is formed linearly so as to extend along the X-axis, and has a circular cross section. The inner diameter (diameter of the inner surface) of the measurement tube 2 is very small. For example, the inner diameter of the measurement tube 2 is about a few millimeters in diameter, which is approximately the same as the wavelength of the ultrasonic waves in the measured fluid. Specifically, the inner diameter of the measurement tube 2 is included in the range of the ultrasonic wavelengths of the measured fluid in the allowable temperature range specified for the ultrasonic flowmeter 1.

[0022] The ultrasonic transducers 3 to 5 are connected to the outer surface of the measurement tube 2 via an acoustic coupling material 6. This allows the ultrasonic transducers 3 to 5 to function as ultrasonic transmitters that transmit ultrasonic waves toward the measurement tube 2 and the fluid to be measured inside the measurement tube 2, and as ultrasonic receivers that receive ultrasonic waves propagating through the measurement tube 2 and the fluid to be measured inside the measurement tube 2. The ultrasonic transducers 3 to 5 are, for example, lead zirconate titanate (PZT) based piezoelectric elements.

[0023] For example, as shown in Fig. 1, the ultrasonic transducers 3 to 5 are cylindrical (disk-shaped) with a circular cross section. Alternatively, the ultrasonic transducers 3 to 5 may be rectangular columnar (rectangular plate-shaped) with a rectangular cross section or columnar (elliptical plate-shaped) with an elliptical cross section.

[0024] The ultrasonic transducers 3, 4 are arranged on the outer surface of the measurement tube 2 so as to be spaced apart at a predetermined distance L in the direction of the flow of the fluid to be measured, i.e., in the X-axis direction. Specifically, the ultrasonic transducers 3, 4 are arranged side by side so as to be spaced apart at a distance L on the circular top portion in the positive Z-axis direction of the outer surface of the measurement tube 2. In this example (FIGS. 1 and 2), the ultrasonic transducer 3 is provided on the upstream side of the flow of the fluid to be measured, and the ultrasonic transducer 4 is provided on the downstream side of the flow of the fluid to be measured.

[0025] The ultrasonic transducer 5 is disposed on the outer surface of the measurement tube 2 so as to face the ultrasonic transducer 3 in a direction perpendicular to the direction of flow of the fluid to be measured, i.e., in the Z-axis direction. Specifically, the ultrasonic transducer 5 is disposed on the circular apex in the negative Z-axis direction on the outer surface of the measurement tube 2 at the same position in the X-axis direction as the ultrasonic transducer 3.

[0026] The acoustic coupling material 6 is a member for acoustically coupling so that ultrasonic waves can propagate between each of the ultrasonic transducers 3 to 5 and the measurement tube 2. The acoustic coupling material 6 is, for example, an adhesive silicone gel.

[0027] The holders 7 are provided for the ultrasonic transducers 3 to 5, respectively, and hold any one of the ultrasonic transducers 3 to 5 in a state in which it is attached to the measuring pipe 2.

[0028] The holding unit 7 is provided for the purpose of achieving stable and efficient propagation (transmission and reception) of ultrasonic waves, and protecting the lead wires (not shown) connecting the transmission and reception processing unit 8 and the ultrasonic transducers 3 to 5. The holding unit 7 may be configured in any manner as long as it can achieve the above-mentioned purpose.

[0029] For example, as shown in FIG. 3, the holding portion 7 includes a housing portion 7A, pressing members 7B and 7C, and a cover member 7D.

[0030] The accommodation portion 7A accommodates therein one of the ultrasonic transducers 3 to 5 and the acoustic coupling material 6. The accommodation portion 7A is made of, for example, a fluororesin such as PFA resin, similar to the measurement tube 2, and is integrated with the measurement tube 2.

[0031] For example, as shown in FIG. 3, the storage section 7A has an internal storage space with a bottom on the radially inner side and an opening on the radially outer side with respect to the measuring tube 2, and an acoustic coupling material 6 is placed on the bottom, and one of the ultrasonic transducers 3 to 5 is placed on the radially outer side of the acoustic coupling material 6.

[0032] The pressing members 7B and 7C are members for pressing one of the ultrasonic transducers 3 to 5 radially inward with an appropriate pressure when the opening of the housing portion 7A is closed by the cover member 7D. The pressing members 7B and 7C are made of, for example, resin.

[0033] The pressing member 7B is placed on the radial outside of one of the ultrasonic transducers 3 to 5, and the pressing member 7C is placed on the radial outside of the pressing member 7B. The radial dimension of the acoustic coupling material 6, one of the ultrasonic transducers 3 to 5, the pressing member 7B, and the pressing member 7C at their natural lengths is configured to be smaller than the radial dimension of the accommodation space of the accommodation section 7A. As a result, the pressing members 7B and 7C can press the ultrasonic transducers 3 to 5 with an appropriate pressure by elastic force and fix them to the measurement tube 2 via the acoustic coupling material 6, as the opening of the accommodation section 7A is closed by the cover member 7D.

[0034] The lid member 7D is attached to the radially outer end surface of the storage section 7A and closes the opening of the storage section 7A. The lid member 7D is made of, for example, resin. Alternatively, the lid member 7D may be made of metal.

[0035] For example, as shown in FIG. 2, the cover member 7D is fixed to the housing portion 7A by a plurality of screws (two in this example).

[0036] The transmission and reception processing unit 8 performs processing related to the transmission and reception of ultrasonic waves using the ultrasonic transducers 3-5.

[0037] The functions of the transmission and reception processing unit 8 are realized by any hardware, or any combination of hardware and software. Furthermore, the hardware for realizing the functions of the transmission and reception processing unit 8 may be mounted on a single board, or may be distributed and mounted on multiple boards. Furthermore, a part or all of the hardware for realizing the functions of the transmission and reception processing unit 8 may be mounted on the same board as a part or all of the hardware for realizing the functions of the measurement processing unit 9.

[0038] The measurement processing unit 9 performs a process of measuring (calculating) the flow rate of the fluid to be measured flowing through the measuring pipe 2 based on the data obtained by the transmission / reception processing unit 8 .

[0039] The functions of the measurement processing unit 9 are realized by any hardware, or any combination of hardware and software, etc. Furthermore, the hardware for realizing the functions of the measurement processing unit 9 may be implemented on one board, or may be distributed and implemented on multiple boards.

[0040] [Transmission and reception processing section] Next, the transmission / reception processing unit 8 will be described with reference to FIGS.

[0041] <Configuration> As shown in FIGS. 4 and 5, the transmission / reception processing unit 8 includes a control unit 10, a transmission circuit 11, a transmission switching circuit 12, a reception switching circuit 13, a reception circuit 14, and an ADC (Analog-Digital Converter) 15.

[0042] The control unit 10 controls the transmission and reception of ultrasonic waves from the ultrasonic transducers 3-5.

[0043] The functions of the control unit 10 are realized by any hardware or any combination of hardware and software. For example, the functions of the control unit 10 are realized mainly by a microcomputer having a CPU (Central Processing Unit), a memory device, an auxiliary storage device, and an interface device for input and output with the outside. The memory device is, for example, an SRAM (Static Random Access Memory). The auxiliary storage device is, for example, an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory.

[0044] For example, the control unit 10 transmits a signal S51 to the transmission switching circuit 12 for connecting the transmission circuit 11 to one of the ultrasonic transducers 3 and 4.

[0045] Also, for example, the control unit 10 transmits a signal S52 to the reception switching circuit 13 for connecting one of the ultrasonic transducers 3 to 5 and the reception circuit 14.

[0046] Also, for example, the control unit 10 transmits to the transmission circuit 11 a transmission command S53 for causing one of the ultrasonic transducers 3 and 4 to transmit an ultrasonic wave.

[0047] Also, for example, the control unit 10 notifies the ADC 15 of the reference time for time measurement by transmitting a signal S54 in which the reference time for time measurement is defined.

[0048] The transmission circuit 11, under the control of the control unit 10, causes one of the ultrasonic transducers 3, 4 to transmit ultrasonic waves via a transmission switching circuit 12.

[0049] For example, when the transmission circuit 11 receives a transmission command S53 from the control unit 10, it transmits an excitation pulse S55 for exciting one of the ultrasonic transducers 3 and 4 to the transmission switching circuit 12.

[0050] Under the control of the control unit 10, the transmission switching circuit 12 switches between a state in which the transmission circuit 11 and the ultrasonic transducer 3 are connected and a state in which the transmission circuit 11 and the ultrasonic transducer 4 are connected.

[0051] For example, when the transmission switching circuit 12 receives a signal S51 for connecting the transmission circuit 11 and the ultrasonic transducer 3 from the control unit 10, the transmission switching circuit 12 connects the transmission circuit 11 and the ultrasonic transducer 3. Similarly, when the transmission switching circuit 12 receives a signal S51 for connecting the transmission circuit 11 and the ultrasonic transducer 4 from the control unit 10, the transmission switching circuit 12 connects the transmission circuit 11 and the ultrasonic transducer 4.

[0052] In addition, when an excitation pulse S55 is input from the transmission circuit 11, the transmission switching circuit 12 outputs a signal to excite one of the ultrasonic transducers 3, 4 that is connected to the transmission circuit 11 by relaying the excitation pulse S55.

[0053] For example, when an excitation pulse S55 is inputted to the transmission switching circuit 12 while the transmission circuit 11 and the ultrasonic transducer 3 are connected, the transmission switching circuit 12 outputs a signal S56 corresponding to the excitation pulse S55 to the ultrasonic transducer 3. This enables the control unit 10 to control the transmission circuit 11 and the transmission switching circuit 12 to transmit ultrasonic waves from the ultrasonic transducer 3.

[0054] Also, for example, when an excitation pulse S55 is inputted to the transmission switching circuit 12 while the transmission circuit 11 and the ultrasonic transducer 4 are connected, the transmission switching circuit 12 outputs a signal S60 corresponding to the excitation pulse S55 to the ultrasonic transducer 4. This allows the control unit 10 to control the transmission circuit 11 and the transmission switching circuit 12 to transmit ultrasonic waves from the ultrasonic transducer 4.

[0055] Under the control of the control unit 10, the receiving switching circuit 13 switches between a state in which the receiving circuit 14 is connected to the ultrasonic transducer 3, a state in which the receiving circuit 14 is connected to the ultrasonic transducer 4, and a state in which the receiving circuit 14 is connected to the ultrasonic transducer 5.

[0056] For example, when the reception switching circuit 13 receives a signal S52 from the control unit 10 for connecting the reception circuit 14 and the ultrasonic transducer 3, the reception switching circuit 13 connects the reception circuit 14 and the ultrasonic transducer 3. Similarly, when the reception switching circuit 13 receives a signal S52 from the control unit 10 for connecting the reception circuit 14 and the ultrasonic transducer 4, the reception switching circuit 13 connects the reception circuit 14 and the ultrasonic transducer 4. Similarly, when the reception switching circuit 13 receives a signal S52 from the control unit 10 for connecting the reception circuit 14 and the ultrasonic transducer 5, the reception switching circuit 13 connects the reception circuit 14 and the ultrasonic transducer 5.

[0057] In addition, when an ultrasonic reception signal is input from one of the ultrasonic transducers 3 to 5 that is connected to the reception circuit 14, the reception switching circuit 13 outputs the ultrasonic signal received by the ultrasonic transducer to the reception circuit 14 by relaying the reception signal.

[0058] For example, when a reception signal S61 is input from the ultrasonic transducer 3 while the reception circuit 14 and the ultrasonic transducer 3 are connected, the reception switching circuit 13 outputs a reception signal S58 corresponding to the reception signal S61 to the reception circuit 14. This allows the control unit 10 to control the reception switching circuit 13 to input the reception signal of the ultrasonic wave from the ultrasonic transducer 3 to the reception circuit 14.

[0059] Furthermore, for example, when a reception signal S57 is input from the ultrasonic transducer 4 while the reception circuit 14 and the ultrasonic transducer 4 are connected, the reception switching circuit 13 outputs a reception signal S58 corresponding to the reception signal S57 to the reception circuit 14. This allows the control unit 10 to input the reception signal of the ultrasonic wave by the ultrasonic transducer 4 to the reception circuit 14 by controlling the reception switching circuit 13.

[0060] Furthermore, for example, when a reception signal S62 is input from the ultrasonic transducer 5 while the reception circuit 14 and the ultrasonic transducer 5 are connected, the reception switching circuit 13 outputs a reception signal S58 corresponding to the reception signal S62 to the reception circuit 14. This allows the control unit 10 to input the reception signal of the ultrasonic wave by the ultrasonic transducer 5 to the reception circuit 14 by controlling the reception switching circuit 13.

[0061] The receiving circuit 14 receives an ultrasonic reception signal from any one of the ultrasonic transducers 3 to 5 via the receiving switching circuit 13, and outputs a signal corresponding to the ultrasonic reception signal at any one of the ultrasonic transducers 3 to 5 to the ADC 15. The receiving circuit 14 may also output a signal corresponding to the ultrasonic reception signal at any one of the ultrasonic transducers 3 to 5 to the ADC 15 by performing a predetermined process such as waveform amplification process on the ultrasonic reception signal from any one of the ultrasonic transducers 3 to 5.

[0062] For example, when an ultrasonic reception signal S58 from any one of the ultrasonic transducers 3 to 5 is input from the reception switching circuit 13 to the reception circuit 14, the reception circuit 14 performs predetermined processing such as waveform amplification and outputs the signal to the ADC 15 as a reception signal S59.

[0063] Under the control of the control unit 10, the ADC 15 converts the received ultrasonic signal, which is an analog signal, into a digital signal (time-series digital data).

[0064] For example, the ADC 15 converts the received signal input from the receiving circuit 14 into time-series digital data based on the reference time for time measurement defined by the signal S54 input from the control unit 10, and transmits it to the measurement processing unit 9 as data D70.

[0065] <Processing flow> An example of the flow of processing by the transmission and reception processing unit 8 will be described.

[0066] (1) First, the transmission / reception processing unit 8 performs processing for causing the ultrasonic transducer 3 to transmit ultrasonic waves and for causing the ultrasonic transducer 4 to receive the ultrasonic waves in the following procedure.

[0067] (1-1) The control unit 10 transmits signals S51 and S52 to the transmission switching circuit 12 and the reception switching circuit 13, respectively, for connecting the transmission circuit 11 and the ultrasonic transducer 3 and for connecting the reception circuit 14 and the ultrasonic transducer 4. As a result, the transmission circuit 11 and the ultrasonic transducer 3 are connected through the transmission switching circuit 12, and the reception circuit 14 and the ultrasonic transducer 4 are connected through the reception switching circuit 13.

[0068] (1-2) When the step (1-1) is completed, the control unit 10 transmits a transmission command S53 to the transmission circuit 11, and transmits a signal S54 that specifies the reference time for time measurement to the ADC 15. This enables the ADC 15 to convert the ultrasonic reception signal at the ultrasonic transducer 4 into time-series digital data based on the reference time that is correlated with the timing of ultrasonic transmission from the ultrasonic transducer 3.

[0069] (1-3) When the transmission circuit 11 receives the transmission command S53 from the control unit 10, it outputs an excitation pulse S55 to the transmission switching circuit 12. As a result, the ultrasonic transducer 3 is excited by a signal S56 corresponding to the excitation pulse S55 output from the transmission switching circuit 12, and an ultrasonic wave is transmitted from the ultrasonic transducer 3 to the measurement tube 2. Then, the ultrasonic wave transmitted from the ultrasonic transducer 3 to the measurement tube 2 propagates as a guide wave through both the measurement tube 2 and the measured fluid inside the measurement tube 2, and is received by the ultrasonic transducer 4.

[0070] (1-4) When a reception signal S58 corresponding to the reception signal S57 of the ultrasonic wave (guide wave) from the ultrasonic transducer 3 at the ultrasonic transducer 4 is input via the reception switching circuit 13, the reception circuit 14 performs a predetermined processing and outputs it to the ADC 15 as a reception signal S59.

[0071] (1-5) The ADC 15 converts the reception signal S59 (analog signal) input from the reception circuit 14 into a digital signal (time-series digital data) based on the reference time of time measurement notified from the control unit 10 through the signal S54, and outputs it as data D70 to the measurement processing unit 9. This makes it possible to store the time-series digital data of the waveform of the ultrasound transmitted from the ultrasonic transducer 3 and received by the ultrasonic transducer 4 in the measurement processing unit 9 (recording unit 20 described later).

[0072] (2) Next, the transmission / reception processing unit 8 performs processing for causing the ultrasonic transducer 4 to transmit ultrasonic waves and for causing the ultrasonic transducer 3 to receive the ultrasonic waves in the following procedure.

[0073] (2-1) The control unit 10 transmits signals S51 and S52 to the transmission switching circuit 12 and the reception switching circuit 13, respectively, for connecting the transmission circuit 11 and the ultrasonic transducer 4 and for connecting the reception circuit 14 and the ultrasonic transducer 3. As a result, the transmission circuit 11 and the ultrasonic transducer 4 are connected through the transmission switching circuit 12, and the reception circuit 14 and the ultrasonic transducer 3 are connected through the reception switching circuit 13.

[0074] (2-2) When the step (2-1) is completed, the control unit 10 transmits a transmission command S53 to the transmission circuit 11, and transmits a signal S54 that specifies the reference time for time measurement to the ADC 15. This enables the ADC 15 to convert the ultrasonic reception signal at the ultrasonic transducer 3 into time-series digital data based on the reference time that is correlated with the timing of ultrasonic transmission from the ultrasonic transducer 4.

[0075] (2-3) When the transmission circuit 11 receives the transmission command S53 from the control unit 10, it outputs an excitation pulse S55 to the transmission switching circuit 12. As a result, the ultrasonic transducer 4 is excited by a signal S56 corresponding to the excitation pulse S55 output from the transmission switching circuit 12, and an ultrasonic wave is transmitted from the ultrasonic transducer 4 to the measurement tube 2. Then, the ultrasonic wave transmitted from the ultrasonic transducer 4 to the measurement tube 2 propagates as a guide wave through both the measurement tube 2 and the measured fluid inside the measurement tube 2, and is received by the ultrasonic transducer 3.

[0076] (2-4) When a reception signal S58 corresponding to a reception signal S61 of an ultrasonic wave (guide wave) from the ultrasonic transducer 4 at the ultrasonic transducer 3 is input via the reception switching circuit 13, the reception circuit 14 performs a predetermined processing and outputs the signal to the ADC 15 as a reception signal S59.

[0077] (2-5) The ADC 15 converts the reception signal S59 (analog signal) input from the reception circuit 14 into a digital signal (time-series digital data) based on the reference time of time measurement notified from the control unit 10 through the signal S54, and outputs it as data D70 to the measurement processing unit 9. This makes it possible to store the time-series digital data of the waveform of the ultrasound transmitted from the ultrasonic transducer 4 and received by the ultrasonic transducer 3 in the measurement processing unit 9 (recording unit 20 described later).

[0078] (3) Next, the transmission / reception processing unit 8 performs processing for causing the ultrasonic transducer 3 to transmit ultrasonic waves and for causing the ultrasonic transducer 5 to receive the ultrasonic waves in the following procedure.

[0079] (3-1) The control unit 10 transmits signals S51 and S52 to the transmission switching circuit 12 and the reception switching circuit 13, respectively, for connecting the transmission circuit 11 and the ultrasonic transducer 3 and for connecting the reception circuit 14 and the ultrasonic transducer 5. As a result, the transmission circuit 11 and the ultrasonic transducer 3 are connected through the transmission switching circuit 12, and the reception circuit 14 and the ultrasonic transducer 5 are connected through the reception switching circuit 13.

[0080] (3-2) When the step (3-1) is completed, the control unit 10 transmits a transmission command S53 to the transmission circuit 11, and transmits a signal S54 that specifies the reference time for time measurement to the ADC 15. This enables the ADC 15 to convert the ultrasonic reception signal by the ultrasonic transducer 5 into time-series digital data based on the reference time that is correlated with the timing of ultrasonic transmission from the ultrasonic transducer 3.

[0081] (3-3) When the transmission circuit 11 receives the transmission command S53 from the control unit 10, it outputs an excitation pulse S55 to the transmission switching circuit 12. As a result, the ultrasonic transducer 3 is excited by a signal S56 corresponding to the excitation pulse S55 output from the transmission switching circuit 12, and an ultrasonic wave is transmitted from the ultrasonic transducer 3 to the measurement tube 2. Then, the ultrasonic wave transmitted from the ultrasonic transducer 3 to the measurement tube 2 propagates as a beam wave through the wall of the measurement tube 2, the measured fluid inside the measurement tube 2, and the wall of the measurement tube 2 in this order, and is received by the ultrasonic transducer 5.

[0082] (3-4) When a reception signal S58 corresponding to the reception signal S62 of the ultrasound (beam wave) from the ultrasound transducer 3 at the ultrasound transducer 5 is input via the reception switching circuit 13, the reception circuit 14 performs a predetermined processing and outputs the signal to the ADC 15 as a reception signal S59.

[0083] (3-5) The ADC 15 converts the reception signal S59 (analog signal) input from the reception circuit 14 into a digital signal (time-series digital data) based on the reference time of time measurement notified from the control unit 10 through the signal S54, and outputs it as data D70 to the measurement processing unit 9. This makes it possible to store the time-series digital data of the waveform of the ultrasound transmitted from the ultrasonic transducer 3 and received by the ultrasonic transducer 5 in the measurement processing unit 9 (recording unit 20 described later).

[0084] For example, the transmission / reception processing unit 8 repeatedly executes one set of the above-mentioned procedures (1) to (3) at predetermined processing intervals during operation of the ultrasonic flowmeter 1. The processing interval is, for example, 1 / 100 seconds.

[0085] Also, the transmission / reception processing unit 8 may repeatedly execute the above-mentioned processes of steps (1) and (2) as one set at every predetermined processing cycle during the operation of the ultrasonic flowmeter 1. The transmission / reception processing unit 8 may execute the process of step (3) once every predetermined number N (>2) of times the processes of steps (1) and (2) are executed. As described later, since the data R3 obtained in step (3) is used to calculate the sound speed C of the measured fluid, taking into consideration the rate of change in the temperature of the measured fluid that affects the sound speed C of the measured fluid, the process of step (3) does not need to be executed so frequently. Therefore, the processing load of the transmission / reception processing unit 8 can be reduced. In this case, the transmission / reception processing unit 8 executes the process of step (3) after the processes of steps (1) and (2), for example, once every predetermined number N of times the processes of steps (1) and (2) are repeated. The predetermined number N is, for example, 50.

[0086] [First example of measurement processing section] Next, a first example of the measurement processing unit 9 will be described with reference to FIG.

[0087] As shown in FIG. 4, the measurement processing section 9 includes a recording section 20, a time calculation section 21, a sound speed calculation section 22, a flow velocity calculation section 23, and a flow rate calculation section 24.

[0088] The functions of the recording unit 20, the time calculation unit 21, the sound speed calculation unit 22, the flow velocity calculation unit 23, and the flow rate calculation unit 24 are realized, for example, mainly by a microcomputer having a CPU, a memory device, an auxiliary storage device, an interface device for input / output, etc. Furthermore, the functions of the recording unit 20, the time calculation unit 21, the sound speed calculation unit 22, the flow velocity calculation unit 23, and the flow rate calculation unit 24 may all be realized by the same hardware (for example, a microcomputer), or at least some of them may be realized by different hardware.

[0089] The recording unit 20 receives and records (stores) the data D70 transmitted from the transmission / reception processing unit 8 (ADC 15).

[0090] For example, the recording unit 20 records the data D70 transmitted from the ADC 15 in the above procedure (1-5) as data R1. The data R1 is digital data of a time series of the waveform of the ultrasonic wave transmitted from the ultrasonic transducer 3 and received by the ultrasonic transducer 4.

[0091] Also, for example, the recording unit 20 records the data D70 transmitted from the ADC 15 in the above procedure (2-5) as data R2. The data R2 is digital data of a time series of the waveform of the ultrasonic wave transmitted from the ultrasonic transducer 4 and received by the ultrasonic transducer 3.

[0092] Also, for example, the recording unit 20 records the data D70 transmitted from the ADC 15 in the above procedure (3-5) as data R3. The data R3 is digital data of the time series of the waveform of the ultrasonic wave transmitted from the ultrasonic transducer 3 and received by the ultrasonic transducer 5.

[0093] The time calculation unit 21 reads out the data R1 and R2 recorded in the recording unit 20 as data D71, and calculates the average propagation time T0 and the propagation time difference ΔT based on the data R1 and R2. The average propagation time T0 is the average of the propagation time T1 from when an ultrasonic wave is transmitted from the ultrasonic transducer 3 to when it is received by the ultrasonic transducer 4, and the propagation time T2 from when an ultrasonic wave is transmitted from the ultrasonic transducer 4 to when it is received by the ultrasonic transducer 3 (T0=(T1+T2) / 2). The propagation time difference ΔT is the difference between the propagation time T1 and the propagation time T2 (ΔT=T2-T1).

[0094] The time calculation unit 21 may calculate the average propagation time T0 and the propagation time difference ΔT based on the data R1 and R2 by arbitrarily applying a known method.

[0095] For example, when the flow velocity of the measured fluid is very small, the average propagation time T0 is about several tens of microseconds, whereas the propagation time difference ΔT is about 1 / 1,000 to 1 / 100,000 of the average propagation time T0. Therefore, the time calculation unit 21 may apply a reference voltage cross method, a reference voltage envelope method, or the like to each of the data R1 and R2 to obtain the propagation times T1 and T2 individually, thereby calculating the average propagation time T0. On the other hand, the time calculation unit 21 may calculate the propagation time difference ΔT from a correlation calculation of the data R1 and R2, without using the propagation times T1 and T2 calculated individually. This makes it possible to calculate the propagation time difference ΔT while suppressing the influence of noise in the data R1 and R2.

[0096] After calculating the average propagation time T0 and the propagation time difference ΔT, the time calculation unit 21 sends the average propagation time T0 and the propagation time difference ΔT to the flow velocity calculation unit 23 as data D73.

[0097] The sound speed calculation unit 22 reads out the data R3 recorded in the recording unit 20 as data D72, and calculates the sound speed C of the fluid to be measured based on the data R3.

[0098] For example, the sound speed calculation unit 22 calculates the propagation time T3 from when an ultrasonic wave is transmitted from the ultrasonic transducer 3 to when it is received by the ultrasonic transducer 5, based on the data R3.

[0099] The sound speed calculation unit 22 may calculate the propagation time T3 by arbitrarily applying a known method based on the data R3. For example, the sound speed calculation unit 22 applies a reference voltage zero crossing method, a reference voltage envelope method, or the like to the data R3 to calculate the propagation time T3.

[0100] The ultrasonic waves (beam waves) transmitted from the ultrasonic transducer 3 and received by the ultrasonic transducer 5 propagate through the wall of the measurement tube 2 at the sound speed Cp of the material. In addition, since the inner diameter a of the measurement tube 2 is very small, the flow velocity distribution in the direction (Z-axis direction) perpendicular to the flow direction (X-axis direction) of the measured fluid can be ignored. Therefore, the ultrasonic waves (beam waves) transmitted from the ultrasonic transducer 3 and received by the ultrasonic transducer 5 propagate through the measured fluid inside the measurement tube 2 at the sound speed C. Therefore, the following formula (1) is established for the propagation time T3 using the thickness h and inner diameter a of the measurement tube 2. The thickness h of the measurement tube 2 corresponds to half the difference between the outer diameter b and inner diameter a of the measurement tube 2 (h=(ba) / 2).

[0101] T3 = a / C + 2h / Cp (1)

[0102] Therefore, based on the calculated propagation time T3, the sound speed calculation unit 22 can calculate the sound speed C of the measured fluid by the following formula (2), which is a modification of formula (1), using the thickness h of the measuring tube 2, the inner diameter a, and the sound speed Cp of the material of the measuring tube 2 as pre-defined constant parameters.

[0103] C = a / (T3-2h / Cp) (2)

[0104] After calculating the sound speed C of the fluid to be measured, the sound speed calculation unit 22 sends the sound speed C of the fluid to be measured to the flow velocity calculation unit 23 as data D74.

[0105] The flow velocity calculation unit 23 calculates the flow velocity V of the measured fluid by the transit time difference method based on the data D73 (average transit time T0 and transit time difference ΔT) input from the time calculation unit 21 and the data D74 (sound speed C) input from the sound speed calculation unit 22.

[0106] In the transit time difference method, the flow velocity V of the fluid to be measured is calculated by utilizing the fact that the flow velocity V of the fluid to be measured is proportional to the transit time difference ΔT (see formula (3)).

[0107] V = γΔT (3)

[0108] Here, the flow velocity V can be expressed by the following formulas (4) and (5) (see, for example, Ultrasonic Technology Handbook (published by The Nikkan Kogyo Shimbun) "1.10 Propagation of sound waves in pipes" and Patent Document 1, etc.).

[0109] V=T0·C 3 ΔT / (2L 2 ) ···(4) γ=T0·C 3 / 2L 2 (5)

[0110] Therefore, the flow velocity calculation unit 23 can calculate the flow velocity V of the measured fluid based on the average propagation time T0, the propagation time difference ΔT, and the sound velocity C of the measured fluid using equation (4) with the distance L between the ultrasonic transducers 3 and 4 as a constant parameter.

[0111] When the flow velocity calculation unit 23 calculates the flow velocity V of the fluid to be measured, it sends the flow velocity V of the fluid to the flow rate calculation unit 24 as data D75.

[0112] The flow rate calculation unit 24 calculates the flow rate Q of the fluid to be measured based on the data D75 (flow velocity V of the fluid to be measured) input from the flow velocity calculation unit 23.

[0113] For example, the flow rate calculation unit 24 calculates the flow rate Q of the fluid to be measured based on the flow velocity V of the fluid to be measured using the inner diameter a of the measuring pipe 2 as a constant parameter, according to the following equation (6).

[0114] Q = (πa 2 / 4)V ···(6)

[0115] The flow velocity V and flow rate Q of the fluid to be measured, which are measured (calculated) by the flow velocity calculation unit 23 and the flow rate calculation unit 24, are displayed, for example, on a display unit or the like provided in the ultrasonic flowmeter 1. In addition, the flow velocity V and flow rate Q of the fluid to be measured, which are measured (calculated) by the flow velocity calculation unit 23 and the flow rate calculation unit 24, may be transmitted to an external device through a predetermined communication line. This allows the user to check the flow velocity V and flow rate Q of the fluid to be measured, which are measured by the ultrasonic flowmeter 1 (measurement processing unit 9), and to use them for flow rate control of the fluid to be measured, etc.

[0116] A series of processes by the time calculation unit 21, the sound speed calculation unit 22, the flow velocity calculation unit 23, and the flow rate calculation unit 24 is performed at predetermined processing intervals, for example, as processes following the above steps (1) to (3) performed by the transmission / reception processing unit 8 at predetermined processing intervals.

[0117] Furthermore, the series of processes by the time calculation unit 21, the sound speed calculation unit 22, the flow velocity calculation unit 23, and the flow rate calculation unit 24 may be performed at a predetermined processing cycle as a process following the above-mentioned processes of steps (1) and (2) performed at a predetermined processing cycle by the transmission / reception processing unit 8. In this case, the process of step (3) is performed once every time steps (1) and (2) are performed a predetermined number N of times, as described above, and the data R3 of the recording unit 20 is updated once every time the data R1 and R2 are updated a predetermined number N of times. Therefore, the sound speed calculation unit 22 may execute a process of calculating the sound speed V of the measured fluid once every time the time calculation unit 21 executes a process of calculating the average propagation time T0 and the propagation time difference ΔT a predetermined number N of times. Then, at a processing timing when the sound speed C of the measured fluid is not calculated by the sound speed calculation unit 22, the flow velocity calculation unit 23 may calculate the flow velocity V of the measured fluid using the sound speed C of the measured fluid most recently calculated by the sound speed calculation unit 22.

[0118] In this way, in this example, the measurement processing unit 9 can measure (calculate) the sound velocity of the measured fluid using the ultrasonic transducers 3 and 5 arranged on the outer surface of the measurement tube 2 so as to face each other in a direction perpendicular to the flow direction of the measured fluid. As a result, the ultrasonic flowmeter 1 can measure the flow rate of the measured fluid based on the measured sound velocity of the measured fluid without performing actual flow calibration. Therefore, it is not necessary to measure or estimate the temperature of the measured fluid in order to take into account the temperature characteristic of the density of the measured fluid, as in the case of calculating the sound velocity of the measured fluid from a theoretical formula, for example. In addition, when a wide variety of measured fluids are expected, such as cleaning fluids for semiconductor manufacturing equipment, it is not necessary to prepare data on the temperature characteristic of density for each measured fluid in advance. Therefore, the ultrasonic flowmeter 1 can measure the flow rate of the measured fluid more simply and accurately without performing actual flow calibration.

[0119] [Second example of measurement processing section] Next, a second example of the measurement processing unit 9 will be described with reference to FIG.

[0120] In the following, the same or corresponding configurations as those in the above-mentioned first example are denoted by the same reference numerals, and the following description will focus on the differences from the above-mentioned first example.

[0121] 5, similar to the first example described above, the measurement processing unit 9 includes a recording unit 20, a time calculation unit 21, a sound speed calculation unit 22, a flow velocity calculation unit 23, and a flow rate calculation unit 24. Unlike the first example described above, the measurement processing unit 9 also includes a temperature calculation unit 25 and a data storage unit 26.

[0122] The temperature calculation unit 25 reads out the data R3 recorded in the recording unit 20 as data D72, and calculates the temperature t of the fluid to be measured based on the data R3.

[0123] For example, the temperature calculation unit 25 calculates the period λc of the waveform of the received signal of the ultrasonic transducer 5 based on the data R3, and calculates the resonant frequency Fc of the ultrasonic transducer 5 from the period λc. The temperature calculation unit 25 then calculates the temperature t of the fluid to be measured based on the calculated resonant frequency Fc of the ultrasonic transducer 5 and the data of the correlation between the resonant frequency of the ultrasonic transducer 5 and the temperature. For example, the ultrasonic transducer 5 such as a lead zirconate titanate-based piezoelectric element has an inherent characteristic that the resonant frequency changes depending on the temperature. Therefore, the temperature calculation unit 25 can calculate the temperature t of the fluid to be measured by comparing the inherent correlation between the resonant frequency and temperature of the ultrasonic transducer 5 with the calculated resonant frequency Fc, assuming that the temperatures of the ultrasonic transducer 5 and the fluid to be measured are equal.

[0124] Data on the correlation between the resonance frequency of the ultrasonic transducer 5 and the temperature is obtained, for example, through an experiment or a computer simulation, and is stored in advance in the data storage unit .

[0125] Furthermore, the temperature calculation unit 25 calculates the sound velocity Cp(t) of the material of the measuring tube 2 at the temperature t based on the temperature t of the fluid to be measured.

[0126] For example, the temperature calculation unit 25 assumes that the temperatures of the measured fluid and the measurement tube 2 are equal, and calculates the sound velocity Cp(t) of the material of the measurement tube 2 at temperature t based on the calculated temperature t of the measured fluid and data on the correlation between the sound velocity and temperature of the material of the measurement tube 2. The sound velocity of the material of the measurement tube 2 has an inherent characteristic that changes depending on temperature. Therefore, the temperature calculation unit 25 can calculate the sound velocity Cp(t) of the material of the measurement tube 2 at temperature t by comparing the inherent correlation between the sound velocity and temperature of the material of the measurement tube 2 with the calculated temperature t of the measured fluid.

[0127] The data on the correlation between the sound speed and temperature of the material of the measuring tube 2 is obtained, for example, through an experiment in which the propagation time T3 is measured using water, whose correlation between the sound speed and temperature is known, as a fluid, and is stored in advance in the data storage unit 26. In addition, the data on the correlation between the sound speed and temperature of the material of the measuring tube 2 may be obtained through a computer simulation or the like, and stored in advance in the data storage unit 26.

[0128] After calculating the temperature t of the fluid to be measured and the sound speed Cp(t) of the material of the measuring tube 2 at temperature t, the temperature calculation unit 25 sends the temperature t of the fluid to be measured and the sound speed Cp(t) of the material of the measuring tube 2 at temperature t to the sound speed calculation unit 22 as data D76.

[0129] The sound speed calculation unit 22 calculates the sound speed C of the measured fluid based on the propagation time T3 and the data D76 (the temperature t of the measured fluid and the sound speed Cp(t) of the material of the measuring tube 2 at the temperature t).

[0130] For example, the sound speed calculation unit 22 calculates the sound speed C(t) of the measured fluid at temperature t based on the propagation time T3, the sound speed Cp(t) of the measuring tube 2 at temperature t, the inner diameter a(t) of the measuring tube 2 at temperature t, and the thickness h(t) of the measuring tube 2 at temperature t using the following equation (7).

[0131] C(t)=a(t) / {T3-2h(t) / Cp(t)} ···(7)

[0132] For example, the following formulas (8) and (9) are established using the linear expansion coefficient α of the measuring tube 2, the reference temperature t0, and the inner diameter a0 and thickness h0 of the measuring tube 2 at the reference temperature t0 as constant parameters. Δt represents the temperature change of temperature t relative to the reference temperature t0 (Δt=t-t0).

[0133] a(t) = a0(1 + α Δt) (8) h(t) = h0(1 + α Δt) (9)

[0134] Therefore, the sound speed calculation unit 22 can calculate the sound speed C(t) of the measurement target fluid at temperature t using the following formula (10) obtained by substituting formulas (8) and (9) into formula (7).

[0135] C(t)=a0(1+α·Δt) / [T3-2h0(1+α·Δt) / Cp(t)] (10)

[0136] When the sound speed calculation section 22 calculates the sound speed C(t) at the temperature t of the measurement target fluid, it sends the sound speed C(t) to the flow velocity calculation section 23 as data D74.

[0137] The flow velocity calculation unit 23 may calculate the flow velocity V by the same process as in the first example described above, except that the sound velocity C(t) is used instead of the sound velocity C.

[0138] The flow rate calculation unit 24 may calculate the flow rate Q by the same process as in the first example described above.

[0139] From the above equations (5) and (6), the flow rate Q is calculated by the square of the ratio of the inner diameter a of the measuring tube 2 and the distance L between the ultrasonic transducers 3 and 4 (=(a / L) 2 ) is proportional to the distance L between the ultrasonic transducers 3 and 4. It can be considered that the inner diameter a of the measurement tube 2 and the distance L between the ultrasonic transducers 3 and 4 change at the same rate depending on the temperature. Therefore, for the inner diameter a and the distance L between the ultrasonic transducers 3 and 4 in the formulas (5) and (6), there is no problem in using fixed values ​​at a specific same temperature without considering the temperature t. However, the flow velocity calculation unit 23 and the flow rate calculation unit 24 may calculate the flow velocity V and the flow rate Q of the measured fluid using the inner diameter a(t) of the measurement tube 2 at the temperature t and the distance L(t) between the ultrasonic transducers 3 and 4 at the temperature t, respectively. For example, when accuracy is required not only for the flow rate Q but also for the flow velocity V, the distance L(t) between the ultrasonic transducers 3 and 4 at the temperature t may be used. In this case, the flow velocity calculation unit 23 can calculate the distance L(t) at the temperature t using the linear expansion coefficient α of the material of the measurement tube 2, the temperature change Δt of the temperature t relative to the reference temperature t0, and the distance L0 between the ultrasonic transducers 3 and 4 at the reference temperature t0.

[0140] In this way, in this example, the measurement processing unit 9 can measure (calculate) the flow rate of the fluid to be measured by measuring (calculating) the temperature t of the fluid to be measured, taking into consideration the sound speed of the material of the measurement tube 2 and the changes due to temperature in the dimensions (inner diameter and thickness) of the measurement tube 2. Therefore, the ultrasonic flowmeter 1 can further improve the measurement accuracy of the flow rate of the fluid to be measured.

[0141] In this embodiment, the temperature t of the fluid to be measured and the sound velocity Cp(t) of the material of the measurement tube 2 at temperature t can be calculated simply by preparing data on the correlation between the resonance frequency of the ultrasonic transducer 5 and temperature and data on the correlation between the sound velocity of the material of the measurement tube 2 and temperature. Therefore, unlike the case where data on the temperature characteristic of density is prepared in advance for each of the assumed fluids to be measured, there is no risk of a wide variety of assumed fluids to be measured and a huge amount of data to be prepared in advance. Therefore, the ultrasonic flowmeter 1 can measure the flow rate of the fluid to be measured more simply and accurately.

[0142] [Other embodiments] Next, another embodiment will be described.

[0143] The contents of the above-described embodiment may be modified or changed as appropriate.

[0144] For example, in the above-described embodiment, as shown in FIG. 4, the accommodating portion 7A of the holding portion 7 is molded integrally with the measuring pipe 2, but it may be molded separately from the measuring pipe 2 and then attached to the measuring pipe 2.

[0145] In the above-described embodiment and its modified and altered examples, the ultrasonic transducer 5 may be attached to a position facing the downstream ultrasonic transducer 4 in the Z-axis direction on the outer surface of the measuring pipe 2. In this case, in step (3) of the transmission and reception processing unit 8, ultrasonic waves are transmitted from the ultrasonic transducer 4 and received by the ultrasonic transducer 5.

[0146] Furthermore, in the above-described embodiments and examples of variations and modifications thereof, in the processing of step (3) by the transmission / reception processing unit 8, ultrasonic waves may be transmitted from the ultrasonic transducer 5 and received by the ultrasonic transducer 3 or ultrasonic transducer 4 that faces the ultrasonic transducer 5 in the Z-axis direction.

[0147] In the above-described embodiment and its modified and altered examples, the transmission switching circuit 12 may be omitted, and a transmission circuit 11 may be provided for each ultrasonic transducer that transmits ultrasonic waves among the ultrasonic transducers 3 to 5. Similarly, the reception switching circuit 13 may be omitted, and a reception circuit 14 may be provided for each ultrasonic transducer that receives ultrasonic waves among the ultrasonic transducers 3 to 5.

[0148] In the above-described embodiment and its modified and altered examples, the propagation time T3 may be calculated by the time calculation unit 21. In this case, the data R3 is sent to the time calculation unit 21, and the data of the propagation time T3 calculated by the time calculation unit 21 is sent to the sound speed calculation unit 22.

[0149] In the above-described embodiment (FIG. 5) and its modified and altered examples, the sound speed calculation unit 22 may calculate the sound speed Cp(t) of the material of the measuring tube 2 at the temperature t.

[0150] In addition, in the above-mentioned embodiment (FIG. 5) and its modified and altered examples, the change due to temperature is taken into account in both the sound speed of the material of the measuring tube 2 and the dimensions of the measuring tube 2 (the inner diameter of the measuring tube 2 and the distance between the ultrasonic transducers 3 and 4), but it may be taken into account in only one of them.

[0151] [Effect] Next, the operation of the ultrasonic flowmeter according to this embodiment will be described.

[0152] In this embodiment, the ultrasonic flowmeter includes a measurement tube, a first ultrasonic vibrator, a second ultrasonic vibrator, and a third ultrasonic vibrator. The ultrasonic flowmeter is, for example, the ultrasonic flowmeter 1 described above. The measurement tube is, for example, the measurement tube 2 described above. The first ultrasonic vibrator is, for example, the ultrasonic vibrator 3 described above. The second ultrasonic vibrator is, for example, the ultrasonic vibrator 4 described above. The third ultrasonic vibrator is, for example, the ultrasonic vibrator 5 described above. Specifically, the measurement tube is provided so as to extend linearly, and the measured fluid flows through it. The first ultrasonic vibrator is attached to the outer surface of the measurement tube. The second ultrasonic vibrator is attached to the outer surface of the measurement tube so as to be spaced apart from the first ultrasonic vibrator along a first direction in which the measurement tube extends as viewed from the first ultrasonic vibrator. The first direction is, for example, the X-axis direction described above. The third ultrasonic transducer is attached to the outer surface of the measurement pipe so as to face the first ultrasonic transducer in a second direction perpendicular to the first direction when viewed from the first ultrasonic transducer. The second direction is, for example, the Z-axis direction described above.

[0153] This allows the ultrasonic flowmeter to transmit and receive ultrasonic waves between the first ultrasonic transducer and the third ultrasonic transducer. Therefore, for example, when the velocity distribution of the measured fluid in the second direction perpendicular to the first direction in which the measured fluid flows can be ignored, the sound speed of the measured fluid can be measured (calculated) from the propagation time of the ultrasonic waves between the first ultrasonic transducer and the second ultrasonic transducer. As a result, the ultrasonic flowmeter can more accurately measure the flow rate of the measured fluid based on the sound speed of the measured fluid without performing actual flow calibration by a propagation time difference method using ultrasonic waves transmitted and received between the first ultrasonic transducer and the second ultrasonic transducer. Also, for example, as in the case of calculating the sound speed of the measured fluid from a theoretical formula, in order to take into account the temperature characteristics of the density of the measured fluid, it is not necessary to prepare data on the temperature characteristics of the density of each measured fluid in advance in accordance with the assumed wide variety of measured fluids. Therefore, the ultrasonic flowmeter can measure the flow rate of the measured fluid more easily and accurately without performing actual flow correction.

[0154] In the present embodiment, the ultrasonic flowmeter may include a flow rate calculation unit. The flow rate calculation unit is, for example, the flow rate calculation unit 24 described above. Specifically, the flow rate calculation unit calculates the flow rate of the measured fluid based on a first time until the ultrasonic wave transmitted from the first ultrasonic transducer is received by the second ultrasonic transducer as a guided wave propagating through the measurement pipe and the measured fluid, a second time until the ultrasonic wave transmitted from the second ultrasonic transducer is received by the first ultrasonic transducer as a guided wave propagating through the measurement pipe and the measured fluid, and a third time until the ultrasonic wave transmitted from one of the first ultrasonic transducer and the third ultrasonic transducer, which is a transmitting ultrasonic transducer, propagates through the measured fluid and is received by the other receiving ultrasonic transducer. The first time is, for example, the above-mentioned propagation time T1. The second time is, for example, the above-mentioned propagation time T2. The third time is, for example, the above-mentioned propagation time T3.

[0155] As a result, the ultrasonic flowmeter measures (calculates) the speed of sound of the measured fluid from the third time, and can calculate the flow rate of the measured fluid using the transit time difference method based on the first time, the second time, and the measured speed of sound of the measured fluid.

[0156] In addition, in this embodiment, the ultrasonic flowmeter may include a sound speed calculation unit and a flow velocity calculation unit. The sound speed calculation unit is, for example, the sound speed calculation unit 22 described above. The flow velocity calculation unit is the flow velocity calculation unit 23 described above. Specifically, the sound speed calculation unit calculates the sound speed of the measured fluid based on the third time. Furthermore, the flow velocity calculation unit calculates the flow velocity of the measured fluid based on the first time, the second time, and the sound velocity of the measured fluid. Then, the flow rate calculation unit may calculate the flow rate of the measured fluid based on the flow velocity of the measured fluid.

[0157] This allows the ultrasonic flowmeter to calculate the flow rate of the fluid to be measured based on the first time, the second time, and the third time.

[0158] In addition, in this embodiment, the sound speed calculation unit may calculate the sound speed C of the measured fluid based on the third time (propagation time T3), the inner diameter a of the measuring tube, the thickness h of the measuring tube, and the sound speed Cp of the material of the measuring tube using the following formula.

[0159] C=a / (T3-2h / Cp) In addition, the flow velocity calculation unit may calculate the flow velocity V of the measured fluid using the following formula based on the average value (average propagation time T0) of the first time (propagation time T1) and the second time (propagation time T2), the difference (propagation time difference ΔT) between the first time (propagation time T1) and the second time (propagation time T2), the distance L between the first ultrasonic transducer and the second ultrasonic transducer, and the sound speed C of the measured fluid.

[0160] V=T0·C 3 ΔT / (2L 2 ) The flow rate calculation unit may calculate the flow rate Q of the fluid to be measured based on the inner diameter a of the measuring pipe and the flow velocity V of the fluid to be measured using the following formula:

[0161] Q = (πa 2 / 4)·V

[0162] This allows the ultrasonic flowmeter to calculate the flow rate of the fluid to be measured based on the first time, the second time, and the third time.

[0163] In addition, in this embodiment, the flow velocity calculation unit and the flow rate calculation unit may calculate the flow velocity and flow rate of the measured fluid every time the first ultrasonic transducer transmits an ultrasonic wave and the second ultrasonic transducer receives a guided wave, and every time the second ultrasonic transducer transmits an ultrasonic wave and the first ultrasonic transducer receives a guided wave.The sound velocity calculation unit may calculate the sound velocity of the measured fluid less frequently than the frequency of the calculation of the flow velocity and flow rate of the measured fluid by the flow velocity calculation unit and the flow rate calculation unit.

[0164] This enables the ultrasonic flowmeter to reduce the processing load associated with calculating the flow rate of the fluid to be measured.

[0165] In addition, in this embodiment, the ultrasonic flowmeter may include a temperature calculation unit. The temperature calculation unit is, for example, the above-mentioned temperature calculation unit 25. Specifically, the temperature calculation unit calculates the temperature of the fluid to be measured based on the waveform of the ultrasonic wave transmitted from the transmitting ultrasonic transducer of the first ultrasonic transducer and the third ultrasonic transducer and received by the receiving ultrasonic transducer. Then, the sound speed calculation unit may calculate the sound speed of the fluid to be measured based on the temperature of the fluid to be measured.

[0166] This allows the ultrasonic flowmeter to calculate the sound speed of the fluid to be measured taking into account the temperature of the fluid, thereby enabling the ultrasonic flowmeter to more accurately measure the flow rate of the fluid to be measured.

[0167] In this embodiment, the temperature calculation unit may calculate the resonance frequency Fc of the transmitting ultrasonic transducer based on the waveform of the ultrasonic wave transmitted from the transmitting ultrasonic transducer of the first ultrasonic transducer and the third ultrasonic transducer and received by the receiving ultrasonic transducer, and may calculate the temperature t of the measured fluid based on the calculated resonance frequency Fc and information on the correlation between the resonance frequency of the receiving ultrasonic transducer and the temperature. Also, the sound speed calculation unit may calculate the sound speed Cp(t) of the material of the measurement tube at temperature t based on the information on the correlation between the sound speed of the material of the measurement tube and the temperature, and the temperature t of the measured fluid, and may calculate the sound speed C(t) of the measured fluid at temperature t using the following formula based on the third time (propagation time T3), the inner diameter a of the measurement tube, the thickness h of the measurement tube, and the sound speed Cp(t) of the material of the measurement tube at temperature t.

[0168] C(t)=a / {T3-2·h / Cp(t)} In addition, the flow velocity calculation unit may calculate the flow velocity V of the measured fluid using the following formula based on the average value (average propagation time T0) of the first time (propagation time T1) and the second time (propagation time T2), the difference (propagation time difference ΔT) between the first time (propagation time T1) and the second time (propagation time T2), the distance L between the first ultrasonic transducer and the second ultrasonic transducer, and the sound velocity C(t) of the measured fluid at temperature t.

[0169] V = T0 C(t) 3ΔT / (2L 2 ) The flow rate calculation unit may calculate the flow rate Q of the fluid to be measured based on the inner diameter a of the measuring pipe and the flow velocity V of the fluid to be measured using the following formula:

[0170] Q = (πa 2 / 4)·V

[0171] This allows the ultrasonic flowmeter to measure (calculate) the speed of sound of the fluid being measured, taking into account the change in the speed of sound of the material of the measurement tube due to temperature, and therefore the ultrasonic flowmeter can more accurately measure the flow rate of the fluid being measured.

[0172] In this embodiment, the temperature calculation unit may calculate the resonance frequency Fc of the receiving ultrasonic transducer based on the waveform of the ultrasonic wave transmitted from the transmitting ultrasonic transducer of the first ultrasonic transducer and the third ultrasonic transducer and received by the receiving ultrasonic transducer, and may calculate the temperature t of the fluid to be measured based on the calculated resonance frequency Fc and information on the correlation between the resonance frequency of the receiving ultrasonic transducer and the temperature. Also, the sound speed calculation unit may calculate the sound speed Cp(t) of the material of the measurement tube at temperature t based on the information on the correlation between the sound speed of the material of the measurement tube and the temperature, and the temperature t of the fluid to be measured, and may calculate the sound speed C(t) of the fluid to be measured by the following formula based on the third time T3, the inner diameter a(t) of the measurement tube at temperature t, the thickness h(t) of the measurement tube at temperature t, and the sound speed Cp(t) of the material of the measurement tube at temperature t.

[0173] C(t)=a(t) / {T3-2·h(t) / Cp(t)} In addition, the flow velocity calculation unit may calculate the flow velocity V of the measured fluid using the following formula based on the average value (average propagation time T0) of the first time (propagation time T1) and the second time (propagation time T2), the difference (propagation time difference ΔT) between the first time (propagation time T1) and the second time (propagation time T2), the distance L between the first ultrasonic transducer and the second ultrasonic transducer, and the sound velocity C(t) of the measured fluid at temperature t.

[0174] V = T0 C(t) 3 ΔT / (2L2 ) The flow rate calculation unit may calculate the flow rate Q of the fluid to be measured based on the inner diameter a of the measuring pipe and the flow velocity V of the fluid to be measured using the following formula:

[0175] Q = (πa 2 / 4)·V

[0176] This allows the ultrasonic flowmeter to measure (calculate) the speed of sound of the fluid to be measured, taking into account the temperature-dependent change in the speed of sound in the material of the measurement tube as well as the temperature-dependent change in the dimensions of the measurement tube, thereby enabling the ultrasonic flowmeter to more accurately measure the flow rate of the fluid to be measured.

[0177] In addition, in this embodiment, the inner diameter a(t) and thickness h(t) of the measuring tube at temperature t may be calculated using the following formula based on the temperature change Δt of temperature t relative to reference temperature t0, the linear expansion coefficient α of the material of the measuring tube, the inner diameter a0 of the measuring tube at reference temperature t0, and the thickness h0 of the measuring tube at reference temperature t0.

[0178] a(t) = a0 (1 + α Δt) h(t) = h0(1 + α Δt)

[0179] This allows the ultrasonic flowmeter to measure (calculate) the sound velocity of the fluid to be measured, taking into account changes in the inner diameter and thickness of the measuring tube due to temperature.

[0180] In the present embodiment, the flow velocity calculation unit and the flow rate calculation unit may calculate the flow velocity and flow rate of the measured fluid each time the first ultrasonic transducer transmits an ultrasonic wave and the second ultrasonic transducer receives a guided wave, and the second ultrasonic transducer transmits an ultrasonic wave and the first ultrasonic transducer receives a guided wave.The temperature calculation unit and the sound speed calculation unit may calculate the temperature and sound speed of the measured fluid less frequently than the frequency of the calculation of the flow velocity and flow rate of the measured fluid by the flow velocity calculation unit and the flow rate calculation unit.

[0181] This enables the ultrasonic flowmeter to reduce the processing load associated with calculating the flow rate of the fluid to be measured.

[0182] In this embodiment, the inner diameter of the measuring pipe may be included in the range of ultrasonic wavelengths in the allowable temperature range of the fluid to be measured.

[0183] This enables the ultrasonic flowmeter to measure the flow rate of the fluid to be measured more easily and accurately, even when the inner diameter of the measurement tube is very thin, approximately the wavelength of the ultrasonic waves of the fluid to be measured.

[0184] In this embodiment, the measuring pipe may be made of resin.

[0185] This enables the ultrasonic flowmeter to more simply and accurately measure the flow rate of the fluid to be measured flowing through the resin measuring tube.

[0186] In the present embodiment, the ultrasonic flowmeter may include a transmitter, a transmission switching unit, a receiver, and a reception switching unit. The transmitter is, for example, the above-mentioned transmission circuit 11. The transmission switching unit is, for example, the above-mentioned transmission switching circuit 12. The receiver is, for example, the above-mentioned reception circuit 14. The reception switching unit is, for example, the above-mentioned reception switching circuit 13. Specifically, the transmitter outputs a signal for the ultrasonic transducer to transmit ultrasonic waves. The transmission switching unit switches between the transmitter and either one of the first ultrasonic transducer and the second ultrasonic transducer, or one of the first ultrasonic transducer, the second ultrasonic transducer, and the third ultrasonic transducer. The receiver receives an ultrasonic signal received by the ultrasonic transducer. The reception switching unit switches between the reception unit and either one of the first ultrasonic transducer, the second ultrasonic transducer, and the third ultrasonic transducer, or between the reception unit and either the first ultrasonic transducer or the second ultrasonic transducer.

[0187] This allows the ultrasonic flowmeter to transmit ultrasonic waves from different ultrasonic transducers using one transmission circuit, and to receive signals corresponding to the ultrasonic waves received by the different ultrasonic transducers using one reception circuit, thereby simplifying the hardware configuration of the ultrasonic flowmeter.

[0188] In this embodiment, the first ultrasonic transducer, the second ultrasonic transducer, and the third ultrasonic transducer may be piezoelectric elements based on lead zirconate titanate.

[0189] This allows the ultrasonic flowmeter to transmit and receive ultrasonic waves using a lead zirconate-titanate based piezoelectric element.

[0190] Although the embodiments have been described in detail above, the present disclosure is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist described in the claims.

[0191] Finally, this application claims priority based on Japanese Patent Application No. 2022-135030, filed on August 26, 2022, the entire contents of which are incorporated by reference into this application. [Explanation of symbols]

[0192] 1 Ultrasonic flowmeter 2 Measuring tube 3 Ultrasonic transducer 4 Ultrasonic transducer 5 Ultrasonic transducer 6 Acoustic coupling material 7 Holding part 7A Storage section 7B Pressing member 7C Pressing member 7D Lid member 8 Transmission and reception processing section 9. Measurement processing section 10 Control section 11 Transmitting circuit 12 Transmission switching circuit 13 Receiving switching circuit 14 Receiving circuit 15 ADC 20 Recording Section 21 Time calculation section 22 Sound velocity calculation section 23 Flow velocity calculation section 24 Flow rate calculation section 25 Temperature calculation section 26 Data storage unit

Claims

1. a measurement tube extending linearly and through which a fluid to be measured flows; A first ultrasonic transducer attached to an outer surface of the measuring tube; a second ultrasonic transducer attached to an outer surface of the measuring pipe so as to be spaced apart from the first ultrasonic transducer along a first direction in which the measuring pipe extends, as viewed from the first ultrasonic transducer; a third ultrasonic transducer attached to the outer surface of the measuring pipe so as to face the first ultrasonic transducer in a second direction perpendicular to the first direction; A transmitting unit that outputs a signal for transmitting an ultrasonic wave; a transmission switching unit that switches between the transmission unit and either one of the first ultrasonic transducer and the second ultrasonic transducer, or between the transmission unit and either one of the first ultrasonic transducer, the second ultrasonic transducer, and the third ultrasonic transducer; a receiving unit to which a received ultrasonic signal is input; a reception switching unit that switches between the reception unit and one of the first ultrasonic transducer, the second ultrasonic transducer, and the third ultrasonic transducer, or between the reception unit and one of the first ultrasonic transducer and the second ultrasonic transducer; A control unit that controls transmission and reception of ultrasonic waves from the first ultrasonic transducer, the second ultrasonic transducer, and the third ultrasonic transducer; a flow rate calculation unit that calculates a flow rate of the fluid to be measured, The control unit executes a first process of controlling the transmission switching unit and the reception switching unit so that an ultrasonic wave transmitted from either one of the first ultrasonic transducer and the second ultrasonic transducer is received by the other one, and executes a second process of controlling the transmission switching unit and the reception switching unit so that an ultrasonic wave transmitted from either one of the first ultrasonic transducer and the third ultrasonic transducer is received by the other one, separately from the first process; The flow rate calculation unit calculates a flow rate of the measurement target fluid based on the ultrasonic waves transmitted and received by each of the first process and the second process. Ultrasonic flow meter.

2. The time calculation unit calculates the flow rate of the measured fluid based on a first time until the ultrasonic wave transmitted from the first ultrasonic transducer is received by the second ultrasonic transducer as a guide wave propagating through the measurement tube and the measured fluid by the first processing of the control unit, a second time until the ultrasonic wave transmitted from the second ultrasonic transducer is received by the first ultrasonic transducer as a guide wave propagating through the measurement tube and the measured fluid by the first processing of the control unit, and a third time until the ultrasonic wave transmitted from one of the transmitting ultrasonic transducers, the first ultrasonic transducer or the third ultrasonic transducer, propagates through the measured fluid and is received by the other receiving ultrasonic transducer by the second processing of the control unit.

2. The ultrasonic flow meter of claim 1.

3. A sound speed calculation unit that calculates the sound speed of the measurement target fluid based on the third time; a flow velocity calculation unit that calculates a flow velocity of the measurement target fluid based on the first time, the second time, and the sound velocity of the measurement target fluid, The flow rate calculation unit calculates a flow rate of the fluid to be measured based on a flow velocity of the fluid to be measured.

3. The ultrasonic flow meter of claim 2.

4. A memory unit that stores data regarding the ultrasound transmitted and received by the second processing, The second process is executed less frequently than the first process; The flow rate calculation unit calculates the flow rate of the fluid to be measured based on data on ultrasonic waves transmitted and received by the most recent first process and data on ultrasonic waves transmitted and received by the second process executed at a past timing different from the most recent execution timing of the first process, the data being stored in the storage unit.

4. An ultrasonic flowmeter according to claim 1 .