Ultrasonic Flowmeter and Measurement Method

Abstract

This ultrasonic flowmeter comprises: a time measuring unit for measuring a plurality of propagation times from a time point at which transmission of ultrasonic waves starts until each crossing time point at which a received signal of the ultrasonic wave crosses a reference level after the received signal has crossed a threshold voltage; and a flow rate measuring unit for extracting a specific propagation time, of which a difference from a reference propagation time lies within a first prescribed range, from among the plurality of propagation times, and using the specific propagation time to calculate a flow rate of a fluid through which the ultrasonic waves propagate.

Description

[Technical field]

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

[0002] There is a known measuring device that transmits ultrasonic waves from one sensor to another, extracts a waveform (trigger waveform) that crosses a trigger level from the received waveform of the ultrasonic waves, and measures the time to the zero-cross point where the extracted trigger waveform crosses the zero line. This measuring device measures the time from the transmission of the ultrasonic waves to the zero-cross point as the ultrasonic propagation time, and uses the measured propagation time to calculate the flow rate of the fluid through which the ultrasonic waves propagate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-322194 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, if a foreign object is mixed into the medium such as a fluid through which the ultrasonic waves propagate, or if the temperature of the medium changes, the received waveform of the ultrasonic waves may change, causing a time shift in the trigger waveform. In this case, the measurement accuracy of the propagation time of the ultrasonic waves may decrease, and the calculation error of the physical quantity of the medium through which the ultrasonic waves propagate (for example, the flow rate of the fluid) may become large.

[0005] The present disclosure provides an ultrasonic flowmeter and a measurement method capable of suppressing a decrease in the measurement accuracy of the propagation time of ultrasonic waves. [Means for solving the problem]

[0006] As a first aspect of the present disclosure, A time measurement unit that measures a plurality of propagation times from the start of transmission of the ultrasonic wave to each crossing time when the received signal crosses a reference level after the received signal of the ultrasonic wave crosses a threshold voltage; A flow rate measurement unit that extracts a specific propagation time within a first predetermined range from the difference from a reference propagation time among the plurality of propagation times, and calculates a flow rate of a fluid through which the ultrasonic wave propagates using the specific propagation time, An ultrasonic flow meter is provided.

[0007] As a second aspect of the present disclosure, Measure a plurality of propagation times from the start of transmission of the ultrasonic wave to each crossing time when the received signal crosses a reference level after the received signal of the ultrasonic wave crosses a threshold voltage, A measurement method is provided that extracts a specific propagation time within a first predetermined range from the difference from a reference propagation time among the plurality of propagation times, and calculates a physical quantity of a medium through which the ultrasonic wave propagates using the specific propagation time.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide an ultrasonic flow meter and a measurement method capable of suppressing a decrease in the measurement accuracy of the propagation time of ultrasonic waves.

Brief Description of the Drawings

[0009]

Figure 1

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Figure 10

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0011] FIG. 1 is a diagram showing a configuration example of an ultrasonic flowmeter according to an embodiment. The ultrasonic flowmeter measures the flow rate of a fluid (gas or liquid) flowing in a flow path by ultrasonic waves. The ultrasonic flowmeter includes two or more ultrasonic transducers arranged along or within a measurement pipe. The two or more ultrasonic transducers include a transmission-side transducer and a reception-side transducer. The transmission-side transducer and the reception-side transducer are arranged such that the direction connecting the transmission-side transducer and the reception-side transducer is obliquely intersecting or coinciding with the flow direction of the fluid. The ultrasonic flowmeter measures the flow rate of the fluid in the measurement pipe from the propagation time of the ultrasonic waves transmitted and received between the transmission-side transducer and the reception-side transducer.

[0012] The ultrasonic flowmeter 300 shown in FIG. 1 includes an ultrasonic probe 10a, an ultrasonic probe 10b, a control unit 35, a transmission unit 31, a switch 33a, a switch 33b, a reception unit 32, a time measurement unit 40, and a flow rate measurement unit 50.

[0013] The control unit 35 performs control to switch whether to transmit the ultrasonic wave e from the ultrasonic transducer 11a of the ultrasonic probe 10a or from the ultrasonic transducer 11b of the ultrasonic probe 10b toward the fluid 102 in the pipe 100.

[0014] The ultrasonic probe 10a is disposed upstream of the fluid 102 flowing in the pipe 100 so as to face the outer surface of the pipe 100. The ultrasonic probe 10a has an ultrasonic vibrator 11a and a resin wedge 12a. The ultrasonic probe 10b is disposed downstream of the fluid 102 flowing in the pipe 100 so as to face the outer surface of the pipe 100. The ultrasonic probe 10b has an ultrasonic vibrator 11b and a resin wedge 12b.

[0015] The wedge 12a has a surface inclined with respect to the outer surface of the pipe 100, and the ultrasonic vibrator 11a is attached to the surface. For this reason, the ultrasonic waves generated by the ultrasonic vibrator 11a are incident on the pipe 100 from the wedge 12a at a predetermined inclination angle, then propagate through the fluid 102, and reach the ultrasonic vibrator 11b.

[0016] The wedge 12b has a surface inclined with respect to the outer surface of the pipe 100, and the ultrasonic vibrator 11b is attached to the surface. For this reason, the ultrasonic waves generated by the ultrasonic vibrator 11b are incident on the pipe 100 from the wedge 12b at a predetermined inclination angle, then propagate through the fluid 102, and reach the ultrasonic vibrator 11a.

[0017] The ultrasonic vibrator 11a is selectively connected to the transmitter 31 or the receiver 32 by the switching operation of the switch 33a. The ultrasonic vibrator 11b is selectively connected to the receiver 32 or the transmitter 31 by the switching operation of the switch 33b.

[0018] The control unit 35 is a circuit that generates selection signals a and b for selecting the vibrator that should transmit ultrasonic waves (that is, one of the vibrators to be excited) between the ultrasonic vibrator 11a and the ultrasonic vibrator 11b, and a transmission timing signal c for instructing the timing of ultrasonic wave transmission.

[0019] When the ultrasonic vibrator 11a is selected as the vibrator to transmit the ultrasonic wave e, the switch 33a selects the ultrasonic vibrator 11a as the vibrator to transmit the ultrasonic wave e according to the selection signal a from the control unit 35. On the other hand, the switch 33b selects the ultrasonic vibrator 11b as the vibrator to receive the ultrasonic wave e according to the selection signal b from the control unit 35.

[0020] The transmission unit 31 transmits an electrical signal d (for example, one or more pulse signals for exciting the ultrasonic vibrator 11a) to the ultrasonic vibrator 11a via the switch 33a according to the transmission timing signal c from the control unit 35, and is a circuit that generates the ultrasonic wave e in the ultrasonic vibrator 11a. The generated ultrasonic wave e passes through the wedge 12a and the pipe 100 and is incident on the fluid 102 in the pipe 100. The ultrasonic wave e incident on the fluid 102 in the pipe 100 propagates to the ultrasonic vibrator 11b of the ultrasonic probe 10b installed on the outer surface on the opposite side of the pipe 100 and is converted into an electrical signal by the ultrasonic vibrator 11b. The electrical signal output from the ultrasonic vibrator 11b is received as a received signal f by the receiving unit 32 via the switch 33b.

[0021] The time measurement unit 40 measures the time from when the ultrasonic wave e is transmitted from the ultrasonic vibrator 11a until it is received by the ultrasonic vibrator 11b as the propagation time Tab. The time measurement unit 40 is, for example, a circuit that measures the propagation time Tab based on the transmission timing signal c indicating the timing when the transmission of the ultrasonic wave e from the ultrasonic vibrator 11a starts and the reception timing signal g indicating the timing when the ultrasonic wave e is received by the ultrasonic vibrator 11b.

[0022] Next, the ultrasonic flowmeter 300 switches the switch 33a and the switch 33b according to a signal from the control unit 35 to reverse the transmission and reception relationship between the ultrasonic probe 10a and the ultrasonic probe 10b.

[0023] When the ultrasonic vibrator 11b is selected as the vibrator for transmitting the ultrasonic wave e, the switch 33a selects the ultrasonic vibrator 11a as the vibrator for receiving the ultrasonic wave e according to the selection signal a from the control unit 35. On the other hand, the switch 33b selects the ultrasonic vibrator 11b as the vibrator for transmitting the ultrasonic wave e according to the selection signal b from the control unit 35.

[0024] The transmitting unit 31 transmits an electrical signal d (for example, one or more pulse signals for exciting the ultrasonic vibrator 11b) to the ultrasonic vibrator 11b via the switch 33b according to the transmission timing signal c from the control unit 35, and is a circuit for generating the ultrasonic wave e in the ultrasonic vibrator 11b. The generated ultrasonic wave e passes through the wedge 12b and the pipe 100 and is incident on the fluid 102 in the pipe 100. The ultrasonic wave e incident on the fluid 102 in the pipe 100 propagates to the ultrasonic vibrator 11a of the ultrasonic probe 10a installed on the outer surface on the opposite side of the pipe 100, and is converted into an electrical signal by the ultrasonic vibrator 11a. The electrical signal output from the ultrasonic vibrator 11a is received as a received signal f by the receiving unit 32 via the switch 33a.

[0025] The time measurement unit 40 measures the time from when the ultrasonic wave e is transmitted from the ultrasonic vibrator 11b until it is received by the ultrasonic vibrator 11a as the propagation time Tba. The time measurement unit 40 is, for example, a circuit that measures the propagation time Tba based on the transmission timing signal c indicating the timing when the transmission of the ultrasonic wave e from the ultrasonic vibrator 11b starts and the reception timing signal g indicating the timing when the ultrasonic wave e is received by the ultrasonic vibrator 11a.

[0026] Note that the order of measuring the propagation time Tab and the propagation time Tba may be reversed.

[0027] The flow rate measurement unit 50 calculates the flow rate Q of the fluid 102 using the measurement times (propagation time Tab and propagation time Tba) obtained from the time measurement unit 40. Next, the calculation of the flow rate Q will be described.

[0028] Regarding the propagation times Tab and Tba, Tab = Lf / (Cf + Vsinθfs ) ···(1) Tba = Lf / (Cf - Vsinθ fs ) ···(2) The following relationship holds. Here, Cf is the speed of sound in the fluid 102 within the pipe 100, V is the flow velocity of the fluid 102, θ fs is the incident angle in the fluid (the refraction angle from the pipe 100 to the fluid 102 or the incident angle from the fluid 102 to the pipe 100), and Lf is the length of the propagation path 110 of the ultrasonic wave e within the pipe 100.

[0029] Solving for V from equations (1) and (2), V = Lf / (2sinθ fs ) × ((1 / Tab) - (1 / Tba)) ···(3) is obtained.

[0030] The flow rate Q is Q = V × A ···(4) where A is the cross-sectional area of the pipe 100. The cross-sectional area A is expressed using the inner radius r of the pipe 100 as A = π × r 2 ···(5) as shown.

[0031] Figure 2 is a diagram for explaining Snell's law for determining the incident angle θ fs in the fluid. According to Snell's law, Cw / sinθ w = Cp / sinθ p = Cf / sinθ fs ···(6) the following relational expression holds. Here, Cw is the speed of sound in the wedge 12a, θ w is the incident angle in the wedge (the incident angle from the wedge 12a to the pipe 100 or the refraction angle from the pipe 100 to the wedge 12a). Cp is the speed of sound in the pipe 100, θ p is the incident angle in the pipe (the refraction angle from the wedge 12a to the pipe 100, the incident angle from the pipe 100 to the fluid 102, or the incident angle from the pipe 100 to the wedge 12a). Cf is the speed of sound in the fluid 102, θ fs is the incident angle in the fluid (the refraction angle from the pipe 100 to the fluid 102 or the incident angle from the fluid 102 to the pipe 100).

[0032] Cw, sinθ w Since Cw and Cf are known values, the incident angle θ of the fluid can be obtained from Equation (6). fs Therefore, the flow rate measurement unit 50 can calculate the flow rate Q based on Equations (1) to (5).

[0033] The flow rate measurement unit 50 is, for example, an arithmetic circuit including a processor such as a CPU (Central Processing Unit) and a memory. The arithmetic circuit may include at least one of the control unit 35 and the time measurement unit 40. Each function (the processing performed by each unit) of the flow rate measurement unit 50, the control unit 35, and the time measurement unit 40 is realized, for example, by a program stored in the memory when the processor operates. Each function may be realized by an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). The control unit 35 or the time measurement unit 40 may be realized by a logic circuit.

[0034] FIG. 3 is a diagram showing a configuration example of the receiving unit. The receiving unit 32 includes an amplifier circuit 36 and a reception timing detection circuit 38. The amplifier circuit 36 amplifies the received signal f input via the switch 33a or the switch 33b, and outputs the received wave i which is the amplified received signal f. The reception timing detection circuit 38 generates a reception timing signal g indicating the timing at which the ultrasonic wave e is received by the ultrasonic oscillator 11a or the ultrasonic oscillator 11b based on the input received wave i.

[0035] FIG. 4 is a diagram for explaining the reception timing signal g. The reception timing detection circuit 38 detects the time point (FIG. 4 exemplifies the zero-crossing time point q8x or the zero-crossing time point q10x) at which the received wave i crosses the reference level V after the received wave i crosses the threshold voltage V. THLD COM

[0036] ​​The reception timing detection circuit 38 detects a specific half-oscillation wave that crosses the threshold voltage V among the plurality of half-oscillation waves included in the received wave i. THLD For example, the reception timing detection circuit 38 detects, as a specific half-oscillation wave, the eighth half-oscillation wave whose amplitude crosses the threshold voltage V at the trigger point c8x, or the tenth half-oscillation wave whose amplitude crosses the threshold voltage V at the trigger point c10x. The reception timing detection circuit 38 detects the time when the trailing edge of the specific half-oscillation wave crosses the reference level V (FIG. 4 illustrates the zero-crossing point q8x or the zero-crossing point q10x), and outputs the stop pulse STOP generated at that time as the reception timing signal g. THLD For example, the reception timing detection circuit 38 detects, as a specific half-oscillation wave, the eighth half-oscillation wave whose amplitude crosses the threshold voltage V at the trigger point c8x, or the tenth half-oscillation wave whose amplitude crosses the threshold voltage V at the trigger point c10x. THLD For example, the reception timing detection circuit 38 detects, as a specific half-oscillation wave, the eighth half-oscillation wave whose amplitude crosses the threshold voltage V at the trigger point c8x, or the tenth half-oscillation wave whose amplitude crosses the threshold voltage V at the trigger point c10x. The reception timing detection circuit 38 detects the time when the trailing edge of the specific half-oscillation wave crosses the reference level V (FIG. 4 illustrates the zero-crossing point q8x or the zero-crossing point q10x), and outputs the stop pulse STOP generated at that time as the reception timing signal g. COM For example, the reception timing detection circuit 38 detects, as a specific half-oscillation wave, the eighth half-oscillation wave whose amplitude crosses the threshold voltage V at the trigger point c8x, or the tenth half-oscillation wave whose amplitude crosses the threshold voltage V at the trigger point c10x. The reception timing detection circuit 38 detects the time when the trailing edge of the specific half-oscillation wave crosses the reference level V (FIG. 4 illustrates the zero-crossing point q8x or the zero-crossing point q10x), and outputs the stop pulse STOP generated at that time as the reception timing signal g.

[0037] The time measurement unit 40 (FIG. 3) measures the time from the transmission timing signal c indicating the transmission start timing of the ultrasonic wave e from the ultrasonic oscillator 11a to the reception timing signal g (stop pulse STOP) indicating the reception timing of the ultrasonic wave e at the ultrasonic oscillator 11b. The time measurement unit 40 outputs the measured value of the time as the propagation time Tab. Similarly, the time measurement unit 40 measures the time from the transmission timing signal c indicating the transmission start timing of the ultrasonic wave e from the ultrasonic oscillator 11b to the reception timing signal g (stop pulse STOP) indicating the reception timing of the ultrasonic wave e at the ultrasonic oscillator 11a. The time measurement unit 40 outputs the measured value of the time as the propagation time Tba.

[0038] However, if the amplitude of the received wave i or the threshold voltage V shown in FIG. 4 deviates from the assumed value, there is a possibility that the reception timing signal g (stop pulse STOP) is generated based on a half-oscillation wave one wavefront or one wave behind. In this case, there is a possibility that a measurement error occurs in the propagation time Tab or the propagation time Tba. THLD However, if the amplitude of the received wave i or the threshold voltage V shown in FIG. 4 deviates from the assumed value, there is a possibility that the reception timing signal g (stop pulse STOP) is generated based on a half-oscillation wave one wavefront or one wave behind. In this case, there is a possibility that a measurement error occurs in the propagation time Tab or the propagation time Tba.

[0039] In the ultrasonic flowmeter of the present embodiment, the reception timing detection circuit 38 detects a specific half-oscillation wave that crosses the threshold voltage V among the plurality of half-oscillation waves included in the received wave i. THLDDetect a plurality of specific vibration half - waves that cross. The reception timing detection circuit 38 detects the trailing edges of a plurality of specific vibration half - waves crossing a reference level V COM Detect a plurality of time points (for example, four or more zero - cross time points) at which the plurality of specific vibration half - waves cross, and output a plurality of stop pulses STOP generated at those plurality of time points as a plurality of reception timing signals g.

[0040] Then, the time measurement unit 40 measures the time from the transmission timing signal c indicating the transmission start timing of the ultrasonic wave e from the ultrasonic oscillator 11a to the reception timing signal g (stop pulse STOP) indicating the reception timing of the ultrasonic wave e at the ultrasonic oscillator 11b for a plurality of zero - cross time points. The time measurement unit 40 outputs the measured values of the time up to each zero - cross time point as a plurality of propagation times Tab. Similarly, the time measurement unit 40 measures the time from the transmission timing signal c indicating the transmission start timing of the ultrasonic wave e from the ultrasonic oscillator 11b to the reception timing signal g (stop pulse STOP) indicating the reception timing of the ultrasonic wave e at the ultrasonic oscillator 11a for a plurality of zero - cross times. The time measurement unit 40 outputs the measured values of the time up to each zero - cross time point as a plurality of propagation times Tba.

[0041] The flow rate measurement unit 50 extracts specific propagation times Tabs within a first predetermined range from the difference between the plurality of propagation times Tab and the reference propagation time Tr, and extracts specific propagation times Tbas within a first predetermined range from the difference between the plurality of propagation times Tba and the reference propagation time Tr. As a result, propagation times (propagation times Tabs, Tbas) with relatively small errors are extracted from the plurality of propagation times, so that a decrease in the measurement accuracy of the ultrasonic propagation time is suppressed. The flow rate measurement unit 50 uses the specific propagation times Tabs, Tbas to calculate the flow rate Q of the fluid through which the ultrasonic wave propagates based on the above formulas (1) to (5), thereby improving the calculation accuracy of the flow rate Q.

[0042] Next, the ultrasonic flowmeter and measurement method of the present embodiment capable of suppressing a decrease in the measurement accuracy of the ultrasonic propagation time will be described in more detail.

[0043] FIG. 5 is a waveform diagram for explaining the propagation time Tab of ultrasonic waves from sensor 1 to sensor 2. FIG. 6 is a waveform diagram for explaining the propagation time Tba of ultrasonic waves from sensor 2 to sensor 1.

[0044] In FIGS. 5 and 6, sensor 1 corresponds to the ultrasonic probe 10a described above, and sensor 2 corresponds to the ultrasonic probe 10b described above. The transmission signal corresponds to the electrical signal d or the ultrasonic wave e described above, and the reception signal corresponds to the reception signal f or the received wave i described above. The trigger level corresponds to the threshold voltage V THLD described above, the trigger waveform corresponds to the specific vibration half-wave described above, and the zero-cross point corresponds to the zero-cross time point described above. t represents time.

[0045] In FIG. 5, in the case of transmitting ultrasonic waves from sensor 1 to sensor 2, the reception timing detection circuit 38 detects five zero-cross points at which the reception signal crosses the reference level (in this example, the zero level) after the reception signal crosses the trigger level. The time measurement unit 40 measures five propagation times Tab (UT1, UT2, UT3, UT4, UT5) from the transmission start time point of the transmission signal to each of the five zero-cross points (see FIG. 7). In FIGS. 5 and 7, UT1 (T 11 ) is the propagation time from the transmission start time point to the first zero-cross point. UT2 (T 11 +T 12 ) is the propagation time from the transmission start time point to the second zero-cross point. UT3 (T 11 +T 12 +T 13 ) is the propagation time from the transmission start time point to the third cross point. UT4 (T 11 +T 12 +T 13 +T 14 ) is the propagation time from the transmission start time point to the fourth cross point. UT5 (T 11 +T 12 +T 13 +T 14 +T 15 ) is the propagation time from the transmission start time point to the fifth cross point.

[0046] UT1, UT2, UT3, and UT4 are, respectively, an example of a first propagation time, an example of a second propagation time longer than the first propagation time, an example of a third propagation time longer than the second propagation time, and an example of a fourth propagation time longer than the third propagation time.

[0047] In FIG. 6, in the case of transmitting ultrasonic waves from sensor 2 to sensor 1, the reception timing detection circuit 38 detects five zero-crossing points at which the received signal crosses the reference level (in this example, the zero level) after the received signal crosses the trigger level. The time measurement unit 40 measures five propagation times Tba (DT1, DT2, DT3, DT4, DT5) from the transmission start time of the transmission signal to each of the five zero-crossing points (see FIG. 7). In FIGS. 6 and 7, DT1 (T 21 ) is the propagation time from the transmission start time to the first zero-crossing point. DT2 (T 21 +T 22 ) is the propagation time from the transmission start time to the second zero-crossing point. DT3 (T 21 +T 22 +T 23 ) is the propagation time from the transmission start time to the third crossing point. DT4 (T 21 +T 22 +T 23 +T 24 ) is the propagation time from the transmission start time to the fourth crossing point. DT5 (T 21 +T 22 +T 23 +T 24 +T 25 ) is the propagation time from the transmission start time to the fifth crossing point.

[0048] DT1, DT2, DT3, and DT4 are, respectively, an example of a fifth propagation time, an example of a sixth propagation time longer than the fifth propagation time, an example of a seventh propagation time longer than the sixth propagation time, and an example of an eighth propagation time longer than the seventh propagation time.

[0049] FIG. 8 is a waveform diagram for explaining the time shift of the trigger waveform. FIG. 9 is a flowchart exemplifying the flow of the propagation time determination process executed by the flow measurement unit 50. The propagation time determination process is periodically repeated. In this example, the flow measurement unit 50 uses the propagation time UT2 from the transmission start point to the second zero-crossing point as the reference propagation time, and determines an appropriate propagation time from among the five propagation times Tab (UT1, UT2, UT3, UT4, UT5). Similarly, in this example, the flow measurement unit 50 uses the propagation time DT2 from the transmission start point to the second zero-crossing point as the reference propagation time, and determines an appropriate propagation time from among the five propagation times Tba (DT1, DT2, DT3, DT4, DT5).

[0050] Note that in FIGS. 8 and 9, * represents U or D. FIGS. 8 and 9 are shared between the case of transmitting ultrasonic waves from sensor 1 to sensor 2 (* is U) and the case of transmitting ultrasonic waves from sensor 2 to sensor 1 (* is D). Also, the "reference value" shown in FIGS. 9 and 10 is an example of the above-mentioned reference propagation time Tr. Next, the process of FIG. 9 will be described with reference to FIG. 8.

[0051] Flow A of the propagation time determination process (FIG. 9) includes the processes of steps S11 to S15. In Flow A, the flow measurement unit 50 determines whether the difference between the currently measured propagation time *T2 and the reference value is within the first predetermined range (step S11). If the difference is within the first predetermined range, the flow measurement unit 50 determines *T2 as the true propagation time. Subsequently, the flow measurement unit 50 updates the reference value (step S12) and the previous value (step S13) to *T2. When the difference between the currently measured propagation time *T2 and the reference value is within the first predetermined range, the flow measurement unit 50 determines that there is no time shift between the currently measured propagation time *T2 and the reference value. The flow measurement unit 50 stores the currently measured five propagation times *T1, *T2, *T3, *T4, *T5 in five buffers *T1b, *T2b, *T3b, *T4b, *T5b, respectively (step S14). As a result, the true propagation time is stored in buffer *T2b. The flow measurement unit 50 clears the counter (step S15).

[0052] Note that the buffers UT1b, UT2b, and UT3b are, respectively, an example of the first buffer, an example of the second buffer, and an example of the third buffer. The buffers DT1b, DT2b, and DT3b are, respectively, an example of the fourth buffer, an example of the fifth buffer, and an example of the sixth buffer.

[0053] Flow B of the propagation time determination process (Fig. 9) includes the processes of steps S21 to S25. In Flow B, since the difference between the propagation time *T2 measured this time and the reference value is outside the first predetermined range, the flow rate measurement unit 50 determines whether the difference between the propagation time *T1 measured this time and the reference value is within the first predetermined range (step S21). If the difference is within the first predetermined range, the flow rate measurement unit 50 determines *T1 as the true propagation time. Subsequently, the flow rate measurement unit 50 updates the reference value (step S22) and the previous value (step S23) to *T1. If the difference between the propagation time *T1 measured this time and the reference value is within the first predetermined range, the flow rate measurement unit 50 determines that a time shift has been detected between the reference propagation time (*T2 in Fig. 8(a)) and the propagation time *T2 when the trigger waveform has moved backward (Fig. 8(b)). The flow rate measurement unit 50 shifts and stores the four propagation times *T1, *T2, *T3, and *T4 measured this time in the four buffers *T2b, *T3b, *T4b, and *T5b, respectively, and stores zero in the buffer *T1b (step S24). As a result, the true propagation time is stored in the buffer *T2b. The flow rate measurement unit 50 clears the counter (step S25).

[0054] The flow C of the propagation time determination process (Fig. 9) includes the processes of steps S31 to S35. In flow C, since the differences between the propagation time *T2 measured this time and the reference value and between the propagation time *T1 measured this time and the reference value are outside the first predetermined range, the flow measurement unit 50 determines whether the difference between the propagation time *T3 measured this time and the reference value is within the first predetermined range (step S31). If the difference is within the first predetermined range, the flow measurement unit 50 determines *T3 as the true propagation time. Subsequently, the flow measurement unit 50 updates the reference value (step S32) and the previous value (step S33) to *T3. If the difference between the propagation time *T3 measured this time and the reference value is within the first predetermined range, the flow measurement unit 50 determines that a time shift has been detected between the reference propagation time (*T2 in Fig. 8(a)) and the propagation time *T2 when the trigger waveform has moved forward (Fig. 8(c)). The flow measurement unit 50 shifts and stores the four propagation times *T2, *T3, *T4, *T5 measured this time in the four buffers *T1b, *T2b, *T3b, *T4b respectively, and stores zero in the buffer *T5b (step S34). As a result, the true propagation time is stored in the buffer *T2b. The flow measurement unit 50 clears the counter (step S35).

[0055] The flow D of the propagation time determination process (Fig. 9) includes the processes of steps S41 to S47. The flow D is a flow that is executed to determine a reference value, for example, when the flow measurement unit 50 is activated. The flow measurement unit 50 increments a counter by one (step 41). When the number of times the difference between the currently measured propagation time *T2 and the previous value is within the third predetermined range has continuously reached the specified number of times, the flow measurement unit 50 updates the reference value and the previous value to *T2. As a result, the reference value and the previous value are updated to a stable *T2. Specifically, the flow measurement unit 50 determines whether the difference between the currently measured propagation time *T2 and the previous value is within the third predetermined range (step S42). If the difference is within the third predetermined range, step S43 is executed. If the difference is outside the third predetermined range, step S45 is executed. When the difference is within the third predetermined range, the flow measurement unit 50 determines whether the counter is equal to or greater than the specified value. If the counter is equal to or greater than the specified value, the reference value is updated to *T2 (step S44). If the counter is less than the specified value, step S46 is executed. The flow measurement unit 50 clears the counter (step S45) and updates the previous value to *T2 (step S46). While passing through flow D, the flow measurement unit 50 stores zeros in five buffers *T1b, *T2b, *T3b, *T4b, and *T5b (step S47).

[0056] The propagation time determination process in FIG. 9 compares the currently measured propagation time with a reference value to detect a time shift of the trigger waveform forward or backward with respect to the reference waveform. Then, the propagation time determination process rearranges and stores the propagation times *T1, *T2, *T3, *T4, *T5 in the buffers *T1b, *T2b, *T3b, *T4b, *T5b to correct the time shift. As a result, the flow rate measurement unit 50 can store the true propagation time (the forward propagation time which is a specific propagation time Tabs) extracted from among the five propagation times Tab (UT1, UT2, UT3, UT4, UT5) in the buffer UT2b. Also, the flow rate measurement unit 50 can store the true propagation time (the reverse propagation time which is a specific propagation time Tbas) extracted from among the five propagation times Tba (DT1, DT2, DT3, DT4, DT5) in the buffer DT2b. The flow rate measurement unit 50 uses the forward propagation time stored in the buffer UT2b and the reverse propagation time stored in the buffer DT2b to calculate the flow rate Q of the fluid through which the ultrasonic wave propagates based on the above formulas (1) to (5), thereby improving the calculation accuracy of the flow rate Q.

[0057] Next, when the difference between the forward propagation time stored in the buffer UT2b and the reverse propagation time stored in the buffer DT2b is within a second predetermined range, a measurement method for calculating the flow rate Q using the reverse propagation time and the forward propagation time will be described with reference to FIG. 10. By this measurement method, a more optimal propagation time is extracted, and the calculation accuracy of the flow rate Q is further improved.

[0058] FIG. 10 is a flowchart illustrating the flow of the propagation time difference calculation process executed by the flow rate measurement unit 50. The propagation time difference calculation process is periodically repeated. The propagation time difference calculation process is executed following the propagation time determination process (FIG. 9), and after the end of the propagation time difference calculation process, the propagation time determination process is executed again. In the propagation time difference calculation process, the propagation time difference ΔT is calculated from the plurality of propagation times stored in a plurality of buffers in the propagation time determination process.

[0059] Flow E of the propagation time difference calculation process (Fig. 10) includes the processes of steps S51 to S52. In flow E, the flow rate measurement unit 50 determines whether the difference between the propagation time stored in buffer UT2b and the propagation time stored in buffer DT2b is within a second predetermined range (step S51). If the difference is within the second predetermined range, the flow rate measurement unit 50 determines that there is no time shift between the propagation time stored in buffer UT2b and the propagation time stored in buffer DT2b. The flow rate measurement unit 50 calculates the propagation time difference ΔT using the propagation time stored in buffer UT2b and the propagation time stored in buffer DT2b (step S52), and calculates the flow rate Q based on the above formulas (1) to (5).

[0060] Flow F of the propagation time difference calculation process (Fig. 10) includes the processes of steps S61 to S63. In flow F, since the difference between the propagation time stored in buffer UT2b and the propagation time stored in buffer DT2b is outside the second predetermined range, the flow rate measurement unit 50 determines whether the difference between the propagation time stored in buffer UT2b and the propagation time stored in buffer DT1b is within the second predetermined range (step S61). If the difference is within the second predetermined range, the flow rate measurement unit 50 determines that there is a time shift similar to the time shift between the reference propagation time (*T2 in Fig. 8(a)) and the propagation time *T2 when the trigger waveform moves backward (Fig. 8(b)) between the propagation time from sensor 1 to sensor 2 and the propagation time from sensor 2 to sensor 1. Therefore, the flow rate measurement unit 50 calculates the propagation time difference ΔT using the propagation time stored in buffer UT2b and the propagation time stored in buffer DT1b (step S62), and calculates the flow rate Q based on the above formulas (1) to (5). Subsequently, the flow rate measurement unit 50 updates the reference value to the propagation time stored in buffer DT1b. As a result, the accuracy of the reference value is improved.

[0061] The flow G of the propagation time difference calculation process (Fig. 10) includes the processes of steps S71 to S73. In flow G, since the difference between the propagation time stored in buffer UT2b and the propagation time stored in buffer DT1b is outside the second predetermined range, the flow measurement unit 50 determines whether the difference between the propagation time stored in buffer UT2b and the propagation time stored in buffer DT3b is within the second predetermined range (step S71). If the difference is within the second predetermined range, the flow measurement unit 50 determines that there is a time shift similar to the time shift between the reference propagation time (*T2 in Fig. 8(a)) and the propagation time *T2 when the trigger waveform moves forward (Fig. 8(c)) between the propagation time from sensor 1 to sensor 2 and the propagation time from sensor 2 to sensor 1. Therefore, the flow measurement unit 50 calculates the propagation time difference ΔT using the propagation time stored in buffer UT2b and the propagation time stored in buffer DT3b (step S72), and calculates the flow rate Q based on the above formulas (1) to (5). Subsequently, the flow measurement unit 50 updates the reference value to the propagation time stored in buffer DT3b. This improves the accuracy of the reference value.

[0062] The flow H of the propagation time difference calculation process (Fig. 10) includes the process of step S81. In flow H, the flow measurement unit 50 determines that there is a time shift of two wavelengths or more between the propagation time stored in buffer UT2b and the propagation time stored in buffer DT2b, clears the reference value to zero (step S81), and starts over from the flow D of the propagation time determination process (Fig. 9).

[0063] In the propagation time difference calculation process of Fig. 10, when there is a time shift between the propagation time stored in buffer UT2b and the propagation time stored in buffer DT2b (when the difference is outside the second predetermined range), the propagation time difference ΔT is calculated and the flow rate Q is calculated using the propagation time stored in DT1b or DT3b without using the propagation time stored in buffer DT2b.

[0064] According to the ultrasonic flowmeter and measurement method of the present embodiment, even when a time shift occurs in the trigger waveform of the received signal during flow measurement by the propagation time difference method, measurement anomalies can be prevented, and the optimal propagation time can be automatically determined from among the five propagation times, enabling the calculation of a highly accurate flow rate Q.

[0065] As described above, the embodiments have been explained. However, the above embodiments are presented as examples, and the present invention is not limited by the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, replacements, changes, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof.

[0066] The measurement method of the present embodiment is not limited to ultrasonic flowmeters and may be applied to devices that measure physical quantities of media through which ultrasonic waves propagate. For example, the measurement method of the present embodiment may be applied to other devices such as ultrasonic level gauges that measure the height level of fluids such as water levels using ultrasonic waves, and ultrasonic thickness gauges that measure the thickness of objects using ultrasonic waves.

Explanation of Reference Numerals

[0067] 10a, 10b Ultrasonic probes 11a, 11b Ultrasonic vibrators 12a, 12b Wedges 31 Transmitter 32 Receiver 33a, 33b Switches 35 Control unit 38 Received timing detection circuit 40 Time measurement unit 50 Flow measurement unit 100 Pipe 102 Fluid 110 Propagation path 300 Ultrasonic flowmeter

Claims

1. a time measurement unit that measures a plurality of propagation times from the start of transmission of the ultrasonic wave to each crossing time when the received signal crosses a reference level after the received signal of the ultrasonic wave crosses a threshold voltage; a flow rate measurement unit that calculates the flow rate of the fluid through which the ultrasonic wave propagates, and the plurality of propagation times when the ultrasonic wave transmitted from the first sensor is received by the second sensor include a second forward propagation time whose difference from a reference propagation time is within a first predetermined range, a first forward propagation time shorter than the second forward propagation time, and a third forward propagation time longer than the second forward propagation time; the plurality of propagation times when the ultrasonic wave transmitted from the second sensor is received by the first sensor include a reverse propagation time whose difference from the reference propagation time is within the first predetermined range; the flow rate measurement unit calculates the flow rate using a specific forward propagation time whose difference from the reverse propagation time is within a second predetermined range among the first forward propagation time, the second forward propagation time, and the third forward propagation time, and the reverse propagation time. An ultrasonic flow meter.

2. The ultrasonic flow meter according to claim 1, wherein the flow rate measurement unit updates the reference propagation time to the specific forward propagation time.

3. a time measurement unit that measures a plurality of propagation times from the start of transmission of the ultrasonic wave to each crossing time when the received signal crosses a reference level after the received signal of the ultrasonic wave crosses a threshold voltage; a flow rate measurement unit that calculates the flow rate of the fluid through which the ultrasonic wave propagates, and the plurality of propagation times when the ultrasonic wave transmitted from the first sensor is received by the second sensor include a first propagation time, a second propagation time longer than the first propagation time, a third propagation time longer than the second propagation time, and a fourth propagation time longer than the third propagation time; the plurality of propagation times when the ultrasonic wave transmitted from the second sensor is received by the first sensor include a fifth propagation time, a sixth propagation time longer than the fifth propagation time, a seventh propagation time longer than the sixth propagation time, and an eighth propagation time longer than the seventh propagation time; when the difference between the second propagation time and the reference propagation time is within a first predetermined range, the flow rate measurement unit stores the first propagation time, the second propagation time, and the third propagation time in a first buffer, a second buffer, and a third buffer. When the difference between the first propagation time and the reference propagation time is within the first predetermined range, the flow rate measurement unit stores zero, the first propagation time, and the second propagation time in the first buffer, the second buffer, and the third buffer. When the difference between the third propagation time and the reference propagation time is within the first predetermined range, the flow rate measurement unit stores the second propagation time, the third propagation time, and the fourth propagation time in the first buffer, the second buffer, and the third buffer. When the difference between the sixth propagation time and the reference propagation time is within the first predetermined range, the flow rate measurement unit stores the fifth propagation time, the sixth propagation time, and the seventh propagation time in the fourth buffer, the fifth buffer, and the sixth buffer. When the difference between the fifth propagation time and the reference propagation time is within the first predetermined range, the flow rate measurement unit stores zero, the fifth propagation time, and the sixth propagation time in the fourth buffer, the fifth buffer, and the sixth buffer. When the difference between the seventh propagation time and the reference propagation time is within the first predetermined range, the flow rate measurement unit stores the sixth propagation time, the seventh propagation time, and the eighth propagation time in the fourth buffer, the fifth buffer, and the sixth buffer. The flow rate measurement unit When the difference between the propagation time stored in the second buffer and the propagation time stored in the fifth buffer is within the second predetermined range, the flow rate is calculated using the propagation time stored in the second buffer and the propagation time stored in the fifth buffer. When the difference between the propagation time stored in the second buffer and the propagation time stored in the fourth buffer is within the second predetermined range, the flow rate is calculated using the propagation time stored in the second buffer and the propagation time stored in the fourth buffer. When the difference between the propagation time stored in the second buffer and the propagation time stored in the sixth buffer is within the second predetermined range, the flow rate is calculated using the propagation time stored in the second buffer and the propagation time stored in the sixth buffer. An ultrasonic flow meter.

4. The flow rate measurement unit When the difference between the propagation time stored in the second buffer and the propagation time stored in the fourth buffer is within the second predetermined range, the reference propagation time is updated to the propagation time stored in the fourth buffer. When the difference between the propagation time stored in the second buffer and the propagation time stored in the sixth buffer is within the second predetermined range, update the reference propagation time to the propagation time stored in the sixth buffer. The ultrasonic flowmeter according to claim 3.

5. Measure a plurality of propagation times from the time when the transmission of the ultrasonic wave starts until each crossing time when the received signal crosses the reference level after the received signal of the ultrasonic wave crosses the threshold voltage. When the ultrasonic wave transmitted from the first sensor is received by the second sensor, the plurality of propagation times include a second forward propagation time whose difference from the reference propagation time is within the first predetermined range, a first forward propagation time shorter than the second forward propagation time, and a third forward propagation time longer than the second forward propagation time. When the ultrasonic wave transmitted from the second sensor is received by the first sensor, the plurality of propagation times include a reverse propagation time whose difference from the reference propagation time is within the first predetermined range. A measurement method for calculating a physical quantity of a medium through which the ultrasonic wave propagates, using a specific forward propagation time and the reverse propagation time, among the first forward propagation time, the second forward propagation time, and the third forward propagation time, whose difference from the reverse propagation time is within the second predetermined range.

6. Measure a plurality of propagation times from the time when the transmission of the ultrasonic wave starts until each crossing time when the received signal crosses the reference level after the received signal of the ultrasonic wave crosses the threshold voltage. When the ultrasonic wave transmitted from the first sensor is received by the second sensor, the plurality of propagation times include a first propagation time, a second propagation time longer than the first propagation time, a third propagation time longer than the second propagation time, and a fourth propagation time longer than the third propagation time. When the ultrasonic wave transmitted from the second sensor is received by the first sensor, the plurality of propagation times include a fifth propagation time, a sixth propagation time longer than the fifth propagation time, a seventh propagation time longer than the sixth propagation time, and an eighth propagation time longer than the seventh propagation time. When the difference between the second propagation time and the reference propagation time is within the first predetermined range, store the first propagation time, the second propagation time, and the third propagation time in the first buffer, the second buffer, and the third buffer. When the difference between the first propagation time and the reference propagation time is within the first predetermined range, zero, the first propagation time, and the second propagation time are stored in the first buffer, the second buffer, and the third buffer. When the difference between the third propagation time and the reference propagation time is within the first predetermined range, the second propagation time, the third propagation time, and the fourth propagation time are stored in the first buffer, the second buffer, and the third buffer. When the difference between the sixth propagation time and the reference propagation time is within the first predetermined range, the fifth propagation time, the sixth propagation time, and the seventh propagation time are stored in the fourth buffer, the fifth buffer, and the sixth buffer. When the difference between the fifth propagation time and the reference propagation time is within the first predetermined range, zero, the fifth propagation time, and the sixth propagation time are stored in the fourth buffer, the fifth buffer, and the sixth buffer. When the difference between the seventh propagation time and the reference propagation time is within the first predetermined range, the sixth propagation time, the seventh propagation time, and the eighth propagation time are stored in the fourth buffer, the fifth buffer, and the sixth buffer. When the difference between the propagation time stored in the second buffer and the propagation time stored in the fifth buffer is within the second predetermined range, the physical quantity of the medium through which the ultrasonic wave propagates is calculated using the propagation time stored in the second buffer and the propagation time stored in the fifth buffer. When the difference between the propagation time stored in the second buffer and the propagation time stored in the fourth buffer is within the second predetermined range, the physical quantity of the medium is calculated using the propagation time stored in the second buffer and the propagation time stored in the fourth buffer. A measurement method for calculating the physical quantity of the medium using the propagation time stored in the second buffer and the propagation time stored in the sixth buffer when the difference between the propagation time stored in the second buffer and the propagation time stored in the sixth buffer is within the second predetermined range.

7. The measurement method according to claim 5 or 6, wherein the physical quantity of the medium is the flow rate of the fluid through which the ultrasonic wave propagates.

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