Ultrasonic flowmeter and flow rate calculation method

Abstract

To enable an increase in current consumption to be avoided while maintaining measurement accuracy more than conventionally possible.SOLUTION: The present invention comprises: a received signal acquisition unit 401 for acquiring a received signal which is received by an ultrasonic sensor 2; a received signal acquisition unit 402 for acquiring a received signal which is received by an ultrasonic sensor 3; and a drive wavenumber control unit 407 for controlling the drive wavenumber of ultrasonic wave transmission by a pair of ultrasonic sensors 2, 3, on the basis of acquisition results by the received signal acquisition unit 401 and the received signal acquisition unit 402. When the drive wavenumber of ultrasonic wave transmission by the ultrasonic sensor 3 is increased by the drive wavenumber control unit 407, a zero-cross point measurement unit 403 measures the duration of the first-half zero-cross point and then, after temporarily stopping measurement, measures the duration of the latter-half zero-cross point. When the drive wavenumber of ultrasonic wave transmission by the ultrasonic sensor 2 is increased by the drive wavenumber control unit 407, a zero-cross point measurement unit 404 measures the duration of the first-half zero-cross point and then, after temporarily stopping measurement, measures the duration of the latter-half zero-cross point.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an ultrasonic flowmeter that measures a flow rate by using ultrasonic waves and a flow rate calculation method. [Background technology]

[0002] 2. Description of the Related Art Conventionally, ultrasonic flowmeters are known that measure the flow rate of a fluid to be measured based on the difference in propagation time between ultrasonic waves transmitted and received by a pair of ultrasonic sensors. Known as such an ultrasonic flow meter is a zero-crossing ultrasonic flow meter, which detects a predetermined number of zero-crossing points of a received signal after the received signal exceeds a threshold, measures the propagation time of ultrasonic waves to the detected zero-crossing points, and calculates the flow rate of a fluid based on the measured propagation time.

[0003] In such ultrasonic flowmeters, when measuring the transit time difference, a measurement error may occur due to the influence of the strength of the received signal or electrical noise received by the receiving circuit.

[0004] In the actual usage environment of an ultrasonic flowmeter, fluctuations in power supply voltage, deterioration of the device, ambient temperature, changes in the composition of the fluid to be measured, etc. are assumed, and the strength of the ultrasonic transmission and reception signals changes depending on these external factors. In addition, depending on the installation environment, the measurement signal may be affected by electrical noise, and the signal-to-noise ratio is not constant.

[0005] In particular, when it is necessary to operate the device for a long period of time using batteries, it is required to maintain measurement accuracy while also saving power.

[0006] In response to this, Patent Document 1 discloses an ultrasonic flowmeter having a measurement circuit that measures the propagation time of transmission from upstream to downstream or downstream to upstream, a fluid discrimination means that determines the type of fluid in the flow path, and a circuit constant correction means that changes the constant of the measurement circuit according to the value of the fluid discrimination means. This ultrasonic flowmeter can measure the flow rate with high accuracy by maintaining the state of the measurement device appropriately in accordance with changes in the fluid.

[0007] Patent Document 2 shows an ultrasonic flowmeter that includes a repeating means for retransmitting ultrasonic waves after receiving them, a timer means for measuring the accumulated time during the repeated transmission from upstream to downstream or from downstream to upstream, and a number setting means for changing the number of times the repeating means is performed according to the signal level of the receiver. This ultrasonic flowmeter changes the number of times the repeating is performed according to the ultrasonic reception sensitivity, making it possible to measure the flow rate with high accuracy. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 4292620 [Patent Document 2] Patent No. 4362890 Summary of the Invention [Problem to be solved by the invention]

[0009] In the ultrasonic flowmeter disclosed in Patent Document 1, in a situation where a fluid with low reception sensitivity is expected, the reception sensitivity is increased by increasing the driving wave number of ultrasonic transmission, thereby improving the measurement accuracy of the flow rate. However, in this ultrasonic flowmeter, no consideration is given to a method for dealing with the increase in reception time and current consumption that accompanies an increase in the driving wave number of ultrasonic transmission. In addition, in this ultrasonic flowmeter, no consideration is given to an increase in measurement error of the propagation time difference due to a difference in sensor characteristics caused by increasing the driving wave number.

[0010] In addition, the ultrasonic flowmeter disclosed in Patent Document 2 aims to improve accuracy by increasing the number of transmissions and receptions when the signal level drops, using the strength of the received signal as an index. However, this ultrasonic flowmeter has problems with the startup of the measurement circuit due to the increase in the number of transmissions and receptions, and the increase in current consumption proportional to the number of data transmissions.

[0011] Here, when aiming for power saving, it is particularly important to reduce the number of times ultrasonic waves are transmitted and received per unit time, and to shorten the operating time of the receiving circuit for each transmission and reception operation. Also, in order to improve the measurement accuracy, it is possible to perform reception in a state where the signal-to-noise ratio is high, or to increase the number of transmissions and receptions, etc. However, increasing the operating time and number of operations of the receiving circuit leads to an increase in current consumption. Furthermore, when the driving wave number of ultrasonic transmission is increased, the amplitude of the latter half of the received signal increases, improving the signal-to-noise ratio. However, the influence of the characteristic differences and individual differences of the ultrasonic sensors tends to become significant, and measurement errors depending on temperature or individual differences of the ultrasonic sensors become a problem.

[0012] An example of the relationship between the signal-to-noise ratio and noise in an ultrasonic flowmeter will be described with reference to Fig. 10. Fig. 10 shows a case where time measurements of three zero crossing points (ZC1 to ZC3) are performed. Figure 10A shows the time measurement of the zero crossing point when the signal-to-noise ratio is high. As shown in Figure 10A, when the signal-to-noise ratio is high, the noise is small and the transmission and reception strength of the ultrasonic waves is high. In other words, in this case, the random variation (random error) due to noise contained in the measurement value is small. On the other hand, Fig. 10B shows the time measurement of the zero crossing point when the signal-to-noise ratio is low. As shown in Fig. 10B, when the signal-to-noise ratio is low, the noise is large and the transmission and reception strength of the ultrasonic waves is low. That is, in this case, the random variation (random error) due to the noise contained in the measurement value is large. Therefore, in the case of Fig. 10B, the measurement value of the time of the zero crossing point varies randomly due to the influence of noise.

[0013] The present invention has been made to solve the above-mentioned problems, and has an object to provide an ultrasonic flowmeter that can avoid an increase in current consumption while maintaining the measurement accuracy as compared to conventional flowmeters. [Means for solving the problem]

[0014] The ultrasonic flowmeter according to the present invention includes a first reception signal acquisition unit that acquires a reception signal received by one of a pair of ultrasonic sensors that transmit and receive ultrasonic waves, a second reception signal acquisition unit that acquires a reception signal received by the other of the ultrasonic sensors, a first zero-cross point measurement unit that measures a time from the start of transmission to a zero-cross point a plurality of times for each of a plurality of unit measurement steps based on a result acquired by the first reception signal acquisition unit, a second zero-cross point measurement unit that measures a time from the start of transmission to a zero-cross point a plurality of times for each of a plurality of unit measurement steps based on a result acquired by the second reception signal acquisition unit, a time difference calculation unit that calculates a time difference between a measurement result by the first zero-cross point measurement unit and a measurement result by the second zero-cross point measurement unit, and a time difference calculation unit that calculates a time difference between a measurement result by the first zero-cross point measurement unit and a measurement result by the second zero-cross point measurement unit. The device is equipped with a flow rate calculation unit that calculates the flow rate of the fluid to be measured based on the calculation result by the calculation unit, and a drive wave number control unit that controls the drive wave number of ultrasonic transmission in a pair of ultrasonic sensors based on the acquisition results by the first received signal acquisition unit and the second received signal acquisition unit, wherein when the drive wave number control unit increases the drive wave number of ultrasonic transmission in the other ultrasonic sensor, the first zero cross point measurement unit measures the time of the first zero cross point, pauses the measurement, and then measures the time of the second zero cross point, when the drive wave number control unit increases the drive wave number of ultrasonic transmission in one ultrasonic sensor, the second zero cross point measurement unit measures the time of the first zero cross point, pauses the measurement, and then measures the time of the second zero cross point. Effect of the Invention

[0015] According to the present invention, since it is configured as described above, it is possible to avoid an increase in current consumption while maintaining the measurement accuracy as compared with the conventional art. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram illustrating a configuration example of an ultrasonic flowmeter according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of the configuration of a calculation unit according to the first embodiment. [Diagram 3]5 is a flowchart showing an example of drive wave number control by a calculation unit in the first embodiment. [Figure 4] 5 is a flowchart showing an example of a flow rate calculation operation by a calculation unit in the first embodiment. [Diagram 5] 5A and 5B are diagrams showing a specific example (state before drive wave number control) of the operation of the calculation unit in embodiment 1, where FIG. 5A shows the received waveform of ultrasonic waves and FIG. 5B shows the transmitted waveform of ultrasonic waves. [Figure 6] 6A and 6B are diagrams showing a specific example (state after drive wave number control) of the operation of the calculation unit in embodiment 1, where FIG. 6A shows the received waveform of ultrasonic waves and FIG. 6B shows the transmitted waveform of ultrasonic waves. [Figure 7] FIG. 11 is a diagram illustrating an example of the configuration of a calculation unit in the second embodiment. [Figure 8] 13 is a flowchart showing an example of a flow rate calculation operation by a calculation unit in the second embodiment. [Figure 9] FIG. 13 is a diagram for explaining the drift of the zero point due to the time difference between each zero crossing point. [Figure 10] 10A and 10B are diagrams showing an example of the relationship between the signal-to-noise ratio and noise in an ultrasonic flowmeter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Embodiment 1 FIG. 1 is a diagram showing a configuration example of an ultrasonic flowmeter according to a first embodiment. An ultrasonic flowmeter measures a fluid by using ultrasonic waves. This ultrasonic flowmeter includes a measuring tube 1, ultrasonic sensors 2 and 3, and a calculation unit 4, as shown in FIG.

[0018] The measuring tube 1 is a cylindrical member through which a fluid to be measured flows.

[0019] The ultrasonic sensor 2 is an ultrasonic transducer that is attached to the upstream side of the side wall of the measurement pipe 1 and transmits and receives ultrasonic waves between it and the ultrasonic sensor 3 inside the measurement pipe 1. That is, the ultrasonic sensor 2 transmits ultrasonic waves to the downstream side (ultrasonic sensor 3) inside the measurement pipe 1, and receives ultrasonic waves from the downstream side (ultrasonic sensor 3) as a reception signal.

[0020] The ultrasonic sensor 3 is an ultrasonic transducer that is attached to the downstream side of the side wall of the measurement pipe 1 and transmits and receives ultrasonic waves between it and the ultrasonic sensor 2 within the measurement pipe 1. That is, the ultrasonic sensor 3 transmits ultrasonic waves to the upstream side (ultrasonic sensor 2) within the measurement pipe 1, and receives ultrasonic waves from the upstream side (ultrasonic sensor 2) as a reception signal.

[0021] The positional relationship between the ultrasonic sensors 2 and 3 is designed according to the propagation paths of the ultrasonic waves used by the ultrasonic sensors 2 and 3.

[0022] The calculation unit 4 calculates the flow rate of the fluid in the measuring pipe 1 based on the results of transmission and reception by the ultrasonic sensor 2 and the results of transmission and reception by the ultrasonic sensor 3.

[0023] As shown in FIG. 2, this calculation unit 4 includes a received signal acquisition unit (first received signal acquisition unit) 401, a received signal acquisition unit (second received signal acquisition unit) 402, a zero cross point measurement unit (first zero cross point measurement unit) 403, a zero cross point measurement unit (second zero cross point measurement unit) 404, a time difference calculation unit 405, a flow rate calculation unit 406, and a drive wave number control unit 407.

[0024] The calculation unit 4 is realized by a processing circuit such as an integrated circuit (IC) or a system large scale integration (LSI), or a central processing unit (CPU) that executes a program stored in a memory or the like.

[0025] The received signal acquisition unit 401 acquires a received signal received by the ultrasonic sensor 2. The received signal acquisition unit 401 has a function of amplifying the received signal acquired from the ultrasonic sensor 2 (an amplifier).

[0026] The received signal acquisition unit 402 acquires the received signal received by the ultrasonic sensor 3. The received signal acquisition unit 402 has a function of amplifying the received signal acquired from the ultrasonic sensor 3 (an amplifier).

[0027] The zero-crossing point measuring unit 403 measures the time from the start of transmission to the zero-crossing point multiple times based on the acquisition result by the received signal acquiring unit 401. The zero-crossing point measuring unit 403 performs the above process for each of the multiple received signals (each unit measurement step). As shown in FIG. 5, for example, a zero-cross point is a point at which the strength of a received signal becomes zero after the start of reception and the strength of the received signal exceeds a threshold (threshold voltage). Usually, the zero-cross point is measured at a point between the start of reception of the received signal and the point at which the received signal has a maximum amplitude. In FIG. 5, FIG. 5B shows a transmission waveform of an ultrasonic wave, and FIG. 5A shows a reception waveform of the ultrasonic wave (waveform of the received signal). Also, in FIG. 5, reference numeral 51 indicates a zero-cross point. Also, the number of zero-cross points at which the zero-cross point measurement unit 403 measures time in one unit measurement step is set in advance. Also, the number of unit measurement steps is set in advance. The zero-crossing point measuring unit 403 has a function (comparator) of comparing the received signal (amplified received signal) acquired by the received signal acquiring unit 401 with a threshold value.

[0028] Furthermore, when the drive wave number control unit 407 increases the drive wave number of ultrasonic transmissions in the ultrasonic sensor 3, the zero-cross point measurement unit 403 measures the time of the first half zero-cross point (first half zero-cross point), pauses the measurement, and then measures the time of the second half zero-cross point (second half zero-cross point). The pause time is set based on the frequency and drive wave number of the ultrasonic waves transmitted by the ultrasonic sensor 3.

[0029] In addition, the first half zero crossing point refers to one or more zero crossing points that are close to the reception start point when multiple zero crossing points that occur from the reception start point of the received signal to the point where the received signal has the maximum amplitude are arranged in chronological order. In addition, the latter zero crossing point refers to one or more zero crossing points that are farther from the reception start point when multiple zero crossing points that occur from the reception start point of the received signal to the point where the received signal has the maximum amplitude are arranged in chronological order, and is a zero crossing point that occurs after the first zero crossing point.

[0030] The zero-crossing point measuring unit 404 measures the time from the start of transmission to the zero-crossing point multiple times based on the acquisition result by the received signal acquiring unit 402. The zero-crossing point measuring unit 404 performs the above process for each of the multiple received signals (each unit measurement step). The number of zero crossing points at which the zero crossing point measuring section 404 measures time in one unit measurement step is set in advance, and the number of unit measurement steps is also set in advance. The zero-crossing point measuring unit 404 has a function (comparator) of comparing the received signal (amplified received signal) acquired by the received signal acquiring unit 402 with a threshold value.

[0031] Furthermore, when the drive wave number control unit 407 increases the drive wave number of ultrasonic transmissions in the ultrasonic sensor 2, the zero-cross point measurement unit 404 measures the time of the first half zero-cross point (first half zero-cross point), pauses the measurement, and then measures the time of the second half zero-cross point (second half zero-cross point). The pause time is set based on the frequency and drive wave number of the ultrasonic waves transmitted by the ultrasonic sensor 2.

[0032] The operations of the received signal acquisition units 401 and 402 and the zero-crossing point measurement units 403 and 404 can be realized by one circuit system. In other words, the above operations can be realized by switching the connection between the above circuits and the ultrasonic sensors 2 and 3 depending on whether transmission and reception is in the forward direction or the reverse direction.

[0033] Time difference calculation unit 405 calculates the time difference between the measurement result by zero cross point measurement unit 403 and the measurement result by zero cross point measurement unit 404. At this time, first, time difference calculation unit 405 calculates an average value by averaging the measurement results in each unit measurement step by zero cross point measurement unit 403 for each zero cross point. Similarly, time difference calculation unit 405 calculates an average value by averaging the measurement results in each unit measurement step by zero cross point measurement unit 404 for each zero cross point. Then, time difference calculation unit 405 calculates the difference between the above two average values ​​for each zero cross point, thereby calculating the time difference at each zero cross point.

[0034] Flow rate calculation unit 406 calculates the flow rate of the fluid in measuring pipe 1 based on the calculation result by time difference calculation unit 405. The operating principle of flow rate calculation unit 406 can adopt the conventional flow rate calculation principle, and the description thereof will be omitted.

[0035] The drive wave number control unit 407 controls the drive wave number of ultrasonic transmission in the ultrasonic sensor 2 and the ultrasonic sensor 3. When the strength of the received signal acquired by the received signal acquisition unit 401 becomes equal to or lower than a threshold or when noise becomes equal to or higher than a threshold, the drive wave number control unit 407 controls the ultrasonic sensor 3 to increase the drive wave number of ultrasonic transmission in the ultrasonic sensor 3. In addition, when the strength of the received signal acquired by the received signal acquisition unit 402 becomes equal to or lower than a threshold or when noise becomes equal to or higher than a threshold, the drive wave number control unit 407 controls the ultrasonic sensor 2 to increase the drive wave number of ultrasonic transmission in the ultrasonic sensor 2.

[0036] Next, an example of the operation of the calculation unit 4 in the first embodiment shown in FIG. 2 will be described. First, an example of drive wave number control by the calculation unit 4 in the first embodiment shown in FIG. 2 will be described with reference to FIG.

[0037] In the example of driving wave number control by the calculation unit 4 in the first embodiment shown in FIG. 2, first, as shown in FIG. 3, the received signal acquisition unit 401 acquires a received signal received by the ultrasonic sensor 2 (step ST301).

[0038] Next, the driving wave number control unit 407 determines whether the strength of the received signal acquired by the received signal acquisition unit 401 is equal to or less than a threshold or whether the noise is equal to or greater than a threshold (step ST302).

[0039] In this step ST302, if the driving wave number control section 407 determines that the intensity is greater than the threshold and the noise is less than the threshold, the sequence returns to step ST301. On the other hand, in step ST302, if the drive wave number control unit 407 determines that the intensity is below the threshold value or that the noise is above the threshold value, it controls the ultrasonic sensor 3 to increase the drive wave number for transmitting ultrasonic waves from the ultrasonic sensor 3 (step ST303).

[0040] Note that, in the above, an example of operation in which the drive wave number control unit 407 controls the drive wave number of ultrasonic transmission in the ultrasonic sensor 3 has been described, but an example of operation in which the drive wave number of ultrasonic transmission in the ultrasonic sensor 2 is controlled is also similar to the above, except that the received signal acquired by the received signal acquisition unit 402 is used.

[0041] Next, an example of the flow rate calculation operation by the calculation unit 4 in the first embodiment shown in FIG. 2 will be described with reference to FIG.

[0042] In the example of the flow rate calculation operation by the calculation unit 4 in the first embodiment shown in FIG. 2, first, as shown in FIG. 4, the received signal acquisition unit 401 and the received signal acquisition unit 402 acquire a received signal (step ST401). That is, the received signal acquisition unit 401 acquires the received signal received by the ultrasonic sensor 2 . Similarly, the received signal acquisition unit 402 acquires the received signal received by the ultrasonic sensor 3 .

[0043] Next, zero-crossing point measuring section 403 and zero-crossing point measuring section 404 measure the time from the start of transmission to the zero-crossing point multiple times for each unit measurement step (step ST402). That is, for each unit measurement step, the zero-cross point measurement unit 403 measures the time from the start of transmission to the zero-cross point multiple times based on the acquisition result by the received signal acquisition unit 401. When the drive wave number control unit 407 increases the drive wave number of ultrasonic transmission in the ultrasonic sensor 3, the zero-cross point measurement unit 403 measures the time of the first half zero-cross point, pauses the measurement, and then measures the time of the second half zero-cross point. In this way, when the drive wave number of ultrasonic transmission is increased, the zero-cross point measurement unit 404 uses the part of the received signal with a large amplitude for the second half zero-cross point, thereby improving the signal-to-noise ratio. Similarly, the zero-cross point measurement unit 404 measures the time from the start of transmission to the zero-cross point multiple times for each unit measurement step, based on the acquisition result by the received signal acquisition unit 402. When the drive wave number control unit 407 increases the drive wave number of ultrasonic transmission in the ultrasonic sensor 2, the zero-cross point measurement unit 404 measures the time of the first half zero-cross point, pauses the measurement, and then measures the time of the second half zero-cross point. In this way, when the drive wave number of ultrasonic transmission is increased, the zero-cross point measurement unit 404 uses the part of the received signal with a large amplitude for the second half zero-cross point, thereby improving the signal-to-noise ratio.

[0044] It is preferable that the zero-crossing point measuring unit 403 and the zero-crossing point measuring unit 404 use the same position as the starting point of the time measurement and the first half zero-crossing point regardless of the presence or absence of a pause. As a method for specifying the same position as the starting point of the time measurement and the first half zero-crossing point, for example, the method disclosed in Patent Document 3 can be mentioned, but is not limited to this. [Patent Document 3] JP 2020-63972 A

[0045] 5 shows a case where the zero-cross point measuring section 403 and the zero-cross point measuring section 404 measure the times of 10 zero-cross points in one unit measurement process. The number of unit measurement processes is, for example, 31.

[0046] The time of the m-th zero cross point in the k-th unit measurement step measured by the zero cross point measuring section 403 is represented as ZCm(k). Moreover, the time of the m-th zero cross point in the k-th unit measurement step measured by the zero cross point measuring section 404 is represented as inverse ZCm(k).

[0047] Next, time difference calculation unit 405 calculates the time difference (ZCmΔt) between the measurement result by zero-cross point measurement unit 403 and the measurement result by zero-cross point measurement unit 404 as shown in the following equation (1) (step ST403). At this time, first, time difference calculation unit 405 calculates an average value by averaging the measurement results in each unit measurement step by zero-cross point measurement unit 403 for each zero-cross point. Similarly, time difference calculation unit 405 calculates an average value by averaging the measurement results in each unit measurement step by zero-cross point measurement unit 404 for each zero-cross point. Then, time difference calculation unit 405 calculates the difference between the above two average values ​​for each zero-cross point, thereby calculating the time difference at each zero-cross point. ZCmΔt=(ΣReverse ZCm(k) / k)-(ΣOrder ZCm(k) / k) (1)

[0048] Next, the flow rate calculation unit 406 calculates the flow rate of the fluid in the measuring pipe 1 based on the calculation result by the time difference calculation unit 405 (step ST404). At this time, when using a conventional method, for example, the flow rate calculation unit 406 can calculate the flow rate of the fluid based on the time difference (Δt) calculated according to the following formula (2). Δt=ΣZCmΔt / m (2)

[0049] In this way, in the ultrasonic flowmeter according to the first embodiment, when the strength of the received signal falls below the threshold or when the noise exceeds the threshold, the driving wave number of ultrasonic transmission is increased in the transmitting ultrasonic sensor of the ultrasonic sensors 2 and 3. Then, in the ultrasonic flowmeter according to the first embodiment, after the time measurement of the first half zero cross point is completed during reception, the measurement is temporarily stopped and a predetermined period has elapsed, after which the time measurement of the second half zero cross point is performed.

[0050] During the measurement pause, the ultrasonic flowmeter according to embodiment 1 stops recording data indicating the time of the zero-crossing point in a memory (not shown) and stops supplying current to the receiving circuit (amplifier, comparator, power supply circuit, etc.), thereby making it possible to reduce current consumption.

[0051] Next, a specific example of the operation of the calculation unit 4 in the embodiment 1 shown in Fig. 2 will be described with reference to Figs. 5 and 6. Figs. 5 and 6 show a case where the calculation unit 4 measures four first-half zero-crossing points and six second-half zero-crossing points. In Figs. 5 and 6, reference numeral 52 indicates a measurement period of the first-half zero-crossing points, and reference numeral 53 indicates a measurement period of the second-half zero-crossing points. Note that the numbers of zero-crossing points and wave numbers in Figs. 5 and 6 are merely examples.

[0052] Fig. 5 shows the state before the drive wave number control (in the case of normal measurement operation). Fig. 5A shows the received waveform of the ultrasonic wave (waveform of the received signal), and Fig. 5B shows the transmitted waveform of the ultrasonic wave. As shown in Fig. 5B, the ultrasonic wave is a rectangular wave with a wave number of 5 waves. In this case, as shown in FIG. 5A, the calculation unit 4 measures the time of the first half zero crossing point and the time of the second half zero crossing point without pausing the measurement midway.

[0053] In contrast to Fig. 5, Fig. 6 shows the state after drive wave number control (in the case of measurement operation in a low signal state). Fig. 6A shows the received waveform of the ultrasonic wave (waveform of the received signal), and Fig. 6B shows the transmitted waveform of the ultrasonic wave. As shown in Fig. 6B, six waves have been added to the five waves before drive wave number control, making the ultrasonic wave a rectangular wave with 11 waves. In this case, as shown in Fig. 6A, the calculation unit 4 first measures the time of the first half zero crossing point, as in the case before the drive wave number control. Immediately after that, the calculation unit 4 pauses the measurement for a predetermined time. The pause time at this time is, for example, a period corresponding to the increase in the drive wave number. In Fig. 6, six waves are added to the wave number, so the pause time is six periods. Thereafter, the calculation unit 4 resumes the measurement and measures the time of the second half zero crossing point. In Fig. 6, reference numeral 61 indicates a pause period.

[0054] In this way, in the ultrasonic flowmeter according to the first embodiment, when the signal-to-noise ratio is reduced and a large error occurs, the driving wave number of ultrasonic transmission is increased to improve the measurement accuracy, and after measuring the time of the zero-cross point immediately after ultrasonic reception, which is less affected by systematic errors, the measurement is paused for a predetermined time, and measurement of the time of the zero-cross point is resumed after a large-amplitude signal, which has a high signal-to-noise ratio and is less affected by accidental errors, arrives. As a result, the ultrasonic flowmeter according to the first embodiment can achieve both reduced current consumption and improved measurement accuracy.

[0055] As described above, according to the first embodiment, the ultrasonic flowmeter includes a received signal acquisition unit 401 that acquires a received signal received by the ultrasonic sensor 2 of the pair of ultrasonic sensors 2, 3 that transmit and receive ultrasonic waves, a received signal acquisition unit 402 that acquires a received signal received by the ultrasonic sensor 3, a zero-cross point measurement unit 403 that measures the time from the start of transmission to the zero-cross point multiple times for each of multiple unit measurement steps based on the acquisition results by the received signal acquisition unit 401, a zero-cross point measurement unit 404 that measures the time from the start of transmission to the zero-cross point multiple times for each of multiple unit measurement steps based on the acquisition results by the received signal acquisition unit 402, a time difference calculation unit 405 that calculates the time difference between the measurement results by the zero-cross point measurement unit 403 and the measurement results by the zero-cross point measurement unit 404, and a time difference calculation unit 406 that calculates the time difference between the measurement results by the zero-cross point measurement unit 403 and the measurement results by the zero-cross point measurement unit 404. The flow rate calculation unit 406 calculates the flow rate of the fluid to be measured based on the calculation result by the output unit 405, and the drive wave number control unit 407 controls the drive wave number of ultrasonic transmission in the pair of ultrasonic sensors 2 and 3 based on the acquisition results by the reception signal acquisition unit 401 and the reception signal acquisition unit 402. When the drive wave number control unit 407 increases the drive wave number of ultrasonic transmission in the ultrasonic sensor 3, the zero cross point measurement unit 403 measures the time of the first zero cross point, pauses the measurement, and then measures the time of the second zero cross point. When the drive wave number control unit 407 increases the drive wave number of ultrasonic transmission in the ultrasonic sensor 2, the zero cross point measurement unit 404 measures the time of the first zero cross point, pauses the measurement, and then measures the time of the second zero cross point. As a result, the ultrasonic flowmeter according to the first embodiment can avoid an increase in current consumption while maintaining the measurement accuracy compared to the conventional one.

[0056] Embodiment 2 In the ultrasonic flowmeter according to the second embodiment, a method for reducing errors due to temperature or individual differences of the ultrasonic sensors 2 and 3 that tend to occur when the driving wave number for ultrasonic transmission in the ultrasonic sensors 2 and 3 is increased will be described.

[0057] Fig. 7 is a diagram showing an example of the configuration of the calculation unit 4 in embodiment 2. In the calculation unit 4 in embodiment 2 shown in Fig. 7, an average value calculation unit (first average value calculation unit) 408, an average value calculation unit (second average value calculation unit) 409, and a difference calculation unit 410 are added to the calculation unit 4 in embodiment 1 shown in Fig. 2, and the processing of the flow rate calculation unit 406 is changed. The other example of the configuration of the calculation unit 4 in embodiment 2 shown in Fig. 7 is similar to the example of the configuration of the calculation unit 4 in embodiment 1 shown in Fig. 2, and the same reference numerals are used and only the different parts will be described.

[0058] Based on the calculation result by time difference calculation section 405, average value calculation section 408 calculates the average value of the time differences at the first half zero crossing points.

[0059] Based on the calculation result by time difference calculation section 405, average value calculation section 409 calculates the average value of the time differences at the latter half zero crossing points.

[0060] The difference calculation section 410 calculates the difference between the average value calculated by the average value calculation section 408 and the average value calculated by the average value calculation section 409 as a correction value.

[0061] Flow rate calculation unit 406 calculates the flow rate of the fluid in measuring pipe 1 based on the calculation result by time difference calculation unit 405 and the calculation result by difference calculation unit 410. At this time, flow rate calculation unit 406 first corrects the time difference calculated by time difference calculation unit 405 with the correction value calculated by difference calculation unit 410. Then, flow rate calculation unit 406 calculates the flow rate of the fluid based on the time difference corrected with the correction value (corrected time difference). The operating principle of flow rate calculation unit 406 can adopt the conventional flow rate calculation principle except for using the corrected time difference, and a description thereof will be omitted.

[0062] Next, an example of the flow rate calculation operation by the calculation unit 4 in the second embodiment shown in FIG. 7 will be described with reference to FIG. Here, the pair of ultrasonic sensors 2, 3 have a phenomenon in which the zero point of the time difference (propagation time difference) used in the fluid measurement drifts with temperature due to differences in sensor characteristics. If the fluctuation width of this drift is within a predetermined range, the measurement accuracy of the ultrasonic flowmeter is satisfied. On the other hand, as shown in Figure 9, when the time difference used in the above flow measurement is broken down into zero crossing points, it can be seen that the later the zero crossing point on the time axis is, the greater the influence of temperature change.

[0063] In flow rate measurement using an ultrasonic flowmeter, if only the time difference of the first zero crossing point is used, the systematic error (such as zero point drift due to temperature change) will be small, but the signal-to-noise ratio will be poor and the number of zero crossing points that can be used to calculate the average will be reduced, resulting in large random error. On the other hand, in flow rate measurement using an ultrasonic flowmeter, if the time difference of the latter zero crossing point is used, the signal-to-noise ratio is good and the random error is small, but the systematic error becomes large.

[0064] Therefore, in the ultrasonic flowmeter according to the second embodiment, the systematic error is quantified from the time difference at the first zero crossing point, and the time difference at the second zero crossing point is corrected using the quantified value as a correction value before measuring the flow rate. As a result, in the ultrasonic flowmeter according to the second embodiment, the systematic error can be reduced while keeping the random error low.

[0065] In the flowchart shown in FIG. 8, the processes in steps ST801 to ST803 are similar to the processes in steps ST401 to ST403 shown in FIG. 4, and therefore the description thereof will be omitted.

[0066] In the flow rate calculation operation example by the calculation unit 4 in the second embodiment shown in FIG. 7, as shown in FIG. 8, the average value calculation unit 408 calculates the average value of the time differences at the first zero crossing points based on the calculation result by the time difference calculation unit 405 (step ST804). At this time, for example, the average value calculation unit 408 calculates the average value (Δt_forward) of the time differences at the first to fourth zero crossing points as shown in the following formula (3). Note that in order to maintain the standard deviation, the average value calculation unit 408 may calculate the final average value (Δt_forward_N) by repeating the calculation of the above average value a number of times and averaging the results. N is a number sufficient to reduce the influence of random errors. Δt_forward=(ZC1Δt+ZC2Δt+ZC3Δt+ZC4Δt) / 4 (3)

[0067] Next, average value calculation section 409 calculates the average value of the time differences at the latter zero crossing points based on the calculation result by time difference calculation section 405 (step ST805). At this time, for example, average value calculation section 409 calculates the average value (Δt_backward) of the time differences at the fifth to tenth zero crossing points as shown in the following formula (4). Note that, in order to maintain the standard deviation, average value calculation section 409 may calculate the final average value (Δt_backward_N) by repeating the calculation of the above average value multiple times and averaging the results. N is set to a number sufficient to reduce the influence of random errors. Δt_backward=(ZC5Δt+ZC6Δt+ZC7Δt+ZC8Δt+ZC9Δt+ZC10Δt) / 6 (4)

[0068] Next, difference calculation section 410 calculates the difference between the average value calculated by average value calculation section 408 and the average value calculated by average value calculation section 409 as a correction value (step ST806). At this time, in the above example, difference calculation section 410 calculates the difference value (correction value) by subtracting the average value of the time differences at the first to fourth zero crossing points from the average value of the time differences at the fifth to tenth zero crossing points, as shown in the following equation (5). This correction value is a correction value for reducing systematic errors in the time differences at the latter zero crossing points. Correction value = Δt_backward_N - Δt_forward_N (5)

[0069] Next, the flow rate calculation unit 406 calculates the flow rate of the fluid in the measuring tube 1 based on the calculation result by the time difference calculation unit 405 and the calculation result by the difference calculation unit 410 (step ST807). At this time, in the above example, the flow rate calculation unit 406 first calculates the average value of the time differences at the fifth to tenth zero crossing points after correction (corrected Δt_backward) by subtracting the correction value from the average value of the time differences at the fifth to tenth zero crossing points as shown in the following formula (6). In this way, the flow rate calculation unit 406 can correct the temperature characteristics of ZC5Δt to ZC10Δt to approach the temperature characteristics of ZC1Δt to ZC4Δt while maintaining the standard deviation of ZC5Δt to ZC10Δt. Then, the flow rate calculation unit 406 calculates the time difference after correction (corrected Δt) by calculating the average value of the time differences at the first to fourth zero crossing points and the average value of the time differences at the fifth to tenth zero crossing points after correction as shown in the following formula (7). Then, the flow rate calculation unit 406 uses this corrected time difference to calculate the flow rate of the fluid. After correction Δt_backward = Δt_backward - correction value (6) Corrected Δt = (Δt_forward + corrected Δt_backward) / 2 (7)

[0070] In the above example, the calculation unit 4 obtains the correction value by using the difference between the time difference at the fifth to tenth zero crossing points and the time difference at the first to fourth zero crossing points. However, the present invention is not limited to this example, and the calculation unit 4 may obtain the correction value by using the time difference at other first half zero crossing points and the time difference at the second half zero crossing points. In other words, the number of zero crossing points used by the calculation unit 4, the number of zero crossing points included in the first half zero crossing points, and the number of zero crossing points included in the second half zero crossing points are not limited to the above example. In addition, the calculation unit 4 can reduce the error of the zero crossing points due to the shift of the reference potential (0 point) and the change in the signal strength (slope) by taking the average of the rise-fall pairs (an even number of zero crossing points).

[0071] Furthermore, the ultrasonic flowmeter according to the second embodiment may be configured to switch between enabling and disabling the correction process described above depending on the flow rate of the fluid flowing through the measuring tube 1.

[0072] In this way, the ultrasonic flowmeter according to the second embodiment compares the time difference at the first zero crossing point with the time difference at the second zero crossing point, and performs correction so that the systematic error at the second zero crossing point is at the same level as the systematic error at the first zero crossing point. This makes it possible to reduce the overall systematic error in the ultrasonic flowmeter according to the second embodiment. As a result, the ultrasonic flowmeter according to the second embodiment makes it possible to reduce errors due to temperature or individual differences in the ultrasonic sensors 2 and 3 that are likely to occur when the driving wave number of the ultrasonic waves in the ultrasonic sensors 2 and 3 is increased.

[0073] It should be noted that within the scope of the present invention, the embodiments may be freely combined, any component of each embodiment may be modified, or any component of each embodiment may be omitted. [Explanation of symbols]

[0074] 1 Measuring tube 2. Ultrasonic Sensor 3. Ultrasonic Sensor 4 Arithmetic section 401 received signal acquisition unit (first received signal acquisition unit) 402 received signal acquisition unit (second received signal acquisition unit) 403 Zero-crossing point measurement unit (first zero-crossing point measurement unit) 404 Zero-crossing point measurement unit (second zero-crossing point measurement unit) 405 Time Difference Calculation Unit 406 Flow rate calculation section 407 Drive Wave Number Control Unit 408 Average value calculation unit (first average value calculation unit) 409 Average value calculation unit (second average value calculation unit) 410 Difference calculation part

Claims

1. a first reception signal acquisition unit that acquires a reception signal received by one of a pair of ultrasonic sensors that transmit and receive ultrasonic waves; a second reception signal acquisition unit that acquires a reception signal received by the other of the ultrasonic sensors; a first zero-crossing point measurement unit that measures a time from a start of transmission to a zero-crossing point multiple times for each of multiple unit measurement steps based on an acquisition result by the first received signal acquisition unit; a second zero-crossing point measurement unit that measures a time from a start of transmission to a zero-crossing point multiple times for each of multiple unit measurement steps based on an acquisition result by the second received signal acquisition unit; a time difference calculation unit that calculates a time difference between a measurement result by the first zero cross point measurement unit and a measurement result by the second zero cross point measurement unit; a flow rate calculation unit that calculates a flow rate of the fluid to be measured based on a result of the calculation by the time difference calculation unit; a drive wave number control unit that controls a drive wave number of ultrasonic transmissions in the pair of ultrasonic sensors based on the results of acquisition by the first reception signal acquisition unit and the second reception signal acquisition unit, When the drive wave number control unit increases the drive wave number of the ultrasonic transmission in the other ultrasonic sensor, the first zero cross point measurement unit performs a time measurement of the first half of the zero cross point, pauses the measurement, and then performs a time measurement of the second half of the zero cross point, When the drive wave number control unit increases the drive wave number of the ultrasonic transmission in the one ultrasonic sensor, the second zero cross point measurement unit measures the time of the first half of the zero cross point, pauses the measurement, and then measures the time of the second half of the zero cross point.

1. An ultrasonic flow meter comprising:

2. The drive wave number control unit increases the drive wave number of ultrasonic transmission in the other ultrasonic sensor when the strength of the received signal acquired by the first received signal acquisition unit becomes equal to or less than a threshold or when noise becomes equal to or more than a threshold, and increases the drive wave number of ultrasonic transmission in the one ultrasonic sensor when the strength of the received signal acquired by the second received signal acquisition unit becomes equal to or less than a threshold or when noise becomes equal to or more than a threshold.

2. The ultrasonic flowmeter according to claim 1.

3. a first average value calculation unit that calculates an average value of time differences at a first half zero crossing point based on a calculation result by the time difference calculation unit; a second average value calculation unit that calculates an average value of time differences at a second zero crossing point based on a calculation result by the time difference calculation unit; a difference calculation unit that calculates a difference between a calculation result by the first average value calculation unit and a calculation result by the second average value calculation unit as a correction value; The flow rate calculation unit calculates a flow rate of the fluid to be measured based on a result of the calculation by the time difference calculation unit and a correction value calculated by the difference calculation unit.

3. The ultrasonic flowmeter according to claim 1 or 2.

4. A step in which a first reception signal acquisition unit acquires a reception signal received by one of a pair of ultrasonic sensors that transmit and receive ultrasonic waves; A second reception signal acquisition unit acquires a reception signal received by the other of the ultrasonic sensors; a first zero-crossing point measuring unit measuring a time from a start of transmission to a zero-crossing point multiple times for each of multiple unit measurement steps based on an acquisition result by the first received signal acquiring unit; a second zero-crossing point measuring unit measuring a time from a start of transmission to a zero-crossing point multiple times for each of multiple unit measurement steps based on an acquisition result by the second received signal acquiring unit; A time difference calculation unit calculates a time difference between a measurement result by the first zero cross point measurement unit and a measurement result by the second zero cross point measurement unit; A flow rate calculation unit calculates a flow rate of the fluid to be measured based on a calculation result by the time difference calculation unit; a drive wave number control unit controlling a drive wave number of ultrasonic transmission in the pair of ultrasonic sensors based on the results of acquisition by the first reception signal acquisition unit and the second reception signal acquisition unit; When the drive wave number control unit increases the drive wave number of the ultrasonic transmission in the other ultrasonic sensor, the first zero cross point measurement unit performs a time measurement of the first half of the zero cross point, pauses the measurement, and then performs a time measurement of the second half of the zero cross point, When the drive wave number control unit increases the drive wave number of the ultrasonic transmission in the one ultrasonic sensor, the second zero cross point measurement unit measures the time of the first half of the zero cross point, pauses the measurement, and then measures the time of the second half of the zero cross point.

4. A method for calculating a flow rate using an ultrasonic flowmeter.

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