JP7675579B2 - Ultrasonic flowmeter and flow rate calculation method - Google Patents

Description

This invention relates to an ultrasonic flowmeter that uses ultrasonic waves to measure flow rate and a flow rate calculation method.

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.

In such ultrasonic flowmeters, when measuring the propagation time difference, measurement errors may occur due to the strength of the received signal or the influence of electrical noise (noise) received by the receiving circuit.

In the actual environment in which an ultrasonic flowmeter is used, fluctuations in the power supply voltage, deterioration of the device, ambient temperature, or changes in the composition of the fluid being measured are expected, 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.

In particular, when it is necessary to operate the device on batteries for long periods of time, it is necessary to maintain measurement accuracy while also being power-efficient.

In response to this, Patent Document 1 shows an ultrasonic flowmeter that has 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 based on 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.

Patent Document 2 also shows an ultrasonic flowmeter that includes a repeating means for retransmitting ultrasonic waves after they are received, a timing 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 depending on the signal level of the receiver. With this ultrasonic flowmeter, the number of repetitions can be changed depending on the reception sensitivity of the ultrasonic waves, making it possible to measure the flow rate with high accuracy.

Patent No. 4292620 Patent No. 4362890

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 transmissions, thereby improving the measurement accuracy of the flow rate. However, this ultrasonic flowmeter does not take into consideration a method for dealing with the increase in reception time and current consumption that accompanies an increase in the driving wave number of ultrasonic transmissions. Furthermore, this ultrasonic flowmeter does not take into consideration the increase in measurement error in the propagation time difference due to differences in sensor characteristics caused by increasing the driving wave number.

In addition, the ultrasonic flowmeter disclosed in Patent Document 2 uses the strength of the received signal as an index, and increases the number of transmissions and receptions when the signal level drops to improve accuracy. However, this ultrasonic flowmeter has problems with starting up the measurement circuit due to the increased number of transmissions and receptions, and with the increase in current consumption proportional to the number of data transmissions.

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.

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.
Fig. 10A shows the time measurement of the zero crossing point when the signal-to-noise ratio is high. As shown in Fig. 10A, when the signal-to-noise ratio is high, the noise is small and the transmission and reception strength of the ultrasonic wave 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 wave 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.

This invention was made to solve the above problems, and aims to provide an ultrasonic flowmeter that can avoid an increase in current consumption while maintaining measurement accuracy compared to conventional methods.

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 the time from the start of transmission to the zero-cross point multiple times for each of a plurality of unit measurement steps based on the results acquired by the first reception signal acquisition unit, a second zero-cross point measurement unit that measures the time from the start of transmission to the zero-cross point multiple times for each of a plurality of unit measurement steps based on the results acquired by the second reception signal acquisition unit, a time difference calculation unit that calculates the time difference between the measurement results by the first zero-cross point measurement unit and the measurement results by the second zero-cross point measurement unit, and a time difference calculation unit that calculates the time difference between the measurement results by the first zero-cross point measurement unit and the measurement results by the second zero-cross point measurement unit. The device includes 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 transmissions in a pair of ultrasonic sensors based on the results acquired by the first and second reception signal acquisition units. When the drive wave number control unit increases the drive wave number of ultrasonic transmissions 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 transmissions 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.

With the above-mentioned configuration, this invention makes it possible to avoid an increase in current consumption while maintaining measurement accuracy compared to conventional methods.

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

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.
The ultrasonic flowmeter measures a fluid by using ultrasonic waves. As shown in FIG. 1, the ultrasonic flowmeter includes a measuring tube 1, an ultrasonic sensor 2, an ultrasonic sensor 3, and a calculation unit 4.

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

The ultrasonic sensor 2 is an ultrasonic transducer that is attached to the upstream side of the side wall of the measuring pipe 1 and transmits and receives ultrasonic waves between the ultrasonic sensor 3 within the measuring pipe 1. In other words, the ultrasonic sensor 2 transmits ultrasonic waves to the downstream side (ultrasonic sensor 3) within the measuring pipe 1, and receives ultrasonic waves from the downstream side (ultrasonic sensor 3) as a received signal.

The ultrasonic sensor 3 is an ultrasonic transducer that is attached to the downstream side of the side wall of the measuring pipe 1 and transmits and receives ultrasonic waves between the ultrasonic sensor 2 within the measuring pipe 1. In other words, the ultrasonic sensor 3 transmits ultrasonic waves to the upstream side (ultrasonic sensor 2) within the measuring pipe 1 and receives ultrasonic waves from the upstream side (ultrasonic sensor 2) as a received signal.

The positional relationship between ultrasonic sensor 2 and ultrasonic sensor 3 is designed according to the propagation path of the ultrasonic waves used by ultrasonic sensor 2 and ultrasonic sensor 3.

The calculation unit 4 calculates the flow rate of the fluid in the measuring tube 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.

As shown in FIG. 2, the 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.

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.

The received signal acquisition unit 401 acquires the 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).

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).

The zero-crossing point measurement 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 acquisition unit 401. The zero-crossing point measurement 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 where the strength of a received signal becomes zero after the strength of the received signal exceeds a threshold (threshold voltage) after reception starts. The zero cross point is usually measured at a point between the reception start point of the received signal and the point where 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 an ultrasonic wave (waveform of a received signal). In FIG. 5, reference numeral 51 indicates a zero cross point. 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. 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.

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.

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.

The zero-crossing point measurement 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 acquisition unit 402. The zero-crossing point measurement 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 unit 404 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 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.

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.

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

The time difference calculation unit 405 calculates the time difference between the measurement result by the zero-cross point measurement unit 403 and the measurement result by the zero-cross point measurement unit 404. At this time, the time difference calculation unit 405 first calculates an average value by averaging the measurement results in each unit measurement process by the zero-cross point measurement unit 403 for each zero-cross point. Similarly, the time difference calculation unit 405 calculates an average value by averaging the measurement results in each unit measurement process by the zero-cross point measurement unit 404 for each zero-cross point. Then, the 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.

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. The operating principle of the flow rate calculation unit 406 can adopt the conventional flow rate calculation principle, and the explanation thereof will be omitted.

The drive wave number control unit 407 controls the drive wave number of ultrasonic transmissions 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 falls below a threshold or when the noise exceeds a threshold, the drive wave number control unit 407 controls the ultrasonic sensor 3 to increase the drive wave number of ultrasonic transmissions in the ultrasonic sensor 3. In addition, when the strength of the received signal acquired by the received signal acquisition unit 402 falls below a threshold or when the noise exceeds a threshold, the drive wave number control unit 407 controls the ultrasonic sensor 2 to increase the drive wave number of ultrasonic transmissions in the ultrasonic sensor 2.

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.

In the example of drive wave number control by the calculation unit 4 in embodiment 1 shown in FIG. 2, as shown in FIG. 3, first, the received signal acquisition unit 401 acquires the received signal received by the ultrasonic sensor 2 (step ST301).

Next, the drive wave number control unit 407 determines whether the strength of the received signal acquired by the received signal acquisition unit 401 is below a threshold or whether the noise is above a threshold (step ST302).

In 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).

The above describes 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. However, the example of operation in which the drive wave number of ultrasonic transmission in the ultrasonic sensor 2 is controlled is similar to the above, except that the received signal acquired by the received signal acquisition unit 402 is used.

Next, an example of the flow rate calculation operation by the calculation unit 4 in the embodiment 1 shown in FIG. 2 will be described with reference to FIG. 4.

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 reception signal acquisition unit 401 acquires the reception signal received by the ultrasonic sensor 2 .
Similarly, the received signal acquisition unit 402 acquires the received signal received by the ultrasonic sensor 3 .

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 a plurality of 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 reception 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 reception signal with a large amplitude for the second half zero-cross point, thereby increasing 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 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 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 reception signal with a large amplitude for the second half zero-cross point, thereby increasing the signal-to-noise ratio.

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.
JP 2020-63972 A

Figure 5 shows a case where the zero-crossing point measurement unit 403 and the zero-crossing point measurement unit 404 measure the times of 10 zero-crossing points in one unit measurement process. The number of unit measurement processes is, for example, 31.

The time of the m-th zero-cross point in the k-th unit measurement step measured by the zero-cross point measuring unit 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 unit 404 is represented as inverse ZCm(k).

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

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 (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)

In this way, in the ultrasonic flowmeter according to the first embodiment, when the strength of the received signal falls below the threshold value or when the noise exceeds the threshold value, the driving wave number for 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, when receiving, after the time measurement of the first half zero cross point is completed, the measurement is temporarily paused and a predetermined period has elapsed, and then the time measurement of the second half zero cross point is performed.

The ultrasonic flowmeter according to embodiment 1 can reduce current consumption by stopping recording data indicating the time of the zero crossing point in a memory (not shown) during the measurement pause and stopping the current supply to the receiving circuit (amplifier, comparator, power supply circuit, etc.).

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. Note that Figs. 5 and 6 show a case in which 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 the measurement period of the first-half zero-crossing points, and reference numeral 53 indicates the measurement period of the second-half zero-crossing points. Note that the number of zero-crossing points and the wave number in Figs. 5 and 6 are merely examples.

Fig. 5 shows a 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.

In contrast to Fig. 5, Fig. 6 shows the state after the 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 are added to the five waves before the 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 period of time. The pause period at this time is, for example, a period corresponding to the increase in the drive wave number. In Fig. 6, six waves have been added, so the pause period 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 denotes a pause period.

In this way, in the ultrasonic flowmeter according to embodiment 1, when a state occurs in which the signal-to-noise ratio decreases and the error is large, the number of drive waves for ultrasonic transmission is increased to improve measurement accuracy, and the measurement is paused for a predetermined period of time after measuring the time of the zero-cross point immediately after ultrasonic reception, which is less affected by systematic errors, and then measurement of the time of the zero-cross point is resumed after a large-amplitude signal with a high signal-to-noise ratio and less affected by random errors arrives. As a result, the ultrasonic flowmeter according to embodiment 1 can achieve both reduced current consumption and improved measurement accuracy.

As described above, according to this embodiment 1, the ultrasonic flowmeter includes a received signal acquisition unit 401 that acquires a received signal received by ultrasonic sensor 2 of a 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 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 measurement accuracy compared to conventional methods.

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.

Figure 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 Figure 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 Figure 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 Figure 7 is similar to the example of the configuration of the calculation unit 4 in embodiment 1 shown in Figure 2, and the same reference numerals are used and only the different parts will be described.

The average value calculation unit 408 calculates the average value of the time difference at the first zero crossing point based on the calculation result by the time difference calculation unit 405.

The average value calculation unit 409 calculates the average value of the time difference at the second half zero crossing point based on the calculation result by the time difference calculation unit 405.

The difference calculation unit 410 calculates the difference between the average value calculated by the average value calculation unit 408 and the average value calculated by the average value calculation unit 409 as a correction value.

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. At this time, the flow rate calculation unit 406 first corrects the time difference calculated by the time difference calculation unit 405 with the correction value calculated by the difference calculation unit 410. The flow rate calculation unit 406 then calculates the flow rate of the fluid based on the time difference corrected with the correction value (the corrected time difference). The operating principle of the flow rate calculation unit 406 can adopt the conventional flow rate calculation principle except for the use of the corrected time difference, and a description of this will be omitted.

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 and 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 rate measurement is resolved for each zero crossing point, it can be seen that the influence of temperature change becomes greater the later the zero crossing point on the time axis.

In flow rate measurement using an ultrasonic flowmeter, if only the time difference of the first zero crossing points is used, the systematic error (such as the drift of the zero point due to temperature changes) 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 between the latter half of the zero crossing point is used, the signal-to-noise ratio is good and the random error is small, but the systematic error becomes large.

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 this 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.

Note that in the flowchart shown in FIG. 8, the processing in steps ST801 to ST803 is similar to the processing in steps ST401 to ST403 shown in FIG. 4, and therefore the description thereof will be omitted.

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 difference at the first zero crossing point 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 the average value calculation unit 408 may calculate the final average value (Δt_forward_N) by repeating the calculation of the above average value multiple times and averaging them in order to maintain the standard deviation. N is a number sufficient to reduce the influence of random errors.
Δt_forward=(ZC1Δt+ZC2Δt+ZC3Δt+ZC4Δt)/4 (3)

Next, the average value calculation unit 409 calculates the average value of the time differences at the latter half zero crossing points based on the calculation result by the time difference calculation unit 405 (step ST805). At this time, for example, the average value calculation unit 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, the average value calculation unit 409 may calculate the final average value (Δt_backward_N) by repeating the calculation of the above average value multiple times and averaging them. N is a number sufficient to reduce the influence of random errors.
Δt_backward=(ZC5Δt+ZC6Δt+ZC7Δt+ZC8Δt+ZC9Δt+ZC10Δt)/6 (4)

Next, the difference calculation unit 410 calculates the difference between the average value calculated by the average value calculation unit 408 and the average value calculated by the average value calculation unit 409 as a correction value (step ST806). At this time, in the above example, as shown in the following formula (5), the difference calculation unit 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. This correction value is a correction value for reducing a systematic error in the time differences at the latter half zero crossing points.
Correction value = Δt_backward_N - Δt_forward_N (5)

Next, the flow rate calculation unit 406 calculates the flow rate of the fluid in the measuring tube 1 based on the calculation results by the time difference calculation unit 405 and the calculation results by the difference calculation unit 410 (step ST807). In this case, in the above example, the flow rate calculation unit 406 first calculates the corrected average value of the time differences at the fifth to tenth zero crossing points (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 average value of the time differences at the first to fourth zero crossing points and the average value of the corrected average values of the time differences at the fifth to tenth zero crossing points, as shown in the following formula (7).The flow rate calculation unit 406 then calculates the flow rate of the fluid using this corrected time difference.
Corrected Δt_backward=Δt_backward−corrected value (6)
Corrected Δt=(Δt_forward+corrected Δt_backward)/2 (7)

In the above, as an example, the calculation unit 4 obtains the correction value 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, this is not limited to the above, and the calculation unit 4 may obtain the correction value 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 in the reference potential (zero 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).

The ultrasonic flowmeter according to embodiment 2 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.

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 for the ultrasonic flowmeter according to the second embodiment to reduce the overall systematic error. 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.

In addition, within the scope of the present invention, it is possible to freely combine the various embodiments, modify any of the components of each embodiment, or omit any of the components of each embodiment.

1 Measuring pipe 2 Ultrasonic sensor 3 Ultrasonic sensor 4 Calculation unit 401 Reception signal acquisition unit (first reception signal acquisition unit)
402 Received signal acquisition unit (second received signal acquisition unit)
403 Zero-cross point measurement unit (first zero-cross point measurement unit)
404 Zero cross point measurement unit (second zero cross point measurement unit)
405 Time difference calculation unit 406 Flow rate calculation unit 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 unit

Claims (4)

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 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,
the second zero-cross point measurement unit, when the drive wave number control unit increases the drive wave number of ultrasonic transmission in one of the ultrasonic sensors, measures the time of a first half of the zero-cross point, pauses the measurement, and then measures the time of a second half of the zero-cross point. The ultrasonic flowmeter according to claim 1, characterized in that 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 lower than a threshold value or when noise becomes equal to or higher than a threshold value, 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 lower than a threshold value or when noise becomes equal to or higher than a threshold value. 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;
3. The ultrasonic flowmeter according to claim 1, wherein 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. 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,
wherein when the drive wave number control unit increases the drive wave number of ultrasonic transmission in one of the ultrasonic sensors, the second zero-cross point measurement unit measures the time of a first half of the zero-cross point, pauses measurement, and then measures the time of a second half of the zero-cross point.

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