JP2023010248A - Ultrasonic flowmeter and flow rate computation method - Google Patents

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 The present invention relates to an ultrasonic flowmeter and a flow rate calculation method for measuring a flow rate using ultrasonic waves.

2. Description of the Related Art Conventionally, an ultrasonic flowmeter is known that measures the flow rate of a fluid to be measured based on the propagation time difference of ultrasonic waves transmitted and received by a pair of ultrasonic sensors.
As this ultrasonic flowmeter, a zero-crossing type ultrasonic flowmeter is known. In the zero-crossing ultrasonic flowmeter, after the received signal exceeds the threshold value, a predetermined number of zero-crossing points of the received signal are detected, and the propagation time of the ultrasonic wave up to the detected zero-crossing point is measured. Determine the flow rate of the fluid based on the propagation time.

In such an ultrasonic flowmeter, when measuring the propagation time difference, a measurement error may occur due to the strength of the received signal or the electrical noise received by the receiving circuit.

In the actual usage environment of the ultrasonic flowmeter, fluctuations in the power supply voltage, deterioration of the device, ambient temperature, or changes in the composition of the fluid to be measured are assumed. signal strength changes. Also, 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 on a battery for a long period of time, it is required to maintain measurement accuracy while saving power.

On the other hand, in Patent Document 1, a measurement circuit for measuring the propagation time of transmission from upstream to downstream or transmission from downstream to upstream, fluid discrimination means for determining the type of fluid in the flow path, and a measurement circuit and a circuit constant correcting means for changing the constant of , by the value of the fluid discriminating means. With this ultrasonic flowmeter, the flow rate can be measured with high accuracy by keeping the state of the measuring device appropriately as the fluid changes.

In addition, in Patent Document 2, repeating means for retransmitting after receiving ultrasonic waves, timing means for measuring the accumulated time during repetition of transmission from upstream to downstream or from downstream to upstream, and a signal from a receiver and a frequency setting means for changing the frequency of the repeating means according to the level. This ultrasonic flowmeter can measure the flow rate with high accuracy by changing the number of repetitions according to the reception sensitivity of ultrasonic waves.

Patent No. 4292620 Patent No. 4362890

In the ultrasonic flowmeter disclosed in Patent Document 1, in a situation where the fluid is expected to have low reception sensitivity, the reception sensitivity is increased by increasing the driving wave number of ultrasonic transmission, and the flow rate measurement accuracy is improved. . However, in this ultrasonic flowmeter, no consideration is given to how to cope with the increase in reception time and current consumption accompanying an increase in the number of driving waves for ultrasonic transmission. Further, in this ultrasonic flowmeter, no consideration is given to the increase in the measurement error of the propagation time difference due to the difference in sensor characteristics due to the increase in the number of driving waves.

Further, in the ultrasonic flowmeter disclosed in Patent Document 2, the strength of the received signal is used as an index, and the accuracy is improved by increasing the number of times of transmission and reception when the signal level drops. However, in this ultrasonic flowmeter, there are problems in startup of the measurement circuit due to an increase in the number of times of transmission and reception, and an increase in current consumption proportional to the number of times of data transmission.

Here, when aiming at power saving, it is particularly important to reduce the number of transmission/reception times of ultrasonic waves per hour and to shorten the operation time of the receiving circuit in each transmission/reception operation.
In addition, if it is desired to improve the measurement accuracy, methods such as performing reception in a state of high signal-to-noise ratio or increasing the number of times of transmission/reception are conceivable. However, an increase in the operating time and number of operations of the receiving circuit leads to an increase in current consumption.
In addition, when the number of driving waves for ultrasonic transmission is increased, the amplitude of the latter half of the received signal increases, so the signal-to-noise ratio improves, but on the other hand, there is a tendency for the influence of characteristic differences and individual differences between ultrasonic sensors to become large. The problem is the occurrence of measurement errors that depend on individual differences in temperature or ultrasonic sensors.

An example of the relationship between the signal-to-noise ratio and noise in an ultrasonic flowmeter will be described with reference to FIG. FIG. 10 shows a case where three zero-crossing points (ZC1 to ZC3) are time-measured.
FIG. 10A shows the time measurement of the zero-cross 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/reception intensity of ultrasonic waves is high. That is, in this case, noise-derived random variations (random errors) contained in the measured values are reduced.
On the other hand, FIG. 10B shows the time measurement of the zero cross 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/reception intensity of ultrasonic waves is low. That is, in this case, the noise-derived random variation (random error) contained in the measured values increases. Therefore, in the case of FIG. 10B, the measured value of the zero-crossing point time varies randomly due to the influence of noise.

SUMMARY OF THE INVENTION The present invention has been 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. there is

An ultrasonic flowmeter according to the present invention includes a first reception signal acquisition unit for acquiring a reception signal received by one of a pair of ultrasonic sensors that transmit and receive ultrasonic waves; A second received signal acquisition unit that acquires the received signal received by the other ultrasonic sensor, and based on the acquisition result by the first received signal acquisition unit, for each of the plurality of unit measurement steps, From the start of transmission to the zero cross point for each of a plurality of unit measurement steps, based on the results obtained by the first zero cross point measurement unit that measures the time from the start to the zero cross point multiple times and the second received signal acquisition unit. a second zero-crossing point measuring unit that measures the time of a plurality of times; a time difference calculating unit that calculates the time difference between the measurement result of the first zero-crossing point measuring unit and the measurement result of the second zero-crossing point measuring unit; A pair of ultrasonic sensors based on the results obtained by the flow rate calculation unit that calculates the flow rate of the fluid to be measured based on the calculation result by the unit, and the first reception signal acquisition unit and the second reception signal acquisition unit and a drive wave number control unit that controls the drive wave number of ultrasonic transmission in the first zero-crossing point measurement unit, when the drive wave number control unit increases the drive wave number of ultrasonic transmission in the other ultrasonic sensor, After measuring the time at the first half of the zero-cross point, the measurement is temporarily suspended, and then the time is measured at the second half of the zero-cross point. When the driving wave number of sound wave transmission is increased, the time measurement of the zero cross point in the first half is performed, and then the time measurement of the zero cross point in the second half is performed after temporarily stopping the measurement.

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.

1 is a diagram showing a configuration example of an ultrasonic flowmeter according to Embodiment 1; FIG. 3 is a diagram illustrating a configuration example of a calculation unit according to Embodiment 1; FIG. 4 is a flow chart showing an example of driving wave number control by a calculation unit in Embodiment 1. FIG. 4 is a flow chart showing an example of flow rate calculation operation by a calculation unit according to Embodiment 1. FIG. 5A and 5B are diagrams showing a specific example of the operation of the arithmetic unit (state before driving wave number control) in Embodiment 1, FIG. 5A showing a received waveform of ultrasonic waves, and FIG. A transmission waveform is shown. 6A and 6B are diagrams showing a specific example of the operation of the arithmetic unit (state after driving wave number control) in Embodiment 1, FIG. 6A showing a received waveform of ultrasonic waves, and FIG. A transmission waveform is shown. FIG. 10 is a diagram illustrating a configuration example of a calculation unit according to Embodiment 2; 10 is a flow chart showing an example of flow rate calculation operation by a calculation unit according to Embodiment 2. FIG. FIG. 5 is a diagram for explaining zero point drift in the time difference between zero crossing points; 10A and 10B are diagrams showing an example of the relationship between the signal-to-noise ratio and noise in an ultrasonic flowmeter.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments 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 Embodiment 1. FIG.
Ultrasonic flow meters use ultrasonic waves to measure fluids. This ultrasonic flow meter comprises a measuring tube 1, an ultrasonic sensor 2, an ultrasonic sensor 3 and a computing section 4, as shown in FIG.

The measurement tube 1 is a cylindrical member in which a 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 measurement tube 1 and transmits and receives ultrasonic waves to and from the ultrasonic sensor 3 within the measurement tube 1 . That is, the ultrasonic sensor 2 transmits ultrasonic waves to the downstream side (ultrasonic sensor 3) in the measuring tube 1, and receives ultrasonic waves from the downstream side (ultrasonic sensor 3) as reception signals.

The ultrasonic sensor 3 is an ultrasonic transducer that is attached to the downstream side of the side wall of the measurement tube 1 and transmits and receives ultrasonic waves to and from the ultrasonic sensor 2 within the measurement tube 1 . That is, the ultrasonic sensor 3 transmits ultrasonic waves to the upstream side (ultrasonic sensor 2) in the measuring tube 1, and receives ultrasonic waves from the upstream side (ultrasonic sensor 2) as reception signals.

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 .

The computing unit 4 computes 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 .

As shown in FIG. 2, the calculation unit 4 includes a reception signal acquisition unit (first reception signal acquisition unit) 401, a reception signal acquisition unit (second reception signal acquisition unit) 402, a zero cross point measurement unit (first zero-cross point measurement unit) 403 , zero-cross point measurement unit (second zero-cross point measurement unit) 404 , time difference calculation unit 405 , flow rate calculation unit 406 and driving wave number control unit 407 .

The calculation unit 4 is implemented by a processing circuit such as an IC (Integrated Circuit), a system LSI (Large Scale Integration), or a CPU (Central Processing Unit) 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 . Note that the received signal acquisition unit 401 has a function (amplifier) for amplifying the received signal acquired from the ultrasonic sensor 2 .

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 (amplifier) for amplifying the received signal acquired from the ultrasonic sensor 3 .

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 results obtained by the reception signal obtaining unit 401 . The zero-cross point measurement unit 403 performs the above processing for each of a plurality of received signals (each unit measurement process).
For example, as shown in FIG. 5, the zero-crossing point is a point at which the strength of the received signal becomes zero after the strength of the received signal exceeds a threshold (threshold voltage) after the start of reception. Note that the zero-crossing point is usually measured from a point between the reception start point of the received signal and the point at which the received signal reaches the maximum amplitude. In FIG. 5, FIG. 5B shows a transmission waveform of ultrasonic waves, and FIG. 5A shows a reception waveform (waveform of a reception signal) of ultrasonic waves. Further, in FIG. 5, reference numeral 51 indicates a zero crossing point. Also, the number of zero-crossing points at which the zero-crossing point measurement unit 403 measures time in one unit measurement process is set in advance. Also, the number of unit measurement steps is set in advance.
Note that the zero-cross point measuring unit 403 has a function (comparator) that compares the received signal (received signal after amplification) acquired by the received signal acquisition unit 401 with a threshold.

Further, when the driving wavenumber of ultrasonic wave transmission in the ultrasonic sensor 3 is increased by the driving wavenumber control unit 407, the zero-crossing point measurement unit 403 measures the time of the first half zero-crossing point (first half zero-crossing point), and then measures the time. is paused, the time of the second half zero-crossing point (second half zero-crossing point) is measured. The pause time is set based on the frequency and driving wave number of ultrasonic waves transmitted by the ultrasonic sensor 3 .

Note that the first half zero-cross point is one or more zero-cross points near the reception start point when a plurality of zero-cross points that occur from the reception start point of the received signal to the point where the received signal reaches the maximum amplitude are arranged in chronological order. Point to a point.
Further, the second half zero-cross point is one or more zero-cross points far from the reception start point when a plurality of zero-cross points occurring from the reception start point of the received signal to the point where the received signal reaches the maximum amplitude are arranged in chronological order. A zero-crossing point that occurs after the first half 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 results obtained by the reception signal obtaining unit 402 . The zero-crossing point measurement unit 404 performs the above processing for each of a plurality of received signals (each unit measurement process).
Note that the number of zero-crossing points at which the zero-crossing point measurement unit 404 measures time in one unit measurement process is set in advance. Also, the number of unit measurement steps is set in advance.
Note that the zero-cross point measurement unit 404 has a function (comparator) that compares the received signal (received signal after amplification) acquired by the received signal acquisition unit 402 with a threshold.

Further, when the driving wavenumber of ultrasonic wave transmission in the ultrasonic sensor 2 is increased by the driving wavenumber control unit 407, the zero-crossing point measuring unit 404 measures the time of the first half zero-crossing point (first half zero-crossing point), and then measures the time. is paused, the time of the second half zero-crossing point (second half zero-crossing point) is measured. The rest time is set based on the frequency and driving wave number of ultrasonic waves transmitted by the ultrasonic sensor 2 .

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 a single circuit. That is, the above operation can be realized by switching the connection between the circuit and the ultrasonic sensors 2 and 3 according to forward transmission/reception and reverse transmission/reception.

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

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

The driving wave number control unit 407 controls the driving wave number of ultrasonic wave 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 is equal to or less than the threshold or the noise is equal to or greater than the threshold, the driving wave number control unit 407 controls the driving wave number of ultrasonic wave transmission in the ultrasonic sensor 3. The ultrasonic sensor 3 is controlled to increase. Further, when the strength of the received signal acquired by the received signal acquisition unit 402 is equal to or less than the threshold or the noise is equal to or greater than the threshold, the driving wave number control unit 407 controls the driving wave number of ultrasonic wave transmission in the ultrasonic sensor 2. is controlled to increase the ultrasonic sensor 2 .

Next, an operation example of the calculation unit 4 according to Embodiment 1 shown in FIG. 2 will be described.
First, an example of drive wave number control by the calculation unit 4 in Embodiment 1 shown in FIG. 2 will be described with reference to FIG.

In the driving wave number control example by the calculation unit 4 in the first embodiment shown in FIG. 2, as shown in FIG. ST301).

Next, driving wave number control section 407 determines whether the intensity of the received signal acquired by received signal acquiring section 401 is equal to or less than the threshold or the noise is equal to or greater than the threshold (step ST302).

In step ST302, when 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, when the driving wave number control unit 407 determines that the intensity is equal to or less than the threshold value or that the noise is equal to or greater than the threshold value, the driving wave number of ultrasonic wave transmission in the ultrasonic sensor 3 is increased. The ultrasonic sensor 3 is controlled (step ST303).

In the above description, an operation example in which the driving wave number control unit 407 controls the driving wave number of ultrasonic wave transmission in the ultrasonic sensor 3 has been described. The operation example is also the same as described above except that the received signal acquired by the received signal acquisition unit 402 is used.

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

In the example of the flow rate calculation operation by calculation section 4 in Embodiment 1 shown in FIG. 2, as shown in FIG. .
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 .

Next, zero-crossing point measurement sections 403 and 404 measure the time from the start of transmission to the zero-crossing point multiple times for each unit measurement process (step ST402).
That is, 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 of the received signal acquisition unit 401 for each unit measurement process. Note that, when the driving wavenumber of ultrasonic wave transmission in the ultrasonic sensor 3 is increased by the driving wavenumber control unit 407, the zero-crossing point measurement unit 403 measures the time of the first half of the zero-crossing point, and then temporarily suspends the measurement. Measure the time of the second half zero cross point. In this way, when the number of driving waves for ultrasonic transmission is increased, the zero-crossing point measurement unit 404 uses a large amplitude portion of the received signal for the second half zero-crossing point, thereby increasing the signal-to-noise ratio. can be done.
Similarly, 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 results obtained by the received signal acquisition unit 402 for each unit measurement process. Note that, when the driving wavenumber of ultrasonic wave transmission in the ultrasonic sensor 2 is increased by the driving wavenumber control unit 407, the zero-crossing point measuring unit 404 measures the time of the first half of the zero-crossing point, and then temporarily suspends the measurement. Measure the time of the second half zero cross point. In this way, when the number of driving waves for ultrasonic transmission is increased, the zero-crossing point measurement unit 404 uses a large amplitude portion of the received signal for the second half zero-crossing point, thereby increasing the signal-to-noise ratio. can be done.

It is desirable that the zero-crossing point measuring section 403 and the zero-crossing point measuring section 404 use the same position as the starting point for time measurement and the first half zero-crossing point regardless of whether or not there is a pause. As a method of specifying the same position as the starting point of time measurement and the first half zero-crossing point, for example, the method disclosed in Patent Document 3 can be cited, but the method is not limited to this.
Japanese Patent Application Laid-Open No. 2020-63972

FIG. 5 shows a case where the zero-crossing point measuring section 403 and the zero-crossing point measuring section 404 measure ten zero-crossing point times in one unit measurement process. Also, the number of unit measurement steps is, for example, 31 times.

Note that the time of the m-th zero-cross point in the k-th unit measurement process measured by the zero-cross point measurement unit 403 is expressed as ZCm(k).
Also, the time of the m-th zero-crossing point in the k-th unit measurement process measured by the zero-crossing point measuring unit 404 is expressed as inverse ZCm(k).

Next, time difference calculation section 405 calculates the time difference (ZCmΔt) between the measurement result of zero-cross point measurement section 403 and the measurement result of zero-cross point measurement section 404, as shown in the following equation (1) (step ST403). At this time, first, the time difference calculation unit 405 calculates an average value by averaging the measurement results in each unit measurement process by the zero-crossing point measurement unit 403 for each zero-crossing 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-crossing point measurement unit 404 for each zero-crossing point. Then, the time difference calculator 405 calculates the time difference at each zero cross point by calculating the difference between the two average values for each zero cross point.
ZCmΔt=(Σ reverse ZCm(k)/k)−(Σ forward ZCm(k)/k) (1)

Next, the flow rate calculator 406 calculates the flow rate of the fluid in the measuring tube 1 based on the calculation result of the time difference calculator 405 (step ST404). At this time, the flow rate calculator 406 can calculate the flow rate of the fluid based on the time difference (Δt) calculated according to the following equation (2), for example, when the conventional method is used.
Δt=ΣZCmΔt/m (2)

As described above, in the ultrasonic flowmeter according to the first embodiment, when the strength of the received signal becomes equal to or less than the threshold or the noise becomes equal to or more than the threshold, the ultrasonic sensors 2 and 3 on the transmission side Increase the driving wave number of ultrasonic transmission in the acoustic sensor. 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 suspended, and after a predetermined period has passed, the time measurement of the second half zero cross point is performed. I do.

Then, the ultrasonic flowmeter according to Embodiment 1 stops recording data indicating the time of the zero-crossing point in the memory (not shown) during the above-mentioned measurement suspension, and also includes a receiving circuit (amplifier, comparator and Power supply circuit, etc.) can reduce current consumption.

Next, a specific example of the operation of the calculation unit 4 in Embodiment 1 shown in FIG. 2 will be described with reference to FIGS. 5 and 6 show a case where the calculation unit 4 measures four zero-cross points in the first half and six zero-cross points in the second half. 5 and 6, reference numeral 52 indicates the measurement period of the first half zero-cross point, and reference numeral 53 indicates the measurement period of the second half zero-cross point. Note that the number of zero-crossing points and wave numbers in FIGS. 5 and 6 are examples.

FIG. 5 shows the state before driving wave number control (in the case of normal measurement operation). FIG. 5A shows a received waveform of ultrasonic waves (waveform of a received signal), and FIG. 5B shows a transmitted waveform of ultrasonic waves. As shown in FIG. 5B, the ultrasonic wave is a rectangular wave with five waves.
In this case, as shown in FIG. 5A, the calculation unit 4 performs the time measurement of the first half zero-cross point and the second half zero-cross point without stopping the measurement in the middle.

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 a received waveform of ultrasonic waves (waveform of a received signal), and FIG. 6B shows a transmitted waveform of ultrasonic waves. As shown in FIG. 6B, the ultrasonic wave has 6 waves added to the 5 waves before the driving wave number control, and the wave number is a rectangular wave with 11 waves.
In this case, as shown in FIG. 6A, the calculator 4 first measures the time of the first half zero-crossing point in the same manner as before the driving wave number control. Immediately after that, the calculation unit 4 suspends the measurement for a predetermined time. The pause time at this time is, for example, a period corresponding to the number of increases in the number of driving waves. In FIG. 6, since 6 waves are added, the rest time is 6 cycles. After that, the calculation unit 4 restarts the measurement and measures the time of the zero-cross point in the second half. In FIG. 6, reference numeral 61 indicates a pause period.

As described above, in the ultrasonic flowmeter according to Embodiment 1, when the signal-to-noise ratio is lowered and a large error occurs, the measurement accuracy is improved by increasing the number of driving waves for ultrasonic transmission, thereby improving the system. After measuring the time of the zero-cross point immediately after receiving ultrasonic waves, which is less affected by errors, the measurement is paused for a predetermined time, and the zero-cross point is reached after a large-amplitude signal with a high signal-to-noise ratio and not easily affected by chance errors arrives. to resume timing. As a result, in the ultrasonic flowmeter according to Embodiment 1, it is possible to achieve both reduction in current consumption and improvement in measurement accuracy.

As described above, according to the first embodiment, the ultrasonic flowmeter acquires the reception signal received by the ultrasonic sensor 2 of the pair of ultrasonic sensors 2 and 3 that transmit and receive ultrasonic waves. A reception signal acquisition unit 401, a reception signal acquisition unit 402 that acquires a reception signal received by the ultrasonic sensor 3, and based on the acquisition results of the reception signal acquisition unit 401, start transmission for each of a plurality of unit measurement processes. The time from the start of transmission to the zero cross point is measured multiple times for each of a plurality of unit measurement steps based on the results obtained by the zero cross point measurement unit 403 that measures the time from the start of transmission to the zero cross point multiple times, and the received signal acquisition unit 402. A zero-crossing point measuring unit 404 that performs measurement, a time difference calculating unit 405 that calculates the time difference between the measurement result of the zero-crossing point measuring unit 403 and the measurement result of the zero-crossing point measuring unit 404, and the measurement based on the calculation result of the time difference calculating unit 405. Based on the results obtained by the flow rate calculation unit 406 that calculates the flow rate of the target fluid and the reception signal acquisition unit 401 and the reception signal acquisition unit 402, the driving wave number for ultrasonic transmission in the pair of ultrasonic sensors 2 and 3 is controlled. When the drive wave number control unit 407 increases the drive wave number of ultrasonic wave transmission in the ultrasonic sensor 3, the zero cross point measurement unit 403 measures the time of the first half of the zero cross point. After that, after the measurement is temporarily suspended, the time of the zero-cross point in the second half is measured. After measuring the time of the zero-crossing points in the second half, the time measurement of the zero-crossing points in the second half is performed after temporarily stopping the measurement. As a result, the ultrasonic flowmeter according to the first embodiment can avoid an increase in current consumption while maintaining measurement accuracy compared to the conventional one.

Embodiment 2.
In the ultrasonic flowmeter according to the second embodiment, there are measures for reducing errors due to individual differences in temperature or the ultrasonic sensors 2 and 3 that are likely to occur when the driving wave number of ultrasonic transmission in the ultrasonic sensors 2 and 3 is increased. I will explain how.

FIG. 7 is a diagram showing a configuration example of the calculation unit 4 according to the second embodiment. Compared to the computing unit 4 according to the first embodiment shown in FIG. 2, the computing unit 4 according to the second embodiment shown in FIG. 7 has an average value computing unit (first average computing unit) 408, A second average value calculator 409 and a difference calculator 410 are added, and the processing of the flow rate calculator 406 is changed. Other configuration examples of the computing unit 4 according to the second embodiment shown in FIG. 7 are the same as the configuration examples of the computing unit 4 according to the first embodiment shown in FIG. Give an explanation.

The average value calculator 408 calculates the average value of the time differences at the first half zero-cross points based on the calculation result of the time difference calculator 405 .

The average value calculator 409 calculates the average value of the time differences at the zero-crossing points in the second half based on the calculation result of the time difference calculator 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 pipe 1 based on the calculation result of the time difference calculation unit 405 and the calculation result of the difference calculation unit 410 . At this time, first, the flow rate calculation unit 406 corrects the time difference calculated by the time difference calculation unit 405 with the correction value calculated by the difference calculation unit 410 . Then, the flow rate calculation unit 406 calculates the flow rate of the fluid based on the time difference corrected by the correction value (time difference after correction). The principle of operation of the flow rate calculation unit 406 can adopt the principle of conventional flow rate calculation, except that the time difference after correction is used, and the explanation thereof will be omitted.

Next, an example of flow rate calculation operation by the calculation unit 4 in Embodiment 2 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 fluid measurement drifts with temperature due to the difference in sensor characteristics. If the variation 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 FIG. 9, when the time difference used in the flow rate measurement is resolved for each zero-crossing point, it can be seen that the later the zero-crossing point on the time axis, the greater the effect of temperature change.

In flow measurement with an ultrasonic flowmeter, if only the time difference of the first half of the zero-cross point is used, the systematic error (drift of the zero point due to temperature change, etc.) is reduced, but the SN is poor, and the number of zero-cross points that can be used for average calculation is The smaller the number, the greater the chance error.
On the other hand, when the time difference between the latter zero crossing points is used in the flow rate measurement by the ultrasonic flow meter, the SN is good and the random error is reduced, but the systematic error is increased.

Therefore, in the ultrasonic flowmeter according to the second embodiment, the systematic error is quantified from the time difference at the first half zero-cross point, and the value is used as a correction value to correct the time difference at the second half zero-cross point. Then, the flow rate is measured. As a result, the ultrasonic flowmeter according to the second embodiment can reduce systematic errors while keeping random errors low.

In the flowchart shown in FIG. 8, the processing from steps ST801 to ST803 is the same as the processing from steps ST401 to ST403 shown in FIG. 4, and the description thereof will be omitted.

In the flow rate calculation operation example by the calculation unit 4 according to the second embodiment shown in FIG. is calculated (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). 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 above calculation of the average value a plurality of times and averaging them. N should be a sufficient number to reduce the effects of random errors.
Δt_forward=(ZC1Δt+ZC2Δt+ZC3Δt+ZC4Δt)/4 (3)

Next, average value calculation section 409 calculates the average value of the time differences at the second half zero-cross points based on the calculation result of time difference calculation section 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 equation (4). 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 above calculation of the average value a plurality of times and averaging them. N should be a sufficient number to reduce the effects of random errors.
Δt_backward=(ZC5Δt+ZC6Δt+ZC7Δt+ZC8Δt+ZC9Δt+ZC10Δt)/6 (4)

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, as shown in the following equation (5), the difference calculation unit 410 calculates the time difference between the first to fourth zero-crossing points from the average value of the time differences between the fifth to tenth zero-crossing points. By subtracting the average value of , a difference value (correction value) is calculated. This correction value is a correction value for reducing the systematic error in the time difference at the latter zero-cross point.
Correction value=Δt_backward_N−Δt_forward_N (5)

Next, the flow rate calculation section 406 calculates the flow rate of the fluid in the measuring tube 1 based on the calculation result of the time difference calculation section 405 and the calculation result of the difference calculation section 410 (step ST807). At this time, in the above example, first, the flow rate calculation unit 406 subtracts the correction value from the average value of the time differences at the fifth to tenth zero-crossing points, as shown in the following expression (6). The average value of the time differences (Δt_backward after correction) at the 5th to 10th zero-crossing points of is calculated. As a result, the flow rate calculation unit 406 can correct the temperature characteristics of ZC5Δt to ZC10Δt so as to approach the temperature characteristics of ZC1Δt to ZC4Δt while maintaining the standard deviation of ZC5Δt to ZC10Δt. Then, as shown in the following formula (7), the flow rate calculation unit 406 calculates the average value of the time differences at the first to fourth zero cross points and the corrected time difference at the fifth to tenth zero cross points. By calculating the average value of the average values, the time difference after correction (Δt after correction) is calculated. Then, the flow rate calculation unit 406 calculates the flow rate of the fluid using this corrected time difference.
Δt_backward after correction=Δt_backward−correction value (6)
Δt after correction=(Δt_forward+Δt_backward after correction)/2 (7)

In the above description, as an example, the calculation unit 4 obtains the correction value using the difference between the time difference between the fifth to tenth zero cross points and the time difference between the first to fourth zero cross points. However, without being limited to this, the calculation unit 4 may obtain a correction value using the time difference at the other first half zero-cross point and the time difference at the second half zero-cross point. That is, 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 examples. Further, the calculation unit 4 averages Rise-Fall pairs (an even number of zero-crossing points), thereby alleviating errors in the zero-crossing points due to shifts in the reference potential (zero point) and changes in signal strength (gradient). .

Further, the ultrasonic flowmeter according to the second embodiment may be configured to switch between enabling and disabling the above-described correction process according to the flow rate of the fluid flowing through the measurement tube 1. FIG.

Thus, in the ultrasonic flowmeter according to Embodiment 2, the time difference at the first half zero-cross point and the time difference at the second half zero-cross point are compared, and the systematic error at the second half zero-cross point is compared with the systematic error at the first half zero-cross point. Make corrections so that they are at the same level. As a result, the ultrasonic flowmeter according to the second embodiment can reduce the overall systematic error. As a result, in the ultrasonic flowmeter according to the second embodiment, it is possible to reduce errors due to temperature or individual differences in the ultrasonic sensors 2 and 3 that tend to occur when the driving wave number of the ultrasonic waves in the ultrasonic sensors 2 and 3 is increased. becomes.

In addition, within the scope of the present invention, it is possible to freely combine each embodiment, modify any component of each embodiment, or omit any component in each embodiment. be.

1 measurement tube 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-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 calculator 406 flow rate calculator 407 driving wave number controller 408 average value calculator (first average value calculator)
409 Average value calculation unit (second average value calculation unit)
410 difference calculator

Claims (4)

a first received signal acquisition unit that acquires a received signal received by one of a pair of ultrasonic sensors that transmit and receive ultrasonic waves;
a second received signal acquisition unit that acquires a received signal received by the other ultrasonic sensor 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 obtained by the first received 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 result obtained by the second received signal acquisition unit;
a time difference calculation unit that calculates the time difference between the measurement result of the first zero-crossing point measurement unit and the measurement result of the second zero-crossing point measurement unit;
a flow rate calculation unit that calculates the flow rate of the fluid to be measured based on the calculation result of the time difference calculation unit;
a drive wave number control unit that controls the drive wave number of ultrasonic wave transmission in the pair of ultrasonic sensors based on the acquisition results of the first received signal acquisition unit and the second received signal acquisition unit,
When the drive wave number control unit increases the drive wave number of ultrasonic wave transmission in the other ultrasonic sensor, the first zero cross point measurement unit measures the time of the zero cross point in the first half, and then performs the measurement once. After the pause, measure the time of the zero cross point in the second half,
When the drive wave number control unit increases the drive wave number of ultrasonic wave transmission in one of the ultrasonic sensors, the second zero cross point measurement unit measures the time of the first half of the zero cross point, and then temporarily performs the measurement. An ultrasonic flowmeter characterized by: measuring the time of the zero-crossing point in the latter half after the pause. The driving wave number control unit controls the transmission of ultrasonic waves in the other ultrasonic sensor when the strength of the received signal acquired by the first received signal acquisition unit is equal to or less than a threshold value or when noise is equal to or greater than a threshold value. When the intensity of the received signal obtained by the second received signal obtaining unit is equal to or less than the threshold or the noise is equal to or greater than the threshold, the number of ultrasonic waves transmitted by the one ultrasonic sensor is increased. 2. The ultrasonic flowmeter according to claim 1, wherein the number of driving waves is increased. a first average value calculation unit that calculates an average value of the time differences at the first half zero crossing points based on the calculation result of the time difference calculation unit;
a second average value calculation unit that calculates an average value of the time differences at the second half zero crossing points based on the calculation result of the time difference calculation unit;
A difference calculation unit that calculates a difference between the calculation result by the first average value calculation unit and the calculation result by the second average value calculation unit as a correction value,
3. The flow rate calculation unit calculates the flow rate of the fluid to be measured based on the calculation result of the time difference calculation unit and the correction value calculated by the difference calculation unit. An ultrasonic flowmeter as described. a step in which a first received signal acquisition unit acquires a received signal received by one of a pair of ultrasonic sensors that transmit and receive ultrasonic waves;
a step in which a second received signal acquisition unit acquires a received signal received by the other ultrasonic sensor of the ultrasonic sensors;
a step in which a first zero-crossing point measurement unit measures the time from the start of transmission to the zero-crossing point a plurality of times for each of a plurality of unit measurement steps based on the results obtained by the first received signal obtaining unit;
a step in which a second zero-crossing point measurement unit measures the time from the start of transmission to the zero-crossing point multiple times for each of a plurality of unit measurement steps, based on the results obtained by the second received signal obtaining unit;
a step in which a time difference calculation unit calculates a time difference between a measurement result obtained by the first zero-crossing point measurement unit and a measurement result obtained by the second zero-crossing point measurement unit;
a flow rate calculation unit calculating a flow rate of a fluid to be measured based on a calculation result by the time difference calculation unit;
a drive wave number control unit controlling the drive wave number of ultrasonic wave transmission in the pair of ultrasonic sensors based on the results obtained by the first reception signal acquisition unit and the second reception signal acquisition unit; death,
When the drive wave number control unit increases the drive wave number of ultrasonic wave transmission in the other ultrasonic sensor, the first zero cross point measurement unit measures the time of the zero cross point in the first half, and then performs the measurement once. After the pause, measure the time of the zero cross point in the second half,
When the drive wave number control unit increases the drive wave number of ultrasonic wave transmission in one of the ultrasonic sensors, the second zero cross point measurement unit measures the time of the first half of the zero cross point, and then temporarily performs the measurement. A flow rate calculation method using an ultrasonic flowmeter, characterized by measuring the time of the zero-crossing point in the latter half after a pause.

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