JP2005345362A - Ultrasonic flow rate measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the measurement accuracy of an ultrasonic flow rate measuring device. <P>SOLUTION: The ultrasonic flow rate measuring device is equipped with a correlation calculating section 31 which executes a correlation calculation between a first time reception waveform f<SB>1</SB>which is transmitted from an ultrasonic probe 21A on the upstream side and received by an ultrasonic probe 21B on the downstream side, and a second time receiving waveform f<SB>2</SB>used as a comparison waveform, and further executes correlation calculation between the first time receiving waveform f<SB>1</SB>which is transmitted from the ultrasonic probe 21B on the downstream side and received by the ultrasonic probe 21A on the upstream side, and the second time receiving waveform f<SB>2</SB>used as the comparison waveform. A decision section 32 derives the arrival the timings Δt<SP>+</SP>, Δt<SP>-</SP>required for calculating arrival the times t<SP>+</SP>, t<SP>-</SP>, based on the result of calculations executed by the correlation calculating section 31. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic flow rate measuring device for measuring the flow rate of open channels such as rivers, canals, and irrigation channels.

  2. Description of the Related Art As a flow measurement device for rivers, canals, irrigation canals, and the like (open water channels), a device using an ultrasonic probe capable of transmitting and receiving ultrasonic waves (ultrasonic flow measurement device) is known. For example, in Non-Patent Documents 1 and 2, the sound velocity in water is affected by the flow velocity, and the sound velocity increases when the component of the ultrasonic wave propagation direction of the flow velocity is positive, and the sound velocity decreases when the component is negative. An ultrasonic flow measuring device using the above is described.

An example of a conventional ultrasonic flow measuring device will be described with reference to FIG. A pair of ultrasonic probes 1A and 1B are arranged on both banks of the river so as to face each other at the same water depth. The ultrasonic probes 1A and 1B are opposed to each other at an angle θ that is not perpendicular to the flow direction F. One ultrasonic probe 1 </ b> A transmits ultrasonic waves having a predetermined frequency and several wavelengths, and the timer 5 starts counting simultaneously with the transmission. The ultrasonic wave propagates through water, which is a medium, and is received by the other ultrasonic probe 1B arranged on the opposite bank. The ultrasonic wave received by the ultrasonic probe 1 </ b> B is amplified by the amplifier 3 of the processing apparatus 10 and then input to the comparator 4. The comparator 4 compares the amplified received signal with a threshold, and stops the timer 5 when the received signal exceeds the threshold. As a result, the arrival time t ^{+ of the} ultrasonic wave between the ultrasonic probes 1A and 1B in the flow direction F is measured. The ultrasonic arrival time t ⁻ in the direction opposite to the flow direction F is measured in the same manner by using the ultrasonic probe 1B as the transmission side and the ultrasonic probe 1A as the reception side. Based on these arrival times t ⁺ and t ⁻ , the flow velocity calculation unit 6 calculates the average flow velocity Vm in the measurement line, and the flow rate measurement unit 7 calculates the flow rate Q based on the average flow velocity Vm.

Hiroyuki Hachiya and two others, “Ultrasonic propagation characteristics in rivers during floods”, Ultrasonic TECHNO, Nihon Kogyo Publishing Co., Ltd., May 20, 2003, Vol. 15, No. 3, p. 40-43 Antonius Laenen, Winchell Smith, “Acoustic Systems for the Measurement of Streamflow”, US Geological Survey Water Source Paper 2213, “(US GEOLOGICAL SURVEY WATER -SUPPLY PAPER 2213) ", UNITED STATES GOVERMENT PREINTING OFFICE, 1983

However, the waveform of the ultrasonic wave when it propagates through water and is received by the ultrasonic probes 1A and 1B becomes unstable due to various factors. Therefore, in a simple comparison between the received signal and the threshold value as in the apparatus of FIG. 11, a phenomenon (missing measurement) that the arrival times t ⁺ and t ⁻ cannot be determined occurs.

  The sound speed C of ultrasonic waves in water is generally expressed by the following equation (1).

  As apparent from the equation (1), the sound velocity C varies depending on the salinity concentration S, so that the received waveform becomes unstable due to the distribution of the salinity concentration in the cross section of the river or in the crossing path. In particular, as shown in FIG. 12, in a tidal river, a state in which salt water 12 is mixed with fresh water 11 is assumed. If the number of times of passing through the salt water region 12 by the ultrasonic propagation path 13 and the angle of incidence or exit to the region 12 are different, the received waveform is disturbed.

  Similarly, as is clear from Equation (1), the water temperature distribution in the cross section and the crossing path is also a factor that makes the received waveform unstable. In particular, water temperature distribution tends to occur in tidal rivers.

  Furthermore, the turbulent flow generated by the opening and closing of the weir also causes the reception waveform to become unstable.

  Furthermore, the ultrasonic probes 1A and 1B themselves have directivity, and there is a distribution in the intensity 14 of the transmitted ultrasonic waves as schematically shown in FIG. The directivity of the ultrasonic probes 1A and 1B themselves also becomes a factor that makes the received waveform unstable in combination with the salinity concentration distribution and the water temperature distribution.

  Accordingly, an object of the present invention is to provide an ultrasonic flow measuring device that prevents occurrence of missing measurement and is excellent in measurement accuracy and reliability.

  The inventor examined the shape of the received waveform of ultrasonic waves that resulted in missing measurements, and obtained the following knowledge.

  Referring to FIG. 14, the received waveform 15 is a waveform in which two types of waveforms are superimposed on a main waveform or a straight waveform 16 that travels straight between ultrasonic probes. One of the waveforms to be superimposed is a waveform 17 that reaches a reception-side ultrasonic probe by passing through a straight waveform 16 and having a high sound velocity by passing through a salt water mass or a high-temperature layer near the water surface. The other is a waveform 18 that arrives at the ultrasonic probe on the receiving side later than the straight waveform 16 due to reflection at the bottom (river bottom) or water surface (river surface) of the open channel. Focusing on the frequency of the straight waveform 16 and the two types of waveforms 17 and 18 superimposed thereon, it has been found that the fundamental waveform 16 maintains the fundamental frequency of the ultrasonic probe on the transmitting side. For example, if the frequency of the transmitted ultrasonic wave is 100 kHz, the frequency of the received straight waveform 16 is also approximately 100 kHz. In addition, if the frequency of the transmitted ultrasonic wave is 30 kHz, the frequency of the received straight waveform 16 is also approximately 30 kHz. On the other hand, in the remaining two types of waveforms, frequency shift and synthesis occur, so the basic waveform of the ultrasonic probe on the transmission side is not maintained. For example, a lens effect is generated in ultrasonic waves that have passed through a salt water mass and a temperature mass, and the waveform 17 is deformed with respect to the straight waveform 16 due to frequency shift and synthesis. In addition, a frequency shift occurs due to the influence of waves reflected on the surface. Therefore, if the characteristic of the linear waveform 16 that the fundamental frequency of the transmission-side ultrasonic probe is maintained is used, the arrival time of the ultrasonic wave from the transmission-side ultrasonic probe to the reception-side ultrasonic probe can be accurately determined. It can be measured with high reliability.

  Based on the above knowledge, the present invention uses correlation calculation to detect the arrival of the main waveform or the straight waveform.

Accordingly, the present invention includes the first and second ultrasonic probes (21A, 21B) disposed on both banks of the open channel (20) so that the opposing direction is inclined with respect to the flow direction, and the first The first arrival time (t ⁺ ), which is the time required for the ultrasonic wave transmitted from the ultrasonic probe to reach the second ultrasonic probe, and the ultrasonic wave transmitted from the second ultrasonic probe. An ultrasonic flow measuring device that measures a flow rate (Q) of an open channel based on a second arrival time (t ⁻ ) that is a time required for a sound wave to reach the first ultrasonic probe. The first received waveform (f ₁ , S ₂ , S ′ ₂ ) transmitted from the first ultrasonic probe and received by the second ultrasonic probe and the first comparison waveform (f ₂₎ performs a correlation operation between the _{S 1,} S _'1), and the second ultrasonic flop Said originating from over blanking the first second received waveform received by the ultrasonic probe _{(f 1, S 2, S} '2) and the second comparative waveform _{(f 2, S 1, S} ' 1 ) And a time required for calculation of the first and second arrival times or the first and second times based on the calculation result of the correlation calculation unit. Provided is an ultrasonic flow measuring device including a determination unit (32) for determining an arrival time itself.

  In the flow rate measuring apparatus according to the present invention, the correlation calculation unit performs a correlation calculation between the reception waveforms of the first and second ultrasonic probes and the comparison waveform, and based on the calculation, the determination unit starts from the first ultrasonic probe. The arrival time (first arrival time) of the ultrasonic wave to the second ultrasonic probe and the arrival time (second arrival time) of the ultrasonic wave from the second ultrasonic probe to the first ultrasonic probe The time required for calculation or the first and second arrival times are determined. Out of the received waveform, disturbance noise superimposed on the ultrasonic wave (straight line part) that goes straight between the first and second ultrasonic probes, that is, the part of the sound velocity higher than the straight part and the water surface due to the presence of salt concentration distribution and temperature distribution Since the portion of the sound velocity lower than the straight portion due to reflection on the bottom surface is disturbed by the waveform, it is canceled by the correlation calculation. Therefore, the ultrasonic wave between the first and second ultrasonic probes has high accuracy and high reliability. Can be measured, and the flow velocity of the open channel can be measured with high accuracy.

  For example, the arrival time of the ultrasonic wave is measured by performing a correlation calculation on the ultrasonic wave waveform received with a time interval.

Specifically, the first and second received waveforms (f ₁ ) and the first received waveform are transmitted from the first ultrasonic probe with a time interval after receiving the second received waveform. A third reception waveform (f ₂ ) received by the acoustic probe and a time interval after reception of the second reception waveform are transmitted from the second ultrasound probe and received by the first ultrasound probe. A sampling unit (29) for sampling the received fourth received waveform (f ₂ ), and the first to fourth received waveforms (f ₁ , f ₂ ) sampled by the sampling unit are stored. A time period from the transmission of ultrasonic waves by the storage unit (30) and the first ultrasonic probe to the start of sampling of the first and third received waveforms (f ₁ , f ₂ ) by the sampling unit At the start of sampling (T ₁₎ and, second is the time until the start of sampling said second of said second and fourth of the received waveform by said sampling unit from the ultrasonic outgoing by the ultrasonic probe (f _{1, f 2)} A timer (26) for measuring the sampling start time (t ₂ ), and the correlation calculation unit converts the third received waveform (f ₂ ) stored in the storage unit to the first comparison waveform. As the first received waveform (f ₁ ) stored in the storage unit and the fourth received waveform (f ₂ ) stored in the storage unit is used as the second comparison waveform. As the second received waveform (f ₁ ) stored in the previous storage unit, and the determination unit performs the first and third receptions based on the calculation result of the correlation calculation unit. Sampling of the waveform by the sampling unit First arrival timing is the time until the arrival of the linear waveform from (Delta] t ⁺⁾ and the second is the time from the start of sampling until the arrival of the linear waveform by the sampling unit for the second and fourth received waveform the arrival timing (Delta] t ^-) is determined and, the first by adding the first arrival timing in the sampling start time to calculate the first arrival time, and the said second sampling start time An adder for calculating the second arrival time by adding the second arrival timing is further provided.

  More specifically, the correlation calculation unit executes the correlation calculation based on the following equation (2).

  By performing a correlation operation on the received waveform and the transmitted waveform, the arrival time of the ultrasonic wave can be measured.

Specifically, the first and second reception waveforms (S ₂ ), the first transmission waveform (S ₁ ) from the first ultrasonic probe corresponding to the first reception waveform, and the Sampling units (29A, 29B) for sampling the second transmission waveform (S ₁ ) from the second ultrasonic probe corresponding to the second received waveform, and the first and second samples sampled by the sampling unit. 2 further includes a storage unit (30A, 30B) for storing the received waveform (S ₂ ) of ₂ and the first and second transmission waveforms (S ₁ ) sampled by the sampling unit, the correlation calculation unit ( 31) performs a correlation operation with the first received waveform (S ₂ ) using the first transmission waveform (S ₁ ) stored in the storage unit (30A) as the first comparison waveform, And memorize | stored in the said memory | storage part (30B) The second outgoing wave (S ₁₎ performing a correlation operation between said second received waveform (S ₂₎ as the second comparative waveforms.

  More specifically, the correlation calculation unit executes the correlation calculation based on the following equation (3).

  By performing a correlation operation on the received waveform and the comparison waveform stored in advance, the arrival time of the ultrasonic wave can be measured.

Specifically, a sampling unit (29) that samples the first received waveform (S ′ ₂ ) and the second received waveform (S ′ ₂ ), and the first sampled by the sampling unit. And a storage unit (30) for storing the _second received waveform (S ′ ₂ ), the first comparative waveform (S ′ ₁ ) representing the transmission waveform of the first ultrasonic probe, and the second A comparison waveform waveform storage unit (41) that stores in advance the second comparison waveform (S ′ ₁ ) representing the transmission waveform of the ultrasonic probe.

  More specifically, the correlation calculation unit executes the correlation calculation based on the following equation.

  In the flow rate measuring apparatus according to the present invention, the correlation calculation unit performs a correlation calculation between the reception waveforms of the first and second ultrasonic probes and the comparison waveform, and based on the calculation, the determination unit starts from the first ultrasonic probe. The arrival time (first arrival time) of the ultrasonic wave to the second ultrasonic probe and the arrival time (second arrival time) of the ultrasonic wave from the second ultrasonic probe to the first ultrasonic probe The time required for calculation or the first and second arrival times are determined. Since disturbance noise is canceled by the correlation calculation, it is possible to measure the arrival time of the ultrasonic wave between the first and second ultrasonic probes with high accuracy and high reliability. Therefore, even in a tidal river where the salinity concentration distribution is remarkable and in a river confluence where the temperature distribution is remarkable, it is possible to measure the arrival time of ultrasonic waves, and hence the flow rate with high accuracy and high reliability.

  Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(First embodiment)
1 and 2 show an ultrasonic flow measuring device according to a first embodiment of the present invention. This ultrasonic flow measuring device is a method of measuring the arrival time of ultrasonic waves by executing transmission and reception of ultrasonic waves in the same direction twice, and performing correlation calculation on the two received waveforms obtained. Adopted.

  The ultrasonic flow measuring device includes a pair of ultrasonic probes 21A and 21B arranged on both banks of the river 20 which is an open channel, and control of transmission and reception of ultrasonic waves by the ultrasonic probes 21A and 21B. And a processing device 23 that executes processing for flow rate measurement including various calculations.

  The ultrasonic probes 21A and 21B include piezoelectric elements for transmitting and receiving ultrasonic waves. The ultrasonic probes 21A and 21B are arranged so as to face each other at an angle θ that is not perpendicular to the flow direction F. The ultrasonic probe 21A is located on the upstream side, and the ultrasonic probe 21B is located on the downstream side. The ultrasonic probes 21A and 21B are arranged at the same height from the riverbed.

  The processing device 23 includes a well-known oscilloscope, personal computer, and various electric / electronic circuits, and includes a pulse generator 25, a timer 26, an amplifier 27, an A / D converter 28, a sampling circuit 29, a memory 30, and a correlation calculation unit 31. , A determination unit 32, an adder 33, a flow velocity calculation unit 34, a flow rate calculation unit 35, and a control unit 36.

The pulse generator 25 outputs a pulse voltage for driving the piezoelectric element to the ultrasonic probes 21A and 21B on the transmission side. The timer 26 measures the sampling start times t ₁ and t ₂ . The sampling start times t ₁ and t ₂ are times from the transmission of ultrasonic waves by one of the ultrasonic probes 21A and 21B to the start of sampling of ultrasonic waves received by the other. The amplifier 27 amplifies analog signals (reception signals) output from the reception-side ultrasonic probes 21A and 21B, and the A / D converter 28 A / D converts the amplified reception signals. The sampling circuit 29 performs sampling of the digitized reception signal, and the memory 30 stores the reception signal sampled by the sampling circuit 29. The correlation calculation unit 31 performs a correlation calculation on the received signal stored in the memory 30. The determination unit 32 determines arrival timings Δt ⁺ and Δt ⁻ based on the calculation result of the correlation calculation unit 31. The arrival timings Δt ⁺ and Δt ⁻ are times from the start of sampling by the sampling circuit 29 to the arrival of the straight waveform. The adder 33 calculates the arrival times t ⁺ and t ⁻ by adding the arrival timings Δt ⁺ and Δt ⁻ to the sampling start times t ₁ and t ₂ . The arrival times t ⁺ and t ⁻ are times required for the ultrasonic waves to reach one of the ultrasonic probes 21A and 21B from the other. The flow velocity calculation unit 34 calculates the average flow velocity V _m from the arrival times t ⁺ , t ^{− and the} like. Flow rate calculation unit 35 calculates the flow rate Q from the average flow velocity V _m. The control unit 36 controls the operation of the elements included in the processing device 23 including the correlation calculation unit 31 and the determination unit 32 and the transmission and reception of signals between them.

For the arrival times t ⁺ , t ⁻ and the arrival timings Δt ⁺ , Δt ⁻ , the subscript “+” indicates that the time is related to the ultrasonic wave from the upstream ultrasonic probe 21A to the downstream ultrasonic probe 21B. “-” Indicates time related to the ultrasonic wave from the downstream side to the upstream side. For example, the arrival time t ⁺ is the time required for the ultrasonic wave transmitted from the upstream ultrasonic probe 21A to reach the downstream ultrasonic probe 21B. Conversely, the arrival time t ^- is the time required for the ultrasonic wave transmitted by the downstream side of the ultrasonic probe 21B reaches the upstream side of the ultrasound probe 21A.

  Next, flow measurement by the ultrasonic flow measurement device of the present embodiment will be described with reference to FIG.

Steps S3-1 to S3-5 are processes for obtaining the arrival time t ⁺ . First, in step S3-1, the first sampling of ultrasonic waves transmitted from the upstream ultrasonic probe 21A and received by the downstream ultrasonic probe 21B is performed. The piezo element of the upstream ultrasonic probe 21 </ b> A excited by the pulse signal supplied from the pulse generator 25 transmits ultrasonic waves having a design frequency (for example, 30 kHz or 100 kHz) for a plurality of periods. Further, the timer 26 starts measuring time when the ultrasonic probe 21A generates the first pulse. The ultrasonic wave transmitted from the ultrasonic probe 21A propagates through water as a medium, is detected by the piezoelectric element of the ultrasonic probe 21B on the downstream side, and is output as an analog electric signal (received signal). As described with reference to FIG. 14, the waveform of the ultrasonic wave detected by the ultrasonic probe 21B on the receiving side is a main waveform or a straight wave waveform (see reference numeral 16) straight from the ultrasonic probe 21A. In addition, various waveforms (see reference numerals 17 and 18) in which delay or advance has occurred due to factors such as water temperature distribution, reflection at the riverbed or river surface, etc. are superimposed.

The reception signal output from the ultrasonic probe 21B is amplified by the amplifier 27, digitized by the A / D converter 28, and sampled by the sampling circuit 29 at a predetermined sampling rate (for example, 1 μsec). The sampling start time t ₁ is counted by the timer 26. The received signal sampled by the sampling circuit 29 is stored in the first area 30 a of the memory 30. The sampling end time includes, for example, the distance L between the ultrasonic probes 21A and 21B, the variable speed range, the arrival time of the ultrasonic wave between the ultrasonic probes 21A and 21B predicted based on the water temperature, and the capacity of the memory 30. It is determined based on.

Next, in step S3-2, the second sampling of the ultrasonic wave transmitted from the upstream ultrasonic probe 21A and received by the downstream ultrasonic probe 21B is performed. This second sampling is executed by the same processing as the first sampling in step S3-1. However, the sampling circuit 29 starts sampling at the same sampling start time t1 as the _first sampling. The sampled received signal is stored in the second area 30 b of the memory 30. When the processing in step S3-2 is completed, the reception waveform of the first region 30a of the memory 30 from the sampling start time t ₁ obtained by the first sampling step S3-1 until the sampling end (first Received waveform) f ₁ is stored, and in the second area 30b, the received waveform (third received waveform) f from the sampling start time t ₁ obtained by the second sampling of step S3-2 to the end of sampling is stored. ₂ is stored.

Next, at step S3-3, a reception waveform _{f 1} stored in the first area 30a of the memory 30, and received waveform _{f 2} stored in the second region 30b are input to the correlation calculation unit 31, these The correlation calculation unit 31 performs correlation calculation on the received waveforms f ₁ and f ₂ . Specifically, the correlation calculation unit 31 executes the correlation calculation shown in the following equation (5). The result of the correlation calculation is output to the determination unit 32.

Next, in step S3-4, the determination unit 32 determines the arrival timing Δt ⁺ . When the correlation calculation of Expression (5) is performed, among the waveforms included in each of the received waveforms f ₁ and f ₂ , the straight waveform holding the fundamental frequency shows a strong correlation, and other waveforms superimposed on the straight waveform Waveforms (noise waveforms that cause delays and advancement and whose waveforms are distorted) have a weak correlation. Accordingly, the straight waveform appears as a peak in the calculation result of the correlation calculation. The determination unit 32 determines this peak. Arrival timing Delta] t ⁺ is obtained as the time from the sampling start time t ₁ to a peak.

4A and 4B are ideal states in which only the straight waveform (see reference numeral 17 in FIG. 14) reaches the ultrasonic probe 21A on the receiving side and no noise waveform (see reference numerals 16 and 18 in FIG. 14) exists. The reception waveform of the ultrasonic probe 21B on the downstream side in FIG. FIG. 4A shows a received waveform f ₁ by the first sampling, and FIG. 4B shows a received waveform f ₂ by the second sampling. Both the received waveforms f1 and f2 reach the ultrasonic probe 21B on the downstream side after 0.5 msec from the start of sampling. FIG. 4C shows the result of the correlation calculation unit 31 executing the correlation calculation of Expression (5) for these received waveforms f ₁ and f ₂ . As is apparent from FIG. 4C, a very clear peak 40 appears in 0.5 sec in the calculation result (correlation function) of the correlation calculation. Therefore, the determination unit 32 determines that the arrival timing Δt ⁺ is 0.5 msec. The reception waveforms f ₁ and f ₂ shown in FIGS. 4A and 4B are virtual waveforms in the ideal state, but it is shown that the arrival timing Δt ⁺ can be accurately determined from the calculation result of the correlation calculation.

Subsequently, in step S3-5, the arrival timing Δt ⁺ is input from the determination unit 32 to the adder 33. As shown in equation (6) below, is added to the arrival timing Delta] t ⁺ a sampling start time t ₁ by the adder 33, the arrival time t ⁺ are calculated.

Step S3-6~S3-10 the arrival time t ^- is a process for obtaining. These processes are for obtaining the arrival time t ⁺ of steps S3-1 to S3-10 except that the downstream ultrasonic probe 21B is the transmitting side and the upstream ultrasonic probe 21A is the receiving side. This is the same as the process. First, in step S3-6, the first sampling of the ultrasonic wave transmitted from the downstream ultrasonic probe 21B and received by the upstream ultrasonic probe 21A is executed. Next, in step S3-7, the second sampling of the ultrasonic wave transmitted from the downstream ultrasonic probe 21B and received by the upstream ultrasonic probe 21A is executed. Furthermore, the correlation calculation is a correlation calculation unit 31 of the received waveform (second received waveform) _{f 1} and received waveform obtained in step S3-7 (fourth receiving waveform) _{f 2} obtained in the step S3-6 Is executed (see equation (5)). In step S3-10, the determination unit 32 determines the arrival timing Δt ⁻ based on the result of the correlation calculation. Finally, in step S3-10, the adder 33 performs the calculation of the following equation (7), whereby the arrival time t ⁻ is calculated. In the formula (7), t ₂ is the time until the ultrasonic sampling the ultrasonic probe 21B of the downstream side is received by the ultrasonic probe 21A on the upstream side from the transmitting ultrasonic waves is started (sampling start time (Normally t ₁ = t ₂ ).

A process for obtaining the arrival time ^{t +} step S3-1～S3-5, arrival time t of the step S3-6～S3-10 ^- process for obtaining may be executed first.

In step S3-11, the flow velocity calculation unit 34 calculates an average flow velocity V _m in the flow direction F of the river 20 along a virtual line (measurement line) connecting the ultrasonic probes 21A and 21B. The arrival times t ⁺ and t ⁻ are input from the adder 33 to the flow velocity calculation unit 34, and the average flow velocity V _m is calculated based on the following equation (8). In the equation (8), the symbol L is the distance between the ultrasonic probes 21A and 21B.

Next, in step S3-12, the flow rate calculation unit 35 calculates the flow rate Q of the river 20. The flow rate calculation unit 35 receives the average flow rate V _m from the flow rate calculation unit 34 and calculates the flow rate Q based on the following equation (9).

  In Expression (9), K is a correction coefficient, and A is an average cross-sectional area of the river 20 in a direction orthogonal to the flow direction F.

FIG. 5A shows an example of received waveforms f ₁ and f ₂ of ultrasonic waves transmitted from the upstream ultrasonic probe 21 A and received by the downstream ultrasonic probe 21. Since both the received waveforms f ₁ and f ₂ are superimposed on the straight waveform (see reference numeral 16 in FIG. 14) and the noise waveform (reference numerals 17 and 18 in FIG. 14), which part of the waveform is the straight waveform. Is not clear. FIG. 5B shows the result of the correlation calculation unit 31 executing the correlation calculation of Expression (5) for these received waveforms f ₁ and f ₂ . The origin of the time axis in FIG. 5 (B) is a sampling start time t _1. A clear peak appears at the time of 0.5 msec in the calculation result of the correlation calculation, and the determination unit 32 determines that the arrival timing Δt ⁺ is 0.5 msec.

As described above, in the present embodiment, the correlation calculation unit 31 performs the correlation calculation represented by the equation (5) for the _two received waveforms f ₁ and f ₂ between the ultrasonic probes 21A and 21B, and makes a determination based on the correlation calculation. Since the unit 32 determines the arrival timings Δt ⁺ and Δt ⁻ , disturbance noise is canceled out, and the ultrasonic arrival times t ⁺ and t ⁻ between the ultrasonic probes 21A and 21B are measured with high accuracy and high reliability. can do. Therefore, even in a tidal river where the salinity concentration distribution is remarkable and in a river confluence where the temperature distribution is remarkable, it is possible to measure the arrival time of ultrasonic waves, and hence the flow rate with high accuracy and high reliability.

(Second Embodiment)
FIG. 6 shows an ultrasonic flow measuring device according to the second embodiment of the present invention. This ultrasonic flow measuring device employs a method of measuring the arrival time by performing a correlation operation on the transmission waveform and reception waveform of the ultrasonic wave.

  The ultrasonic flow measuring device includes an amplifier 27A for sampling a transmission waveform, an A / D converter 28A, a sampling circuit 29A, and a memory 30A, an amplifier 27B for sampling a received waveform, and an A / D converter 28B. A sampling circuit 29B and a memory 30B.

  Next, flow measurement using the ultrasonic flow measurement device of the present embodiment will be described with reference to FIG.

Steps S7-1 to S7-3 are processes for obtaining the arrival time t ⁺ . First, in step S7-1, the transmission waveform of the ultrasonic wave transmitted from the upstream ultrasonic probe 21A and the reception waveform of the ultrasonic wave on the downstream ultrasonic probe 21B are sampled. Ultrasound probe 21A of the excited upstream by a pulse signal supplied from the pulse generator 25 is an ultrasonic plurality of cycles originating outgoing waveform (first outgoing waveform) S ₁ is an amplifier 27A, A / D converter 28A, the signal is sampled by the sampling circuit 29A and stored in the memory 30A. The timer 26 starts timing simultaneously with the transmission of ultrasonic waves by the upstream ultrasonic probe 21A. Simultaneously with the transmission of ultrasonic waves by the upstream ultrasonic probe 21A, the reception waveform (first reception waveform) S of the downstream ultrasonic probe 21 by the amplifier 27B, the A / D converter 28B, and the sampling circuit 29B. ₂ sampling is started and stored in the memory 30B. Outgoing waveform S ₁ and the end time of sampling the received waveform S _2, for example ultrasound probe 21A, the distance between 21B L, the variable range of the flow rate, an ultrasonic probe 21A which is predicted based on the water temperature, among 21B Ultra It is determined based on the arrival time of the sound wave and the capacity of the memory 30.

Next, at step S7-2, the outgoing waveform _{S 1} stored in the memory 30A, and received waveform _{S 2} stored in the memory 30B is input to the correlation calculation unit 31, these waveforms _S 1, to _{S 2} On the other hand, the correlation calculation shown in the following equation (10) is executed. The result of the correlation calculation is output to the determination unit 32.

Next, in step S7-3, the determination unit 32 determines the arrival time t ⁺ . Of the waveforms included in the transmission waveform S ₁ and the reception waveform S ₂ , the straight waveform has a strong correlation, but the noise waveform has a weak correlation, so the straight waveform appears as a peak in the calculation result of the correlation calculation. The determination unit 32 determines this peak. In the first embodiment, since the received waveform sampling is started at the sampling start times t ₁ and t ₂ after the ultrasonic wave is transmitted, the peak of the calculation result of the correlation calculation is the arrival timings Δt ⁺ and Δt ⁻ . The arrival times t ⁺ and t ⁻ can be obtained by adding the sampling start times t ₁ and t ₂ to these. On the other hand, in the present embodiment, since the sampling of the transmission waveform S1 and the reception waveform S2 is started simultaneously with the transmission of the ultrasonic wave, the peak of the calculation result of the correlation calculation is the arrival times t ⁺ and t ⁻ itself.

Step S7-4~S7-6 the arrival time t ^- is a process for obtaining. These processes are for obtaining the arrival time t ⁺ of steps S7-1 to S7-3 except that the downstream ultrasonic probe 21B is the transmitting side and the upstream ultrasonic probe 21A is the receiving side. It is the same as the processing. First, in step S7-4, sampling of the transmission waveform of the ultrasonic wave transmitted from the ultrasonic probe 21B on the downstream side and the reception waveform at the ultrasonic probe 21A on the upstream side of this ultrasonic wave is executed. Next, at step S7-5, outgoing waveform (second outgoing waveform) _{S 1} and the received waveform (second received waveform) correlation calculation _{S 2} is executed by the correlation calculation unit 31 (formula (10) see ). Further, in step S7-6, the determination unit 32 based on the result of the correlation calculation, the arrival time t ^- determines.

After the arrival times t ⁺ and t ⁻ are obtained, in step S7-7, the flow velocity calculation unit 34 calculates the average flow velocity Vm by the above equation (8), and in step S7-8, the flow rate calculation unit 35 calculates the above equation. The flow rate Q is calculated by (9).

FIG. 8 (A) shows been and outgoing waveform S ₁ of the ultrasonic wave emitting from an upstream side of the ultrasound probe 21A, the illustration of the received waveform S ₂ by the ultrasonic downstream of the ultrasonic probe 21B. The reception waveform S ₁ has a clear waveform with uniform amplitude, but the reception waveform S ₂ has a non-clear straight waveform (see reference numeral 16 in FIG. 14) due to superposition of noise waveforms (see reference numerals 17 and 18 in FIG. 14). . FIG. 8B shows the result of the correlation calculation unit 31 executing the correlation calculation of Expression (10) for these waveforms S ₁ and S ₂ . The origin of the time axis in FIG. 8 (B) is a time when the ultrasonic probe 21A has transmitted the ultrasonic wave (the time of starting the sampling of the outgoing waveform S ₁ and the received waveform S _2). In the calculation result of the correlation calculation, a clear peak 40 appears at the time of 0.3 msec, and the determination unit 32 determines that the arrival time t ⁺ is 0.3 mse.

  Since the other configuration and operation of the second embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference numerals and description thereof is omitted.

(Third embodiment)
FIG. 9 shows an ultrasonic flow measuring device according to a third embodiment of the present invention. This ultrasonic flow rate measuring apparatus employs a method of measuring the arrival time of ultrasonic waves by performing a correlation operation on the ultrasonic transmission waveform S ′ ₂ and the comparative waveform S ′ ₁ . The ultrasonic flow measuring device stores a comparison waveform memory in which two types of comparison waveforms S ′ ₁ corresponding to the output waveform of the upstream ultrasonic probe 21A and the output waveform of the downstream ultrasonic probe 21B are stored in advance. A portion 41 is provided.

Referring to FIG. 10, steps S10-1 to S10-3 are processes for obtaining arrival time t ⁺ . In step S <b> 10-1, an ultrasonic reception waveform (first reception waveform) S ′ ₂ transmitted from the upstream ultrasonic probe 21 </ b> A and received by the downstream ultrasonic probe 21 </ b> B is sampled and stored in the memory 30. Remembered. Then, step S10-2 smell, performing a correlation calculation shown in the following equation (11) with respect to ₁ the correlation calculating unit 31 'compares waveform S _2' received waveform S. The result of the correlation calculation is output to the determination unit 32.

Next, in step S10-3, the determination unit 32 shows that the straight waveform has a strong correlation among the waveforms included in the reception waveform S ′ ₂ and the comparison waveform S ′ ₁ , but the noise waveform has a weak correlation. The straight waveform appears as a peak in the calculation result of the correlation calculation. The determination unit 32 determines this peak as the arrival time t ⁺ .

Step S10-4~S10-6 the arrival time t ^- is a process for obtaining. These processes are for obtaining the arrival time t ⁺ of steps S10-1 to S10-3 except that the downstream ultrasonic probe 21B is the transmitting side and the upstream ultrasonic probe 21A is the receiving side. It is the same as the processing.

  After the arrival times t + and t− are obtained, in step S10-7, the flow velocity calculation unit 34 calculates the average flow velocity Vm according to the above equation (8), and in step S10-8, the flow rate calculation unit 35 calculates the above equation ( The flow rate Q is calculated according to 9).

  Since the other configurations and operations of the third embodiment are the same as those of the first embodiment, the same elements are denoted by the same reference numerals and description thereof is omitted.

1 is a schematic plan view showing an ultrasonic flow measuring device according to a first embodiment of the present invention. It is a schematic sectional view in the direction orthogonal to the flow direction showing the ultrasonic flow measuring device according to the first embodiment of the present invention. It is a flowchart for demonstrating operation | movement of the ultrasonic flow measuring device which concerns on 1st Embodiment of this invention. (A) is a waveform diagram showing an example of the first received waveform, (B) is a waveform diagram showing an example of the second received waveform, and (C) shows the correlation between the received waveforms of (A) and (B). It is a waveform diagram. (A) is a wave form diagram which shows an example of the 1st and 2nd received waveform, (B) is a wave form diagram which shows the correlation of the received waveform of (A). It is a schematic top view which shows the ultrasonic type flow measuring apparatus which concerns on 2nd Embodiment of this invention. It is a flowchart for demonstrating operation | movement of the ultrasonic flow measuring device which concerns on 2nd Embodiment of this invention. (A) is a waveform diagram showing an example of a transmission waveform and a reception waveform, and (B) is a waveform diagram showing a correlation between the transmission waveform and the reception waveform of (A). It is a schematic top view which shows the ultrasonic type flow measuring apparatus which concerns on 3rd Embodiment of this invention. It is a flowchart for demonstrating operation | movement of the ultrasonic flow measuring apparatus which concerns on 3rd Embodiment of this invention. It is a schematic plan view showing a conventional ultrasonic flow rate measuring device. It is the schematic for demonstrating distribution of salt water concentration. It is the schematic for demonstrating the directivity of the output of an ultrasonic probe. It is the schematic for demonstrating the relationship between a rectilinear waveform and the waveform superimposed on it.

Explanation of symbols

20 River 21A, 21B Ultrasonic probe 23 Processing device 25 Pulse generator 26 Timer 27, 27A, 27B Amplifier 28, 28A, 28B A / D converter 29, 29A, 29B Sampling circuit 30, 30A, 30B Memory 30a First region 30b 2nd area 31 Correlation calculation part 32 Judgment part 33 Adder 34 Flow velocity calculation part 35 Flow rate calculation part 36 Control part 40 Peak 41 Comparison waveform memory | storage part F Flow direction L Distance (theta) The angle with respect to a flow direction

Claims (7)

1st and 2nd ultrasonic probe arrange | positioned so that the opposing direction may incline with respect to a flow direction may be provided, and the ultrasonic wave transmitted from the said 1st ultrasonic probe may be said 2nd. A first arrival time, which is a time required to reach the ultrasonic probe, and a time required for the ultrasonic wave transmitted from the second ultrasonic probe to reach the first ultrasonic probe. An ultrasonic flow measuring device for measuring a flow rate in an open channel based on a second arrival time,
Performing a correlation operation between a first received waveform transmitted from the first ultrasonic probe and received by the second ultrasonic probe and a first comparative waveform; and the second ultrasonic probe. A correlation calculation unit that performs a correlation calculation between the second received waveform transmitted from and received by the first ultrasonic probe and the second comparative waveform;
An ultrasonic flow rate comprising: a determination unit that determines the time required for calculating the first and second arrival times or the first and second arrival times based on the calculation result of the correlation calculation unit; measuring device. The first and second received waveforms and a third received from the first ultrasonic probe with a time interval after reception of the first received waveform and received by the second ultrasonic probe The received waveform and the fourth received waveform that is transmitted from the second ultrasonic probe and received by the first ultrasonic probe with a time interval after reception of the second received waveform are sampled. A sampling unit;
A storage unit for storing the first to fourth received waveforms sampled by the sampling unit;
A first sampling start time which is a time from the transmission of ultrasonic waves by the first ultrasonic probe to the start of sampling of the first and third received waveforms by the sampling unit; and the second ultrasonic probe. A timer for measuring a second sampling start time which is a time from the transmission of an ultrasonic wave to the sampling start of the second and fourth received waveforms by the sampling unit;
The correlation calculation unit performs a correlation calculation with the first reception waveform stored in the storage unit using the third reception waveform stored in the storage unit as the first comparison waveform, and the storage Performing a correlation operation with the second received waveform stored in the previous storage unit as the second comparative waveform stored in the fourth received waveform,
The determination unit, based on the calculation result of the correlation calculation unit, a first arrival timing that is a time from the start of sampling by the sampling unit for the first and third received waveforms until the arrival of the straight waveform, Determining the second arrival timing which is the time from the start of sampling by the sampling unit for the second and fourth received waveforms to the arrival of the linear waveform;
The first arrival timing is added to the first sampling start time to calculate the first arrival time, and the second arrival timing is added to the second sampling start time to obtain the second An adder for calculating the arrival time of
The ultrasonic flow rate measuring apparatus according to claim 1. The ultrasonic flow measurement device according to claim 2, wherein the correlation calculation unit performs the correlation calculation based on the following equation.

The first and second reception waveforms, the first transmission waveform from the first ultrasonic probe corresponding to the first reception waveform, and the second super waveform corresponding to the second reception waveform A sampling unit for sampling a second transmission waveform from the acoustic probe;
A storage unit for storing the first and second received waveforms sampled by the sampling unit and the first and second transmission waveforms sampled by the sampling unit;
The correlation calculation unit performs a correlation calculation with the first reception waveform using the first transmission waveform stored in the storage unit as the first comparison waveform, and stores the first transmission waveform stored in the storage unit. The ultrasonic flow rate measuring apparatus according to claim 1, wherein a correlation calculation with the second received waveform is executed using the two transmitted waveforms as the second comparative waveform.
The ultrasonic flow measurement device according to claim 4, wherein the correlation calculation unit performs the correlation calculation based on the following equation.

A sampling unit for sampling the first received waveform and the second received waveform;
A storage unit for storing the first and second received waveforms sampled by the sampling unit;
Comparison waveform waveform storage that stores in advance the first comparison waveform representing the transmission waveform of the first ultrasound probe and the second comparison waveform representing the transmission waveform of the second ultrasound probe. And
The ultrasonic flow rate measuring device according to claim 1, comprising: The ultrasonic flow measurement device according to claim 6, wherein the correlation calculation unit performs the correlation calculation based on the following equation.

Images