JP2004264195A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter in which the time required for detecting an arrival time difference is relatively shortened to save energy, with no increase in consumption amount of a battery. <P>SOLUTION: A first oscillator 21 is switched to a reception side while a second oscillator 31 is switched to a transmission side by a switching means 7 (S4), and an ultrasonic wave is transmitted from the second oscillator 31 toward the first oscillator 21 positioned on the upper stream side (S5). Here, the ultrasonic reception waveform which is received with the first oscillator 21 is sampled and A/D converted at a prescribed cycle in the direction of time axis, acquiring each sampling value (2)(S6). Based on each sampling value (2) acquired in S6 and a sampling value (1) that corresponds to the one stored in a sampling value storage area 42a at S3, a correlation coefficient between (1) and (2) is acquired (S7). The value of time axis where the correlation coefficient indicates a maximum value is directly read to acquire an arrival time difference ΔT, for calculating a flow rate Q (S8). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic flow meter.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a flow rate measuring device that measures the flow rate of a fluid such as city gas or water, an ultrasonic flow meter that measures a flow velocity using an ultrasonic wave is known. As a measurement principle at that time, a “propagation time difference method” is generally used. In this method, a pair of ultrasonic transmission / reception units are provided on the upper side and the lower side in the fluid flow direction of the flow path, and transmission / reception of the ultrasonic signal is alternately switched, so that the ultrasonic transmission unit (transmission side transducer) on the upper side in the flow direction. The time required to reach the ultrasonic receiving unit (reception-side transducer) on the downstream side in the flow direction (hereinafter referred to as forward arrival time) and the flow from the ultrasonic transmission unit (transmission-side transducer) on the downstream side in the flow direction In this method, the average flow velocity and flow rate of the fluid flowing through the flow path are determined from the time difference from the time required to reach the ultrasonic receiver (reception-side vibrator) on the upper side in the direction (hereinafter referred to as the reverse arrival time).
[0003]
To find the time difference between the forward arrival time and the reverse arrival time,
{Circle around (1)} In the ultrasonic reception waveform, a waveform portion that exceeds (or falls below) a predetermined threshold value is used as a trigger wave, and a zero-cross point where the amplitude of the trigger wave becomes zero is detected on the received waveform by a “zero-cross method”. A method of measuring the forward arrival time and the backward arrival time, respectively, and calculating the time difference (see Patent Document 1);
(2) A high-speed A / D converter such as a DSP (Digital Signal Processor) under the assumption that the forward ultrasonic wave reception waveform and the reverse ultrasonic wave reception waveform are almost equal (combined). The two waveforms are sampled by the element in the time axis direction at predetermined cycles, A / D converted, and the corresponding sampling values of both waveforms are subtracted to obtain a correlation coefficient. A method for directly obtaining a time difference from the reverse arrival time (see Patent Document 2);
Etc. are known.
[0004]
[Patent Document 1]
JP 2002-13958 A [Patent Document 2]
JP-A-11-241934 [0005]
[Problems to be solved by the invention]
In each of these methods, an arrival time difference is detected each time from a pair of ultrasonic reception waveforms obtained by alternately switching transmission and reception of an ultrasonic signal, and an average flow velocity and a flow rate are measured each time. However, in a gas meter, for example, there are many cases where the flow rate of the gas flowing through the gas pipe does not actually change much. That is, in a factory facility, a usage form in which a constant flow rate is used is normal, and in a general household, a time period in which gas is not used is considerably long. Therefore, if the arrival time difference is always detected every time, the time spent for detecting the arrival time difference becomes relatively long, and the consumption of the battery as the power source for measurement increases. Further, useless consumption of the battery is not preferable from the viewpoint of energy consumption. In particular, in the correlation method, the detection accuracy of the arrival time difference is high, but the amount of data processing is large, so that the battery consumption becomes severe.
[0006]
Therefore, an object of the present invention is to provide an ultrasonic flowmeter capable of saving energy without increasing the amount of battery consumption by relatively shortening the time spent for detecting the arrival time difference.
[0007]
Means for Solving the Problems and Effects of the Invention
To solve the above problems, the ultrasonic flowmeter according to the present invention,
A pair of ultrasonic transmission / reception units is installed in the flow path for passing the fluid, and ultrasonic waves are transmitted between the pair of ultrasonic transmission / reception units in both the lower and upper directions of the flow direction of the fluid, and reach. In an ultrasonic flow meter that measures the flow rate of a fluid based on the time difference of time,
Storage means for sampling and A / D converting an ultrasonic reception waveform in any one direction in a predetermined cycle in a time axis direction and storing each sampled value;
Thereafter, similarly obtained ultrasonic reception waveforms in the same direction are each sampled in a predetermined cycle in the time axis direction and A / D converted, and each sampled value obtained by the sampling is stored in the storage means. Flow rate change determination means for determining that the flow rate is constant when the difference from the sampling value to be performed is smaller than a predetermined threshold,
It is characterized by having.
[0008]
According to this ultrasonic flow meter, when the flow rate change determination means determines that the flow rate is constant (no flow rate change), the arrival time difference (hence, the fluid flow rate) is not measured, but only when it is determined that the flow rate has changed. Therefore, the time spent for detecting the arrival time difference is relatively shortened, so that the amount of battery consumption can be suppressed and energy can be saved.
[0009]
Therefore, in order to solve the above problems, the ultrasonic flowmeter according to the present invention, as a first specific embodiment,
A pair of ultrasonic transmission / reception units is installed in the flow path for passing the fluid, and ultrasonic waves are transmitted between the pair of ultrasonic transmission / reception units in both the lower and upper directions of the flow direction of the fluid, and reach. In an ultrasonic flow meter that measures the flow rate of a fluid based on the time difference of time,
Storage means for sampling and A / D converting an ultrasonic reception waveform in any one direction in a predetermined cycle in a time axis direction and storing each sampled value;
Similarly, the obtained ultrasonic reception waveform in the other direction is similarly sampled at predetermined cycles in the time axis direction and A / D converted, and each sampling value obtained by the sampling and the corresponding value stored in the storage means are obtained. Correlation coefficient calculation means for obtaining a correlation coefficient based on the sampling value to be calculated,
Flow rate calculating means for calculating the flow rate of the fluid based on the time difference between the arrival time and the time at which the correlation coefficient obtained by the correlation coefficient calculating means has a maximum value,
Further, the one-way ultrasonic reception waveform obtained thereafter is similarly similarly sampled at predetermined cycles in the time axis direction and A / D converted, and each sampled value obtained thereby and stored in the storage means. Flow rate change determination means for determining that the flow rate is constant when the difference from the corresponding sampling value is smaller than a predetermined threshold,
It is characterized by having.
[0010]
Further, in order to solve the above problems, the ultrasonic flowmeter according to the present invention, as a second specific embodiment,
A pair of ultrasonic transmission / reception units is installed in the flow path for passing the fluid, and ultrasonic waves are transmitted between the pair of ultrasonic transmission / reception units in both the lower and upper directions of the flow direction of the fluid, and reach. In an ultrasonic flow meter that measures the flow rate of a fluid based on the time difference of time,
Storage means for sampling and A / D converting an ultrasonic reception waveform in any one direction in a predetermined cycle in a time axis direction and storing each sampled value;
Thereafter, similarly obtained ultrasonic reception waveforms in the same direction are each sampled in a predetermined cycle in the time axis direction and A / D converted, and each sampled value obtained by the sampling is stored in the storage means. Flow rate change determination means for determining that the flow rate is constant when the difference from the sampling value to be performed is smaller than a predetermined threshold,
In the flow rate change determining means, when it is determined that the difference is greater than the threshold value and the flow rate has changed, each of the sampling values relating to the one-way ultrasonic reception waveform obtained later is stored in the storage means. The ultrasonic wave is transmitted in the other direction, and the ultrasonic wave reception waveform is similarly sampled and A / D-converted at predetermined cycles in the time axis direction. Correlation coefficient calculation means for obtaining a correlation coefficient based on a sampling value and a corresponding sampling value stored in the storage means,
Flow rate calculating means for calculating the flow rate of the fluid based on the time difference between the arrival time and the time at which the correlation coefficient obtained by the correlation coefficient calculating means has a maximum value,
It is characterized by having.
[0011]
Further, in order to solve the above problems, the ultrasonic flowmeter according to the present invention, as a third specific embodiment,
A pair of ultrasonic transmission / reception units is installed in the flow path for passing the fluid, and ultrasonic waves are transmitted between the pair of ultrasonic transmission / reception units in both the lower and upper directions of the flow direction of the fluid, and reach. In an ultrasonic flow meter that measures the flow rate of a fluid based on the time difference of time,
Storage means for sampling and A / D converting an ultrasonic reception waveform in any one direction in a predetermined cycle in a time axis direction and storing each sampled value;
Similarly, the obtained ultrasonic reception waveform in the other direction is similarly sampled at predetermined cycles in the time axis direction and A / D converted, and each sampling value obtained by the sampling and the corresponding value stored in the storage means are obtained. Correlation coefficient calculation means for obtaining a correlation coefficient based on the sampling value to be calculated,
Flow rate calculating means for calculating the flow rate of the fluid based on the time difference between the arrival time and the time at which the correlation coefficient obtained by the correlation coefficient calculating means has a maximum value,
Further, the one-way ultrasonic reception waveform obtained thereafter is similarly similarly sampled at predetermined cycles in the time axis direction and A / D converted, and each sampled value obtained thereby and stored in the storage means. A flow rate change determination unit that determines that the flow rate is constant when a difference from a corresponding sampling value is smaller than a predetermined threshold value,
In the flow rate change determination means, when it is determined that the difference is larger than the threshold value and the flow rate has changed, each storage value obtained afterward in one direction of the ultrasonic reception waveform in the storage means The ultrasonic wave is transmitted again in the other direction, and the ultrasonic wave reception waveform is similarly sampled at predetermined cycles in the time axis direction by the correlation coefficient calculating means, and A / D conversion is performed. Transform, to obtain a correlation coefficient based on each sampling value obtained thereby and the corresponding sampling value stored in the storage means,
The flow rate calculating means sets a time at which the correlation coefficient obtained by the correlation coefficient calculating means has a maximum value as a time difference between the arrival times, and calculates a flow rate of the fluid based on the time difference.
[0012]
Therefore, according to these ultrasonic flowmeters, the sampling value used in the correlation coefficient calculation or the flow rate change determination can be stored in the storage unit and used in the next flow rate change determination or the correlation coefficient calculation. Therefore, sampling data can be utilized without waste, and battery consumption can be reduced. In particular, since the arrival time difference is measured by the correlation method as in these ultrasonic flowmeters, battery consumption can be suppressed even when the amount of data processing increases.
[0013]
If the correlation coefficient calculating means starts sampling the ultrasound reception waveform after a delay time determined in accordance with the propagation distance of the ultrasound with reference to the time of ultrasound transmission, the arrival time difference can be measured. Therefore, it is possible to narrow down and acquire only the sampling data actually required, thereby reducing the consumption of the battery and reducing the storage capacity of the storage means.
[0014]
On the other hand, in the case where the flow rate change determination means starts sampling the ultrasonic reception waveform after the elapse of a delay time determined according to the propagation distance of the ultrasonic wave with respect to the time of transmission of the ultrasonic wave, the determination of the flow rate change is also performed. Therefore, it is possible to narrow down and acquire only the sampling data actually required, thereby reducing the consumption of the battery and reducing the storage capacity of the storage means.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a basic configuration of an embodiment of an ultrasonic flowmeter used as a general residential gas meter or the like. In the flow path 1 for flow measurement of the ultrasonic flow meter 100, a flow measurement gas (fluid) flows along the flow direction axis O in the illustrated flow direction (average flow velocity v). A pair of ultrasonic transmitting and receiving units 2 and 3 are attached to the wall 10 of the flow channel 1. In FIG. 1, the ultrasonic transmission / reception unit 2 (transmission / reception vibrator 21 (first vibrator) on the upper side in the flow direction of the fluid and the ultrasonic transmission / reception unit 3 on the lower side in the flow direction of the fluid (the transmission / reception vibrator 31 (second vibration ) Are arranged in a transmission type Z arrangement facing each other with the flow path 1 interposed therebetween.
[0016]
In the measurement flow path 1, the flow direction axis O is linear between at least the pair of ultrasonic transmission / reception units 2 and 3, and the shape and the cross-sectional area of the axial cross section are the same in the flow direction. When the measurement object is a gas, the axial cross-sectional shape of the measurement flow path 1 may be any as long as it forms a space closed by the wall 10. For example, any one of a circular shape, an elliptical shape, a square shape, a rectangular shape, and the like can be used. May be adopted. If the measurement target is a liquid such as water, an open shape (for example, a semicircular shape) in which the zenith of the wall 10 is open to the atmosphere may be adopted as the axial cross-sectional shape of the measurement flow path 1. .
[0017]
The ultrasonic transmission / reception unit 2 includes a transmission / reception vibrator 21 (first vibrator) that is fixed to the wall 10 of the flow channel 1 and includes a piezoelectric element, a vibration plate, an electrode plate, and the like. On the other hand, the ultrasonic transmission / reception unit 3 is fixed to the wall 10 on the lower side in the flow direction from the ultrasonic transmission / reception unit 2 (first vibrator 21), and is a transmission / reception vibrator composed of a piezoelectric element, a vibration plate, an electrode plate and the like 31 (second vibrator). Further, the pair of ultrasonic transmission / reception units 2 and 3 include a transmission unit 22 including a drive voltage circuit for oscillating the first vibrator 21 or the second vibrator 31, and the first vibrator 21 or A receiving unit 32 including a voltage detection circuit for detecting a voltage generated by the second vibrator 31; Thereby, the first vibrator 21 transmits the ultrasonic wave toward the lower side (the ultrasonic transmitting / receiving unit 3 side) in the flow direction of the fluid, and receives the ultrasonic wave transmitted by the second vibrator 31. On the other hand, the second vibrator 31 transmits the ultrasonic wave toward the upstream side (the ultrasonic transmitting / receiving unit 2 side) in the flow direction of the fluid, and receives the ultrasonic wave transmitted by the first vibrator 21.
[0018]
In FIG. 1, the average velocity of the gas is v, the velocity of sound propagating in the gas is c, and the angle between the traveling direction of the ultrasonic wave (measurement line M) and the flow direction of the gas (flow direction axis O) is θ (hereinafter, measurement line). When the propagation distance of the ultrasonic wave is L, the forward arrival time Td and the backward arrival time Tu are respectively expressed as follows.
Td = L / (c + v · cos θ) (1)
Tu = L / (cv · cos θ) (2)
The following equations are obtained from the equations (1) and (2).
v = K (L / 2 cos θ) (Tu−Td) / (Tu · Td) (3)
Q = v · A (4)
Here, K is a correction coefficient, A is a cross-sectional area of the flow path 1, and Q is a gas flow rate.
Therefore, from the measurement of the forward arrival time Td and the backward arrival time Tu (arrival time difference ΔT), the average flow velocity v and the flow rate Q of the gas are obtained. As described above, by eliminating the sound speed c depending on the temperature and the contained components of the gas from the equation (3), the measured value (the arrival time Td, Tu; the arrival time difference ΔT) and the constant value (the propagation distance L, the line angle) θ) has the advantage of obtaining the flow velocity v.
[0019]
Therefore, as shown in FIG. 1, the ultrasonic flow meter 100 includes a measurement control unit 4 and a switching unit 7 as a measurement unit. The switching means 7 has a reception signal switching means 71 for switching a signal to be processed by the receiving means 32 and a transmission switching means 72 for switching the transducers 21 and 31 to be transmitted.
[0020]
The measurement control unit 4 has a CPU 41, a RAM 42, a ROM 43, an input / output interface 44, and the like, and is configured by a microcomputer connected to a bus 45 so as to be able to transmit and receive. The ROM 43 has a flow rate measurement program storage area 43a. In this area 43a, a control program for measuring the flow rate and the like are stored. The RAM 42 stores a sampling value described later in a sampling value storage area 42a as a work area, and has a function of a sampling value storage unit (storage unit). The CPU 31 has functions as a correlation coefficient calculation unit, a flow rate calculation unit, and a flow rate change determination unit, which will be described later.
[0021]
Next, the operation of the measuring unit of the ultrasonic flowmeter 100 will be described with reference to the timing chart of FIG. 2 and the flowchart of FIG.
First, the first vibrator 21 is switched to the transmitting side and the second vibrator 31 is switched to the receiving side by the switching means 7 (S1), and the ultrasonic wave is directed from the first vibrator 21 to the second vibrator 31 on the downstream side in the flow direction. Is transmitted (S2). At this time, the ultrasonic reception waveform received by the second transducer 31 is sampled at predetermined cycles in the time axis direction and A / D converted, and the respective sampling values (1) are stored in the sampling value storage area 42a of the RAM 42. It is stored (S3).
[0022]
Subsequently, the first vibrator 21 is switched to the receiving side and the second vibrator 31 is switched to the transmitting side by the switching means 7 (S4). A sound wave is transmitted (S5). At this time, the ultrasonic receiving waveform received by the first transducer 21 is sampled at predetermined cycles in the time axis direction and A / D converted, and the respective sampling values (2) are obtained (S6). A correlation coefficient between (1) and (2) is obtained based on each sampling value (2) obtained in S6 and the corresponding sampling value (1) stored in the sampling value storage area 42a in S3 ( S7). Note that, when acquiring the sampling value (2) in S6, as shown in FIG. 2, the ultrasonic wave transmission time (S5) is set as a reference and is determined corresponding to the ultrasonic wave propagation distance L (see FIG. 1). After the elapse of the delay time, sampling of the ultrasonic reception waveform is started. Therefore, it is possible to acquire only necessary sampling values while suppressing battery consumption, and this also reduces the storage capacity of the sampling value storage area 42a.
[0023]
FIG. 4A shows the sampling value {1} stored in the sampling value storage area 42a in S3, and FIG. 4B shows the sampling value {2} obtained in S6. Using FIG. 4A and FIG. 4B, the correlation coefficient of FIG. 4C is calculated by the correlation method (S7). Then, in FIG. 4C, the value of the time axis at which the correlation coefficient shows the maximum value is directly read to obtain the arrival time difference ΔT, and the flow rate Q is calculated from the above-described equations (3) and (4) (S8). ). Here, in this embodiment, the sampling value is directly used when calculating the correlation coefficient. However, other calculation methods such as, for example, obtaining the correlation coefficient by approximating the obtained sampling data by approximation may be used. You can also.
[0024]
Again, the switching means 7 switches the first vibrator 21 to the transmitting side and the second vibrator 31 to the receiving side (S9). The ultrasonic wave is directed from the first vibrator 21 to the second vibrator 31 on the downstream side in the flow direction. Is transmitted (S10). At this time, the ultrasonic receiving waveform received by the second transducer 31 is sampled at predetermined cycles in the time axis direction, A / D converted, and the respective sampled values (3) are obtained (S11). Then, the difference between each sampled value (3) obtained in S11 and the corresponding sampled value (1) stored in the sampled value storage area 42a in S3 is obtained, and when this difference is smaller than a predetermined threshold value (S12). NO), it is determined that the flow rate Q is constant, and the process returns to S10, and the transmission of the ultrasonic wave from the first transducer 21 (S10) and the acquisition of the sampling value (3) (S11) are repeated. When the difference is larger than the threshold value (YES in S12), it is determined that the flow rate Q has changed, and each sampling value (3) obtained in S11 is rewritten and input to the sampling value storage area 42a (S13), and the flow goes to S4. To return. At the time of acquiring the sampling value {circle around (3)} in S11, as shown in FIG. 2, the ultrasonic wave transmission time (S10) is set as a reference and is determined corresponding to the ultrasonic wave propagation distance L (see FIG. 1). After the elapse of the delay time, sampling of the ultrasonic reception waveform is started. Therefore, it is possible to acquire only necessary sampling values while suppressing battery consumption, and this also reduces the storage capacity of the sampling value storage area 42a.
[0025]
FIG. 5A shows the sampling value {circle around (3)} acquired in S11, and FIG. 5 (b) shows the sampling value {3} between the sampling value {3} and the sampling value {1} stored in the storage area 42a in S3. The state where the difference is compared with a threshold value (S12) is shown.
[0026]
When returning to S4, the first vibrator 21 is switched to the receiving side and the second vibrator 31 is switched to the transmitting side again by the switching means 7 (S4). An ultrasonic wave is transmitted toward 21 (S5). At this time, the ultrasonic receiving waveform received by the first transducer 21 is sampled at predetermined cycles in the time axis direction and A / D converted, and the respective sampling values (2) are obtained (S6). Based on each sampling value (2) obtained in S6 and the corresponding sampling value (3) stored in the sampling value storage area 42a in S3 (rewritten in S13), (3) and (2). Is obtained (S7). Then, similarly to the above, the value of the time axis at which the correlation coefficient shows the maximum value is directly read to obtain the arrival time difference ΔT, and the flow rate Q is calculated (S8).
[0027]
In the embodiment, only the case where the ultrasonic transmission / reception units 2 and 3 (transmission / reception transducers 21 and 31) are arranged in the transmission type Z arrangement has been described. However, the present invention is also applicable to other arrangement systems such as the reflection type V arrangement. Applicable.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a basic configuration of one embodiment of an ultrasonic flowmeter according to the present invention.
FIG. 2 is a timing chart showing the operation of a measuring unit.
FIG. 3 is a flowchart of FIG. 2;
FIG. 4 is an explanatory diagram showing a processing method for calculating a correlation coefficient.
FIG. 5 is an explanatory diagram showing a processing method of flow rate change determination.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Flow paths 2 and 3 Ultrasonic transceiver 21 First transducer (transmitter / receiver)
31 Second transducer (transmitter / receiver transducer)
4 Measurement control unit 41 CPU (correlation coefficient calculation means, flow rate calculation means, flow rate change determination means)
42 RAM (storage means)
100 ultrasonic flow meter

Claims (6)

A pair of ultrasonic transmission / reception units is installed in the flow path for passing the fluid, and ultrasonic waves are transmitted between the pair of ultrasonic transmission / reception units in both the lower and upper directions of the flow direction of the fluid, and reach. In an ultrasonic flow meter that measures the flow rate of a fluid based on the time difference of time,
Storage means for sampling and A / D converting an ultrasonic reception waveform in any one direction in a predetermined cycle in a time axis direction and storing each sampled value;
Thereafter, similarly obtained ultrasonic reception waveforms in the same direction are each sampled in a predetermined cycle in the time axis direction and A / D converted, and each sampled value obtained by the sampling is stored in the storage means. Flow rate change determination means for determining that the flow rate is constant when the difference from the sampling value to be performed is smaller than a predetermined threshold,
An ultrasonic flowmeter comprising: A pair of ultrasonic transmission / reception units is installed in the flow path for passing the fluid, and ultrasonic waves are transmitted between the pair of ultrasonic transmission / reception units in both the lower and upper directions of the flow direction of the fluid, and reach. In an ultrasonic flow meter that measures the flow rate of a fluid based on the time difference of time,
Storage means for sampling and A / D converting an ultrasonic reception waveform in any one direction in a predetermined cycle in a time axis direction and storing each sampled value;
Similarly, the obtained ultrasonic reception waveform in the other direction is similarly sampled at predetermined cycles in the time axis direction and A / D converted, and each sampling value obtained by the sampling and the corresponding value stored in the storage means are obtained. Correlation coefficient calculation means for obtaining a correlation coefficient based on the sampling value to be calculated,
Flow rate calculating means for calculating the flow rate of the fluid based on the time difference between the arrival time and the time at which the correlation coefficient obtained by the correlation coefficient calculating means has a maximum value,
Further, the one-way ultrasonic reception waveform obtained thereafter is similarly similarly sampled at predetermined cycles in the time axis direction and A / D converted, and each sampled value obtained thereby and stored in the storage means. Flow rate change determination means for determining that the flow rate is constant when the difference from the corresponding sampling value is smaller than a predetermined threshold,
An ultrasonic flowmeter comprising: A pair of ultrasonic transmission / reception units is installed in the flow path for passing the fluid, and ultrasonic waves are transmitted between the pair of ultrasonic transmission / reception units in both the lower and upper directions of the flow direction of the fluid, and reach. In an ultrasonic flow meter that measures the flow rate of a fluid based on the time difference of time,
Storage means for sampling and A / D converting an ultrasonic reception waveform in any one direction in a predetermined cycle in a time axis direction and storing each sampled value;
Thereafter, similarly obtained ultrasonic reception waveforms in the same direction are each sampled in a predetermined cycle in the time axis direction and A / D converted, and each sampled value obtained by the sampling is stored in the storage means. Flow rate change determination means for determining that the flow rate is constant when the difference from the sampling value to be performed is smaller than a predetermined threshold,
In the flow rate change determining means, when it is determined that the difference is greater than the threshold value and the flow rate has changed, each of the sampling values relating to the one-way ultrasonic reception waveform obtained later is stored in the storage means. The ultrasonic wave is transmitted in the other direction, and the ultrasonic wave reception waveform is similarly sampled and A / D-converted at predetermined cycles in the time axis direction. Correlation coefficient calculation means for obtaining a correlation coefficient based on a sampling value and a corresponding sampling value stored in the storage means,
Flow rate calculating means for calculating the flow rate of the fluid based on the time difference between the arrival time and the time at which the correlation coefficient obtained by the correlation coefficient calculating means has a maximum value,
An ultrasonic flowmeter comprising: A pair of ultrasonic transmission / reception units is installed in the flow path for passing the fluid, and ultrasonic waves are transmitted between the pair of ultrasonic transmission / reception units in both the lower and upper directions of the flow direction of the fluid, and reach. In an ultrasonic flow meter that measures the flow rate of a fluid based on the time difference of time,
Storage means for sampling and A / D converting an ultrasonic reception waveform in any one direction in a predetermined cycle in a time axis direction and storing each sampled value;
Similarly, the obtained ultrasonic reception waveform in the other direction is similarly sampled at predetermined cycles in the time axis direction and A / D converted, and each sampling value obtained by the sampling and the corresponding value stored in the storage means are obtained. Correlation coefficient calculation means for obtaining a correlation coefficient based on the sampling value to be calculated,
Flow rate calculating means for calculating the flow rate of the fluid based on the time difference between the arrival time and the time at which the correlation coefficient obtained by the correlation coefficient calculating means has a maximum value,
Further, the one-way ultrasonic reception waveform obtained thereafter is similarly similarly sampled at predetermined cycles in the time axis direction and A / D converted, and each sampled value obtained thereby and stored in the storage means. A flow rate change determination unit that determines that the flow rate is constant when a difference from a corresponding sampling value is smaller than a predetermined threshold value,
In the flow rate change determination means, when it is determined that the difference is larger than the threshold value and the flow rate has changed, each storage value obtained afterward in one direction of the ultrasonic reception waveform in the storage means The ultrasonic wave is transmitted again in the other direction, and the ultrasonic wave reception waveform is similarly sampled at predetermined cycles in the time axis direction by the correlation coefficient calculating means, and A / D conversion is performed. Transform, to obtain a correlation coefficient based on each sampling value obtained thereby and the corresponding sampling value stored in the storage means,
The flow rate calculating means sets a time at which the correlation coefficient obtained by the correlation coefficient calculating means has a maximum value as a time difference between the arrival times, and calculates a fluid flow rate based on the time difference. Sound flow meter. 5. The correlation coefficient calculating means according to claim 2, wherein sampling of an ultrasonic reception waveform is started after a lapse of a delay time determined in accordance with an ultrasonic wave propagation distance with reference to a time of ultrasonic transmission. Item 2. The ultrasonic flowmeter according to item 1. 6. The method according to claim 1, wherein the flow rate change determination unit starts sampling the ultrasonic reception waveform after a lapse of a delay time defined in accordance with the propagation distance of the ultrasonic wave with reference to the transmission time of the ultrasonic wave. The ultrasonic flowmeter according to the item.

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