JPWO2006080182A1 - Ultrasonic flow meter, 2-type combined ultrasonic flow meter - Google Patents

Abstract

The flow velocity distribution measuring unit 11 obtains the flow velocity distribution along the measurement line based on the measurement result by the sensor 1 or the like. The power / standard deviation calculation processing unit 12 calculates the power and standard deviation for each channel based on the Doppler shift frequency and its average value, the Doppler spectrum, etc. obtained in the process by the flow velocity distribution measuring unit 11. Based on the calculation result, the state of the fluid to be measured is determined.

Description

  The present invention relates to an ultrasonic flow meter.

  Conventionally, there is a clamp-on type ultrasonic flowmeter as a flow measurement technique using ultrasonic waves. In this clamp-on type ultrasonic flowmeter, a material for transmitting sound waves to the pipe, that is, a wedge, is installed on a part of the outer peripheral surface of the pipe to which the fluid to be measured passes. The flowmeter measures the flow rate of the fluid to be measured by transmitting sound waves to the inside of the pipe through the wedge. As a clamp-on type ultrasonic flowmeter, flow measurement technology using the pulse Doppler method (hereinafter referred to as pulse Doppler method) and flow measurement technology using the propagation time difference method (hereinafter referred to as propagation time difference method) are known. Yes.

  The pulse Doppler method measures the flow rate of the fluid from the moving speed of the suspended particles and the like, assuming that the suspended particles and bubbles contained in the fluid move at the same speed as the fluid. As described above, the non-steady state fluid can be measured with high accuracy without contact. The flow measurement technique described in Patent Document 1 transmits ultrasonic pulses (group) at a constant interval to a fluid to be measured in a pipe, and is reflected by foreign matters such as bubbles (reflectors on the measurement line) mixed in the fluid. This is an application of the principle of Doppler shift, in which the frequency of the ultrasonic echo wave is changed by a magnitude proportional to the flow velocity. That is, the Doppler shift is calculated based on the echo wave, the flow velocity distribution of the fluid to be measured is obtained, and the flow rate is calculated by integration calculation based on the flow velocity distribution, thereby obtaining the flow rate of the fluid to be measured.

  The above-mentioned pulse Doppler method has high accuracy and high-speed response compared to the propagation time difference method, and is excellent in bubble resistance. Furthermore, by providing multiple measurement lines, high-precision measurement is possible even when there is a drift. There are features. However, the pulse Doppler method enables measurement by having a certain amount of reflector in the fluid to be measured to a certain degree, so that there is not enough reflector or the reflector is biased. However, there is a problem that high-precision measurement cannot be performed.

  On the other hand, the propagation time difference method uses one or more pairs of transmission / reception integrated transducers to compare the ultrasonic propagation time from the upstream side to the downstream side and the ultrasonic propagation time from the downstream side to the upstream side. By using the difference, the average flow velocity and flow rate of the non-measurement fluid are calculated. This method is suitable for measuring the flow rate of liquid or pure water with less impurities compared to the pulse Doppler method. In other words, in the propagation time difference method, if a large amount of impurities such as bubbles are mixed in the fluid to be measured, high-accuracy measurement may be difficult.

In the conventional ultrasonic flowmeter, measurement is performed by either the pulse Doppler method or the propagation time difference method.
Conventionally, for example, an invention described in Patent Document 2 has been proposed.

  The invention described in Patent Document 2 includes a time difference type ultrasonic flow meter and a Doppler type ultrasonic flow meter, and is a time difference type ultrasonic flow meter below a predetermined flow rate threshold, and a Doppler type above a threshold value. Switch to an ultrasonic flowmeter.

  However, the Doppler method in Patent Document 2 is different from the pulse Doppler method. That is, the Doppler method in Patent Document 2 is a method generally called a continuous wave method, and the pulse Doppler method is a pulse wave method. The Doppler method (continuous wave method) in Patent Document 2 is described in, for example, Non-Patent Document 1 and the like. However, if briefly described, the velocity of the fluid to be measured at one point on the central axis of the pipe is described. This is a technique for calculating the flow rate from the fluid velocity obtained by using Doppler shift. On the other hand, the pulse Doppler method is a method of calculating the flow rate using the obtained flow velocity distribution by obtaining the flow velocity at specific positions (plural) in the pipe. Therefore, Patent Document 2 has a description that the Doppler method has a problem that accuracy is lower than that of the time difference method. On the other hand, the pulse Doppler method has higher measurement accuracy than the propagation time difference method as described above.

  As described above, the flow measurement technique using the pulse Doppler method has many advantages over the propagation time difference method. However, depending on the state of the fluid to be measured (the amount of the above-mentioned reflector, the deviation, etc.), the propagation time difference method It may be better to use. Here, the state of the fluid to be measured is not constant at a certain measurement point (installation point of the ultrasonic flowmeter) but changes. Therefore, even if a certain amount of reflector exists in the measured fluid at a certain point in time to a certain degree, there may be a situation where there is not enough reflectors at another point in time and / or the reflectors are biased. .

Therefore, an ultrasonic flow meter in which the pulse Doppler method and the propagation time difference method are mixed for each measurement point and a method of switching both in accordance with the state of the fluid to be measured can be considered.
However, conventionally, it has been difficult to automatically determine the state of the fluid to be measured by the apparatus. Conventionally, the flow velocity distribution obtained during the processing for the flow rate calculation is displayed, or the received signal of the reflected ultrasonic echo wave is displayed. The state of the measurement fluid was judged empirically.

  As described above, it is desirable to automatically determine the state of the fluid to be measured by the apparatus. Then, it is desired to perform flow rate measurement with higher accuracy by switching between the pulse Doppler method and the propagation time difference method based on the determination result.

On the other hand, in the method described in Patent Document 2, the switching is merely performed based on the flow rate, and does not determine the state of the fluid to be measured such as the amount of the reflector and the uniformity, The criteria for switching are not adequately appropriate. Further, as described above, Patent Document 2 is not related to the pulse Doppler method in the first place. By using the pulse Doppler method, measurement with higher accuracy is possible even in an unsteady state.
JP 2000-97742 A JP 2004-184245 A "Flow measurement for instrumentation engineers A to Z" pages 128-131, author: Japan Metrology Equipment Industry Association, publisher: Kogyo Kogyosha, November 1, 1995, first edition

  An object of the present invention is to determine the state of a fluid to be measured in a pulse Doppler type ultrasonic flowmeter so that the accuracy of a measurement result can be known. Further, a combined use of a pulse Doppler method and a propagation time difference method The type of ultrasonic flow meter is configured, and the pulse Doppler method is switched to the propagation time difference method according to the determination result of the state of the fluid to be measured. It is to provide an ultrasonic flow meter, a two-system combined ultrasonic flow meter, and the like that can measure a flow rate without using a flow rate.

  The pulse Doppler type ultrasonic flowmeter of the present invention includes, for each channel, power calculation means for calculating power indicating the intensity of the echo signal based on a Doppler spectrum obtained based on the measured echo signal, and each channel. For each channel, the standard deviation calculating means for calculating the standard deviation based on the Doppler shift frequency obtained based on the measured echo signal and the average value thereof, and the power or / and the standard deviation for each channel, respectively. A state discriminating unit for discriminating the state of the fluid to be measured by comparing with a predetermined threshold value is provided.

  The calculated power indicates the state of the reflector contained in the fluid to be measured (proportional to the number, etc.), and the standard deviation indicates the flow stability. For example, when the power is larger than the threshold value and the standard deviation is smaller than the threshold value, the state of the fluid to be measured can be regarded as having a certain amount of reflector and a uniform flow. In other words, it can be considered that high-precision measurement can be performed by the pulse Doppler method. In this way, since the state of the fluid to be measured can be automatically determined, for example, by displaying the determination result, the supervisor can know the certainty of the measurement result.

  Further, by applying the method for determining the state of the fluid to be measured to an ultrasonic flowmeter of the combined use of the pulse Doppler method and the propagation time difference method, both measurement methods can be switched at an appropriate time.

  That is, the two-method combined ultrasonic flowmeter of the present invention is a combined ultrasonic flowmeter of the pulse Doppler method and the propagation time difference method, and normally uses the pulse Doppler method for each channel. And a power calculation means for calculating power indicating the intensity of the echo signal based on a Doppler spectrum obtained based on the measured echo signal, and a Doppler shift frequency obtained based on the measured echo signal for each channel. And a standard deviation calculating means for calculating the standard deviation based on the average value thereof, and for each channel, the power or / and the standard deviation are respectively compared with a predetermined threshold value, thereby determining the state of the fluid to be measured. A state determination unit for determining and a switch for determining whether to temporarily switch to the propagation time difference method according to the determination result by the state determination unit. Configured to have a means.

  The state discriminating means can determine whether it is in a state where high-accuracy measurement can be performed by the pulse Doppler method, so if it is determined that the measurement accuracy has deteriorated, temporarily switch to the propagation time difference method. Thus, it is possible to prevent a significant deterioration in measurement accuracy.

  For example, the state determination unit determines whether or not the measurement accuracy is deteriorated for each channel, and the switching unit has the measurement accuracy deteriorated by the state determination unit. When the number of determined channels is equal to or greater than a preset ratio, the measurement method is switched to the propagation time difference method.

Further, for example, the power is a total power obtained by integrating the Doppler spectrum or an averaged power obtained by dividing the total power by the number of acquisitions.
Further, for example, instead of the standard deviation calculated based on the Doppler shift frequency and the average value thereof, a value obtained by normalizing the calculated standard deviation by the average value of the Doppler shift frequency is used.

  Further, for example, when an arbitrary number of measurements or measurement time is set in advance and the switching means is temporarily switched to the propagation time difference method, the measurement by the propagation time difference method is performed by the set number of measurements or measurement time. May be performed.

  Also, for example, when the switching means is temporarily switched to the propagation time difference method, the measurement result by the propagation time difference method is corrected and output so as to change gently from the measurement result by the pulse Doppler method immediately before the switching. You may make it do.

  According to the ultrasonic flowmeter of the present invention, the two-type combined ultrasonic flowmeter, etc., it is possible to know the certainty of the measurement result by determining the state of the fluid to be measured in the pulse Doppler type ultrasonic flowmeter. In addition, by configuring an ultrasonic flow meter that combines the pulse Doppler method and the propagation time difference method, and switching the pulse Doppler method to the propagation time difference method according to the determination result of the state of the fluid to be measured, It makes it possible to measure the flow rate without degrading the measurement accuracy while taking advantage of the high-precision measurement by the Doppler method. In addition, since the discrimination accuracy is high, switching is performed at an appropriate time.

It is a structure and functional block diagram of the pulse Doppler type ultrasonic flowmeter by this example. It is a figure which shows the discrimination criterion of the state of the to-be-measured fluid based on an experimental result. It is a figure which shows the discrimination criterion of the state of the to-be-measured fluid based on an experimental result. It is a figure which shows the discrimination criterion of the state of the to-be-measured fluid based on an experimental result. It is a configuration / function block diagram of a two-system combined ultrasonic flowmeter according to this example. It is a flowchart figure of the flow measurement process of this example. It is a modification of the process of FIG. It is a figure for demonstrating the process discriminate | determined using a success rate. It is a figure for demonstrating the response | compatibility method when both measurement systems switch frequently in a short time. It is a figure for demonstrating the response | compatibility method when both measurement systems switch frequently in a short time. It is a figure for demonstrating the response | compatibility method when both measurement systems switch frequently in a short time. It is a figure for demonstrating the response | compatibility method when both measurement systems switch frequently in a short time. It is a figure shown about a channel.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration / function block diagram of a pulse Doppler type ultrasonic flowmeter according to this example, which can determine the state of a fluid to be measured.

  The illustrated pulse Doppler type ultrasonic flowmeter includes a sensor 1, a transmitter 2, an emitter 3, an amplifier 4, an A / D converter 5, a display device 6, and a CPU / MPU 10. The CPU / MPU 10 executes a predetermined application program stored in its built-in memory or an external memory (not shown), whereby a flow velocity distribution measurement unit 11, a power / standard deviation calculation processing unit 12, and a flow rate calculation processing unit 13 are executed. The processing of each functional unit is executed.

  The sensor 1 is an ultrasonic transducer and is attached to a wedge 8 installed on a part of the outer peripheral surface of a pipe wall 7 of a pipe through which a fluid to be measured flows. The sensor 1 outputs an ultrasonic pulse based on the electrical signal generated by the transmitter 2 and the emitter 3. This ultrasonic pulse is, for example, a straight beam having a diameter of about 5 mm, enters the fluid flowing through the pipe via the wedge 8 and the tube wall 7, and is reflected by the reflector 9 (such as bubbles) contained in the fluid. Is done. The reflected echo is received by the sensor 1 and converted into an electrical signal, and then output to the amplifier 4.

  The transmitter 2 generates an electric signal having a fundamental frequency f0, and the emitter 3 outputs the electric signal from the oscillator 2 in a pulse shape at predetermined time intervals (1 / Fprf). Accordingly, the ultrasonic pulse having the fundamental frequency f0 is output from the sensor 1 at predetermined time intervals. The basic frequency f0 is basically a required frequency determined in inverse proportion to the inner diameter of the pipe. The sensor 1 is attached to the wedge 8 so as to be inclined at a certain angle with respect to the pipe, and the ultrasonic pulse travels in the fluid along the illustrated measurement line. . In addition to the bubbles, the reflector 9 includes particles such as fine powder, foreign matter having an acoustic impedance different from that of the fluid to be measured, and the like.

The reflected echo electrical signal output from the sensor 1 is amplified by the amplifier 4, digitized by the A / D converter 5, and input to the CPU / MPU 10.
In the CPU / MPU 10, the flow velocity distribution measuring unit 11 and the flow rate calculation processing unit 13 are existing processing units. When the digital signal is input, first, the flow velocity distribution measuring unit 11 detects the fluid to be measured. A flow velocity distribution is calculated, and the flow rate calculation processing unit 13 calculates the flow rate of the fluid to be measured based on the flow velocity distribution. The apparatus further includes a power / standard deviation calculation processing unit 12.

As described above, in the measurement by the pulse Doppler method, the transmission / reception of the ultrasonic pulse is repeatedly performed many times at a predetermined repetition period (1 / Fprf).
The flow velocity distribution measuring unit 11 calculates the flow velocity at each position on the measurement line based on the measurement results obtained many times, and obtains the flow velocity distribution based on the calculated flow velocity at each position (measurement point). When calculating the flow velocity, a Doppler shift (difference between the transmission pulse frequency and the reception echo frequency) component is extracted, and the flow velocity is calculated based on the Doppler shift frequency fd and the like.

  Here, each position (measurement point) does not mean one point, but each area (referred to as a channel) formed by dividing a measurement region (for example, a region corresponding to a pipe radius in a direction perpendicular to the tube axis). ). Naturally, it is unpredictable which area the reflector 9 passes through, but it is also unpredictable where in each area the reflector 9 flows for each area. . That is, the pulse Doppler system handles a probabilistic event, and it is difficult to obtain a true value. Therefore, for example, if 256 times of flow velocity measurement is performed for each channel, the average value is calculated and used as the flow velocity at each position (measurement point). Then, a Doppler spectrum is calculated for each channel based on the measurement results for 256 times. It should be noted that, for each measurement execution, which channel is the measurement point (the position where the reflector 9 was present) can be determined based on the time taken from the transmission of the ultrasonic pulse to the reception of the reflected echo. .

  First, the power / standard deviation calculation processing unit 12 is based on data (such as the Doppler shift frequency fd or Doppler spectrum) obtained in the flow rate calculation process by the flow rate distribution measuring unit 11, for example, Reference 1 (“Basics”). Ultrasonic Medicine, Shinichi Yagi, Nobuyuki Endo, Ikuo Hirata, Junichi Ito; Ishiyaku Shuppan Co., Ltd .; October 10, 2002, first edition, third edition, pages 26-31), Reference 2 ( As described below, the “Ultrasound Medical Dictionary” is written for each channel as described below by the method described in the textbook of Ultrasonic Medicine, Shujunsha, Shujunsha, September 8, 2000. , Power (P) and standard deviation σ are calculated.

  For each channel, for example, as described in Reference Documents 1 and 2, first, a power spectrum having the horizontal axis of Doppler shift frequency fd and the vertical axis of power, that is, Doppler spectrum P (fd), is obtained. Then, using this Doppler spectrum P (fd), the power (P) in the channel is calculated by the following equation (1).

The power (P) indicates the intensity of the echo wave and is proportional to the number of reflectors in the fluid to be measured, as described in the above-mentioned reference 1.

Further, the average Doppler shift frequency which is an average value of the Doppler shift frequency fd
From (primary moment), variance σ ² (secondary moment), which is a statistic that specifies the degree of variation in Doppler shift frequency fd, can be expressed by the following equation (2).

The square root (√) of the dispersion is the standard deviation σ. This standard deviation indicates the variation in the time domain of the measurement results for each channel (flow stability) for each channel. If this variation is within a practical range, the measurement results are valid. it is conceivable that.

  As described above, the power (P) indicates the state (number, etc.) of the reflector included in the fluid to be measured, and the standard deviation indicates the flow stability. When the power is large and the standard deviation is large, the state of the fluid to be measured indicates that the reflector is contained to some extent and the flow is uneven. In addition, when the power is large and the standard deviation is small, the state of the fluid to be measured indicates that the reflector is contained to some extent and the flow is uniform. Further, when the power is small and the standard deviation is large, the state of the fluid to be measured indicates that there is little (or no) reflector and non-uniform flow.

  Here, the inventor of the present application has confirmed the conditions (state of the fluid to be measured) under which a high-accuracy flow rate measurement, which is a feature of the flow meter, in the pulse Doppler ultrasonic flow meter can be performed based on experiments and the like. That is, as shown in FIG. 2A, it was confirmed that when the condition that the power is large and the standard deviation is small is satisfied, the flow rate can be measured with high accuracy without any problem.

  As a specific example, for example, as shown in FIG. 2B by an experiment using SUS50A piping, the average flow velocity of the fluid to be measured is 0.4 (m / s) to 2 (m / s) as shown in FIG. 2B. In some cases, the measurement accuracy is good, there are few variations in the measurement results, and at an average flow velocity of 0.2 (m / s), it is possible to confirm the deterioration of the measurement accuracy and the large variations in the measurement results. Then, the inventor further obtained the experimental result shown in FIG. 2C as a result of calculating the power (P) and the standard deviation while sequentially changing the average flow velocity of the fluid to be measured.

  As shown in FIG. 2C, each flow velocity in the range of 0.4 (m / s) to 2 (m / s), which is an average flow velocity that can be measured with high accuracy, is applied to the classification shown in FIG. 2A. In this case, the condition “power is large and standard deviation is small” is almost applicable. In this experimental result, the threshold value for separating “large” and “small” is roughly 10 7 to 8 to the power (P), and the standard deviation is about 1 to 1.5 (rad). It can be judged that it is near.

  Here, in this experiment, the flow rate is changed to obtain the power and standard deviation at each flow rate, but this does not mean that normality / abnormality is determined by the flow rate. Since it is known to some extent how the state of the fluid to be measured changes by changing the flow velocity, the flow velocity is used as a parameter. That is, in this experiment, bubbles are included in the fluid so as to be substantially uniform with a substantially constant amount. However, the faster the flow velocity, the greater the number of reflectors 9 that pass through the measurement line per unit time. Thus, the flow rate suggests the number of reflectors in the fluid. In this experiment, bubbles are used as the reflector, and the bubbles in the water naturally have the property of floating. However, when the flow velocity is high, the bubbles are swept away as they are, so the variation is small. On the other hand, if the flow rate is slow, the bubbles emerge on the way, and the bubbles are biased to the upper side in the gravity direction of the pipe.

As described above, the above experimental results, for example, do not always mean that normal measurement can be performed when the flow velocity is 2 m / s, but only the state of the fluid to be measured is reproduced by the flow velocity.
The power (P) and standard deviation are calculated according to the number of reflectors in the fluid and variations.

  In other words, the power / standard deviation calculation processing unit 12 calculates the power indicating the intensity of the echo signal based on the Doppler spectrum obtained based on the measured echo signal for each channel. And a standard deviation calculation unit for calculating the standard deviation based on the Doppler shift frequency obtained based on the measured echo signal and the average value for each channel, and the power or / and for each channel. It can be said that it comprises a state discriminating unit (both not shown) for discriminating the state of the fluid to be measured by comparing the standard deviation with a predetermined threshold value.

  As described above, the power (P) and the standard deviation calculated by the power / standard deviation calculation processing unit 12 are displayed on the display device 6, for example, and the operator or the like currently measures the threshold based on the experimental result. The state of the fluid can be judged and it can be confirmed whether the measurement accuracy has deteriorated. Alternatively, the threshold value or the like is set in advance in the power / standard deviation calculation processing unit 12 and, for example, if the condition “high power and small standard deviation” is not satisfied, the measurement accuracy is deteriorated. You may make it display on the display apparatus 6. FIG. That is, these display contents serve as an index for knowing the certainty of the measurement result.

  By using the power and the standard deviation as described above, the state of the fluid to be measured can be accurately expressed, and thus the “index for knowing the accuracy of the measurement result” is highly reliable. Furthermore, by setting an appropriate threshold value based on the experimental results as described above, the reliability of the determination as to whether or not the measurement accuracy has deteriorated is also high. In the two-method combined ultrasonic flow meter described later, Will be switched when appropriate.

  That is, by applying the method for determining the state of the fluid to be measured to the two-method combined ultrasonic flow meter shown in FIG. 3 described below, the measurement accuracy can be improved while taking advantage of the high measurement accuracy of the pulse Doppler method. When the state becomes worse, the deterioration of measurement accuracy can be suppressed by switching to the propagation time difference method.

FIG. 3 is a configuration / function block diagram of the two-method combined ultrasonic flowmeter according to this example.
Note that the two systems are the pulse Doppler system and the propagation time difference system as described above.
The two-type ultrasonic flowmeter shown in the figure includes a sensor 1, a sensor 21, a sensor 22, a switch 23, an amplifier 24, an amplifier 25, a switching unit 26, an A / D converter 27, a CPU / MPU 28, a transmission circuit 29, and a display. It comprises a device 30 and an input device 31.

  The sensor 1 is an ultrasonic transducer for the pulse Doppler system shown in FIG. In FIG. 3, a sensor 21 and a sensor 22 which are a pair of ultrasonic transducers for the propagation time difference method are further provided. The sensors 21 and 22 themselves may be the same as the sensor 1 and can be shared. That is, the sensor 1 may be deleted and the sensor 21 may be used for the pulse Doppler method.

The transmission circuit 29 includes, for example, the transmitter 2 and the emitter 3 shown in FIG.
The switch 23 is a switch for switching between using the sensor 1 and using the sensors 21 and 22. When the switch 23 is switched to the sensor 1 side, the electrical signal output from the transmission circuit 29 is input to the sensor 1 to emit an ultrasonic pulse, which is reflected by the reflector 9 or the like. The echo electrical signal output from is input to the amplifier 24. On the other hand, when the switch 23 is switched to the sensor 21 or 22 side, the electrical signal output from the transmission circuit 29 is input to the sensor 21 or 22, and an ultrasonic pulse is emitted. The electric signal (received wave) received and output by is input to the amplifier 25.

Similarly to the amplifier 4, the amplifiers 24 and 25 are simply signal amplification circuits, the amplifier 24 amplifies the echo electric signal, and the amplifier 25 amplifies the received wave.
The switching unit 26 inputs the amplified output signal of either one of the amplifiers 24 and 25 to the A / D converter 27. Of course, when the sensor 1 is used, the switching unit 26 is switched to the amplifier 24 side. The A / D converter 27 A / D converts any one of the amplified output signals and outputs the digital signal to the CPU / MPU 28.

  The CPU / MPU 28 has the function units of the flow velocity distribution measurement unit 11, the power / standard deviation calculation processing unit 12, and the flow rate calculation processing unit 13 in the same manner as the CPU / MPU 10 of FIG. When the calculation processing unit 12 determines that the measurement accuracy is deteriorated as described above, the calculation processing unit 12 includes a switching control unit (not illustrated) that switches the switching unit 26 and the switch 23 to the propagation time difference method side. Moreover, it has a processing function part (not shown) which performs the flow volume calculation process by a propagation time difference system.

  When the CPU / MPU 28 calculates the flow rate by any of the above methods, the flow rate is displayed on the display device 30. Moreover, you may display on the display apparatus 30 which said system is used now.

FIG. 4 shows a flowchart of the flow rate measurement process executed by the CPU / MPU 28.
In this example, the flow rate measurement is normally performed by the pulse Doppler method, and only when it is determined that the measurement accuracy has deteriorated, the switching to the propagation time difference method is performed.

  Accordingly, in normal times, the switch 23 and the switching unit 26 are switched to the sensor 1 side, and when the digital signal of the echo wave detected by the sensor 1 is input from the A / D converter 27, the flow velocity distribution measurement is performed. The flow rate is calculated by the unit 11 (step S11). As described above, the power / standard deviation calculation processing unit 12 uses the Doppler spectrum P (fd) obtained in the processing process, and the power (P) and standard are calculated. The deviation σ is calculated (step S12).

  As described above, since the threshold value X for the power (P) and the threshold value Y for the standard deviation σ are set and registered in advance, the power (P) and the standard deviation calculated in step S12 are respectively set to the threshold values. Compared with X and Y, for example, when power (P) ≧ X and standard deviation ≦ Y, that is, when the condition “power is large and standard deviation is small” is satisfied (step S13, YES). Then, the pulse Doppler system is continued as it is, and the flow rate calculation processing unit 13 calculates the flow rate (step S14), and outputs the calculation result and the like to the display device 30 (step S19).

  On the other hand, when the condition of “power (P) ≧ X and standard deviation ≦ Y” is not satisfied (step S13, NO), the mode is switched to the propagation time difference method. That is, first, after switching the switch 23 and the switching unit 26, the ultrasonic pulse is transmitted from the sensor 21 and received by the sensor 22, the ultrasonic pulse is transmitted from the sensor 22 and received by the sensor 21 (step S15), If both have been received normally (step S16, YES), the average flow velocity and flow rate of the fluid to be measured are calculated based on the difference in propagation time between the two (step S17), and the result is output to the display device 30. If at least one of the signals cannot be normally received (step S16, NO), an abnormality process is performed (step S18).

  In the above description, the process of step S13 is “power (P) ≧ X and standard deviation ≦ Y” as a determination condition. However, the present invention is not limited to this example, and only “power (P) ≧ X” is a determination condition. Alternatively, only “standard deviation ≦ Y” may be set as the determination condition. According to the experimental results shown in FIG. 2C, it is possible to discriminate to some extent even using only the standard deviation. The power is proportional to the number of reflectors in the fluid to be measured, and it is known that accurate measurement cannot be performed if the number of reflectors is small in the pulse Doppler method. This is because it can be discriminated to some extent.

FIG. 5 shows a modification of the process of FIG.
The process of steps S21 to S26 shown in FIG. 5 is almost the same as the process of steps S11 to S19 of FIG. 4 (the process of step S25 is the process of steps S15 to S18 of FIG. 4). The difference is that the user sets arbitrary threshold values Xs and Ys at an arbitrary time in advance (step S27), and the determination in step S23 is performed in place of the threshold values Xs and Y in step S13. Ys is used. That is, the manufacturer of the above-mentioned two-method combined ultrasonic flowmeter sets the threshold values X and Y based on the experimental results and other experiences and intuitions, but the optimum threshold values are the piping conditions and the properties of the fluid to be measured. It depends on etc. Therefore, for each user, thresholds Xs and Ys can be arbitrarily set that the user considers appropriate. This displays a threshold setting screen (not shown) on the display device 30, and the user operates the input device 31 to input a desired threshold value. The input device 31 is a touch panel, a keyboard, or the like.

  The flow velocity is calculated for each position (channel) in the direction perpendicular to the pipe axis of the pipe (pipe section direction) as described above. However, the processes in FIGS. 4 and 5 use only some of the channels. However, it was not explained whether all channels were used only. Although it is conceivable that only one arbitrary channel or an arbitrary part (plurality) of channels may be used, a technique that is considered appropriate for determining with high determination accuracy is shown in FIG. The description will be given with reference.

  In the processing example shown in FIG. 6, first, the threshold values Xs and Ys are arbitrarily set on the user side in advance as in FIG. 5, and the threshold value Zs of an arbitrary success rate is set. The success rate threshold Zs can be set to any value between 0% and 100%, but the present inventor considers that about 70% is appropriate from the experimental results and the like. Note that the values X and Y set by the manufacturer may be used as the power and standard deviation threshold values as in FIG. Similarly, the threshold set for the success rate may be a value set by the manufacturer.

  In FIG. 6, the processing in steps S31 and S32 is the same as that in steps S11 and S12, but the power (P) and standard deviation are calculated for all channels.

  Then, for each channel, the power (P) and standard deviation are compared with the threshold values Xs and Ys to determine whether or not the measurement accuracy is deteriorated, and it is determined that the measurement accuracy is not deteriorated. Count the number of channels. Then, the success rate = n / N is calculated from the count number n and the total channel number N. Then, the calculated success rate is compared with the success rate threshold value Zs. If the success rate ≧ Zs (step S34, YES), the pulse Doppler method is used as it is, and the flow rate calculation processing unit 13 performs the flow rate calculation. Execute (Step S35). On the other hand, if the success rate <Zs (step S34, NO), the process is switched to the propagation time difference method, and the processes of steps S15 to S18 described in FIG. 4 are executed (step S36).

  Here, the calculation of the power (P) and the standard deviation described above is affected by the set parameters. For example, power (P) is affected by the number of acquisitions. The number of acquisitions is, for example, 256 in the above description, and the power (P) increases as the number of acquisitions increases. Since it is affected by the parameters in this way, there is a case where normality / abnormality cannot be evaluated centrally by the threshold value.

Therefore, in order to prevent the power (P) and the standard deviation from fluctuating depending on the setting parameters, the power (P) and the standard deviation may be calculated as follows.
The power (P) may be a value averaged by the number of acquisitions. That is, the power (P) calculated by the above equation (1) divided by the number of acquisitions (power (P) / number of acquisitions) may be used as the calculation result of the power (P).

Alternatively, the standard deviation is the average Doppler shift frequency calculated from the standard deviation σ obtained based on the equation (2).
Value normalized by

It is good. This is the average Doppler shift frequency even if the value of σ is the same.
This is because the meaning differs depending on whether the value of is large or small. That is, even if the values of σ are the same, the average Doppler shift frequency

When the value of is small, the variation is larger than when the value is large. Of course, in these cases, the threshold values X, Y, etc. are also determined based on averaged or standardized values.

  The standard deviation is the standard deviation of the Doppler shift frequency fd, but may instead be the standard deviation of the Doppler shift phase angle ωd. The relationship between the Doppler shift frequency fd and the Doppler shift phase angle ωd is expressed by the following equation (3). Therefore, the standard deviation of the Doppler shift phase angle ωd is obtained by multiplying the standard deviation of the Doppler shift frequency fd calculated from the square root of the calculation result of the expression (2) by 2πT. T is the pulse repetition period 1 / Fprf.

The two-method combined ultrasonic flow meter described above is based on pulse Doppler measurement and is temporarily switched to the propagation time difference method only when it is determined that the measurement accuracy is deteriorated based on the threshold value. Depending on the state of the fluid to be measured, for example, the calculation result of the power and the standard deviation may be almost the same value as the threshold value.In this case, the threshold value is not exceeded or exceeded by a slight fluctuation. It can be a situation where switching occurs frequently. However, since the measurement result by the pulse Doppler method and the measurement result by the propagation time difference method are slightly different as shown in FIG. 7A, for example, when both measurement methods are frequently switched in a short time, the measurement result is, for example, FIG. 7B. As shown in FIG.

  In the pulse Doppler method, ultrasonic pulse transmission / reception is performed, for example, 256 times to measure the flow velocity of one channel, an average value is obtained, and it is further determined whether or not the measurement method is switched. On the other hand, for the propagation time difference, after processing 256 times, correlation calculation, calculation of propagation time, propagation time difference, temperature correction, etc. are performed, and finally the flow velocity and flow rate of the fluid to be measured are calculated. Accordingly, the processing time until the flow rate calculation in the propagation time difference method and the pulsed Doppler method is on the same order, and can be in a state as shown in FIG. 7B, for example.

  The ultrasonic flowmeter measures and displays the flow rate, but also displays the flow velocity, and it is often the case that a monitor or the like refers to this to determine whether there is an abnormality. For this reason, if the flow velocity fluctuates frequently as described above, it may be misunderstood that an abnormality has occurred. In addition, there is a considerable influence on the output flow rate value.

In this example, the following two ways are proposed to deal with this problem, but the present invention is not limited to this example.
The first method is a method in which, when the pulse Doppler method is switched to the propagation time difference method, the measurement by the propagation time difference method is continued until a predetermined time t elapses or until the measurement number n is executed. The value of t or n can be set by the user, for example, and is set arbitrarily in advance. For example, if 20 is set as n, after switching to the propagation time difference method, measurement by the propagation time difference method is continuously performed 20 times, and then returning to the pulse Doppler method, and switching of the measurement method is determined. In this way, frequent switching between both measurement methods in a short time can be prevented. Even in the situation shown in FIG. 7B, the measurement result is as shown in FIG. 7C, for example.

In the second method, the flow velocity measurement result by the pulse Doppler method immediately before switching from the pulse Doppler method to the propagation time difference method is set to v1, and each flow velocity measurement result up to the number of measurements n by the propagation time difference method after switching is v2 _k (k ; an integer from 1 to n, v2 _k is calculated, when the mean flow rate measurement results of the k th), the flow velocity v after switching, the following formula for each of performing measurement by the propagation time difference method To do.

v = (a _k −1) v1 + a _k × v2 _k
(Where n is the number of measurements set in the same manner as in the first method, and a _k = (1 / n) × k).

  According to the above calculation formula, the value of the flow velocity v gradually approaches the value of the measurement result by the propagation time difference method from the value close to v1, so that the output flow velocity value does not change rapidly, for example, in FIG. As shown, it gradually changes with the passage of time.

Then, when measuring n times, switch to the pulse Doppler method.
The second method is particularly effective when the difference between v1 and v2 is large.
By the first or second method, it is possible to suppress output disturbance due to switching of the measurement method.

Finally, the position (channel) on the measurement line is temporarily shown in FIG.
CH1, CH2, CH3, etc. shown in FIG. 8 correspond to positions (channels) on the measurement line.
According to the ultrasonic flowmeter of the present invention, the two-type combined ultrasonic flowmeter, etc., it is possible to know the certainty of the measurement result by determining the state of the fluid to be measured in the pulse Doppler type ultrasonic flowmeter. In addition, by configuring an ultrasonic flow meter that combines the pulse Doppler method and the propagation time difference method, and switching the pulse Doppler method to the propagation time difference method according to the determination result of the state of the fluid to be measured, It makes it possible to measure the flow rate without degrading the measurement accuracy while taking advantage of the high-precision measurement by the Doppler method. In addition, since the discrimination accuracy is high, switching is performed at an appropriate time.

[0006]
FIG. 2A is a diagram showing a criterion for determining a state of a fluid to be measured based on an experimental result.
FIG. 2B is a diagram for explaining a discrimination method (reference) based on an experimental result.
FIG. 2C is a diagram for explaining a discrimination method (reference) based on an experimental result.
FIG. 3 is a configuration / function block diagram of a two-system combined ultrasonic flowmeter according to this example.
FIG. 4 is a flowchart of the flow rate measurement process of this example.
FIG. 5 is a modification of the process of FIG.
FIG. 6 is a diagram for explaining processing for determination using a success rate.
[FIG. 7A] It is a figure for demonstrating the response | compatibility method when both measurement systems switch frequently in a short time.
[FIG. 7B] It is a figure for demonstrating the response | compatibility method when both measurement systems switch frequently in a short time.
[FIG. 7C] It is a figure for demonstrating the response | compatibility method when both measurement systems switch frequently in a short time.
[FIG. 7D] It is a figure for demonstrating the response | compatibility method when both measuring methods switch frequently in a short time.
FIG. 8 is a diagram showing a channel.
BEST MODE FOR CARRYING OUT THE INVENTION
[0025]
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration / function block diagram of a pulse Doppler type ultrasonic flowmeter according to this example, which can determine the state of a fluid to be measured.
[0026]
The illustrated pulse Doppler type ultrasonic flowmeter includes a sensor 1, a transmitter 2, an emitter 3, an amplifier 4, an A / D converter 5, a display device 6, and a CPU / MPU 10. The CPU / MPU 10 executes a predetermined application program stored in its built-in memory or an external memory (not shown), whereby a flow velocity distribution measurement unit 11, a power / standard deviation calculation processing unit 12, and a flow rate calculation processing unit 13 are executed. The processing of each functional unit is executed.
[0027]
The sensor 1 is an ultrasonic transducer and is attached to a wedge 8 installed on a part of the outer peripheral surface of a pipe wall 7 of a pipe through which a fluid to be measured flows. The sensor 1 outputs an ultrasonic pulse based on the electrical signal generated by the transmitter 2 and the emitter 3. This ultrasonic filter

[0007]
Luth is a straight beam having a diameter of about 5 mm, for example, enters the fluid flowing through the pipe via the wedge 8 and the tube wall 7 and is reflected by the reflector 9 (such as bubbles) contained in the fluid. The reflected echo is received by the sensor 1 and converted into an electrical signal, and then output to the amplifier 4.
[0028]
The transmitter 2 generates an electrical signal having a fundamental frequency f0, and the emitter 3 outputs the electrical signal from the transmitter 2 in a pulse shape at predetermined time intervals (1 / Fprf). Accordingly, the ultrasonic pulse having the fundamental frequency f0 is output from the sensor 1 at predetermined time intervals. The basic frequency f0 is basically a required frequency that is determined in inverse proportion to the inner diameter of the pipe. The sensor 1 is attached to the wedge 8 so as to be inclined at a certain angle with respect to the pipe, and the ultrasonic pulse travels in the fluid along the illustrated measurement line. . In addition to the bubbles, the reflector 9 includes particles such as fine powder, foreign matter having an acoustic impedance different from that of the fluid to be measured, and the like.
[0029]
The reflected echo electrical signal output from the sensor 1 is amplified by the amplifier 4, digitized by the A / D converter 5, and input to the CPU / MPU 10.
In the CPU / MPU 10, the flow velocity distribution measuring unit 11 and the flow rate calculation processing unit 13 are existing processing units. When the digital signal is input, first, the flow velocity distribution measuring unit 11 detects the fluid to be measured. A flow velocity distribution is calculated, and the flow rate calculation processing unit 13 calculates the flow rate of the fluid to be measured based on the flow velocity distribution. The apparatus further includes a power / standard deviation calculation processing unit 12.
[0030]
As described above, in the measurement by the pulse Doppler method, transmission / reception of the ultrasonic pulse is repeatedly performed many times at a predetermined repetition period (1 / Fprf).
The flow velocity distribution measuring unit 11 calculates the flow velocity at each position on the measurement line based on the measurement results obtained many times, and obtains the flow velocity distribution based on the calculated flow velocity at each position (measurement point). When calculating the flow velocity, a Doppler shift (difference between the transmission pulse frequency and the reception echo frequency) component is extracted, and the flow velocity is calculated based on the Doppler shift frequency fd and the like.
[0031]
Here, each position (measurement point) does not mean one point, but each area (referred to as a channel) formed by dividing a measurement region (for example, a region corresponding to a pipe radius in a direction perpendicular to the tube axis). ). Of course, it is predicted which area the reflector 9 will pass through.

[0014]
In step S23), the determination in step S23 is to use the threshold values Xs and Ys in place of the threshold values X and Y in step S13. That is, the manufacturer of the above-mentioned two-method combined ultrasonic flowmeter sets the threshold values X and Y based on the experimental results and other experiences, etc., but the optimum threshold depends on the piping conditions and the properties of the fluid to be measured. It will change. Therefore, for each user, thresholds Xs and Ys can be arbitrarily set that the user considers appropriate. This displays a threshold setting screen (not shown) on the display device 30, and the user operates the input device 31 to input a desired threshold value. The input device 31 is a touch panel, a keyboard, or the like.
[0059]
The flow velocity is calculated for each position (channel) in the direction perpendicular to the pipe axis of the pipe (pipe section direction) as described above. However, the processes in FIGS. 4 and 5 use only some of the channels. However, it was not explained whether all channels were used only. Although it is conceivable that only one arbitrary channel or an arbitrary part (plurality) of channels may be used, a technique that is considered appropriate for determining with high determination accuracy is shown in FIG. The description will be given with reference.
[0060]
In the processing example shown in FIG. 6, first, the threshold values Xs and Ys are arbitrarily set on the user side in advance as in FIG. 5, and the threshold value Zs of an arbitrary success rate is set. The success rate threshold Zs can be set to any value between 0% and 100%, but the present inventor considers that about 70% is appropriate from the experimental results and the like. Note that the values X and Y set by the manufacturer may be used as the power and standard deviation threshold values as in FIG. Similarly, the threshold set for the success rate may be a value set by the manufacturer.
[0061]
In FIG. 6, the processing in steps S31 and S32 is the same as that in steps S11 and S12, but the power (P) and standard deviation are calculated for all channels.
[0062]
Then, for each channel, the power (P) and standard deviation are compared with the threshold values Xs and Ys to determine whether or not the measurement accuracy is deteriorated, and it is determined that the measurement accuracy is not deteriorated. Count the number of channels. Then, the success rate = n / N is calculated from the count number n and the total channel number N. Then, the calculated success rate is compared with the success rate threshold value Zs. If the success rate ≧ Zs (step S34, YES), the pulse Doppler method is used as it is, and the flow rate calculation processing unit 13 performs the flow rate calculation. Execute (step S35)

[0018]
You can.
[0077]
Finally, the positions (channels) on the measurement line are shown in FIG.
CH1, CH2, CH3, etc. shown in FIG. 8 correspond to positions (channels) on the measurement line.
According to the ultrasonic flowmeter of the present invention, the two-type combined ultrasonic flowmeter, etc., it is possible to know the certainty of the measurement result by determining the state of the fluid to be measured in the pulse Doppler type ultrasonic flowmeter. In addition, by configuring an ultrasonic flow meter that combines the pulse Doppler method and the propagation time difference method, and switching the pulse Doppler method to the propagation time difference method according to the determination result of the state of the fluid to be measured, It makes it possible to measure the flow rate without degrading the measurement accuracy while taking advantage of the high-precision measurement by the Doppler method. In addition, since the discrimination accuracy is high, switching is performed at an appropriate time.

Claims (11)

In pulse Doppler type ultrasonic flowmeter,
For each channel, based on a Doppler spectrum obtained based on the measured echo signal, power calculating means for calculating power indicating the intensity of the echo signal;
Standard deviation calculating means for calculating the standard deviation for each channel based on the Doppler shift frequency obtained based on the measured echo signal and its average value;
A state discriminating unit that discriminates the state of the fluid to be measured by comparing the power or / and the standard deviation with a predetermined threshold value for each channel,
A pulse Doppler type ultrasonic flowmeter characterized by comprising: A combined ultrasonic flow meter with a pulse Doppler method and a propagation time difference method,
In normal times, the pulse Doppler method shall be used.
For each channel, based on a Doppler spectrum obtained based on the measured echo signal, power calculating means for calculating power indicating the intensity of the echo signal;
Standard deviation calculating means for calculating the standard deviation for each channel based on the Doppler shift frequency obtained based on the measured echo signal and its average value;
A state discriminating unit that discriminates the state of the fluid to be measured by comparing the power or / and the standard deviation with a predetermined threshold value for each channel,
Switching means for deciding whether or not to temporarily switch to the propagation time difference method according to the determination result by the state determination means;
2 type combined use ultrasonic flowmeter characterized by having. The state determination means determines whether or not the measurement accuracy is deteriorated for each channel,
The switching means switches the measurement method to a propagation time difference method when the number of channels determined that the measurement accuracy is deteriorated by the state determination means is equal to or higher than a preset ratio. The two-system combined ultrasonic flowmeter according to claim 2.   4. The two-system combined ultrasonic flow rate according to claim 2, wherein the power is a total power obtained by integrating the Doppler spectrum or an averaged power obtained by dividing the total power by the number of acquisitions. Total.   3. A value obtained by normalizing the calculated standard deviation by an average value of the Doppler shift frequency is used instead of the standard deviation calculated based on the Doppler shift frequency and an average value thereof. Or 2 type | mold combined use type ultrasonic flowmeter of 3 description.   The standard deviation calculating means calculates the standard deviation of the Doppler shift phase angle using the Doppler shift phase angle and its average value instead of the Doppler shift frequency and its average value. 2 type combined use ultrasonic flowmeter of description.   The two-type combined ultrasonic flowmeter according to claim 2, further comprising an input means for setting and changing the threshold value. Set any number of measurements or measurement time in advance,
3. The combined use of the two methods according to claim 2, wherein when the switching means is temporarily switched to the propagation time difference method, the measurement by the propagation time difference method is performed for the set number of measurements or measurement time. Type ultrasonic flowmeter.     When the switching means is temporarily switched to the propagation time difference method, the measurement result by the propagation time difference method is corrected and output so as to change gradually from the measurement result by the pulse Doppler method immediately before the switching. The two-system combined ultrasonic flowmeter according to claim 2. In the computer in the pulse Doppler type ultrasonic flowmeter,
A function for calculating the power indicating the intensity of the echo signal based on the Doppler spectrum obtained based on the measured echo signal for each channel;
A function for calculating the standard deviation for each channel based on the Doppler shift frequency obtained based on the measured echo signal and its average value,
A function for determining the state of the fluid to be measured by comparing the power or / and the standard deviation with a predetermined threshold value for each channel;
A program to realize In the computer in the ultrasonic flow meter of the combined use type of the pulse Doppler method and the propagation time difference method,
In normal times, the pulse Doppler method shall be used.
A function for calculating the power indicating the intensity of the echo signal based on the Doppler spectrum obtained based on the measured echo signal for each channel;
A function for calculating the standard deviation for each channel based on the Doppler shift frequency obtained based on the measured echo signal and its average value,
A function for determining the state of the fluid to be measured by comparing the power or / and the standard deviation with a predetermined threshold value for each channel;
A function for determining whether to switch to the propagation time difference method according to the determination result by the state determination means;
A program to realize