JP2001324363A - Ultrasonic flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reduce influence of noise due to reflection or reverberation of ultrasonic waves in a flow passage in a pulse Doppler ultrasonic flow meter. SOLUTION: In this ultrasonic flow meter, scattered waves generated when ultrasonic waves 4 emitted from an ultrasonic wave transmitting/receiving means 3 are scattered in fluid are received in a plurality of measurement positions individually with gate time control by means of a gate circuit 15, and on the basis of Doppler deviation caused in the received scattered wave in each of the measurement positions, a flow velocity distribution in the flow passage is found, and then, a flow rate is found from the flow velocity distribution. The ultrasonic flow meter is provided with a storing means 11 taking in a signal waveform of noise due to reflection or reverberation of ultrasonic waves and storing it as a canceling noise signal and a computing means 13 finding a difference between a measured signal and the canceling noise signal, and a noise signal can be removed from the measurement signal by this differential processing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flowmeter for measuring the flow rate of a fluid by utilizing the Doppler shift of ultrasonic waves, and more particularly, for example, for rainwater drainage, agricultural water, industrial water or sewage water. The present invention relates to an ultrasonic flowmeter suitable for flow measurement for performance evaluation or the like performed as maintenance management of a fluid machine already installed.

[0002]

2. Description of the Related Art A flow rate detector (ultrasonic flow meter) which emits an ultrasonic pulse into a fluid and measures the flow rate of the fluid by utilizing the Doppler shift in scattering in the fluid is disclosed in, for example, Japanese Unexamined Patent Publication No. Hei 10-239127 and
No. 0-281832, and Japanese Patent Application Laid-Open No. 5-281832.
No. 1929 and Japanese Patent Application Laid-Open No. 10-246660, or "Consideration on High-Accuracy Flow Rate Calculation in Ultrasonic Pulse Doppler Method" (Transactions of the Japan Society of Mechanical Engineers, Vol. 64, No. 622, June 1998) And co-authors by Hiroshi Shirahata et al., Pp. 148-155.

[0003] In the pulse Doppler type ultrasonic flowmeter known in the art, for example, when measuring the flow rate in the discharge pipe of a drainage pump, the ultrasonic flowmeter is placed on the outer surface of the pipe wall of the flow path (discharge pipe) to be measured. A sound wave transmitter / receiver is attached, and a pulse of an ultrasonic wave having a predetermined frequency is transmitted from the ultrasonic wave transmitter / receiver in a burst shape. Then, the ultrasonic wave scattered by minute particles such as sand and air bubbles mixed in the drainage flowing through the pipeline is received by the above-mentioned transducer. The received wave contains a signal that has undergone a Doppler shift of a frequency based on the moving speed of the fine particles, that is, the flow velocity of the wastewater. Therefore, the Doppler shift frequency is obtained by frequency analysis, and the flow velocity V can be detected from the following equation (1). V = CΔf / 2f0cosθ (1) Here, C is the speed of sound in the fluid to be measured, f0 is the frequency of the transmitted ultrasonic wave, Δf is the Doppler shift frequency, and θ is the traveling direction of the ultrasonic wave and the flow path wall. Angle.

The flow velocity V is detected at a plurality of positions in the radial direction of the flow path. Each detection position L is obtained by the following equation (2). L = C · t · sin θ / 2 (2) where t is a gate timing time for receiving scattered ultrasonic waves. The detection position can be changed according to the gate timing of the signal capture. By changing the gate time in this manner, a flow velocity distribution in the radial direction of the flow path can be obtained, and the flow rate can be obtained by integrating the flow velocity distribution with respect to the cross section of the flow path.

[0005]

In such an ultrasonic flowmeter as described above, the acoustic impedance (the physical property value obtained by multiplying the density of the medium by the speed of sound) between the fluid to be measured and the pipe wall of the flow path through which the fluid flows is measured. Since there is a great difference, there is a problem that the measurement accuracy is reduced due to the reflected noise of the ultrasonic wave generated at the boundary surface or the large noise caused by the reverberation. That is, the reflected wave of the ultrasonic wave generated at the interface between the fluid and the pipe wall and the reverberant wave generated because the reflected wave is hardly attenuated cause noise of a large amplitude. And this noise lowers the signal-to-noise ratio for Doppler signals of small amplitude, resulting in regions where measurement is practically impossible, reducing the measurement accuracy of the flow rate and narrowing the measurement range. .

Regarding such a problem, Japanese Patent Laid-Open No.
Japanese Patent No. 2881832 discloses one solution. In this method, the measurement accuracy is increased or a wide measurement range can be obtained by extrapolating data other than the vicinity of the tube wall in the vicinity of the tube wall where the transmitter / receiver is noisy. This method can be said to be effective as such. However, the degree of improvement obtained is still insufficient. That is, while large noise concentrates near the tube wall on which the transducer is mounted, noise due to reflection or reverberation by the tube wall on the opposite side of the tube wall on which the transducer is mounted also lowers the S / N ratio to a considerable extent. Therefore, in order to perform high-accuracy measurement over a wide range, it is necessary to take measures against noises other than those near the tube wall where the transducer is mounted.

Here, it is conceivable to cope with a large noise in the vicinity of the tube wall where the transducer is mounted by mounting the transducer at a plurality of locations on the flow channel wall. That is, for example, if two transducers are installed so as to face each other with the flow path interposed therebetween, low-noise data can be obtained by the facing transducers in the vicinity of the respective mounting pipe walls. The influence of large noise in the vicinity can be eliminated. However, in the case of existing rainwater drainage pumping equipment, for example, only a curved pipe portion has a very limited portion in which the flow pipe is exposed to the outside. Also, the position where the transducer can be attached is limited also in the exposed curved tube portion, and in many cases, the opposed installation of the transducer cannot be performed. In other words, in a flow rate measurement performed for an existing fluid machine for performance inspection or the like, it is often impossible to use a method of eliminating the influence of noise by using a plurality of transducers.

Regarding the reduction of noise in a Doppler type ultrasonic flowmeter, a method using a filter is disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 5-1929.
No. 46660 discloses a method using a phase difference. Although these methods can reduce noise as such, they cannot be said to be sufficient. That is, the range of noise that can be removed by the filter is narrow, and is not so effective in removing noise due to reflection or reverberation. In addition, there are restrictions on noise conditions that can be removed by the phase difference method.

Accordingly, an object of the present invention is to provide an ultrasonic flowmeter capable of measuring the fluid flow rate in a flow path with higher accuracy by more effectively reducing the influence of noise accompanying the measurement. Is to do. The object of the present invention is
It is an object of the present invention to provide an ultrasonic flowmeter capable of performing high-accuracy flow measurement even in a measurement under conditions where the mounting of a transducer is limited as in an existing fluid machine.

[0010]

According to the present invention, there is provided, in the present invention, an ultrasonic wave radiated from a transmitting means or an ultrasonic wave transmitting / receiving means attached to a pipe wall of a flow path through which a fluid flows, and is scattered in the fluid. The generated scattered waves are received at each of a plurality of measurement positions by controlling the gate time, and the flow velocity distribution of the fluid in the radial direction in the flow path based on the Doppler shift occurring in the received scattered waves at each of the measurement positions In the ultrasonic flowmeter adapted to determine the flow rate of the fluid in the flow path from the flow velocity distribution, captures the signal waveform of noise caused by reflection or reverberation of ultrasonic waves by the flow path pipe wall. With the storage means for storing as a noise signal for cancellation, the noise signal for cancellation stored in the storage means and a measurement signal obtained by measurement for flow velocity distribution measurement It is characterized by comprising a calculating means for calculating the difference.

According to the present invention, for the above purpose, in the present invention, a scattered wave generated by scattering ultrasonic waves radiated from a transmitting means or an ultrasonic wave transmitting / receiving means attached to a pipe wall of a flow path through which a fluid flows is described. The flow is received at a plurality of measurement positions by controlling the gate time, and the flow velocity distribution of the fluid in the radial direction in the flow path is obtained based on the Doppler shift occurring in the received scattered wave at each measurement position. In the ultrasonic flowmeter adapted to obtain the flow rate of the fluid in the flow path from the distribution, the amplitude is equal to or larger than a predetermined value within one cycle of the Doppler signal extracted from the measurement signal received by the ultrasonic wave transmitting / receiving means. Has means for monitoring the width of the section which is
When the width of the section is smaller than a predetermined width, the gate time is controlled so that a signal is taken in a portion excluding the section.

According to the present invention for the above purpose, according to the present invention, a scattered wave generated when ultrasonic waves radiated from a transmitting means or an ultrasonic wave transmitting / receiving means attached to a pipe wall of a flow path through which a fluid flows are scattered in the fluid. The flow is received at a plurality of measurement positions by controlling the gate time, and the flow velocity distribution of the fluid in the radial direction in the flow path is obtained based on the Doppler shift occurring in the received scattered wave at each measurement position. In an ultrasonic flowmeter adapted to obtain the flow rate of the fluid in the flow path from the distribution, the ultrasonic flowmeter has means for monitoring the magnitude of the amplitude in the Doppler signal extracted from the measurement signal received by the ultrasonic wave transmitting / receiving means. The gate time is controlled so as to take in a signal only in a portion where the amplitude is equal to or smaller than a predetermined value.

[0013]

FIG. 1 is a functional block diagram showing a configuration example of an ultrasonic flowmeter according to a first embodiment. Although the figure shows a case where only one ultrasonic probe, which is an ultrasonic transducer, is used, the same applies to the case where a plurality of ultrasonic probes are used. In the following, a case where the ultrasonic flowmeter of FIG. 1 is used for measuring the flow rate of a fluid 2 flowing through a flow path 1 formed of a steel pipe or a cast iron pipe in an existing rainwater drainage pump facility, for example, The following describes an example in which the capacity of the existing rainwater drainage pump equipment is inspected by measuring the water flow rate.

An ultrasonic probe 3 for transmitting and receiving an ultrasonic pulse is attached to the tube wall 1w of the flow path. The ultrasonic probe 3 is supplied with a burst-wave-shaped electric signal having a predetermined period and a predetermined pulse number generated by the transmission pulse generator 5 under the control of the flow meter controller 14 and then amplified by the transmission amplifier 7. . The ultrasonic probe 3 converts this electric signal into an ultrasonic wave 4 and radiates it into the fluid 2. FIG. 2 shows an example of a burst-wave-like ultrasonic wave 4 radiated into a fluid, together with an electric signal used for its generation and a relationship with a gate signal described later. The number of pulses included in the burst wave is, for example, 256, and the measurement at each measurement point (each measurement position) is repeated the number of times corresponding to the number of pulses. That is, assuming that N measurement points are set in the flow path 1 in the radial direction, the measurement according to the pulse number is repeated for each of the N measurement points. In FIG. 2, one ultrasonic pulse is drawn in three cycles, but actually includes a cycle corresponding to the frequency of the emitted ultrasonic wave.

The radiated ultrasonic waves 4 are scattered by scattering fine particles such as fine sand contained in the fluid 2. The scattered ultrasonic waves undergo Doppler shift corresponding to the moving speed of the scattering fine particles, that is, the flow velocity of the fluid 2. Then, a part of the scattered ultrasonic wave which has undergone the Doppler shift enters the ultrasonic probe 3 and is converted into an electric signal, and is received as a measurement signal. The output signal from the ultrasonic probe 3 is amplified by the receiving amplifier 7. The output of the receiving amplifier 7 is input to a balanced modulator 8 serving as frequency shift detecting means together with a pulse signal (reference signal) from the transmission pulse generator 5 and mixed there, and then passes through a low-pass filter 9. Accordingly, a low-frequency signal on which information on the Doppler shift is superimposed, that is, a Doppler signal, is extracted from the output signal of the ultrasonic probe 3. FIG. 3 shows an example of the phase waveform of the signal. The Doppler signal is obtained as a waveform in which the waveform synchronized with the pulse period of the transmission ultrasonic wave is continuous with a number corresponding to the number of pulses included in the burst wave. As shown in FIG. 3, a wave having a large amplitude is generated in the period A of the waveform of one cycle of the pulse transmission cycle. This is due to noise or the like caused by a reflected wave or a reverberation wave at the boundary surface between the pipe wall and the flow path due to the flow measurement by the pulse Doppler method. The noise is fixedly generated in accordance with the conditions of the measurement system including the material and structure of the tube wall of the flow path to be measured, has a substantially constant waveform, and has a substantially uniform waveform. It becomes particularly large near the wall 1w. Therefore, a wave having a large amplitude is generated in the portion A. The Doppler signal is superimposed on this large amplitude noise signal. Therefore, if this is to be processed as it is, the desired Doppler signal may not be obtained due to the problem that the amplitude is saturated in the sampling and holding circuit 16 at the subsequent stage.

Here, the method of obtaining the Doppler shift component will be described with reference to FIGS. 5 and 6. FIG. 5 is similar to FIG. 3, but shows more periods than in FIG. FIG. 6 is a diagram of FIG.
,... And the like (the period of the received signal) at a constant gate timing (gate position) at a gate time T _G
Are displayed again as a temporal change in each cycle of the signal taken in. As shown in the figure, in each cycle (indicated by numerals 1, 2, 3, 4, and 5 in the figure), a Doppler signal phase voltage which represents a phase change due to Doppler shift in voltage. DS has changed, and the frequency of this change is the Doppler shift frequency to be obtained. That is, the Doppler shift component is calculated at each cycle (the cycle of the received signal).
Is obtained based on the fact that the amplitude of the reception signal at the time of the gate timing fluctuates in a cycle corresponding to the flow velocity of the fluid at the measurement position (the moving velocity of the scattering fine particles),
It is obtained as the difference between the periods of the varying amplitude.

Next, FIG. 1 is used for reference for understanding the present invention.
The processing of the Doppler signal in the conventional ultrasonic flowmeter shown in FIG. 2 will be described. The Doppler signal output from the low-pass filter 9 is subjected to position extraction in the gate circuit 15. In other words, the gate timing is set by the gate circuit 15 controlled by the signal from the transmission pulse generator 5, and the Doppler signal at a specific measurement point is captured. The specific position Doppler signal thus generated is formed into a continuous wave at the measurement point by passing through the sampling and holding circuit 16 for holding the extracted voltage.
That is, assuming that one burst wave is formed by 256 pulses as described above, one measurement point has 256 pulses.
There will be signal acquisitions twice, and these 256 signals are shaped into a continuous wave for the measurement point.

The specific position Doppler signal converted into a continuous wave by the sampling and holding circuit 16 is input to a frequency analyzer 17 via a filter 17. For example, the frequency analyzer 17 using a spectrum analyzer, FFT (Fast Fourier Trasform), or the like obtains a Doppler shift frequency at a measurement point from a specific position Doppler signal. Then, the flow velocity at the measurement point is calculated by the flow velocity / flow rate calculator 19 from the Doppler shift frequency according to the above equation (1). The measurement position can be sequentially moved by changing the gate timing, whereby the flow velocity distribution in the flow path is obtained. The flow velocity / flow rate calculator 19 calculates the flow rate using this flow velocity distribution.

As described above, a large amplitude noise signal overlaps with the received signal. Therefore, in the above-described signal processing in the conventional ultrasonic flowmeter, there is a case where a target Doppler signal cannot be extracted due to the influence of the noise. Specifically, it is practically impossible to extract a Doppler signal in a portion where the amplitude of noise is particularly large as in the portion A in FIG. In the present invention, in order to solve this problem, a noise waveform is separately taken in, and the noise component is removed from the measurement signal by subtracting the noise waveform from the measurement signal waveform when processing the measurement signal. . Such processing is possible because the noise is fixed according to the conditions of the measurement system as described above. In other words, since the noise waveform is fixed, the Doppler signal from which the noise component has been removed is obtained by taking the difference between the noise waveform separately captured and held and the measurement signal waveform at each gate timing. It is possible to obtain

The acquisition of the noise waveform is usually performed prior to the flow rate measurement. However, for example, when the flow rate measurement performed for the performance inspection of the existing fluid machine does not require the real-time property, It is also possible to perform the measurement after acquiring a measurement signal for measuring the flow rate. The noise waveform can be captured even when the fluid is not flowing through the flow path, or can be captured even when the fluid is flowing through the flow path. The reason why the noise waveform for noise cancellation can be captured even in the state where the fluid is flowing in the flow path is based on the above-described method of acquiring the Doppler shift component. That is, the Doppler shift component is obtained as a difference between amplitude values that are different for each measurement that is repeated a predetermined number of times at one measurement point. Therefore, in the example used in the above description, the measurement signal in a cycle of, for example, Is stored as a reference signal, and by subtracting this from each of the other signals,..., The noise component can be canceled and the Doppler shift component can be obtained as it is.

Hereinafter, the signal processing in the ultrasonic flowmeter (FIG. 1) of the present embodiment will be described by taking as an example the case where a noise waveform is taken in a state where no fluid is flowing in the flow path before the flow rate measurement. First, in a state where water is not flowing through the flow channel 1, an ultrasonic pulse for one cycle is emitted to the flow channel 1 in accordance with a command from the flow meter controller 14. The emitted ultrasonic pulse generates a reverberation wave due to reflection on the tube wall 1w of the flow path 1 and repetition of the reflected wave, and these mainly generate a noise wave. This noise wave enters the ultrasonic probe 3 and is received as a noise signal. The noise signal passes through the receiving amplifier 7, the balanced modulator 8, and the low-pass filter 9 similarly to the measurement signal described above,
The measurement signal is output as a low-frequency signal (cancellation noise signal) capable of canceling a noise signal included in the measurement signal. The noise signal for cancellation is
A / which inputs analog signals and outputs digital signals
After being converted from an analog signal to a digital signal by the D converter 11, the waveform is stored in the storage circuit 11 using a semiconductor storage element such as a RAM.

When the acquisition of the noise waveform is completed in this manner, the emission of the burst wave for flow measurement and the reception of the scattered wave scattered by the fluid are performed as described above, and the low-pass is accordingly performed. The filter 9 outputs a Doppler signal on which a noise signal is superimposed.
In the case of the present invention, this Doppler signal is inputted to a subtractor 13 which is an arithmetic means, taken out of a storage circuit 11, inputted with a digital signal, and outputted as an analog signal.
After being converted from a digital signal to an analog signal by the converter 12, a difference between the digital signal and the noise signal input to the subtractor 13 is obtained, whereby the noise is removed. FIG. 4 shows an example of a signal obtained by removing noise from the signal of FIG. 3 in this way. As shown in the figure, the signal from which noise has been removed has a waveform sufficient to effectively extract a minute Doppler signal. The signal processing after the noise is removed is the same as that in the conventional ultrasonic flowmeter described above.

In the above description, it is assumed that the noise waveform is fetched for the entire period. However, the portion where the amplitude of the noise signal is larger than a certain value, specifically, the portion A in FIG. Only a noise waveform may be fetched. That is, noise cancellation is performed only for a portion where the influence of noise is large. By doing so, the capacity of the storage circuit 11 can be saved. When the measurement is repeated at each measurement position as described above, it is also possible to take in only the noise waveform near each measurement position and cancel the noise at each measurement position with this partial noise waveform. The capacity of the storage circuit 11 can also be saved by this method. Further, the noise waveform is acquired a plurality of times, that is, a noise signal is acquired for a plurality of cycles (a plurality of pulses), and a noise signal obtained as an average value from the plurality of noise signals is stored as a noise signal for cancellation. This is also a preferred mode. By doing so, noise can be more effectively reduced. In other words, if the noise is captured only in one cycle, if there is specific noise in that cycle, this specific noise may make it impossible to effectively perform noise cancellation. By taking the above, such a problem can be avoided.

By canceling the noise as described above, the target Doppler signal can be more effectively extracted, but the following processing can be added to this. FIG. 7 shows the waveform of the output signal from the low-pass filter 9 similar to that of FIG.
Is limited to a narrow range in the vicinity of the tube wall 1w to which is attached. This is due to conditions such as the material and thickness of the tube wall 1w. In such a case,
Rather than measuring the entire area of the pulse transmission cycle, only the section B where reflection and reverberation noise are small is measured. The flow meter controller 14 performs control to limit the signal capture range to the section B. That is, the width of the section A is monitored by the flow meter controller 14, and if it is less than a certain value, a signal is taken in only the section B.

When the signal capture range (capture position) is limited as described above, there are the following two methods for processing the section A in which no signal is captured. One is a method of extrapolating the section A based on the signal in the section B. An example thereof is disclosed in JP-A-10-281832. Another method is to use ultrasonic probes in pairs. That is, an ultrasonic probe is attached to each of the positions facing each other across the flow path, and a signal is not taken in by one of the ultrasonic probes, and the signal is taken in by the other ultrasonic probe. Such a method can be used only when the condition of the fluid machine to be measured permits the use of the ultrasonic probe.For example, in an existing rainwater drainage pump facility, the flowing water pipe is only a curved pipe part. In many cases, a part of the ultrasonic probe is exposed to the outside. Under such conditions, it is generally difficult to use the ultrasonic probe in pairs.

As described above, the method of limiting the signal capturing section under the condition that the width of the section A is equal to or less than a certain value can suppress the section in which an actual signal cannot be obtained to a certain value or less, thereby increasing the measurement accuracy. be able to. Therefore, by appropriately combining such a signal capturing section restriction method with the above-described noise canceling method, more accurate flow rate measurement becomes possible. However, depending on the conditions, there are cases where the flow rate measurement can be performed with the required accuracy by using only the signal acquisition section limitation method without using the noise cancellation method.In such a case, measurement can be performed using only the signal acquisition section limitation method. It may be performed. The width of the section A that determines whether or not to use the section restriction method as described above is appropriately selected in consideration of conditions such as required measurement accuracy.

The above-described concept of restricting the signal capturing section can be used in other forms. For example, FIG.
When the measurement signal of the phase waveform as shown in is obtained,
The Doppler signal is buried in the noise signal as a whole.
However, it is possible to effectively extract a Doppler signal from a portion where the amplitude of the noise signal is small. Therefore,
A minute section (time) P in which the amplitude of the noise signal is equal to or less than a certain value
1, P2, P3,... Pi are extracted, and a gate position is set only in the vicinity of the section to take in signals. These controls are performed by the flow meter controller 14 in the configuration example of FIG.
Will do. In this case as well, the level of the amplitude is appropriately selected in consideration of the necessary conditions such as the measurement accuracy.

FIG. 9 is a functional block diagram showing an example of the configuration of an ultrasonic flowmeter according to the second embodiment. The ultrasonic flowmeter according to the present embodiment is of a type capable of measuring the flow rate with high accuracy even when a backflow portion is generated in the flow path.
For example, when inspecting the capacity of an existing rainwater drainage pump facility, the flow pipe of the pump facility is only exposed at the curved pipe portion, and the flow rate measurement is performed at this curved pipe portion. There are cases where it is inevitable. In the curved pipe portion, the non-uniformity of the flow velocity becomes large, and a negative flow velocity, that is, a reverse flow may also occur. Therefore, if the flow velocity of the backflow cannot be measured, high-precision flow measurement cannot be performed. The ultrasonic flowmeter according to the present embodiment can meet such a demand.

Therefore, in the ultrasonic flowmeter according to the present embodiment, two signal processing circuits from the receiving amplifier 7 to the frequency analyzer 18 are provided for the real part and the imaginary part. Each of the two signal processing circuits detects a real part Doppler signal and an imaginary part Doppler signal. Then, the frequency analyzer 18 performs frequency analysis with a complex signal of the real part signal and the imaginary part signal as input, thereby enabling discrimination analysis of a normal flow and a reverse flow.

Hereinafter, signal processing in the present embodiment will be described. The transmission pulse generator 5 generates and outputs a transmission pulse signal 22 in response to a transmission pulse control signal 26 from the flow meter controller 14, and modulates a signal 23 to be output to each balanced modulator 8 in the two signal processing circuits. , 2
4 is generated. The transmission amplifier 6 amplifies the transmission pulse signal 22 and outputs it as an ultrasonic probe transmission / reception signal 20. The ultrasonic probe 3 emits an ultrasonic wave corresponding to the ultrasonic probe transmission / reception signal 20 into the flow path 1. A part of the scattered wave generated by the radiated ultrasonic wave being scattered in the fluid 2 flowing through the flow path 1 enters the ultrasonic probe 3 and is converted into an electric signal, and is received as a measurement signal. The output signal from the ultrasonic probe 3 is amplified by the receiving amplifier 7 and becomes a receiving amplifier output signal 21. The reception amplifier output signal 21 is input to each balanced modulator 8 as a modulated signal. Each balanced modulator 8 converts the modulated signal 21 into the modulated signal 2
The signals are modulated by the signals 3 and 24, and a real part modulation output 27 to an imaginary part modulation output 28 are output. Here, the modulation signals 23 and 24 are
The repetition frequency is the same as the repetition frequency of the transmission pulse, and the phase of each signal is different by 90 degrees.

Each low-pass filter 9 outputs the real-part modulated output 2
7 and the imaginary part modulation output 28, only low-frequency components are passed, and a real part low-pass filter output signal 29 to an imaginary part low-pass filter output signal 30 are output. The real part low-pass filter output signal 29 and the imaginary part low-pass filter output signal 30 are input to storage circuits (difference processing circuits) 25 of respective systems together with storage circuit control signals 31 to 32 from the flow meter controller 14. Each difference processing circuit 2
Numeral 5 stores the waveform of the noise signal previously acquired as described above, and calculates the difference between the noise signal and the low-pass filter output signals 29 to 30 to obtain the real part difference output signal 33 or the imaginary part. Difference output signal 34
Is output. Each gate circuit 15 outputs the real part difference output signal 3
With the 3 to imaginary part difference output signal 34 and the gate signals 31 to 32 as inputs, the above-described position extraction is performed, and the real part gate output signal 37 to the imaginary part gate output signal 38 are output. Each sampling hold circuit 16
Receives the real part gate output signal 37 to the imaginary part gate output signal 38 and the sampling signals 41 to 42 from the flow meter controller 14, and outputs the real part sampling hold output signal 39 to the imaginary part sampling hold output signal 40. . Each of the filter circuits 17 receives the real part sampling hold output signal 39 to the imaginary part sampling hold output signal 40 and outputs the real part filter output signal 43 to the imaginary part filter output signal 44. Both the real part filter output signal 43 and the imaginary part filter output signal 44 are input to the frequency analyzer 18. The frequency analyzer 18 performs a frequency analysis on the real part filter output signal 43 and the imaginary part filter output signal 44, and outputs the frequency analysis output signal 4
5 is output. Then, the flow velocity / flow rate calculator 19 calculates the flow velocity and the flow rate from the frequency analysis output signal 45. Normally, the calculation result is displayed on a display or the like (not shown).

FIG. 10 shows a specific configuration example of the storage circuit 25 of FIG. The first low-pass filter 46 receives the low-pass filter output (29, 30) as an input, and is set to pass a component determined by the sampling frequency of the analog-to-digital conversion circuit 48 and the band of the difference processing component. Only the components below the cutoff frequency are passed, and a first low-pass filtered output signal 58 is output. The sampling hold circuit 47
It receives a first low-pass filtered output signal 58 and the sampling and holding signal 54 from the storage control circuit 53 and outputs a sampling and holding output 59. The analog-to-digital converter 48 includes a sampling hold output 59 and an analog-to-digital conversion control signal 55 from the storage controller 53.
And an analog-to-digital conversion output signal 60 is output. Here, the sampling period and the number of quantization bits of the analog-to-digital conversion circuit 48 are set to values that provide a frequency band and a dynamic range effective for reducing noise as described above. The sampling period is the repetition period (t) of the transmission pulse and the transmission period (T
Set to a value that can be synchronized with s).

The storage element 49 receives the analog-to-digital conversion output signal 60 and the storage element control signal 56 from the storage control circuit 53 as inputs, and outputs the analog-to-digital conversion output signal 6.
A signal for a predetermined period of 0 is stored as a noise signal for cancellation. The stored signal is output as the storage output signal 61 by the storage element control signal 56 when necessary. The latch circuit 50 is for aligning the timing of the storage element output signal 61, receives the storage output signal 61 and the latch control signal 57, and outputs a latch output signal 62. The digital-to-analog conversion circuit 51 receives the latch output signal 62 as an input,
3 is output. The second low-pass filter 52 receives the digital-to-analog conversion output signal 63 as an input, and outputs a second low-pass filter output signal 64. Here, the second low-pass filter 52
Is set to the same value as the cutoff frequency of the first low-pass filter 46, for example. The difference circuit 66, which is a calculating means, receives the second low-pass filter output signal 64 and the low-pass filter outputs (29, 30) as inputs and outputs a difference output signal 34 which is a difference signal between the two input signals. Here, the difference circuit 66 is set by the amplitude or the gain of both signals so that the noise component to be reduced can be removed as much as possible. The storage control circuit 53 receives the storage circuit control signal group 32 including the storage timing control signal, the difference timing control signal, and the storage element recording / reading control clock signal output from the flow meter controller 14, and performs the above-described control. Signal 5
4, 55, 56 and 57 are generated and output. As described above, in the present embodiment, a circuit configuration using a digital memory such as a semiconductor memory is used as a component of the storage element 49, but the same processing can be performed by using an analog memory instead. In this case, there is an advantage that the analog-to-digital converter 48, the digital-to-analog converter 51 and related circuits are not required.

FIG. 11 shows a case where the noise canceling signal is stored as an average for a plurality of periods described above.
5 shows a configuration example of the storage element 49 at 0. Adder circuit 67
Receives an analog-to-digital conversion output signal 60 and a storage element output signal 61, adds them, and outputs an addition circuit output signal 65. The adder circuit 67 can obtain a noise cancel signal (adder circuit output signal 65) as an average value by dividing by the number of average value samples of the analog-to-digital conversion output signal 60 in advance and adding the result.
The memory 68 receives the addition circuit output signal 65 and the control signal 56 as inputs, stores the addition circuit output signal 65, and outputs it as a storage element output signal 61 when necessary.

Although the ultrasonic flowmeter in each of the above embodiments is basically based on an analog system, the configuration of the present invention described above is applied to a system based on digital processing instead. It is possible.

[0036]

As described above, according to the present invention, it is possible to effectively reduce the influence of noise caused by the reflection or reverberation of ultrasonic waves on the flow channel wall, and to reduce the flow rate by the pulse Doppler method. Measurement can be performed with higher accuracy. Further, according to the present invention, high-precision measurement can be performed even under conditions where there are many restrictions on flow rate measurement, such as a performance test for an existing fluid machine.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an ultrasonic flowmeter according to a first embodiment.

FIG. 2 is a diagram showing a pulse waveform of an ultrasonic wave together with an electric signal used for its generation and a relationship with a gate signal.

FIG. 3 is a phase waveform diagram of a Doppler signal before removing a noise component.

FIG. 4 is a phase waveform diagram of a Doppler signal after removing a noise component.

FIG. 5 is a pulse waveform diagram of an ultrasonic wave.

FIG. 6 is a voltage change diagram re-displayed as a temporal change at each fetch of a signal fetched at each gate timing in FIG. 5;

FIG. 7 is a phase waveform diagram of a Doppler signal in an example in which a section in which a noise component having a large amplitude rides is narrow.

FIG. 8 is a phase waveform diagram of a Doppler signal in which a noise component having a large amplitude and a noise component having a large amplitude are mixed.

FIG. 9 is a block diagram illustrating a configuration of an ultrasonic flowmeter according to a second embodiment.

10 is a block diagram of an internal configuration of a storage circuit in the ultrasonic flow meter of FIG.

11 is a block diagram of an internal configuration of the storage element in FIG. 10 in a case where a noise cancellation signal is stored as an average for a plurality of periods.

FIG. 12 is a block diagram showing a configuration of a conventional ultrasonic flowmeter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flow path 2 Fluid 3 Ultrasonic probe (ultrasonic transmission / reception means) 4 Ultrasound 8 Balanced modulator (frequency shift detection means) 11 Storage circuit (storage means) 13 Subtractor (arithmetic means) 14 Flow meter controller ( Monitoring means) 15 gate circuit 49 storage element (storage means) 66 difference circuit (arithmetic means)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kyoyoshi Okamura 603, Kandachi-cho, Tsuchiura-shi, Ibaraki Industrial Machinery Systems Division, Hitachi Engineering Co., Ltd. (72) Inventor Masaharu Kobayashi 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside Hitachi Image Information Systems Co., Ltd. (72) Inventor Hitoshi Aoki 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Co., Ltd. Hitachi Image Information Systems Co., Ltd. (72) Koji Yagawa 603, Kandamachi, Tsuchiura-shi, Ibaraki Co., Ltd. Tsuchiura Technology F-term (reference) 2F035 DA08 DA13

Claims (5)

[Claims] An ultrasonic wave radiated from a transmission means or an ultrasonic wave transmission / reception means attached to a pipe wall of a flow path through which a fluid flows is scattered in the fluid and a plurality of scattered waves generated by controlling a gate time are measured. Received at each position, the flow velocity distribution of the fluid in the radial direction in the flow path is determined based on the Doppler shift occurring in the received scattered wave at each measurement position,
In the ultrasonic flow meter adapted to obtain the flow rate of the fluid in the flow channel from the flow velocity distribution, a noise signal waveform caused by reflection or reverberation of the ultrasonic wave by the flow channel tube wall is taken in, and noise for cancellation is taken. A storage unit for storing the signal as a signal, and an arithmetic unit for calculating a difference between a measurement signal obtained by measurement for measuring the flow velocity distribution and a noise signal for cancellation stored in the storage unit. Ultrasonic flow meter. 2. The ultrasonic flowmeter according to claim 1, wherein the noise signal is taken in a plurality of times, and a plurality of the obtained noise signals are averaged to form a canceling noise signal. 3. A frequency shift detecting means for extracting a Doppler signal from a measurement signal received by an ultrasonic wave transmitting / receiving means, and a calculating means for calculating a difference between a Doppler signal extracted by the frequency shift detecting means and a noise signal. 3. The ultrasonic flowmeter according to claim 1, wherein two processing systems are provided. 4. A method for measuring a plurality of scattered waves generated by scattering ultrasonic waves radiated from a transmitting means or an ultrasonic wave transmitting / receiving means attached to a pipe wall of a flow path through which a fluid flows in said fluid by controlling a gate time. Received at each position, the flow velocity distribution of the fluid in the radial direction in the flow path is determined based on the Doppler shift occurring in the received scattered wave at each measurement position,
In the ultrasonic flow meter adapted to obtain the flow rate of the fluid in the flow path from the flow velocity distribution, the amplitude is set to a predetermined value within one cycle of the Doppler signal extracted from the measurement signal received by the ultrasonic wave transmitting / receiving means. Means for monitoring the width of the section that is greater than or equal to, and when the width of the section is smaller than a predetermined width, the gate time is controlled so as to capture a signal for a portion excluding the section. An ultrasonic flowmeter characterized in that: 5. A method for measuring a plurality of scattered waves generated by scattering ultrasonic waves radiated from a transmitting means or an ultrasonic wave transmitting / receiving means attached to a pipe wall of a flow path through which a fluid flows in said fluid by controlling a gate time. Received at each position, the flow velocity distribution of the fluid in the radial direction in the flow path is determined based on the Doppler shift occurring in the received scattered wave at each measurement position,
In the ultrasonic flow meter adapted to obtain the flow rate of the fluid in the flow path from the flow velocity distribution, means for monitoring the magnitude of the amplitude in the Doppler signal extracted from the measurement signal received by the ultrasonic wave transmitting / receiving means An ultrasonic flowmeter, wherein the gate time is controlled so as to take in a signal only in a portion where the amplitude is equal to or smaller than a predetermined value.