JP2004286673A - Ultrasonic vortex flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set a cut-off frequency so as not to be affected by amplitude variation of a reception signal caused by contamination of bubbles or the like. <P>SOLUTION: In this ultrasonic vortex flowmeter 10, a vortex signal output from a phase comparing circuit 29 is converted into a binary signal (vortex pulse signal)comprising only a high level and a low level in a comparator circuit 32 to be input into a counter part 40. A frequency setting part 42 of a computing circuit 34 sets the cut-off frequency of a bandpass filter part 38 for passing the vortex signal, based on a data stored in a memory 44 (an aperture and a flow rate range (vortex frequency range) of the flowmeter or the like), and based on the frequency of the vortex pulse signal measured by the counter part 40. In the computing circuit 34, the vortex signals A/D-converted by an A/D-conversion part 36 are converted into a pulse sequence, after processed by a digital tracking filter, based on the set cut-off frequency, and are integrated to compute a flow rate, so as to output a flow rate signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic vortex flowmeter, and more particularly, an ultrasonic vortex that transmits ultrasonic waves into a fluid to be measured to detect Karman vortices generated downstream of the vortex generator and measures the flow rate of the fluid to be measured. It relates to a flow meter.
[0002]
[Prior art]
In general, in a conventional ultrasonic vortex flowmeter, a vortex generator extending in a direction perpendicular to the flow direction is provided in a flow path in which a fluid to be measured flows, and one or two vortex generators are provided downstream of the vortex generator. A set of ultrasonic sensors is provided to detect Karman vortices generated downstream of the vortex generator. One set of ultrasonic sensors is provided in the flow path so as to face each other, one is a transmitting side that transmits ultrasonic waves, and the other is a receiving side that receives ultrasonic waves propagated in the fluid to be measured It becomes.
[0003]
In this type of ultrasonic vortex flowmeter, an ultrasonic reception signal propagated through a Karman vortex generated alternately in proportion to the flow velocity in the flow path, and an ultrasonic signal supplied to the transmission side. The Doppler effect that the ultrasonic wave receives from the Karman vortex is detected as a sinusoidal phase modulation amount (vortex signal) by comparing the phase with the transmission signal of the sound wave.
[0004]
In addition, in an ultrasonic vortex flowmeter using two sets of ultrasonic sensors, by comparing the phases of two ultrasonic signals that propagate the fluid from the opposite directions relative to the Karman vortex flow, Only the phase change as a phase modulation amount received from the Karman vortex is extracted by canceling the influence of the sound velocity change of the fluid to be measured.
[0005]
The conventional ultrasonic vortex flowmeter configured as described above is theoretically configured to extract the Doppler effect received by the ultrasonic wave from the Karman vortex as a phase change, so that it is independent of the type of fluid being measured. Vortices can be detected.
[0006]
Generally, disturbance noise received from flow noise or piping vibration is superimposed on the vortex signal. Therefore, by adopting a filter, it is possible to obtain the original clean sine wave of the vortex signal. Further, as a filter for shaping the waveform of the vortex signal composed of alternating phase difference signals, there are a bandpass filter with a fixed cutoff frequency and a tracking filter that changes the cutoff frequency in accordance with the frequency of the vortex signal.
[0007]
In that case, the original fundamental frequency of the Karman vortex is detected from the noisy vortex signal by fast Fourier transformation (FFT), and the cutoff frequency of the bandpass filter is set so that the frequency is centered. It is necessary to set the cutoff frequency so that the amplitude of the vortex signal is maximized by setting or sweeping (changing) the cutoff frequency of the bandpass filter over a wide range.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-296084
[Problems to be solved by the invention]
However, in the conventional ultrasonic vortex flow meter, in the case of the tracking filter, the fast Fourier transform (FFT) processing for detecting the frequency of the vortex signal and the switching processing of the cutoff frequency are complicated. There was a problem that it took time to detect the frequency.
[0010]
In addition, the ultrasonic vortex flowmeter is easily affected by bubbles because ultrasonic waves do not propagate in the gas when bubbles are mixed in the fluid to be measured. Therefore, if bubbles exist in the fluid, not only disturbance noise but also large noise received from the bubbles is superimposed on the vortex signal, and if a large amount of large bubbles are mixed, there is a possibility that the Karman vortex cannot be detected. .
[0011]
Furthermore, if bubbles are mixed into the fluid to be measured, the amplitude of the received voltage is modulated by blocking the propagation of the ultrasonic waves when the bubbles pass, and phase modulation is performed at the stage of signal processing in the circuit. Is superimposed on the vortex signal.
[0012]
The amplitude modulation amount of the received voltage due to such bubbles depends on the relationship between the propagating ultrasonic beam width and the bubble size, and the noise due to the bubbles appearing in the phase difference may be larger than the amplitude of the vortex signal. .
[0013]
Therefore, when noise larger than the amplitude of the vortex signal is superimposed as the bubble passes, it is output as an erroneous pulse. In addition, when a bubble large enough to block the propagation of the ultrasonic wave passes, the reception voltage cannot be secured, resulting in a problem that the vortex pulse is lost.
[0014]
If the amplitude modulation of the vortex signal is large, even if the fundamental frequency is detected by performing fast Fourier transform (FFT) processing on the vortex signal, vortex signal loss and noise output due to air bubbles are irregular. Occur. As a result, the frequency component of the vortex signal changes irregularly in the vicinity of the original vortex signal frequency, which causes a problem that the center frequency of the bandpass filter cannot be set.
Accordingly, an object of the present invention is to provide an ultrasonic vortex flowmeter that solves the above-described problems.
[0015]
[Means for Solving the Problems]
In order to solve the above problems, the present invention has the following features.
The invention according to claim 1 is provided between the vortex signal generation means and the calculation means, and includes a filter means for passing a frequency in a predetermined frequency band, and a filter corresponding to the diameter of the flow path of the flowmeter body. Storage means for storing the frequency band of the vortex signal to be passed, and setting means for reading out the frequency band corresponding to the diameter of the flow channel of the flow meter body from the storage means and setting the cutoff frequency of the filter based on the frequency band; The vortex signal is relatively simple by making the pass frequency band of the filter follow the frequency of the Karman vortex without performing complex arithmetic processing such as fast Fourier transform (FFT) processing on the vortex signal. A stable vortex signal can be detected with the circuit configuration.
[0016]
According to the second aspect of the present invention, the frequency detecting means for detecting the frequency of the vortex signal from the vortex signal is provided, and the setting means has a frequency band and a frequency corresponding to the diameter of the flow passage of the flow meter main body stored in the storage means. The filter cut-off frequency is calculated from the frequency detected by the detection means, and the calculated cut-off frequency is set in the filter. Complexity such as fast Fourier transform (FFT) processing is performed on the vortex signal. By making the pass frequency band of the filter follow the Karman vortex frequency without performing arithmetic processing, a stable vortex signal can be detected with a relatively simple circuit configuration.
[0017]
According to the third aspect of the present invention, the output state of the vortex signal is predicted according to the amplitude change of the envelope of the reception signal output from the ultrasonic receiver, and the frequency of the signal obtained by waveform shaping the vortex signal is obtained. The cutoff frequency of the filter is set on the basis of this, and the passing frequency band of the filter is made to follow the frequency of the Karman vortex without performing complicated arithmetic processing such as fast Fourier transform (FFT) processing on the vortex signal. Thus, a stable vortex signal can be detected with a relatively simple circuit configuration.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0019]
FIG. 1 is a block diagram showing a circuit configuration of an embodiment of an ultrasonic vortex flowmeter according to the present invention.
[0020]
As shown in FIG. 1, the ultrasonic vortex flowmeter 10 includes a flowmeter body 14 having a flow path 12 through which the fluid to be measured flows, and a flow of the fluid to be measured in the flow path 12 of the flowmeter body 14. And a vortex generator 16 extending in a vertical direction perpendicular to a direction (indicated by an arrow in FIG. 1). The vortex generator 16 has a substantially pentagonal cross section when viewed from above.
[0021]
Then, in the process in which the fluid to be measured flows downstream while colliding with the vortex generator 16 facing the upstream side, Karman vortices 17 are alternately generated on the left and right sides of the vortex generator 16. Since the frequency of the Karman vortex 17 is proportional to the flow velocity of the fluid to be measured, the flow velocity of the fluid to be measured is obtained by detecting the number of Karman vortices 17 generated in the fluid to be measured. Calculate the flow rate.
[0022]
There are various sizes of the ultrasonic vortex flowmeter 10 and there are various sizes of the upstream end face of the vortex generator (the size of the vortex generator). The diameter and the size of the vortex generator are proportional to each other, that is, the size of the vortex generator is set to increase in proportion to the increase in the diameter.
[0023]
Next, the detailed structure of the ultrasonic vortex flowmeter 10 of the present embodiment will be described below.
[0024]
Further, the ultrasonic transmitter 20 and the ultrasonic receiver 22 are attached to the inner wall of the flow path on the downstream side of the vortex generator 16 so as to face each other. The ultrasonic transmitter 20 and the ultrasonic receiver 22 have an ultrasonic sensor made of a piezoelectric element. When a drive signal is input from the drive circuit 24 to the ultrasonic transmitter 20, the ultrasonic transmitter The ultrasonic wave transmitted from 20 propagates through the fluid to be measured flowing through the flow path 12 and is received by the ultrasonic receiver 22.
[0025]
A Karman vortex 17 is generated downstream of the vortex generator 16 at a period proportional to the flow velocity of the fluid to be measured flowing in the flow path 12. At that time, the ultrasonic wave propagating in the flow path 12 is modulated in the process of passing through the Karman vortex 17 generated downstream of the vortex generator 16. Therefore, the generation frequency (vortex signal) of the Karman vortex 17 is detected from the phase difference between the detection signal output from the ultrasonic receiver 22 and the drive signal, and the fluid to be measured flowing in the flow path 12 is detected based on this frequency. Measure the flow rate.
[0026]
The ultrasonic transmitter 20 and the ultrasonic receiver 22 are connected to the flow rate calculation unit 26. The flow rate calculation unit 26 passes through the flow path 12 based on the frequency of the Karman vortex 17 obtained from the phase difference between the drive signal input to the ultrasonic transmitter 20 and the received signal output from the ultrasonic receiver 22. Calculate the flow rate of the fluid to be measured.
[0027]
The flow rate calculation unit 26 includes the drive circuit 24, the reception circuit 28, the phase comparison circuit 29 (vortex signal generation means), the filter amplifier circuit (amplification circuit) 30, the comparator circuit 32, and the calculation circuit 34. The arithmetic circuit (CPU) 34 includes an A / D conversion unit 36, a band pass filter unit 38 (filter), a counter unit 40, a frequency setting unit 42 (setting unit), a memory 44 (storage unit), and a flow rate integrating unit 46. (Calculation means), and performs bandpass filter processing, filter cutoff frequency calculation processing, and flow rate calculation.
[0028]
The drive circuit 24 has an oscillator that outputs an excitation signal having a constant period, and outputs a drive signal in which the voltage is changed to a sine wave based on the excitation signal from the oscillator to the ultrasonic transmitter 20.
[0029]
When receiving the ultrasonic signal propagated through the flow path 12, the ultrasonic receiver 22 outputs the received signal to the receiving circuit 28. In the reception circuit 28, the reception signal is amplified and output to the phase comparison circuit 29. Then, the phase comparison circuit 29 generates a signal (vortex signal) indicating a phase difference between the drive signal output from the drive circuit 24 and the reception signal output from the reception circuit 28. The vortex signal output from the phase comparison circuit 29 is amplified by the filter amplifier circuit 30, input to the A / D conversion unit 36 of the arithmetic circuit (CPU) 34, converted into a digital signal, and then the bandpass filter unit 38. Is filtered.
[0030]
Further, the vortex signal output from the phase comparison circuit 29 is zero-cross-comparated by the comparator circuit 32 and converted into a binary signal (vortex pulse signal) consisting only of a high level and a low level, and is sent to the counter unit 40. Entered. The counter unit 40 measures the frequency of the vortex pulse signal.
[0031]
The frequency setting unit 42 of the arithmetic circuit (CPU) 34 is measured by the data stored in the memory 44 (individual information for each flow meter such as the diameter of the flow meter and the flow range (vortex frequency range)) and the counter unit 40. Based on the frequency of the vortex pulse signal, the cut-off frequency of the bandpass filter unit 38 that passes the vortex signal is set.
[0032]
Therefore, in the arithmetic circuit (CPU) 34, the vortex signal A / D converted by the A / D converter 36 is subjected to digital tracking filter (BPF) processing based on the cutoff frequency set above. After that, it is converted and integrated into a pulse train to calculate the flow rate and output a flow rate signal.
[0033]
Here, a flow rate calculation by the flow rate calculation unit 26 and a method of setting a cutoff frequency will be described.
The drive circuit 24 drives the ultrasonic transmitter 20 to propagate ultrasonic waves into the fluid to be measured. The ultrasonic wave propagated in the fluid to be measured is phase-modulated from the Karman vortex 17 generated alternately, received by the ultrasonic receiver 22 and converted into an electric signal.
[0034]
The ultrasonic signal received by the ultrasonic receiver 22 is amplified by the receiving circuit 28 and shaped into a pulsed rectangular wave. The ultrasonic signal waveform-shaped by the receiving circuit 28 is phase-compared with the drive signal by a phase comparison circuit 29 as a vortex detection circuit, and a signal (vortex signal) indicating this phase difference is output from the phase comparison circuit 29.
[0035]
That is, when the Karman vortex 17 is generated, the phase comparison circuit 29 outputs an alternating sine wave synchronized with the Karman vortex 17 as a phase difference signal (vortex signal). This vortex signal is amplified by the amplifier filter circuit 30, passes through the bandpass filter unit 38 in the vortex signal frequency range determined for each inner diameter of the flow path 12 (diameter of the flowmeter), and then is input to the flow rate integrating unit 46 to be flowed. Calculated.
[0036]
The vortex signal is zero-cross-compared by the comparator circuit 32 and input to the I / O port of the arithmetic circuit (CPU) 34 as a vortex pulse. In the arithmetic circuit 34, the vortex pulse input to the I / O port is input to the counter unit 40, the frequency is calculated, and the band is applied to the vortex signal input from the A / D conversion unit 36 based on the aperture and flow rate range. The center frequency of the pass filter unit 38 is set (setting of a cutoff frequency).
[0037]
In the memory 44 (storage means), the vortex signal frequency range (vortex frequency range) to be passed according to the caliber of the flow meter and the flow rate measurable range that can be measured by the flow meter are classified according to the caliber of the flow meter. Individual information is registered in advance.
[0038]
Further, when the diameter of the flow meter is designated, the frequency setting unit 42 reads individual information including the vortex frequency range corresponding to the diameter from the memory 44, and uses the vortex frequency range as the cutoff frequency of the bandpass filter unit 38. This is set as the range.
[0039]
More specifically, when the frequency setting unit 42 sets fp (Hz) as the frequency of the vortex pulse signal obtained by zero-crossing the vortex signal including the missing or erroneous noise input to the counter unit 40 with a small hysteresis. When the aperture of the flowmeter is 3 / 8B or less, the pass band of the bandpass filter unit 38 is made to follow the frequency fp so as to be in the range of (fp (Hz) to fp × 3 (H,)), When the diameter of the flow meter is 1 / 2B or more, the pass band of the band-pass filter unit 38 is made to follow the frequency fp so as to be in the range of (1/4 × fp (Hz) to fp (Hz)).
[0040]
Here, the relationship between the vortex pulse frequency and the cut-off frequency of the bandpass filter unit 38 will be described with reference to the experimental results shown in FIGS.
In the ultrasonic vortex flowmeter 10, the inner diameter of the flow path 12 (the diameter of the flowmeter), the ultrasonic propagation beam, and the state of bubbles generated in the fluid are experimentally confirmed, and the vortex signal under each condition From this state, the relationship between the center frequency of the vortex signal and the cut-off frequency of the band-pass filter unit 38 is set as follows for each inner diameter of the flow path 12.
[0041]
When the inner diameter of the flow path 12 is small, the ultrasonic propagation beam width is also narrowed. Therefore, the ratio of the bubble diameter to the propagation beam width is increased, and even if a small amount of bubbles are mixed, the ultrasonic wave is blocked and the vortex pulse is lost. The tendency to become strong.
[0042]
On the other hand, when the inner diameter of the flow path 12 is large, the ultrasonic beam width is wide, so the ratio of the bubble diameter to the ultrasonic beam is small, and the vortex signal missing state is reduced. On the other hand, high-frequency noise is superimposed on the vortex signal due to the influence of amplitude modulation of the received signal due to the passage of bubbles in the fluid.
[0043]
Therefore, the flow rate pulse becomes higher than the actual vortex signal frequency due to the erroneous output of the noise.
[0044]
Also, when the deviation between the vortex pulse frequency and the original vortex frequency in the absence of the vortex signal, and the deviation between the vortex pulse frequency and the original vortex frequency when there are many erroneous outputs due to bubble contamination, It is possible to easily set the center frequency of the bandpass filter unit 38 for the vortex signal (set the cut-off frequency) based on the frequency of the vortex pulse signal including the missing or erroneous output due to. Therefore, the vortex frequency can be obtained without performing complex fast Fourier transform (FFT) processing on the vortex signal as in the prior art.
[0045]
Further, as a modification, by monitoring the reception amplitude change (AM modulation) of the ultrasonic wave received from the bubble, it is determined whether the vortex pulse signal is in a missing state or an erroneous output, and the deviation from the vortex signal frequency is determined. It is possible to set the cut-off frequency of the bandpass filter unit 38 for the vortex signal by prediction.
[0046]
2A to 2D are waveform diagrams showing vortex signals when a fluid to be measured (liquid) is caused to flow through the flow path 12 at a flow rate of 2 L / min. FIGS. 3A to 3D show vortex signals of an ultrasonic vortex flowmeter having a diameter of 3 / 8B (inner diameter of the flow path 12) when air is mixed into the fluid to be measured (liquid) at a volume ratio of 1%. FIG. FIGS. 2A, 2B and 3A, 3B are waveform diagrams of signals input to the bandpass filter unit 38 and frequency analysis. FIGS. 3 (C) and 3 (D) are waveform diagrams of the signal that has passed through the band-pass filter unit 38 and frequency analysis.
[0047]
As shown in FIGS. 2A to 2D, the original vortex frequency is about 400 Hz. However, as shown in FIGS. It can be seen that the center frequency is difficult to identify because the vortex frequency changes randomly as the (envelope) undulates irregularly.
[0048]
At this time, the frequency of the vortex pulse signal obtained by zero-crossing the vortex signal at the time of bubble mixing is reduced to about 200 Hz due to missing pulses.
[0049]
Further, as shown in FIGS. 2A to 2D, when the flow rate is 2 L / min, the signal that has passed through the band-pass filter unit 38 is cut so as to cut a low frequency region as a result of frequency analysis. It can be seen that the vortex signal has a stable waveform by setting the off frequency.
[0050]
In addition, as shown in FIGS. 3A to 3D, in the case of a flowmeter having a caliber of 3 / 8B, as a result of frequency analysis of the signal that has passed through the band-pass filter unit 38, the frequency is low and high. It can be seen that the vortex signal has a stable waveform by setting the cut-off frequency so as to cut the region.
[0051]
4A to 4D are waveform diagrams showing vortex signals at the diameter 1 / 2B (inner diameter of the flow path 12) of the ultrasonic vortex flowmeter.
[0052]
As shown in FIGS. 4A to 4D, in the case of a flowmeter having a caliber of 1 / 2B, the frequency of the vortex signal when no bubbles are mixed is about 60 Hz, and the frequency of the vortex pulse signal when bubbles are mixed Is about 130 Hz.
[0053]
From this experimental result, in a flow meter having a large internal diameter of the flow path 12 and having a diameter of 1/2 B or more, the vortex pulse signal erroneously outputs noise due to bubbles, and the vortex pulse signal frequency tends to be higher than the basic vortex signal frequency. . On the other hand, in a flowmeter having a diameter of 3 / 8B, the vortex signal frequency tends to be lower than the basic vortex pulse signal frequency due to lack of the vortex signal.
[0054]
Further, it has been found that the deviation between the vortex pulse signal frequency and the basic vortex signal frequency is a value approximately two to three times regardless of the diameter of the flowmeter. From this, the range of the cut-off frequency of the bandpass filter unit 38 is (fp (Hz) when the frequency of the vortex pulse that compares the vortex signals is fp (Hz) in the case of a flowmeter having a diameter of 3 / 8B. ) To fp × 3 (Hz)), a band including a basic vortex signal frequency can be configured and a stable vortex signal can be obtained.
[0055]
Further, in a flowmeter having a diameter of ½ B or more, a stable vortex signal can be obtained by setting a range of (1/4 × fp (Hz) to fp (Hz)) as a pass band.
[0056]
Further, whether the vortex pulse is lost or noise is erroneously output can be predicted from the change in the ultrasonic reception amplitude due to the bubbles, and therefore the state of the ultrasonic reception amplitude change is monitored. If a situation occurs where the received voltage is lower than that required for the circuit, it is determined that there are many vortex signals missing, and the pass band of the bandpass filter unit 38 is set to (fp (Hz) to fp × 3 (Hz)) is preferable.
[0057]
In addition, if the amplitude modulation is performed by bubbles even if the received amplitude change does not fall below the required voltage, it is considered that there is a high possibility that noise is erroneously output. Is preferably set to a range of (1/4 × fp (Hz) to fp (Hz)).
[0058]
Here, a modified example will be described.
FIG. 5 is an enlarged longitudinal sectional view showing a main part of the modification. In FIG. 5, the same parts as those in the embodiment shown in FIG.
[0059]
As shown in FIG. 5, the ultrasonic vortex flowmeter 50 is obtained by adding an amplitude monitoring circuit 52 and an amplitude determination unit (setting means) 54 to the ultrasonic vortex flowmeter 10 described above.
[0060]
In the amplitude monitoring circuit 52, an envelope signal (envelope) corresponding to the amplitude change obtained by amplitude (AM) demodulation of the ultrasonic reception by the reception circuit 28 is input to the A / D conversion unit 36 of the arithmetic circuit 34. In the arithmetic circuit 34, the envelope signal (envelope) converted into a digital signal by the A / D conversion unit 36 is input to the amplitude determination unit 54.
[0061]
The amplitude determination unit 54 determines whether or not the amplitude of the ultrasonic reception signal (voltage value) is less than a predetermined value registered in advance. Then, when the frequency at which the received voltage falls below the specified value is high (see FIG. 2A), the amplitude determination unit 54 predicts that the vortex pulse is in a missing state, and passes through the bandpass filter unit 38. To decide.
[0062]
Furthermore, when the amplitude determination unit 54 is subjected to amplitude modulation within a range in which the received voltage does not fall below the specified value (see FIGS. 3A and 4A), the state of erroneous output due to noise is determined. Determination is made to determine the pass band of the band-pass filter unit 38.
[0063]
In the above-described embodiment, the configuration in which the pair of ultrasonic sensors are arranged at positions facing each other is given as an example. However, the configuration is not limited thereto, and a configuration in which a plurality of ultrasonic transmitters and ultrasonic receivers are provided is a pair. Of course, the Karman vortex may be detected from the phase difference from the received signal.
[0064]
【The invention's effect】
As described above, according to the first aspect of the present invention, the filter means provided between the vortex signal generation means and the calculation means, and allows the passage of the frequency in the predetermined frequency band, and the flow path of the flowmeter main body. The storage means for storing the frequency band of the vortex signal to be passed through the filter in correspondence with the diameter, and the frequency band corresponding to the diameter of the flow channel of the flow meter body is read from the storage means, and the filter is cut off based on the frequency band Since the setting means for setting the frequency is provided, by causing the vortex signal to follow the frequency of the Karman vortex without performing complicated arithmetic processing such as fast Fourier transform (FFT) processing on the vortex signal, A stable vortex signal can be detected with a relatively simple circuit configuration.
[0065]
According to the second aspect of the present invention, the frequency detecting means for detecting the frequency of the vortex signal from the vortex signal is provided, and the setting means is a frequency band corresponding to the diameter of the flow channel of the flow meter main body stored in the storage means. And the frequency detected by the frequency detection means, and calculates the cut-off frequency of the filter, and sets the calculated cut-off frequency in the filter. Therefore, complex vortex signals such as fast Fourier transform (FFT) processing are performed. By making the pass frequency band of the filter follow the Karman vortex frequency without performing arithmetic processing, a stable vortex signal can be detected with a relatively simple circuit configuration.
[0066]
According to the third aspect of the present invention, the output state of the vortex signal is predicted according to the amplitude change of the envelope of the reception signal output from the ultrasonic receiver, and the waveform-shaped signal of the vortex signal is waveform-shaped. Since the cutoff frequency of the filter is set based on the frequency, the pass frequency band of the filter is made to follow the frequency of the Karman vortex without performing complicated arithmetic processing such as fast Fourier transform (FFT) processing on the vortex signal. Thus, a stable vortex signal can be detected with a relatively simple circuit configuration.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a circuit configuration of an embodiment of an ultrasonic vortex flowmeter according to the present invention.
FIG. 2 is a waveform diagram showing a vortex signal when a fluid to be measured (liquid) flows through a flow path 12 at a flow rate of 2 L / min.
FIG. 3 is a waveform diagram showing a vortex signal of an ultrasonic vortex flowmeter having a diameter of 3 / 8B (inner diameter of a flow path 12) when air is mixed with a fluid to be measured (liquid) at a volume ratio of 1%.
FIG. 4 is a waveform diagram showing a vortex signal at a diameter 1 / 2B (inner diameter of a flow path 12) of the ultrasonic vortex flowmeter.
FIG. 5 is a block diagram showing a circuit configuration of a modification of the ultrasonic vortex flowmeter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10,50 Ultrasonic vortex flowmeter 12 Flow path 14 Flowmeter main body 16 Vortex generator 17 Karman vortex 20 Ultrasonic transmitter 22 Ultrasonic receiver 24 Drive circuit 26 Flow rate calculation part 28 Receiving circuit 29 Phase comparison circuit (vortex signal) Generation means)
32 Comparator circuit 34 Arithmetic circuit 36 A / D converter 38 Band pass filter (filter)
40 Counter unit 42 Frequency setting unit (setting means)
44 Memory (storage means)
46 Flow rate integration unit (calculation means)
52 Amplitude Monitoring Circuit 54 Amplitude Determination Unit

Claims (3)

A flow meter body in which a flow path for the fluid to be measured is formed;
A vortex generator provided in the flow path so as to be orthogonal to the flow direction;
An ultrasonic transmitter that transmits ultrasonic waves by a transmission signal of a predetermined period;
An ultrasonic receiver for receiving the ultrasonic wave transmitted from the ultrasonic transmitter;
With
Using the received signal affected by the Karman vortex generated downstream of the vortex generator received by the ultrasonic receiver, a vortex signal indicating a phase modulation amount generated in the received signal due to the generation of the Karman vortex Vortex signal generating means for generating;
A calculation means for calculating the flow rate of the fluid under measurement from the period of the vortex signal generated by the vortex signal generation means;
In the ultrasonic vortex flowmeter consisting of
Filter means provided between the vortex signal generation means and the calculation means, and allows a frequency in a predetermined frequency band to pass through;
Storage means for storing the frequency band of the vortex signal to be passed through the filter in correspondence with the diameter of the flow path of the flow meter body;
A setting means for reading a frequency band corresponding to the diameter of the flow passage of the flow meter body from the storage means, and setting a cutoff frequency of the filter based on the frequency band;
An ultrasonic vortex flowmeter characterized by comprising: A frequency detection means for detecting the frequency of the vortex signal from the vortex signal is provided,
The setting means calculates a cutoff frequency of the filter from the frequency band corresponding to the diameter of the flow passage of the flow meter main body stored in the storage means and the frequency detected by the frequency detection means, and the calculation The ultrasonic vortex flowmeter according to claim 1, wherein the cut-off frequency is set in the filter. The ultrasonic vortex flowmeter according to claim 1 or 2,
The setting means predicts an output state of the vortex signal in accordance with a change in amplitude of a reception signal envelope output from the ultrasonic receiver, and based on a frequency of a signal obtained by shaping the vortex signal. An ultrasonic vortex flowmeter characterized by setting a cutoff frequency of a filter.

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