JP2004170326A - Ultrasonic vortex flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect accurate Karman's vortices through the use of continuous regions in the relation between a phase difference and its converted voltage by using a simple constitution without the need for a phase shifter of a complicated constitution or complicating the constitution of a phase comparator. <P>SOLUTION: In this ultrasonic vortex flowmeter, an oscillator and a receiver for transmitting and receiving ultrasonic waves are opposed to each other via a channel on the downstream side of a vortex generating body inserted in a fluid to be measured. The phase comparator detects the phase difference between an oscillator signal and a receiver output signal, and a phase difference-voltage converter converts the phase difference into a voltage signal. The ultrasonic vortex flowmeter is provided with both a phase switching device which operates in such a way as to invert the phase of either the oscillator signal or the receiver output signal inputted in the phase comparator and a phase switching determining device for controlling this. When the phase difference comes close to a discontinuous part in converter characteristics, this is detected to invert the phase of the phase switching device. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic vortex flowmeter that measures a flow rate or a flow velocity of a fluid to be measured using ultrasonic waves.
[0002]
[Prior art]
As is well known, when a columnar generator is inserted into a fluid, the flow separates on both sides of the vortex generator, and a regular vortex, that is, a Karman vortex, is generated alternately downstream of the vortex generator. Since the number of generated Karman vortices is proportional to the flow velocity or flow rate of the fluid, the flow rate or flow velocity can be accurately measured by detecting the Karman vortex.
[0003]
It is well known that a means utilizing ultrasonic waves is used to detect such Karman vortices. In this technique, the number of Karman vortices generated in a fluid is detected by a continuous ultrasonic signal, and thereby the flow rate or the flow velocity of the fluid to be measured is measured.
[0004]
FIG. 6 is a diagram showing a schematic configuration of a general ultrasonic vortex flowmeter based on the prior art. There is a vortex generator in the pipe, and there is an ultrasonic oscillator and an ultrasonic receiver facing the downstream. The ultrasonic wave transmitted from the oscillator travels through the fluid and reaches the receiver. At this time, a Karman vortex is generated downstream of the vortex generator in proportion to the flow rate, so that the ultrasonic wave from the oscillator excited by the oscillator is affected by the Karman vortex and reaches the receiver from the oscillator. Affected by time.
[0005]
The oscillator signal and the receiver signal are compared by a phase comparator, and a phase difference signal between the two is output. By converting this phase difference signal into a voltage signal with a phase difference-voltage converter, Karman vortices can be detected, and the flow rate or flow velocity can be measured.
[0006]
Since the receiver signal has passed through the fluid over a predetermined distance, a unique phase lag occurs even if the flow velocity is zero. When a Karman vortex is generated in the fluid at a predetermined flow velocity, the inherent phase lag is modulated by the Karman vortex and undergoes a phase change. This phase change is detected as a substantially sinusoidal signal, thereby measuring the flow rate or flow velocity.
[0007]
FIG. 7 shows the relationship between the phase difference and the phase difference voltage obtained by converting the phase difference into a voltage. If the phase difference changes between 2nπ and 2 (n + 1) π [n = integer], the voltage changes continuously, but becomes discontinuous at 2nπ [n = integer]. In terms of points, accurate Karman vortices cannot be detected. In order to solve this problem, there is known an ultrasonic vortex flowmeter in which the phase is forcibly shifted by a phase shifter so that discontinuity does not occur and always changes within a range of 2π (see Patent Document 1). ).
[0008]
FIG. 8 is a diagram showing a schematic configuration of such a first known ultrasonic vortex flowmeter. A phase shifter is provided in addition to the configuration shown in FIG. The phase shifter controls the amount of phase in a path input from the oscillator signal to the phase comparator based on the phase difference voltage output from the phase difference-to-voltage converter. This makes it possible to stabilize the operation state of the phase comparator in an optimum region of the operation range.
[0009]
However, such an ultrasonic vortex flowmeter requires a phase shifter having a complicated configuration, and it is difficult to perform a large phase shift.
[0010]
Further, a second known ultrasonic vortex flowmeter in which the above-described discontinuity is prevented from occurring is known (see Patent Document 2). This is configured to have a plurality of phase difference-voltage conversion characteristics set so as to be shifted so as to partially overlap each other, and to use an optimum characteristic in response to a change in the phase difference. Such an ultrasonic vortex flowmeter does not require a phase shifter, but has a complicated configuration of a phase comparator.
[0011]
[Patent Document 1]
Japanese Utility Model Publication No. 57-25142 [Patent Document 2]
Japanese Patent No. 3116189
[Problems to be solved by the invention]
Therefore, the present invention solves the above problems, does not require a phase shifter having a complicated configuration, and does not complicate the configuration of the phase comparator. The purpose is to detect an accurate Karman vortex using the continuous region in the relationship of the converted voltage.
[0013]
[Means for Solving the Problems]
An ultrasonic vortex flowmeter according to the present invention comprises: an ultrasonic wave transmitting / receiving oscillator and a receiver, which are provided via a flow path on the downstream side of a vortex generator inserted into a fluid to be measured; An oscillator for exciting the oscillator, a phase comparator for detecting a phase difference between the oscillator signal and the output signal of the receiver, and a phase difference-to-voltage converter having a continuous part and a discontinuous part in a characteristic for converting the phase difference into a voltage. And a container. The converter converts the output phase difference of the phase comparator into a voltage signal, and extracts a phase modulation component due to Karman vortex from the output voltage signal of the converter to measure the flow rate or the flow velocity of the fluid to be measured. According to the present invention, in such an ultrasonic vortex flowmeter, a phase switch that operates to invert the phase of one of an oscillator signal input to a phase comparator and a receiver output signal, and a phase difference conversion circuit A phase switching determiner that detects a discontinuity in the device characteristics and outputs a signal to the phase switch in order to invert the phase of the phase switch by detecting the discontinuity.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on examples. FIG. 1 is a diagram illustrating a schematic configuration of a first ultrasonic vortex flowmeter embodying the present invention. There is a vortex generator in the pipe, and there is an ultrasonic oscillator and an ultrasonic receiver facing the downstream. Ultrasonic waves oscillated from the oscillator excited by the oscillator travel through the fluid and reach the receiver. At this time, a Karman vortex is formed downstream of the vortex generator in proportion to the flow rate, so that the ultrasonic wave emitted from the oscillator is affected by the Karman vortex and is affected by the time to reach the receiver.
[0015]
The oscillator signal and the receiver signal are compared by a phase comparator, and a phase difference signal between the two is output. By converting this phase difference signal into a voltage signal with a phase difference-voltage converter, Karman vortices can be detected, and the flow rate or flow velocity can be measured. The above configuration and operation are the same as those of the above-described conventional technology.
[0016]
In the configuration illustrated in FIG. 1, a phase switch is inserted in a path to a phase comparator that inputs an oscillator signal. The switching of the phase switch is controlled by a phase switch determiner that determines the output of the phase comparator. That is, the oscillator signal is inverted by the phase switcher (π phase shift) based on the signal of the phase switcher, and then input to the phase comparator.
[0017]
That is, if the phase of the output signal of the receiver is φ2, the average phase of the output signal is φ2 ′, and the variation phase caused by the Karman vortex is ± Δφ, the phase of the output signal is
φ2 = φ2 ′ ± Δφ, which is applied to the first input of the phase comparator. On the other hand, since the signal having the phase φ1 is input to the second input of the phase comparator via the phase shifter, the phase difference output from the phase comparator is
φ1−φ2 = (φ1−φ2 ′) ± Δφ, and a DC signal component based on (φ1−φ2 ′) of the output phase difference is determined by the phase switching determiner to control the phase switcher. Become. Further, the Karman vortex signal based on the fluctuation phase ± Δφ is detected as a sine wave AC signal via a band-pass filter, whereby the flow rate or flow velocity of the fluid is measured.
[0018]
According to the present invention, (φ1−φ2 ′) corresponding to the DC signal component of the output phase difference is determined when approaching the non-linear region of the phase difference-phase difference voltage characteristic and input to the phase comparator. By inverting the phase of one of the signals (oscillator signal in FIG. 1), the operation region is moved so as not to be over the non-linear region.
[0019]
This operation will be further described with reference to FIG. 3A and 3B are diagrams showing the relationship between the phase difference and the phase difference voltage, respectively. FIG. 3A shows a case where the phase difference of the phase comparator approaches 0, and FIG. It is a figure explaining operation at the time of approaching.
[0020]
As shown in FIG. 3A, for example, when the phase difference voltage is V1 [the phase difference (φ1−φ2 ′) corresponding to the DC signal component is θ1], the phase difference voltage V becomes When it becomes smaller and becomes V1 (the phase difference becomes θ1), a phase switching signal is output from the phase switching determiner. In response to the signal, the phase switch shifts (inverts) the phase of the oscillator signal by π and sets the phase difference to θ1 + π. In this way, the measurement point is shifted from near 0π of the discontinuity point, and the flow rate is measured where the phase difference voltage can be measured continuously. If the phase shift is not performed, the phase difference in consideration of the fluctuation phase ± Δφ instantaneously becomes 0 or less, the phase difference signal becomes discontinuous, and the flow rate cannot be measured. Therefore, it is necessary to switch before θ1−Δφ = 0π can occur.
[0021]
Similarly, as shown in FIG. 3B, when the phase difference voltage is set to V2 (phase difference θ2) as the phase switching point, the phase difference voltage becomes large, and when the phase difference voltage becomes V2 (phase difference θ2). A phase switching signal is output from the phase switching determiner. In response to the signal, the phase switch shifts (inverts) the phase of the oscillator signal by π, and sets the phase difference to θ2−π. Thus, the flow rate is shifted from the vicinity of 2π at the discontinuous point, and the flow rate is measured where the phase difference voltage can be continuously measured. Therefore, it is necessary to switch so that θ2 + Δφ = 2π does not hold.
[0022]
FIG. 4 is a diagram specifically illustrating an electric circuit portion of the ultrasonic vortex flowmeter illustrated in FIG. 1. The phase comparator that compares the oscillator signal with the receiver signal can be configured by a flip-flop. Further, the phase switch for switching the phase of the oscillator signal can be constituted by an exclusive OR circuit EXOR.
[0023]
It is possible to apply either a sine wave signal or a rectangular wave signal to the oscillator. When a sine wave signal is applied, the oscillator signal and the receiver signal are each shaped into a rectangular wave signal through a waveform shaping circuit (not shown), and then input to the phase comparator. These oscillator signal and receiver signal are input to the set and reset terminals of the flip-flop constituting the phase comparator. As a result, as shown in FIG. 5, a rectangular wave signal having a pulse width corresponding to the phase difference between the oscillation wave and the reception wave is output.
[0024]
Next, this rectangular wave signal is input to a phase difference-to-voltage converter that can be formed by an integrating circuit including a resistor and a capacitor. The output fluctuation component is extracted as a flow rate (or flow velocity) signal through a band-pass filter. The DC component is input to each of two comparators of the phase switching determiner. One of the two comparators detects a voltage corresponding to a phase difference close to 0π, and the other detects a voltage corresponding to a phase difference close to 2π. As the phase difference θL to be detected near 0π, a value in the vicinity thereof larger than Δφ is set. In addition, as the phase difference θH near 2π to be detected, a value in the vicinity thereof smaller than (2π−Δφ) is set.
[0025]
By detecting either near 0π or near 2π, the inverting circuit is inverted to maintain its state, and by inputting to one input terminal of the exclusive OR circuit EXOR constituting the phase switch, the other is input. And inverts the phase of the oscillator signal input to the terminal.
[0026]
FIG. 2 is a diagram illustrating a schematic configuration of a second ultrasonic vortex flowmeter embodying the present invention. 1 in that a phase switch is inserted in the path from the receiver to the phase comparator. The switching of the phase switch is similarly controlled by a phase switch determiner that determines the output of the phase comparator. That is, the receiver signal is configured to be inverted (phase shift of π) by the phase switch based on the signal of the phase switch determiner, and then input to the phase comparator. Even with such a configuration, it operates in the same manner as the configuration illustrated in FIG.
[0027]
【The invention's effect】
According to the present invention, in the phase comparison of the ultrasonic vortex flowmeter, when the phase difference signal is around 0π or 2π, it is possible to avoid the discontinuity of the phase difference signal. By discriminating that it has approached 0π or 2π, and by inverting the phase difference of the oscillator signal or the receiver signal and shifting it by π, a discontinuous state of the phase difference signal is eliminated by a simple circuit in a wide phase range. be able to. This allows for accurate detection of Karman vortices and, therefore, of flow or flow velocity.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a schematic configuration of a first ultrasonic vortex flowmeter embodying the present invention.
FIG. 2 is a diagram illustrating a schematic configuration of a second ultrasonic vortex flowmeter embodying the present invention;
3A and 3B are diagrams illustrating a relationship between a phase difference and a phase difference voltage, wherein FIG. 3A illustrates an operation when the phase difference of the phase comparator approaches 0, and FIG. 3B illustrates an operation when the phase difference approaches 2π. FIG.
FIG. 4 is a diagram specifically illustrating an electric circuit portion of the ultrasonic vortex flowmeter illustrated in FIG.
FIG. 5 is a diagram illustrating the operation of a flip-flop constituting the phase comparator illustrated in FIG. 4;
FIG. 6 is a diagram showing a schematic configuration of a general ultrasonic vortex flowmeter based on the prior art.
FIG. 7 is a diagram showing a relationship between a phase difference of a general ultrasonic vortex flowmeter and a phase difference voltage obtained by converting the phase difference into a voltage.
FIG. 8 is a diagram showing a schematic configuration of a first known ultrasonic vortex flowmeter.

Claims (3)

An oscillator for transmitting and receiving ultrasonic waves and a receiver opposed to the downstream side of the vortex generator inserted into the fluid to be measured via a flow path, an oscillator for exciting the oscillator, and an oscillator signal. A phase comparator for detecting a phase difference between the output signals of the receiver, and a phase difference-voltage converter having a continuous part and a discontinuous part in the characteristic of converting the phase difference into a voltage, and In the ultrasonic vortex flowmeter, which converts the output phase difference of the comparator into a voltage signal and extracts the phase modulation by the Karman vortex from the output voltage signal of the converter to measure the flow rate or flow velocity of the fluid to be measured. ,
A phase switch that operates to invert the phase of any one of the oscillator signal and the receiver output signal input to the phase comparator,
A phase switching determiner that detects when the phase difference approaches a discontinuous portion of the converter characteristic and outputs a signal to a phase switch to invert the phase of the phase switch,
Ultrasonic vortex flowmeter consisting of The phase switching determiner determines based on a DC signal component of the output of the phase difference-voltage converter, and a Karman vortex signal based on the AC signal component is detected through a band-pass filter, whereby a fluid flow rate or The ultrasonic vortex flowmeter according to claim 1, wherein the flow velocity is measured. The ultrasonic system according to claim 1, wherein the detection by the phase switching determiner when approaching a discontinuous portion is detected when the phase difference of the phase comparator approaches 0 and approaches 2π. Vortex flow meter.

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