JP2927295B2 - Vortex flow meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vortex flowmeter, and detects a phase modulation given to an ultrasonic wave propagating in a fluid by a Karman vortex generated in a fluid by a vortex generator to detect the Karman vortex. The present invention relates to a vortex flowmeter that measures the flow rate or flow velocity of a fluid by detecting the generation of a fluid.

2. Description of the Related Art As a conventional vortex flowmeter, as proposed in Japanese Utility Model Publication No. 57-25141 or Japanese Patent Publication No. 58-32333,
2. Description of the Related Art There is known an apparatus that measures a flow rate of a fluid by providing a vortex generator in a fluid and detecting the number of generated Karman vortices generated downstream thereof using ultrasonic waves.

FIG. 6 is a configuration diagram of an example of a conventionally known vortex flowmeter. In the figure, an ultrasonic wave generated by the oscillator 1 and transmitted into the fluid from the ultrasonic transmitter 2a propagates along a path perpendicular to the traveling direction of the fluid and parallel to the paper of FIG. Detected by 2b. The output signal of the ultrasonic receiver 2b is supplied to the phase comparator 4 via the phase controller 3 (this signal is referred to as α). On the other hand, an oscillation signal branched from the output of the oscillator 1 separately from the ultrasonic wave passing through the fluid is supplied to the other input terminal of the phase comparator 4 via the phase controller 5 (this signal is referred to as β). .

In the phase comparator 4, the phases of the two signals α and β are compared. In this case, the ultrasonic signal α that has passed through the fluid in a state where no Karman vortex is generated has a certain phase difference with respect to the original oscillation signal β.

FIG. 7 is a cross-sectional view of the cross section of the pipeline 6 as viewed from the upstream side. In FIG. 7, a vortex generator 7 that stands in the vertical direction (the direction of the arrow Y) is fixed to the inner wall of the pipe 6. The ultrasonic transmitter 2a and the ultrasonic receiver 2b are arranged such that the ultrasonic wave propagation path from the ultrasonic transmitter 2a extends in a horizontal direction (arrow X direction) orthogonal to the extending direction of the vortex generator 7 (arrow Y direction). It is provided to be formed.

In FIG. 6, when a fluid whose flow rate or flow velocity is to be measured flows from the upper side to the lower side in the pipe 6 in the same figure, a well-known vortex generated by being inserted inside the pipe 6 is contained in the fluid. On the downstream side of the body 7, a regular, so-called Karman vortex is generated alternately on the left and right sides. In this case, when the ultrasonic wave passing through the fluid propagates through the fluid, the ultrasonic wave encounters the Karman vortex generated by the vortex generator 7, and the ultrasonic wave travels in the lateral direction of the Karman vortex (parallel to the paper of FIG. 6). And the velocity component in the direction in which the ultrasonic wave propagates) is subjected to phase modulation. Therefore, the phase difference between the two signals α and β supplied to the phase comparator 4 indicates a different phase difference from the above-mentioned constant phase difference when the ultrasonic wave passing through the fluid does not encounter the Karman vortex. By detecting the change in the phase difference and extracting the change from the output terminal 8a through the filter 8, the number of generated Karman vortices in proportion to the flow velocity or the flow rate can be detected, and thus the flow rate or the flow velocity of the fluid to be measured can be measured. It becomes possible.

However, the phase of the ultrasonic wave propagating in the fluid undergoes a change due to an external factor such as a temperature change of the fluid other than the Karman vortex. Due to a phase change due to an external factor such as a temperature change, the phase difference between the two signals supplied to the phase comparator 4 may deviate from the linear operation range of the phase comparator 4.

In order to prevent this, a phase change generated by an external factor is extracted by the filter 8, and this output is supplied to the phase controllers 3 and 5, and the phase difference between the two ultrasonic waves supplied to the phase comparator 4 is calculated as described above. By controlling the phase comparator 4 to be within the linear operation range, it is possible to cope with a case where the phase of the ultrasonic wave largely changes due to an external factor such as a temperature change.

Problems to be Solved by the Invention However, in the vortex flowmeter shown in FIGS. 6 and 7, when the flow rate increases and the flow velocity in the direction of flow of the Karman vortex becomes faster than the speed of sound in the fluid, the vortex flowmeter propagates in the fluid. The amount of phase modulation that the ultrasonic signal receives from the Karman vortex becomes too large, and as a result, a problem occurs that the phase difference between the signals α and β deviates from the linear operation range of the phase comparator 4.

Furthermore, when the amount of phase modulation increases, the frequency of the ultrasonic wave propagating in the fluid is modulated, and the frequency changes to deviate from the reception frequency band of the ultrasonic receiver 2b. For this reason, the ultrasonic signal propagated in the fluid cannot be received, and accurate flow rate measurement cannot be performed. In addition, when the sound velocity in the fluid is low, the phase modulation amount is large even at the same flow velocity as compared with the case where the sound velocity is high, so when measuring a gas such as a gas with a low sound velocity in the fluid compared to the liquid. When the large flow rate is measured, the phase modulation amount becomes too large, and the measurable flow rate range is narrowed accordingly.

As a countermeasure against such a problem, there is a method of lowering the frequency of the ultrasonic signal to suppress the amount of phase modulation received by the Karman vortex to the ultrasonic signal propagating in the fluid. However, lowering the frequency of the ultrasonic signal raises a new problem that the size of the transducers of the ultrasonic transmitter 2a and the ultrasonic receiver 2b increases, and there is a limit to the size of the transducer due to manufacturing technology. Therefore, it was difficult to effectively reduce the amount of phase modulation.

Therefore, an object of the present invention is to provide a vortex flowmeter that has solved the above-mentioned problems.

Means for Solving the Problems The present invention provides a vortex generator provided on a pipe inner wall through which a fluid to be measured flows so as to extend in a direction perpendicular to the flow direction, and a pipe downstream of the vortex generator. An ultrasonic transmitter fixed to a wall, an ultrasonic receiver fixed to a pipe wall such that a straight line connecting the ultrasonic transmitter is inclined with respect to an extending direction of the vortex generator, And detecting the vortex generated by the vortex generator by comparing the phase of the oscillation signal from the ultrasonic transmitter with the phase of the reception signal from the ultrasonic receiver.

According to the present invention, a pipe is provided such that a straight line connecting the ultrasonic transmitter fixed to the pipe wall on the downstream side of the vortex generator and the ultrasonic transmitter is inclined with respect to the extending direction of the vortex generator. Since the apparatus includes the ultrasonic receiver fixed to the road wall, it is possible to shorten the distance that the ultrasonic wave receives the phase modulation from the Karman vortex, thereby reducing the amount of phase modulation received by the ultrasonic wave.

Embodiment FIG. 1 is a side sectional view showing the inside of a pipe 6 of a vortex flowmeter according to an embodiment of the present invention. In this figure, when the fluid in the pipe 6 flows from left to right, Karman vortices are generated downstream by the vortex generator 7.

FIG. 2 (A) is a cross-sectional view of FIG. 1 taken along the line II A-II A, and an oscillator 1 as an ultrasonic source, an ultrasonic transmitter 9a,
And an ultrasonic receiver 9b for receiving ultrasonic waves, a phase comparator 4, and the like. In the figure,
The fluid will flow from the front side to the back side of the paper perpendicular to the paper.

FIG. 2 (B) shows an attached state of the ultrasonic transmitter 9a and the ultrasonic receiver 9b inserted and fixed in the pair of attachment holes 6a, 6b of the pipe 6. Each of the mounting holes 6a and 6b is bored toward the axis P in the conduit 6, and the mounting holes 6a and 6b are provided on the same straight line. The mounting holes 6a and 6b are formed such that a broken line connecting the centers thereof is inclined at a predetermined angle θ with respect to a horizontal line (dashed line) perpendicular to the direction in which the vortex generator 7 extends.

Each of the ultrasonic transmitter 9a and the ultrasonic receiver 9b includes a vortex generator 7
In the extended surfaces of (FIG. 1 II A-II A cross section) parallel to the plane (FIG. 1 II B-II B section), the tip portion 9a _1, 9b ₁ attachment hole 6a, and 6b The large-diameter portions 9a ₂ and 9b _{2 which} are inserted and project outward from the pipeline 6 are fixed to the outer circumference of the pipeline 6 by mounting bolts (not shown). The tip portions 9a ₁ and 9b ₁ of the ultrasonic transmitter 9a and the ultrasonic receiver 9b vibrate in contact with the fluid flowing in the pipeline 6. The ultrasonic oscillator 9a and the ultrasonic receiver 9b
The ultrasonic wave a is attached so that the propagation direction of the ultrasonic wave a is inclined at a predetermined angle θ with respect to a direction (horizontal line) perpendicular to the extending direction of the vortex generator 7.

Further, as described above, since the mounting holes 6a and 6b are drilled toward the axis P of the conduit 6, the ultrasonic transmitter 9a and the ultrasonic receiver 9b are arranged to face each other via the axis P. Have been. Therefore,
The ultrasonic wave transmitted from each ultrasonic transmitter 9a passes through the axis P and is detected by the ultrasonic receiver 9b.

FIG. 3 is a schematic diagram showing a positional relationship between the Karman vortex generated in the fluid by the vortex generator 7 and the ultrasonic transmitter 9a and the ultrasonic receiver 9b. In the figure, the arrow indicated by the broken line indicates the propagation direction of the ultrasonic wave a. The figure also shows the state at the time when the Karman vortex 13a has already passed through the propagation path of the ultrasonic wave a transmitted from the ultrasonic transmitter 9a and the next Karman vortex 13b has approached the propagation path of the two ultrasonic waves. Is shown.

4 (A) and 4 (B) show pulsed waveforms of an ultrasonic signal (reception signal) α of an oscillation signal β when the Karman vortex passes through the propagation path of the ultrasonic wave a as shown in FIG. The mutual phase relationship is shown. In FIG. 3, the phase of the ultrasonic wave a transmitted from the ultrasonic transmitter 9a is advanced with respect to the signal β because the Karman vortex 13b has a true text in the same direction as the traveling direction of the ultrasonic wave a.

As the Karman vortex 13b moves downstream from the state shown in FIG. 3, the advance of the phase of the ultrasonic wave a decreases,
When the vicinity of the center of the Karman vortex passes through the propagation path of the ultrasonic wave, the advance of the phase of the ultrasonic wave a disappears. Thereafter, when the latter half of the Karman vortex passes through the propagation path of the ultrasonic wave, the phase of the ultrasonic wave a is delayed. As described above, when one Karman vortex passes through the propagation path of the ultrasonic wave, the phase difference of the ultrasonic wave a changes like a sine wave for a half cycle. This ultrasonic a
By detecting the change in the phase difference of the above, the occurrence of the Karman vortex can be detected, and by counting the Karman vortex per unit time, the flow velocity and the flow rate of the fluid can be measured.

Note that a circuit configuration to which signals from the oscillator 1 and the ultrasonic receiver 9b are input is the same as the conventional one.

At this time, if the phase difference between the ultrasonic signal α and the oscillation signal β becomes ψ, the phase comparator 4 outputs a voltage _ψ corresponding to the phase difference よ_り from the output terminal 8a.

On the downstream side of the vortex generator 7, Karman vortices 13a and 13b having different vortex directions are generated alternately as shown in FIG. 3, so that the phase of the ultrasonic signal α advances when the Karman vortex 13a passes. When the next Karman vortex 13b passes, the phase is delayed. Then, the phase difference of the ultrasonic signal α with respect to the oscillation signal β is obtained as shown in FIG.

In FIGS. 2 (A) and 3, since the ultrasonic transceivers 9a and 9b are mounted so as to be inclined at an angle θ with respect to the horizontal direction, the amount of phase modulation received by the ultrasonic waves a from the Karman vortex is reduced. If Δψ, then Is required. (Where, L: propagation distance of ultrasonic wave a, f: frequency of ultrasonic wave a, c: velocity of sound in fluid, v: flow velocity of Karman vortex orthogonal to the flow direction of fluid) The flow velocity v perpendicular to the direction (see FIG. 3) is proportional to the flow velocity V of the fluid.

In FIG. 2 (A), the distance D between the sensors between the ultrasonic transmitter 9a and the ultrasonic receiver 9b is the same as the inner diameter of the pipe 6 and is constant. Therefore, by changing the angle θ, the propagation distance L at which the ultrasonic wave a undergoes phase modulation by the Karman vortex is L =
Dcosθ. Conventionally, L = D (see FIG. 7), but according to the present embodiment, L <D due to the angle θ.

When the propagation distance L is reduced, the phase modulation amount of the ultrasonic wave received from the Karman vortex in the constant Karman vortex flow velocity range (flow rate range) can be reduced from the above equation (1).

FIG. 5 is a graph showing the relationship between the phase difference between the signals α and β and the output voltage of the phase comparator 4. As shown in FIG. 5, the phase difference between the two signals α and β is changed from −360 degrees to 360 degrees. In the range up to degrees, the output voltage of the phase comparator 4 changes linearly.

 Here, an example of the flow rate measurement will be described.

When the fluid flowing through the pipe 6 is air at 20 ° C., the distance between the sensors D = 50 mm, the frequency of the ultrasonic wave a is 200 kHz, and the speed of sound in the air is
Assuming 343 m / s, the phase modulation amount Δψ that the ultrasonic wave receives from the Karman vortex is given by the above equation (1) Is represented by

The maximum velocity v of the Karman vortex within the linear operation range of the phase comparator 4 is θ = 0 ° (shown in FIG. 7). Becomes Therefore, v ≒ 11.3m in the range of Δψ <± 360 °
/ s.

On the other hand, in the vortex flowmeter in which the propagation path of the ultrasonic wave is inclined at the angle θ as in the present invention, for example, when θ = 60 °,
L = Dcos60, and from the above equation (1), Becomes Therefore, v ≒ 22.0 m / s, and θ =
It is possible to measure up to about twice the flow rate as compared with the case of 0.

The angle θ is not limited to 60 ° and may be set to an arbitrary angle so that the flow rate measurement range can be appropriately widened.

Effect of the Invention As described above, the vortex flowmeter according to the present invention has an ultrasonic transmitter fixed to a pipe wall on the downstream side of the vortex generator, and a straight line connecting the ultrasonic transmitter to the vortex generator. And an ultrasonic receiver fixed to the pipe wall so as to be inclined with respect to the extending direction. Therefore, the phase modulation is reduced by reducing the propagation distance L in which the ultrasonic wave receives the phase modulation from the Karman vortex. it can. Therefore, when measuring gas, etc., Kalman can be measured by the fact that the phase modulation is large due to the low speed of sound in the fluid and exceeds the linear operation range of the phase comparator, or the received signal cannot be obtained due to the frequency modulation. The flow velocity range (flow rate range) of the vortex can be prevented from being narrowed, and the flow rate measurement range can be widened using a conventional circuit.

Also, by changing the mounting angle of the ultrasonic transmitter so that the ultrasonic wave propagation distance is constant even when the pipe diameter (distance between sensors) is different, the amount of phase modulation received by the ultrasonic wave from the Karman vortex can be reduced. It has features that it can be reduced to widen the flow rate measurement range and that the ultrasonic sensor can be shared even if there is a difference in pipe diameter.

[Brief description of the drawings]

FIG. 1 is a side sectional view of an embodiment of the present invention, and FIG. 2 (A) is a block diagram in which main circuits are added to a longitudinal sectional view along line IIA-IIA of FIG. FIG. (B) shows II B− in FIG.
II A longitudinal sectional view along the line B, FIG. 3 is a schematic diagram showing the relationship between the vortex generator and the Karman vortex and the ultrasonic transceiver, and FIG. 4 illustrates the phase relationship between the oscillation signal and the reception signal. FIG. 5 is a waveform diagram for converting a phase difference of an ultrasonic wave into a voltage in a phase comparator, and FIG. 6 and FIG.
FIG. 1 is a block diagram and a sectional view of an example of a conventional vortex flowmeter. 1 ... ultrasonic oscillator, 4 ... phase comparator, 6 ... pipe,
7 ... vortex generator, 9a ... ultrasonic transmitter, 9b ... ultrasonic receiver, 13a, 13b ... Karman vortex.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01F 1/32

Claims (1)

(57) [Claims] 1. A vortex generator provided on an inner wall of a conduit through which a fluid to be measured flows so as to extend in a direction perpendicular to the flow direction, and fixed to a pipe wall downstream of the vortex generator. An ultrasonic transmitter, and an ultrasonic receiver fixed to a pipe wall such that a straight line connecting the ultrasonic transmitter is inclined with respect to an extending direction of the vortex generator, and the ultrasonic wave A vortex flowmeter for detecting the vortex generated by the vortex generator by comparing the phases of an oscillation signal from a transmitter and a reception signal from an ultrasonic receiver.