JPH0792396B2 - Vortex flowmeter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vortex flowmeter, and in particular, detects the phase modulation applied to an ultrasonic wave propagating in a fluid by a Karman vortex generated in the fluid by a vortex generator to detect the generation of the Karman vortex. The present invention relates to a vortex flowmeter for measuring the flow rate or flow velocity of a fluid.

2. Description of the Related Art As proposed in, for example, JP-B-57-25141 or JP-B-58-32333, a vortex generator is provided in a fluid, and the number of Karman vortices generated downstream of the vortex generator is determined by using ultrasonic waves. There is known a device that measures the flow rate of a fluid by detecting the flow rate of the fluid.

FIG. 6 is a block diagram of an example of a conventionally known vortex flowmeter. In the figure, the ultrasonic wave generated by the ultrasonic oscillator 1 and transmitted from the ultrasonic transmitter 2a into the fluid propagates along a path perpendicular to the traveling direction of the fluid and parallel to the paper surface of the figure. It is detected by the receiver 2b. The output signal of the ultrasonic receiver 2b is supplied to the phase comparator 4 via the phase controller 3 (this signal is designated as α). On the other hand, the oscillation signal branched from the output of the ultrasonic oscillator 1 apart 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 To).

The phase comparator 4 compares the phases of the two signals α and β. In this case, the ultrasonic signal α that has passed through the fluid in the state where the Karman vortex is not generated has a constant phase difference with respect to the original oscillation signal β.

In FIG. 6, the fluid whose flow rate or flow velocity is to be measured is pipe 6
When the fluid flows in the inside of the pipe from the upper side to the lower side in the figure, a well-known vortex generator 7 inserted and arranged in the inside of the pipe line 6 in the fluid.
A regular so-called Karman vortex is generated alternately on the left and right sides on the downstream side. In this case, when the ultrasonic wave passing through the fluid propagates through the fluid and encounters the Karman vortex generated by the vortex generator 7, the Karman vortex has a lateral direction (parallel to the paper surface of FIG. The flow velocity component in the direction in which the sound wave propagates) undergoes phase modulation. Therefore, the phase difference between the two signals α and β supplied to the phase comparator 4 shows a phase difference different from the above-mentioned constant phase difference when the ultrasonic wave passing through the fluid does not encounter the Karman vortex.
By detecting this change in the phase difference and taking it out from the output terminal 8a via the filter 8, the number of Karman vortices generated, which is proportional to the flow velocity or flow rate, can be detected, and thus the flow rate or flow velocity of the fluid to be measured can be measured. It will be possible.

However, the phase of the ultrasonic wave propagating in the fluid undergoes changes due to external factors such as the temperature change of the fluid other than the Karman vortex. 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 due to the phase change due to an external factor such as the temperature change.

In order to prevent this, a phase change amount caused by an external factor is extracted by the filter 8, the 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 so that it falls within the linear operation range, it is possible to deal with the case where the phase difference of the ultrasonic waves greatly changes due to external factors such as temperature changes.

Problems to be Solved by the Invention In the above vortex flowmeter, an attempt is made to prevent the phase of an ultrasonic signal passing through a fluid from deviating from the linear operation range of the phase comparator 4 due to an external factor such as a temperature change. The circuits such as the phase controllers 3 and 5 become very complicated, and at the same time, in the flow of low Reynolds number, the SN ratio of the ultrasonic signal for detecting the generation of the Karman vortex becomes low, so that the ultrasonic wave There is a problem in that it is necessary to increase the frequency and the gain of the amplifier for amplifying the signal, which increases the power consumption.

Further, if inexpensive phase controllers 3 and 5 are used, the amount of phase is finite. Therefore, if the amount of change in the phase due to an external factor exceeds a certain limit, the vortex flowmeter cannot deal with it. There was a problem.

Further, as a conventional vortex flowmeter, for example, JP-A-50-136066
There is a structure as seen in the publication. In the vortex flowmeter of this publication, a first ultrasonic transmitter for transmitting ultrasonic waves and ultrasonic waves transmitted from the first ultrasonic transmitter are provided on the inner wall of the flow passage on the downstream side of the cylindrical vortex generator. A first ultrasonic receiver for receiving is provided, and the distance l /
2 is provided with a second ultrasonic transmitter that transmits ultrasonic waves to a distant position and a second ultrasonic receiver that receives ultrasonic waves transmitted from the second ultrasonic transmitter, Is configured to combine the output of the ultrasonic receiver and the output of the second ultrasonic receiver on the downstream side.

However, in the vortex flowmeter of the above publication, the first ultrasonic wave propagation path and the second ultrasonic wave propagation path are separated by a distance l / 2 (where l is the vortex generation interval in the same rotation direction), and therefore the same. , The Karman vortex generated by the vortex generator gradually becomes smaller toward the downstream side. Therefore, the output of the second ultrasonic receiver is lower than the output level of the first ultrasonic receiver. The level gets smaller.

Furthermore, although changes in the phase of the ultrasonic waves caused by external factors such as temperature changes affect the phases of the two ultrasonic waves in the same manner, the change in the traveling direction of the first ultrasonic propagation path Since the output direction of the first ultrasonic receiver and the output of the second ultrasonic receiver on the downstream side are combined in the same direction as the traveling direction of the second ultrasonic wave propagation path, ultrasonic waves caused by external factors are generated. Is affected by the change in the phase of, and the measurement accuracy decreases.

The present invention has been made in view of the above points, and an object of the present invention is to provide a vortex flowmeter that has a simple configuration and can detect a Karman vortex with high sensitivity.

Means for Solving the Problems The present invention is provided in a conduit through which a fluid passes, extends in a direction orthogonal to the flow direction of the fluid, and generates a vortex on the downstream side at a cycle proportional to the flow rate. A vortex generator, a first ultrasonic transmitter which is provided on the downstream side of the vortex generator and transmits an ultrasonic signal in a direction orthogonal to the flow direction of the fluid, and the first ultrasonic transmitter A first ultrasonic wave transmitting device which receives the ultrasonic wave signal transmitted from the first ultrasonic wave transmitter and forms a first ultrasonic wave propagation path between the ultrasonic wave signal and the first ultrasonic wave transmitter, The ultrasonic receiver of, and the distance from the vortex generator is provided at the same position as the distance from the vortex generator to the first ultrasonic transmitter,
A second ultrasonic transmitter that transmits an ultrasonic signal to a vortex passing through the first ultrasonic propagation path from a direction opposite to the first ultrasonic propagation path with respect to the winding direction of the vortex. And a second ultrasonic wave propagation path that is provided so as to face the second ultrasonic wave transmitter and has a distance from the vortex generator that is the same as the first ultrasonic wave propagation path. The second ultrasonic receiver that does this is compared with each output signal output from the first and second ultrasonic receivers, and the vortex generated by the vortex generator is detected by the phase difference between the two signals. And a phase comparator.

Action Since the pair of ultrasonic wave propagation paths are formed so as to be located at the same distance from the vortex generator so that the same Karman vortex can be detected at the same time, the first and second ultrasonic wave paths are formed. The output level output from the sound wave receiver becomes the same level, and the vortex detection accuracy is high.

On the other hand, the lateral component of the Karman vortex has opposite effects on the phase of an ultrasonic wave in which the two propagation paths are parallel and opposite to each other, and the Karman vortex crosses the two propagation paths at the same time. That is, if the phase of one ultrasonic wave is advanced by the Karman vortex, the phase of the other ultrasonic wave is always delayed.

Therefore, by comparing the phases of the two ultrasonic signals with a phase comparator, the influence of external factors such as temperature change is canceled and the phase change of the two ultrasonic waves caused by the Karman vortex is emphasized. Becomes

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

FIG. 2 is a cross-sectional view of FIG. 1 cut along the line AB, an oscillator 1 which is an ultrasonic source, ultrasonic transmitters 9a and 10a, and an ultrasonic receiver 9b for receiving respective ultrasonic waves. , 10b and the phase comparator 11 are also shown. In the figure,
The fluid will flow from the front side to the back side of the paper perpendicular to the paper. The ultrasonic transmitters 9a and 10a and the ultrasonic receivers 9b and 10b are provided at positions at the same distance from the vortex generator 7 to the downstream side, respectively, and a pair of ultrasonic receivers 9b and 10b are provided.
The same Karman vortex can be detected at the same time.

FIG. 3 is a schematic diagram showing the positional relationship between the Karman vortices generated in the fluid by the vortex generator 7 and the ultrasonic transmitters 9a, 10a and the ultrasonic receivers 9b, 10b. In the figure, the arrow shown by the broken line indicates the propagation direction of the ultrasonic waves, and as can be seen from the figure, the traveling directions of the two ultrasonic waves are opposite. Further, in the figure, when the Karman vortex 13a has already passed through the propagation paths of the two ultrasonic waves transmitted from the ultrasonic transmitters 9a and 10a, and the next Karman vortex 13b approaches the propagation paths of the two ultrasonic waves, Is shown.

4 (A) and (B) show the waveforms of the two ultrasonic signals a and b pulsed as the Karman vortex passes through the propagation paths of the two ultrasonic waves as shown in FIG. It shows the relationship. In FIG. 3, the ultrasonic wave a transmitted from the ultrasonic transmitter 9a has the Karman vortex 13b just as the ultrasonic wave a.
Of the ultrasonic wave b transmitted from the ultrasonic transmitter 10a has a direction opposite to the lateral direction component of the Karman vortex 13b. As a result, the phase is delayed.

As the Karman vortex 13b moves downstream from the state shown in FIG. 3, both the phase advance of the ultrasonic wave a and the phase delay of the ultrasonic wave b decrease, and two ultrasonic waves propagate near the center of the Karman vortex. At the time of passing through the path, neither the phase advance of the ultrasonic wave a nor the phase delay of the ultrasonic wave b disappears. Thereafter, when the latter half of the Karman vortex passes through the propagation paths of the two ultrasonic waves, the phase of the ultrasonic wave a is delayed and the phase of the ultrasonic wave b is advanced. In this way, when one Karman vortex passes through the propagation path of the ultrasonic wave, the phase difference between the ultrasonic waves a and b changes like a sine wave for a half period. The generation of Karman vortices can be detected by detecting the change in the phase difference between the ultrasonic waves a and b, and the flow velocity and flow rate of the fluid can be measured by counting the Karman vortices per unit time. It will be possible.

Further, since the ultrasonic transmitters 9a and 10a and the ultrasonic receivers 9b and 10b are provided at the same distance downstream from the vortex generator 7 so that the same Karman vortex can be detected, the Karman vortex is The ultrasonic transmitters 9a, 10a and the ultrasonic receivers 9b, 10b will simultaneously pass through a pair of ultrasonic propagation paths formed between them, and the output levels of the ultrasonic receivers 9b, 10b will be similar. Therefore, the accuracy of vortex detection by the phase comparator 11 is improved.

At this time, if the phase difference between the two ultrasonic signals a and b becomes θ, the phase comparator 11 determines the voltage Vθ corresponding to the phase difference θ.
Is output from the output terminal 12.

FIG. 5 shows the phase difference between the two ultrasonic signals a and b and the phase comparator 11
Is a graph showing the relationship with the output voltage of the phase comparator 11, as shown in the figure, the output voltage of the phase comparator 11 is linear in the range of the phase difference between the two ultrasonic waves a and b from 0 degree to 180 degrees. Change.

When the temperature of the fluid to be measured changes, the phase of ultrasonic waves propagating in the fluid to be measured also changes accordingly. Moreover, external factors such as temperature changes have the same effect on the above-mentioned two ultrasonic wave propagation methods. That is, if a change occurs that delays the phase of one ultrasonic wave, the phase of the ultrasonic wave propagating in the opposite direction is also delayed.

Waveforms shown by broken lines in FIGS. 4A and 4B respectively indicate that the phases of the ultrasonic waves shown by solid lines are delayed due to external factors such as temperature change. In this case, the same figure (A)
If the phase of the waveform a shown in Fig. 2 is delayed by φ, similarly, the waveform b shown in Fig. 7B is also delayed by φ, and the relative phase difference θ between the two waveforms a and b is outside the temperature change. It will not be substantially changed even when the dynamic factors are added. Therefore, by comparing the phases of the two signals a and b in the phase comparator 11, it becomes possible to purely detect only the phase change due to the Karman vortex, and in this case, the phase changes received by the two ultrasonic waves are detected. Can be detected additively (intensifying each other), so that the Karman vortex can be detected with higher sensitivity as compared with the conventional device using only one ultrasonic transceiver.

In the above embodiment, the propagation paths of the two ultrasonic waves in the fluid to be measured are parallel to each other, and the Karman vortex crosses the two ultrasonic propagation paths at the same time, but the present invention is not limited to this. For example, the two ultrasonic wave propagation paths may intersect with each other, or the pair of ultrasonic wave propagation paths may not be parallel to each other, and for example, the first ultrasonic wave propagation path may be different from the first ultrasonic wave propagation path. The ultrasonic wave transmitter 9 so that the second ultrasonic wave propagation path is inclined at an angle.
The distance between a and 10a and the distance between the ultrasonic receivers 9b and 10b may be set to different dimensions.

EFFECTS OF THE INVENTION As described above, according to the present invention, the distance from the vortex generator to the first ultrasonic wave propagation path and the distance from the vortex generator to the second ultrasonic wave propagation path are the same. Since the first and second ultrasonic wave propagation paths are formed, the pair of ultrasonic wave propagation paths can simultaneously detect the same Karman vortex, and thus the first ultrasonic wave propagation path and the second ultrasonic wave propagation path can be detected. The output level at the time of vortex detection with and becomes the same level, and the vortex detection accuracy can be improved.

Further, the first and second ultrasonic transmitters and the first and second ultrasonic transmitters are arranged such that the ultrasonic wave traveling direction of the second ultrasonic wave propagation path is opposite to the first ultrasonic wave propagation path. Because it is arranged,
For example, if the phase of the ultrasonic wave in the first ultrasonic wave propagation path advances,
Since the phase of the ultrasonic wave in the second ultrasonic wave propagation path is delayed, and the Karman vortex is detected by the phase difference between the outputs from the pair of ultrasonic wave transmitters, the Karman vortex is detected regardless of external factors such as temperature change. Vortex can be detected. Therefore,
The influence of external factors can be canceled, and the vortex detection accuracy is further enhanced.

Therefore, it is not necessary to use a complicated circuit such as a phase controller, and it is possible to cancel the phase change of the ultrasonic wave due to an external factor such as temperature change and vibration of the pipeline or pump with a simple configuration. It becomes possible to detect the Karman vortex with much higher sensitivity than the conventional vortex flowmeter. This makes it possible to reduce the frequency of the ultrasonic waves and the gain of the output amplifier, further simplifying the circuit configuration, and reducing power consumption and operating costs.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, FIG. 2 is a block configuration diagram in which a main circuit is added to the transverse sectional view of FIG. 1, and FIG. 3 is a vortex generator, a Karman vortex and an ultrasonic wave. FIG. 4 is a perspective view showing the relationship with the transceiver, FIG. 4 is a waveform diagram for explaining the relationship between the phases of two ultrasonic waves, and FIG. 5 is the position when the phase difference between the two ultrasonic waves is converted into a voltage. FIG. 6 is a block diagram showing an example of a conventional vortex flowmeter. 1 ... Oscillator, 9a, 10a ... Ultrasonic transmitter, 9b, 10b ... Ultrasonic receiver, 3, 5 ... Phase controller, 11 ... Phase comparator,
6 ... Pipe line, 7 ... Vortex generator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinzo Suzuki 4-28-6 Oizumi Gakuencho, Nerima-ku, Tokyo (56) References JP-A-54-121780 (JP, A) JP-A-50-136066 ( JP, A)

Claims (1)

[Claims] 1. A vortex generator, which is provided in a conduit through which a fluid passes, extends in a direction orthogonal to the flow direction of the fluid, and generates a vortex on the downstream side at a period proportional to the flow rate, and the vortex. A first ultrasonic transmitter provided on the downstream side of the generator and transmitting an ultrasonic signal in a direction orthogonal to the flow direction of the fluid; and a first ultrasonic transmitter provided so as to face the first ultrasonic transmitter, A first ultrasonic receiver that receives the ultrasonic signal transmitted from the first ultrasonic transmitter and forms a first ultrasonic propagation path with the first ultrasonic transmitter; The distance from the vortex generator is provided at the same position as the distance from the vortex generator to the first ultrasonic transmitter,
A second ultrasonic transmitter that transmits an ultrasonic signal to a vortex passing through the first ultrasonic propagation path from a direction opposite to the first ultrasonic propagation path with respect to the winding direction of the vortex. And a second ultrasonic wave propagation path that is provided so as to face the second ultrasonic wave transmitter and has a distance from the vortex generator that is the same as the first ultrasonic wave propagation path. The second ultrasonic receiver that does this is compared with each output signal output from the first and second ultrasonic receivers, and the vortex generated by the vortex generator is detected by the phase difference between the two signals. A vortex flowmeter comprising a phase comparator and the vortex flowmeter.