JPS5910576Y2 - Karman vortex flowmeter - Google Patents

Description

[Detailed description of the invention] This invention relates to a Karman vortex flowmeter that measures the flow rate by installing a vortex generation column in the measurement fluid flowing in a conduit and detecting the number of Karman vortices generated downstream of the column using ultrasonic waves. It is something.

Conventionally, this kind of Karman vortex flowmeter has a method of measuring the flow rate of fluid flowing inside the pipe by installing a vortex generation column in the pipe and detecting the number of Karman vortices generated downstream of the column using ultrasonic waves. This is proposed in Japanese Patent No. 51-24154.

According to this method, when detecting a Karman vortex, the ultrasonic wave emitted from the ultrasonic transmitter is modulated by the Karman vortex and received by the receiver, but at this time, the ultrasonic wave emitted from the transmitter spreads while spreading. It also propagates and reaches the inner wall of the opposing conduit.

The disadvantage is that it reflects off the inner wall and interferes with the ultrasonic wave propagating from the transmitter, creating a standing wave, or it reflects several times on the inner wall of the conduit and is received by the receiver as noise, making stable measurements impossible. was there.

In particular, with conventional means, when the measuring fluid is air, the speed of ultrasonic waves propagating in the air changes significantly depending on the temperature, so the wavelength of ultrasonic waves with a constant frequency changes accordingly, and a standing wave is generated at a specific temperature. This has the disadvantage that normal reception is no longer possible.

This idea was devised to eliminate such drawbacks, and includes a sound-absorbing material that absorbs and attenuates ultrasonic waves on the inner wall of the conduit.
The present invention provides a novel Karman vortex flowmeter that can reduce the reflection of ultrasonic waves on the inner wall and eliminate the effects of standing waves and reflected waves.

Hereinafter, one embodiment of this invention will be described in detail with reference to FIGS. 1 and 2.

In Figure 1, 1 is a conduit for flowing the measurement fluid, 2 is a conduit 1
The inner wall of the acoustic absorber is made of a sound-absorbing material made of, for example, non-woven fabric or synthetic leather, which absorbs and attenuates ultrasonic waves.

3 is a vortex generating column arranged as shown in FIG. 1 in the flow of the measurement fluid (indicated by an arrow in FIG. 1); 4 is a vortex generating column 3;
This shows the Karman vortex generated by

5 is an ultrasonic transmitter, 8 is an oscillation device, 7 is an ultrasonic receiver,
8 is a receiving device, and 9 is an expansion conduit.

Note that the length L of the straight pipe portion of the conduit 1 downstream of the vortex generating column 3 is less than twice the width D of the conduit 1, and the width of the expansion conduit 9 is larger than the width D of the conduit 1. .

FIG. 2 shows another embodiment of this invention, in which the inner wall of the expansion conduit 10 has an uneven structure.

In the structure as described above, when a measuring fluid such as air in the conduit 1 flows in the direction of the arrow in FIG. 1, a Karman vortex 4 is generated by the vortex generating column 3.

The ultrasonic transmitter 5 is driven by an oscillation device 6 and transmits ultrasonic waves to a receiver 7.

At this time, the receiver 7 receives the modulated ultrasonic wave, which is modulated by the Karman vortex while propagating through the fluid.

Then, the receiving device 8 detects the number of Karman vortices generated.

Since the ultrasonic waves emitted from the ultrasonic transmitter 5 propagate through the measurement fluid while spreading, they also reach the inner wall 2 of the conduit other than the receiver 7, and this inner wall 2 is made of an ultrasonic sound-absorbing material. Therefore, it absorbs ultrasound waves and does not reflect them.

Therefore, no standing waves or reflected waves are generated within the conduit 1, and stable measurements can be performed.

On the other hand, the length L of the straight pipe portion of the conduit 1 downstream of the vortex generating column 3 was conventionally required to be at least five times the width D of the conduit 1, but this can be shortened to The overall length could be shortened by making the pipe width twice as large or less and connecting it to the expansion pipe 9, which has a large pipe width.

In this case, the ultrasonic waves also reach the inner wall of the expansion conduit 9. The ultrasonic waves reflected by this inner wall enter the conduit 1, which has a small channel width, and are almost attenuated by the time they reach the receiver 7. It will not adversely affect the measurements.

Further, in the embodiment shown in FIG. 2, when the expansion pipe 10 is curved downstream of the straight pipe part of the conduit 1, the ultrasonic waves reflected by the inner wall A of the curved part of the expansion pipe 10 are directly transmitted to the receiver. The inner wall of the expansion conduit 10 is made uneven so that the ultrasonic waves are diffusely reflected so that the ultrasonic waves do not reach the ultrasonic wave 7.

As explained above, according to this invention, by providing a sound absorbing material capable of absorbing ultrasonic waves in the conduit, the reflection of ultrasonic waves on the inner wall of the conduit is reduced, and the generation of standing waves and reflected waves are reduced. Since the influence has been removed, stable flow rate measurement can be performed over a wide range from low temperatures to high temperatures.

In addition, by connecting an expansion pipe with a large pipe width to the straight pipe part of the pipe downstream of the vortex generating column, the length of the straight pipe part can be made shorter than before, and the total length of the pipe can be made shorter than before. It can be made shorter.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram showing an embodiment of this invention. FIG. 2 is a structural diagram showing another embodiment of this invention. In the figure, 1 is a conduit, 2 is an inner wall made of sound-absorbing material, 3 is a vortex generation column, 4 is a Karman vortex, 5 is an ultrasonic transmitter, 7 is an ultrasonic receiver, and 9 and 10 are expansion pipes. It is.

Claims (3)

[Scope of utility model registration request] (1) A conduit through which a fluid to be measured flows, a vortex generation column disposed within the conduit that generates Karman vortices, an ultrasonic vortex detection device that detects the number of Karman vortices generated by this vortex generation column, and the above-mentioned an expansion conduit connected to the straight pipe section of the conduit downstream of the vortex generating column and having a conduit width larger than the conduit width of the conduit; and a sound absorbing material provided on the inner wall of the straight pipe section and capable of absorbing ultrasonic waves. A Karman vortex flowmeter characterized by comprising: (2) The Karman vortex flowmeter according to claim 1, which is a registered utility model, characterized in that the inner wall of the expansion pipe is uneven. (3) The Karman vortex flowmeter according to claim 1, wherein the sound absorbing material is made of nonwoven fabric, synthetic material, or leather.