JPH03183913A - Karman vortex sensor - Google Patents

Abstract

PURPOSE:To accurately detect the number of generated Karman vortexes with good sensitivity under any severe conditions by inserting both tip parts of a rod member into two tubes and coupling them, and detecting the vibration of a detection body as the displacement of the rod member. CONSTITUTION:Both end parts of a tube body 4 whose tip parts are formed in a U shape are inserted into hole parts 3a and 3b bored in a flange 2. The rod member 5 formed by bending, for example, a metallic thin tube in a U shape are inserted into both the end parts of the tube body 4 and fixed from outside the flange 2. When fluid flows, the triangular column 12 of a sensor holder 10 becomes an obstacle to generate Karman vortexes behind it and the pressure of the Karman vortexes is applied to the tube body 4 in the holder 10 through a through hole 15 from alternate side. The tube body 4, therefore, vibrate at right angles to the flow direction in synchronism with the generation of the Karman vortexes. The frequency of the vibration is equal to the flow rate and transmitted to the member 5 with good sensitivity and transduced into the displacement of its peak part 5a, and the displacement is detected from variation in the reflection quantity, etc., of an optical fiber 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a Karman vortex sensor used to measure a flow rate using a Karman vortex.

[Prior Art] In recent years, the use of Karman vortex flowmeters has become widespread. This Karman vortex flow meter places an obstacle in the fluid, and Karman vortices are generated alternately at intervals β determined by the shape of the obstacle and the flow velocity of the fluid, and move in the direction of the flow at a speed smaller than the flow velocity. do. If the flow velocity at this time is (l) and the moving speed of the vortex is ul, the number of vortices generated within a unit time is (u-ul)e, so count the number of vortices generated per unit time. , separately measured vortex speed ul and vortex spacing β
Accordingly, the flow velocity of the fluid is measured.

[Problem to be solved by the invention] In order to detect the number of vortices, that is, the frequency,
Various methods have been proposed. However, it is difficult to accurately measure the flow rate, especially under severe conditions such as high temperature and high pressure, and it is difficult to say that it is possible to accurately measure the flow rate even under normal usage conditions or in the microflow range.

It is an object of the present invention to provide a Karman vortex sensor that eliminates the above-mentioned drawbacks, can accurately and sensitively detect the number of Karman vortices generated even under severe conditions, and has a wide measurement range.

[Means for Solving the Problems] In order to achieve the above object, in the Karman vortex sensor according to the present invention, two holes are provided in a base body to be attached to a pipe, and two holes are provided inside the base body. A flat detection object is supported by two tubes, these tubes are inserted into the holes, and the space between them is sealed and fixed, and a substantially U-shape is formed on the outside of the base. The formed rod-like members are arranged, and both tip ends of these rod-like members are inserted into the two tube bodies to connect them, and the vibration of the detection body is detected as a displacement of the rod-like member. It is something.

[Operation] The Karman vortex sensor having the above configuration extracts the displacement of the substantially flat detection body inserted into the fluid as the displacement of the substantially U-shaped rod member connected to the outside.

[Example] The present invention will be explained in detail based on illustrated embodiments.

FIG. 1 is a sectional view of the Karman vortex sensor 1, and FIG. 2 is a sectional view taken along line A-A in FIG. Holes 3a, 3b
Both ends of a long tube body 4 made of, for example, a thin metal tube having a U-shaped tip end are inserted and fixed from inside the flange 2. This pipe body 4 and the hole 3a of the flange 2
, 3b are sufficiently sealed by brazing or the like. Further, from the outside of the flange 2, a rod-shaped member 5, for example, a metal thin tube bent into a U-shape, is inserted into both ends of the tube body 4 for a sufficiently long length and is fixed.

In this case, the tip of the rod-shaped member 5 is joined to the tube body 4 below the flange 2, and
It is preferable to provide a gap with the inner wall of the tube body 4 near points a and 3b. Further, an optical fiber holding member 7 is attached to the outside of the flange 2 by a coupling 6, and an optical fiber 8 is inserted into the center of the holding member 7 to optically detect the displacement of the top portion 5a of the rod-shaped member 5. It is now possible to do so.

Figures 3 and 4 show this Karman vortex sensor 1 installed,
A measuring unit is shown which forms part of the pipe line to be measured. The tubular body 4, which serves as the detection body of the Karman vortex sensor 1, is fixed by a flange 2 and inserted into a long hole 11 cut out in the sensor holder 10, and the U-shaped tubular body 4 is viewed as a flat body. Its direction is parallel to the flow path. As shown in FIG. 4, this sensor holder 10 has a substantially triangular prism 12 in cross section with its bottom facing upstream and which becomes an obstacle in the fluid. A through hole 15 is provided which is fixed across the pipe line 14 and communicates with the elongated hole 11 from both sides at approximately the center of the pipe line 14 .

When the fluid flows in the direction of the arrow as shown in FIGS. 3 and 4, the triangular prism 12 of the sensor holder 10 becomes an obstacle, and a Karman vortex is generated behind it, and pressure due to the Karman vortex is generated through the through hole 15. are applied to the tube 4 in the sensor holder 10 alternately from both sides.

Therefore, the tube body 4 vibrates in a direction perpendicular to the flow direction in synchronization with the generation of Karman vortices. The frequency of this vibration matches the magnitude of the flow rate extremely well, and the vibration of this tube body 4 is transmitted to the rod-shaped member 5 with high sensitivity, and the rod-shaped member 5
is converted into a displacement of the top 5a of the optical fiber 8.
It can be detected by changes in the amount of reflection caused by

Furthermore, in order to further improve the sensitivity, by providing the tube 4 with fins 16 as shown in FIGS. 5 and 6, it becomes possible to vibrate the tube 4 more sensitively. Furthermore,
The detection body may have a plate 17 supported by two tubes 4a and 4b as shown in FIGS. 7 and 8.

Moreover, the rod-shaped member 5 does not necessarily have to be a rod-shaped body, and a tubular body may be used. Further, the shape may be not a U-shape but a shape close to a U-shape, for example, a U-shape without any problem.

Further, for detecting the displacement of the top portion 5a of the rod-shaped member 5, other methods such as piezo elements or electromagnetic detection may be used instead of using light as in the embodiment.

In this embodiment, since the detection surface is supported by the tubular body, extremely sensitive measurement is possible, and furthermore, since it is sealed, it can sufficiently withstand measurements under severe conditions.

[Effects of the Invention] As explained above, the Karman vortex sensor according to the present invention has the following effects:
It has extremely high sensitivity, making it possible to measure even minute flow rates that were previously impossible to measure.

[Brief explanation of drawings]

The drawings show an embodiment of the Karman vortex sensor according to the invention,
Figure 1 is a sectional view of the same, Figure 2 is a sectional view taken along line A-A in Figure 1, Figure 3 is a sectional view of the state in use, and Figure 4 is taken along line B-B in Figure 3. 5 is a side view of another embodiment, FIG. 6 is a sectional view taken along line C-C in FIG. 5, and FIG. 7 is a side view of still another embodiment. 7 is a sectional view taken along line DD in FIG. 7. FIG. Reference numeral 1 is a Karman vortex sensor, 2 is a flange, 3a and 3b are holes, 4 is a tube, 5 is a rod-shaped member, is an optical fiber, and O is a sensor holder.

Claims (1)

[Claims] 1. Two holes are provided in the base body to be attached to the conduit, a substantially flat detection body placed inside the base body is supported by two tube bodies, and these tube bodies are inserted into the holes. The space between the hole and the hole is sealed and fixed, and approximately U is formed on the outside of the base.
A rod-shaped member formed in a letter shape is arranged, both tips of these rod-shaped members are inserted into the two tube bodies to connect them, and vibration of the detection body is detected as a displacement of the rod-shaped member. Features Karman vortex sensor.