JPH0634416A - Vortex flowmeter - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a vortex flowmeter that can accurately measure the flow rate even with a small flow rate. [Structure] A vortex generator 3 is provided in the flow path 2. Vortex generator 3
Attach the vibration sensor-4 on top of the. Pressure sensors 7 and 8 are attached to the front and rear of the lower part of the vortex generator 3, respectively. The vibration sensor-4 and the pressure sensors-7 and 8 are connected to the computing unit 5, respectively. When the flow rate is small, the flow rate can be converted and measured from the difference in pressure detected by the pressure sensors 7 and 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Karman vortex flowmeter, and more particularly to a vortex flowmeter capable of accurately measuring a flow rate even when a passing flow rate is small. As is well known, the Karman vortex flowmeter detects the number of Karman vortices generated when a fluid passes through a vortex generator provided in a flow path and converts the fluid flow velocity or the passing flow rate.

[0002]

2. Description of the Related Art As a conventional Karman vortex flowmeter, for example, one disclosed in Japanese Patent Laid-Open No. 2-275317 has been used. This is one in which the passage opening / closing valve and the vortex flowmeter are integrally formed.The through valve shaft of the ball valve is used as a vortex generator, and the vibration caused by the vortex is detected by the vibration sensor provided on the above through valve shaft. The flow rate through the valve is measured by the flow velocity calculated based on the detected frequency and the opening area of the ball valve. The flow rate calculation formula is the following formula (1),
It is as in (2). f = St · u / d (1) Q = Fu (2) where f is the vortex frequency, St is the Strouhal number in the tube, and u
Is the flow velocity of the fluid passing through the vortex generator, d is the vortex generator width (diameter in the case of a cylinder), F is the fluid passage cross-sectional area, and Q is the flow rate.

[0003]

SUMMARY OF THE INVENTION In the above conventional one,
There is a problem that a small flow rate cannot be measured, that is, the ratio of the minimum measurable flow rate to the maximum measurable flow rate: the rangeability is small and the measurement target is limited. Vortex flowmeter
Stroke in the range of a given Reynolds number in the flow path
The Hull number is constant, and the flow rate is measured by utilizing the proportional relationship between the vortex frequency and the fluid flow velocity in this range.The Reynolds number becomes smaller and the Strouhal number is not constant when the flow rate decreases. Rangeability is reduced because measurement becomes impossible.

Therefore, a technical problem of the present invention is that the flow rate can be accurately measured even if the flow rate of the measurement fluid is small and the rangeability is increased, whereby the measurement range is limited by the flow rate. There is no vortex flowmeter.

[0005]

Means for Solving the Problems The technical means of the present invention taken to solve the above technical problem is to provide a vortex generator and a vortex detecting means in a flow path of a measurement fluid and pass the flow path. In order to measure the flow rate, the pressure detection means for detecting the fluid pressure is attached to the vortex generator, and the force due to the flow of the fluid passing through the flow path is calculated from the signal from the pressure detection means to determine the passing flow rate. It is provided with a computing unit for computing.

[0006]

The operation of the above technical means is as follows.
When the flow rate passing through the flow meter is large, the number of vortices generated by the vortex generator can be detected by the vortex detector to convert and measure the flow rate as in the conventional vortex flow meter.

When the flow rate of the flow meter is small, the number of vortices generated in the vortex generator and the fluid flow velocity do not have a proportional relationship, and the flow rate cannot be measured by the number of vortices. Therefore, when the flow rate is low as described above, the passage flow rate can be calculated and measured by the signal from the pressure detecting means attached to the vortex generator. That is, the force of the fluid exerted on the object by the flow of the fluid is proportional to the momentum of the fluid, and when the flow rate is small and the flow velocity can be regarded as almost constant, the fluid force and the flow rate have a proportional relationship. Flow rate can be converted from force. Further, pressure detecting means is provided at the front and rear of the vortex detector, the dynamic pressure of the fluid is detected by the pressure detecting means of the front part, and the static pressure of the fluid is detected by the pressure detecting means of the rear part. It is also possible to convert and measure the passing flow rate from the pressure difference.

[0008]

EXAMPLES Examples showing specific examples of the above technical means will be described (see FIGS. 1 and 2). Flow path 2 in flowmeter body 1
And the vortex generator 3 is provided in the central portion. A vibration sensor-4 as a vortex detecting means is attached to the upper part of the vortex generator 3,
Further, it is connected to the arithmetic unit 5 arranged on the upper side through a connecting line 6. At the lower part of the vortex generator 3, pressure sensors 7 and 8 as pressure detecting means are attached. The pressure sensors 7 and 8 are also connected to the arithmetic unit 5 by connecting lines (not shown). Signals from the pressure sensors 7 and 8 are connected to a flow rate conversion unit via a comparison unit, an amplification unit, a voltage / current conversion unit, etc. (not shown) in the calculation unit 5. The cross section of the vortex generator 3 has a flow path 2 as shown in FIG.
The upstream side of is formed wider than the downstream side.

Next, the operation will be described. When the flow rate passing through the flow passage 2 is larger than a predetermined amount, the vibration sensor 4 detects the number of vortices generated by the vortex generator 3, and the calculator 5 calculates the vortex number and the cross-sectional area of the flow passage 2 or the fluid. The flow rate is converted from the specific weight of the above and displayed. When the flow rate passing through the flow path 2 is smaller than a predetermined amount, the flow rate is converted from the flow rate based on the number of vortices in the vortex generator 3, and the flow rate passing through is converted from the pressure detected by the pressure sensors 7 and 8. That is, the pressure difference before and after the vortex generator 3 is detected from the pressure difference between the pressure detected by the pressure sensor 7 provided at the front part of the vortex generator 3 and the pressure detected by the pressure sensor-8 provided at the rear part. Then, the flow rate of passage can be converted by the calculation unit 5 from this pressure difference.

In this embodiment, pressure sensors-7 and 8
Although the example in which the vortex generator 3 is provided before and after the lower part of the vortex generator 3 is shown, the vortex generator 3 is also provided in the central part and the upper part of the vortex generator 3 to provide the flow path 2
It is also possible to detect the liquid level inside by a pressure sensor and measure the passing flow rate at a low flow rate.

[0011]

The present invention produces the following unique effects. As described above, according to the present invention, when the flow rate is small, the passing flow rate can be measured from the force of the fluid flow, and when the flow rate increases, the flow rate can be measured by detecting the number of vortices generated by the vortex generator. You can Therefore, the measurement can be performed from a small flow rate, the rangeability is increased, and the measurement target is not limited.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of an embodiment of a vortex flowmeter of the present invention.

FIG. 2 is a sectional view taken along the line AA ′ in FIG.

[Explanation of symbols]

 1 Flowmeter main body 2 Flow path 3 Vortex generator 4 Vibration sensor-5 Calculation unit 7,8 Pressure sensor-

Claims (1)

[Claims] 1. A vortex generator and a vortex detecting means are provided in a flow path of a measurement fluid to measure a flow rate passing through the flow path, wherein pressure detecting means for detecting a fluid pressure is attached to the vortex generator. A vortex flowmeter provided with a calculation unit that calculates a force due to a flow of a fluid passing through the flow passage and calculates a passage flow rate based on a signal from the pressure detection unit.