JPH0634417A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To obtain a vortex flow meter which can accurately measure the flow rate of a fluid even when the flow rate is small. CONSTITUTION:A vortex generating body 3 is provided in a flow passage 2 and a vibration sensor 4 is attached to the top of the body 3. Then a hot-wire flow rate sensor 7 is fitted to the front side of the body 3. The sensors 4 and 7 are connected to an arithmetic section 5. Therefore, when the flow rate of a fluid flowing through the passage 2 is small, the flow rate can be measured from a signal detected by means of the sensor 7 by converting the signal.

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 the method for measuring the flow rate, a hot wire type flow sensor is attached to the vortex generator, and a calculation section for calculating the flow rate passing through the flow path is provided by a signal from the hot wire type flow sensor.

[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 passing flow rate can be calculated and measured by the signal from the hot-wire type flow rate sensor attached to the vortex generator. That is, the hot wire type flow sensor
The flow rate is measured by generating a certain amount of heat in the sensor and taking away the amount of heat generated by the fluid according to the amount of fluid passing through. Is something that can be measured.

[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. A hot wire type flow sensor 7 is attached to the front part of the vortex generator 3. The hot wire type flow sensor-7 is also connected to the computing unit 5 by a connecting wire 8. The signal from the hot wire type flow sensor-7
The calculation unit 5 is connected to a flow rate conversion unit via a comparison unit, an amplification unit, a voltage / current conversion unit, etc., which are not shown. The cross section of the vortex generator 3 is formed such that the upstream side of the flow path 2 is wider than the downstream side as shown in FIG.

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 less than a predetermined amount, the flow rate is converted from the number of vortices in the vortex generator 3 and the flow rate is converted from the detection signal of the hot-wire flow sensor 7.

[0010]

The present invention produces the following unique effects. As described above, according to the present invention, the flow rate can be measured by the hot wire type flow sensor when the flow rate is small, 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 Hot wire type flow 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 a hot wire type flow sensor is attached to the vortex generator, and the flow sensor. A vortex flowmeter provided with a calculation unit for calculating a flow rate passing through the flow path in accordance with a signal from the vortex flowmeter.