JPS58219421A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To make the lower limit of a measurable flow rate small, to control a pressure loss to a value lower than a reference value, and to expand range ability, by providing a width varying mechanism, which variably controls the width of a vortex generating body. CONSTITUTION:A vortex generating body 2, which is provided in a pipe 1, is constituted by a fixed part 2a and a variable width part 2b. A width detecting means 5 outputs an electric signal corresponding to the width size of the vortex generating body 2. A pressure detector 6 detects the pressure difference between the upstream and downstream of the vortex generating body 2. An electric control circuit 7 compares the electric signal from the pressure detector 6 and the electric signal from a reference pressure setter 8 and imparts the deviation signal to a width varying mechanism 4. A vortex generating frequency signal from a vortex detecting means 3 and the signal from the width detecting means 5 are inputted to a flow rate operating device 9, thereby computing the flow rate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes Karman vortices that are periodically generated alternately left and right behind a vortex generator placed in a flowing fluid.
This relates to a vortex device that measures the flow rate of fluid.

The operating principle of the Karman vortex flowmeter is, as is well known, that within a wide Reynolds number range, the vortex generation frequency f is equal to the flow velocity U.
This is an application of the fact that it is linearly proportional to . That is, f = St-... (1) However, St
i Stroll number (proportionality constant) d; The width of the vortex generator is established.

On the other hand, if the flow rate flowing through the pipe is Q, then the flow rate Q is proportional to the flow velocity U, so in equation (1), if the stronor number St and the width d of the vortex generator are constant, the flow rate Q is It is often proportional to the vortex generation frequency f, that is, Q=, f... (2)
holds true. However, k is a proportionality constant determined from the Strovall number, the pipe cross-sectional area, the volume reduction ratio of the vortex generator installation part, the vortex generator, etc. In other words, the vortex flowmeter measures the volumetric flow rate by dividing the frequency f of the Karman vortex, which occurs periodically, into the vortex generation frequency, as is clear from equation (2).

Conventionally, this type of flowmeter is (1) Wide range ability.

(2) Pressure drop is small compared to other flowmeters.

(3) Since the accuracy can be expressed as a percentage of the indicated value (or reading) rather than the full scale, it is more accurate than an orifice flowmeter, especially in the low flow rate range.

(4) In addition, the output is a digital output, and a signal suitable for computer input can be obtained. Furthermore, there are no mechanically moving parts and the structure is simple.

Because it has many characteristics such as
It has been used as an industrial measuring instrument.

Recently, this type of flowmeter has been applied to the field of consumer equipment, but the required performance in this case is stricter than that of industrial measuring instruments, with wider rangeability and lower pressure drop. Something is required.

Incidentally, the minimum measurable flow rate of this type of flowmeter is determined from the Reynolds number and the sensor sensitivity for detecting the vortex generation frequency f. Generally speaking, the lower limit of the Reynolds number Re is determined from the viewpoint of sensor sensitivity, and the flow velocity near the vortex generator is determined by U.
When the width of the vortex generating body is d1 and the kinematic viscosity coefficient of the fluid is ν, the lower limit value of the Raines number is around 2000.

The ratio of the width d of the vortex generator to the pipe diameter is within a certain range from the viewpoint of vortex regularity and stability.
In general, there is a relationship between The principle is the same in the field of consumer equipment, where the lower limit of measurable flow rate is required to be smaller than in the case of industrial measuring instruments.

5be, -1. On the other hand, if the pressure loss is △p (hereinafter in the present invention, △p may be referred to as pressure difference) and the specific weight of the fluid is γ, then △pIlx:γU ・・・・・・・・・・・・・(5
).

Therefore, (3L) As is clear from equations (4) and (5), the larger the width d of the vortex generator for a given pipe diameter, the smaller the flow velocity U becomes. The low flow rate sensitivity increases, that is, the measurable lower limit of the flow rate becomes smaller, but as the flow rate increases, the pressure drop increases, and therefore, there is a problem that rangeability is limited.

On the other hand, if the width d of the vortex generator is made smaller, the sensor sensitivity will decrease and the measurable range will be relatively shifted toward the high flow rate region, resulting in the problem that the lower limit of the measurable flow rate will become larger. .

The present invention solves the two conventional drawbacks, and aims to reduce the lower limit of measurable flow rate, control pressure drop below a predetermined reference value, and expand rangeability. 6, +8:+.

In order to achieve this object, the present invention provides a vortex flow meter including a width variable mechanism section that can vary the width of a vortex generator, a width detection means for detecting this width, and a pressure difference between the upstream and downstream sides of the vortex generator. It has a pressure detector that detects the vortex generation frequency signal of the vortex detection means, and an electric control circuit that controls the width variable mechanism so that the pressure difference of the pressure detector is constant. It is equipped with a flow rate calculator that calculates the flow rate based on the output signal of the width detection means.

With this configuration, even if the measurement point changes from a low flow rate area to a high flow rate area or from a dog flow meter area to a low flow rate area, the signal and reference of the pressure detector that detects the pressure difference between the upstream and downstream of the vortex generator and the standard The width variable mechanism section operates to keep the pressure difference constant based on the deviation signal from the value.

In other words, the width of the vortex generating body is automatically variably controlled so that it becomes smaller or larger. Therefore, this makes it possible to reduce the lower limit of the flow rate that can be measured, and
The pressure drop is below the standard value, and measurement with a wide range of capabilities is possible.

7. Hereinafter, one embodiment of the present invention will be described using FIGS. 1 to 4.

In FIGS. 1 and 2, 1 is a pipe through which the fluid to be measured flows;
2 is a triangular prism-shaped vortex generator, which includes a fixed part 2a and a variable middle part 2.
It is composed of b. 3 is an ultrasonic vortex detection means; 4
is a variable width mechanism section consisting of a motor, gears, cams, etc., for continuously variable control of the variable middle section 2b of the vortex generator 2;
5 is a width detecting means such as a potentiometer that is continuously variable controlled and is generated in response to an electric signal corresponding to the width of the vortex generator 2; 6 is a width detector that detects the pressure difference between the upstream and downstream sides of the vortex generator 2; 6& is the 11th pressure detector], and 6b is a pressure conduit. 7Il-1: An electric control circuit that compares the electric signal of the pressure detector 6 with the electric signal from the reference pressure setting device 8 and supplies the deviation signal to the variable mechanism section 4-1 consisting of a motor etc. be. 9 indicates the vortex generation frequency signal from the vortex detection means 3 and the vortex generator 2 set at this time.
A flow rate calculator 10 operates in response to a signal from a width detecting means 5 for detecting the width of the vortex, and 10 is a Karman vortex.

FIG. 3 is a characteristic diagram showing the relationship between flow rate and pressure difference (pressure drop) of the vortex flowmeter of the present invention. The curve passing through the points al and a2a5 corresponds to the conventional example when the width of the vortex generator 2 is fixed to dMAX.

Figure 4 is a characteristic diagram showing the relationship between the vortex generation frequency f and the flow rate Q of the vortex flowmeter of the present invention, and the straight line passing through the point Sfl''2+85 fixes the width of the vortex generator 2 to dMAX. This corresponds to the conventional example when

In the above configuration, QMA of the minimum flow rate in Fig. 3)
[When the flow rate increases from the state where it is flowing, q.

Until now, the pressure difference ΔP changes from ΔPMIN to ΔPM□, 1 based on the conventional characteristic curve (a+ to 1L2). q
.

When the flow rate increases further by Δq, the pressure difference Δp becomes equal to the predetermined reference pressure Δ
Since the deviation is larger than pMAX, the deviation signal is sent from the electric control circuit 7 to the motor of the variable width mechanism section 4, and the width of the variable middle part 2b of the vortex generator is variably controlled from dMAX to dl. Pressure ΔI) is automatically controlled to the same value as MAX.

Correspondingly, the vortex generation frequency f9, , - in FIG.
,, will increase by Δf from fo to fl. At this time, that is, at the 43rd point in FIG. 3 and the 86th point in FIG.
After receiving both electric signals of dl, the flow rate calculator 9 calculates the flow rate.

Then, when the flow rate is further increased from the state where the flow rate is ql and the width is dl, that is, from point a3, the width of the variable rlJ portion 2b changes from dl to d2. The maximum rated flow rate qMAI is controlled so that it gradually narrows to d3.
Correspondingly, the vortex generation frequency f also increases, and at the maximum rated flow rate I and width dMIN, it reaches the value fMX.

However, if the flow rate decreases, the variable middle part 2b will change to a2.
The width is controlled to increase between a and a4.
Then, the pressure difference becomes less than the reference voltage △pMmX, so
dMAR becomes constant. Correspondingly, the vortex generation frequency f is fa between S2 and 84 where the variable central portion 2b is variably controlled.
The width of the variable middle part 2b is dM.
Between Sl and 82, which becomes constant, ftχN to fa'
! It changes with

10- and the vortex generation frequency signal from the vortex detection means 3 and l
] Upon receiving the signal from the detection means 6, the flow rate calculator 9 calculates the flow rate value at that time.

In addition, as is clear from the shape of the vortex generator 2 and the relative arrangement within the pipe line 1 in FIG. Even if the width of the variable middle part 2b changes from dMmd) to dM□d, the Strovall number St remains constant within the wide Reynolds number range.

In this way, the triangular prism-shaped vortex generator 2 having the variable middle part 2b is arranged in the center of the pipe 1, and the pressure difference between the upstream and downstream of the vortex generator 2 is constant in response to an increase or decrease in the flow rate measurement points. Since the variable middle part 2b is automatically controlled so that
Standard pressure △1) M! The flow rate can be measured under the following control. Looking at it from a different perspective, if we use a conventional vortex flowmeter with the width of the vortex generating body 2 fixed at dMAX, it is possible to measure the pressure drop below △pMAI. In the vortex flowmeter of the present invention, the range between qo is expanded from (IMI)l to qM□X.

Furthermore, if we look at it differently and assume that the measurable range of the conventional vortex flow meter is from qMII+ to CLM MUX, the maximum pressure drop at this time (equal to the pressure difference △p) is △pMhx. . However, in the vortex flowmeter of the present invention, the small △l) MA
It is something that becomes x.

As is clear from the above description, the vortex placement system of the present invention includes a variable mechanism section (11) that variably controls the width of the vortex generator, and the pressure difference between the upstream and downstream sides of the vortex generator is constant. By variably controlling the width of the vortex generator so that In other words, the effect of further expanding the range ability can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view from above showing an embodiment of the vortex flowmeter of the present invention, FIG. 2 is a schematic sectional view from the side of the vortex flowmeter, and an explanatory diagram of the control signal system. Figure 3 is
FIG. 4 is a characteristic diagram showing the relationship between the flow rate and pressure difference (pressure drop) of the vortex flowmeter according to an embodiment of the present invention. FIG. FIG. 1... Pipeline, 2... Vortex generator, 3...
... Vortex detection means, 4 ... Width variable mechanism section, 5
...+i detection means, 6 ... pressure detector, 7 ... electric control circuit, 9 ... flow rate calculator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4

Claims (2)

[Claims] (1) Provide a pipe line through which the fluid to be measured flows, a vortex generator provided in the pipe line, and vortex detection means for detecting the Karman vortex generated thereby, and variably control r1 of the vortex generator. a width detecting means for detecting the width, a pressure detector for detecting the pressure difference between the upstream and downstream sides of the vortex generator, and a pressure difference signal of the pressure detector and a reference value. d] A vortex flowmeter comprising a flow rate calculator which has an electric control circuit for controlling a variable mechanism section and calculates a flow rate based on the output signals of the vortex detection means and the width detection means. (2) The shape of the vortex generator is a triangular prism, and the width of the vortex generator is arranged so that the width of the vortex generator, whose apex angle faces the flow of the fluid to be measured and is determined by the remaining two apex angles, can be variably controlled. A vortex flowmeter according to claim 1. 2 base゛