JPS58219419A - 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 pressure detector 5 detects the pressure difference between the upstream and downstream of the vortex generating body 2. An electric control circuit 6 compares the electric signal from the pressure detector 5 and the electric signal from a reference pressure setter 7, and imparts the deviation signal to a width varying mechanism 4 comprising a step motor and the like. The vortex generating frequency signal from a vortex detecting means 3 and the signal outputted to the width varying mechanism 4 from the electric control circuit 6 are inputted to a flow rate operator 8. Thus the flow rate is computed.

Description

[Detailed Description of the Invention] Page 2 The present invention utilizes Karman vortices that are periodically generated alternately left and right behind a vortex generator placed in a flowing fluid.
This invention relates to a vortex flow meter that measures the flow rate of fluid.

The operating principle of the Karman vortex flow meter is based on the well-known fact that the vortex generation frequency f is linearly proportional to the rate-determining V over a wide Reynolds number range. That is, f: St, ・・・・・・Song...
(1) However, St nistrovar number (proportionality constant) d: width of the vortex generator holds true.

On the other hand, if the flow rate flowing through the pipe is Q, the flow rate Q is proportional to the flow velocity V, so in equation (1), if the Strovall number St and the width d of the vortex generator are constant, the flow rate Q is proportional to the generation of the vortex. It will be proportional to the frequency f. In other words, Q=kf ・・・・・・・・・・・・・・・
・(2) will come true. However, k is a proportionality constant determined from the Matrohar number, the pipe cross-sectional area, the area reduction ratio of the vortex generator installation part, the vortex generator dl, etc. That is, as is clear from Equation (2), the vortex placement method measures the volumetric flowmeter by detecting and counting the generation frequency f of the Karman vortex that is periodically generated downstream of the vortex generator.

Conventionally, this type of flowmeter has (1) wide rangeability; Q) Pressure drop is small compared to other flowmeters. (3) Accuracy is not relative to full scale but to the indicated value (or reading)
Since it can be expressed as a percent of (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
~500 mj/B) is 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 on this type of flow rate side is determined from the Reynolds number and the sensor sensitivity for detecting the vortex generation frequency f. In general, 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 V.
, 1] of the vortex generator d.

Reynolds number -d Re-□ when the terminology coefficient of the fluid is V...
(3) ■ The lower limit value is around 2000 1°, but the ratio of dl d of the vortex generator to the pipe diameter remains within a certain range from the point of view of vortex regularity and stability. Yes, generally 0015(-(0,4...group......(
4). 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.

6/・ On the other hand, if the pressure loss is Δp (hereinafter ΔP may be referred to as pressure difference) and the specific weight of the fluid is γ, then ΔPocγV ・・・・・・・・・・・・・・・
...There is a relationship in (5).

Therefore, as is clear from equations (3), (4), and (5) above, the larger the width d of the vortex generator is for a given pipe diameter, the greater the flow velocity V becomes, so the low flow sensitivity becomes increases, that is, the lower limit of measurable flow rate decreases,
On the other hand, as the flow rate increases, the pressure drop increases, and therefore,
There was a problem with range abilities being limited.

On the other hand, if the Ill d of the vortex generator is made smaller, the sensor sensitivity will decrease and the measurable range will be relatively shifted towards the large flow area, so there is a problem that the lower limit of the measurable flow rate will become sharper. .

The present invention solves the above-mentioned conventional drawbacks, and aims to reduce the lower limit of measurable flow rate, control pressure drop to below a predetermined reference value, and expand rangeability. It is a page.

In order to achieve this object, the present invention provides a vortex flowmeter that includes a variable mechanism section that can vary the vortex generator, and a pressure sensor 8 that detects the pressure difference between the upstream and downstream sides of the vortex generator.
(comprising: an electric control circuit for controlling the width variable mechanism so that the pressure difference of the pressure detector is constant;
The vortex generation frequency of the vortex detection means is doubled by %! It is equipped with a flow one-way computing unit that controls the flow rate based on the output signal of the electric control circuit.

With this configuration, from low flow area to large flow area or C
Even if the measurement point changes from the L-large meteor force to the low-flow -L region, the width variable mechanism section is activated by the deviation signal between the standard value and the pressure detection type signal that detects the pressure difference between the flow and the downstream of the vortex generator. 1) It operates to keep the force difference constant, that is, the vortex generator is automatically variably controlled so that its dl becomes smaller or larger. Therefore, this allows the lower limit of measurable flow rate to be reduced, and the pressure drop is below the standard value.
Furthermore, it becomes possible to measure a wide range of range abilities.

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

In FIGS. 1 and 2, 1 is a pipe through which the fluid to be measured flows;
Reference numeral 2 denotes a triangular prism-shaped vortex generator, which is composed of a fixed part 2a and a variable 11 part 2b. 3 is an ultrasonic vortex detection means;
Reference numeral 4 denotes a lJ variable mechanism section consisting of a step motor, gears, cams, etc., for continuously variable control of the variable part 11 2b of the vortex generator 2, and 5 detects the pressure difference between the upstream and downstream sides of the vortex generator 2. 6a is a pressure detection outlet, and 5b is a pressure conduit. And 6 is the electric signal of pressure detector 5,
This is an electric control circuit that compares the electric signal from the reference pressure setting device 7 and outputs the deviation signal to the intermediate variable mechanism section 4 consisting of a step motor or the like. Reference numeral 8 designates a flow rate calculator which operates upon receiving the vortex generation frequency signal from the vortex detection means 3 and the same signal output from the electric control circuit 6 to the variable mechanism section 4, and 9 a Karman vortex.

FIG. 3 is a characteristic diagram showing the relationship between the flow rate and pressure difference (or pressure loss) in the eddy current arrangement according to the present invention. al, a2. A curve passing through each point of a5 corresponds to the conventional example when l] of the vortex generator 2 is fixed to dM 8.

Moreover, FIG. 4 is a characteristic diagram showing the relationship between the vortex generation frequency f and the flow rate Q of the vortex flow meter of the present invention, in which a straight line passing through each point sl, s2°S5 indicates that rjJ of the vortex generator 2 is dMAX. This corresponds to the conventional example when fixed to .

” In the configuration described above, qMI of the minimum flow rate in Fig. 3
When the flow rate increases from a state where it is flowing at N, q.

Until now, the pressure difference ΔP changes from ΔPMIN to ΔPMA][1, as compared to the conventional characteristic curve (a+ to a2).
When the flow rate further increases by Δq, the pressure difference ΔP increases to the predetermined reference pressure 32 by the reference pressure setting device 7
Since the deviation signal is transmitted from the electric control circuit 6 to the step motor of the variable mechanism section 4, the deviation signal of the variable section 2b of the vortex generator 2 is changed from dMAX to dl.
The reference pressure Δp is automatically controlled to be the same value as the reference pressure Δp and the value X is automatically controlled.

Correspondingly, the vortex generation frequency f in Fig. 4 is fo
Δf increases from to fl. And at this time,
In other words, the flow m at point a5 in Figure 3 and point 83 in Figure 4
The values are /+ of the vortex detection means 3 and electricity 91. - The flow rate calculator 8 receives both electrical signals dl from the control circuit 6 and calculates the flow rate.

Further, when the flow rate is increased from the state where the flow rate is ql and the width is dI, that is, from point a5, the width of the variable portion 2b changes from dl to d2. The flow rate is controlled to gradually become narrower to d3, and at the maximum rated flow rate qMx, it becomes dMIN. Correspondingly, the vortex generation frequency f also increases, and at the maximum rated flow rate qMA][, width dMIN, the value becomes fMX.

In addition, when the grain size decreases, conversely, the variable middle part 2b becomes a2
l] is controlled to increase between and a4, and the pressure difference between al and a2 becomes less than the reference pressure ΔPMiX, so
dMAX becomes constant. Correspondingly, the vortex generation frequency f is f between S2 and 84 where the variable central portion 2b is variably controlled.
, change from fMAX''!! to 1~, still variable middle part 2b
The width is dM [fMIN between Sl and 82 where it becomes constant
It changes from f to f. Then, upon receiving the vortex generation frequency signal from the vortex detection means 3 and the signal from the electric control circuit 6, the flow rate calculator 8 calculates the flow rate value at that time.

Page 10, $-, the shape of the vortex generator 2 and the pipe line 1 in Fig. 1
As is clear from the relative arrangement within, the vortex generator 2 is
If the i4 columnar shape is arranged so that its apex angle faces the flow, d'' of the variable 11 section 2b will change from dMAX to dMru.
-i, the Strovall number St remains constant within a wide range of Reynolds numbers.

In this way, a triangular prism-shaped vortex generator r1.2 having a variable middle part 2b is arranged in the center of the pipe line 1, and the pressure difference between the upstream and downstream of the vortex generator 2 is adjusted according to the increase or decrease of the flow rate measurement point. Since the variable 11 section 2b is automatically controlled so that qMXH remains constant, as is clear from FIG.
The flow rate can be measured by controlling the reference pressure ΔPMkX or less over the period from IMkX to IMkX.

Looking at it from a different perspective, if the width of the vortex generator 2 is fixed to dMAX and it becomes a conventional vortex flowmeter, then the pressure loss is ΔPM
The measurable flow rate range to be measured below is between qMIN and (lo), but in the vortex flowmeter of the present invention, it is expanded from (IMI to qMix'!).

Looking at it from a different perspective, if the measurable flow rate range of the conventional vortex flow meter is from qMrx to qMx, then the maximum pressure drop (equal to the pressure difference ΔP) is Δpl, M! become. However, the eddy current meter of the present invention results in a small ΔPMAI.

As is clear from the above description, the vortex flowmeter of the present invention has a width variable mechanism section that variably controls the width of the vortex generator, and the pressure difference between the upstream and downstream sides of the vortex generator is By variably controlling the width of the vortex generator so that it remains constant and calculating the flow rate based on both the changed width and the vortex generation frequency, it becomes possible to measure with a much smaller pressure drop than before. In other words, the effect of further expanding the range ability can be obtained.

[Brief explanation of the drawing]

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 of the vortex flowmeter seen from the side, and an explanatory diagram of the control signal system. A characteristic diagram showing the relationship between the flow rate and pressure difference (or pressure drop) of a vortex flowmeter according to an embodiment of the present invention. Fig. 4 is a characteristic diagram showing the relationship between the vortex generation frequency and flow rate of the vortex flowmeter according to an embodiment of the present invention. It is. 1... Pipeline, 2... Vortex generator, 3...
... Vortex detection means, 4 ... Width variable mechanism section, 6.
...Pressure detector, 6...Electric control circuit, 8
...Flow rate calculator. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] (1) A pipe line through which the fluid to be measured flows, a vortex generator provided in the pipe, and vortex detection means for detecting the Karman vortex generated thereby are provided, and the width of the vortex generator is variably controlled. It includes a variable width mechanism and a pressure detector that detects a pressure difference between upstream and downstream sides of the vortex generator, and controls the variable width mechanism based on a pressure difference signal from the pressure detector and a reference value. A vortex flowmeter comprising an electric control circuit and a flow rate calculator that calculates the flow rate based on the output signal of the vortex detection means and the electric control circuit. Q) A patent claim in which the shape of the vortex generator is a triangular prism, the apex angle thereof is opposed to the flow of the fluid to be measured, and the width of the vortex generator determined by the remaining two apex angles is variably controlled. The vortex flowmeter according to item 1.