JPS58219422A - 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 signal processing circuit part 5 converts a vortex frequency signal, which is detected by a vortex generating means 3, into a specified electric signal. A comparing and judging part 6 receives the electric signal from the signal processing circuit part 5 and compares the signal with a reference frequency. An electric operating circuit part 7 receives the electric signal from the comparing and judging part 6 in order to control the width of the variable width part 2b of the vortex generating body 2 and outputs the electrical signal to a width varying mechanism 4. A flow rate operating part 9 selects one of flow rate operation expresions stored in a memory part 8 and computes the value of the flow rate based on the vortex frequency signal from the signal processing circuit part 5.

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 invention relates to a vortex flow meter that measures the flow rate of fluid.

As is well known, the operating principle of the Karman vortex flow meter is based on the fact that the vortex generation frequency 3.times.-number f is linearly proportional to the flow velocity U over a wide range of Reynolds numbers. That is, f=st- (1) However, St Strobar number (constant of proportionality) d Width of the vortex generator is established.

On the other hand, if the flow rate flowing through the pipe is Q, the flow rate Q (is proportional to the flow velocity U, so in equation (1), the Strovall number St is
If [1]d of the vortex generator is constant, the flow Ft'tQ will be proportional to the vortex generation frequency f.

That is, Q=Kf (2) holds true. However, the proportionality constant is determined from the number of strontals, the cross-sectional area of the pipe, the area reduction rate of the vortex generator, the vortex generator, etc. That is, as is clear from equation (2), the vortex flow meter measures the volumetric flow rate by detecting and counting the generation frequency f of the Karman vortex that is periodically generated in the wake of the vortex generator.

Conventionally, this type of flowmeter has a wide range of 1,1 non-scillability. 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 combination and evening inputs can be obtained. Furthermore, there are no mechanically moving parts and the structure is simple. Because it has many characteristics such as
0 tnV h) 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, which requires wider rangeability and lower pressure. It is required that it be a loss.

Incidentally, the minimum flow rate that can be measured by this type of flowmeter is determined from the Reynolds number and the sensor sensitivity for detecting the vortex generation frequency f. In general, the lower limit value of the Reynolds number Re is determined from the viewpoint of sensor sensitivity, and the lower limit value of the flow velocity near the vortex generator is U1. .

In addition, the ratio of "1] d of the vortex generator to the pipe diameter is within a nearly constant range from the viewpoint of the regularity and stability of the vortex, and is generally o, 1es (-<0.4・・・・・・・・・・(4)
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 that of industrial measuring instruments.

On the other hand, if the pressure loss is ΔP (in the present invention, ΔP is sometimes referred to as pressure difference) and the specific weight of the fluid is γ, then the relationship ΔP deficiency γU ・・・・・・・・・(5) be.

Therefore, as is clear from equations (3), (4), and (5), for a given pipe diameter, the larger the rlld of the vortex generator, the larger the flow velocity U, which reduces the flow rate. The flow rate sensitivity increases, that is, the measurable flow rate lower limit value decreases by 6 pages, but on the other hand, as the flow rate increases, the pressure loss increases, resulting in a problem that rangeability is restricted.

On the other hand, if the width d of the vortex generator is made smaller, the sensor sensitivity will be lowered and the measurable range will be relatively shifted towards 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 above conventional drawbacks, and aims to reduce the lower limit of measurable flow rate, control pressure loss to a predetermined basic value, and expand rangeability. It is something to do.

In order to achieve this object, the present invention provides a vortex flowmeter that includes: a width variable mechanism section that variably controls the width of a vortex generating body; a signal processing circuit section that processes a vortex generation frequency signal detected by a vortex detection means; In order to control the pressure difference between the upstream side and downstream side of the vortex generator to a predetermined set value or less, an electric operating circuit section is provided for controlling the medium variable mechanism section in multiple stages, and the above-mentioned medium variable mechanism section is switched in stages. The storage unit that stores the vortex generator formula 71 corresponds to “1” of the vortex generator, receives the vortex frequency signal from the signal processing circuit unit, and converts this signal into a predetermined reference frequency. Comparing and determining the selected flow rate calculation formula, the IJ variable mechanism unit is driven by the selected flow rate calculation formula. It is composed of a flow rate calculation unit that calculates a flow rate value based on the vortex frequency signal from the signal processing circuit unit.

With this configuration, even if the measurement point changes from a small flow meter area to a large flow meter area or from a large flow area to a small flow rate area, the flow is generated in proportion to the flow j11. The vortex frequency signal is compared with the reference frequencies, and when the vortex frequency signal becomes larger or smaller than the reference frequency, the 11] variable mechanism section is activated]- and the vortex generator's 11]
are switched step by step. At the same time, the vortex generator 1]
A flow rate calculation formula corresponding to is also selected.

Therefore, it is possible to control the pressure loss to below the reference value and perform reuse measurement with expanded rangeability.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 4.

In FIGS. 1 and 2, 1 is a pipe through which the fluid to be measured flows;
2VJ - triangular prism-shaped vortex generator with fixed part 2a and variable r
ll section 2b.

Attachment 3: Ultrasonic vortex detection means, 4 is variable 1 of vortex generator 2
1) A medium variable mechanism section consisting of a step motor, gears, cams, etc. for variable control of section 2b step by step; 5 is a signal for converting the vortex frequency signal detected by the vortex generating means 3 into a predetermined electric signal; Processing circuit section. 6 receives the electrical signal from the signal processing circuit section 5, and selects a predetermined reference frequency (fo, fj, f2, f' in FIG. 4).
A comparison/judgment unit 7 receives an electric signal from the comparison/judgment unit 6 and sends an electric signal to the variable mechanism unit 4 in order to control the variable middle part 2b of the vortex generating body 2 stepwise. This is an electrical operation circuit unit that outputs. 8 is l of the vortex generator 2
Flow rate calculation formulas Q1 (g), Q2 (2), which indicate the relationship between the flow rate Q and the vortex frequency signal f when Jd is used as a parameter.
Remember Q3(2). Notes on applications of microprocessors, etc. 9 ・−.

Memory part 9 is the three styles mfi stored in memory part 8!
This is a flow rate calculation unit that calculates a flow rate value from one flow M calculation formula selected from among the equations by the comparison/judgment unit 6 and the vortex frequency signal D from the signal processing circuit unit 6.

1o is a Karman vortex street that is periodically generated downstream of the vortex generator 2.

FIG. 3 shows each rll (i.e., dl, d2.d3
It is a diagram showing the relationship between the flow rate Q and the pressure loss ΔP in three stages of
It shows that it is between MIN and ΔPMAX.

Still, Figure 4 shows the vortex generation method [IJd is d+, d2゜d
, is a diagram showing the relationship between the vortex frequency signal f and the flow rate Q in the case of three-stage switching.
9 or dl, the vortex frequency signal f is f.

This shows that when the flow rate changes from qo to fl, the flow rate value changes from qo to ql.
The calculation formula is expressed as Q+(].Then, II] d is 1111''■10, --... The flow rate calculation formula for the next switching is d2, Q2
(A), d3 indicates Q3 (A).

-1] In the configuration described above, when the fluid to be measured starts to flow, the width of the variable middle portion 2b of the vortex generating body 2 is dl at the maximum l].

When the flow rate is gradually increased from this state, the vortex frequency signal f from the signal processing circuit section 6 is first compared with the reference frequency fa in the comparison/judgment section 6, and when f<fo, the flow rate is not calculated. Then, as far as the gap is under the condition of fo<f<fl, the vortex generator 2
The r9 of the variable part 2b outputs an electrical signal to dl as much as possible and maintains it in that state, and the comparison/judgment part 6 Qd
7) Select the flow rate calculation formula. Therefore, as long as the condition fO≦f≦f1 is satisfied at this time, the flow rate value can be determined by the flow rate calculation unit 9 from the vortex frequency signal f from the signal processing circuit unit 5 and the flow rate calculation formula Q1(j). Calculated.

As the flow rate m increases from this state and the maximum flow rate value q1 that can be calculated using Ql(a) increases by Δq, the vortex generation frequency decreases by Δf. , f>:h, the comparison/judgment section 6 outputs an electric signal to the electrical operation circuit section 7 to switch the width of the variable 111 section 2b from dl to d2.

Therefore, the relationship between the vortex frequency signal f and the flow rate Q is a relational expression when 11 of the variable rlJ portion 2b of the vortex generator 2 is constant at d2. Then, while the condition C < f < f2 is satisfied, the flow rate calculation formula Q2 (g) is similarly selected;
Based on this and the vortex frequency signal f, the flow rate value is calculated. When the diversion increases to f > f2, similarly lJ of the variable 11 part 2b becomes the minimum 1 from d2 to d3]
It is variable. And under the condition f2<f<f3, the flow h
The flow rate is calculated using the third calculation formula Q3[).

Conversely, if the number of drifters is reduced from this state and the condition f<f2 is reached, the variable 11 section 2b switches from d3 to d2, and fl
<Under the condition of f<f2, the flow rate calculation formula is Q2(/'),
When the condition of f<f+ is reached, it switches from d2 to dl, and f
Under the condition of O≦f≦f1, the flow rate values are calculated in the same manner using the flow rate calculation formula (1).

In addition, as is clear from the shape of the vortex generator 2 in FIG. 1 and the relative position within the pipe line 1, the vortex generator 2 has a triangular prism shape, and is arranged so that its apex angle faces the flow. Even if 111 of the variable 11 portion 2b determined by the remaining bivertical angle changes from dl to d5, the Strovall number sty remains constant within a wide Raynor number range.

In this way, by arranging the triangular prism-shaped vortex generator 2 having the variable middle part 2b in the center of the pipe line 1 and controlling the lJ of the variable 1J part 2b in multiple stages in response to the increase/decrease of the flow rate measurement points, the vortex is mainly generated. Maximum allowable pressure loss value ΔI which predetermines the pressure loss determined by the ri1 dimension of body 2) MAX (minimum flow 11
Minimum pressure loss value Δ1) Mtn or more determined by 1 value qo"-),
This makes it possible to measure the flow rate.

Looking at it from a different perspective, if we use a conventional vortex flowmeter when the vortex generator 2 (1) is fixed at dl, then the pressure loss is Δ1)M□
Measurable flow rate range for measuring from 8 to 5
However, in the vortex flowmeter of the present invention, from qo to q
It has been expanded to 3.

Looking at it from a different perspective, if the measurable flow rate range of a conventional vortex flow meter is from qo to q5, then 137',
-5゛The maximum pressure loss will be Δp4mX. However, in the vortex flowmeter of the present invention, the value of ΔpMAX is smaller than this.

As is clear from the explanation below, the vortex flow meter of the present invention has a [1] variable mechanism section that variably controls II+ of the vortex generating body, and has a variable mechanism section that variably controls the vortex frequency signal detected by the vortex detection means. While comparing with a predetermined reference frequency,
``The width of the vortex generator is controlled stepwise by driving the variable mechanism so that the pressure drop determined in the vortex generator becomes less than a set value, and the width of the vortex generator is controlled in steps. By calculating the flow rate using a flow rate calculation formula corresponding to , it becomes possible to measure with smaller pressure loss than before. In other words, it has the effect of further expanding its range ability.

In addition to the invention mentioned above, if the maximum allowable pressure drop ΔpMAX can be set to an arbitrary value to determine the flow rate measurable range, the maximum allowable pressure drop can be set by increasing the number of switching stages in the vortex generator This also provides the effect of further reducing the difference in minimum pressure loss.

14 pages

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional view seen from the second part showing an embodiment of the vortex flowmeter of the present invention, and Figure S2 is a schematic cross-sectional view seen from the side of the hot water distribution flowmeter and an explanatory diagram of the control signal system. , FIG. 3 is a characteristic diagram showing the relationship between the flow rate and pressure drop of the vortex flowmeter according to an embodiment of the present invention, and FIG. 4 is a characteristic diagram showing the relationship between the vortex frequency signal and the flow rate of the vortex flowmeter. 1... Pipeline, 2... Vortex generator, 3...
... Vortex detection means, 4 ... Medium variable mechanism section, 6 ...
. . . Signal processing circuit section, 6 . . . Comparison/discrimination section, 7
......Electrical operation circuit section, 8......Storage section,
9...Flow rate calculation section. Name of agent: Patent attorney Toshi Nakao, Idiot 1
Figure 2 Figure 3

Claims (3)

[Claims] (1) Provide a pipe line through which the fluid to be measured flows, a vortex generator provided in the pipe line, and a vortex detection means for detecting the Karman vortex generated by the vortex generator, and [1] of the vortex generator is detected by the vortex detection stage; a signal processing circuit unit that processes the frequency signal of the Karman vortex; In order to make the pressure difference between the flow and the F flow less than a predetermined set value, the vortex generating body is 1
1); a storage unit that stores a plurality of flow rate calculation formulas corresponding to 1];
Receiving the vortex frequency signal from the signal processing circuit section, comparing this vortex frequency signal with a predetermined basic frequency, and transmitting an output signal for driving the variable mechanism section 1 to the electrical operation circuit section. and a comparison/discrimination section that selects the flow rate calculation formula, and a flow rate calculation unit that calculates a flow rate value based on the selected flow rate calculation formula and the vortex frequency signal from the signal processing circuit unit. Vortex flow meter consisting of. (2) 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 arranged so as to be variably controlled] 7. A vortex flowmeter according to claim 1. (3) After the output signal that drives the variable width mechanism is sent to the electric operation circuit, even if the flow rate increases or decreases, the “I
The vortex flowmeter according to claim 1, further comprising a built-in timer for holding the J variable mechanism.