JPH07209044A - Vibration type flow meter - Google Patents

Abstract

PURPOSE:To provide a vibration type flow meter which can remove the influence of change of Strouhal number at a low flow speed and enlarge the width of the range of measurable flow rate up to a low flow rate. CONSTITUTION:The vibration type flow meter to measure flow rate by utilizing fluid vibration has a vibration type flow meter body 21 provided in a measuring passage, a measuring sensor 22 for pressure loss which is provided in the measuring passage to measure the pressure loss of measured fluid, and a processing circuit 24 to correct Strouhal number on a measuring signal sent from the measuring sensor 22 for pressure loss and a measuring signal sent from the vibration type flow meter body 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillating flow meter which can eliminate the influence of the change of the Strouhal number at a low flow rate and can expand the range of flow rate measurable range to a low flow rate.

[0002]

2. Description of the Related Art FIG. 3 is a structural explanatory view of a conventional example which has been generally used in the past. As vibration type flow meters utilizing fluid vibration, there are vortex flow meters and edge tone flow meters.
Here, the vortex flowmeter will be described as an example.

As a conventional vortex flowmeter, for example, the 3rd fluid measurement symposium lecture meeting title "Flow rate characteristics of vortex flow rate in various fluids", issued January 27, 1986
It is shown in P53 to P56 issued by the Society of Instrument and Control Engineers.

In the vortex flowmeter, a vortex generator is placed in the flow passage as shown in FIG. 3, the flow velocity is obtained by measuring the frequency of the Karman vortex generated from the vortex generator, and the flow passage cross-sectional area is added to this flow velocity. By applying it, the flow rate that can be obtained is measured.

In FIG. 3, 11 is a pipe through which the fluid to be measured flows, and 12 is a vortex generator provided vertically to the pipe 11. Reference numerals 13 and 14 denote a pair of pressure measurement holes provided on the left and right sides of the vortex generator 12 toward the flow.

Reference numerals 15 and 16 are pressure guiding pipes for guiding the pressure fluctuations taken in from the pressure measuring holes 13 and 14. 17
Is a pressure sensor to which the pressure fluctuations from the pressure guiding tubes 15 and 16 are input. Reference numeral 18 is a signal processing circuit that processes the detected value of the pressure sensor 17. 19 is a Karman vortex.

In the above structure, the vortex generated by the vortex generator 12 causes a pressure fluctuation in the measurement fluid, and this pressure fluctuation is detected by the pressure sensor 17 and processed by the signal processing circuit 18.

Here, when the product of the frequency f of the generated Karman vortex and a certain representative length d is divided by the flow velocity u, the Strouhal number St becomes a dimensionless quantity, which is as shown in FIG. Therefore, the flow velocity can be measured relatively easily by measuring the frequency using the following equation (1). u = (f · d) / St (1)

A flow meter utilizing fluid vibration is reliable because it has no moving parts, and it can be used for a wide range of flow rate measurements because it can measure non-conductive fluids regardless of the type of measurement fluid, liquid or gas. Has been.

[0010]

However, in such a device, as can be seen from FIG. 4, the Strouhal number becomes a non-constant value as the flow velocity decreases, so that (1)
When the formula is used, the error becomes large in the low flow velocity region, it is not suitable for low flow velocity measurement, and the flow rate measurement range becomes small.

The present invention solves this problem. An object of the present invention is to provide an oscillating flow meter capable of eliminating the influence of the change of the Strouhal number at a low flow rate and expanding the range of flow rate measurable range to a low flow rate.

[0012]

In order to achieve this object, the present invention relates to a vibration type flow meter which measures a flow rate by utilizing fluid vibration, and a vibration type flow meter main body provided in a measurement flow path. A pressure loss measurement sensor provided in the measurement flow path for measuring the pressure loss of the measurement fluid, and a calculation for correcting the Strouhal number from the measurement signal of the pressure loss measurement sensor and the measurement signal of the vibration type flow meter main body And a processing circuit, which constitutes a vibration type flow meter.

[0013]

With the above construction, the vibration frequency of the fluid to be measured is measured by the vibration type flow meter main body. The pressure loss measurement sensor measures the pressure loss of the measured fluid. The arithmetic processing circuit corrects the Strouhal number from the measurement signal of the pressure loss measurement sensor and the measurement signal of the vibration type flow meter main body. Hereinafter, detailed description will be given based on examples.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of the essential structure of an embodiment of the present invention. In the figure, the same symbols as those in FIG. 3 represent the same functions. Only parts different from FIG. 3 will be described below.

Reference numeral 21 is a vibration type flow meter main body. 22 is
The pressure loss measuring sensor is provided in the measurement flow path 23 and measures the pressure loss of the measurement fluid.

In this case, the pressure guiding pipe 221 provided on the upstream side of the measurement flow passage 23, the pressure guiding pipe 222 provided on the downstream side of the measurement flow passage 23, the pressure of the measurement fluid in the pressure guiding pipe 221 and the conduction of pressure. It comprises a differential pressure sensor 223 for measuring the differential pressure with the pressure of the measuring fluid in the pressure pipe 222.

Reference numeral 24 is an arithmetic processing circuit for correcting the Strouhal number from the measurement signal of the pressure loss measuring sensor 22 and the measurement signal of the vibration type flow meter main body 21. In this case, a microprocessor is used.

In the above structure, the vibration type flow meter main body 2
At 1, the vibration frequency of the measurement fluid is measured. The pressure loss measurement sensor 22 measures the pressure loss of the measurement fluid. In the arithmetic processing circuit 24, the Strouhal number St is calculated from the measurement signal of the pressure loss measurement sensor 22 and the measurement signal of the vibration type flow meter main body 21.
Correction process.

The basic principle in this case will be described below. The Strouhal number St is defined as St = f · d / u (2), and the Reynolds number Re is defined as Re = u · d / ν (3). Here, u is the average flow velocity of the fluid passing through the vibration type flow meter, and ν is the kinematic viscosity coefficient of the fluid.

Further, in the vibration type flow meter, there is a certain functional relationship between the Strouhal number St and the Reynolds number Re which is determined only by the shape. St = F (Re) (4) When this relationship is illustrated, the horizontal axis of FIG. 4 is replaced with the Reynolds number Re which is a dimensionless number. The curve is called a Reynolds number Re-Strouhal number St curve.

Between the differential pressure ΔP and the kinematic viscosity coefficient ν (5)
There is a relationship like an expression. ν = D ² · ΔP / (32 · L · u · ρ) (5) where D is the diameter of the measurement channel, ΔP is the differential pressure, L is the distance between the pressure guiding pipe 221 and the pressure guiding pipe 222, and ρ Is the density of the fluid.

The pipe diameter D of the measurement flow path 23 and the representative length d of the vibration type flow meter have a relationship as shown in equation (6). D = α · d (6) By substituting the equations (5) and (6) into the equation (3), Re = 32 · L · ρ · u ² / (α ² · d · ΔP) (7) Becomes

When the function F of the equation (4) is an nth-order equation of Re, St = C _n · Re ⁿ + C _{n -1} · Re ^n-1 + ... + C ₁ · Re + C ₀ (8)

Substituting the equations (2) and (7) into these and rearranging u, C _n ^' .u ^{2n + 1} + C ^' _n- 1.u ^{2 (n-1) +1} + C ^' _{n- 2} · u ^{2 (n−2) +1} + ... + C ^′ ₁ · u ^{2 + 1} + C ₀ · u−fd = 0 (9) and the (2n + 1) th order equation for u is obtained.

[0025] ^{_{Here, C 'n = C n ·}} ((32Lρ) / (α 2 dΔP)) n C' n - 1 = C n-1 · ((32Lρ) / (α 2 dΔP)) n-1 ………………… C ^′ ₁ = C ₁ · ((32Lρ) / (α ² dΔP)) ¹ .

In this equation, it is possible to determine that the shape of the vibration type flow meter is determined except for u, f, ΔP and ρ. Since the density ρ hardly changes with temperature, it is possible to obtain sufficient accuracy by measuring once at somewhere on the measurement line. Therefore, by measuring the frequency f and the differential pressure ΔP, all the coefficients of the equation (9) are determined. Therefore, the flow velocity u can be obtained by solving the equation (9) using the Newton method or the like.

The generation frequency f of the Karman vortex is detected as the fluctuation frequency of the output voltage of the pressure sensor in the vibration type flow meter main body 21. Since the differential pressure ΔP is detected by the differential pressure sensor 223, when they are input to the microprocessor 24 and the processing for solving the equation (9) is performed in the microprocessor 24, the flow velocity u is obtained and the measurement flow path interruption The flow rate is obtained by multiplying the area.

As a result, according to the present invention, by providing the correction mechanisms 22 and 24 for measuring the differential pressure, it is possible to correct the Strouhal number, and the vibration type flow meter has a large measurement error and cannot be measured until now. It is possible to accurately measure even low flow rates, and obtain a vibrating flow meter that greatly expands the flow measurement range.

Further, since the kinematic viscosity of the fluid can be measured by using the equation (5), the measurement flow path 23
Is flowing. It is possible to know the type of the measurement fluid, and there are various advantages especially in controlling the process.

FIG. 2 is an explanatory view of the essential structure of another embodiment of the present invention. In this embodiment, the Strouhal number St is a constant Reynolds number R regardless of the Reynolds number Re.
The bypass flow passage 31 is provided to secure a laminar flow state when the fluid in the measurement flow passage 23 becomes a turbulent flow at a flow rate of e ₁ or less.

Therefore, it is necessary to determine the conduit diameter D ', the conduit length and the interval L of the bypass passage so that the fluid passing through the bypass passage 31 is in a laminar flow state. In such a case, the differential pressure ΔP and the kinematic viscosity coefficient ν have a relation as shown in the fifth equation. ν = D' ² · ΔP / (32 · L · u '· ρ) (10) Here, u ′ is the average flow velocity of the fluid passing through the bypass channel 31, and ρ is the fluid density.

The conduit diameter D of the bypass passage 31 ^'and between the characteristic length d of the vibratory flowmeter relationship such as equation (11). D '= α'd (11)

Further, the average flow velocity u'in the bypass passage 31.
The relationship between the mean flow velocity u in the vibration type flow meter and the average flow velocity u in the vibration type flow meter is as shown in equation (12). u ′ = β · u (12) By substituting the equations (10), (11), and (12) into the equation (3), Re = 32 · L · ρ · β · u ² / (α ′ ² · d · ΔP) (13)

[0034] (4) and n the following equation for the function F of the formula Re, the ^{_{St = C n · Re n +}} C n-1 · Re n-1 + ...... + C 1 · Re + C 0 (14).

Substituting equations (2) and (13) into this, u
Can be summarized as follows: C ^″ _n · u ^{2n + 1} + C ^″ _n-1 · u ^{2 (n-1) +1} + C ^″ _n-2 · u ^{2 (n-2) +1} + …… + C ^'' ₁ · u ^{2 + 1} + C ₀ · u−fd = 0 (15) Then, the following equation for u is (2n + 1).

Here, C ^″ _n = C _n · ((32Lρβ) / (α ² dΔP)) ⁿ C ^″ _n−1 = C _n−1 · ((32Lρβ) / (α ² dΔP)) ^{n -1} ........................... C ^'' ₁ = C ₁ · ((32Lρβ) / (α ² dΔP)) ¹ .

As a result, according to the present embodiment, since the bypass flow passage 31 is provided to ensure the laminar flow state, the differential pressure sensor 223 can accurately detect the pressure loss,
It is possible to obtain a vibrating flow meter that enables more accurate Strouhal number correction.

Although it has been described that the pressure loss is detected by using the differential pressure sensor 223 in the above embodiment,
For example, the pressure guiding pipes 221 and 222 are not limited to this.
It is also possible to directly attach a pressure gauge to each of them and detect the pressure loss from the difference between the measured values of the pressure gauge. In short, any measurement sensor capable of detecting pressure loss may be used.

[0039]

As described above, according to the present invention, in the vibration type flow meter for measuring the flow rate by utilizing the fluid vibration, the vibration type flow meter main body provided in the measurement flow path and the vibration type flow meter main body provided in the measurement flow path are provided. A pressure loss measurement sensor for measuring the pressure loss of the measured fluid, and an arithmetic processing circuit for correcting the Strouhal number from the measurement signal of the pressure loss measurement sensor and the measurement signal of the vibration type flow meter main body. A vibrating flow meter characterized by the above is constructed.

As a result, according to the present invention, it is possible to correct the Strouhal number by providing the correction mechanism for measuring the pressure loss, and the vibration type flowmeter has a large measurement error and cannot be measured. It is possible to obtain a vibrating flow meter that can measure even the flow rate with high accuracy and greatly expands the flow rate measurement range.

Therefore, according to the present invention, it is possible to realize an oscillating flow meter in which the influence of the change of the Strouhal number at a low flow rate is eliminated and the range of flow rate measurable range can be expanded to a low flow rate.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a main part configuration of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a main part configuration of another embodiment of the present invention.

FIG. 3 is an explanatory diagram of a configuration of a conventional example that is generally used in the past.

FIG. 4 is an operation explanatory diagram of FIG. 3;

[Explanation of symbols]

 11 ... Pipe line 12 ... Vortex generator 13 ... Pressure measuring hole 14 ... Pressure measuring hole 15 ... Pressure guiding tube 16 ... Pressure guiding tube 17 ... Pressure sensor 18 ... Signal processing circuit 19 ... Karman vortex 21 ... Oscillating flow meter main body 22 ... Pressure Loss measuring sensor 221 ... Pressure guiding tube 222 ... Pressure guiding tube 223 ... Differential pressure sensor 23 ... Measuring flow path 24 ... Microprocessor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenta Mikita 2-9-32 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Co., Ltd.

Claims (1)

[Claims] 1. A vibrating flow meter for measuring a flow rate by utilizing fluid vibration, wherein a vibrating flow meter main body provided in a measurement flow passage and a pressure provided in the measurement flow passage for measuring pressure loss of the measurement fluid. A vibration type flow meter comprising: a loss measuring sensor; and an arithmetic processing circuit for correcting the Strouhal number based on the measurement signal of the pressure loss measuring sensor and the measurement signal of the vibration type flow meter main body.