JPH08219841A - Coriolis flow meter - Google Patents

Abstract

PURPOSE: To enable stable flow measurement hardly affected with disturbance by providing brace bars supporting a flow tube and a counter balance in the vicinity of the inside of both sides coupling blocks. CONSTITUTION: Both ends of a flow tube 3 and a counterbalance 4 are fixed to coupling blocks 12a, 12b in parallel, and the flow tube 3 and the counterbalance 4 are supported by brace bars 13a, 13b at insides of both blocks 12a, 12b. Thereby, when the flow tube 3 and the counter balance 4 are two points- supported by the blocks 12a, 12b and the brace bars 13a, 13b and resonance driven, the supporting positions become stable so as not to receive outside effect. Constant elasticity or low linear expansion coefficient material is used as the material of the counterbalance 4 so that the counterbalance 4 side as a vibration element is allowed not to receive any vibration heat effect, and the temperature correction of frequency characteristics is conducted based on the detected temperature of the flow tube 3 with an excellent heat response so that a mass amount or density is measured with an excellent response so as to improve accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Coriolis flowmeter, and more particularly to a counter having a straight tubular flow tube for obtaining a mass flow rate utilizing Coriolis force and having both ends fixed in parallel with the flow tube. The present invention relates to a straight tube Coriolis flowmeter of an alternating drive type with a balance.

[0002]

2. Description of the Related Art When a flow tube with a mass flow rate of m is supported at both ends and an alternating vibration is applied around the support point at an angular velocity of ω, the flow tube has a Coriolis proportional to the vector product of the mass flow rate of m and the angular velocity of ω. Force F acts. The flow tube is deformed by this Coriolis force F, and a phase difference proportional to the Coriolis force is generated. The Coriolis flowmeter is a mass flowmeter that detects the phase difference to determine the mass flow rate m, and further selects the angular velocity ω as the natural frequency ω ₀ around the support point to measure the fluid density ρ from ω _0. be able to. As described above, the flow tube is a main part for generating the Coriolis force of the Coriolis flowmeter and for obtaining the density, and is roughly classified into a straight tube and a curved tube in shape.

Needless to say, the straight pipe type Coriolis flowmeter has the simplest shape and is small and easy to maintain. However, the straight pipe which responds to the Coriolis force has a large bending rigidity. Therefore, the sensitivity is low and it is disadvantageous in terms of SN ratio. The simplest way to increase the signal-to-noise ratio is to make the flow tube thin and long, but the thin tube is easily affected by the pressure of the fluid, and if it is made long, the natural frequency is affected by thermal expansion and the natural frequency. ω ₀
Changes, causing an error in the mass flow rate m to be obtained based on the principle of Coriolis force generation.

The present inventors have proposed the following Coriolis flowmeter in order to eliminate the above-mentioned drawbacks of the straight pipe type Coriolis flowmeter.

FIG. 5 is a view for explaining a conventional straight pipe type Coriolis flowmeter, and FIG. 5A is a view A in FIG. 5B.
5A is a sectional view taken along the line BB in FIG. 5A, in which 1 is an outer cylinder, 2a and 2b are connection flanges, 3 is a flow tube, and 4 is a flow tube. Is counter balance, 5
Reference numerals a and 5b are connection blocks, 6 is a drive unit, 7 and 8 are detection units, and 9 is a weight.

In the Coriolis flowmeter shown in FIG. 5, the flow tube 3 and the counter balance 4 are coaxially fixed at both ends,
A weight 9 is fixed to the central portion of the counter balance 4 and adjusted so that the natural frequencies of the weights are equal to each other, and the drive tube 6 drives the flow tube 3 and the counter balance 4 to resonate. 8, the phase difference signal due to the Coriolis force of the flow tube 3 is detected.

That is, the Coriolis force can be detected with high sensitivity by efficiently driving the flow tube 3 with a large amplitude by the resonance drive, and further, both ends of the flow tube 3 are expanded into a trumpet shape. , The rigidity in the axial direction was substantially lowered to remove the influence of the length change due to the thermal expansion and contraction of the flow tube 3 due to the change of the fluid temperature, and the both ends were fixed so that the stable measurement result was obtained with respect to the temperature change. The shortcomings of the Coriolis flowmeter in the flow tube are eliminated.

On the other hand, looking at the configuration of the vibration system of the Coriolis flowmeter shown in FIG. 5, the flow tube 3 is fixedly supported by the connecting blocks 5a and 5b together with the counterbalance 4, and further, both ends of the flow tube 3 are supported. Is connected to the inner peripheral wall of the connection flanges 2a and 2b at the ends 3a and 3b of the expanded shape. The vibration mode of this flow tube 3 is
As shown in FIG. 4A, the flow tube 3 has points P and Q.
It is fixedly supported by, and the extension is fixed at the B position, and the counter balance 4 shown by the broken line between P and Q is driven.
It is resonantly driven by and vibrates with three curvatures of Na at both ends and Ma at the center.

That is, the Coriolis flowmeter shown in FIG. 5 is efficiently driven by resonance driving with a smaller energy, and since the vibration between B and P has a small rigidity, the stress in the vicinity of the fixed position B is also small, It enables long-term stable measurement.

Further, the Coriolis flowmeter measures the flow rates of fluids having different physical and chemical properties. For example, when a fluid having a temperature different from room temperature flows, the flow tube immediately responds to heat and reaches the fluid temperature, but the temperature of the counter balance 4 changes slowly with respect to the fluid temperature change. Indicates that the Young's modulus of the tube material of the flow tube 3 and the counter balance 4 changes according to the temperature change.

The natural frequencies f ₁ and f ₂ of the flow tube 3 and the counter balance 4 at the time of measurement are expressed as follows.

[0012]

[Equation 1]

Here, in (1) and (2), f ₁ = f
_The mass M _B is adjusted to be ₂ .

[0014]

The conventional straight pipe type Coriolis flowmeter shown in FIG. 5 is supported by a low-rigidity flow tube 3b having an expansion portion so as to be movable in the axial direction, and therefore, the connecting block. 5a and 5b are P in FIG.
Since it is fixedly supported by (Q), the connecting block 5a,
5b receives a rotational moment, and also has three curvatures Na,
Since Ma and Na are given to the flow tube 3, the rigidity of the connecting blocks 5a and 5b itself is easily affected, and the supporting portions of the connecting blocks 5a and 5b are easily moved due to disturbance, and the zero point and the measured value vary. Occurs.

When the temperature of the fluid to be measured changes, the Young's modulus also changes and the spring constant K changes, and the flow tube 3 and the counter balance 4 have their natural frequencies f ₁ and f ₁ according to the equations (1) and (2). f ₂ changes. That is, the temperature of the flow tube 3 immediately responds so as to be equal to the fluid temperature, but the temperature of the counter balance 4 changes slowly. As a result, the coupled cycle also changes slowly, and it takes time to stabilize. Therefore, even if the counter balance 4 is corrected by the fluid temperature, the cycle changes slowly, and it is impossible to correct the response with good response.

The present invention has been made to solve the above-mentioned problems, and makes use of the advantages of a straight pipe type Coriolis flowmeter to provide a small flowmeter, and to improve the drawback of low sensitivity to high sensitivity. At the same time, it is an object of the present invention to provide a straight pipe type Coriolis flowmeter capable of removing the instability factor of the support position of the flow tube and correcting the characteristic change due to the temperature change of the fluid with good response.

[0017]

In order to solve the above problems, the present invention provides (1) a straight tubular flow tube liquid-tightly fixed at both ends to a flow tube, and a connecting block near both ends of the flow tube. Of the Coriolis acting on the flow tube when the flow tube and the counter balance are driven in opposite phases around the connection block. In a straight pipe type Coriolis flow meter for obtaining a mass flow rate from a force, one or a plurality of pairs of brace bars for supporting the flow tube and counter balance are provided in the vicinity of the inside of the connecting block on both sides, and further,
(2) In (1) above, a flexible tube that is fluid-tightly movable in the axial direction of the flow tube is provided between the flow tube to which both ends of the flow tube are fixed and the connection block. In addition, each of the flow tube and the counter balance has a weight for equalizing its natural frequency, and the weight is supported flexibly in the axial direction and rigid in the driving direction. Further, (3)
In (1) or (2) above, the counterbalance is one or a plurality of straight pipes, columnar bodies, or plate-like bodies, and the counterbalance is arranged at a position symmetrical with the flow tube. (4) In any one of (1) to (3) above, the material of the counter balance is a constant elastic material or a low linear expansion coefficient material.

[0018]

[Operation] A straight flow tube and a counterbalance are fixed in parallel to two spaced connection blocks and both ends are fixed.
Further, by supporting the flow tube and the counter balance on both inner sides of the connecting block with brace bars, the connecting block and the brace bar are supported at two points, and the supporting position when the flow tube and the counter balance are resonantly driven is external. It shall be stable and not affected. Furthermore, by making the material of the counterbalance a constant elasticity or low linear expansion coefficient material, the influence of vibration heat on the counterbalance side as a vibrating element is eliminated, and the frequency characteristic is based on the temperature detected by the flow tube with good thermal response. The temperature is corrected and the mass flow rate and density are measured with good response to improve the accuracy.

[0019]

【Example】

Examples 1 and 2 (corresponding to claims 1 and 2) Hereinafter, the Coriolis flowmeter of the present invention will be described with reference to the drawings. First, the means for stabilizing the support position in the alternating drive of the flow tube, and the means for improving the thermal response will be described.

FIG. 1 shows a Coriolis flowmeter according to the present invention.
1A is a sectional view taken along the line AA of FIG.
6B is a sectional view taken along the line BB of FIG.
It is a straight pipe type similar to the Coriolis flowmeter shown in, and in the figure, 10a and 10b are brace bars.
The same reference numerals as those in FIG. 5 are attached to the portions having the same functions as those in FIG.

In the Coriolis flowmeter shown in FIG. 1, similarly to the Coriolis flowmeter shown in FIG. 5, the flow tube 3 and the counterbalance 4 are coaxially supported by the connecting blocks 5a and 5b, and the coaxial connection is made. The member is the flow tube 3
Penetrates the connecting blocks 5a and 5b and is fixedly supported on the inner wall surfaces of the connection flanges 2a and 2b at both ends expanded in a trumpet shape.

Further, the flow tube 3 and the counterbalance 4 which are coaxially connected and supported by the connecting blocks 5a and 5b are inner sections close to the connecting blocks 5a and 5b.
It is supported by flat brace bars 10a and 10b. One of the flow tube 3 and the counter balance 4 supported by the brace bars 10a and 10b, for example, in the figure, a weight 9 is provided at the center of the counter balance 4 for equalizing the natural frequencies of the respective weights. Further, a drive unit 6 for resonantly driving the flow tube 3 and the counter balance 4 and detection units 7 and 8 for detecting a phase difference signal due to Coriolis force are provided.

The Coriolis flowmeter shown in FIG. 2 is a view for explaining another embodiment. FIG. 2A is a sectional view taken along the line AA of FIG. 2B, and FIG. ) Is the arrow A- of FIG.
It is a sectional view taken along the line A, in which 11 is a counter balance and 1
2a and 12b are connecting blocks, and 13a and 13b are brace bars.

In the Coriolis flowmeter shown in FIG. 2, the flow tube 3 and the counter balance 11 are connected to and supported by the connecting blocks 12a and 12b in parallel with different axes, and the flow tube 3 and the counter are located inside the connecting blocks 12a and 12b. The balance support 11 is supported, and the connection support member is fixedly supported on the inner walls of the connection flanges 2a and 2b at the expanded end portions 3a and 3b of the flow tube 3 as in FIG.

The straight tube type Coriolis flowmeter shown in FIGS. 1 and 2 has a similar vibration mode when it is resonantly driven by the drive unit 9, and this is shown in FIGS. 4 (b), (c), ( Description will be made based on d).

FIG. 4 (b) has one curvature Mb due to vibration by free support, and the support is one point support.
As shown in FIG. 7, it is difficult to be affected by the characteristic change of the supporting portion when fixedly supported, and stable vibration can be obtained.
FIG. 4C shows the brace bars 10a (13a) and 10b.
FIG. 13 is a diagram showing a vibration mode between (13b), where the brace bar 10a (1
The flow tube 3 between 3a) and 10b (13b) has a single curvature Mc and performs a single vibration motion.
(13a) and the connecting block 5a (12a) have a curvature Nc opposite to the curvature Mc.

The intervals between the sections P and C are small, and since the brace bars 10a (13a) and 10b (13b) rotate about the support points P and Q by the spring action due to the vibration, the positions P and Q are changed. , It can be rotated at a stable position and efficiently with low energy.

In FIG. 4 (d), a plurality of brace bars are provided between the connecting blocks, and the flow tube 3 and the counter balance 4 (11) (not shown) are respectively provided with Pa, Pb and Q.
It shows a vibration mode when it is supported between a and Qb.

As in the case of FIG. 3C, the vibration in the case of FIG. 4D also causes the flow tube 3 to perform a single vibration motion having one curvature Md between the positions supported by the inner brace bar, and P
It can be efficiently driven without moving the positions of b and Qb. Further, the characteristic change at the fixed end gradually decreases according to the number of brace bars, so that more stable vibration occurs between Pb and Qb, and stable mass flow rate measurement becomes possible.

[Third Embodiment] (Corresponding to Claim 3) In the Coriolis flowmeter shown in FIGS. 1 and 2, the brace bar is composed of one tubular body and is coaxial with the flow tube.
Although they are provided in parallel, as long as the parallel condition is satisfied in FIG. 2, they need not be tubular bodies, or even a single body.

FIG. 3 is a sectional view for explaining the arrangement of the brace bar according to the present invention. FIG. 3 (a) shows four counter balances, and FIGS. 3 (b) and 3 (c) show two. Indicates
In the figure, 14a, 14b, 14c, 14d, 16a, 16
b is a counter balance, and 15 and 17 are brace bars.

FIG. 3A shows four counter balances 1
4a to 14d are rod-shaped bodies, which are arranged symmetrically with respect to the plane passing through the axis 0 of the flow tube 3 and the axis 0.
The counter balances 14a to 14d are arranged on the circumference of a radius r centering on the axis 0 and fixed to the brace bar 15.

FIG. 3B shows two counter balances 1
6 a and 16 b are provided at positions axially symmetrical with respect to a vibration direction passing through the axis 0 of the flow tube 3 or a plane orthogonal to the vibration direction, and fixed to the brace bar 17.

Furthermore, the flow tube 3 according to FIG.
When the flow tube 3 vibrates in the arrow (+ Y) direction, the counter balances 14a to 14d vibrate in the opposite (−Y) direction. The counter balances 14a, 14b and 14c,
14d are also symmetrical with respect to the vibration direction, respectively.
The flow tube 3 and the counter balances 16a and 16b according to (b) and (c) are arranged in the vibrating direction Y or at a right angle.

In the vibrations shown in FIGS. 3 (a), 3 (b), and 3 (c), the counter balances 14 and 16 are composed of a plurality of rod-shaped bodies, and therefore are used for resonance drive with the flow tube 3. Since the mass per wire can be reduced, the overall size can be reduced, and the accuracy of the Coriolis flowmeter mounting posture is not affected. Although the number of counter balances is 2 and 4 in FIG. 3, the number is not limited to this number, and the number that can be resonantly driven may be selected.

[Embodiment 4] (Corresponding to Claim 4) If the fluid temperature to be measured changes from t ₁ to t ₀ at time T, the temperature of the flow tube 3 becomes the fluid temperature t.
It changes from t ₁ to t ₀ in response to _0, and as a result, the Young's modulus of the material of the flow tube 3 changes and the spring constant K changes. Therefore, the natural frequency f ₁ changes according to the equation (1), and if the temperature is constant, the vibration cycle is kept constant. This is referred to as cycle A.

At this time, if the material of the counter balance 4 (11) is a constant elasticity material such as Ni span C, the Young's modulus does not change with temperature, so the natural frequency f ₂ is (2).
It is constant according to the formula, and the cycle is constant even if the fluid temperature changes. This is cycle B. Therefore, the coupled cycle of the flow tube 3 and the counter balance 4 (11) changes according to the cycle A and the cycle B, but it changes in response to the fluid temperature t, so that the fluid temperature t is detected and there is no error. Period τ
Is detected.

Thus, the counter balance 4 (11)
By using a constant elastic material, it responds to changes in the fluid temperature without delay, and the cycle correction is performed in a simple manner only by the fluid temperature, and an accurate fluid density can be obtained according to the corrected cycle. it can. Even if the counter balance is made of a low linear expansion coefficient material such as Invar, it maintains a constant length with respect to changes in the fluid, temperature, and environmental temperature. Therefore, the mass flow rate and density with excellent responsiveness are obtained by the same means. be able to.

[0039]

As is apparent from the above description, the present invention has the following effects. Effects corresponding to claims 1 and 2: In a straight tube type Coriolis flowmeter, since a pair of flat brace bars are supported between a flow tube fixed at both ends coaxially or in parallel and a counter balance to drive resonance, The flow tube efficiently vibrates between brace bars and maintains a stable support position, so stable flow rate measurement that is not easily affected by disturbance can be performed. Effect corresponding to claim 3: Counterbalance is a plurality of rod-shaped bodies or tubular bodies, and with respect to a plane passing through the flow tube axis,
Since it is supported axisymmetrically, it is possible to make the flowmeter compact and less susceptible to the mounting posture. Effect corresponding to claim 4: Since the material of the counter balance is a constant elastic material or a low thermal expansion material, the Young's modulus or length is kept constant with respect to temperature changes, and there is no periodic fluctuation. Since the temperature of the tube changes immediately in response to the fluid temperature, the coupled cycle can be corrected depending only on the temperature of the flow tube, and an accurate cycle corresponding to the fluid density and mass flow rate can be obtained.

[Brief description of drawings]

FIG. 1 is a Coriolis flow meter according to the present invention.

FIG. 2 is a diagram for explaining another embodiment of the Coriolis flowmeter according to the present invention.

FIG. 3 is a cross-sectional view for explaining the arrangement of brace bars according to the present invention.

FIG. 4 is a diagram for explaining an outline of a vibration mode of a straight pipe type Coriolis flowmeter.

FIG. 5 is a diagram for explaining a conventional straight pipe type Coriolis flowmeter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Outer cylinder, 2a, 2b ... Connection flange, 3 ... Flow tube, 4 ... Counter balance, 5a, 5b ... Connection block, 6 ... Drive part, 7, 8 ... Detection part, 9 ... Weight, 10a,
10b ... Brace bar, 11 ... counter balance, 12a, 12b ... connection block, 13a, 1
3b ... brace bar, 14a, 14b, 14c, 14
d, 16a, 16b ... Counter balance, 15, 17 ...
Brace bar.

Front page continuation (72) Inventor Seki Hijimi 3-10-8 Kamiochiai, Shinjuku-ku, Tokyo Within Oval Co., Ltd. (72) Inventor Shingo Gomi 3-10-8 Kamiochiai, Shinjuku-ku, Tokyo Within Oval Co., Ltd.

Claims (4)

[Claims] 1. A straight tubular flow tube liquid-tightly fixed at both ends to a flow tube, and a counter balance fixed at both ends coaxially or axially parallel to the flow tube via connecting blocks near both ends of the flow tube. A straight pipe type Coriolis flowmeter for determining a mass flow rate from a Coriolis force acting on the flow tube when the flow tube and the counter balance are driven around the connection block in opposite phases. A Coriolis flowmeter, characterized in that one or a plurality of pairs of brace bars that support the flow tube and counter balance are provided near the inside of the block. 2. A flow tube integrally formed by providing a flexible tube capable of moving the flow tube in an axially liquid-tight manner between a flow tube to which both ends of the flow tube are fixed and a connection block. 2. The Coriolis flowmeter according to claim 1, further comprising a weight for equalizing the natural frequencies of the counter balance and the counter balance, and the weight is supported flexibly in the axial direction and rigid in the driving direction. 3. The counter balance is one or a plurality of straight pipes, columnar bodies, or plate-like bodies, and the counter balance is arranged at a position symmetrical with the flow tube. Coriolis flowmeter described in. 4. The Coriolis flowmeter according to claim 1, wherein the counterbalance material is a constant elasticity material or a low linear expansion coefficient material.