JP2984192B2 - Coriolis flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Coriolis flow meter, and more particularly, to a straight tubular flow tube for obtaining a mass flow rate utilizing Coriolis force, and a counter fixed at both ends in parallel with the flow tube. The present invention relates to a straight tubular Coriolis flowmeter of a type that is driven alternately between a balance and a balance.

[0002]

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

[0003] Needless to say, a Coriolis flow meter of the straight pipe type has the simplest shape, and is small in size and easy to maintain. Therefore, the sensitivity is small, and this is disadvantageous in terms of the SN ratio. The simplest way to increase the SN ratio is to make the flow tube thin and long. However, the thin tube is easily affected by the pressure of the fluid. ω ₀
Changes, and an error occurs in the mass flow rate m to be obtained based on the principle of generation of the Coriolis force.

[0004] The present inventors have proposed the following Coriolis flowmeter in order to eliminate the above-mentioned disadvantages of the straight tube type Coriolis flowmeter.

FIG. 5 is a view for explaining a conventional straight tube type Coriolis flowmeter, and FIG. 5 (a) is an arrow A of FIG. 5 (b).
5A is a cross-sectional view taken along the line BB of FIG. 5A, wherein 1 is an outer cylinder, 2a and 2b are connection flanges, 3 is a flow tube, Is counterbalance, 5
Reference numerals a and 5b denote connection blocks, 6 denotes a drive unit, 7 and 8 denote detection units, and 9 denotes a weight.

In the Coriolis flowmeter shown in FIG. 5, a flow tube 3 and a counterbalance 4 are fixed at both ends coaxially.
The weight 9 is fixed to the center of the counter balance 4 and adjusted so that the respective natural frequencies are equal. The driving unit 6 drives the flow tube 3 and the counter balance 4 in resonance, and the detecting unit 7, 8, a phase difference signal due to the Coriolis force of the flow tube 3 is detected.

That is, by efficiently driving the flow tube 3 with a large amplitude by resonance driving, the Coriolis force can be detected with high sensitivity, and furthermore, by forming the both ends of the flow tube 3 into a trumpet-like shape. The rigidity in the axial direction was substantially reduced to eliminate the influence of the length change due to the thermal expansion and contraction of the flow tube 3 due to the fluid temperature change, and both ends were fixed so that stable measurement results could be obtained with respect to the temperature change. It eliminates the disadvantages of Coriolis flowmeters in flow tubes.

On the other hand, looking at the configuration of the vibration system of the Coriolis flow meter shown in FIG. 5, the flow tube 3 is fixedly supported by the connection blocks 5a and 5b together with the counter balance 4, and furthermore, both ends of the flow tube 3 Are connected to the inner peripheral walls of the connection flanges 2a, 2b at the ends 3a, 3b of the expanded shape. The vibration mode of the flow tube 3 is
As shown in FIG. 4 (a), the flow tube 3 is at points P and Q
, And the extension portion is fixed at the position B, and the counter balance 4 shown by a broken line between P and Q by driving.
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 with smaller energy for resonance driving, and has a small rigid vibration between B and P, so that the stress near the fixed position B is small, Long-term stable measurement is possible.

The Coriolis flowmeter measures the flow rate of fluids having different physical and chemical properties. For example, when a fluid having a temperature different from the room temperature flows, the flow tube immediately responds thermally and becomes a fluid temperature, but the temperature of the counter balance 4 changes slowly with respect to the fluid temperature change. Means 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
₂ so as to mass M _B is adjusted.

[0014]

The conventional straight-tube Coriolis flowmeter shown in FIG. 5 is supported by a low-rigidity flow tube 3b having an expanded portion so as to be movable in the axial direction. 5a and 5b are P in FIG.
(Q), the connecting block 5a,
5b receives a rotational moment and has three curvatures Na,
Since Ma and Na are applied to the flow tube 3, the rigidity of the connection blocks 5a and 5b themselves is easily affected by the change. Further, the support portion by the connection blocks 5a and 5b is easily moved by disturbance, and the zero point and the measured value vary. Occurs.

When the temperature of the measurement fluid changes, the Young's modulus changes and the spring constant K changes, and the flow tube 3 and the counter balance 4 change the natural frequencies f ₁ and f ₁ according to the equations (1) and (2). f ₂ is changed. That is, the temperature of the flow tube 3 responds immediately to become equal to the fluid temperature, but the temperature of the counterbalance 4 changes slowly. As a result, the coupling cycle also changes slowly, and it takes time to stabilize. Therefore, even if the counter balance 4 is corrected based on the fluid temperature, the cycle changes slowly, and it is impossible to perform correction with good responsiveness.

SUMMARY OF THE INVENTION 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 disadvantage of low sensitivity to high sensitivity. It is another object of the present invention to provide a straight tube type Coriolis flowmeter capable of removing a cause of instability of a support position of a flow tube and correcting a characteristic change due to a temperature change of a fluid with good response.

[0017]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a straight tube flow tube which is connected to a flow tube in a liquid-tight manner, and the flow tube is connected via a connection block near both ends of the flow tube. A counter balance fixed at both ends coaxially or axially parallel to the tube, and when the flow tube and the counter balance are driven in opposite phases around the connection block, the mass is reduced from the Coriolis force acting on the flow tube. a Coriolis flowmeter straight tube type for obtaining the flow rate, the Coriolis flowmeter provided with one or more pairs of brace bars for supporting said flow tube and said counter balance to the connecting block inside the vicinity of both sides, the flow between the flow tube ends of the tube are connected and the coupling block, both of said flow tubes
At its end, it expands into a trumpet shape that can move in a liquid-tight manner in the axial direction with the flow tube.
A tensioned end is provided, and a weight that equalizes the natural frequency of each of the flow tube and one of the counter balance is provided, and is softly supported in the axial direction and rigidly supported in the driving direction. It was done.

[0018]

[Function] A straight tubular flow tube and a counterbalance are fixed in parallel to two separate connecting blocks at both ends.
Furthermore, by supporting the flow tube and the counterbalance with the brace bar on both inner sides of the connection block, the connection block and the brace bar are supported at two points, and the support position when the flow tube and the counterbalance are driven by resonance is set to the outside. Be stable without being affected. Furthermore, the counterbalance material is made of a material having constant elasticity or a low coefficient of linear expansion, thereby eliminating the influence of vibration heat on the counterbalance side as a vibration element. The temperature is corrected and the mass flow rate and density are measured with good response to improve the accuracy.

[0019]

[Embodiments 1 and 2 ] A Coriolis flowmeter according to the present invention will be described below with reference to the drawings. First, the means for stabilizing the support position in the alternating drive of the flow tube, and then the means for improving the thermal response will be described.

FIG. 1 shows a Coriolis flow meter according to the present invention.
FIG. 1A is a cross-sectional view taken along the line AA of FIG.
FIG. 6B is a cross-sectional view taken along the line BB of FIG.
Is a straight pipe type similar to the Coriolis flowmeter shown in Fig. 1, and 10a and 10b are brace bars in the figure.
Parts having the same functions as those in FIG. 5 are denoted by the same reference numerals as those in FIG.

In the Coriolis flow meter shown in FIG. 1, a flow tube 3 and a counterbalance 4 are coaxially connected and supported by connecting blocks 5a and 5b, similarly to the Coriolis flow meter shown in FIG. The member is a flow tube 3
Are penetrated through the connecting blocks 5a and 5b, and are fixedly supported on the inner wall surfaces of the connecting 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 connection blocks 5a and 5b are located in an inner section close to the connection blocks 5a and 5b.
It is supported by flat brace bars 10a and 10b. Either the flow tube 3 supported by the brace bars 10a and 10b or the counterbalance 4, for example, in the figure, a weight 9 for adjusting the natural frequency of each is provided at the center of the counterbalance 4. Further, a drive unit 6 for driving the flow tube 3 and the counter balance 4 in resonance is provided with detection units 7 and 8 for detecting a phase difference signal due to Coriolis force.

The Coriolis flowmeter shown in FIG. 2 is a view for explaining another embodiment. FIG. 2 (a) is a sectional view taken along the line AA of FIG. 2 (b), and FIG. ) Is the arrow A- in FIG.
FIG. 2 is a sectional view taken along line A, in which 11 is a counterbalance, 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 counterbalance 11 are connected to and supported by connecting blocks 12a and 12b in parallel to each other, and the flow tube 3 and the counter balance are provided inside the vicinity of the connecting blocks 12a and 12b. The connection support member has a structure supporting the balance 11, and the connection support member is fixedly supported on the inner walls of the connection flanges 2a, 2b at the expanded end portions 3a, 3b of the flow tube 3 as in FIG.

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

FIG. 4B shows a case where one vibration is caused by free support and has one curvature Mb.
As shown in (2), when the fixed support is used, the vibration is hardly affected by the characteristic change of the support portion, and a stable vibration can be obtained.
FIG. 4C shows the brace bars 10a (13a) and 10b.
FIG. 13B is a diagram showing a vibration mode during (13b), in which the brace bar 10a (1
The flow tube 3 between 3a) and 10b (13b) has a single curvature Mc and makes a simple vibration motion, and the brace bar 10a
(13a), the link block 5a (12a) moves with a curvature Nc opposite to the curvature Mc.

The interval between the sections P and C is a section of a small distance, and the brace bars 10a (13a) and 10b (13b) rotate around the support points P and Q by spring action due to vibration. It is driven to rotate at a stable position and efficiently with low energy.

FIG. 4D shows that 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 connected to Pa, Pb and Q.
This shows a vibration mode when supported between a and Qb.

As in the case of FIG. 3 (c), the vibration in the case of FIG. 4 (d) is such that the flow tube 3 makes a simple vibration with one curvature Md between the positions supported by the inner brace bar,
It is driven efficiently without moving the positions of b and Qb. Further, since the characteristic change of the fixed end is sequentially reduced in accordance with the number of the brace bars, the vibration between Pb and Qb becomes more stable, and the stable mass flow rate measurement becomes possible.

[Embodiment 3 ] In the Coriolis flow meter shown in FIGS. 1 and 2, the brace bar is constituted by one tube, and is coaxial with the flow tube.
Although they are provided in parallel, in FIG. 2, if the parallel condition is satisfied, they do not need to be a tubular body and further need not be a single body.

FIG. 3 is a cross-sectional view for explaining the arrangement of the brace bar according to the present invention. FIG. 3 (a) shows a case where the counter balance is four, and FIGS. Indicates that
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.
Reference numerals 4a, to 14d denote rods, which are arranged symmetrically to the axis 0 with respect to a plane passing through the axis 0 of the flow tube 3,
The counter balances 14 a to 14 d are arranged on a circumference having a radius r around 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 axially symmetric positions in a vibration direction passing through the axis 0 of the flow tube 3 or a plane perpendicular to the vibration direction, and are fixed to the brace bar 17.

Further, the flow tube 3 shown in FIG.
And the counter balances 14a to 14d are such that when the flow tube 3 vibrates in the direction of the arrow (+ Y), the counter balances 14a to 14d vibrate in the opposite (-Y) direction, and 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 vibration direction Y or at right angles.

In the vibrations shown in FIGS. 3 (a), 3 (b) and 3 (c), since the counter balances 14 and 16 are composed of a plurality of rods, they are driven by the flow tube 3 in resonance. Since the mass per unit can be reduced, the size can be reduced as a whole, and the accuracy of the mounting posture of the Coriolis flowmeter is not affected. In FIG. 3, the number of counter balances is set to two or four. However, the number is not limited to this number.

[0036] In Example 4 time T, when the fluid temperature of the measured changes from _{t 1} to _{t 0,} the temperature of the flow tube 3, the _{t 0} from _{t 1} in response to the fluid temperature _{t 0} 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 is changed in accordance with the equation (1), if the temperature constant, the oscillation period is kept constant. This is referred to as a period A.

At this time, if the material of the counterbalance 4 (11) is a constant elastic material such as Ni span C, the Young's modulus does not change with temperature, so that the natural frequency f ₂ is (2)
It is constant according to the equation, and the period is constant even if the fluid temperature changes. This is referred to as a cycle B. Accordingly, the coupling cycle between the flow tube 3 and the counterbalance 4 (11) changes according to the cycles A and B, but 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)
Is made to be a constant elastic material, it responds to the fluid temperature change without delay, and the cycle correction is performed in a simple form only by the fluid temperature, and the accurate fluid density can be obtained according to the corrected cycle. it can. Even if the counterbalance is made of a material having a low linear expansion coefficient such as invar or the like, a constant length is maintained with respect to changes in fluid, temperature, and environmental temperature. be able to.

[0039]

As is apparent from the above description, according to the present invention, a straight tubular flow tube liquid-tightly connected to a flow tube, and the flow tube via a connecting block near both ends of the flow tube. And a counter balance fixed at both ends coaxially or axially parallel to the flow tube and the front.
When the counter balance is driven around the connecting block in the opposite phase, a straight pipe type Coriolis flow meter that obtains a mass flow rate from the Coriolis force acting on the flow tube, and is located near the inside of the connecting block on both sides. in Coriolis flowmeter provided with one or more pairs of brace bars for supporting said counterbalance and the flow tube, said flow tube having both ends of the flow tube is connected
Between the connection block, at both ends of the flow tube
Expanded into a trumpet shape that can move in a liquid-tight manner in the axial direction with the flow tube.
With the provision of the end, has a weight that equals the natural frequency of each one of the <br/> counterbalance to the flow tube, since the supporting rigidly in the drive direction in the axial direction with a soft Since the flow tube efficiently vibrates between the brace bars in a simple vibration and maintains a stable support position, a stable flow rate measurement that is hardly affected by disturbance can be performed. In addition, if the counter balance is a plurality of rods or tubes and is supported axially symmetrically with respect to a plane passing through the flow tube axis, it is possible to provide a small-sized flowmeter that is not easily affected by the mounting posture. Furthermore, if the counterbalance material is made of a constant elastic material or a low thermal expansion material, the Young's modulus or length is kept constant with temperature changes, there is no periodic fluctuation, whereas the flow tube responds immediately to the fluid temperature. As a result, the coupling cycle changes in a correctable manner depending only on the temperature of the flow tube, and an accurate cycle corresponding to the fluid density and the mass flow rate can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a view for explaining another embodiment of the Coriolis flow meter according to the present invention.

FIG. 3 is a cross-sectional view illustrating an arrangement of a brace bar according to the present invention.

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

FIG. 5 is a view for explaining a conventional straight tube type Coriolis flow meter.

[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: Connected Block, 13a, 1
3b: brace bar, 14a, 14b, 14c, 14
d, 16a, 16b ... counter balance, 15, 17 ...
Brace bar.

Continuing on the front page (72) Inventor Seki Hijimi 3-10-8 Kamiochiai, Shinjuku-ku, Tokyo Inside the oval company (72) Inventor Shingo Gomi 3-10-8, Kamiochiai, Shinjuku-ku, Tokyo Inside the oval company (56) References JP-A-6-160148 (JP, A) JP-A-5-248913 (JP, A) JP-A-6-201428 (JP, A) JP-A-4-52517 (JP, A) International Published 95/3528 (WO, A1) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01F 1/84

Claims (1)

(57) [Claims] 1. A flow tube having a straight tubular shape and connected in a liquid-tight manner 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. and, when said flow tube and said counterbalance is driven in an opposite phase around the connecting block, a straight tube type Coriolis flow meter for determining the mass flow rate from a Coriolis force acting on the flow tube, both sides of the in Coriolis flowmeter provided with one or more pairs of brace bars for supporting said flow tube and said counter balance to the connecting block inside the vicinity, and the flow tube with both ends connected to said flow tube and said connecting block In between, both sides of the flow tube
At its end, it expands into a trumpet shape that can move in a liquid-tight manner in the axial direction with the flow tube.
A tensioned end is provided, and the flow tube and
The counter has a weight to equalize the natural frequency of each one of the balance, the Coriolis flowmeter being characterized in that supported rigidly in the drive direction in the axial direction with a soft.