JP2801842B2 - 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 flowmeter, and more particularly, to a counterbalance type Coriolis flowmeter and driving means.

[0002]

2. Description of the Related Art When a measuring tube is supported at both ends and a central portion of the supported measuring tube is alternately driven in a direction perpendicular to an axis, when a fluid moves, an inflow side around the central portion of the measuring tube is formed. And a phase difference occurs on the outflow side. This phase difference is based on the Coriolis force and is a value proportional to the mass flow rate. Coriolis flow meters that detect the phase difference and measure the mass flow rate are well known.

[0003] As mentioned above, Coriolis flow meters are usually
It has a driving means for driving the measuring tube supported at both ends, and is driven at the natural frequency of the measuring tube which minimizes the driving energy. Therefore, a sensor for detecting the amplitude of the measuring tube, the driving means, and the measuring tube (shared with Coriolis detection),
A positive feedback loop is formed by an amplifier circuit that amplifies the sensor signal and drives the driving unit, and the driving is performed so that the amplitude becomes constant.

[0004] The driving means is composed of, for example, an electromagnetic coil and a core, and uses an electromagnetic force for applying an AC power to the electromagnetic coil to alternately attract the core. These driving means are mounted between a fixed substrate and a measuring tube supported on both ends of the substrate in parallel with the substrate. However, in order to drive the measuring tube more efficiently, instead of the substrate, a vibrating body (counter balance: CB) having a natural frequency equal to the natural frequency of the measuring tube, such as a tube, a column, or a plate-like body. ), The both ends of the CB are supported in parallel with the support for supporting the measuring tube, and a driving means is mounted between the measuring tube and the CB, and the measuring tube and the CB are tuned (tuned) by the driving means. Hawk) drive.

However, since the flow meter measures the flow rate of the fluid according to the purpose, various types of measurement fluid flow through the measurement tube. As a result, the natural frequency of the measurement tube supported at both ends changes according to the density of the measurement fluid. Further, even for the same fluid, the density changes according to the temperature of the measurement fluid, and the natural frequency changes. However, the natural frequency of the CB in which the measurement fluid does not flow is constant, and a natural frequency difference is generated between the natural frequency of the CB and the natural frequency of the measurement tube, so that there is a problem that efficient driving cannot be performed.

The present applicant has previously proposed a straight pipe type Coriolis flowmeter which is not thermally affected by a measurement pipe due to external vibration, pipe stress or temperature change. The Coriolis flowmeter has a main body including a coaxial outer cylinder, a measurement tube, and a counterbalance tube (CBT) of the measurement tube. That is, the main body has a cylindrical outer cylinder whose both ends are connected to the flow tube,
A measuring pipe through which fluid flows by a straight pipe coaxial with the outer cylinder; and a CBT supporting the measuring pipe coaxially. The integrally configured measuring pipe and CBT are liquid-tightly sealed in the axial direction of the outer cylinder. It is arranged movably.

[0007] The measuring tube is electromagnetically driven with the CBT,
A sensor detects a phase difference of the measurement tube generated by acting on the measurement tube based on the Coriolis force, and obtains a mass flow rate proportional to the phase difference. Since the Coriolis flowmeter of this structure is connected to the pipe only by the outer cylinder, the pipe and the CBT, which are the main parts, are not subjected to piping stress and bending moment, and the measurement pipe is moved into the outer cylinder. Since it is supported as possible, it is not affected by thermal deformation.

Since the measurement tube and the CBT have different shapes, the natural vibrations are different from each other, the natural frequency of the CBT is higher than that of the measurement tube, and efficient driving cannot be performed. For this reason, the natural frequency is made equal to the natural frequency of the measuring tube by attaching heavy weights to the CBT having a high natural frequency and increasing the mass. However, when the density of the measurement fluid changes, the natural frequency of the measurement tube changes. Each time, the weight of the weight must be adjusted, and this adjustment is complicated. Also,
This method could not cope with a density change due to a temperature change of the same fluid.

In addition, the above-mentioned general counterbalance type Coriolis flow rate having a CB which is not coaxial with the straight measuring pipe but is supported in parallel with the measuring pipe on a support plate fixedly penetrating the measuring pipe. A similar problem occurs in the case of a counterbalance type Coriolis flowmeter having a curved measuring tube having both ends fixed to a meter or a supporting member and a curved measuring tube in which a CBT is supported by the supporting member.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and is an essential part of a mass flow meter comprising a CB and a measuring tube supported by the CB and through which a measuring fluid flows. By automatically equalizing the natural frequencies of the fluids, it is possible to efficiently and stably drive many kinds of fluids or the same fluid having different temperatures without special adjustment, and furthermore, the influence of external vibration and temperature. It is an object of the present invention to provide a Coriolis flowmeter having no influence.

[0011]

To achieve the above object, the present invention provides (1)
A support member, a measurement tube having both ends supported by the support member and through which a measurement fluid flows, a counterbalance having both ends supported by the support member, and a counterbalance disposed on the counterbalance and the measurement tube and having the measurement tube extend in a longitudinal direction. A vibrator driven in a right angle direction, a sensor for detecting a displacement generated between the counter balance according to Coriolis force acting on the measurement tube, and a counter balance according to a density of the fluid. A frequency controller for driving in the displacement direction at a frequency equal to the changing natural frequency; and (2) in (1), the counter balance is a tube, and (3) (1) In (1), the counterbalance is a straight pipe. (4) In any of (1) to (3), both ends are connected to a flow pipe, and the same as the measurement pipe. (5) In the above (1), a frame body whose both ends are connected to a flow tube and which is fixed to the measurement tube at both ends of the measurement tube; A support plate fixed to both ends of the measurement tube in the frame, and both ends of the counter balance fixed between the support plates; and (6) in (1), the measurement tube is a curved tube. And (7) the above (5)
In the above, the counter balance is a curved tube,
(8) In any one of the above (1) to (5), a drive current of a vibrator for driving the integrated measurement tube and the counter balance in opposite phases is detected, and the drive current is detected. A frequency controller that drives the counterbalance in the direction of displacement of the counterbalance at a frequency of the measurement tube that changes in accordance with the density of the fluid so as to minimize (1) In any one of (1) to (8), a weight for fixing the counter balance to a frequency equal to the natural frequency of the measuring tube under predetermined conditions is fixed to the center outer wall surface of the counter balance in advance. The Coriolis flowmeter according to any one of claims 1 to 8, wherein: It is characterized by the following. Hereinafter, a description will be given based on examples of the present invention.

FIG. 1 is a configuration diagram for explaining an example of a Coriolis flow meter according to the present invention. In the figure, 1 is a flange, 2 is an end face plate, 3 is an outer cylinder, 4 is a CBT (counter balance tube). Reference numeral 5 is a measuring tube, 6 is a vibrator, 7 and 8 are sensors, 9 is a frequency controller, 10 is a leaf spring, 11 is a seal ring, 20 is a control converter, and 21 is a flow output terminal.

In FIG. 1, the flanges 1, 1 and the outer cylinder 3 are coaxially and integrally mounted, and the flanges 1, 1 are joined to a flow tube (not shown) through which a measurement fluid flows. The outer cylinder 3 has a highly rigid outer peripheral wall. The CBT 4 is a tube having the same length as the measuring tube 5 and a larger diameter than the measuring tube 5.
4 and the measuring tube 5 are coaxially fixed to the end plates 2 and 2.

A guide tube 2b extending coaxially to the flange 1 is formed on the end plates 2, 2 on which the CBT 4 and the measuring tube 5 are fixed coaxially, and the outer peripheral surface 2a of the end plates 2, 2 is
A cylindrical guide surface 3a formed on the side surface of the outer cylinder 3 and a guide tube 2b formed on the end face plates 2 and 2 are elastically supported by a cylindrical guide surface 1a formed in the flow direction of the flange 1. It is stretched in the axial direction by leaf springs 10 and 10 and is movably disposed to eliminate the influence of disturbance vibration, piping stress, temperature expansion, and the like, and to isolate the vibrating body such as the measuring tube 5 and the CBT 4. Maintains stable vibration as a tuning fork with mass balance. At this time, the measuring pipe 5 is connected coaxially with the flow pipe, and the measuring fluid flows through the measuring pipe 5. However, the measuring fluid is sealed by the seal rings 11 so that it does not flow into the outer cylinder 3. I have.

A vibrator 6 is mounted at a central position between the CBT 4 and the measuring tube 5, and a phase difference proportional to Coriolis force acting on the measuring tube 5 is detected at a symmetric position of the vibrator 6. A pair of sensors 7 and 8 are attached. Also,
A frequency controller 9 is attached to a central portion between the outer cylinder 3 and the CBT 4, and a measuring converter 5 is provided by a control converter 20 described later.
The CBT 4 is driven and controlled at a frequency equal to the natural frequency of.

In the Coriolis flow meter shown in FIG. 1, the outer cylinder 3 integral with the flanges 1, 1 joined to the flow pipe receives pipe stress, but the CBT 4 and the measuring pipe 5, which are the main parts of the mass flow meter, , Which are joined to the end face plates 2 and 2 so as to be elastically movable in a direction perpendicular to the shaft and movably in a liquid-tight manner in the axial direction. In contrast, stable flow measurement can be performed.
The vibration exciter 6 is attached to the center of the CBT 4 and the measuring tube 5, and when the frequency controller 9 is not operating, the CBT 4
The measuring tube 5 and the measuring tube 5 are driven in opposite phases in the middle of each natural frequency defined by the spring constant of the CBT 4 and the measuring tube 5.

The vibrator 6 includes an electromagnetic coil and a yoke (core), and the core is electromagnetically attracted in accordance with a current applied to the electromagnetic coil. The sensors 7 and 8 have the same structure, and include a detection coil and a permanent magnet disposed to face the detection coil. For example, the detection coil is a CBT4.
The permanent magnet is attached to the measuring tube 5.

At the start of the measurement, when the power of the control converter 20 is input, the vibration detected by one of the sensors, for example, the sensor 7, that is, the vibration signal of the frequency determined by the CBT 4 and the measuring tube 5, , Are input to the control converter 20 via the signal line 7a. This vibration signal is DC-converted in the control converter 20 and gain-controlled in inverse proportion to the DC level obtained by the conversion.
Is driven at a constant amplitude by the closed loop that drives the vibrator 6 via

The CBT 4 and the measuring tube 5 are connected to the end plates 2, 2
The length is equal because both ends are fixed. In this state, the natural frequency of the CBT 4 is f _S , the spring constant is K _S ,
The mass and M _S, the natural frequency f _M of the measuring tube 5, the spring constant K _M, mass M _M, when the mass of the measuring fluid contained in the measuring tube 5 and M _L,

[0020]

(Equation 1)

In general, (K _S /
M _S)> because it is _{(K M / M M + M} L), at _{f S> f M ... (3} ), the natural frequency f _S of CBT4 is greater than the natural frequency f _M of the measuring pipe 5. Therefore, adding a weight to the CBT,
The natural frequency f _{S of the} BT and the natural frequency f _M of the measuring tube are set substantially equal to each other so that f _S ≒ f _M.

On the other hand, when the natural frequency f _S of the CBT 4 and the natural frequency f _M of the measuring tube 5 are set to be equal to each other by the principle of the tuning fork, f _S = f _M , the CBT 4 and the measuring tube 5 have a constant amplitude. The driving energy of the vibrator 6 driven in the opposite phase, that is, the driving current is the lowest. f _S = f _M
It is necessary to select either to reduce the spring constant K _{S of the} CBT 4 or to increase the mass M _S. In the present invention, the spring constant K _{S of the} CBT 4 is reduced equivalently.

FIGS. 2A and 2B are diagrams for explaining a method of driving the CBT and the measuring tube according to the present invention. FIG. 2A shows a vibration waveform W ₅ of the measuring tube ₅ and FIG. 2B shows a CBT 4. Shows the vibration waveform W ₄ , D ₅ and D ₅ s are the drive voltage waveforms of the measuring tube, and D ₄ and D ₅ s
D ₄ s is a frequency control voltage waveform of the CBT (FIG. 2)
(C), (d)).

As shown in FIG. 2, the vibration waveform W of the CBT 4
₄ and the vibration waveform W ₅ of the measuring tube 5, the phase is 180 ° it said. In FIG. 2A, a vibration waveform W ₅ obtained by driving the measuring tube 5 has a drive voltage waveform D ₅ s (drive voltage) that is 90 ° ahead of the vibration waveform W ₅ shown in FIG. 2C. The waveform D ₅ s is shown as a sine wave, but may be driven by a rectangular wave D ₅ . That is, when the speed lowest vibration waveform W ₅ becomes the peak value, the driving voltage waveform D ₅ s becomes zero voltage,
When the vibration waveform W ₅ passes the speed best zero level,
Drive voltage waveform D ₅ s is the maximum amplitude.

On the other hand, the CBT shown in FIG.
On the fourth side, the CBT4 is driven so that the spring constant K _S is apparently reduced. When the spring constant K _S is reduced, the amplitude increases when vibrated with the same force. Conversely, when the vibration is applied in the direction of increasing the amplitude, the spring constant K _S apparently decreases. Therefore, as shown in FIG. 2D, the vibration waveform W ₄ and the drive voltage waveform D ₄ s have the same phase, and the vibration waveform W ₄
Is negative (0 to t ₁ ), a negative force (−
F) acts, when positive is (t ₁ ~t ₂₎ is, CBT4
A positive force (+ F) acts on. Conversely, when increasing the spring constant Ks of the CBT ₄ , the phase of the drive voltage D ₄ s may be reversed.

The frequency controller 9 has a drive voltage waveform D ₄ s
The magnitude of the voltage waveform D ₄ s is determined by the control calculator 20 so that the drive current of the vibrator 5 is minimized. In this state, the natural frequency f _S of the CBT 4 and the natural frequency f _M of the measuring tube 5 are equal, and f _S = f _M
Becomes

FIG. 3 is a view for explaining another embodiment of the Coriolis flowmeter according to the present invention. In the figure, reference numeral 12 denotes a weight, and 13 denotes a cap. , The same reference numerals as in FIG.

The weight 12 is attached to the center of the CBT 4 so that the natural frequency of the measuring tube 5 and that of the CBT 4 are equal when there is no measuring fluid in the measuring tube 5 or when a predetermined measuring fluid is flowing. Is determined in advance so that the weight 12
Is CBT from the through hole of the outer cylinder 3 from which the cap 13 is removed.
4 and is adjusted to have a predetermined weight.

By adjusting the weight 12, the driving voltage waveform D ₄ s applied to the frequency controller 9 is reduced in a normal flow rate measurement, and is reduced even if the adjusted fluid density is increased. The density range of the measurement fluid that can be measured is widened. Further, the density of the measurement fluid can be known from the equation (2). In the above, a straight tubular Coriolis flowmeter in which the CBT and the measuring tube 5 are coaxial has been described. However, the present invention can be similarly applied to a general counterbalance type Coriolis flowmeter.

FIG. 4 shows a Coriolis flowmeter according to the invention.
FIG. 13 is a configuration diagram for explaining another embodiment, in which 30 in FIG.
Is a measuring tube, 31 is a frame, 32 and 33 are support plates, 34 is C
In B (counter balance), the parts that operate the same as in FIG. 1 are given the same reference numerals as in FIG.

FIG. 4 shows a general straight-tube counter-balance type Coriolis flowmeter.
Is connected to the piping by flanges 30a and 30b, and frame bodies 31 are fixed near both ends. The measurement tube 30 in the frame 31 has a support plate 32 fixed through the measurement tube 30.
A CB 34 through which fluid does not flow is fixed to the support plates 32 and 33 in parallel with the measurement tube 30. The vibrator 6 is fixed to the center of the measuring tube 30 between the CB 34 and the sensors 7 and 8 are similarly fixed at symmetric positions with respect to the vibrator 6. Here, the frequency controller 9 is attached between the frame body 31 and the CB 34,
B34 is driven in the direction of displacement of CB34 so as to have the same frequency as the natural frequency of measurement tube 30.

FIG. 5 is a structural perspective view for explaining still another embodiment of the Coriolis flowmeter according to the present invention, in which 40 is a bending measuring tube, 41 is a supporting member, and 42 is a CBT.
Parts having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

The measuring tube 40 in which the fluid flows in the direction of arrow Q is
The support member 41 is penetrated and fixed on the YY line, and the orthogonal axis X-
It is arranged symmetrically to X-rays. CB where the measurement fluid does not flow
Reference numeral 42 is fixed to the support member 41 in parallel with the measurement tube 40. The vibrator 6 is fixed between the measurement tube 40 and the CB 42 on the axis XX, and is vibrated in the opposite phase like a tuning fork. The sensors 7 and 8 are disposed at positions symmetrical to the axis XX and parallel to the axis YY. The frequency controller 9 is disposed between the CB 42 and the support member 41 and has the same frequency as the measurement tube 40. So that C
It is driven in the same displacement direction as B42.

[0034]

According to the present invention, a CBT and a measuring tube coaxially supported by the CBT are provided as a mass flow rate measuring unit so as to be axially and liquid-tightly movable in an outer cylinder flange-connected to the flow tube.
Since the natural frequency of T is always made equal to the natural frequency of the measuring tube, even if the temperature is different for various kinds of fluids or the same fluid, without specially adjusting the CBT weight,
It is possible to provide a Coriolis flowmeter that can be driven efficiently and stably, has no external vibration or temperature influence, and can calculate the density of the measurement fluid with high accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining an example of a Coriolis flow meter according to the present invention.

FIG. 2 is a diagram for explaining a method of driving a CBT and a measurement tube according to the present invention.

FIG. 3 is a view for explaining another embodiment of the Coriolis flowmeter according to the present invention.

FIG. 4 is a configuration diagram for explaining another embodiment of the Coriolis flowmeter according to the present invention.

FIG. 5 is a structural perspective view for explaining still another embodiment of the Coriolis flow meter according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Flange, 2 ... End plate, 3 ... Outer cylinder, 4, 34, 42
... Counter balance tube (CBT), 5 ... Measurement tube,
6 ... Exciter, 7,8 ... Sensor, 9 ... Frequency controller, 10
... leaf spring, 11 ... seal ring, 12 ... weight, 13 ... cap, 20 ... control converter, 21 ... flow rate output end, 31 ...
Frames, 32, 33: Support plate, 40: Curve measuring tube, 41:
Support members.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-248913 (JP, A) JP-A-6-94501 (JP, A) JP-A-3-41319 (JP, A) JP-A-6-419 160148 (JP, A) Fully open sho 63-129826 (JP, U) Fully open sho 63-30723 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01F 1/84

Claims (9)

(57) [Claims] 1. A support member, a measurement tube having both ends supported by the support member and through which a measurement fluid flows, a counter balance having both ends supported by the support member, and a counter balance and the measurement tube are provided. A vibrator for driving the measuring tube in a direction perpendicular to the longitudinal direction, a sensor for detecting a displacement generated between the counter balance according to Coriolis force acting on the measuring tube, and A frequency controller driven in the direction of displacement at a frequency equal to the natural frequency that varies according to the density of the Coriolis flowmeter. 2. The Coriolis flowmeter according to claim 1, wherein said counterbalance is a tube. 3. The Coriolis flowmeter according to claim 1, wherein said counter balance is a straight pipe. 4. The Coriolis flowmeter according to claim 1, wherein both ends are connected to a flow tube, and a cylindrical outer cylinder is arranged coaxially with said measurement tube. 5. A frame body having both ends connected to a flow tube and fixed to the measurement tube at both ends of the measurement tube; a support plate fixed to both ends of the measurement tube in the frame body; 2. The Coriolis flowmeter according to claim 1, wherein both ends of said counter balance are fixed between plates. 6. The Coriolis flowmeter according to claim 1, wherein said measurement tube is a curved tube. 7. The Coriolis flowmeter according to claim 5, wherein said counter balance is a curved tube. 8. A drive current of a vibrator for driving the integrated measuring tube and the counterbalance in opposite phases is detected, and the drive current is minimized to change according to the density of the fluid. The Coriolis flowmeter according to any one of claims 1 to 5, further comprising a frequency controller that drives the counterbalance in a direction in which the counterbalance is displaced by the frequency of the measurement tube. 9. A counterweight having a frequency equal to the natural frequency of the measuring tube under predetermined conditions is fixed to a center outer wall surface of the counterbalance in advance. The Coriolis flowmeter described in Crab.