JP2000046617A - Coriolis mass flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a Coriolis mass flowmeter capable of aiming improvement of a mass flow measurement performance by improving insulatability of internal vibration, and simultaneously capable of improving stability of a density measurement performance or a mass flow measurement performance at the time of density change. SOLUTION: This flowmeter is so composed that measurement fluid flows in a vibrating tube 31, and that the vibrating tube 31 is deformedly vibrated by Coriolis force generated by the flow of the measurement fluid and angular vibration of the vibrating tube 31. In this case, this flowmeter is equipped with the vibrating tube 31 in which the measurement fluid flows and which vibrates in a resonance frequency, and plural compensating vibrators 32 having one end connected to the position of a node of the vibration or the periphery thereof of the vibrating tube 31 and having a resonance frequency different from the resonance frequency of the vibrating tube 31. And besides, the compensating vibrators 32 are equipped with compensating vibrator exciters 34, for shaking forcedly in the same frequency as the vibrating tube 31, so as to cancel the vibration of a joint between the compensating vibrators 32 and the vibrating tube 31 or of a fixed point 35 of the vibrating tube 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for improving the mass flow measurement performance by improving the insulation of internal vibrations.
The present invention relates to a Coriolis mass flowmeter having improved density measurement performance and stability of mass flow measurement performance when density changes.

[0002]

2. Description of the Related Art FIG. 5 is an explanatory view of the structure of a conventional example generally used in the prior art.
This is shown in the conventional example of No. 2. In the figure, the vibration tube 1 to the flange 2, both ends attached flow measurement fluid FL _o therein.

[0003] The flange 2 is for attaching the vibration tube 1 to a pipeline. The exciter 3 is a vibration tube 1
To excite the vibrating tube 1.

The vibration detecting sensors 4 and 5 are provided on both sides of the vibrating tube 1 and detect the vibration of the vibrating tube 1. Both ends of the vibration tube 1 are fixed to the housing 6.

[0005] In the above configuration, the measurement fluid is caused to flow through the vibration tube 1 and the exciter 3 is driven. Assuming that the angular velocity “ω” in the vibration direction of the exciter 3 and the flow velocity “V” of the measurement fluid (hereinafter, a symbol surrounded by “” represents a vector amount),

The mass flow rate can be measured by measuring the amplitude of the vibration proportional to the Coriolis force where a Coriolis force of Fc = −2 m “ω” × “V” acts.

However, in such an apparatus,
The vibrating tube 1 vibrates approximately under the condition that both ends are fixed.
With a Coriolis mass flowmeter of limited size, the endpoints cannot be completely fixed and will vibrate slightly.

As described above, if the vibration isolation is insufficient, there are the following problems. (1) Since the Q value becomes low, the vibration inside the Coriolis mass flowmeter becomes unstable, and it becomes susceptible to extra vibration noise other than the excitation vibration.

(2) Large energy is required for excitation, and power consumption increases. (3) The degree of vibration leakage greatly changes due to the installation method, environmental changes such as piping stress and temperature, and external factors, the vibration state of the vibrating tube 1 also changes, and the zero point and span easily change.

That is, Coriolis flowmeters which are weak and inaccurate with respect to these environmental changes and external factors tend to be formed.

FIG. 6 shows a Coriolis mass flowmeter, filed by the applicant of the present invention, and filed by the present applicant in view of this problem. In the figure,
Configurations with the same symbols as those in FIG. 5 represent the same functions. Hereinafter, FIG.
Only the differences will be described.

[0012] the vibration tube 11 is a vibrating tube straight tubular measuring fluid FL _o flows. The compensation vibrator 12 is
At least one compensating vibrator provided in parallel with the vibrating tube 11. In this case, one compensation vibrator 1
2 are used. The combined body 13 includes the vibration tube 11
And a portion that serves as a node of vibration of the compensating vibrator 12 are connected.

The exciter 14 is provided between the central part of the vibration tube 11 and the central part of the compensation vibration body 12, and excites the vibration tube 11 and the compensation vibration body 12. The vibration detection sensor 15 is provided between the vibration tube 11 and the compensation vibration body 12, and detects a relative vibration between the vibration tube 11 and the compensation vibration body 12.

In the above configuration, when the measurement fluid is flowed through the vibrating tube 11 and the exciter 14 is driven, a Coriolis force acts. The vibrating tube 1 is proportional to the Coriolis force.
By measuring the amplitude of the vibration of No. 1, the mass flow rate can be measured.

Thus, the vibration tube 11 and the compensation vibration body 1
In the place where the joint of the vibration body 2 and the coupling body 13 is a node of the vibration,
The vibration tube 11, the compensation vibration body 12, and the combined body 13
By connecting to the flow meter housing 6, the vibration of the vibration system including the vibration tube 11, the compensation vibration body 12, and the coupling body 13 can be confined inside.

That is, as shown in FIG. 6, when the directions of the X, Y, and Z axes are determined, the exciter 14
The compensating vibrator 12 vibrates in the Y direction in opposite directions as shown in the figure. This vibration system is just
3 is formed so as to be a node of vibration, so that even in the excited state, the combined body 13 hardly moves.

[0017]

However, in the prior application of FIG. 6, the vibration isolation is improved. However, within one of the vibration system, since the compensation vibrator 12 is present, when the density of the measuring fluid FL _o is changed, the vibration tube 11, the vibration balance collapses the compensation vibrator 12, vibration isolation Performance decreases.

The compensating vibrator 12 includes a vibrating tube 11
Generally, the integrated vibration system functions as an integrated vibration system composed of the compensation vibration body 12 and the integrated vibration system.

[0019] For example, when there is a change in density measurement fluid FL _o, the resonant frequency of the whole vibration system changes gradually. In addition to the vibrating tube 11 that is directly related to the density change, there is a compensation vibrator 12 that is not related to the density change, and they vibrate as an integrated vibration system.

[0020] Therefore, compared with the case of only the vibration tube 11, changes in the resonance frequency when the density of the measuring fluid FL _o has changed becomes gradual, the relationship of the density and the resonance frequency of the measurement fluid FL _o becomes nonlinear .

Since the change rate of the resonance frequency with respect to the density change is small, the S / N ratio is inferior, and it is difficult to measure the density with high resolution. Further, it is difficult to measure the density with high accuracy and stability because of the nonlinearity.

The present invention solves this problem. An object of the present invention is to improve the insulation of internal vibration,
It is an object of the present invention to provide a Coriolis mass flowmeter that improves the density measurement performance and the stability of the mass flow measurement performance when the density changes while improving the mass flow measurement performance.

[0023]

In order to achieve the above object, the present invention provides: (1) a measuring fluid flowing in a vibrating tube, and a flow of the measuring fluid and a Coriolis force generated by angular vibration of the vibrating tube; In a Coriolis mass flowmeter for deforming and vibrating the vibrating tube, a vibrating tube in which the measurement fluid flows and vibrates at a resonance frequency, and one end of which is connected to a position or a vicinity of a vibration node of the vibrating tube, A plurality of compensating vibrators having a resonance frequency different from the resonance frequency, and the vibrating tube being attached to the compensating vibrating body so as to cancel vibration at a connection point between the compensating vibrating body and the vibrating tube or at a fixed point of the vibrating tube. And a compensating vibrator exciter for forcibly exciting at the same frequency. (2) A fixed-point vibration detection sensor provided near the fixed point of the vibrating tube, and the magnitude of the excitation force of the compensating vibrator exciter so that the detection output of the fixed-point vibration detection sensor is minimized. A Coriolis mass flowmeter according to (1), further comprising a control circuit for controlling the mass flow rate. It is what constituted.

[0024]

In the above construction, when the measuring fluid is flowed through the vibrating tube and the exciter is driven, Coriolis force acts.
By measuring the amplitude of the vibration proportional to the Coriolis force, the mass flow rate can be measured.

Thus, the vibrating tube is excited by the exciter so as to vibrate in the first mode resonance state.

On the other hand, the compensating vibrator is vibrated by the compensating vibrator exciter so as to vibrate at a frequency exactly equal to the vibration frequency of the vibrating tube and in the opposite phase.

The compensating vibrator exciter generates a signal having the same frequency as the signal based on the output of the vibration detecting sensor to generate an exciting force.

Finally, the vibration tube and the compensating vibrator vibrate in opposite directions and cancel each other, so that the connecting portion,
Alternatively, at the fixed point, so that there is almost no vibration,
The goal is to vibrate the compensating vibrator.

Thus, the vibration tube and the compensation vibration body
By connecting the vibrating tube and the compensating vibrator to the flowmeter housing at a location that is a node of the vibration of the vibrating system, the vibration of the vibrating system consisting of the vibrating tube, the compensating vibrator, and the combined body can be confined inside. I made it. Hereinafter, a detailed description will be given based on embodiments.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram of a main part configuration of an embodiment of the present invention. In the figure, the configuration of the same symbol as FIG. 6 represents the same function. Hereinafter, only differences from FIG. 6 will be described.

[0031] In Figure, the vibration tube 31 is a vibrating tube measuring fluid FL _o flows oscillates at the resonance frequency.

One end of the compensating vibrator 32 is connected or connected 33 at or near a node of vibration of the vibrating tube 31, and a plurality of compensating vibrators having a resonance frequency different from the resonance frequency of the vibrating tube 31 are provided. Body.

In this case, two compensation vibrators 32 are used. The compensating vibrator exciter 34 includes the compensating vibrating body 32
A vibration is applied to the compensation vibrator 32 at the same frequency as the vibration tube 31 so as to cancel the vibration at the connection point 33 between the vibration tube 31 and the fixed point 35 of the vibration tube 31.

In the above configuration, as shown in FIG. 2, the vibration tube 31 is vibrated by the exciter 14 so as to vibrate in a first-order mode resonance state.

On the other hand, the compensation vibrator 32 is
1 and at the opposite phase (the vibrations cancel each other out at the connecting portion 33 as shown in FIG.
Vibrates in the opposite direction to become a node of vibration. ) Is vibrated by the compensating vibrator exciter 34 so as to vibrate.

The compensating vibrator exciter 34 generates a signal having the same frequency as that of the output of the vibration detecting sensor 15 based on the output of the vibration detecting sensor 15 to generate an exciting force. As for the phase, the vibration tube 31 is in a resonance state, while the compensation vibration body 32 is in a non-resonance state.

Therefore, the exciting forces of the exciter 14 and the compensating vibrator exciter 34 need to be oscillated at phases different from each other by 90 degrees.

Finally, the vibrating tube 31 and the compensating vibrating body 32 vibrate in opposite directions and cancel each other,
The purpose is to vibrate the compensating vibrator 34 so that the vibration is almost eliminated at the connecting portion 33 or the fixed point 35.

As a result, in the present invention, a resonance state can be basically formed by a vibration system including only the vibration tube 31.
Compensation as a vibrating body, since the extra weight does not exist in the vibration system, the resonance frequency and the density change in the measured fluid FL _o be greatly changed, the relationship between the density and the resonance frequency of the measurement fluid FL _o, more linear Can be.

[0040] Density measurements of the measuring fluid FL _o is determined from the resonant frequency. Therefore, if the change rate of the resonance frequency with respect to the density change is large, a Coriolis mass flowmeter having an excellent S / N ratio and capable of measuring the density with high resolution can be obtained.

Further, by increasing the linearity, more accurate and stable density measurement becomes possible. Further, the density measurement value is used for density correction of the mass flow rate and measurement of the volume flow rate. Therefore, a Coriolis mass flowmeter that can expect high accuracy and high stability in mass flow rate and volume flow rate measurement can be obtained.

The vibrating system in the resonance state is the vibrating tube 31.
Even if only the compensation vibrator 32 in the non-resonant state,
By performing active forced vibration synchronized with the vibration tube 31 that is performing resonant vibration, the compensation vibrator 32 is
To an effective vibration state, and at their connecting portions 33,
The vibrations cancel each other, and the vibration isolation from the outside can be made possible.

By realizing vibration isolation and confining the vibration of the vibration system inside, the following advantages are obtained. (1) Since the internal vibration system can realize a high Q value, the influence of external noise is relatively small even if external noise is applied, and the vibration is stable, a Coriolis mass flowmeter resistant to external vibration noise can be obtained.

(2) Since stable excitation can be realized with small energy, a Coriolis mass flowmeter with low current consumption can be obtained.

(3) If the amount of vibration energy dissipated to the outside changes, or if the balance of the amount dissipated upstream and downstream is disturbed, the internal vibration system is affected, and the zero point and span fluctuate. In the present invention, the vibration can always be confined inside, so that there is no need to worry about this, and a highly accurate Coriolis mass flowmeter can be obtained.

FIG. 3 is an explanatory diagram of a main part configuration of another embodiment of the present invention. In this embodiment, the fixed point vibration detection sensor 4
1 is provided near the fixed point 35 of the vibration tube 31.

As shown in FIG. 4, the control circuit 42 controls the compensation vibrator exciter 34 based on the detection output signal of the fixed-point vibration detection sensor 41 so that the detection output of the fixed-point vibration detection sensor 41 is minimized. Controls the magnitude of the excitation force.

The vicinity of this result, even if the density or the temperature change or the like of the measurement fluid FL _o, by adjusting the magnitude of the vibration of the compensation vibrator 32, the fixed point 35 of the vibration tube 3 and the flow meter housing 6 Can always be controlled to zero or a value close to zero.

That is, since the vibration isolation can be performed at a higher level, which is stable to environmental changes, a Coriolis mass flowmeter which is resistant to external vibration noise, consumes low current, and has high accuracy can be obtained.

[0050]

As described above, according to the first aspect of the present invention,
According to, basically, the vibration system only vibration tube,
A resonance state can be formed. Since there is no extra mass in the vibration system, such as a compensating vibrator, when the density of the measurement fluid changes, the resonance frequency also changes greatly, and the relationship between the density of the measurement fluid and the resonance frequency can be made more linear.

The density of the measurement fluid is determined from the resonance frequency. Therefore, if the change rate of the resonance frequency with respect to the density change is large, a Coriolis mass flowmeter having an excellent S / N ratio and capable of measuring the density with high resolution can be obtained.

In addition, the increased linearity enables more accurate and stable density measurement. Further, the density measurement value is used for density correction of the mass flow rate and measurement of the volume flow rate. Therefore, a Coriolis mass flowmeter that can expect high accuracy and high stability in mass flow rate and volume flow rate measurement can be obtained.

Even if the vibration system that is in the resonance state is only the vibration tube, it is possible to apply active forced vibration synchronized with the vibration tube that is performing resonance vibration to the non-resonant compensation vibration body, The compensating vibrator is brought into an effective vibrating state, and the vibrations are canceled at the connecting portions thereof, so that the vibration can be isolated from the outside.

By realizing vibration isolation and confining the vibration of the vibration system inside, the following advantages are obtained. (1) Since the internal vibration system can realize a high Q value, the influence of external noise is relatively small even if external noise is applied, and the vibration is stable, a Coriolis mass flowmeter resistant to external vibration noise can be obtained.

(2) Since stable excitation can be realized with a small amount of energy, a Coriolis mass flowmeter with low current consumption can be obtained.

(3) If the amount of vibration energy dissipated to the outside changes, or if the balance of the amount dissipated upstream and downstream is disturbed, the internal vibration system is affected and the zero point and span fluctuate. In the present invention, the vibration can always be confined inside, so that there is no need to worry about this, and a highly accurate Coriolis mass flowmeter can be obtained.

According to the second aspect of the present invention, the control circuit controls the compensation vibrator exciter based on the detection output signal of the fixed point vibration detection sensor so that the detection output of the fixed point vibration detection sensor is minimized. The magnitude of the excitation force is controlled.

As a result, even if there is a change in the density or temperature of the measurement fluid, the vibration near the fixed point between the vibrating tube and the flow meter housing is always reduced to zero by adjusting the magnitude of the vibration of the compensating vibrator. Alternatively, it can be controlled to a value close to zero.

That is, since the vibration isolation can be performed at a higher level, which is stable against environmental changes, a Coriolis mass flowmeter which is resistant to external vibration noise, consumes low current, and has high accuracy can be obtained.

Therefore, according to the present invention, the density measurement performance and the stability of the mass flow measurement performance at the time of density change are improved while improving the insulation of the internal vibration and improving the mass flow measurement performance. A Coriolis mass flow meter can be realized.

[Brief description of the drawings]

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

FIG. 2 is an operation explanatory diagram of FIG. 1;

FIG. 3 is an explanatory diagram of a main part configuration of another embodiment of the present invention.

FIG. 4 is an explanatory diagram of a main part configuration of FIG. 3;

FIG. 5 is an explanatory diagram of a configuration of a conventional example generally used in the related art.

FIG. 6 is an explanatory view of the configuration of another conventional example generally used in the prior art.

[Explanation of symbols]

 2 Flange 6 Housing 14 Exciter 15 Vibration detection sensor 31 Vibration tube 32 Compensating vibrator 33 Connecting part 34 Compensating vibrator exciter 35 Fixed point 41 Fixed point vibration detecting sensor 42 Control circuit

Claims (2)

[Claims] 1. A Coriolis mass flowmeter for deforming and vibrating a vibrating tube by a flow of a measuring fluid in a vibrating tube and a Coriolis force generated by the flow of the measuring fluid and an angular vibration of the vibrating tube. A vibrating tube that vibrates at a resonance frequency, a plurality of compensation vibrators having one end connected to or near a position serving as a node of vibration of the vibration tube and having a resonance frequency different from the resonance frequency of the vibration tube; The compensating vibrator is provided with a compensating vibrator exciter that forcibly vibrates at the same frequency as the vibrating tube so as to cancel vibration at a connecting point between the vibrating body and the vibrating tube or a fixed point of the vibrating tube. Features a Coriolis mass flow meter. 2. A fixed-point vibration detecting sensor provided near the fixed point of the vibrating tube; and a vibrating force of the compensating vibrator exciter so that a detection output of the fixed-point vibration detecting sensor is minimized. The Coriolis mass flowmeter according to claim 1, further comprising a control circuit for controlling the size.