JPH08136312A - Vibration-type measuring instrument - Google Patents

Abstract

PURPOSE: To obtain a high vibration Q by fully utilizing the advantages of a straight pipe and at the same time preventing vibration energy from being leaked externally. CONSTITUTION: In a vibration-type measuring instrument for measuring the mass flow rate or density of fluid consisting of support mechanisms (3a, 3b, and 4) for supporting a measurement pipe 2, a vibration generator 5 for vibrating the measurement pipe 2, vibration sensors 6a and 6b for detecting the vibration of the measurement pipe 2, an entrance conduit 7a for leading measurement fluid to the measurement pipe 2, an exit conduit 7b for leading the measurement fluid from the measurement pipe 2, and a housing 8 for including the elements, the stiffness of the support mechanisms and additional masses 11a-11d are adjusted and the node of vibration is formed in the support mechanisms, thus preventing vibration energy from being leaked externally and obtaining a high vibration Q.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow meter for measuring a mass flow rate by utilizing a Coriolis force generated based on a mass flow rate of a fluid flowing in at least one straight tubular measuring pipe to be vibrated, or a measurement. A vibrating densimeter that measures the density of the fluid in the measuring tube from the change in the resonance frequency of the measuring tube that changes according to the change in the density of the fluid in the tube, or a vibrating measuring instrument having both functions, especially a straight tube The present invention relates to a vibration type measuring instrument having an improved method of connecting a support mechanism for supporting a housing to a housing.

[0002]

As is well known in the prior art, a Coriolis mass flowmeter measures the mass flow rate of a fluid based on the Coriolis force generated in proportion to the mass flow rate of the fluid flowing in an oscillating measuring tube. Since it is a direct measurement type mass flow meter, the mass flow rate can be measured with high accuracy. Further, in order to stabilize the measurement and reduce the driving energy of the measuring tube, the measuring tube is usually driven at its resonance frequency. Therefore, the density of the fluid in the measuring pipe can be simultaneously measured by the change of the resonance frequency. That is, it becomes possible to obtain a vibration type measuring device having multiple functions, which can simultaneously measure the mass flow rate and the density of a fluid with the same detector.

Vibration-type measuring instruments of this type are roughly classified into those having a U-shaped or S-shaped curved measuring tube,
Some have a straight measuring tube. Further, the number of vibrating measuring tubes is two, and the measuring fluid is branched and guided to the two measuring tubes, or the two measuring tubes are continuously connected to resonate the two measuring tubes. There are those with a structure and those with a single measuring tube.

A straight tube-shaped measuring tube, in other words, the vibration-type measuring apparatus as a whole has a measuring fluid flow path in the measuring instrument including a fluid inflow portion and an outflow portion which is one straight tubular shape. The fluid resistance is small, that is, the pressure loss can be reduced, and there is no liquid pool inside the detection part, and the inside of the measuring tube can be easily cleaned. Further, in comparison with the curved tubular measuring tube or the configuration having a plurality of measuring tubes, the structure is simplified, that is, the manufacturing cost is reduced, but on the other hand, there are the following disadvantages.

1) Since the vibration energy of the measuring pipe leaks to the outside through the fixed portion of the measuring pipe, a high Q of vibration cannot be obtained. As a result, the vibration frequency becomes unstable, and when used as a flow meter, for example, the zero point becomes unstable. 2) Since the relative vibration between the measuring pipe and the support mechanism that supports the measuring pipe is detected, it is easily affected by external vibration. For this reason,
Various innovations have been made in the past.

In order to ensure the vibration characteristics of the measuring pipe while making the most of the merit of one measuring pipe, for example, US Pat.
In the specification of No. 823,614 (first conventional example), one straight tubular measuring tube is rigidly fixed by using a supporting mechanism having sufficiently high rigidity. With this configuration, the displacement of the support portion of the measuring tube becomes small, and the state approaches a so-called vibration node state, so that a vibration system having a relatively high Q of vibration can be configured.

However, considering practical use, there is a limit in weight and size in increasing the rigidity of the support mechanism. In other words, it is not possible to form an ideal vibration node just by approaching the vibration node, and as a result, there is a leakage of vibration energy. In addition, with such a structure, when connecting with a relatively short pipe material, that is, with a relatively rigid (rigid) external pipe using a flange or the like, the loss of vibration energy increases and the Q of vibration decreases, It has been confirmed by experiments that stable vibration cannot be obtained.

As an improvement measure for the first conventional example, there is, for example, one disclosed in Japanese Patent Laid-Open No. 4-41319 (second conventional example). In this example, a resonator is separately provided to prevent vibration energy from leaking to the outside. However, even with such a structure, there are two major problems. One is that the density of the fluid in the measuring tube is not always constant and changes, or the fluid having a completely different density may be measured, so that the resonance frequency of the measuring tube including the measuring fluid changes. However, since the measurement fluid is not introduced into the resonator, the measurement fluid does not change the resonance frequency. Therefore, the resonance state of the measuring tube and the resonator is not kept constant, and the characteristics are not stable.

Secondly, despite the fact that the structure is simplified by using only one measuring tube, by providing a resonator, the structure becomes complicated as in the case of having a plurality of measuring tubes.
The point is that manufacturing costs cannot be reduced. As a means for dealing with such a problem, Japanese Patent Laid-Open No. 58-178
No. 217 (third conventional example), US Pat. No. 5,287,
No. 754 specification (fourth conventional example) is proposed.

In the third conventional example, the measuring tube is firmly connected to the inner base at both ends thereof, and the inner base is connected to the inlet through a flexible joint whose both ends are softly supported by O-rings made of rubber or the like. It is connected at the outlet to an outer base which is connected to the external conduit. With such a structure, the outer base and the inner base are vibrationally separated to prevent the vibration energy of the measuring tube from leaking, and
Disturbances are prevented from entering through external piping. Therefore, it is possible to realize a vibration system having a high Q of vibration and to have characteristics that are not easily affected by disturbance.

In the third conventional example, since the organic material such as the O-ring is used to support it softly, the elasticity and viscosity of the material easily change with time, and it is difficult to guarantee the characteristics for a long time. In addition, in the third conventional example, since the inner base and the outer base are softly supported, if a shocking external force is applied during transportation, a strong force is applied to the joint and the joint and the O-ring are deformed. , The inner base is supported on the outer base by an O-ring. However, also in this case, similarly to the above-mentioned reason, when the characteristics of the elastic body change with time and harden, external vibration is likely to be transmitted this time.

The fourth conventional example is an improvement of the third conventional example.
Although the measuring pipe is not a straight pipe here, it is also applicable to the case of a straight pipe. That is, here, the Coriolis conduit for flowing the measurement fluid is fixed at both ends of the measurement tube by a support mechanism having a higher resonance frequency than that of the third conventional example.
The support mechanism is configured to be directly connected to and supported by the housing through a metallic inlet conduit and outlet conduit. And
The resonance frequency of the detection unit including the support mechanism and the inlet conduit and the outlet conduit is made sufficiently smaller than the resonance frequency of the support mechanism, that is, the support mechanism is supported softly.

By doing so, changes over time in its elastic properties can be almost ignored, and while there is the advantage that stable properties can be guaranteed over a long period of time, the above-mentioned O
-Because there is no damping action peculiar to rubber materials such as rings, resonance may occur when disturbance near the resonance frequency of the detection section acts, causing damage to the inlet conduit and the outlet conduit. Therefore, although the third conventional example shows an example in which the supporting mechanism is supported by the supporting and supporting springs like the O-ring that supports the inner base on the outer base, resonance of the vibration system including this is shown. When a disturbance having a frequency equal to the frequency acts, resonance also occurs, and the stress applied to the inlet conduit and the outlet conduit becomes a problem.

Particularly, in a piping system in which this type of flow meter is installed, a low frequency of 200 Hz or less is dominant (if necessary, for example, "Yokogawa Technical Report", Vol. 34, No. 1, 1990,
pp49-52), it can be seen that there is a problem in the configuration in which a low resonance frequency is provided without providing any damping element as described above.

[0015]

As is apparent from the above-mentioned detailed description, the object of the present invention is to make use of the advantages of the straight pipe type, such as low pressure loss, easiness of cleaning, and simple structure, while at the same time measuring pipe. By preventing the vibration energy from leaking and realizing a vibration system with a high Q of vibration, the influence of disturbance is prevented by the high frequency stability and its own filter effect, and it is possible to avoid low-frequency disturbance and shock during transportation. It is an object of the present invention to provide a highly reliable vibration measuring instrument capable of preventing damage to the inlet conduit and the outlet conduit by eliminating large displacement.

[0016]

In order to solve such a problem, in the invention of claim 1, at least one vibration is applied.
In a vibration type measuring instrument capable of measuring at least one of a mass flow rate and a density of a fluid flowing in a straight tubular measuring tube of a book, a supporting mechanism for supporting the measuring tube, a vibration generator for exciting the measuring tube, and a measurement At least 1 to detect tube vibration
Two vibration sensors, an inlet conduit for guiding the measuring fluid to the measuring pipe, an outlet conduit for guiding the measuring fluid from the measuring pipe, a housing containing each of the elements, and a nodal position of the vibration are formed in the support mechanism. Nodal point forming means is provided, and the support mechanism is fixed or supported at the nodal point position to the housing via a coupling member.

In the invention of claim 1, the nodal position of the vibration can be adjusted by the rigidity of the support mechanism and the additional mass added to the support mechanism (invention of claim 2). Then, the additional mass can be added to the position where the vibration amplitude of the support mechanism is maximum (the invention of claim 3). Further, in the invention of claim 2 or 3, a mass adjusting mechanism for the additional mass can be provided (invention of claim 4), and in the inventions of claims 1 to 4, the node position of the vibration is set to the support mechanism. Can be formed at both end positions (invention of claim 5), and in the inventions of claims 2 to 5, the support mechanism and the additional mass can be integrally formed (invention of claim 6).

[0018]

[Function] By adjusting the rigidity and the added mass of the support mechanism,
A vibration node having no displacement relative to the housing or the like is formed, and the support mechanism is coupled to the housing or the like at that position. Since the nodal point is a point without displacement, when fixed or supported at the nodal point, the force acting on the supporting member is small, and therefore the energy loss is small. Therefore, high vibration Q can be realized.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a longitudinal sectional view showing a first embodiment of the present invention, and FIG. 2 is a lateral sectional view thereof (A-A sectional view of FIG. 1).
Is. The measuring device 1 is configured as follows. That is, 2 is a straight tube measuring tube, 3a and 3b are fixing members fixed to both ends of the straight tube measuring tube 2 by a method such as brazing or welding, and 4 is a straight tube measuring tube of the fixing members 3a and 3b. In order to cancel the vibration in the vibration direction of 2, the fixing members 3a, 3
b is a cylindrical beam connected by means such as welding or screwing.

Reference numeral 5 denotes a magnet attached to the center of the straight tubular measuring tube 2 and a coil fixed to the cylindrical beam 4, and a vibration generator 6a, 6b for vibrating (exciting) the measuring tube 2. Is a velocity sensor (a displacement sensor or an acceleration sensor) that detects the vibration of the measuring tube 2 and is composed of a magnet attached at a symmetrical position of the measuring tube 2 with a vibration generator 5 sandwiched between it and a coil attached to the cylindrical beam 4. Good). Although a pair of speed sensors is provided here,
This is based on the assumption that the flow rate is measured using the frequency or phase difference, and only one is required for the density.

Reference numerals 7a and 7b denote inlet conduits and outlet conduits integrally manufactured with the measuring pipe 2, which are respectively coupled to flanges 9a and 9b connected to external pipes for introducing and discharging the measuring fluid. . 11a, 11b, 11c,
Reference numeral 11d denotes an annular additional mass that is coupled to the cylindrical beam 4 by a method such as screwing, welding, brazing or the like, and the above-mentioned elements constitute a detecting portion. The housing 8 is joined to the flanges 9a and 9b by means of welding or the like so as to include this detecting portion.

Here, the additional mass and its mounting position are adjusted so that a node of vibration is formed in the cylindrical beam 4 with respect to the resonance frequency of the measuring tube 2, and at that node, as shown in FIG. The support mechanism composed of 3a, 3b and the cylindrical beam 4 is fixed or supported to the housing 8 by the coupling pins 12a-12d via the coupling rings 10a, 10b. Further, the shape of the additional mass has a small contact area so that the bending rigidity of the cylindrical beam 4 is less affected.

In such a configuration, the straight tubular measuring tube 2
Is excited at the resonance frequency by the vibration generator 5 and the drive circuit 14. The vibration of the measuring tube 2 at that time is detected by the speed sensor 6
a, 6b, and outputs are input to the signal processing circuit 13, respectively, and a well-known predetermined operation is performed here to be converted into a mass flow rate or density signal.

FIG. 3 is a longitudinal sectional view showing a second embodiment, and FIG.
Is a lateral (BB) sectional view of the same. The difference from the first embodiment is that, as indicated by reference numeral 11, the additional masses are collected in one place and are collectively installed at the central portion of the cylindrical beam 4, that is, at the position where the vibration amplitude is maximized. Since the rigidity of the cylindrical beam 4 is sufficiently larger than the rigidity of the straight tubular measuring tube 2, the vibration amplitude of the cylindrical beam 4 is considerably smaller than that of the measuring tube 2, but vibrates with a small amplitude. Since the measuring tube 2 is vibrating in the basic mode of lateral vibration here, the cylindrical beam 4 also has the largest amplitude in the central portion. Therefore, it is effective to add the additional mass to the central part in a concentrated manner, and the total mass can be reduced when the vibration nodes are formed at the same position.

Now, the formation of the nodes will be described with reference to FIG. Note that FIG. 5 shows the straight tubular measuring tube 2 shown in FIG.
It shows the vibration amplitude of the support mechanism when is excited at its resonance frequency. This shows the result of vibration analysis using the finite element method for the detector shown in FIG. 3, and how the vibration amplitude at each point of the support mechanism changes with the additional mass added to the support mechanism as a parameter. Indicates what to do.

That is, the horizontal axis of FIG. 5 shows the position in the longitudinal direction when the center of the support mechanism is zero, and the vertical axis shows the vibration amplitude at each point of the support mechanism. From the figure, by adding an additional mass of 2 kg to the cylindrical beam 4 of the support mechanism, the amplitude of the central portion of the cylindrical beam 4 is reduced from about 4 μm without the additional mass to about 2 μm, which is an average value. It can be seen that the vibration amplitude is also decreasing. Similarly, the added mass is 4K
When the g and 6 Kg are increased, a part where the amplitude phase is reversed (a part where the amplitude value becomes negative in FIG. 5) appears.
The point where the vibration amplitude curve crosses the zero line, that is, the vibration amplitude is zero, is the vibration node.

It is more effective to collectively attach the added mass to the position where the vibration amplitude is larger as shown in FIG. 3 than to disperse the attached mass as shown in FIG. To do this,
This is because the added mass can be lightened when the nodes are formed at the same position. In addition, in FIG. 5, comparing the cases where the added mass is 4 kg and 6 kg, since the node position of 4 kg is formed closer to the end of the support mechanism, the vibration node is set to the end of the support mechanism. It can be seen that the additional mass can be minimized if it is formed.

In the above, the method of changing the mass of the additional mass applied to the support mechanism in forming the nodes has been described. However, the support mechanism including the fixing members 3a and 3b and the cylindrical beam 4 shown in FIGS. It can also be changed by the rigidity, that is, the material, the wall thickness, the diameter, and the like. However, it is necessary to design the support mechanism in consideration of strength, etc., and it is more difficult to adjust the variation during manufacturing than to adjust the additional mass. It can be said that it is advantageous to adjust. In any case, the vibration node may be formed in the support mechanism by adjusting the rigidity and the additional mass of the support mechanism.

In the above case, the inlet conduit,
The rigidity of the outlet conduit is preferably low in terms of vibration, and for that purpose, it is desirable that the outlet conduit be made of a material such as a diaphragm or bellows, which is difficult to transmit the force. Further, the vibration type measuring device should be designed in terms of material and structure in consideration of the pressure of the measuring fluid and the corrosion resistance to the measuring fluid. In this way, energy leakage from the connection between the inlet and outlet conduits can be minimized.

FIG. 6 is a cross sectional view showing the third embodiment.
This is characterized in that adjustable masses 15a and 15b are added to those shown in FIGS. This makes it possible to adjust the variation during manufacturing. Since the other points are the same as those in FIGS. 2 and 4, description thereof will be omitted.

FIG. 7 is a cross sectional view showing the fourth embodiment.
This is characterized in that the nodes of vibration are formed at both ends of the cylindrical beam 4 in contrast to those shown in FIGS. As is clear from the simulation result of FIG. 5, when the nodes of vibration are formed in the cylindrical beam 4, it is possible to make the mass lightest by adjusting the additional mass so as to be formed at both ends of the cylindrical beam 4. It can be said that it paid attention.

In any of the above embodiments, the additional mass and the cylindrical beam can be integrally manufactured by a method such as casting or die casting. By doing so, not only the number of parts can be reduced, but also the step for attaching the additional mass can be omitted, and the cost can be reduced.

[0033]

According to the present invention, the measuring tube, the support mechanism,
Vibration system (detection part) consisting of inlet conduit and outlet conduit
By adjusting the rigidity of the support mechanism and the additional mass in the support mechanism, a vibration node is formed in the support mechanism, and the node is fixed or supported by the housing at this node position, so that a high Q of vibration can be obtained. In addition, since the detecting portion is not largely moved by disturbance or impact force, it is possible to prevent damage to the inlet conduit and the outlet conduit. Furthermore, since the Q of the vibration can be increased, the vibration frequency is stabilized, and as a result, the zero point can be stabilized. In addition, since the loss of vibration energy is small, there is also an advantage that the energy for driving the measuring tube can be reduced.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the first embodiment of the present invention.

FIG. 3 is a vertical sectional view showing a second embodiment of the present invention.

FIG. 4 is a cross sectional view showing a second embodiment of the present invention.

FIG. 5 is an explanatory diagram for explaining the operation principle of the present invention.

FIG. 6 is a transverse sectional view showing a third embodiment of the present invention.

FIG. 7 is a cross sectional view showing a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Measuring device, 2 ... Straight tubular measuring tube, 3a, 3b ... Fixing material, 4 ... Cylindrical beam, 5 ... Vibration generator, 6a, 6b ... Vibration sensor, 7a ... Inlet conduit, 7b ... Outlet conduit, 8 ... Housing , 9a, 9b ... Flange, 10a, 10b ... Coupling ring, 11, 11a, 11b, 11c, 11d ... Additional mass, 12a, 12b, 12c, 12d ... Coupling pin, 1
3 ... Signal processing circuit, 14 ... Driving circuit, 15a, 15b ...
Adjusted mass.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Susumu Murata 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. No. 1 within Fuji Electric Co., Ltd.

Claims (6)

[Claims] 1. A vibrating measuring instrument capable of measuring at least one of a mass flow rate and a density of a fluid flowing in at least one straight tubular measuring pipe to be vibrated, a supporting mechanism for supporting the measuring pipe, and a measuring device. A vibration generator that vibrates the pipe, at least one vibration sensor that detects vibration of the measurement pipe, an inlet conduit that guides the measurement fluid to the measurement pipe, an outlet conduit that guides the measurement fluid from the measurement pipe, and the above-mentioned elements. And a nodal point forming means for forming a nodal point position of the vibration in the supporting mechanism, and fixing or supporting the supporting mechanism to the housing via a coupling member at the nodal point position. Vibration type measuring instrument. 2. The vibration measuring instrument according to claim 1, wherein the nodal position of the vibration is adjusted by the rigidity of the support mechanism and the additional mass added to the support mechanism. 3. The vibration measuring instrument according to claim 2, wherein the additional mass is added to a position where the vibration amplitude of the support mechanism is maximized. 4. The vibration measuring instrument according to claim 2, further comprising a mass adjusting mechanism for adjusting the additional mass. 5. The vibration nodal points are formed at both ends of the support mechanism.
The vibration type measuring instrument according to any one of 1. 6. The vibration measuring instrument according to claim 2, wherein the support mechanism and the additional mass are integrally molded.