JPH1078340A - Mass flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the frequency of Coriolis vibration of a measuring tube higher than the natural frequency of a support mechanism with an easy and inexpensive structure by setting the length participating in vibration of the support mechanism long, compared with that of the measuring tube. SOLUTION: A support mechanism for connecting both ends of a straight tube-like measuring tube 2 is formed of fixing members 3a, 3b and a cylindrical beam 4. The connecting part of the fixing members 3a, 3b to the measuring tube 2 is formed so that the axial thickness is larger toward the vibrating side of the measuring tube 2 than the thickness of the connecting part with the cylindrical beam 4. Thus, the length participating in vibration of the cylindrical beam 4 is large, compared with the length participating in vibration of the measuring tube 2 to make the natural frequency of the cylindrical beam 4 lower than the frequency of Coriolis vibration of the measuring tube 2. Since the length participating in vibration of the support mechanism is set long to the length participating vibration of the measuring tube 2 without reducing its thickness, stable vibration can be measured without being interfered by the reduction in circumferential natural value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flowmeter for measuring a mass flow rate by utilizing a Coriolis force generated based on a mass flow rate of a fluid flowing through at least one measurement pipe to be vibrated, and in particular, to a lighter mass flowmeter. The present invention relates to a mass flow meter that can be simplified and can improve usability, reliability, and measurement accuracy.

[0002]

2. Description of the Related Art Coriolis-type mass flow meters directly measure 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 a vibrating measuring tube. High precision measurement of flow rate is possible. Generally, this type of flow meter is roughly classified into a type having a U-shaped or S-shaped curved measuring tube and a type having a straight measuring tube. In addition, two vibrating measuring tubes
And then divert the measurement fluid to two measurement tubes,
Alternatively, as a configuration for continuously connecting two measurement tubes,
A structure that resonates two measuring tubes, or
There is one having a single measuring tube (for example, one having two measuring tubes is disclosed in Japanese Patent Publication No. 6-46167).

As one measuring tube, there is one shown in FIG. 3 submitted by the applicant (Japanese Patent Application No. 7-49371:
It is also called a proposal device). This is a supporting mechanism which comprises fixing members 3a and 3b and a cylindrical beam 4 and supports both ends of the measuring tube 2,
A vibration generator 5 for exciting the measuring tube 2, two vibration sensors 6a and 6b for detecting the vibration, an inlet conduit 7a for guiding the measuring fluid to the measuring tube, and an outlet conduit 7b for guiding the measuring fluid from the measuring tube. A housing 8 or the like to be included is provided, and the frequency or the frequency of the Coriolis vibration given to the measuring tube 2 is
Higher than the natural frequency of the support mechanism, for example,
S / N by making the order higher than twice, preferably higher than 2
This enables high and stable vibration.

Further, when the frequency of Coriolis vibration is increased, (1) the phase difference between two upstream and downstream vibration sensors is used. (2) A speed sensor or an acceleration sensor is used as a sensor. It has also been pointed out that the above effects can be further improved by taking such measures.

[0005]

When the frequency of the Coriolis vibration applied to the measuring tube is made higher than the natural frequency of the supporting mechanism, as described in the above proposed apparatus,
The resonance frequency of the support mechanism is lowered, or the natural frequency of the measurement tube, for example, the third mode or the fifth mode is used as Coriolis vibration applied to the measurement tube. But,
Especially when using the higher order mode of the measuring tube, when designing for many types of apertures (size of the measuring tube) in order to correspond to many applications, measurement to be used without interference of unnecessary vibration mode In some cases, the natural frequency of the higher-order mode of the tube is not always sufficiently high with respect to the natural frequency of the support mechanism.

For example, if the rigidity of the support mechanism is reduced by reducing the thickness of the support mechanism, the eigenvalue in the circumferential direction is reduced, and interference is likely to occur. In addition, when the additional mass is used, there are problems that the structure becomes complicated and the cost increases, and that an additional mass of an unrealistic size is used. Therefore, an object of the present invention is to make the frequency of Coriolis vibration higher than the natural frequency of the support mechanism with a simple and inexpensive configuration.

[0007]

In order to solve such a problem, according to the present invention, at least one measuring pipe is provided, and a Coriolis force is generated when a fluid flows through the measuring pipe. Vibration, and to measure the flow rate of the fluid flowing in the measurement pipe by applying Coriolis vibration to measure the flow rate of the fluid using this Coriolis force, by applying to the measurement pipe,
A support mechanism made of a cylindrical beam and a fixed material and connecting both ends of the measurement tube, a vibration generator that applies vibration to the measurement tube, and at least two or more vibration sensors that detect vibration of the measurement tube,
An inlet conduit for introducing the measuring fluid into the measuring tube, an outlet conduit for leading the measuring fluid out of the measuring tube, and a housing enclosing each of these components are provided. The length is made longer so that the frequency of Coriolis vibration applied to the measuring tube is higher than the basic natural frequency of the support mechanism.

[0008] In the first aspect of the present invention, the thickness of the fixing member in the axial direction is greater at the joint portion with the measurement tube on the vibration side of the measurement tube than at the joint portion with the cylindrical beam. According to the second aspect of the present invention, a notch is provided on a joint portion of the fixing member with the measuring tube on a side opposite to a side of the fixing tube which is subject to vibration of the measuring tube. Can be formed (the invention of claim 3). Also,
According to the first to third aspects of the present invention, the frequency of Coriolis vibration applied to the measuring tube can be higher than √2 times the fundamental natural frequency of the support mechanism (the fourth aspect of the invention). The frequency of the Coriolis vibration applied to the measurement tube may be a higher natural frequency than the basic natural frequency of the support mechanism (the invention of claim 5). In addition, 1
In the inventions of the first to fifth aspects, the flow rate can be measured based on the phase difference between the output signals from the two or more vibration sensors (the invention of the sixth aspect). In the inventions of the first to sixth aspects, the flow rate sensor is used as the vibration sensor. A speed sensor or an acceleration sensor can be used (the invention of claim 7).

[0009]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention. In the figure, reference numeral 2 denotes a straight tube measuring tube, 3a and 3b are fixing members fixed to both ends of the straight tube measuring tube 2 by a technique such as brazing or welding, and 4 is a straight tube of the fixing members 3a and 3b. It is a cylindrical beam to which the fixing members 3a and 3b are joined by means such as welding in order to cancel the vibration of the measuring tube 2 in the vibration direction. This fixing material 3
The support mechanism for connecting both ends of the straight tube-shaped measuring tube 2 is formed by the a and 3b and the cylindrical beam 4.

Reference numeral 5 denotes a magnet attached to the center of the straight tube-shaped measuring tube 2 and a coil fixed to the cylindrical beam 4, and a vibration generator for vibrating the measuring tube 2;
Reference numerals a and 6b denote magnets mounted at symmetric positions of the measuring tube 2 with the vibration generator 5 interposed therebetween, and coils fixed to the cylindrical beam 4, and an electromagnetic pickup for detecting vibration of the measuring tube 2, for example, a speed It is a sensor. Although two sensors are provided here, they can be provided as needed.

Reference numeral 7a denotes an inlet conduit, 7b denotes an outlet conduit, which is manufactured integrally with the measuring tube 2 here. These are connected to the end surface of the housing 8 to transfer the measurement fluid to the measurement tube 2.
Are introduced and derived respectively. The housing 8 includes the above-mentioned components and is connected to the flanges 9a and 9b by means of screws or welding. Reference numeral 20 denotes a drive circuit, and reference numeral 21 denotes a phase difference detection type signal processing circuit. With such a configuration,
The straight tube measuring tube 2 is moved by the vibration generator 5 and the driving circuit 20
The Coriolis vibration is, for example, excited at the natural frequency of the third mode.

The above is a supplementary description of the proposed device shown in FIG. 3, but the present invention is further configured as follows. That is, the frequency or frequency of the Coriolis vibration of the measuring tube 2 depends on the outer shape and thickness of the measuring tube 2 and the length between the fixing members 3a and 3b (the distance between arrows A and B in FIG. Of the vibration, also referred to as the length of the vibration). Conventionally, the vibration length of the measuring tube 2 and the length of the cylindrical beam 4 (the distance between arrows C and D in FIG. 1; hereinafter, also referred to as the length exerted on the vibration of the support mechanism) are conventionally equalized. (See FIG. 3).

On the other hand, in the present invention, as shown in FIG.
The thickness of the fixing members 3a, 3b in the axial direction at the joint with the measuring tube 2 is made larger on the vibration side of the measuring tube 2 than at the joint with the cylindrical beam 4. In this way, the length of the cylindrical beam 4 exerted on the vibration is made longer than the length of the measuring tube 2 exerted on the vibration, and the natural frequency of the cylindrical beam 4 is made lower than the frequency of the Coriolis vibration. That's it.

FIG. 2 is a block diagram showing a modification of FIG.
As is apparent from FIG. 1, this example has a notch in the joint between the fixing members 3a and 3b with the measuring tube 2 on the side opposite to the side that exerts vibration on the measuring tube 2 in FIG. Since the portion 10 is formed, it is possible to make the natural frequency of the cylindrical beam 4 lower than the frequency of Coriolis vibration by doing so. Note that the configuration of FIGS. 1 and 2 is the same as that of the proposed device, that is, the configuration in which the frequency of Coriolis vibration applied to the measurement tube is higher than 基本 2 times the basic natural frequency of the support mechanism. A device having a higher-order natural frequency than the basic natural frequency of the support mechanism, and a device which performs flow measurement based on a phase difference between output signals from two or more vibration sensors,
Furthermore, it is needless to say that the present invention can be applied to a device using a speed sensor or an acceleration sensor as a vibration sensor.

[0015]

According to the present invention, since the length of the support mechanism which is applied to the vibration of the measuring tube is made longer than the length which is applied to the vibration of the measuring tube without reducing the thickness thereof, the circumferential direction is increased. There is an advantage that stable vibration can be stably measured without receiving interference due to a decrease in the eigenvalue of. Further, there is an advantage that the structure is simple and inexpensive because no additional mass or the like is required.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a modification of FIG.

FIG. 3 is a configuration diagram showing a proposed device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Measuring device, 2 ... Linear 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, 10 ... notch, 2
0: drive circuit, 21: phase difference detection type signal processing circuit.

Claims (7)

[Claims] 1. A Coriolis system comprising at least one measuring tube, wherein the vibration is such that a Coriolis force is generated when a fluid flows through the measuring tube, and the Coriolis force measures the flow rate of the fluid using the Coriolis force. In order to measure the flow rate of the fluid flowing through the measurement tube by applying vibration to the measurement tube, a support mechanism made of a cylindrical beam and a fixing member and connecting both ends of the measurement tube, a vibration generator that applies vibration to the measurement tube, At least two or more vibration sensors for detecting vibration of the measuring tube, an inlet conduit for introducing a measuring fluid into the measuring tube, an outlet conduit for leading the measuring fluid from the measuring tube, and a housing containing these components. The length of the support mechanism is made longer than the length of the measurement tube, and the frequency of Coriolis vibration applied to the measurement tube is
A mass flowmeter characterized by being higher than a fundamental natural frequency of the support mechanism. 2. The fixing member according to claim 1, wherein the thickness of the fixing member in the axial direction is larger on the vibration side of the measurement tube than on the side of the junction with the cylindrical beam. The mass flow meter according to claim 1. 3. The mass according to claim 2, wherein a cutout portion is formed on a joint portion of the fixing member with the measurement tube, the cutout portion being formed on a side opposite to a side of the fixing tube that vibrates the measurement tube. Flowmeter. 4. The method according to claim 1, wherein the frequency of Coriolis vibration applied to the measuring tube is higher than √2 times the fundamental natural frequency of the support mechanism. Mass flow meter. 5. The method according to claim 1, wherein a frequency of the Coriolis vibration applied to the measuring tube is a higher natural frequency than a basic natural frequency of the support mechanism. Mass flow meter. 6. The mass flow meter according to claim 1, wherein the flow rate is measured based on a phase difference between output signals from the two or more vibration sensors. 7. The mass flow meter according to claim 1, wherein a speed sensor or an acceleration sensor is used as the vibration sensor.