JP3407236B2 - Mass flow meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a mass flow rate using a Coriolis force generated based on a mass flow rate of a fluid flowing through at least one measurement pipe to be vibrated. The mass flowmeter to measure, especially the vibration mode in the circumferential direction of the measuring tube, which is generated depending on the mass of the vibration generator and vibration detecting sensor when the diameter of the measuring tube becomes large The present invention relates to a Coriolis-type mass flowmeter with improved measurement accuracy. 2. Description of the Related Art Generally, a Coriolis-type mass flow meter directly measures a mass flow rate of a fluid based on a Coriolis force generated in proportion to a mass flow rate of a fluid flowing in a vibrating measuring tube. Therefore, highly accurate measurement is possible. This type of mass flow meter is roughly classified into a type having a curved measuring tube such as a U-shaped or S-shaped type, and a type having a linear measuring tube. Among them, one having a linear measuring tube, two vibrating measuring tubes, and branching a measuring fluid to two measuring tubes, and a structure of resonating the two measuring tubes (for example, And Japanese Patent Publication No. 5-69452), or a single measuring tube. FIG. 3 shows a single measuring tube, for example, proposed by the present inventors (see Japanese Patent Application No. 7-49371: also referred to as a proposed device). this is,
A support mechanism (fixing members 3a, 3b) for supporting both ends of the measuring tube 2
And a cylindrical beam 4), a vibration generator 5 for applying vibration to the measurement tube 2, two vibration detection sensors 6a and 6b for detecting vibration of the measurement tube 2, and an inlet conduit 7a for guiding a measurement fluid to the measurement tube 2. , An outlet conduit 7 for taking out the measurement fluid from the measurement tube 2
b and a housing 8 containing them, so that the frequency of Coriolis vibration applied to the measuring tube 2 is higher than the natural frequency of the support mechanism. The primary resonance frequency of the resonance frequency of the measuring tube is determined by the mass of the fixed end and the measuring tube and the density of the fluid. Those having such a curved measurement tube have a relatively low resonance frequency, for example, 100 Hz. However, the one having one or two straight measuring tubes has a relatively high resonance frequency of, for example, 1000 Hz in the case of the first mode, and 5400 Hz particularly when the main vibration is set to the third mode. For example, it is easy to approach various other resonance modes as shown in FIGS. 4A shows a resonance mode based on the mass (magnet or the like) of the vibration generator, FIG. 4B shows a resonance mode in the circumferential direction, and FIG. 4C shows a resonance mode based on the vibration detection sensor. The resonance frequency in the circumferential direction is determined by the diameter, thickness, length to the fixed end of the measuring tube, and the mass added intensively such as a magnet of a vibration generator or a vibration sensor. When it is considered as a mass flow meter, it is desirable to reduce the thickness and the length in view of the reduction in size and weight and the generated phase difference. In the case of a small diameter, the weight and size are not so large, but in the case of a large diameter, the thickness is reduced and the length is shortened in order to reduce the weight and size. In this case, the vibration generator and the vibration sensor are fixed only via pins fixed on the measuring tube by brazing or the like. (Varies depending on the thickness and length of the measuring tube, vibration generator, vibration sensor, etc.) and interferes with the main vibration, so that the stability of the main vibration is impaired or the zero point fluctuation characteristics deteriorate. A problem arises in that high-precision measurement cannot be performed. That is, in order to suppress the vibration in the circumferential direction and increase the generated phase difference, the thickness must be increased and the length must be increased, and it is difficult to reduce the size and weight. Therefore,
An object of the present invention is to suppress vibration near the main vibration while reducing the size and weight. [0006] In order to solve such a problem, according to the first aspect of the present invention, a ring-shaped member is installed at the installation position of a vibration generator or a vibration sensor on a measuring tube . Addition forte,
At least one between the vibration generator and the vibration detection sensor and between the vibration detection sensor and the support mechanism ,
To suppress vibration in the circumferential direction with the sensor part as the fixed end.
At least one ring-shaped member is installed. As described above, in the large-diameter measuring tube, even in the case where the wall thickness is small and the length is short, it is possible to suppress the circumferential mode in the vicinity of the first, second and third-order transverse vibration. Becomes FIG. 1 is a sectional view showing a first embodiment of the present invention, in which (a) is an overall configuration diagram, and (b) is a partially enlarged view of a vibration generating section. In the figure, reference numeral 2 denotes a straight tube measuring tube, and 3a and 3b denote fixing members fixed to both ends of the straight tube measuring tube 2 by a technique such as brazing or welding.
Is a cylindrical beam to which the fixing members 3a and 3b are joined by welding or the like in order to cancel the vibration of the fixing members 3a and 3b in the vibration direction of the straight tubular measuring tube 2. The fixing members 3a, 3
The b and the cylindrical beam 4 form a support mechanism for connecting both ends of the straight measuring tube 2. A ring-shaped member 10a for suppressing a circumferential vibration mode is fixed to the center of the straight tubular measuring tube 2 by means such as brazing or welding. A pin 11a for positioning the magnet 12a is fixed on the ring-shaped member 10a by means such as brazing or welding, and the magnet 12a is inserted into the pin 11a.
It is fixed with a nut 13a. Reference numeral 5 denotes a vibration generator for vibrating the measuring tube 2 which comprises a magnet 12a attached to the center of the straight tubular measuring tube 2 and a coil fixed to the cylindrical beam 4. Ring-shaped members 10b and 10c for suppressing circumferential vibration modes are fixed on the measurement tube 2 at symmetrical positions around the vibration generator 5 by means such as brazing or welding. I have. Pins 11b, 1 for positioning the magnets 12b, 12c are provided on the ring-shaped members 10b, 10c.
1c is inserted and fixed with nuts 13b and 13c. Reference numerals 6a and 6b denote magnets 12b and 12c and coils fixed to the cylindrical beam 4, and are velocity sensors (electromagnetic pickups) for detecting the vibration of the measuring tube 2.
7a is an inlet conduit, 7b is an outlet conduit, which is manufactured integrally with the measuring tube 2. These are connected to the end surface of the housing 8 to introduce and discharge the measurement fluid to and from the measurement tube 2 respectively. The housing 8 includes the above-described elements, and includes a flange 9.
a, 9b are connected by means such as screwing or welding. In FIG. 1, the ring-shaped member is provided on both the vibration generator 5 and the vibration sensors 6a and 6b, but may be provided on either one of them. In such a configuration, for example, an outer diameter φ4
2.7, wall thickness (t) 2.3 mm, length 580 mm,
When the ring-shaped member 10a is not provided, the vibration in the circumferential direction due to the mass of the magnet 12a is 2600 Hz, whereas the third mode of the measurement tube lateral vibration is 2390 Hz, which is generated with a difference of 210 Hz. Therefore, a ring-shaped member 10a of φ50 × t3 is provided for the vibration generator, and a φ5 × t3 is provided for the vibration detection sensor.
By adding the ring members 10b and 10c of 0 × t2, the vibration in the circumferential direction due to the mass of the magnet 12a is 3500.
Hz and the interference with the main vibration can be reduced. FIGS. 2A and 2B are sectional views showing a second embodiment of the present invention, wherein FIG. 2A is an overall configuration diagram, and FIG. 2B is a partially enlarged view of a vibration generator. As is clear from the figure, this example shows that the vibration generator 5 on the measuring pipe 2 and the vibration detection sensors 6a, 6
b, the ring-shaped members 10d and 10e are fixed by means such as brazing or welding, and the ring-shaped members 10f are fixed between the vibration detection sensors 6a and 6b on the measuring tube 2 and the fixing members 3a and 3b. , 10g are fixed by means such as brazing or welding. Note that two or more ring-shaped members may be provided between the vibration generator and the vibration detection sensor and between the vibration detection sensor and the support mechanism, and between the vibration generator and the vibration detection sensor or between the vibration detection sensor and the support mechanism. More than one may be provided. According to the present invention, the following effects can be expected. (1) By installing a ring-shaped member at the installation position of the vibration generator or vibration sensor on the measurement tube, even if the wall thickness is small and the length is short in a large-diameter measurement tube, primary and secondary vibrations can be obtained. Next, 3
It is possible to suppress the circumferential mode generated near the next. (2) In addition to the above, between the vibration generator and the vibration detection sensor,
By installing one or more ring-shaped members on at least one of the vibration detection sensor and the support mechanism, it is possible to suppress a circumferential vibration mode in which the vibration generator unit and the vibration detection sensor unit are fixed ends. it can. (3) As a result, since there is no vibration mode in the circumferential direction near the main vibration, the vibration is generated stably, and the stability of the zero point and the zero point fluctuation are improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing a first embodiment according to the present invention. FIG. 2 is a sectional view showing a second embodiment according to the present invention. FIG. 3 is a sectional view showing the proposed device. FIG. 4 is an explanatory diagram for explaining deformation in a circumferential direction in FIG. 3; [Description of Signs] 1 ... Measuring device, 2 ... Measuring tube, 3a, 3b ... Fixing material, 4 ...
Cylindrical beam, 5 ... vibration generator, 6a, 6b ... sensor, 7
a ... inlet conduit, 7b ... outlet conduit, 8 ... housing, 9
a, 9b: flange, 10a to 10e: ring-shaped member,
11a to 11c: pins, 12a to 12c: magnets, 13a
... 13c nut, 20 drive circuit, 21 phase difference detection type signal processing circuit.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-6-3174 (JP, A) JP-A-2-42319 (JP, A) JP-A-7-55525 (JP, A) JP-A-5-555 248913 (JP, A) JP 4-63326 (JP, B2) (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01F 1/84

Claims (1)

(57) Claims 1. A measuring tube, a vibration generator for applying vibration to the measuring tube, a vibration detecting sensor for detecting vibration of the measuring tube, and the measuring tube fixed. A mass flow meter for measuring a mass flow rate of a fluid based on the Coriolis principle, wherein at least one of the vibration generator and the vibration detection sensor includes a ring-shaped member. Installed in the measurement tube through , further,
Between the vibration generator and the vibration detection sensor, the support mechanism and the vibration detection
At least one of the output sensors has a vibration generator
In order to suppress circumferential vibration with the output sensor as the fixed end
A mass flowmeter , wherein one or more ring-shaped members are installed .