JP3224442B2 - 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 structure of a straight pipe type Coriolis flowmeter which is less affected by distortion due to attachment to piping and thermal expansion due to a change in environmental temperature.

[0002]

2. Description of the Related Art One end or both ends of a flow tube through which a measurement fluid flows is supported, and when the flow tube is vibrated around a support point in a direction perpendicular to the flow direction of the flow tube, the flow tube acts on the flow tube (sensor tube). A mass flow meter (Coriolis flow meter) utilizing the fact that the Coriolis force is proportional to the mass flow rate is well known. The sensor tube in this Coriolis flowmeter is an essential part and determines the characteristics of the flowmeter. A straight tube is a basic shape of the sensor tube. The straight pipe type has the advantage of having a straight pipe extending in the flow direction, so that the shape is small and the inside of the pipe is easy to clean, but the sensitivity is low, and
There is a disadvantage in that the N-ratio is reduced and more attention must be paid to disturbances.

As a known document related to the present invention, there is JP-A-62-238419. This relates to a Coriolis flow meter using a straight pipe arranged in parallel as a vibrating pipe, and will be described below.

FIG. 3 is a view for explaining a conventional straight tube type Coriolis flowmeter. In FIG.
1, 36 are flanges, 32 is an inlet, 37 is an outlet, 3
3, 34, 38 and 39 are branch pipes, 40a and 40b are sensor tubes, 41 is an exciter, 42 and 43 are detectors, 44
Is a converter.

In FIG. 3, support members 30 and 35 are bilaterally symmetrical and have branch pipes 33 and 34 and 38 and 39 communicating with an inlet 32 and an outlet 37, respectively.
And 38 and 34 and 39, sensor tubes 40a and 40b, which are straight pipes of the same size, communicate in parallel with each other and are fixedly supported. An exciter 4 composed of coils 41a and 41b is provided at the center of the sensor tubes 40a and 40b.
1, the coil 41a is disposed on the sensor tube 40a side, the core 41b is disposed on the sensor tube 40b side, and the core 41b is disposed in the center of the coil 41a, and the excitation in the sensor tubes 40a and 40b is further performed. Between the support point of the container 41 and the support members 30 and 35,
A detector 43 including a magnet 43a and a coil 43b, and a detector 42 including a magnet 42a and a coil 42b are provided. These detectors 42 and 43 and the exciter 41
Is connected to the converter 44.

[0006] In the Coriolis flow rate type shown in FIG. 3, first, a coil 41 of an exciter 41 is driven by a converter 44, and a detection voltage output to one of the detection coils of the detector 42 or 43 is supplied to the converter 44. A closed loop for positive feedback is formed, and the coil 41a is controlled to have a constant amplitude so as to attract and repel the core 41b.
Vibration is performed in the opposite phase to 0b. Since the sensor tubes 40a and 40b, through which the fluid flows due to the excitation, are driven in opposite rotational directions with respect to the support point, the detector tubes 4a and 4b
A vibration detection signal by excitation, a Coriolis force proportional to the vector product of the rotational angular velocity and the mass flow rate are superimposed on 3 and 42, and a phase difference signal proportional to the Coriolis force is provided between the detectors 42 and 43. It is detected and converted into a mass flow rate by the converter 43 and output.

The above-mentioned straight tube type Coriolis flowmeter is mounted coaxially with the pipe by joining flanges 31 and 36 between pipe flanges (not shown). However, the pipe shaft is generally not necessarily coaxial but slightly curved. Also,
The distance between the pipe flanges and the distance between the flanges 31 and 36 including the thickness of the sealing material such as packing generally do not match. Further, a change in the temperature of the measurement fluid and a change in the environmental temperature occur. The above personnel give stress changes such as bending stress and tensile compression to the sensor tubes 40a and 40b which are the main parts of the Coriolis flow rate type. These changes in stress cause changes in the natural frequencies of the sensor tubes 40a and 40b and asymmetric changes in amplitude, and as a result, there has been a problem that the instrumental difference of the Coriolis flowmeter changes greatly.

[0008]

[Object] The present invention has been made in view of the above circumstances,
Utilizing the features of the straight pipe type, the effects of compression, tension, and bending on the Coriolis flow meter that occur when the pipe is installed are reduced, and the thermal expansion effect on the temperature of the fluid and environmental temperature changes is eliminated, resulting in excellent stability. It is an object of the present invention to provide a straight tube type Coriolis flowmeter.

[0009]

To achieve the above object, the present invention provides (1)
An outer cylinder in which a first support plate is fixed near one flange and a second support plate is fixed near the other flange in a cylinder having flanges at both ends for connection to a pipe through which a measurement fluid flows. A parallel sensor tube having one end fixed to the first support plate and the other end movably supported by the second support plate in a liquid-tight manner, and through which the measurement fluid flows; A base holder movably supported by the outer cylinder and holding the parallel sensor tube at both ends, and an excitation disposed at the center of the sensor tube and driving the sensor tube in opposite phase in a direction perpendicular to the axis. And a pair of detectors disposed on the sensor tube at positions symmetrical to the vibrator and detecting a phase difference of the sensor tube based on Coriolis force. )
The base holder and the sensor tube are made of the same material. Hereinafter, a description will be given based on examples of the present invention.

FIG. 1 is a longitudinal sectional view for explaining an example of a Coriolis flow meter according to the present invention. In FIG.
2, 3 are flanges, 4 is an inlet, 5 is an outlet, and 6 is a first.
Support plate, 7 is a second support plate, 8 is a base holder, 9, 10
Is a base plate, 11 and 12 are sensor tubes, 13
Is an exciter, 14 and 15 are detectors, 16 is a support projection, 17
Is an O-ring.

In FIG. 1, an outer cylinder 1 is a tubular body having an inflow port 4 and an outflow port 5 at both ends and an intermediate portion 1a having an enormous constant cross section. (Not shown). A first port having through holes 6a and 6b near the boundary between the inlet 4 of the inlet 4 and the intermediate portion 1a.
The support plate 6 is fixed to the outer cylinder 1, and the second support plate 7 having through holes 7 a and 7 b provided with O-rings 17 near the boundary between the outlet 5 of the outlet 5 and the intermediate portion 1 a is formed by the outer cylinder 1. It is stuck to. One ends of straight sensor tubes 11 and 12 are fixed to the through holes 6a and 6b of the first support plate 6, respectively, and the other ends penetrate through the through holes 7a and 7b, respectively, and are axially fluid-tight by an O-ring 17. The sensor tube 1 is movably supported in the
1 and 12 are arranged in parallel.

A cylindrical base holder 8 having a diameter smaller than the inner diameter of the outer cylinder 1 is disposed coaxially with the outer cylinder 1 in an intermediate portion 1 a of the outer cylinder 1. Both end faces of the base holder 8 are a base plate 9 and a base plate 10, respectively. The base plates 9 and 10 have through holes 9a, 9b and 10 through which sensor tubes 11, 12 having one end fixed are penetrated.
a, 10b are perforated. The sensor tube 11 is fixed to the base holder 8 with through holes 9a and 10a,
The sensor tube 12 is fixed by the through holes 9b and 10b.

On the outer peripheral surface of the base holder 8 on the outlet 5 side, a plurality of level support projections 16 or annular support projections 1 are provided.
The base holder 8 is movably supported on the inner wall surface of the outer cylinder 1 at the free ends of the sensor tubes 11 and 12. The shape of the support portion of the support protrusion 16 may be spherical or needle-like. The point is that the base holder 8 is
Can be supported so as to be movable.

The sensor tube 11 is located between the base plates 9 and 10 which support the sensor tubes 11 and 12.
An exciter 13 is attached to and 12. Exciter 13
Is composed of, for example, a yoke 13a and a coil 13b. The yoke 13a is fixed to the sensor tube 11 and the coil 13b is fixed to the sensor tube 12, and the coil 13b has a predetermined frequency, preferably the natural vibration of the sensor tubes 11, 12. Driven by the number of excitation power supplies, the sensor tube 11
And 12 are driven in opposite phases in a direction perpendicular to the axis.

Regarding the exciter 13, the sensor tube 11,
The detectors 14 and 15 are mounted at twelve symmetric positions. The detectors 14 and 15 have the same characteristics.
a, 15a and coils 14b, 15b,
4a and 15a are connected to the sensor tube 11 and coils 14b and
When the sensor 15b is fixed to the sensor tube 12 and driven by the exciter 13, a phase difference signal of the sensor tubes 11, 12 generated in proportion to the Coriolis force is detected.

The Coriolis flowmeter configured as described above is:
When the pipe is connected, if a bending moment as shown by arrows FP acts, the outer cylinder 1 is bent in the P direction with the flanges 2 and 3 as fulcrums. In accordance with the bending, compression occurs on the upper side in the figure of the outer cylinder 1 and expansion occurs on the lower side. However, the support protrusions 16 move in opposite directions on the A side and the B side to prevent the bending stress from acting on the base holder 8. . Therefore, no stress acts on the sensor tubes 11 and 12 fixed to the base plates 9 and 10 in the base holder 8.

When a compressive force or a tensile stress acts between the flanges 2 and 3 to change the length, the sensor tubes 11 and 12 are fixed by the first support plate 6 and the second support portion 7 side is a free end, so the sensor tube 1
Since no external force acts on the sensor tubes 1 and 12, and the sensor tubes 11 and 12 are fixed at both ends in the base holder 8, the vibration conditions of the sensor tubes 11 and 12 do not change.

The same effect is obtained when the environment of the Coriolis flow meter changes. However, if the material of the sensor tubes 11 and 12 is different from the material of the base holder 8 and there is a difference in thermal expansion, thermal distortion occurs and changes in the natural vibration of the sensor tubes 11 and 12. It is necessary to select the same material for the tubes 11, 12 and the base holder 8. In order to completely eliminate thermal expansion, it is necessary to use a constant expansion material such as invar.

FIG. 2 is a view showing a structure in which the base plate and the first support plate of FIG. 1 are integrated. In FIG. 2, reference numeral 20 denotes a main support member. The same reference numbers are given.

The main support member 20 has a structure in which the base plate 9 and the first support member 6 shown in FIG. 1 are integrally formed to support the sensor tubes 11 and 12 at two points. The number of parts is small and machining accuracy is improved. The second support member 7 for movably supporting the free ends of the sensor tubes 11 and 12 is formed integrally with the base plate 10, and the support protrusion 16 is formed on the integrated structure member. The same effect can be obtained by supporting with a.

[0021]

As is clear from the above description, according to the present invention, a straight tube type Coriolis flowmeter is constructed and a parallel sensor tube is fixed at one end in an outer cylinder integral with a mounting flange.
The other end is a free end, and furthermore, a predetermined structure of the sensor tube is double-supported and fixed by a base holder supported at a single point on the outer cylinder in the outer cylinder. The influence of thermal stress due to thermal expansion can be further eliminated without being affected by piping stress when attached between the pipe flanges, and a stable straight pipe Coriolis flowmeter can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view for explaining an example of a Coriolis flow meter according to the present invention.

FIG. 2 is a diagram showing a structure in which a base plate and a first support plate of FIG. 1 are integrated.

FIG. 3 is a view for explaining a conventional straight tube type Coriolis flow meter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Outer cylinder, 2, 3 ... Flange, 4 ... Inlet, 5 ... Outlet, 6 ... First support plate, 7 ... Second support plate, 8 ... Base holder, 9, 10 ... Base plate, 11, 12 ... Sensor tube, 13 ... Exciter, 14, 15 ... Detector, 16 ... Support protrusion, 20 ... Main support member.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 1/84

Claims (2)

(57) [Claims] 1. A cylindrical body having flanges at both ends for connection to a pipe through which a measurement fluid flows. A first support plate is fixed near one flange in the cylinder, and a second support plate is mounted near the other flange. And a parallel sensor tube having one end fixed to the first support plate and the other end movably supported by the second support plate in a liquid-tight manner, and through which a measurement fluid flows. The second support plate is movably supported by the outer cylinder,
A base holder for holding the parallel sensor tube at both ends, an exciter disposed at the center of the sensor tube, and driving the sensor tube in an opposite phase in a direction perpendicular to the axis;
A Coriolis flowmeter, comprising: a pair of detectors disposed on the sensor tube at positions symmetrical to the vibrator and detecting a phase difference of the sensor tube based on Coriolis force. 2. The Coriolis flowmeter according to claim 1, wherein the base holder and the sensor tube are made of the same material.