CN105953852B

CN105953852B - Mass flowmeter

Info

Publication number: CN105953852B
Application number: CN201610366153.7A
Authority: CN
Inventors: 杨云博
Original assignee: Beijing Xinhua Department Of Instrument Science And Technology Co ltd
Current assignee: Beijing Xinhua Department Of Instrument Science And Technology Co ltd
Priority date: 2016-05-27
Filing date: 2016-05-27
Publication date: 2022-04-29
Anticipated expiration: 2036-05-27
Also published as: CN105953852A

Abstract

The present invention relates to a mass flowmeter. The mass flow meter includes a sealed housing and a measurement assembly disposed within the housing. The measuring assembly comprises a vertically arranged float disc, which is spaced apart from the inner wall of the housing and is capable of damped movement within the housing, and a measuring tube, which is connected fixedly to the float disc by two spaced apart fastening elements, as a fluid flow path. The portion of the measuring tube lying between the two mountings forms a single measuring section, in which the vibration exciter and the detector are arranged. The mass flow meter according to the invention has only one measuring tube, so that a high accuracy of the mass flow meter is ensured.

Description

Mass flowmeter

Technical Field

The invention relates to a metering device, in particular to a mass flowmeter.

Background

In various fields of petrochemical industry, natural gas, medicine, food, etc., it is required to precisely meter or control the flow rate of a fluid, and in such a case, a flow meter must be used. The most common flowmeter is the coriolis mass flowmeter, which has many advantages including high accuracy, reliability, and stability.

In the prior art, a conventional coriolis mass flowmeter usually comprises a housing, two measuring tubes arranged in parallel or two parallel measuring sections twisted from one measuring tube, a flow splitter, an exciter and a detector. In order to achieve a high measurement accuracy of the coriolis mass flowmeter, it is necessary that the two measuring tubes or the two measuring segments are identical and that the quantities of fluid in the two measuring tubes are also identical. However, in practical cases, it is difficult to satisfy the above-described conditions, which results in difficulty in controlling the measurement accuracy of the coriolis mass flowmeter.

Disclosure of Invention

In view of the above problems, the present invention provides a mass flowmeter. The mass flow meter according to the invention has only one measuring tube, so that a high accuracy of the mass flow meter is ensured.

The mass flow meter according to the invention comprises a closed housing and a measuring assembly arranged in the housing. The measuring assembly comprises a vertically arranged float disc, which is spaced apart from the inner wall of the housing and is capable of damped movement within the housing, and a measuring tube, which is fixedly connected to the float disc by two spaced apart fastening members, which serves as a fluid flow path. The portion of the measuring tube lying between the two mountings forms a single measuring section, in which the vibration exciter and the detector are arranged.

The mass flow meter according to the invention has only one measuring tube and a single measuring section, which completely eliminates all measuring errors caused by two measuring tubes or two measuring sections, thereby greatly improving the measuring accuracy of the mass flow meter. Because the floating disc is not contacted with the shell and does damping motion, the vibration change of the external environment hardly influences the vibration states of the floating disc and the measuring pipe on the floating disc, namely, the adverse effect of the external environment on the measuring precision is almost completely avoided, and the measuring precision of the mass flow meter is further and greatly improved. Furthermore, since there is only one measuring tube, no fluid splitter is required, which simplifies the construction of the mass flow meter and reduces its manufacturing costs.

In one embodiment, the float is connected to the inner wall of the housing and supported inside the housing by a plurality of elastic members disposed in a vertical plane. The elastic piece not only can absorb the vibration transmitted to the inside of the shell from the outside, but also can reduce the vibration of the floating disc caused by the vibration of the measuring pipe as much as possible, so that the vibration state of the measuring pipe is kept not to be disturbed or changed to the greatest extent, and the measurement precision of the mass flow meter is improved.

In one embodiment, an even number of elastic members are provided, and the even number of elastic members are symmetrically arranged. When the measuring tube vibrates, the floating disc is subjected to alternating vibratory forces of the measuring tube, which produces vibration. Through the elastic element of symmetrical arrangement, can avoid floating plate and casing to produce resonance, vibration energy can not pass to the casing through the elastic component promptly, and the vibration that comes from the external world simultaneously also can not pass to the floating plate through the elastic component, influences the vibration of surveying the buret. Therefore, the measurement accuracy of the mass flowmeter is greatly improved.

In one embodiment, the ratio of the mass of the float disk to the mass of the measurement tube is at least 1000: 1. That is, the mass of the float is much greater than the mass of the measurement tube (even if it is filled with the liquid being measured), which causes the natural frequency of the float to be much greater than the natural frequency of the measurement tube. For example, a ratio of the mass of the float plate to the mass of the measuring tube of at least 1000:1 means: at the same elastic coefficient, the natural frequency of the floating disc is 31.6 times lower than that of the measuring tube, so that the resonance of the floating disc and the measuring tube can be almost completely avoided, which contributes to further improving the measuring accuracy of the mass flowmeter.

In one embodiment, the resilient member is a spring. The spring has a coefficient of elasticity k =4 ± 0.5 kgf/mm. When the spring has an elastic coefficient of less than 3.5kgf/mm, the spring may be deformed to make it difficult to stably support the floating plate. When the spring has a spring constant greater than 4.5kgf/mm, the spring is difficult to be stretched or compressed by an external force, which results in an approximately rigid connection between the float and the housing. The rigid connection cannot isolate external vibration and prevent the vibration energy of the floating disc (or the measuring pipe) from being transmitted outside, thereby adversely affecting the measurement accuracy of the mass flow meter.

In a preferred embodiment, the spring is mounted in a pre-stressed manner. The pre-stressed spring will apply a force to the float from all directions to ensure that the float can only move within a small range. Therefore, even if the mass flow meter is subjected to extremely large collision accidentally, the floating disc cannot move violently in the shell, and the measuring pipe and the mass flow meter are protected greatly. In one embodiment, the pre-compression of the spring may be 1-1.6 mm.

In a specific embodiment, the floating plate has a rectangular parallelepiped shape, and the number of the springs is 4 and is connected to four side walls of the floating plate, respectively. Researchers have found that if a floating plate is supported by springs with a number greater than 4, at least two springs on the same side wall of the floating plate cause unstable vibration state of the floating plate due to different stress conditions, which greatly affects the measurement accuracy of the mass flowmeter. Therefore, according to the scheme of the invention, the situation that the vibration state of the floating disc is unstable can be avoided by only arranging one spring on each side wall, and the measurement precision of the mass flowmeter is further improved.

In one embodiment, the vibration exciters are arranged at the centre of the measuring section and the detectors are two in number and arranged symmetrically about the exciters. The exciter vibrates the measuring section of the measuring tube via a closed-loop control system. When no fluid exists in the measuring tube, the signals detected by the two vibration detectors are homodromous signals, namely the signals have no phase difference. When the fluid flows through the measuring tube, due to the Coriolis effect, the signals detected by the two vibration detectors are shifted in phase, i.e. a phase difference is generated, and the phase difference is in direct proportion to the mass flow of the fluid in the measuring tube, so that the mass flow of the fluid is measured.

In one embodiment, the measuring section comprises two extension zones extending in a vertical direction and a measuring zone extending in a horizontal direction and communicating with the two extension zones. The exciter is located at the center of the measurement region, and the two vibration detectors are located at the connection of the measurement region and the extension region. The junction of the measurement region and the extension region is the bend of the entire measurement section, so the vibration detector can measure the maximum phase shift at the junction, which helps to improve the measurement accuracy of the mass flow meter.

In one embodiment, the housing may also be filled with a dry inert gas. For example, nitrogen gas, carbon dioxide gas, or the like may be used. These gases prevent the elastic member, the floating plate, and the measurement pipe from being corroded, thereby enabling the mass flow meter to maintain stable performance for a long time.

In one embodiment, the region of the measuring tube outside the two fastening elements forms an inlet section and an outlet section, on which the temperature sensor is arranged. Based on the data measured by the temperature sensor, the sensitivity of the measuring tube to the vibration frequency and mass flow due to changes in the temperature of the liquid can be compensated for.

Compared with the prior art, the invention has the advantages that: (1) the mass flow meter of the invention has only one measuring tube and one measuring segment, which completely eliminates all measuring errors caused by two measuring tubes and/or two measuring segments, thereby greatly improving the measuring precision of the mass flow meter. (2) The setting of floating plate makes external environment can not influence the vibration state of surveying buret on floating plate and the floating plate almost, has still avoided the vibration transmission of floating plate to outside casing and the casing moreover, and this makes mass flow meter's measuring accuracy obtain further improving by a wide margin. (3) Since there is only one measuring tube, there is no need to provide a flow divider, which simplifies the construction of the mass flow meter and reduces its manufacturing costs.

Drawings

The invention will be described in more detail hereinafter on the basis of embodiments and with reference to the accompanying drawings. Wherein:

fig. 1 schematically shows the structure of a mass flow meter according to a first embodiment of the present invention.

Fig. 2 is a view in the direction a of fig. 1.

Fig. 3 schematically shows a measuring tube.

Figure 4 schematically shows a floating disc.

Fig. 5 schematically shows another type of measuring tube.

In the drawings, like parts are provided with like reference numerals. The drawings are not to scale.

Detailed Description

The invention will be further explained with reference to the drawings.

Fig. 1 is a schematic structural diagram of a mass flow meter 1 according to a first embodiment of the present invention. As shown in fig. 1, the mass flow meter 1 includes a sealed case 2 and a measurement unit 3 disposed in the case 2. The measuring unit 3 comprises a vertically arranged float disk 4 and a measuring tube 5 fixedly mounted on the float disk 4, on which measuring tube 5 a vibration detector 61 and

detectors

62, 63 are mounted. The inlet section 57 and the outlet section 58 of the measuring tube 5 extend outside the housing 2, so that the fluid to be measured can flow out of the measuring tube 5 (or the mass flow meter 1). It will be appreciated that the locations where the inlet and outlet of the measurement tube 5 pass through the housing 2 are also sealed. The float 4 is spaced from the inner wall of the housing 2 and is dampable in its movement within the housing 2. The applicant explains the damping movement of the float 4 as follows: the vibrating float 4 is subjected to a resistance force so that its motion amplitude is gradually attenuated with time. This movement is very similar to the damped vibration of a spring vibrator.

As shown in fig. 1 and 4, the floating plate 4 has a substantially rectangular parallelepiped shape. Of particular note are: the measuring section 53 of the measuring tube 5 should be completely within the confines of the float disk 4. In one embodiment, the length L of the float 4 is 30-50 mm greater than the effective length of the measuring section 53, and the width W is 30-50 mm greater than the effective width of the measuring section 53, so as to ensure that the measuring section 53 and the components mounted thereon are within the confines of the float 4. Of course, the float 4 may have any other suitable size or shape. In the embodiment shown in FIG. 1, the length L and width W of the float 4 define a mounting surface 41 of the float 4; the length L or width W and thickness D define the sides 42 of the float 4. The measuring tube 5 is fixedly mounted on the mounting surface 41 of the float 4 by two spaced-apart

mountings

51, 52.

The ratio of the mass of the float 4 to the mass of the measuring tube 5 is at least 1000: 1. This makes the natural frequency of the floating plate 4 significantly different from the natural frequency of the measuring pipe 5, and resonance of the floating plate 4 with the measuring pipe 5 can be almost completely avoided, which contributes to further improving the measurement accuracy of the mass flow meter 1.

In order to achieve a damped movement of the float 4, in the embodiment shown in fig. 1 four

springs

11, 12, 13, 14 arranged in a vertical plane are used to connect the float 4 with the housing 2. For example, the spring 11 is connected between the top side wall 421 of the floating plate 4 and the housing 2, the spring 12 is connected between the bottom side wall 422 of the floating plate 4 and the housing 2, the spring 13 is connected between the lateral side wall 423 of the floating plate 4 and the housing 2, and the spring 14 is connected between the lateral side wall 424 of the floating plate 4 and the housing 2. Thus, the

springs

11 and 12 apply force to the floating plate 4 only in the vertical direction, and the

springs

13 and 14 apply force to the floating plate 4 in the horizontal direction and the vertical direction. The floating disc 4 is spaced from the housing 2 by the support of the

springs

11, 12, 13, 14. In addition, when the float 4 vibrates, the springs absorb the vibration to provide a damping motion to the float 4. The use of

springs

11, 12, 13, 14 for supporting the float 4 is advantageous, since these springs can absorb vibration energy from the environment in order to avoid that external vibrations disturb the vibrations of the measuring tube 5. In addition, these springs can also absorb the vibration energy of the floating plate 4 to reduce the vibration amplitude thereof. In this way, the measurement accuracy of the mass flow meter 1 can be greatly improved.

Preferably, the four

springs

11, 12, 13, 14 are arranged symmetrically. In this way, when the float 4 vibrates, the springs provided to face each other can apply a force in the same direction to the float 4, which contributes to reducing the vibration of the float 4 or maintaining the float 4 in a stable vibration state, thereby improving the measurement accuracy of the mass flowmeter 1. In addition, when the measuring pipe 5 vibrates, the four

springs

11, 12, 13, 14 arranged symmetrically can prevent the floating plate 4 from generating resonance with the shell 2, namely, vibration energy can not be transmitted to the shell 1 through the springs, and vibration from the outside can not be transmitted to the floating plate 4 through the springs, so that the measuring precision of the mass flowmeter 1 is greatly improved.

The four springs 11, 12, 13, 14 are also mounted in a pre-stressed manner. For example, the pre-compression of the spring may be 1-1.6 mm. These pre-stressed springs apply force to the float 4 from all directions to ensure that the float 4 can only move within a small range. Thus, even if the mass flow meter 1 is subjected to an unexpected large impact, the floating plate 4 does not move violently in the casing, which provides a great protection for the measuring tube 5 and the mass flow meter 1.

The spring constants of these springs were k =4 ± 0.5 kgf/mm. It will be appreciated that the spring constants of these springs may be different from each other, for example, the spring constants of the

springs

13 and 14 may be larger than those of the

springs

11 and 12, since the weight of the floating plate 4 and the components provided thereon may cause the

springs

13 and 14 in the horizontal direction to bend downward, which is disadvantageous for stabilizing the vibration state of the floating plate 4 or reducing the vibration of the floating plate 4. Further, the spring constant of these springs should not be excessively large (e.g., greater than 4.5 kgf/mm), because the excessively large spring constant greatly reduces the ability of the springs to absorb vibration, which is also not advantageous in stabilizing the vibration state of the floating plate 4 or reducing the vibration of the floating plate 4. Also, the spring constant of the spring should not be too small (e.g., less than 3.5 kgf/mm), because the too small spring constant makes the spring unable to support the floating plate 4, and is also not advantageous in stabilizing the vibration state of the floating plate 4 or reducing the vibration of the floating plate 4.

It will be appreciated that any other type of resilient member may be used instead of the springs described above, such as rubber cushions or the like, and will not be described in further detail herein.

In the exemplary embodiment shown in fig. 1, the region of the measuring tube 5 between the

fastening elements

51, 52 forms a measuring section 53, while the regions outside the

fastening elements

51, 52 form an inlet section 57 and an outlet section 58. Preferably, the measurement section 53 includes two

extension areas

54, 55 extending in the vertical direction and a measurement area 56 extending in the horizontal direction and communicating with the two

extension areas

54, 55. Overall, the measuring section 53 is symmetrical, with the axis of symmetry being a perpendicular extending through the center of the measuring region 56. Furthermore, the measuring tube 5 is integrally formed, for example, by bending a straight measuring tube 5 to obtain the

extension regions

54, 55 and the measuring region 56. The measuring section 53 may also be of any other suitable shape, for example generally trapezoidal in form (as shown in fig. 5).

In the embodiment shown in figure 1, the vibration exciter 61 is located at the centre of the measurement region 56 and the

vibrators

62, 63 are located at the junction of the measurement region and the extension region. Overall, the

resonators

62, 63 are symmetrical with respect to the actuator 61. In the measuring tube 5 shown in fig. 5, the exciter 61 and the

vibration detectors

62, 63 may also be similarly arranged. Both the exciter 61 and the

vibrators

62, 63 are devices commonly used in the art. For example, the exciter 61 is used to vibrate the measuring section 53, and the

vibration pickups

62, 63 detect the vibration data of the measuring section 53, from which the mass flow rate of the fluid flowing through the measuring tube 5 can be calculated on the basis of the coriolis effect. The measurement principle will not be explained in detail here.

In order to further increase the measurement accuracy of the mass flowmeter 1, a temperature sensor 7 may also be provided on the inlet section 57 or the outlet section 58 of the measurement pipe 5. Since the measuring section 53 starts from the

fixtures

51, 52, the temperature sensor 7 provided on the inlet section 57 or the outlet section 58 does not affect the vibration of the measuring section 53, and thus the measurement accuracy of the mass flowmeter 1.

In addition, dry inert gas may be filled in the case 2. For example, nitrogen gas, carbon dioxide gas, etc. These gases prevent the spring, the floating plate 4, and the measurement pipe 5 from being corroded, thereby enabling the mass flow meter 1 to maintain stable performance for a long time.

While the invention has been described with reference to a preferred embodiment, various modifications may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In particular, the technical features mentioned in the embodiments can be combined in any way as long as there is no structural conflict. It is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A mass flowmeter comprises a closed shell and a measuring assembly arranged in the shell,

the measuring assembly comprises a vertically arranged float disc and a measuring tube serving as a fluid flow path, the float disc being spaced apart from the inner wall of the housing and being capable of damped movement within the housing, the measuring tube being fixedly connected to the float disc by two spaced apart fixing elements,

the part of the measuring tube between the two mountings forms a single measuring section, in which a vibration exciter and a detector are arranged; the floating disc is connected with the inner wall of the shell through a plurality of elastic pieces arranged in a vertical plane and is supported in the shell; the elastic piece is a spring, the spring is installed in a pre-compression mode, the floating disc is cuboid, the number of the springs is 4, the springs are respectively connected with the four side walls of the floating disc, and the 4 springs are symmetrically arranged.

2. A mass flow meter according to claim 1, wherein the housing is filled with a dry inert gas.

3. A mass flow meter according to claim 1, wherein the ratio of the mass of the float disc to the mass of the measurement pipe is at least 1000: 1.

4. A mass flow meter according to any of claims 1 to 3, wherein the vibration exciters are provided at the centre of the measurement section, and the detectors are two in number and are provided symmetrically about the exciters.

5. A mass flow meter according to claim 4, wherein the measurement section comprises two extension zones extending in a vertical direction and a measurement zone extending in a horizontal direction and communicating with the two extension zones,

the exciter is located at the center of the measuring region, and the two vibration detectors are located at the connection of the measuring region and the extension region.