CN101858765A - Quasi straight tube Coriolis mass flow meter - Google Patents

Abstract

Quasi-straight tube type Coriolis mass flowmeter, used for direct and high-precision measurement of mass flow, including: two straight tube type measuring tubes with the same structure and parallel, vibrator, two detectors, four constant distance plate, two flanges, two end connecting pipes, two flow dividers and four counterweights; the invention effectively improves the characteristics and quality factor of the resonant sensor, greatly reduces the volume of the flowmeter, reduces The influence of the flow field, small flow resistance, low pressure loss, simple installation and processing, the measuring tube has good dynamic balance characteristics, and can measure the mass flow rate of liquids with high viscosity and high impurity content, which will further expand the Coriolis mass flowmeter. Wide range of applications to meet the needs of industrial development for the accuracy and range of flow measurement. It has a great promotion effect on saving raw materials, reducing production costs, reducing environmental pollution, improving profit margins and product quality.

Description

Quasi straight tube Coriolis mass flow meter

technical field

The invention relates to a Coriolis mass flowmeter (CMF), in particular to a straight-tube type Coriolis mass flowmeter, which belongs to the field of testing and measuring instruments and is used for direct and high-precision measurement of mass flow.

Background technique

The development of mass flow measurement technology is the focus of the development of national science and technology in the field of process control. In order to achieve high-accuracy and high-reliability measurement of various media under complex environmental conditions, Coriolis Mass Flowmeter (CoriolisMass Flowmeter, CMF, also known as Coriolis mass flowmeter) has become one of the important development technologies in this field because of its superior performance, and it meets the major needs of the country. CMF can directly measure the mass flow of the fluid in the pipeline with high accuracy, and use the Coriolis effect generated when the fluid flows through the vibrating pipeline to affect the vibration phase or amplitude at both ends of the pipeline to measure the quality and stability of the fluid flowing through the pipeline. Good, high reliability, large range ratio, suitable for high viscosity fluids and other characteristics.

The Coriolis mass flowmeter is measured by the principle that when the fluid flows in the vibrating tube, a Coriolis force proportional to the mass flow rate will be generated. At present, people generally use the vibrating tube type Coriolis principle flowmeter, which is mainly composed of a primary instrument and a secondary instrument. The primary instrument (that is, the sensitive unit a of the Coriolis mass flow sensor includes measuring tubes a1, a2, excitation device a5 and vibration pickup a3, a4; secondary instrument b includes closed-loop control unit b1 and flow solution unit b2, which are the control and signal processing systems of the primary instrument respectively. The primary instrument (i.e. Coriolis mass flow sensor) is Sensitive components output vibration signals related to the measured flow; closed-loop control unit b1 provides excitation signals to the exciter a5 to keep the measuring tubes in a resonant state, and track the vibration frequencies of the measuring tubes a1 and a2 in real time; The calculation unit b2 processes the output signals of the sensor vibrators a3 and a4 and outputs measurement information, from which the mass flow and density of the measured fluid can be determined, as shown in Figure 8.

The traditional vibrating tube CMF is divided into single tube type and double tube type according to the configuration of the measuring tube. The single-tube type is easily disturbed by external vibrations, and the double-tube type is often used. Since the two tubes have the same shape and similar natural frequency, they are easy to vibrate, but the flow conditions of the measured medium in the two tubes are the same, and the phases of the up and down vibrations are opposite. The effect produced by the force is also opposite, and the entire flowmeter is always in a state of force balance. In fact, because the pipe-end distributor cannot guarantee that the flow rates in the two pipes are absolutely equal, it is also impossible to ensure that the deposits and wear in the two pipes are also absolutely consistent. At the same time, it is difficult to ensure that the two pipes are thoroughly cleaned at the same time, so the measurement will occur. Cause zero drift, resulting in additional errors. At present, most of the products are still double-tube type. This structure is easier to realize phase measurement, which is compatible with the current technology and process level.

According to the shape of the measuring tube, there are bent tube type and straight tube type. The elbow type is mainly composed of an elbow section and a straight pipe section. In the prior art, many shapes of pipe types are disclosed, such as U-type, Ω-type, △-type, ring-type, C-type, B-type, T-type, Water drop type, fly swatter type. The pipe wall is thicker, the rigidity is small, and it is less affected by corrosion; its resonance frequency is also low, generally 70-120Hz; the phase difference reflecting the mass flow rate is milliseconds, and the electronic signal is easier to process; but the elbow type is easy to accumulate Gas and fluid residues cause additional errors, and the manufacturing process is more complicated than the straight tube type. In terms of technology development, due to the volume size, structural shape, and performance characteristics of the traditional elbow-type CMF sensor are constrained by the installation environment and measurement requirements, which seriously restrict the development needs, requiring it to be small in size, low pressure loss, high precision, Develop in the direction of high sensitivity, good stability, and easy processing. The mainstream technology and products of CMF sensors are mostly U-shaped and △-shaped measuring tube structures, which have large volume and pressure loss.

The straight tube type is opposite to the curved tube type. Due to its high rigidity and high resonance frequency, it is generally 700~1000Hz, and its amplitude is small, about 60μm; due to its high frequency, it is relatively different from the general mechanical vibration frequency in industry. Large, so it is not easy to be disturbed by external vibration; it is not easy to accumulate gas and residue, and the overall size is small; in order to prevent the resonance frequency from being too high, the tube wall is designed to be thinner, about 1/4~1/ of the elbow 2, so the wear resistance and corrosion resistance are poor. However, the phase difference is on the order of microseconds, and the processing of electrical signals is difficult, which seriously limits the measurement range of CMF, and the sensitivity of this traditional vibrating straight tube CMF is low and is affected by temperature fluctuations. The straight tube type or similar straight tube type CMF developed and applied at home and abroad, such as the published patents are: Coriolis mass flowmeter (patent application number is 00129058.4), which is made into a bow that bends in one direction. It is a curved pipe, the flow rate is not stable, and the fluid is easy to generate adsorption and precipitation on the inner wall of the pipe; the installation and processing are complicated, and the dynamic balance characteristics are poor.

At present, there are some restrictive factors in the developed CMF: for example, the overall performance of the CMF measuring tube design is poor, the installation of the pipeline is unstable, and the mechanical realization of the tube shape is difficult; the CMF is sensitive to external vibration interference; the CMF system cannot be used for Measure low density media. When measuring gas-containing liquids, if the gas content is too large, the measurement accuracy will be affected; the measuring tube is affected by the design, processing and installation process, and its dynamic balance characteristics are poor, which directly affects the performance of the CMF and is irreversible.

Therefore, it is necessary to design a new type of straight pipe that combines the advantages of traditional bent pipe and straight pipe. The quasi-straight tube Coriolis mass flowmeter of the present invention is designed for the above problems. Its volume is small, the influence of the flow field is small, the flow resistance is small, the low pressure loss is simple, the installation and processing are simple, and the measuring tube has good dynamic balance. It can measure the mass flow rate of liquids with high viscosity and high impurity content. The overall performance of CMF is high and the measurement range is wide. Further enriching the types of CMF products and increasing core competitiveness is also one of the trends in the development of this type of sensor.

Contents of the invention

The technology of the present invention solves the problem: Overcoming the deficiencies of the prior art, a straight tube type Coriolis mass flowmeter is provided, which greatly reduces the volume of the flowmeter, reduces the influence of the flow field, and has low flow resistance and low pressure. The measuring tube has good dynamic balance characteristics, and can measure the mass flow of liquid with high viscosity and high impurity content, which improves the overall performance and measurement range of CMF.

The technical solution of the present invention: a quasi-straight tube type Coriolis mass flowmeter, which is characterized in that it includes: two quasi-straight tube type measuring tubes with the same structure and parallel, a vibrator, two detectors, four Spacer plate, two flanges, two end connection pipes, two flow dividers, housing;

The two flanges are symmetrically located at the outermost ends of the flowmeter, and are integrally formed with the two end connecting pipes; the two end connecting pipes are respectively connected to the quasi-straight pipe type measuring pipe through two flow dividers. Two flow dividers distribute the process medium evenly into two parallel straight-like measuring tubes;

The middle of the straight pipe type measuring pipe is the first part of the straight pipe section, and the left and right halves are symmetrical with respect to the center line of the first part of the straight pipe section. , The second part of the arc pipe section, the second part of the straight pipe section, each part adopts a smooth arc transition;

The vibrator is used in conjunction with a coil and a magnet coaxially. The vibrator is installed at the central axis of two similar straight tube-type measuring tubes. The coil of the vibrator is installed on a quasi-straight tube type measuring On the tube, the magnet of the exciter is installed on another type of straight tube measuring tube;

The two detectors are used in cooperation with coils and magnets, and are located at the center of the first part of the arc pipe section;

Two spacer plates are respectively welded at the two ends of the two parallel quasi-straight tube-type measuring tubes, and the four spacer plates fix the two parallel quasi-straight tube-type measuring tubes;

The outer shell is welded and fixed to the outer end surfaces of the shunts at both ends, and has the functions of support, protection and vibration isolation.

Two counterweights are respectively provided on the two parallel straight tube-like measuring tubes, and the position and quality of each counterweight can be adjusted to ensure good dynamic balance characteristics of the measuring tubes.

The best installation positions of the two spacer plates at both ends of the straight tube type measuring tube are: one is located at the junction of the second part of the straight pipe section and the second part of the arc section, and is perpendicular to the second part of the straight pipe section; One at the center of the second partial arc segment and coincident with the normal of the second partial arc segment.

The distance between the centers of the two parallel quasi-straight tube-type measuring tubes is 2.5D-3D, and D is the outer diameter of the quasi-straight tube-type measuring tube.

There are two holes on the spacer plate with the same size as the outer diameter D of the quasi-straight tube type measuring tube, the distance between the two holes is 2.5D~3D, and the quasi-straight tube type measuring tube is fixed at the same time by vacuum brazing.

The principle of the present invention: according to the Coriolis effect, the two straight-tube measuring tubes are fixedly welded on both sides of the measuring tubes with double spacer plates, and the two measuring tubes are parallelly and firmly welded to the shunt, and The end connection tube is connected to form a tuning fork to eliminate the influence of external vibration. Under the excitation of the electromagnetic exciter, the two measuring tubes vibrate at their natural frequency, and the vibration phase is opposite. Due to the vibration effect of the measuring tube, each fluid microgroup flowing in the tube gets a Coriolis acceleration, and the measuring tube is subjected to a Coriolis force opposite to the acceleration direction. Because the Coriolis force on the inlet and outlet sides of the quasi-straight measuring tube is opposite, the measuring tube is twisted, and the twisting degree is inversely proportional to its torsional rigidity, and proportional to the instantaneous mass flow rate in the tube. The two electromagnetic detectors located on the inlet side and the outlet side of the measuring tube detect two vibration signals during each vibration of the tuning fork. The phase difference of the two signals is related to the twist of the detection tube, that is, the instantaneous flow rate Proportional. By calculating the phase difference between these signals, the mass flow rate can be calculated.

In summary, the present invention has the advantages compared with the prior art:

(1) The present invention adopts a new type of straight tube type, which effectively improves the characteristics and quality factor of the resonant sensor, greatly reduces the volume of the flowmeter, reduces the influence of the flow field, and has small flow resistance , Low pressure loss, can measure the mass flow of liquid with high viscosity and high impurity content, simple processing, low cost, and further improve the overall performance and measurement range of CMF.

(2) The present invention adopts a double-distance mode, that is, two distance plates are used on both sides of the measuring tube, and are connected and fixed by vacuum brazing. The optimal installation position of the distance plate in the present invention is determined by the modal analysis and harmonic response analysis in the finite element analysis, one is located at the junction of the lower straight pipe section and the arc section, and is perpendicular to the straight pipe section; the other is located at It is at the center of the lower arc segment and coincides with the arc normal. The resonant frequency of the measuring tube is high, the stability is good, and the shock resistance is strong.

(3) The measuring tube of the present invention is provided with a corresponding counterweight, and the position and quality of the counterweight can be adjusted. According to the characteristics of detecting the unbalance of each measuring tube itself, the counterweights of different masses are placed on the corresponding positions of the measuring tubes, so that the measuring tubes are completely symmetrical, and the measuring tubes have good dynamic balance characteristics to ensure that the sensor is under dynamic conditions. balance.

(4) The exciter and detector of the present invention are all used in conjunction with coils and magnets, the exciter is installed at the center of the straight pipe sections of the two relative measuring tubes, and the detector is positioned at the center of the circular arc pipe section on both sides of the upper end of the measuring tube place. Together form a good closed-loop system, so that the Coriolis sensor flow tube has a stable natural frequency working state, the influence of external disturbance is small, and the self-regulation ability is strong.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the straight tube type CMF of the present invention;

Fig. 2 is the front view of the structure of the straight tube type CMF of the present invention;

Fig. 3 is a top view of the structure of the straight tube type CMF of the present invention;

Fig. 4 is the schematic diagram of the mechanical structure of a single straight tube type measuring tube of the present invention;

Fig. 5 is the installation schematic diagram of sensor of the present invention;

Fig. 6 is a schematic diagram of the installation structure of the double distance plate of the present invention;

Fig. 7 is a structural schematic diagram of a distance plate of the present invention;

Fig. 8 is a structure diagram of a typical existing double U-tube CMF system.

Detailed ways

As shown in Fig. 1, the quasi-straight tube type CMF of the present invention comprises two quasi-straight tube type measuring tubes 1, 2 with the same structure and size, a vibrator 3, two detectors 4, 5, four fixed distance Plates 6, 7, 8, 9, two flanges 10, 11, two end connecting pipes 12, 13, two flow dividers 14, 15, housing 16, four counterweights 17, 18, 19, 20.

The two flanges 10, 11 are respectively located at the outermost ends of the CMF of the quasi-straight pipe type, and the two end connecting pipes 12, 13 are formed integrally with the two flanges 10, 11; The part between the two quasi-straight measuring tubes 1, 2 is called a flow divider 14, 15. Two flow dividers distribute the process medium evenly into the two measuring tubes. The measuring tube of the dual flow path is split and merged through the inlet and outlet splitters. Four spacer plates 6, 7, 8, 9 are fixedly welded on both sides of the quasi-straight tube type measuring tube 1, 2, and the two quasi-straight tube type measuring tubes 1, 2 are parallelly and firmly welded to the shunt 14 , 15, and connected with end connecting pipes 12,13. The shell 16 is welded and fixed to the outer end surfaces of the shunts 14 and 15 at both ends, and has the functions of support, protection and vibration isolation.

Assume that the fluid to be measured flows in on the left and flows out on the right. The fluid to be measured enters the flow divider 14 through the inlet port connecting pipe 12 connected by the flange 10, and is equally and evenly divided into two streams of fluid, and enters into two quasi-straight tube type measuring tubes 1 and 2, and two streams on the other side The fluid is converged through the flow divider 15 to the outlet connection pipe connected by the flange 11 .

As shown in Figure 1, four counterweights 17,18,19,20 of the present invention are correspondingly placed on two class straight tube type measuring tubes 1,2, the first part of the straight tube section 21 of each measuring tube Different positions are equipped with two corresponding counterweights, which make the measurement pipeline completely symmetrical and ensure the dynamic balance of the sensor.

As shown in Fig. 1, the two quasi-straight measuring tubes 1 and 2 vibrate at their natural frequency under the excitation of the electromagnetic exciter 3, and the vibration phase is opposite. Two detectors 4 and 5 (the detectors are electromagnetic detectors) located at the inlet and outlet sides of the two quasi-straight measuring tubes 1 and 2 detect two vibration signals, and the phase difference of the two signals is the same as The torsion of the measuring tube is directly proportional to the instantaneous flow rate. By calculating the phase difference between these signals, the mass flow rate can be calculated.

Detectors 4 and 5 are coaxially used by coils and magnets, and are installed in the center of the circular arc pipe sections 22 and 23 on both sides of the upper part of two parallel quasi-straight tube-type measuring tubes 1 and 2. The centers of the tubular measuring tubes 1 and 2 are symmetrical.

The vibrator 3 is installed at the central axis of the measuring tube, its coil is installed on one measuring tube 1 through a fixing piece, and the magnet is installed on the other measuring tube 2 . The vibrator 3 is used to excite the measuring tube, and make the measuring tube in a state of simple harmonic vibration through the closed-loop control system. The vibration exciter used in the present invention is used in conjunction with a coil and a magnet, and is respectively installed at the center of the first straight pipe section 21 of the two opposite measuring pipes to make the flow pipe of the Coriolis sensor vibrate at a natural frequency. When the coil is actuated, it causes the flow tube to vibrate at its normal frequency.

As shown in Fig. 4, the center of the two straight tube type measuring tubes 1 and 2 of the present invention is the first part of the straight tube section 21, and the first part of the straight tube section 21 is connected to the first part of the arc tube section 22, 23 in turn, oblique The pipe sections 24, 25, the second arc pipe sections 26, 27, the second straight pipe sections 28, 29, the left and right halves are symmetrical with respect to the center line of the first straight pipe section 21. Each part adopts a smooth arc transition, which reduces the influence of the flow field and the flow resistance is small. The first part of the straight pipe section 21 is used in the middle of the two quasi-straight pipe measuring pipes 1 and 2 to stabilize the flow rate, and the fluid is not easy to be adsorbed and precipitated on the inner wall of the vibrating pipe; the inclined pipe sections 24 and 25 can improve the Coriolis effect, improve sensitivity and range scope. This structure has the advantages of simple structure, small volume, easy cleaning, less wear, etc., and is suitable for self-emptying and cleaning. Therefore, the mass flow rate of oil, slurry, etc. with high viscosity and high impurity content can be determined.

The pipes of the two types of straight pipe measuring pipes 1 and 2 are generally 316L stainless steel, titanium, Hastelloy, and other materials. The present invention has low requirements on the pipes, so cheap 316L stainless steel pipes can be used. The two measuring tubes 1 and 2 of the present invention are parallel, the outer diameter is D, and the distance between the centers of the two parallel measuring tubes is 2.5D to 3D.

As shown in Figures 4 and 5, the best installation positions of the two spacer plates 6, 7, 8, and 9 at both ends of the straight tube type measuring tube 1, 2 of the present invention are: a pair of spacer plates 6, 9 are located at the first The junction of the two straight pipe sections 28,29 and the second part of the arc section 26,27, and perpendicular to the second part of the straight pipe section 28,29, as shown at point 31 in Figure 5; another pair of distance plates 7,8 are located at At the center of the second partial arc segment 26, 27, and coincident with the normal line of the second partial arc segment 26, 27, as shown at point 32 in FIG. 5 . The arc angle a of the elbow section is 45°. The detectors 4 and 5 are respectively installed at points 33 and 34 at the center positions 33 and 34 of the circular arc pipe sections 22 and 23 on both sides of the upper two parallel quasi-straight tube measuring tubes 1 and 2. The tubes 1 , 2 are symmetrical about their centers; the vibrator 3 is mounted at a point 35 measuring the central axis of the tubes.

As shown in FIG. 6 , two distance plates 6 , 7 , 8 , 9 are respectively used on both sides of the quasi-straight tube measuring tubes 1 , 2 . The distance plate fixes the two quasi-straight tube measuring tubes 1 and 2 at the same time through vacuum brazing without causing deformation, so that the characteristics of the two quasi-straight tube measuring tubes 1 and 2 are exactly the same, and at the same time, it provides flow measurement The required finite twist and bend The change of the position of the double spacer in the straight pipe will change the resonant frequency of the sensor, so the position of the double spacer in the straight pipe is determined according to the designed frequency, reducing the vibration of the internal measuring pipe Coupling, and makes the measuring tube strong shock resistance.

As shown in Fig. 7, two sizes are arranged on each spacer plate of the present invention and the same hole of outer diameter D of class straight tube type measuring tube 1,2, and the distance between two holes is similar straight tube type measuring tube 1,2. 2, generally 2.5D to 3D.

Claims (5)

1. quasi-linear tube Coriolis mass flowmeter is characterized in that comprising: the parallel class straight pipe type measuring tube (1,2) in the identical back of two root architectures, vibrator (3), two detecting devices (4,5), four distance plates (6,7,8,9), two flanges (10,11), two end connecting pipes (12,13), two shunts (14,15), shell (16);

The symmetrical respectively outermost two ends that are positioned at flowmeter of two flanges (10,11), and being formed in one processes with two end connecting pipes (12,13) respectively; Two end connecting pipes (12,13) are connected with class straight pipe type measuring tube (1,2) by two shunts (14,15) respectively, and two shunts are assigned to process medium in two parallel class straight pipe type measuring tubes (1,2) equably;

The centre of described class straight pipe type measuring tube (1,2) is first's straight length (21), and left and right sides halves is symmetrical structure with respect to first's straight length (21) center line, first's straight length (21) both sides connect first's circular arc pipeline section (22,23), inclined tube section (24,25), second portion circular arc pipeline section (26,27), second portion straight length (28,29) respectively successively, and each several part all adopts level and smooth arc transition;

Described vibrator (3) is used by coil and magnet, described vibrator (3) is installed in the position of two class straight pipe type measuring tubes (1,2) central axis, the coil of vibrator (3) is installed on the class straight pipe type measuring tube (1) by fixture, and the magnet of vibrator (3) then is installed on the another kind of straight pipe type measuring tube (2);

Described two detecting devices (4,5) are used by coil and magnet coaxial cooperation, are positioned at the center of described first circular arc pipeline section (22,23);

Two ends at described two parallel class straight pipe type measuring tubes (1,2) are welded with two distance plates (6,7 or 8,9) respectively, and four distance plates (6,7,8,9) are fixing with two parallel class straight pipe type measuring tubes (1,2);

Described shell (16) is fixing with the outer face welding of two ends shunt (14,15), has the effect of support, protection and vibration isolation.

2. quasi-linear tube Coriolis mass flowmeter according to claim 1, it is characterized in that: on described two parallel class straight pipe type measuring tubes (1,2), respectively be furnished with two balancing weights (17,18,19,20), the position of each balancing weight and quality are all adjustable, guarantee the mobile equilibrium of measuring tube.

3. quasi-linear tube Coriolis mass flowmeter according to claim 1 and 2, it is characterized in that: the best position of two distance plates at described class straight pipe type measuring tube (1,2) two ends is: an intersection that is positioned at second portion straight length (28,29) and second portion arc section (26,27), and vertical with second portion straight length (28,29); Another is positioned at the center of second portion arc section (26,27), and overlaps with the normal of second portion arc section (26,27).

4. quasi-linear tube Coriolis mass flowmeter according to claim 1 and 2 is characterized in that: the center distance of described two parallel class straight pipe type measuring tubes (1,2) is 2.5D-3D, and D is the external diameter of class straight pipe type measuring tube (1,2).

5. quasi-linear tube Coriolis mass flowmeter according to claim 1 and 2, it is characterized in that: two sizes and class straight pipe type measuring tube (1, the 2) hole that outer diameter D is identical are arranged on the described distance plate, distance between two holes is 2.5D～3D, and the mode of vacuum brazing is fixed class straight pipe type measuring tube (1,2) simultaneously.

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