HK1028103B - Coriolis flowmeter having corrugated flow tube - Google Patents

Description

Coriolis flowmeter having corrugated flow tube

Technical Field

The present invention relates to Coriolis (Coriolis) flowmeters, and more particularly, to Coriolis (Coriolis) flowmeters having a corrugated flow tube.

Background

Straight tube Coriolis (Coriolis) mass flowmeters are known in the art. They may be constructed of a flowmeter having a single straight flow tube, a cylindrical balance tube surrounding the flow tube, and a stationary larger housing surrounding the flow tube and the balance tube. The balance tube is rigidly secured to the flow tube at each end by a strut. The thick end plate secures the housing to the flow tube at each end thereof. The flow tube extends beyond the end of the housing and is flanged to the pipeline. The flow meter housing provides physical protection for the flow meter elements enclosed in the housing. These components may include sensitive devices such as drivers, sensors, and related electronics. It is desirable to physically protect these components from the environment in which the flow meter is used. The housing, which is advantageously made of a sufficiently thick, relatively strong material, provides this protection.

In use, the flow tube is vibrated electromechanically, shifting the phase relative to the balance tube, which is provided to reduce vibration that may be associated with a single unbalanced flow tube. These vibrations impart Coriolis (Coriolis) accelerations to the material flowing through the flow tube. The reaction to Coriolis (Coriolis) acceleration causes a small deformation to the shape of the vibrational mode of the flow tube. A sensor attached to or associated with the flow tube measures this deformation. These sensors may be of the velocity type or of the displacement type. The material flow rate is proportional to the time delay or phase delay between the signals generated by two such sensors positioned along the length of the straight flow tube. A single sensor may also be used. The output signal of the sensor is applied to electronics which derive the required information about the material in the flow tube, such as the mass flow rate.

Dual straight tube Coriolis (Coriolis) flow meters are also known. These meters are similar to single straight tube flow meters except that they have a second flow tube parallel to the first flow tube. This second flow tube replaces the balance bar of the single flow tube flow meter embodiment. The two flow tubes are connected at their ends to a flow splitting manifold that divides the received material flow between the two flow tubes. Dual flow tube flow meters may or may not have struts connecting the flow tubes to one another. The tubes of a dual tube Coriolis (Coriolis) mass flowmeter are vibrationally phased with respect to each other rather than a balanced tube. Otherwise, they operate the same as a single straight tube meter.

Mass flow measurement in both types of straight tube Coriolis (Coriolis) flow meters relies on deformation or bending of the flow tube caused by Coriolis (Coriolis) forces generated by material flow and concurrent electromechanical vibrations experienced by the flow tube. Coriolis (Coriolis) mass flowmeters are often desired to have an accuracy of up to 0.1 percent of the reading. To achieve this accuracy, flow tube deformation must be dependent only on the Coriolis force generated, and not on external forces and stresses, such as those caused by differences in operating temperatures between different portions of the flow meter. These stresses may produce undesirable axial tension or compression in the flow tube.

Axial tension tends to stiffen the flow tubes and weaken their response to the Coriolis (Coriolis) forces generated. This results in a low reading of the true flow information generated by Coriolis (Coriolis) forces. Likewise, axial compression softens the flow tube, resulting in a higher reading of the Coriolis (Coriolis) flow information being generated. Traditionally, straight tube Coriolis (Coriolis) flow meters have been fabricated with the end of the housing being extremely stiff so that forces generated by externally applied loads are transmitted by the stiff housing end to the housing and not to the flow tube. This successfully isolates the flow tube from external loads, however, the stiffness of the housing and the housing ends creates problems caused by thermal expansion/contraction of the flow tube and temperature differences between the flow tube and the meter.

In a straight tube Coriolis (Coriolis) flowmeter (U.S. patent No. 4768384), the temperature differential that often exists between the material in the flow tube and the air outside the meter housing can cause the flow tube to have a different temperature than the case. This causes the flow tube to thermally expand by an amount different from that of the housing. The rigid housing end limits this differential expansion and generates an axial force that axially compresses (or stretches) the flow tube, causing high axial stresses in the flow tube and errors in the displayed flow rate.

Thus, the temperature differential between the flow tube and its housing causes axial stress on the flow tube, either axial compression or axial tension. In addition to affecting meter accuracy, these stresses may exceed the yield stress of the material comprising the flow tube. The axial tensile stress may shear the flow tube from the housing end, or may shear the flow tube itself. Stress can also permanently deform the flow tube material, permanently changing its correction factor and rendering it useless. For example, if a stainless steel flow tube is 20 inches (50.8cm) long and heated 200 degrees Fahrenheit (F) to 100 degrees Celsius (C) from the sheath, it will expand 0.036 inches (0.009cm) more than the sheath. If the housing and housing ends are relatively stiff, this expansion may produce about 50000 pounds per square inch (3.44 x 10 pounds per square meter) in the flow tube⁸Newtons) of compressive stress. This stress may be high enough to cause the flow tube to yield or deform. A similar situation exists when the flow tube is cooler than the housing, the difference being onlyStress is tensile rather than compressive.

Two devices have traditionally been used to reduce thermally induced stresses. The most common of them (us patent 5476013) is to make the flow tubes of a material with a lower coefficient of thermal expansion than the material of which the housing is made. Titanium is typically used to make flow tubes because of its low coefficient of thermal expansion and its good corrosion resistance. Stainless steel has a coefficient of thermal expansion of about twice that of titanium, and is used to make the housing. The heat flow from the hotter (in this example) flow tube and the heat loss to the cooler atmosphere determine the temperature of the enclosure. By properly designing the heat conduction path from the flow tube to the housing, the flow meter is designed so that the equilibrium temperature of the housing is at the midpoint between the material flow temperature and the ambient air temperature. Since the housing has a coefficient of expansion that is twice that of the flow tubes, this results in axial stress of the flow tubes, which is independent of the temperature of the fluid. However, the difference in thermal expansion coefficient between the tube and the housing ensures that the stress of the tube is now a function of the ambient temperature. In hot weather, the shell will expand more than the tube, causing the tube to stretch, while in cold weather, the shell will contract more than the tube, causing the tube to compress. This fixation of thermal stress is simply traded for sensitivity to fluid temperature for sensitivity to ambient temperature.

Another important issue with manufacturing the housing and flow tube from different materials is the cost of manufacturing. Titanium is expensive and difficult to machine. It cannot be welded to stainless steel using conventional procedures and can only be brazed to a stainless steel housing with difficulty.

Another widely used method of reducing thermally induced tube stresses is to design a geometric strain relief into the flow tube. Bent tube flow meters fall into this category. It includes flow meters with flow tubes that are U-shaped (us 4252028), V-shaped, and all other irregular shapes with non-straight tubes (us 4891991). In the case of a straight tube flow meter, the strain relief is conventionally located between the end of the housing and the strut rod adjacent the end of the housing. In this position, the flow tube is kinematically inactive, and therefore the nature of the strain relief does not affect the dynamics of the vibrating portion of the flow tube. Among the various designs of strain relief devices used are 0-rings, slip joints (U.S. patent No. 4803867), metal bellows (U.S. patent No. 5663509), and a reduction in the diameter of the flow tube, which acts as a membrane. These methods of strain relief devices function properly for their intended function, but they have their own particular problems.

The main problem with bellows and sliding joint designs is that they are not easily cleaned. This is an important issue in that cleanability is one of the most common reasons customers choose a straight tube meter. Flow meters that use flow tube diameter constrictions near the ends of the tube as strain relief devices often suffer from a large fluid pressure drop. Other geometric designs are possible, however, they all have disadvantages such as cleanability, pressure drop or drainage.

The problems associated with thermal stresses between the flow tube and the surrounding housing are discussed above. In a single flow tube flowmeter having a balance tube fixed to a flow tube, the relationship between the balance tube and the flow tube is the same as the relationship between the housing and the flow tube in terms of temperature difference and thermal stress. The balance tube is typically rigidly secured to the flow tube by the end of the balance tube. The problem of expansion between the flow tube and the balance tube is therefore the same as described above between the flow tube and the housing.

It should also be appreciated that while there are a number of techniques for minimizing the problem of flow tube expansion/contraction for meters having thick, inflexible outer casings, none are without drawbacks. In particular, the problems of thermal gradients and ambient temperature changes remain unsolved.

Disclosure of Invention

The present invention overcomes the problems described above and advances are made in the art by providing a flow meter in which the geometry of the flow tubes makes their dynamically active region axially flexible. The flexibility of the flow tubes in the axial direction allows them to contract and expand (when present) in the axial direction relative to the meter housing and balance tube, thereby reducing axial stresses on the flow tubes. This allows the flow tube, the meter case and the balance tube to be made of the same material. Furthermore, by providing a flexible region in the dynamically active region of the flow tube, the meter can be made to have greater accuracy with respect to measuring flow and density.

The present invention provides a Coriolis (Coriolis) flowmeter having flow tube means, drive means (D) for vibrating said flow tube means, and sensor means (S1, S2) connected to said flow tube means for detecting Coriolis (Coriolis) deflections of said flow tube means resulting from material flow through said vibrating flow tube means, said sensor means being responsive to Coriolis (Coriolis) deflections of said flow tube means for generating output information related to said material flow rate;

said flow tube means having a movable portion which is vibrated by said drive means; and

a stationary portion attached to said flow tube apparatus for maintaining said stationary portion substantially unmoved during vibration of said movable portion of said flow tube apparatus;

a bellows portion in the movable portion of the flow tube device for changing a vibration characteristic of at least one vibration mode of the flow tube device;

wherein said bellows portion is in one or more flow tube segments that are located within said movable portion of said flow tube apparatus and that are subjected to substantial bending moments in a vibrational mode that alter said vibrational characteristics of that mode; and wherein the step of (a) is,

the movable part of the flow tube device is simultaneously subjected to a low bending moment in a vibration mode, the vibration characteristics of which are not changed.

The flow tubes of the invention achieve greater axial flexibility than the flow tubes of the prior art by virtue of the corrugated shape of the regions that are active in their dynamics rather than the regions that are inactive in their dynamics. These corrugations are similar to those in a typical stainless steel pipe in that periodic increases and decreases in pipe diameter occur in the axial direction of the pipe. The corrugations increase the axial flexibility of the flow tube by changing the axial deformation of the flow tube wall due to pure tension or compression, as seen in straight wall flow tubes, to wall bending plus greatly reduced tension and compression. The curvature of the wall of the corrugated flow tube is asymmetric, which allows the flow tube to remain straight when deformed in the axial direction.

Thus, the corrugated flow tube solves the thermal stress problem because the surrounding meter housing and/or balance bar, which has a lower temperature than the flow tube, can compress the corrugated flow tube in the axial direction without creating sufficient stress to damage the flow tube or significantly alter the flow sensitivity. Also, surrounding flow tube housings and/or balance tubes that are hotter than the flow tube temperature can axially stretch the corrugated flow tube without damaging or changing sensitivity.

The corrugated portion of the kinematically active region of the flow tube has the further advantage: the sensitivity to material flow is improved over conventional flow tubes. The corrugated tube can be bent with very little force and has no permanent deformation, except that it can be compressed in the axial direction with very little force and has no permanent deformation. Softening the flow tube when bent has three effects on the sensitivity of the flowmeter. Two of these effects cancel each other out, while the third effect improves flow sensitivity. A uniformly corrugated flow tube reduces stiffness, which results in a lower drive frequency. The frequency reduction has two effects. First, it reduces Coriolis (Coriolis) forces for a given material flow rate. The Coriolis (Coriolis) force is proportional to the angular velocity of the tube. The decrease in flow tube frequency reduces the angular velocity and Coriolis (Coriolis) forces. The reduction in force results in a reduction in deformation of the (flow-induced) tube. The reduction in flow-induced tube deformation results in a reduction in the time delay between the signals generated by the two flow tube sensors, and in addition, the reduction in frequency also results in a reduction in tube velocity. The reduction in tube speed results in a longer time delay for a given tube deformation. The results were: the effects of the tube velocity reduction (increase in time delay) and coriolis (coriolis 1is) force reduction (decrease in time delay) cancel each other out, causing the time delay (flow signal) between the sensors to be frequency independent.

The third effect of the ripple on the sensitivity of the flowmeter is: the easier bending results in a greater response to the Coriolis (Coriolis) force generated. The net effect is that the flow meter with a corrugated flow tube is significantly more sensitive to material flow than a flow meter with a conventional flow tube. The effect of the reduction in drive frequency is offset by the effect of the reduction in tube velocity. However, an increase in the response of the tube to Coriolis (Coriolis) forces results in a net increase in the sensitivity of the meter.

The position of the corrugations along the flow tube need not be uniform and, in fact, there are several benefits to having non-uniform positions of the corrugations. The deformed shape of the flow tube resulting from the driving vibration when there is no material flow is taken as the driving mode shape. It has two points, called inflection points, at which the direction of flow tube curvature changes. For a small area around these inflection points, there is no curvature and therefore there may be no bending moment. (a bending moment on a generally straight tube will always result in a bent tube.) because there is no bending moment at the inflection point of the drive mode, corrugations can be provided there, which are easily bent, will have little effect on the drive mode shape or flow tube drive frequency. However, in the Coriolis (Coriolis) deflection shape, there is a large curvature and bending moment at these same locations on the tube (drive mode inflection points). Thus, the corrugated portions at these locations (drive mode inflection points) cause a significant reduction in stiffness with respect to the Coriolis (Coriolis) force generated. During material flow, the tube periodically deflects in the drive mode shape while being deformed (with 90 degree phase shift) by Coriolis (Coriolis) forces. Thus, selectively placing the corrugations at the inflection point for the drive mode provides the flowmeter with a high drive frequency and a high Coriolis (Coriolis) force, and, at the same time, a high sensitivity to Coriolis (Coriolis) forces.

The use of corrugations at the inflection points of the flow tube vibration mode to have little effect on the stiffness of the flow tube or the frequency in that mode, or alternatively at high flow tube flex points to have a large effect on the stiffness and frequency of the flow tube, can be used to tune vibration modes other than the drive mode. For example, sometimes a higher vibration mode will occur at a frequency several times higher than the drive mode. This may cause interference with the flow signal resulting from the deformation of the measuring tube at the drive frequency. This disturbance can be avoided by using one of the frequencies of flow tube movement by corrugations in a region of the flow tube where one mode shape has high curvature and the other mode shape has low curvature or an inflection point.

Another advantage of a corrugated flow tube is that: the use of the corrugated portion makes it possible to measure the material density with high accuracy. Coriolis (Coriolis) flow meters measure density from the natural frequency of the flow tube in the drive mode. The flow tube is corrected for density by recording the natural frequency of the flow tube, which contains two different materials (typically air and water) of known density. The density of the further material is then determined by interpolation (or extrapolation) from their natural frequencies. A large flow tube frequency shift between air and water will have a higher density resolution than a small frequency shift. Corrugated flow tubes have a higher density accuracy than straight walled tubes due to the higher frequency of movement between air and water due to the increased containment volume of the corrugated portion.

Another advantage of providing the corrugations in the kinematically active areas of the flow tube is that: this allows sufficient space for multiple corrugations without increasing the length of the meter. The multiple corrugations allow each corrugation to be smaller because each corrugation needs to accommodate a smaller amount of axial bending. For example, if a flow tube is to expand/contract a given amount due to thermal differences and if it is desired to relieve axial stresses on the flow tube due to such thermal expansion/contraction, then it should be recognized that: the number of expansions/contractions that must be accommodated by each bellows is related to the number of bellows that can be used to accommodate the expansion/contraction. These plurality of small corrugated portions are characterized in that the difference between the large diameter and the small diameter is smaller than the difference between the large corrugated portions. This small difference results in a better ability to clean the tube and a smaller pressure drop than in tubes with a few large corrugations.

Drawings

These and other advantages and objects of the present invention will be better understood by reading the following detailed description in conjunction with the drawings, in which:

FIG. 1 illustrates a corrugated straight tube Coriolis (Coriolis) flowmeter;

FIG. 2 illustrates a dual straight tube Coriolis (Coriolis) flowmeter having a corrugated flow tube;

FIGS. 3 and 4 illustrate a Coriolis (Coriolis) flowmeter having a pair of generally U-shaped corrugated flow tubes corrugated over only a portion of the flow tubes;

FIG. 5 illustrates a Coriolis (Coriolis) flow tube having a corrugated outer portion and a smooth, non-corrugated inner portion;

fig. 6 and 7 illustrate mode shapes for some of the vibrational modes that may occur in the straight Coriolis flow tube of fig. 1.

Detailed Description

Figure 1 shows a Coriolis flow meter 100 having a corrugated flow tube 110 surrounded by a cylindrical balance bar 104 and housing 103, with housing 103 surrounding balance bar 104 and flow tube 110. The ends of flow tubes 110 extend through housing end 108 and are secured to flanges 109, which in turn may be secured to a flow system (not shown). The flow tube has an inlet 114 and an outlet 116. A short tube 111 connects the inlet 114 to the end 112 of the flow tube 110 and a short tube 111 connects the outlet 116 to the end 117 of the flow tube 110. The end 112 is rigidly secured to the housing end 108 and the end 113 of the balance bar 104. End 117 is rigidly connected to the right end 108 of the housing and to the right end 113 of the cylindrical balance bar 104.

The magnet M associated with the sensors S1, S2 and the driver D is attached to the flow tube 110. Conductors 124,125 and 126 connect sensing devices S1, S2 and drive device D, respectively, to meter electronics 102, which includes well known circuitry required to apply drive signals to drive D via path 125 and to receive sensor signals indicative of Coriolis (Coriolis) vibrations of flow tube 110 via paths 124 and 126. Meter electronics 102 receives the sensor signals and derives information about the flow of material through flow tube 110 in a known manner. This information may include material density, volumetric flow rate, and material flow rate, and is applied to path 123.

During operation of the flowmeter 100, thermal differences may occur between the flow tube 110, the surrounding cylindrical balance bar 104, and the surrounding cylindrical housing 103. These thermal differences may cause axial stresses in the flow tube 110 because the flow tube is to expand/contract relative to the amount that these thermal changes cause the balance bar 104 and/or housing 103 to attempt to expand/contract. Thick end 113 of balance bar 104 and thick end 108 of housing 103 prevent flow tube 110 from expanding/contracting axially relative to balance bar 104 and housing 103. For example, thick end 113 of balance bar 104 prevents flow tube 110 from having a different axial length than balance bar 104. The same is true with respect to the relationship between the length of the flow tube 110 and the housing end 108. Any attempt to expand/contract the flow tube in an axial direction by an amount different from the number of balance bar 104 and/or housing end 108 will result in an axial stress on flow tube 110. The corrugations 106 substantially reduce this stress and they bend in the axial direction so that the flow tube 110 may maintain the same length as the end 113 of the balance bar 104 and the shell end 108 of the housing 103. The corrugations allow flow tube 110 to expand/contract in unison with balance bar 104 and housing 103, substantially eliminating axial stresses on flow tube 110.

Description of FIG. 2

Fig. 2 shows a flow meter 200 having a pair of straight corrugated flow tubes 203 and 204 contained in a housing 103. The two flow tubes 203 and 204 are joined at an apex 206 to form an inlet 112. The two flow tubes are joined at an apex 207 to form an outlet 117. The inlet 112 and outlet 117 terminate in a flange 109. The inlet portion 112 is connected to the left end 108 of the housing and the outlet portion 117 is attached to the right end 108 of the housing. The material flow entering the inlet 114 on the left flows to the right, encounters the apex 206, splits there, and flows through the flow tubes 203 and 204. The outputs of flow tubes 203 and 204 merge at apex 207 and flow tube portion 117 to outlet 116 and flange 109. In fig. 1 and 2, a flow tube spool 111 connects the housing end 108 with the flange 109. The flow tube 200 also includes sensors S1 and S2 and a driver D, along with a magnet M that works in conjunction with them. Conductive paths connecting the transducers and drivers to meter electronics that can be compared to meter electronics 102 of fig. 1 are not shown in order to reduce the complexity of the diagram. The kinematically active portion of the flow tubes 203 and 204 is the portion between the strut rods 221 and 222. The stationary portions of the flow tube are to the left of strut rod 221 and to the right of strut rod 222.

Description of FIGS. 3 and 4

Fig. 3 and 4 illustrate a Coriolis (Coriolis) flow meter 300 having a pair of substantially U-shaped flow tubes 309 and 309A. With respect to fig. 3, the flow tube 309 has a top piece 310 and a pair of side legs 307 and 308. The top piece comprises a left corrugated portion 303 and a right corrugated portion 304. The left leg includes a lower straight portion 312, a post rod 302 connected to the lower end of the straight portion 312, and a straight portion 305 connecting the lower portion of the post rod 302 and the upper surface of the manifold 311 to each other. The right leg includes parts corresponding to the left leg, which include a straight portion 313, a strut bar 302, and a straight portion 306 connecting the lower surface of the right strut bar 302 and the upper surface of the manifold 311 to each other. As shown in fig. 3 and 4, the sensors S1 and S2 are connected to the flow tubes 309 and 309A together with the driver D. Stub pipes 111 connect the ends of the manifold 311 to flanges 109 that can connect the flow meter 300 to a flow system (not shown).

In FIG. 4, the aft flow tube 309A has corresponding components as described above for the flow tube 309 of FIG. 3, except that a suffix A is provided for each aft flow tube in FIG. 4.

In fig. 3 and 4, the corrugations 303, 303A, 304 and 304A add to the deformability of the upper members 309, 309A, making them more bendable and more sensitive to Coriolis forces generated by the concurrent material flow as the flow tube is vibrated by the drive D.

The portion of the flow tube above the strut bar 302 is the active portion of the flow tube; the flow tube portions 305, 306, 305A and 306A are stationary portions of the flow tube. In use, as is known in the art, the driver D vibrates the flow tubes 310 and 310A, moving in phase relative to each other about the strut bar 302 as a pivot point. The manifold 311 of fig. 3 has been omitted from fig. 4 for simplicity of illustration. However, it will be appreciated that in use, material enters the flow meter 300 and the short pipe 111 of the flow meter through the left flange 109 and continues into the manifold 311 which splits the received material flow and flows in parallel through the flow pipes 309, 309A. The material flows out of the flow tube and again into manifold 311 where they join together and continue out through right flow tube spool 111 and right flange 109.

The corrugations 303, 304, 303A and 304A increase the flexibility of the upper members 309, 309A of the flow tube for detecting Coriolis (Coriolis) vibrations. The corrugated portions are located at a position where bending stress is low for the driving frequency mode, and therefore, they have little influence on the driving frequency, but slightly lower the driving frequency due to slightly increased mass. However, as will be described in greater detail below, the corrugations 303 and 304 are locations of high stress for flow tube deformation due to Coriolis forces. The location of the corrugations 303 and 304 on the flow tubes 309 and 309A allows for increased bending capability of the flow tubes with respect to Coriolis forces generated. This increased sensitivity to the Coriolis (Coriolis) effect results in an increase in the amplitude of the signals from sensors S1 and S2. This allows the associated meter electronics 102 (of fig. 1) to generate material flow information with increased accuracy.

Description of FIG. 5

Figure 5 shows a Coriolis (Coriolis) flow tube 501 having a corrugated outer portion 502 and a smooth, non-corrugated inner portion 504. The flow channel 504 is smooth because the space inside the flow tube 501 between the outside of the wall of the flow channel 504 and the interior wall portion 508 of the flow tube is filled with a material having a low modulus of elasticity. The low elastic modulus material (such as rubber) allows the bellows portion to expand and contract in the axial direction with very little restriction. This material fills the interior 503 of flow tube 501 and it is internally corrugated in the corrugated region. This material also fills the space 507 between the outer surface of the channel 504 and the inner surface of the outer wall 508.

The embodiment of figure 5 provides a flow channel 504 that is smooth to facilitate its cleaning for applications where the interior of the flow tube must be cleaned periodically. This is important in the food processing industry where one flow meter may be used for flow measurement of different materials. In these applications, it is important to clean the flow meter at the end of the processing of one material before the processing of the other material. This requirement is met by the embodiment of fig. 5 by providing a corrugated flow tube 501 that includes a smooth flow channel 504 surrounded by a flexible material in the interior 503 and 507 of the flow tube 501. The embodiment of fig. 5 provides smooth internal flow channels 504 while maintaining the advantages of corrugations 502 so that flow tube 501 may be deformed in the same manner as flow tube 110 of fig. 1. The flow tube 501 is axially flexible so that it can maintain a fixed overall axial length while withstanding a wide range of thermal operating conditions.

Description of FIGS. 6 and 7

Fig. 6 shows the first three vibration modes of a straight flow tube such as 110 of fig. 1. The first or drive mode is shown as element 601. Element 602 represents a second vibration mode that is very similar in shape to a Coriolis (Coriolis) deflection mode. Element 603 represents a third vibration mode. With respect to element 601, flow tube 110 has corrugations 620 and 621 in flow tube sections 604 and 605. The flow spool piece 608 is connected to a drive D (not shown in fig. 6) that receives drive signals from associated electronics 102, which are shown in fig. 1 and not in fig. 6. These drive signals cause the flow tube to vibrate in a first bending mode or drive mode depicted by element 601. In this mode, the flow tube 110 has a point of maximum deflection 608 and points of inflection 604 and 605. These inflection points are the locations where the curvature of the tube changes sign. They are substantially straight and free of bending moments for a small distance on either side of the center of the inflection point indicated by the + sign. The point of maximum deflection 608 is near the intersection of the imaginary line 631 and the flow tube 110. The right side of the flow tube 110 also has an inflection point 605 near the intersection of the dashed line 632 with the flow tube 110. The flow tube 110 is substantially straight for a small distance on each side of the + sign representing an inflection point. Because the flow tube 110 near the inflection points 605 and 604 is relatively free of bending moments, the corrugated portions 620, 621 near the inflection points 604 and 605 have little effect on the drive frequency.

Element 602 depicts the shape of a Coriolis (Coriolis) deflection mode of flow tube 110 caused by the simultaneous presence of drive mode vibrations applied by drive D and material flow through flow tube 110. The shape of the Coriolis (Coriolis) deflection mode depicted by element 602 is greatly exaggerated as compared to element 601, since the amplitude of the Coriolis (Coriolis) deflection mode is much smaller than the drive vibration mode. With respect to the shape 602 of the Coriolis (Coriolis) deflection mode, segment 606 is curved, while segment 609 is straight and has no bending moment, and segment 611 is curved. The curved sections 606 and 611 experience the greatest bending moment and thus the corrugations 620 and 621 soften the flow tube 110 increasing its bending flexibility. This increases the deflection sensitivity of the flow tube 110 to the Coriolis (Coriolis) force generated. This in turn increases the signal from the sensors S1 and S2 (fig. 1) to the meter electronics 102 so that it produces more accurate material flow information.

The location of the corrugation near the intersection of the flow tube with dashed lines 632 and 633 has been described above. In fig. 6, the drive frequency of the member 601 is not affected because the corrugations 620, 621 are in the straight sections 604, 605 of the flow tube. This position provides the maximum Coriolis (Coriolis) sensitivity of member 602 because corrugations 620, 621 are in the maximum bends 606 and 611 of the Coriolis (Coriolis) response.

Piece 603 of fig. 6 shows the deflected shape of the third vibration mode of flow tube 110. In element 603, the position of the corrugations 620, 621 has little effect on the third vibration mode because the corrugations are in the straight sections 607, 612 of the flow tube response.

Sometimes occurs in the use of Coriolis (Coriolis) flow meters: one high frequency vibration mode is at or near the frequency of the ambient vibration around the flow meter. These ambient vibrations may come from pumps or plant machinery and are often multiples of the 60Hz (50 Hz in europe) supply frequency. This coincidence of the natural frequency of the tube with the ambient vibration is undesirable and can cause undesirable vibrations in the flow tube of a Coriolis (Coriolis) flowmeter. This may have a negative impact on the accuracy of the flow information generated by the flow meter. Prior art devices have employed special devices such as shock absorbers and the like to isolate Coriolis (Coriolis) flow meters from these undesirable vibrations.

The present invention allows the use of selectively positioned corrugations in the flow tube to tune the flow tube's vibration frequency so that its higher modes are not coincident with the frequency of the ambient vibration. This is illustrated in FIG. 7, where corrugations 720 and 721 are positioned such that they change the frequency of the third mode of vibration of flow tube 110, as illustrated by element 703.

Assume that the flow tube 110 response illustrated by element 703 is at the same frequency as normal ambient noise (300Hz) and that it is desired to move the flow tube frequency to minimize the ambient noise that would otherwise be generated by applying unwanted vibrations to the third vibration mode 703. In this case, corrugations 720, 721 are provided where lines 732 and 733 intersect flow tube 110. 701 is reduced somewhat because the corrugations 720, 721 are now adjacent to the curved section of the flow tube (704, 705). With respect to element 702, the corrugations at 706 and 711 have little effect on Coriolis (Coriolis) sensitivity because they occur at the inflection points. With respect to the member 703, the corrugations 720, 721 are located at the peaks 707 and 712 of the flow tube curvature and bending moments. This softens the flow tube in this mode of vibration and lowers the natural frequency (280Hz) of this mode, better isolating it from the frequencies (300Hz) associated with ambient noise than the flow tube position associated with dashed lines 634 and 635 in FIG. 6.

It is to be understood that the claimed invention is not limited to the description of the preferred embodiment, but encompasses other modifications and variations within the scope and spirit of the inventive concept.

Claims (20)

1. A coriolis flowmeter having flow tube means, drive means (D) for vibrating said flow tube means, and sensor means (S1, S2) connected to said flow tube means for detecting coriolis deflections of said flow tube means resulting from material flow through said vibrating flow tube means, said sensor means being responsive to coriolis deflections of the flow tube means for generating output information related to said material flow;

said flow tube means having a movable portion which is vibrated by said drive means; and

a stationary portion that remains substantially motionless during vibration of the movable portion;

a bellows portion in the movable portion of the flow tube device for changing a vibration characteristic of at least one vibration mode of the flow tube device;

wherein certain flow tube sections of said bellows in one or more locations in said movable portion of said flow tube apparatus are subjected to substantial bending moments in a vibrational mode for changing the vibrational characteristics of said flow tube apparatus; and wherein the corrugations are simultaneously subjected to a low bending moment in another vibration mode for not changing the vibration characteristics of the flow tube apparatus.

2. The coriolis flowmeter of claim 1 wherein said flow tube means is a single flow tube (110).

3. The coriolis flowmeter of claim 1 wherein said flow tube means comprises more than one flow tube (203, 204).

4. The coriolis flowmeter of claim 1 wherein said flow tube means is substantially straight.

5. The coriolis flowmeter of claim 1 wherein said flow tube means (110) has an irregular shape and has at least one curved section in its active portion.

6. The coriolis flowmeter of claim 1 wherein said flow tube means (309) is substantially U-shaped.

7. The coriolis flowmeter of claim 1 wherein said corrugations are provided for substantially the entire length of said active region.

8. The coriolis flowmeter of claim 1 wherein said corrugated portion is provided as a segment that is shorter than the entire length of said active portion.

9. The coriolis flowmeter of claim 1 wherein said flow tube segment including said corrugated portion is substantially straight in at least one vibrational mode shape of said active portion.

10. The coriolis flowmeter of claim 1 wherein said flow tube segment including said corrugated portion is substantially curved in at least one vibrational mode shape of said active portion.

11. The coriolis flowmeter of claim 9 wherein said vibrational mode shape in said flow tube segment comprising said substantially straight corrugations is a vibrational drive mode shape.

12. The coriolis flowmeter of claim 10 wherein said vibrational mode shape in said substantially curved flow tube segment including said corrugated portion is a vibrational drive mode shape.

13. The coriolis flowmeter of claim 1 wherein said flow tube means is substantially straight and wherein corrugations in said active portion reduce axial stresses on said flow tube means.

14. The coriolis flowmeter of claim 13 further comprising:

a housing (103) surrounding said flow tube means;

an end member (108) on each end of said housing fitted to an end section of said flow tube apparatus;

said movable portion of said flow tube means being between said end members;

the location of the corrugations (106) is axially disposed along the flow tube apparatus for reducing axial stresses on the flow tube apparatus caused by thermal differences between the flow tube apparatus and the housing.

15. The coriolis flowmeter of claim 14 wherein:

the flow tube apparatus comprises a single flow tube; and is

The flow meter further includes a balance bar (104) surrounding the flow tube and positioned within the housing;

an end member (113) on said balance bar attached to said flow tube;

said movable portion of said flow tube being between said end members of said balance bar;

the corrugations (106) may also reduce axial stresses on the flow tube caused by thermal differences between the flow tube and the balance bar.

16. The coriolis flowmeter of claim 1 wherein said corrugations (502) define an outer surface of said flow tube means and a mating inner surface of said flow tube means and wherein said flow tube means further comprises:

a liner having a cylindrical smooth inner surface inside said flow tube means;

the liner comprises a deformable material occupying the space between the mating inner surface of the flow tube device and the cylindrical smooth inner surface of the liner.

17. The coriolis flowmeter of claim 1 wherein said flow tube means (309) is substantially U-shaped and comprises a pair of side legs (307, 308), a top member (310) bridging said side legs (307, 308) and said corrugations (303, 304) being above said top member (310), said top member (310) being in a position of low bending stress for a drive frequency mode of said flow tube means.

18. The coriolis flowmeter of claim 9 wherein said flow tube segment includes a portion of said flow tube means having a substantially lower bending stress at said active portion of one vibrational drive mode for altering the vibrational characteristics of another vibrational mode.

19. The coriolis flowmeter of claim 11 wherein said flow tube segment including said corrugations is substantially straight in a higher vibrational mode shape and in said vibrational drive mode shape and curved in said coriolis deflection mode shape.

20. The coriolis flowmeter of claim 1 wherein:

said flow tube means comprising a first substantially straight flow tube (203) and a second substantially straight flow tube (204), said first and second substantially straight flow tubes (203, 204) being positioned substantially parallel to each other and each having a stationary part which is immobile and a movable part which is vibrated by said drive means and comprising said corrugated parts;

a housing (103) surrounding said first and second substantially straight flow tubes (203, 204);

said housing having housing ends attached to opposite end portions of said first and second substantially straight flow tubes (203, 204);

the corrugations are effective to retain the flow tubes at an axial length determined by the axial length of the housing (103) during thermal changes of the flow tube apparatus relative to the housing (103).