HK1100695B - Coriolis flow meter and an operating method thereof - Google Patents

Description

Coriolis flowmeter and method of operating the same

Technical Field

The present invention relates to force balancing for Coriolis (Coriolis) flowmeters.

Background

Vibrating flow tube sensors (e.g., coriolis mass flowmeters) typically operate by sensing the motion of one or more vibrating flow tubes containing material. Properties associated with the material within the flow tube (e.g., mass flow and density) can be determined by processing signals from motion sensors associated with the flow tube. The vibration modes of the material-filled vibration system are generally influenced by a combination of the mass, stiffness and damping characteristics of the loading flow tube and the material contained therein.

A typical coriolis mass flowmeter may include two flow tubes connected in series with a pipeline or other transport system and in which materials, such as fluids and slurries, are transported. Each flow tube can be viewed as having a set of natural vibration modes including, for example, pure bending, torsional, radial, and coupled modes. In a typical coriolis mass flow measurement application, two U-shaped flow tubes positioned parallel to each other are excited to vibrate in a first out-of-phase bending mode about their end nodes. An end node at the end of each tube defines the bending axis of each tube. There is a plane of symmetry between the two flow tubes. In the most common mode of vibration, the motion of the flow tubes periodically bends towards or away from each other relative to the plane of symmetry. Excitation is typically provided by an actuator (e.g., an electromechanical device such as a voice coil type driver) that periodically pushes the flow tube in anti-phase at its resonant frequency.

As the material flows through the vibrating flow tube, the motion of the flow tube is measured by motion sensors (commonly referred to as pick-off sensors) spaced along the flow tube. The mass flow rate may be determined by measuring the time delay or phase difference between the movements at the pickup sensor locations. The size of the measured delay is very small; typically measured in nanoseconds. Therefore, the output of the pickup sensor needs to be very accurate.

Coriolis mass flowmeter accuracy can be affected by non-linearities and asymmetries in the flowmeter structure or by unwanted motion caused by external forces. For example, a coriolis mass flowmeter with unbalanced components can cause its housing and connecting lines to vibrate externally at the drive frequency of the flowmeter. The coupling between the desired flow tube vibration and the undesired external vibration of the entire meter means that the damping of the meter external vibration also damps the flow tube vibration, and the rigid meter support raises the flow tube frequency, while the flexible meter support lowers the flow tube frequency. It has been experimentally observed that flowmeters with high external amplitudes vary with the flow tube frequency with the stiffness of the support. This is a problem because the fluid density is determined by the flow tube frequency. Frequency is also an indication of flow tube stiffness. Changes in the stiffness of the flow tube caused by the stiffness of the brace bar change the calibration factor of the flow meter. Direct coupling between the drive vibration and the local environment (via external vibration) also results in an unstable zero signal (the flow signal that occurs when there is no flow).

The undesirable external vibrations interfere with the output signal of the flow meter by an amount that depends on the stiffness and damping of the brace. Because the characteristics of the support are generally unknown and can change over time and temperature, the effect of the unbalanced components cannot be compensated for and can significantly affect the flow meter characteristics. The effects of these unbalanced vibrations and support variations can be reduced by using a balanced flow meter design.

The balancing vibration as described above traditionally involves only a single vibration direction: the Z direction. The Z direction is the direction of displacement of the flow tube when it vibrates in anti-phase. This is commonly referred to as the drive direction. Other directions may include an X-direction along the pipeline and a Y-direction perpendicular to the Z and X-directions. This reference coordinate system is important and will be referred to repeatedly.

There is also a secondary source of unwanted vibration in the Y direction caused by the geometry of the flow tube. The geometry of the flow tubes is typically configured such that the motion of the flow tube centroid is toward and away from each other relative to the plane of symmetry. Thus, the vibrational momentum of the flow tube (and fluid) mass is largely cancelled out. To avoid Y-motion of the flow tube centroids, each centroid must lie in its respective plane containing its bending axis and parallel to the plane of symmetry. These planes will be referred to as balance planes. If the plane of symmetry is vertical, then the center of mass must be located directly above the bending axis to ensure that the Y-direction vibrations are cancelled.

There are also secondary vibratory forces in the Y direction caused by drivers, pickoff sensors and other masses connected to the vibrating portion of the flow tube. For simplicity, these additional vibrating components are collectively referred to as vibrating components. If the center of mass of the vibrating member attached to each flow tube is displaced from the balance plane of the flow tube, a Y-direction vibrating force is generated. This is because the bending motion of the flow tube has a rotational component. If the driver mass is offset from the balance plane in the Z-direction, the rotational component of the flow tube motion causes the driver mass to have a motion component in the Y-direction. The origin of this Y-direction motion can be understood by considering the extreme excursion of the mass. If the mass is offset from the balance plane by 45 degrees (from the bending axis), the rotational component of the motion causes it to move in equal amounts in the Y and Z directions when vibrated. The equal offset masses on the two vibrating flow tubes balance the force in the Z direction but do not balance the force in the Y direction.

EP1248084a1 discloses a solution to the problem of Y-direction vibration by fixing offset masses on opposite sides of the flow tube as the drive masses so that the resultant center of mass is located on the balance plane of the flow tube.

Even when these masses are equal and located on the balance plane of the flow tube, secondary unbalanced vibrational forces can be generated in the Z-direction. These forces, which are the object of the present invention, are generated when the masses secured to the flow tubes have unequal moments of inertia about a line connecting the end nodes of each respective tube (hereinafter referred to as the bending axis).

Disclosure of Invention

The present invention improves the balance of a coriolis flowmeter structure by designing the vibrating elements such that the moment of inertia of each element is equal to the moment of inertia of the other drive element. The expression for the moment of inertia of an object is:

wherein:

i-moment of inertia

mass m

r-mass increment from the axis of rotation of the componentIs a distance of

M is the total mass of the component

R is the radius of gyration of the part

The moment of inertia is greatly affected by the distance term r, which is a squared term. For a driver in a coriolis flow meter, the axis of rotation is unknown because the flow tube is bent rather than rotating. Fortunately, as long as the flowmeter geometry is symmetrical (has the same mass at the same location), the choice of axis of rotation is not critical. The parallel shift theorem states that the moment of inertia about an axis is equal to the moment of inertia about a parallel axis through the center of mass plus the mass times the square of the distance between the two axes. If we set the moment of inertia of the two drive parts about any axis of symmetry to be equal, the distance from said any axis to the centre of mass of the drive member is equal and the masses are equal, the parallel axis terms cancel out. This means that in order to set the moments of inertia of the drive components equal one only needs to locate the centroids symmetrically and to make the moments of inertia around the centroids equal to each other.

The driver and coil assembly (including their support elements) are manufactured in a distributed manner such that the mass of the magnet and its support elements is equal to the mass of the coil and its support elements. In addition, the magnets and their elements and the coils and their elements are configured and mounted such that the centers of mass of the elements, when combined with the center of mass of their respective flow tubes, are located on the flow tube balance plane. Their moments of inertia about their centers of mass are also made equal. Having both elements (coil and magnet) of the same mass and positioning the resultant center of mass on the balance plane helps reduce undesirable vibrations inside the meter. Having equal moments of inertia for both components helps to further reduce unwanted vibrations.

However, it is sometimes difficult to set the moments of inertia of these components about their centroids to be equal. In this case, alternative methods may be used. Because both mass and moment of inertia affect the Z-direction meter balance, a small moment of inertia for one flowtube can be balanced by a larger mass on the same flowtube. This technique essentially uses the parallel-shift theorem to balance the moment of inertia about the (assumed position) axis of rotation.

As can be seen from the above summary, a driver embodying the present invention includes a magnet component and a coil component. It can further be seen that the component containing the magnet component and the device containing the coil component are manufactured and mounted on their respective flow tubes in such a way that the mass of the driver component is equal to the mass of the coil component; the coil and magnet components have their combined center of mass (with the flow tube) located on their respective balance planes; and the magnet part and the coil part have equal moments of inertia about their centroids. Mounting such a drive coil assembly to the bottom of the first flow tube and mounting the magnet assembly to the bottom of the second flow tube provides a dynamically balanced structure that causes the flow tubes to vibrate in anti-phase and prevents the generation of undesirable internal vibrations.

Further in accordance with the present invention, the pickoff sensors are designed, fabricated and mounted on the flow tube in the same manner as the driver. In other words, each pickoff sensor has a magnet component secured to the first flowtube, a coil component secured to the second flowtube, and a distributed component that provides a dynamic balancing element that does not significantly contribute to the generation of undesirable vibrational forces within the flowmeter.

Various aspects of the invention

One aspect of the invention includes a coriolis flow meter comprising:

a first flow tube and a second flow tube adapted to vibrate in anti-phase about a plane of symmetry;

a drive system adapted to vibrate each flow tube about an axis connecting end nodes of each flow tube;

a first vibrating component comprising a first vibrating drive system component secured to the first flowtube;

a second vibrating member comprising a second vibrating drive system component secured to the second flowtube;

said first and second vibratory drive system components having equivalent sizes and positions such that the moment of inertia of said first flowtube plus said first vibratory drive system component is substantially equal to the moment of inertia of said second flowtube plus said second vibratory drive system component;

the end node of the first flow tube and the combined center of mass of the first flow tube plus the first vibration drive system component are located on a first balance plane parallel to the plane of symmetry; and is

The end node of the second flow tube and the combined center of mass of the second flow tube plus the second vibration drive system component are located on a second balance plane parallel to the plane of symmetry.

Preferably, the first and second oscillatory drive system components are sized to have substantially equal masses.

Preferably, the first vibratory drive system component comprises a driver coil component secured to the first flowtube; and is

The second vibratory drive system component includes a magnet component of the driver secured to the second flow tube and coaxially aligned with the coil component.

Preferably, the first vibrating member further comprises a first sensor member, and the second vibrating member comprises a second sensor member.

Preferably, the first sensor component is fixed to the first flow tube; and is

The second sensor component is secured to the second flow tube.

Preferably, the first and second oscillatory drive system components are sized to have substantially equal masses.

Another aspect of the invention includes a method of operating a coriolis flow meter, comprising:

a first flow tube and a second flow tube adapted to vibrate in anti-phase about a plane of symmetry;

a drive system adapted to vibrate each flow tube about an axis connecting end nodes of each flow tube; the method comprises the following steps:

securing a first vibrating member comprising a first vibrating drive system component to the first flow tube;

securing a second vibrating member comprising a second vibrating drive system component to the second flow tube;

manufacturing and positioning the first and second vibratory drive system components to be of equivalent size and location such that the moment of inertia of the first flowtube plus the first vibratory drive system component is substantially equal to the moment of inertia of the second flowtube plus the second vibratory drive system component;

the method further comprises the steps of:

positioning an end node of the first flow tube and a resultant center of mass of the first flow tube plus the first vibrational drive system component on a first balance plane parallel to the plane of symmetry; and

positioning an end node of the second flow tube and a resultant center of mass of the second flow tube plus the second vibratory drive system component on a second balance plane parallel to the plane of symmetry.

Preferably, the method further comprises the step of: the first and second vibratory drive system components are sized to have substantially equal masses.

Preferably, the method further comprises the step of:

securing the first vibratory drive system component to the first flow tube, the first vibratory drive system component comprising a coil component of a driver; and

securing the second vibratory drive system component to the second flow tube and coaxially aligned with the coil component, the second vibratory drive system component comprising a magnet component of the driver.

Preferably, the method further comprises: the first vibratory drive system component further includes a first sensor component and the second vibratory drive system component further includes a second sensor component. The method further comprises the steps of:

securing a first sensor component to the first flow tube; and

securing a second sensor component to the second flow tube.

Preferably, the method further comprises: the first and second sensor components are sized to have substantially equal mass.

Drawings

The above and other advantages and methods 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 conventional prior art Coriolis flow meter;

FIG. 2 illustrates a typical drive for a prior art Coriolis flow meter;

FIG. 3 shows a perspective view of a Coriolis flow meter in which the present invention is implemented;

FIG. 4 illustrates the Coriolis flowmeter of FIG. 3 with a portion of the housing removed;

FIG. 5 illustrates the flow tubes and support rods of the Coriolis flowmeter of FIG. 3;

FIG. 6 illustrates a perspective view of the drive system D of the Coriolis flow meter of FIG. 3;

FIG. 7 shows a vertical cross-sectional view of the flow tube of FIG. 4 secured to a drive element embodying the present invention;

FIG. 8 shows a detail of the drive system D secured to the first and second flowtubes; and

fig. 9 shows details of the pick-off sensors and the manner in which they are secured to the flow tube.

Detailed Description

Fig. 1-9 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. Therefore, the present invention should not be limited to the specific examples described below, but should be defined by the claims and their equivalents.

Description of FIG. 1

Fig. 1 shows a coriolis flow meter 5 that includes a flow meter assembly 10 and meter electronics 120. Meter electronics 120 is connected to meter assembly 10 via leads 100 to provide density, mass flow rate, volume flow rate, accumulated mass flow, temperature, and other information on path 126. It will be apparent to those skilled in the art that the present invention can be used with any type of coriolis flow meter regardless of the number of drivers, pickoff sensors, flow tubes, or the mode of vibration operation.

The flowmeter assembly 10 includes a pair of flanges 101 and 101 ', manifolds 102 and 102', drive system D, pickoff sensors LPO, RPO, and flow tubes 103A and 103B. The drive system D and pickoff sensors LPO, RPO are connected to flow tubes 103A and 103B.

Flanges 101 and 101 'are secured to manifolds 102 and 102'. Manifolds 102 and 102' are secured to opposite ends of spacer 106. Spacers 106 maintain the spacing between manifolds 102 and 102' to prevent unwanted vibrations in flow tubes 103A and 103B. When the flowmeter assembly 10 is inserted into a piping system (not shown) carrying the material under test, the material enters the flowmeter assembly 10 through the flange 101, passing through the inlet manifold 102; at the inlet manifold, all material is directed into flow tubes 103A and 103B, through flow tubes 103A and 103B and back to outlet manifold 102'; at the outlet manifold 102 ', the material exits the flowmeter assembly 10 through the flange 101'.

Flow tubes 103A and 103B are selected and suitably mounted to inlet manifold 102 and outlet manifold 102 ' such that they have substantially the same mass distribution, moment of inertia, and modulus of elasticity about bending axes W-W and W ' -W ', respectively. These axes contain the tube end nodes (stagnation points) for each flow tube. The flow tubes extend outwardly from the manifold in a substantially parallel manner.

Drive system D drives flowtubes 103A and 103B in opposite directions about their respective bending axes W and W' and in a first out of bending (out of bending) mode known as a flow meter. The drive system D may comprise one of many well-known means, such as a magnet mounted to the flow tube 103A and an opposing coil mounted to the flow tube 103B. An alternating current flows through the opposing coil to cause the two flow tubes to vibrate in anti-phase. Appropriate drive signals are applied by meter electronics 120 to drive system D via leads 110. The description of fig. 1 is intended only as an example of the operation of a coriolis flow meter and is not intended to limit the teachings of the present invention.

The meter electronics 120 transmits sensor signals on leads 111 and 111', respectively. Meter electronics 120 generates a drive signal on lead 110 that causes drive system D to vibrate flow tubes 103A and 103B in anti-phase. The meter electronics 120 processes the left and right velocity signals from the pickoff sensors LPO, RPO to calculate the mass flow rate. The pathway 126 provides an input and output means that allows the meter electronics 120 to interface with an operator.

Description of FIG. 2

Fig. 2 shows a drive system D for a preferred embodiment of a coriolis flow meter 5. In a preferred exemplary embodiment, the drive system D is a coil and magnet assembly. One of ordinary skill in the art will note that other types of drive systems, such as piezoelectrics, may be used.

The drive system D has a magnet assembly 210 and a coil assembly 220. The bracket 211 extends outwardly from the magnet assembly 210 and the coil assembly 220 in opposite directions. The brackets 211 are wings that extend outwardly from the flat base and have a generally curved edge 290 on the bottom side, the edge 290 being made to receive the flow tube 103A or 103B. The bent edge 290 of the bracket 211 is then welded or otherwise secured to the flow tubes 103A and 103B to connect the drive system D to the coriolis flowmeter 5.

The magnet assembly 210 has a magnet holder 202 as a base. A bracket 211 extends from a first side of the magnet holder 202. Walls 213 and 214 extend outwardly from the outer edge of the second side of the magnet holder 202. Walls 213 and 214 control the direction of the magnetic field of magnet 203 so that it is perpendicular to the windings of coil 204.

Magnet 203 is a generally cylindrical magnet with first and second ends. The magnet 203 is fitted in a magnet sleeve (not shown). The magnet sleeve and magnet 203 are secured to a second surface of the magnet holder 202 to secure the magnet 203 in the magnet assembly 210. Magnet 203 typically has a magnetic pole (not shown) affixed to its second side. The pole (not shown) is a cap that fits over the second end of magnet 203 to direct the magnetic field into coil 204.

The coil assembly 220 includes a coil 204 and a bobbin 205. The bobbin 205 is fixed to the bracket 211. The bobbin 205 has a bobbin extending from the first surface around which the coil 204 is wound. The coil 204 is mounted on the bobbin 205 and opposes the magnet 203. The coil 204 is connected to the wire 110, which applies an alternating current to the coil 204. The alternating current causes coil 204 and magnet 203 to attract and repel each other, which in turn causes flow tubes 103A and 103B to vibrate in opposition to each other.

Description of FIG. 3

Fig. 3 discloses a coriolis flow meter 300 embodying the present invention. The flowmeter 300 includes a spacer 303 and a manifold 307, the spacer 303 surrounding the lower portions of the flow tubes 301, 302, the left end of the flow tube inscribed to the flange 304 via a constriction 308, and the right end of the flow tube connected to the flange 305 via a constriction 320. Fig. 3 also shows the outlet 306 of the flange 305, the left pickoff LPO, the right pickoff RPO and the drive system D. The right pickoff RPO is shown in more detail and includes a magnet structure 315 and a coil structure 316. Element 314, located on the bottom of manifold spacer 303, is an opening for receiving leads 100 from meter electronics 120, which leads 100 extend internally to drive system D and pickoffs LPO and RPO. The flow meter 300 is adapted to be connected in use to a pipeline or the like via flanges 304 and 305.

Description of FIG. 4

Fig. 4 is a cross-sectional view of the flow meter 300. This view removes the front of the manifold spacer 303 so that the components inside the manifold spacer can be shown. These components, which are shown in FIG. 4 but not in FIG. 3, include outer end support bars 401 and 404, inner support bars 402 and 403, right end flow tube outlets 405 and 412, flow tubes 301 and 302, and curved flow tube portions 414, 415, 416 and 417. In use, flow tubes 301 and 302 vibrate about their bending axes W and W'. The outer end support bars 401 and 404 and the inner support bars 402 and 403 help to determine the location of the bending axes W and W'. Element 406 is a mounting fixture for connecting wires to drive system D and transducers LPO and RPO, which wires are not shown in fig. 4 for simplicity. Surface 411 is the flow meter inlet; surface 306 is the meter outlet.

Elements 405 and 412 are the inner surfaces of the right ends of flow tubes 301 and 302. The bending axes W and W' are shown extending the entire length of the flow meter 300.

Description of FIG. 5

Fig. 5 constitutes an end view of flow tubes 301 and 302, which are shown deflected outwardly relative to each other by drive system D (not shown in fig. 5). Fig. 5 also shows inner support rods 402 and 403, outer support rods 401 and 404, and outlets 405 and 412. The depiction of the outward deflection of the flow tubes 301, 302 is shown exaggerated to facilitate an understanding of their operation. In use, the drive system D deflects the flowtube to a magnitude that is too small to be perceptible by the human eye. Bending axes W and W' of flow tubes 301 and 302 are also shown.

Description of FIG. 6

Fig. 6 discloses a drive system D having a coil part C and a magnet part M. The coil portion C is shown with an end 601 with a bolt (not shown) extending axially through the entire coil portion C. Surface 604 is the axially outer end of coil section C. Element 602 is a coil spacer surrounding coil portion C. Surface 603 is a spacer. The element 604 supports wires (not shown) that are connected to the coil winding ends of the coil section C. Element 605 is the outer surface of the coil former. Element 606 is a surface around which the wire of coil section C is wound. Element 608 is the wire of coil portion C.

The right magnet portion comprises a holder 609, a cylindrical magnet holder 610 surrounding the inner magnet, a transition surface 612, a weight and magnet holder 613, and a surface 611 at the left end of the magnet holder.

In use, a sinusoidal signal from meter electronics 120 energizes coil 608 via wire 110. The field produced by the excited coils 608 interacts with the magnetic field at the magnet ends causing the coil elements C and magnet elements M to move in axial anti-phase under the excitation signal from the meter electronics 120. In this case, the right end portion of the coil element C (including the coil 608 and the surface 607) in fig. 6 axially enters and exits the magnetic holder 609. As shown in fig. 8, the upper surface of coil spacer 602 is fixed to the lower surface of flow tube 301. In a similar manner, the upper surface of the magnet holder 610 is secured to the lower surface of the flow tube 302. The vibratory motion of the coil and magnet components of drive system D causes flow tubes 301 and 302 to undergo similar vibratory motion, causing flow tubes 301 and 302 to vibrate in anti-phase with the drive signal on path 110.

Description of FIG. 7

Fig. 7 is a cross-sectional view of flow tubes 301 and 302 taken along their longitudinal axial middle portions and a cross-sectional view of coil component C and magnet component M of drive system D. The top surface of coil 602 is secured to the lower surface of flow tube 301. The top surface of magnet spacer 610 is secured to the lower surface of flow tube 302. Members 602 and 610 may be secured to the flow tube using brazing and/or spot welding. A bolt 701 having an end 601 is received in the coil spacer 602 and extends inwardly through the spacer 303 and terminates at element 606. Element 606 is fixed to element 704; the element 704 includes a surface around which the coil 608 of fig. 6 is wound.

The magnet assembly M of the drive system D comprises an element 702 on its right outer end. The left end of magnet M is element 703; the middle of magnet M is element 710. The right portion 702 is received in a weight 613. When the coil component C of the drive system D is energized, the right side portion of the coil component C and the left side portion 703 of the magnet component M vibrate axially inward and outward relative to each other, and in this case, cause similar inward and outward vibrations of the flow tubes 301 and 302.

When drive system D vibrates flow tubes 301 and 302, flow tube 301 vibrates about bending axis W' and flow tube 302 vibrates about bending axis W. This is shown more clearly in figures 4 and 5. Vertical line 716 is in the balance plane of flow tube 301. The balance plane 716 includes the bending axis W' and is parallel to the symmetry plane 708. Vertical line 717 is in the balance plane of flow tube 302. Balance surface 717 contains the bending axis W and is also parallel to plane of symmetry 708, which is located midway between balance surfaces 716 and 717.

Flow tubes 301 and 302 vibrate about their respective bending axes W' and W similar to a tuning fork. However, the two flow tubes themselves are not precisely dynamically balanced structures and therefore can assume low levels of undesirable vibration generated within the coriolis flow meter of which they are a part.

Fig. 7 shows bending axes W' and W, which are located slightly inward with respect to centerlines 706 and 707 of flow tubes 301 and 302. These bending axes W' and W are generally located on the flow tube centerlines 706 and 707. However, in the present invention as shown in FIG. 7, the bending axes W' and W are shown as being offset from the flow tube centerlines 706 and 707 due to the mass and stiffness of the structure to which the flow tube is attached. The flow tube centroids 712 and 715 (ignoring connected components) are located on the flow tube centerlines 706 and 707. As the flow tubes bend inward, their centers of mass 715 and 712 follow a circumferential path about bending axes W' and W. It can thus be seen that the centroids move slightly upward as they approach their respective balancing surfaces 716 and 717. Likewise, as the flow tube centroids 715 and 712 move away from their respective balance faces 716 and 717, they move downward. Unless equilibrium is reached, vertical motion of the flow tube centroids 715 and 712 will cause the flow meter to vibrate in the Y-direction.

The mass of the driver of a typical flow meter causes a dynamic imbalance when the driver is secured to the flow tube of a typical coriolis flow meter. Such a drive is shown in fig. 2 and can be seen to include a first structure 220 secured to a first flow tube and a second structure 210 secured to a second flow tube. Such drivers add significant mass to the vibrating structure of the flow tube. And the driver adds mass in such a way that a large part of the mass is located in the space between the two flow tubes. The mass comprises elements 204, 203, 205, 213 and 214 of the driver in fig. 2.

If the driver configuration of fig. 2 were added to the flowtubes 301,302 in place of the drive system D of the present invention, the flowmeter would likely remain unbalanced because the center of mass of the driver components in fig. 2 is located between the radial centers 706 and 707 of the flowtubes 301 and 302. These centroids will be further from the inner sides of the balance faces 716 and 717. Due to this position, the center of mass of the driver component moves downward when the flow tubes are moved toward each other and upward when the flow tubes are moved away from each other. This will counteract the Y-direction imbalance from the bare flow tube, but unfortunately, with the prior art driver, the effect of the drive component offset completely overwhelms the effect of the flow tube centroid offset from the balance plane. This dynamic imbalance in turn produces a large amount of undesirable vibration in such a flow meter.

The drive system D of the present invention includes coil and magnet components C and M secured to the bottom of the respective flow tubes 301 and 302 in a manner that allows the flow tubes to operate with a minimum amount of undesirable vibration. According to the invention, this is achieved by designing, manufacturing and configuring the coil component C and the magnet component M such that they are each constructed as a dynamically balanced structure with equal and identical inertia characteristics. These elements are independently fixed to the bottom of flow tubes 301 and 302. They are arranged axially aligned with each other such that the axial centres of the coil and the magnet have a common central axis, enabling the two elements to vibrate in anti-phase along their common axis. Securing the drive element C having center of mass 718 to the flow tube 301 having center of mass 715 results in a resultant center of mass 727 located on balance surface 716. Likewise, a drive element M having a center of mass 713 is secured to flow tube 302 having center of mass 712 to create a resultant center of mass 714 located on balance surface 717. Positioning these composite centers of mass on the balance surfaces 716 and 717 ensures that the added components do not interfere with the vibrational balance of the meter and therefore do not produce any unwanted vibrations in the Y-direction.

The coil component C and the magnet component M of the drive system D are designed, manufactured and configured to have vibration characteristics as described below. First, the mass of the coil component C of the drive system D is made equal to that of the magnet portion M. The center of mass 718 of the coil and the center of mass 713 of the magnet are made to have equal distances from the bending axes W and W'. Next, the rotational inertias of the coil part C and the magnet part M are configured such that the rotational inertias of each part are substantially equal. The moment of inertia of the various elements can be expressed as:

wherein:

i-moment of inertia of the component

m-mass of each incremental element

r-distance from each incremental element to the centre of mass of the component

Finally, the center of mass of each drive member is arranged such that the combined center of mass of each drive member and its respective flow tube is located on balance surfaces 716 and 717. Designing the driver according to these rules ensures a dynamic balance structure that enables the flow tube to vibrate in anti-phase while avoiding the generation of unwanted vibrations.

Description of FIG. 8

Fig. 8 discloses details of the drive system D of fig. 6 and 7 when attached to the bottom of the flow tubes 301 and 302. Fig. 8 shows the end 601 of the bolt extending through the coil C. It also shows end faces 614 of the coil portions, coil spacer covers 602, coil surfaces 603, wire terminals 604 and coil elements 609. Fig. 8 also shows elements 609, 610, 612 and 613 of the magnet assembly M. Fig. 8 shows wires 806 and 807 extending from the support 802 to the coil terminals 604. Conductors 806 and 807 are connected by conductor 110 (not shown) to apply excitation signal 110 from meter electronics 120 to coil portion C. Brackets 801, 802, 803, 804, and 805 are mounting brackets to support wires 806 and 807. Coil spacer element 602 is secured to the bottom of flow tube 301 and magnet spacer 610 is secured to the bottom of flow tube 302 in the same manner.

Description of FIG. 9

Fig. 9 shows more detail of the pickoffs RPO and LPO of fig. 3 secured to the top of flow tubes 301 and 302. Each sensor has a coil part C and a magnet part M in the same manner as the drive system D. Coil component C has spacer 315 fixed to the top of flow tube 301; the magnet assembly M has a spacer 316 secured to the top of the flow tube 302. The sensor RPO has a conductor 907 which is connected to the conductor lines 111 and 111' of fig. 1 by means which are not shown in detail in fig. 9. These wires are supported by a support 906. Coil component C has elements 902 and 904 to support the coil wires and also has an axially inner end surface 903. The magnet member M has an inner end 905 corresponding to the element 609 of the magnet member M in fig. 6.

The transducers RPO and LPO are designed, configured and manufactured in the same manner as the drivers so that each component has an equal mass, a center of mass located on the balance plane, and an equal moment of inertia. This ensures that the sensor components are configured as a dynamically balanced structure that can be secured to the flow tube as shown, thereby enabling the flow tube to operate in a manner that does not produce undesirable vibrations.

It is to be clearly understood that the claimed invention is not limited to the description of the preferred embodiments herein, but is intended to cover other modifications and variations within the scope and spirit of the inventive concept.

Claims (11)

1. A coriolis flow meter comprising:

a first flow tube (301) and a second flow tube (302) adapted to vibrate in anti-phase with respect to a plane of symmetry (708);

a drive system (D) adapted to vibrate each flow tube about an axis connecting end nodes of each flow tube;

a first vibrating component (D, LPO, RPO) comprising a first vibrating drive system component secured to the first flow tube;

a second vibrating member comprising a second vibrating drive system component secured to the second flowtube;

said first and second vibratory drive system components having equivalent sizes and positions such that the moment of inertia of said first flowtube plus said first vibratory drive system component is equal to the moment of inertia of said second flowtube plus said second vibratory drive system component;

it is characterized in that the preparation method is characterized in that,

an end node (W') of the first flow tube and a resultant center of mass (727) of the first flow tube plus the first oscillatory drive system component are located on a first balance plane (716) parallel to the plane of symmetry (708); and is

An end node (W) of the second flow tube and a resultant center of mass (714) of the second flow tube plus the second vibratory drive system component are located on a second balance plane (717) parallel to the plane of symmetry (708).

2. The coriolis flowmeter of claim 1 characterized in that: the first and second vibratory drive system components are sized to have equal mass.

3. The coriolis flowmeter of claim 1 characterized in that:

the first vibratory drive system component including a driver coil component secured to the first flowtube; and is

The second vibratory drive system component includes a magnet component of the driver secured to the second flow tube and coaxially aligned with the coil component.

4. The coriolis flowmeter of claim 1 characterized in that: the first vibrating component further comprises a first sensor component (602), and the second vibrating component comprises a second sensor component (610).

5. The coriolis flowmeter of claim 4 characterized in that:

the first sensor component (602) is fixed to the first flow tube (301); and

the second sensor component (610) is secured to the second flow tube (302).

6. The coriolis flowmeter of claim 5, characterized in that: the first and second vibratory drive system components are sized to have equal mass.

7. A method of operating a coriolis flow meter comprising the steps of:

a first flow tube and a second flow tube adapted to vibrate in anti-phase about a plane of symmetry;

a drive system adapted to vibrate each flow tube about an axis connecting end nodes of each flow tube; the method comprises the following steps:

securing a first vibrating member comprising a first vibrating drive system component to the first flow tube;

securing a second vibrating member comprising a second vibrating drive system component to the second flow tube;

manufacturing and positioning the first and second vibratory drive system components to be of equivalent size and location such that the moment of inertia of the first flowtube plus the first vibratory drive system component is equal to the moment of inertia of the second flowtube plus the second vibratory drive system component;

characterized in that the method further comprises the steps of:

positioning an end node of the first flow tube and a resultant center of mass of the first flow tube plus the first vibrational drive system component on a first balance plane parallel to the plane of symmetry; and

positioning an end node of the second flow tube and a resultant center of mass of the second flow tube plus the second vibratory drive system component on a second balance plane parallel to the plane of symmetry.

8. The method of claim 7, further comprising the steps of: the first and second vibratory drive system components are sized to have equal mass.

9. The method of claim 7, further comprising the steps of:

securing the first vibratory drive system component to the first flow tube, the first vibratory drive system component comprising a coil component of a driver; and

securing the second vibratory drive system component to the second flow tube and coaxially aligned with the coil component, the second vibratory drive system component comprising a magnet component of the driver.

10. The method of claim 7, wherein: the first vibratory drive system component further comprises a first sensor component, the second vibratory drive system component further comprises a second sensor component; the method further comprises the steps of:

securing a first sensor component to the first flow tube; and

securing a second sensor component to the second flow tube.

11. The method of claim 10, further comprising the step of:

the first and second sensor components are sized to have equal mass.