JPH07119640B2 - Coriolis mass flowmeter and electromechanical device used in said flowmeter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a Coriolis mass flowmeter, and more particularly to an electromechanical device for electromechanical or mechanical-electrical conversion used in a Coriolis mass flowmeter.

PRIOR ART In response to the need to measure the amount of material being conveyed through a pipeline, various flow meters based on different design principles have been developed. Widely used flow meters measure volumetric flow. Positive displacement flow meters are inaccurate for determining the amount of material being delivered because the density of the material changes with its temperature, the fluid being delivered is multiphase, such as a slurry, or the fluid is a non-Newtonian fluid, such as mayonnaise or other food products. Furthermore, in chemical reactions, where the mass ratio of reactants is important, positive displacement flow meters are of little use.

A mass flow meter provides a direct indication of the mass, but not the volume, of a material being pumped through a pipeline. Many methods for measuring the mass flow of a stream involve exerting a force on the stream and measuring some effect on that force.

A Coriolis flowmeter is known as a mass flowmeter.
6 as described in the specification.

Many Coriolis mass flow meters generate Coriolis forces by sinusoidally oscillating a pipe about a pivot axis perpendicular to the pipe's length. In these meters, the Coriolis force manifests itself as radial motion of objects within the rotating conduit. Material flowing through the pipe moves radially and is therefore accelerated. The Coriolis reaction force due to the moving fluid mass is transmitted to the pipe itself and manifests as a deformation or displacement of the pipe in the direction of the Coriolis force vector in the plane of rotation.

The main problem with this vibrator is that the Coriolis force, and therefore the displacement, is relatively small compared to the driving force and to the large vibrations. Furthermore, the vibrator system provides hinge or pivot points for vibration to take advantage of the inherent bending elasticity of the pipe itself, which does not require separate rotating or flexible joints, improving mechanical reliability and durability. Also, by using the resonant frequency of vibration, the required driving energy can be reduced.

Energy is supplied to the tube by a drive mechanism that applies a periodic force to vibrate the tube. A typical drive mechanism is an electromechanical drive, which moves in proportion to the voltage applied to the coil. In a vibrating flowmeter, the applied voltage is periodic, usually a sine wave. As mentioned above, the period of the input voltage, and therefore the drive force, must be matched to the resonant frequency of the tube, minimizing the energy required to maintain the vibration.

The Coriolis force due to this vibration and the mass flow in the tube is measured by a sensor located on the flowmeter tube. In some cases, it is desirable to locate the sensor close to the drive mechanism, for example, this location allows for accurate determination of the Coriolis force.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the performance of electromagnetic drivers and sensors, particularly to eliminate magnetic interference between closely spaced drivers and sensors and to improve the sensitivity of the driver-sensor combination.

The above and other objects of the present invention are achieved by various combinations of the following features: The invention is defined by the following claims.

In accordance with the present invention, a shielded electromechanical device for use in a Coriolis mass flowmeter converts mechanical and electrical energy and moves relative to a distal end of the flowmeter, the distal end including a proximal end and a distal end. A coil assembly is coupled to the distal end and a magnetic assembly is coupled to the proximal end. The coil assembly defines an interior space. A magnetic assembly is coupled to the proximal end and includes at least one magnetic member having a magnetic orientation substantially aligned with an axis connecting the proximal and distal ends. The magnetic assembly is disposed within the interior space and interacts magnetically with the coil assembly. A shield assembly surrounds the coil assembly and the magnetic assembly and is adapted to reduce magnetic fields external to the shield assembly.

In another embodiment of the present invention, a shielded electromechanical device is adapted to convert mechanical energy into electrical energy. Mechanical energy is imparted to the device by moving a magnetic assembly relative to a coil assembly,
The coil assembly generates electrical energy in response to mechanical movement.

In another embodiment, the shielded electromechanical device converts electrical energy into mechanical energy, where the electrical energy is applied to a coil assembly and a magnetic assembly moves relative to the coil assembly in response to the electrical energy.

In another embodiment, the shield assembly includes a proximal shield and a distal shield, the proximal shield attached to the proximal end of the electromechanical device and the distal shield attached to the distal end of the electromechanical device.

In another preferred embodiment of the invention, one of the shields fits within the other shield for relative movement.

In another embodiment, the shield assembly is made of a magnetically conductive material such as steel.

In another embodiment, the magnetic assembly comprises a magnetic member having a magnetic orientation substantially aligned with an axis extending between the proximal and distal ends.

In yet another embodiment, the magnetic assembly includes a pole piece disposed adjacent to the first magnetic member.

In another embodiment, the magnetic assembly includes a second magnetic member whose magnetic orientation is also substantially aligned with the aforementioned axis extending between the proximal and distal ends.

In a related aspect, the magnetic orientations of the first and second magnetic members are opposite, and the magnetic assembly further includes a pole piece disposed between the first and second magnetic members, the pole piece being made of a highly magnetically conductive material.

In another related aspect, the coil assembly defines an interior space within which a magnetic assembly is disposed, the coil assembly being substantially cylindrical and magnetically interacting with the magnetic assembly.

In another aspect of the present invention, a Coriolis mass flow meter includes:
The device includes a support and a continuous loop of conduit having its inlet and outlet ends fixedly attached to the support. A shielded electromagnetic driver acts on the loop to oscillate the loop about an oscillation axis. A sensor is provided adapted to measure the magnitude of the Coriolis force resulting from mass flow within the oscillating portion of the loop. The shielded electromagnetic driver includes a proximal end and a distal end. A coil assembly is connected to the distal end and a magnetic assembly is connected to the proximal end and cooperates with the coil assembly. A shield assembly surrounds the coil assembly and the magnetic assembly and is adapted to attenuate magnetic fields external to the shield assembly.

In another embodiment, the sensor includes a proximal end and a distal end.
A magnetic assembly is mounted to the proximal end and a coil assembly is mounted to the distal end. A shield assembly surrounds the coil assembly and the magnetic assembly and is adapted to attenuate magnetic fields external to the shield assembly.

In yet another embodiment, the driver and sensor are disposed adjacent the loop. The flow meter includes a second continuous loop of conduit having its inlet and outlet ends fixedly attached to a support. The first and second continuous loops of conduit are substantially parallel. The driver and sensor are disposed between the loops.

In another embodiment of the present invention, the flow meter includes a second driver and a second sensor, the driver oscillatory driving the loop about an oscillation axis at different points along the loop.

In yet another embodiment of the present invention, the portion of the loop between the pair of drivers is a substantially straight portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a brief description of the drawings will be given.

FIG. 2 is a schematic side view of the device of FIG. 1; FIG. 3 is a schematic diagram showing three modes of operation of the device of FIGS. 1 and 2; FIG. 4 is a cross-sectional view of an electromechanical drive unit according to the present invention; FIG. 5 is a schematic diagram of another embodiment of the electromechanical drive unit of FIG. 4; and FIG. 6 is a cross-sectional view of an electromechanical sensor according to the present invention.

The mechanical structure shown and described is in a perpendicular configuration relative to the main flow of fluid, i.e., the direction of flow in the straight section of the pipeline. The invention is applicable to parallel and other configurations. The illustrated device is designed as a flow meter for various products, such as petroleum-based fuels. The flow meter and electromechanical drive described below can be implemented in various variations.

Figure 1 shows a dual loop, dual drive and sensing device in which the ends of the tubes are connected to a single rigid manifold that is aligned with the main flow of fluid and adapted to accept torsional loads. Figures 1 and 2 show the same embodiment.

The mass flow meter 10 shown in Figures 1 and 2 is designed for insertion into a pipeline (not shown) having a small compartment in which to place the flow meter.
The pipeline is provided with spaced opposing flanges (not shown) that mate with the flowmeter mounting flange 12. The flanges 12 are welded to a short length of pipe 14 that is connected to a central manifold block 16 that supports two parallel planar loops 18, 20.
The shapes and structures of the loops 18 and 20 are substantially identical. Therefore, the following description will be primarily directed to loop 18, with loop 20 provided as a supplement. Manifold block 16 is preferably a generally rectangular casting including a flat, horizontal upper surface or top 21 and the integral pipe section 14. Portions of block 16 are hollowed out to reduce weight. Ends of loop 18 define straight, preferably vertical, parallel inlet and outlet sections or legs 22 and 24 that are secured adjacent to each other, e.g., by butt welding, to manifold top surface 21.
The lower portion of the loop 18 forms a long straight section 26 that passes beneath the manifold block 16. The straight section 26 of the loop 18 is connected to the upright legs 22, 24 by angled sections 30, 32, respectively. The connections 30, 32 between each straight section of the loop 18 are of large radius to minimize resistance to flow. Specifically, the upright legs 22, 24 are connected to the angled sections 30, 32 via top bends 34, 36, and both ends of the lower straight section 26 are connected to the angled sections 30, 32 via downward bends 38, 40.

The parallel inlet and outlet portions 22, 24 of both loops 18, 20 pass through corresponding perforated separator or node plates 42, 44;
Plates 42, 44 are parallel to upper manifold surface 21 and spaced from surface 21 by a predetermined distance.
The loops are welded to act as stress separators and define a common mechanical base for each loop.

Electromechanical driver and detector assemblies are mounted between the loops 18, 20 and on the downward bends 38, 40. Each assembly consists of an electromagnetic driver 46 and a sensor 48 positioned adjacent to each other between the tubes 18, 20. Electrical connections to the driver and sensor are made by leads 50-53 which extend along the exterior of the tubes, pass through plates 42, 44 and connect to an electrical socket 54.

When the drive units 46 at both ends of the tube in FIG. 2 are energized with currents of the same magnitude but opposite signs (180 degrees phase difference), the linear section 2
6 is intended to rotate about a perpendicular bisecting plane 58 (which intersects the tube at point c as shown in FIG. 2), which is preferably a common plane of symmetry for the straight portions of both loops.

The energizing current to the driver is repeatedly reversed (e.g., controlled as a sine wave) so that the linear portion 26 of the loop 18
The linear portion 26 moves in an oscillatory manner in a horizontal plane around the line 56-56. The locus of motion of each linear portion 26 is bow-tie shaped.
The amount of lateral movement at the downward bends 38, 40 is 1 inch for a nominal diameter pipe with a flow length of about 60 cm (2 ft) in the straight section 26.
This displacement acts as a torsional displacement around the axis of the upstanding parallel legs 22, 24, displacing them from the node plate 44.
A similar complementary oscillatory motion occurs in the linear portion of 20.

Three modes of motion of the linear portions of loops 18 and 20 are shown in Figures 3a, 3b, and 3c. As shown in Figure 3b, each tube loop oscillates around point c. Both loops oscillate synchronously in opposite directions; that is, when loop 18 moves clockwise, loop 20 moves counterclockwise. That is, both loops are driven around point c with a 180-degree phase difference. As a result, their respective ends, e.g., A and C in Figure 3, periodically move closer together and apart. This type of driving motion produces a Coriolis effect in the direction shown in Figure 3a. The Coriolis effect causes the entire plane of loops 18 and 20 to move.
The Coriolis effect is greatest when the two straight sections 26 are parallel to each other as shown in Figure 3a, because the sinusoidally varying angular velocity is then greatest. Since the Coriolis motion of each loop is in opposite directions, the straight sections 26 are parallel to each other as shown in Figure 3a.
The loops move somewhat closer together and then apart, as shown in Figure 3c. An undesirable motion for this device is when both loops move in the same direction, as shown in Figure 3c. This motion is easily caused by axial waves in the pipeline, since the loops are oriented perpendicular to the pipeline.

The sensor 48 senses the oscillatory motion of the straight section of the tube and outputs a signal representative of the oscillatory driving force as modified by the Coriolis reaction force caused by the accelerating fluid. Because the driver 46 and sensor 48 are located in close proximity, special care must be taken to prevent magnetic coupling; that is, the magnetic field of the driver 46 tends to induce voltages in the sensor 48, generating spurious signals. For this reason, it is desirable to provide shielding around the driver and sensor to prevent this.

Shielded Drive: A preferred embodiment of the drive assembly 46 is shown in FIG. 4. Of course, this shielded drive converts electrical and mechanical energy. Specifically, the drive converts electrical energy (electrical signals) into mechanical energy (mechanical motion). As shown, the drive assembly 46 includes a proximal end 62 attached to the fluid conduit 18 by a proximal mounting bracket 64 and a distal end 66 attached to the fluid conduit 20 by a distal mounting bracket 68.

Proximal end 62 comprises a magnetic assembly 72 disposed within proximal end shield 70. The proximal end shield is made of soft carbon steel and is cup-shaped, having a cylindrical wall 71 and a flat bottom 73, which is attached to proximal end mounting bracket 64. The dimensions of the proximal end shield are limited by the size and shape of the drive assembly. Proximal end shield 70 acts as a magnetic path reflector, helping to contain magnetic flux within the magnetic assembly. Located in the center of shield 70 is an elongated magnet assembly 72 having a pair of magnets 75, 76 separated by a center pole piece 78. The magnetic orientations of the magnets are in opposite directions along an axis 80-80 defined by the drive assembly.
That is, the magnetic orientations of the magnets 75, 76 are parallel and opposite to one another. In the embodiment shown in FIG. 4, the north poles of the magnets 75, 76 are positioned so that they face the central pole piece 78. Those skilled in the art will appreciate that alternative arrangements, such as having the south poles facing the pole piece 78, may be used. The pole pieces may be made of any known magnetizable material. A preferred material is mild steel. This arrangement of the magnets 75, 76 and the central pole piece 78 concentrates the magnetic flux in a narrow area adjacent the pole piece, maximizing interaction with the coil assembly 82.

The distal end 66 of the drive assembly 60 consists of a coil assembly 82 disposed within a distal end shield 84. The coil assembly 82 includes a coil carrier 86, which is connected at its distal end to the distal end shield 84, which is attached to a distal end mounting bracket 68, which is connected to the fluid conduit 20 by a non-magnetic rivet 106. A bobbin 94 is integrally formed at the distal end of the coil carrier 86. The coil carrier 86 may be made of a non-conductive material to minimize the generation of eddy currents within the coil carrier 86. The bobbin 94 has a winding 96 therearound to form an electromagnetic coil 98.

The coil and coil carrier define an interior space 100 having a generally cylindrical portion 102 and a frusto-conical end portion 104 tapering from the cylindrical portion 102 to accommodate a rivet 106. The cylindrical interior space is large enough to allow free movement of the magnet assembly and to allow maximum interaction of the magnetic field generated by the magnet assembly with the coil assembly.

The proximal and distal shields 70 and 84 are movable relative to one another to minimize leakage of magnetic flux from the device. To this end, the proximal and distal shields are generally cylindrical and overlapping, with one member fitting within the other for free movement; that is, the shields are bayonet-fit. In the embodiment of FIG. 4, both shield members are cylindrical, with the proximal member having a smaller diameter than the distal member and fitting within the distal member for movement along an axis 80-80 defined by the cylindrical shapes of the shields. Leakage of magnetic flux into and out of the device is minimized by the shields and the shielded, enclosed magnetic assembly. Notches (not shown) may be provided in the cylindrical surface of the distal shield to prevent the formation of eddy currents and reduce magnetic flux. Low external magnetic flux allows any number of actuators and sensors to be placed in close proximity without magnetic interference, and the actuators and sensors are not magnetically affected. Another advantage of this arrangement is that multiple magnet assemblies result in linearly increasing forces: relative motion between the proximal and distal ends due to driving currents in the coils does not substantially change the permanent magnetic field, and thus a linear driving force is achieved.

Referring to FIG. 5, another embodiment of an electromagnetic drive is shown. Drive 110 comprises an elongated, soft carbon steel shield 112 having a circular cross section along the axis 114--114 of the shield. The shield has shoulder portions 116, 118, which reduce the open area at each end of the shield and provide an opening through which an elongated magnetic member 120 moves. An annular projection 124 is provided on an inner surface 122 of the shield and projects toward the center of the shield. An electromechanical coil 126 is mounted on the annular projection 124. The elongated magnetic member 120 is disposed in the center of the shield 124. The magnetic member 120 consists of two magnets 128, 130 and three pole pieces 132, 134, 136. The two magnets 128, 130 are disposed on either side of the central pole piece 132, with their magnetic orientations parallel and opposite to each other and parallel to the axis 114-114 of the magnetic member. In the embodiment of FIG. 5, the north poles of the magnets 128, 130 face each other. However, if desired, the south poles may face each other.
128, 130 at the end opposite to the pole piece 132.
6 are attached to the magnets 128, 130 and pole pieces 132,
134, 136 form an elongated magnet assembly which exhibits high efficiency and linearity.

Electromagnetic Design The design of this electromagnetic device is to minimize the current supplied to the coil to generate the maximum force. The force is given by the following equation:

F = N I l B (1) Where, F: force (Newtons) N: number of turns in the coil l: average length per turn of the coil (m) I: coil current (amperes) B: radial density of flux (tesla) To maximize B and maintain linearity of the force, two magnets should be arranged with their pole pieces back to back as shown in Figures 4 and 5. This arrangement causes the flux to vary radially within the area occupied by the coil. The air gap between the pole piece and the shield does not change during the movement of the permanent magnet, reducing nonlinearity.

The embodiment of FIG. 5 has a soft carbon steel shell, three pole pieces, and two
This embodiment concentrates the radial flux in the coil area, thereby obtaining the maximum driving force for a given coil current.

A finite element analysis program was used to calculate the coil inductance and the average radial flux in the coil area. The model was used to determine the optimum electromagnet design to obtain maximum force for a given current flow rate. In the numerical model, the permeability of the soft carbon steel was set to 100, while the permanent magnet and air were set to 1. The permanent magnet remanence was 0.9 Tesla. The calculated average flux density was 477.2 mT. The coil inductance was calculated by simulating the coil as a permanent magnet strip located in the center of the assembly.
The flux distribution through the simulated coil was calculated. The mathematical relationship between the flux and the radial distance was determined. The geometric relationship used was the equation y = k x ⁿ (2) where y is the flux, x is the distance, k and n are the distances between the flux and the radial distance.
is a constant determined by the program.

The average flux is calculated using Equation 2 to determine the effective radial distance. This effective distance is used to estimate the effective annular area of the coil flux (A _m ) and the effective path length of the coil flux (1 _m ). The inductance (L) is then calculated using these: L = NμA _m /l _m (3) where N is the number of turns in the coil and μ is the permeability of free space. The result in Figure 5 is 7·465 mH when N is 450.

An electromagnetic device was constructed to verify the results of the model.
The air gap between the pole piece and the shell is filled with a plastic tube, which fits over the coil and centers the assembly. 450 turns of magnet wire are wound around this tube to form the coil assembly. A small hole (e.g., hole 10 in FIG. 4) is inserted through the tube.
A hole (9) was formed at one end of the shell to allow for the insertion of a Hall-effect sensor to measure the flux density. Two rare-earth magnets with remanence values of 0.85 and 0.93 were used. The magnets were 20 mm in diameter and 10 mm long. The maximum flux density measured was approximately 500 gauss. The inductance measured by an impedance bridge device was 7.75 mH. The experimental results were very close to those predicted by the finite element method, demonstrating the reliability of the theoretical work.

An intrinsically safe mass flow meter must have a low current limit to meet safety requirements so that it will not ignite gases in a flammable environment. Factors that determine the value of the supply current include the coil inductance and resistance, the barrier resistance, the supply voltage, and the cable characteristics. For a large Coriolis mass flow meter, such as a 3-inch diameter fluid conduit, a large drive force is required if the tube is thick and short (necessary for a compact device). This requires a large supply current and would not meet safety requirements. Alternatively, the force can be reduced by using a long tube with a thin wall. This would result in a larger meter and would not be able to use high voltages. Thus, the advantages of the device according to the present invention are clear: a large force can be generated with a small current, resulting in a relatively small and robust device.

Shielded Sensor The shielded sensor assembly 48 is similar to the driver 46 and includes:
6. The sensor assembly 48, like the driver 46,
The sensor converts electrical and mechanical energy. The sensor differs from an electromechanical actuator in that it effectively converts mechanical energy (mechanical motion) into electrical energy (electrical signal). The shielded sensor assembly includes a proximal end 152 attached to flow tube 18 by a proximal mounting bracket 154 and a distal end 156 attached to flow tube 20 by a distal mounting bracket 158.

The proximal end 152 is secured to the proximal end shield by a non-magnetic rivet 162.
The shield includes a coil assembly 162' positioned within 160. The shield is made of mild carbon steel and is cup-shaped with a cylindrical wall 161.
and a flat bottom 163 attached to the proximal mounting bracket 154. The dimensions of the proximal shield member are determined by the overall size and shape of the sensor assembly. At the distal end of the coil assembly is an integral bobbin 169 which is surrounded by wire to form an electromagnetic coil 171. The coil assembly may be formed from a non-magnetic material to prevent the formation of eddy currents. The coil assembly includes generally cylindrical portions 170, 171 and frusto-conical portions 172, 173, with frusto-conical portion 173 being substantially cylindrical.
162. The inner space is generally cylindrical and tapers to an opening 166 that accommodates the rivet 162. The generally cylindrical interior space is large enough to allow movement of the magnet assembly, yet small enough for maximum interaction between the magnetic field emanating from the magnet assembly and the coil assembly.

The distal end 156 includes a distal shield member 176 and a magnetic assembly 178 disposed within the proximal shield. The shield member 176 is made from soft carbon steel and is generally cup-shaped with a cylindrical wall 180 and a flat bottom 182 that is attached to the distal end mounting bracket 158. The dimensions of the distal shield are determined by the overall size and shape of the sensor assembly. The center of the shield member 176 contains the magnet 182 and pole piece.
184. The magnetic orientation of the magnet 178 is along an axis 186-186 defined by the sensor assembly.

As with the shielded actuator described above, the proximal and distal shield members of the shielded sensor are relatively movable, minimizing the escape of magnetic flux into and out of the device. This is accomplished by providing a cylindrical shape for the proximal and distal shield members, allowing a bayonet fit between them for relative movement. In the embodiment of FIG. 6, both members are cylindrical, with the distal shield member having a smaller diameter than the proximal shield member and fitting within the proximal shield member for relative movement along its axis. The shield members provide a shielded, enclosed magnetic assembly, thereby minimizing magnetic flux leakage from the device. The absence of external magnetic flux allows for close placement of any number of actuators and sensors without mutual interference, and prevents the proximal actuators and sensors from interacting magnetically with each other.

Many other modifications, additions, or omissions besides those described above may be made to the illustrated and described embodiments and still be practiced within the spirit or scope of the invention as defined in the following claims or equivalents thereof.

Claims (25)

[Claims] [Claim 1] A shielded electromechanical device used in a Coriolis mass flow meter as a driver for converting electrical energy into mechanical energy or as a sensor for converting mechanical energy into electrical energy, comprising: a base end and a terminal end; a coil assembly coupled to the terminal end; a magnetic assembly coupled to the base end and cooperating with the coil assembly; and a shield assembly surrounding the coil assembly and the magnetic assembly to reduce the magnetic field outside thereof, the shield assembly including a base end shield connected to the base end and a terminal end shield connected to the terminal end, one of the base end shield and the terminal end shield fitted within the other to allow relative movement. 2. The electromechanical device of claim 1,
An electromechanical device, wherein the shield assembly is constructed from a magnetically permeable material. 3. The electromechanical device of claim 2,
1. An electromechanical device, wherein the shield assembly is constructed from steel. 4. The electromechanical device of claim 1,
An electromechanical device, characterized in that the magnetic assembly is made up of magnetic members. 5. The electromechanical device of claim 4,
An electromechanical device characterized in that the magnetic field lines of the magnetic member are oriented generally parallel to an axis extending between the proximal and distal ends. 6. The electromechanical device of claim 4,
The electromechanical device, wherein the magnetic assembly further comprises a pole piece disposed adjacent the magnetic member. 7. The electromechanical device of claim 1,
An electromechanical device comprising a coil assembly defining an interior space, and a magnetic assembly disposed within the interior space. 8. The electromechanical device of claim 7,
An electromechanical device in which the coil assembly is generally cylindrical and magnetically interacts with the magnetic assembly. 9. A Coriolis mass flowmeter, comprising:
1. A shielded electromechanical device for use as a drive that converts electrical energy to mechanical energy or a sensor that converts mechanical energy to electrical energy, comprising: a proximal end and a distal end; a coil assembly coupled to the distal end; a magnetic assembly coupled to the proximal end and cooperating with the coil assembly, the magnetic assembly comprising first and second magnetic members and pole pieces, the pole pieces being positioned adjacent to the first magnetic member and the second magnetic member being positioned adjacent to the pole pieces; and a shield assembly surrounding the coil assembly and the magnetic assembly to reduce magnetic fields external thereto. 10. The electromechanical device of claim 9, wherein the magnetic field lines of the first and second magnetic members are oriented substantially parallel to an axis extending between the proximal and distal ends. 11. The electromechanical device according to claim 10, wherein the magnetic lines of force of the first and second magnetic members are in opposite directions. 12. The electromechanical device of claim 11, wherein the first and second magnetic members and the pole pieces are disposed on an axis extending between the proximal and distal ends. 13. The electromechanical device of claim 12, further comprising end pole pieces positioned adjacent to the first and second magnetic members and on an axis extending between the proximal and distal ends. 14. The electromechanical device of claim 13, wherein the pole pieces and end pole pieces are constructed from a highly magnetically permeable material. 15. The electromechanical device of claim 14, wherein the highly magnetically permeable material is steel. 16. A Coriolis mass flow meter comprising: a support; a continuous first conduit loop having an inlet end and an outlet end affixed to the support; a shielded electromechanical driver for acting on the first conduit loop to oscillate it about an oscillation axis, the driver comprising: a proximal end and a distal end; a coil assembly coupled to the distal end; a magnetic assembly coupled to the proximal end and cooperating with the coil assembly; and a shield assembly surrounding the coil assembly and the magnetic assembly to reduce magnetic fields external thereto; and a sensor for measuring the magnitude of the Coriolis force resulting from mass flow in the portion of the first conduit loop undergoing oscillating motion, the sensor comprising: a proximal end and a distal end; the coil assembly coupled to the distal end; and a magnetic assembly coupled to the proximal end and cooperating with the coil assembly. a sensor including a coil assembly and a shield assembly that surrounds the magnetic assembly to reduce a magnetic field outside thereof, wherein the drive unit and the sensor are arranged in parallel on a first conduit loop. 17. A Coriolis mass flowmeter according to claim 16, further comprising a second continuous conduit loop having its inlet and outlet ends fixed to the support. 18. A Coriolis mass flowmeter according to claim 17, wherein the first and second conduit loops are arranged substantially parallel to each other. 19. A Coriolis mass flowmeter according to claim 17, wherein the driver and the sensor are disposed between the first and second conduit loops. 20. A Coriolis mass flowmeter as claimed in claim 19, wherein the base end of the driver and the base end of the sensor are connected to one of the first and second conduit loops, and the distal end of the electromechanical driver and the distal end of the sensor are connected to the other. 21. A Coriolis mass flow meter comprising: a support; a continuous first conduit loop having an inlet end and an outlet end affixed to the support; a shielded electromechanical driver for acting on the first conduit loop to oscillate the loop about an oscillation axis, the driver comprising: a proximal end and a distal end; a coil assembly coupled to the distal end; a magnetic assembly coupled to the proximal end and cooperating with the coil assembly; and a shield assembly surrounding the coil assembly and the magnetic assembly to reduce an external magnetic field therebetween; and a continuous second conduit loop having an inlet end and an outlet end affixed to the support; A Coriolis mass flow meter, characterized in that a driving unit and a sensor are disposed between first and second conduit loops, a base end of the driving unit and a base end of the sensor are connected to one of the first and second conduit loops, a distal end of the driving unit and a distal end of the sensor are connected to the other conduit loop, and the driving unit and the sensor are disposed in parallel. 22. A Coriolis mass flow meter comprising: a support; a continuous conduit loop having an inlet end and an outlet end affixed to the support; a shielded electromechanical first drive section for acting on the conduit loop to oscillate it about an oscillation axis, the first drive section having proximal and distal ends; a coil assembly coupled to the distal end; a magnetic assembly coupled to the proximal end and cooperating with the coil assembly; and a shield assembly surrounding the coil assembly and the magnetic assembly to reduce magnetic fields external thereto; and a first sensor for measuring the magnitude of the Coriolis force resulting from mass flow in the portion of the conduit loop undergoing oscillating motion, the first sensor having proximal and distal ends; the coil assembly coupled to the distal end; and a magnetic assembly coupled to the proximal end and cooperating with the coil assembly. A Coriolis vibratory flowmeter comprising: a first sensor having a coil assembly and a shielding assembly surrounding a magnetic assembly to reduce an external magnetic field; an electromechanical second drive unit; and a second sensor, wherein the first and second drive units are configured to drive a conduit loop at different points along the loop about a vibration axis. 23. A Coriolis vibratory mass flowmeter according to claim 22, wherein the portion of the conduit loop between the first and second drive sections is a substantially straight portion. 24. A Coriolis mass flowmeter comprising: a support; first and second continuous conduit loops arranged in parallel, each having an inlet end and an outlet end fixed to said support; a shielded driver disposed between said first and second conduit loops for acting on said conduit loops to vibrate said loops about an oscillation axis, said driver having a base end connected to one of said first and second conduit loops;
and a terminal end connected to the other of the conduit loops; a coil assembly coupled to the terminal end; a magnetic assembly coupled to the base end and cooperating with the coil assembly; and a shield assembly surrounding the coil assembly and the magnetic assembly to reduce an external magnetic field, the shield assembly including a base end shield connected to the base end and a terminal end shield connected to the terminal end, one of the base end shield and the terminal end shield fitted to the other so that they can move relative to each other; and a sensor for measuring the magnitude of the Coriolis force generated as a result of mass flow in the portion of the conduit loop undergoing oscillating motion. [Claim 25] A Coriolis type vibratory flowmeter as described in claim 24, wherein the sensor comprises: a base end and a terminal end; a coil assembly coupled to the terminal end; a magnetic assembly coupled to the base end and cooperating with the coil assembly; and a shield assembly surrounding the coil assembly and the magnetic assembly to reduce external magnetic fields.