Abstract:
A method of manufacturing a Coriolis flowmeter for the measurement of a process material requiring an ultra high level of purity. This is achieved by forming the entire flow path of the Coriolis flow meter from a PFA plastic material that does not transfer ions from the Coriolis flowmeter to the process material flowing through the flowmeter.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a method of manufacturing a Coriolis flowmeter that measures a flow of process material having an ultra high level of purity.  
         PROBLEM  
         [0002]    It is known to use Coriolis effect mass flowmeters to measure mass flow and other information pertaining to materials flowing through a pipeline as disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and Re. 31,450 to J. E. Smith of Feb. 11, 1982. Flowmeters have one or more flow tubes of astraight, curved or irregular configuration. Each flow tube has a set of natural vibration modes which may be of a simple bending, torsional, or twisting type. Each material filled flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes are defined in part by the combined mass of the flow tubes and the material within the flow tubes. If desired, a flowmeter need not be driven at a natural mode.  
           [0003]    Material flows into the flowmeter from a connected material source on the inlet side. The material passes through the flow tube or flow tubes and exits the outlet side of the flowmeter.  
           [0004]    A driver applies force to oscillate the flow tube. When there is no material flow, all points along a flow tube oscillate with an identical phase in the first bending mode of the flow tube. Coriolis accelerations cause each point on the flow tube to have a different phase with respect to other points on the flow tube. The phase on the inlet side of the flow tube lags the driver; the phase on the outlet side leads the driver. Pickoffs are placed on the flow tube to produce sinusoidal signals representative of the motion of the flow tube. The phase difference between two sensor signals is divided by the frequency of oscillation to obtain a delay which is proportional to the mass flow rate of the material flow.  
           [0005]    It is known to use flowmeters having different flow tube configurations. Among these configurations are single tube, dual tube, straight tube, curved tube, and flow tubes of irregular configuration. Most of the flowmeters are made of metal such as aluminum, steel, stainless steel and titanium. Glass flow tubes are also known. In addition, all straight serial path flowmeters currently in the art are made out of metal, particularly Titanium, or are metal tubes lined with plastic, particularly PTFE or PFA.  
           [0006]    The positive attributes of Titanium in these types of flowmeters are its high strength and low coefficient of thermal expansion (CTE). The negative attributes of Titanium are its metallic properties and cost of manufacturing. For example, in semiconductor wafer processing, metal ions are a contaminant. Metal ions in contact with the wafer areas of an integrated circuit can cause a short circuit and ruin the device. Also, a Titanium flowmeter is difficult and expensive to produce.  
           [0007]    Flow tubes lined with PFA, as disclosed in U.S. Pat. No. 5,403,533 to Dieter Meier, attempted to combine the positive attributes of both technologies but encountered new challenges that could not be solved until the present invention. Metal flow tubes lined with PFA still allowed metal ions to migrate through the thin coating layer of PFA and into the flow stream, causing contamination. Also, the flow tube material and the PFA liner had different thermal properties. This caused the PFA liner to disengage from the flow tube creating leaks and performance problems. The manufacturing process for lining the metal flow tubes with PFA is also extremely costly. The prior art also suggests plastic flow tubes and plastic flowmeters. This includes prior art in which the entirety of the flowmeter is plastic as well as that in which only the flow tube is formed of plastic. Much of this prior art is directed to metal flowmeters and merely contains an assertion that a flowmeter may be made of various materials such as steel, stainless steel, titanium or plastic. This prior art is not instructive in so far as concerns the disclosure of a plastic Coriolis flowmeter that can accurately output information over a range in operating conditions including temperature.  
           [0008]    The mere substitution of a plastic flow tube for a metal flow tube will produce a structure that looks like a flowmeter. However, the structure will not function as a flowmeter to generate accurate output information over a useful range of operating conditions. The mere assertion that a flowmeter could be made out of plastic is nothing more than the abstraction that plastic can be substituted for metal. It does not teach how a plastic flowmeter can be manufactured to generate accurate information over a useful range of operating conditions.  
           [0009]    It is a problem in some applications that the typical Coriolis flow meter may contaminate the process material. This is undesirable for systems in which material of an ultra high level of purity must be delivered by the flowmeter to a user application. This is the case in the fabrication of semi-conductor wafers which requires the use of a process material that is free of contaminants including ions migrating from the tubes of the process material flow path. In such applications, the flow tube can be a source of contaminants. The metal walls of a flow tube can release ions into the process material flow. The released ions can cause the chips on a semi-conductor wafer to be defective. The same is true for a glass flow tube which can release the lead ions from the glass into the process material flow. The same is also true for the flow tubes formed of conventional plastics.  
           [0010]    A plastic termed PFA is free from this objection since the material of which it is composed does not release deleterious ions into the material flow. The use of PFA for a flow tube is suggested in U.S. Pat. No. 5,918,285 to Vanderpol. This suggestion is incidental to the Vanderpol disclosure since the patent discloses no information regarding how a flowmeter having a PFA flow tube could be manufactured to generate accurate flow information.  
         SOLUTION  
         [0011]    The above and other problems are solved and an advance of the art is achieved by the present invention which discloses a Coriolis flowmeter having at least one flow tube formed of perfluoroalkoxy copolymer (PFA) plastic which is coupled to a driver and to at least one pick-off sensor to enable the PFA flow tube to function as part of Coriolis flowmeter that can provide accurate output information over range of operating conditions for a material flow and ultra high purity suitable for use in applications such as semi-conductor fabrication and the like which require the material flow to be free of contaminants and to the ionic level.  
           [0012]    A flow path constructed entirely of PFA has many of the benefits of Titanium and PFA lined flow tubes without the drawbacks. PFA is a fluoropolymer with superior chemical resistance, little metal ion release, low particle generation, and is manufacturable without expending large amounts of capital. PFA material is strong and can be extruded into high quality thin wall tubing. Thin-walled PFA tubing has low flexural stiffness enabling a higher sensitivity to mass flow rate and improved immunity to elastic dynamic interaction between the flow tube and the process pipeline. The material and physical properties of PFA allow larger tube vibration amplitudes at higher stress levels and resulting near infinite fatigue life span. Also, the higher vibration amplitude allows the use of small low-mass transducers, which in turn improves density sensitivity and immunity to mount variation.  
           [0013]    A first preferred exemplary embodiment of the invention comprises a flowmeter having a single PFA plastic flow tube vibrationally connected to a massive metal base which vibrationally balances the end nodes of the flow tube. In this embodiment, the base is U-shaped and the plastic flow tube extends through holes in the outer portion of the leg of the U. The plastic flow tube is affixed to the base structure by means of an O-ring or an appropriate adhesive, particularly cyanoacrylate, which surrounds the flow tube and rigidly adheres the flow tube to the metal base. The center of the flow tube is affixed to an electro-magnetic driver which receives a drive signal from suitable meter electronics to vibrate the flow tube transversely to the longitudinal access of the flow tube. The flow tube is also coupled to pick-off sensors which detect the Coriolis response of the material flow within the vibrating flow tube. Connected to the base and terminating the flow tube are process connections, also made out of PFA.  
           [0014]    PFA is a fluorinated polymer that is chemically inert and has a very low surface energy, making it difficult to bond to using common adhesives or solvents. In order to facilitate the bonding between the PFA components of the flowmeter and non-PFA components. A preferred method of manufacturing includes a process whereby the PFA components are etched. Etching changes the exterior surface chemistry of the PFA components allowing them to be bonded to non-PFA components. The etching process entails submersing the PFA components into a heated bath containing a glycol diether, preferably diglyme-sodium naphthalene, and gently agitate the PFA components for a period of time.  
           [0015]    Another characteristic of PFA, specific to tubing, is that its method of manufacture results in tubing that has inherent bends or curvature that need to be eliminated from the tubing prior to manufacturing it into a flowmeter. A preferred method of eliminating unwanted curvatures in the tubing prior to processing is to straighten the flow tube through an annealing process. The annealing process comprises placing the flow tube in a straightening fixture. The fixture restrains the tube in a straight form suitable for processing into a flowmeter. The flow tube and fixture are the heated for a period of time and then removed and allowed to cool to room temperature. Upon reaching room temperature the flow tubes are removed from the fixture resulting in a straight flow tube.  
           [0016]    As described in the first preferred embodiment, the flow tube has coupled to it pick-off means. In one embodiment the pick-off means are of the coil/magnet form. The magnet is attached to the flow tube using an adhesive and the coil is attached to the base using either an adhesive or mechanical connection. In an alternative embodiment, the pick-offs are optical devices which send and receive a light beam and which is modified by the motion of the flow tube. In order to facilitate the use of optical pick-offs potions of the flow tube are made opaque. This allows the light to be reflected off the flow tube or absorbed by the opaque coating instead of being passed through the normally translucent flow tube. The flow tube can be made opaque through various means including using coatings or paints. The optical sensing embodiment offers the advantage of lighter weight on the vibrating flow tube.  
           [0017]    As described in the first preferred embodiment the flow tube is coupled to a process connection to form a flow path of PFA. In a further embodiment this connection is achieved by flaring the flow tube so as to allow it to be inserted over the nipple of the process connection. In another embodiment the flow tube is inserted into the thru-hole of the process connection and sealed at the face of the process connection.  
           [0018]    In a preferred embodiment the tube is sealed to the face of the process connection by the process of laser welding. Laser welding is a non-contact form of welding that generates heat at the interface between the flow tube and the face of the process connection. Other methods of sealing the flow tube to the face of the process connection are heated tip welding, ultrasonic welding, and adhesives.  
           [0019]    In addition to the tube being coupled to the process connection the process connection is also coupled to the base. The preferred method of coupling the process connection to the base is to form a hole in the base and secure the end of the process connection into the hole. The process connection can be secured by tapping the base hole and threading the process connection end into the tapped hole. An alternative to the above method is to simply bond the process connection end into the base hole using an adhesive. An additional method of securing the process connection to the base is to form a locking hole in the base. The hole is formed such that the centerline of the locking hole intersects with the centerline of the receiving hole. After the holes are formed and the process connection end is inserted into the receiving hole, a locking mechanism is inserted in to locking hole to secure the process connection. A preferred embodiment for locking the process connection into the receiving hole is to tap the locking hole and thread into the locking hole a set screw that what compress the process connection and prevent movement.  
           [0020]    Other flow tube configurations are provided in accordance with other embodiment of the inventions. The invention may be practiced with the use of dual flow tubes vibrating in phase opposition. These dual tubes may either be of the straight type, they may be u-shaped, or they may be of an irregular configuration. The use of dual flow tubes is advantageous in that it provides a dynamically balanced structure and reduces the mass of the base required to mount the flow tubes.  
           [0021]    In accordance with yet another embodiment, when dual straight flow tubes are used, they may be mounted on the base and vibrated in phase opposition in either a horizontal plane or a vertical plane. Vibration in a horizontal plane perpendicular to the bottom surface of the U-shaped base eliminates vertical shaking of the flowmeter structure but permits horizontal shaking if the dual flow tubes are not dynamically balanced. The mounting of the flow tubes in a vertical plane with respect to each other limit any undesired vertical vibrations.  
           [0022]    An additional embodiment that can be associated with any tube configuration is the implementation of a temperature measurement device. A preferred embodiment is the use of a Resistive Temperature Device (RTD) attached to a flow tube. In accordance with another embodiment the temperature can be measured using an infrared temperature measurement device. The benefits to this device is that it is non-contact and can be located off the tube, thereby reducing mass on the tube.  
           [0023]    In summary, the flowmeter embodying the present invention is advantageous in that it provides for the measurement and delivery of an ultra pure process material in applications that require the delivered material to be free of contamination. This level of purity is provided by the use of a PFA plastic flow tube which is chemically inert and which is superior to metals and glass permit ion transfer from the flow tube material to the processed material. The processed material may typically comprise a slurry which is an organic compound used as a polishing agent in the fabrication of wafers in the semi-conductor industry. This polishing operation serves to provide a flat surface for the wafers. The polishing operation can take from 60 to 90 seconds and during this time the slurry must be free from any contaminants including ions transferred from the flow tube material to the slurry. The deposit of even a single undesired ion onto a semi-conductor wafer can short circuit all or a portion of the wafer and render it useless.  
           [0024]    It can be seen that an aspect of the invention is a method of manufacturing a Coriolis flowmeter adopted to extend a received process material flow having an ultra high level of purity free from contamination due to ion transfer from said Coriolis flow meter to said process material; said method comprising the steps of:  
           [0025]    coupling a flow tube means to a base;  
           [0026]    affixing a driver to said flow tube means;  
           [0027]    coupling a pick-off means to said flow tube means; and  
           [0028]    affixing inlet and outlet ends of said flow tube means to at least one process connection to form an ultra pure flow path for a process material flow through said flow tube means.  
           [0029]    Preferably said step of coupling a flow tube means to said base further comprises the step of using said flow tube means formed from PFA to maintain said process material flow free from contamination due to ion transfer from material of a flow tube to process material.  
           [0030]    Preferably said step of coupling said flow tube to said base is proceeded by the step of etching said flow tube to create a surface suitable for coupling and affixing flowmeter components.  
           [0031]    Preferably said etching step comprises the step of using an etching solution containing a glycol diether.  
           [0032]    Preferably said etching step comprises the step of heating said etching solution to an elevated temperature.  
           [0033]    Preferably said etching step comprises the step of agitating said flow tube means in said etching solution.  
           [0034]    Preferably said step of coupling said flow tube to a base is proceeded by the step of straightening said flow tube means to eliminate any inherent curvature or unwanted residual bends.  
           [0035]    Preferably said straightening step comprises the steps of:  
           [0036]    placing said flow tube means in a straightening fixture;  
           [0037]    heating said flow tube means and said straightening fixture;  
           [0038]    cooling said flow tube means and said straightening fixture;  
           [0039]    removing said flow tube means from said straightening fixture.  
           [0040]    Preferably said step of joining said flow tube means to said base comprises the step of attaching said flow tube means to said base using adhesive.  
           [0041]    Preferably said step of attaching said flow tube means to said base using said adhesive comprises the step of using cyanoacrylate adhesive.  
           [0042]    Preferably said step of joining said flow tube means to said base comprises the step of coupling said flow tube to said base using an O-ring.  
           [0043]    Preferably said step of affixing said driver means to said flow tube means further comprises the step of attaching said driver means to said flow tube means using adhesive.  
           [0044]    Preferably said step of affixing said driver means to said flow tube means further comprises the step of using cyanoacrylate adhesive.  
           [0045]    Preferably said step of affixing said pick-off means to said flow tube means further comprises the step of attaching said pick-off means to said flow tube using adhesive.  
           [0046]    Preferably said step of affixing said pick-off means to said flow tube means further comprises the step of using cyanoacrylate adhesive.  
           [0047]    Preferably said method of manufacturing a Coriolis flow meter further comprises coupling said at least one process connection to said base.  
           [0048]    Preferably said step of joining said process connection to said base comprises the steps of:  
           [0049]    forming a receiving hole into said base;  
           [0050]    securing a fixed portion of said process connection into said receiving hole.  
           [0051]    Preferably said step of securing said fixed portion of said process connection into said receiving hole comprises the step of adhering said fixed portion of said process connection into said receiving hole.  
           [0052]    Preferably said step of securing said fixed portion of said process connection into said receiving hole further comprises the step of using cyanoacrylate adhesive.  
           [0053]    Preferably said step of securing said fixed portion of said process connection into said receiving hole comprises the step of threading a fixed portion of said process connection into said receiving hole Preferably said step of securing said fixed portion of said process connection into said receiving hole comprises the steps of:  
           [0054]    forming a locking hole whose centerline intersect the centerline of the receiving hole; and  
           [0055]    inserting a locking mechanism into said locking hole to prevent said fixed portion of said process connection from moving.  
           [0056]    Preferably said step of inserting a locking mechanism into said locking hole comprises inserting a set screw that compresses said fixed portion of said process connection.  
           [0057]    Preferably said step of coupling said process connection to said base comprises the step of adhering a fixed portion of said of said process connection onto said base.  
           [0058]    Preferably said step of adhering a fixed portion of said of said process connection onto said base further comprises the step of using cyanoacrylate adhesive.  
           [0059]    Preferably said step of affixing said end of said flow tube means to said at least one process connection comprises the steps of:  
           [0060]    flaring said end of said flow tube means; and  
           [0061]    inserting said flared end of said flow tube means onto conical stub of said at least one process connection.  
           [0062]    Preferably said step of affixing said end of said flow tube means to said at least one process connection comprises the steps of:  
           [0063]    inserting said end of said flow tube means through said at least one process connection until said end of said flow tube means are flush with face of said at least one process connection; and  
           [0064]    sealing said end of said flow tube means to said face of said at least one process connection.  
           [0065]    Preferably said step of sealing said end of said flow tube means to said face of said at least one process connection comprises the step of adhering said end of said flow tube means to said face of said at least one process connection.  
           [0066]    Preferably said step of sealing said end of said flow tube means to said face of said at least one process connection comprises the step of ultrasonically welding said end of said flow tube means to said face of said at least one process connection.  
           [0067]    Preferably said step of sealing said end of flow tube means to said face of said at least one process connection comprises the step of heat tip welding said end of said flow tube means to said face of said at least one process connection.  
           [0068]    Preferably said step of sealing said end of flow tube means to said face of said at least one process connection comprises the step of laser welding said end of said flow tube means to said face of said at least one process connection.  
           [0069]    Preferably said step of coupling said pick-off means comprises the step of making portions of said flow tube means opaque in order to facilitate use of optical pick-offs.  
           [0070]    Preferably said Coriolis meter is characterized by affixing a temperature sensing device to said Coriolis flowmeter.  
           [0071]    Preferably said step of affixing a temperature sensing device comprises the step of affixing a resistance temperature measuring device to said Coriolis flowmeter. Preferably said step of affixing a temperature sensing device comprises the step of affixing an infrared temperature measuring device to said Coriolis flowmeter.  
           [0072]    An additional aspect of the invention includes, a Coriolis flowmeter for measuring a process material flow having an ultra high level of purity; said Coriolis flowmeter comprising:  
           [0073]    a base;  
           [0074]    flow tube means coupled to said base;  
           [0075]    a driver affixed to said flow tube means for vibrating said flow tube means at the resonant frequency of said flow tube means with process material flow;  
           [0076]    pick-off means coupled to said flow tube means for generating signals representing induced Coriolis deflections of the portions of said vibrating material filled flow tube means proximate said pick-off means; and  
           [0077]    at least one process connection means coupled to said flow tube means to form an ultra pure flow path for a process material to flow through.  
           [0078]    Preferably said Coriolis flowmeter is formed of PFA to maintain said process material flow free from contamination due to ion transfer from said flow tube means to said process material.  
           [0079]    Preferably said Coriolis flow meter comprises an O-ring for coupling said flow tube means to said base.  
           [0080]    Preferably said Coriolis flow meter is characterized in that said process connection means is coupled to said base.  
           [0081]    Preferably said base comprises at least one receiving hole for securing a fixed portion of said process connection means.  
           [0082]    Preferably said receiving hole for securing a fixed portion of said process connection means is threaded.  
           [0083]    Preferably said base comprises at least one locking hole for securing said process connection means into said receiving hole.  
           [0084]    Preferably said locking hole for securing said process connection means into said receiving hole is threaded.  
           [0085]    Preferably said locking hole for securing said process connection means into said receiving hole comprises a locking mechanism.  
           [0086]    Preferably said locking mechanism for securing said process connection means into said receiving hole is a set screw.  
           [0087]    Preferably said process connection means is of the flare connection type.  
           [0088]    Preferably said flow tube means comprises portions that are opaque preventing light from passing through said flow tube means.  
           [0089]    Preferably said Coriolis flowmeter further comprises a temperature sensing device.  
           [0090]    Preferably said temperature sensing device is of the resistive type.  
           [0091]    Preferably said temperature sensing device is of the infrared type. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0092]    These and other advantages and features of the present invention may be better understood in connection with a reading of the following detailed description thereof in connection of the drawings in which:  
         [0093]    [0093]FIG. 1 discloses a perspective view of a first exemplary embodiment of the invention.  
         [0094]    [0094]FIG. 2 is a top view of the embodiment of FIG. 1.  
         [0095]    [0095]FIG. 3 is a front view of the embodiment of FIG. 1.  
         [0096]    [0096]FIG. 4 is a cross-sectional view taken along lines  4 - 4  of FIG. 2.  
         [0097]    [0097]FIG. 5 is a perspective view of an alternative embodiment having a pair of base elements.  
         [0098]    [0098]FIG. 6 discloses a dynamically balanced flowmeter having a U-shaped base.  
         [0099]    [0099]FIGS. 7 and 8 disclose a flowmeter having optical pick-offs.  
         [0100]    [0100]FIGS. 9 and 10 disclose flowmeters having dynamic balancers.  
         [0101]    [0101]FIG. 11 discloses a flowmeter having a pair of substantially U-shaped flow tubes.  
         [0102]    [0102]FIGS. 12 and 13 discloses another embodiment of a flowmeter having a pair of dynamically balanced straight flow tubes.  
         [0103]    [0103]FIG. 14 discloses an alternative embodiment having a single flow tube and no return tube.  
         [0104]    [0104]FIG. 15 discloses an alternative embodiment having two flow tubes vibrated in phase opposition.  
         [0105]    [0105]FIG. 16 discloses an alternative embodiment having a single flow tube. 
     
    
     DETAILED DESCRIPTION  
       [0106]    Description of FIG. 1  
         [0107]    [0107]FIG. 1 is a perspective view of a first possible exemplary embodiment of the invention and discloses a flowmeter  100  having a flow tube  102  inserted through legs  117 ,  118  of base  101 . Pick-offs LP 0  and RP 0  and driver D are coupled to flow tube  102 . Flowmeter  100  receives a process material flow from supply tube  104  and extends the flow through process connection  108  to flow tube  102 . Flow tube  102  is vibrated at its resonant frequency with material flow by driver D. The resulting Coriolis deflections are detected by pick-offs LP 0  and RP 0  which apply signals over conductors  112  and  114  to meter electronics  121 . Meter electronics  121  receives the pick-off signals, determines the phase difference between, determines the frequency of oscillation and applies output information pertaining to the material flow over output path  122  to a utilization circuit not shown.  
         [0108]    The material flow passes from flow tube  102  and through tube  106  which redirects the material flow through return tube  103  through process connection  107  to exit tube  105  which delivers the material flow to a user application. This user application may be a semiconductor processing facility. The process material may be a semiconductor slurry which is applied to the surface of a semiconductor wafer to form a flat surface. The PFA material used in the flow tubes shown on FIG. 1 ensures that the process material is free of impurities such as ions which could be transferred from the walls of metals or glass flow tubes.  
         [0109]    In use, flow tube  102  is of a narrow diameter approximating that of a soda straw and of negligible weight such as, for example, 0.8 gram plus 0.5 gram for the process material. This excludes the weight of the magnets. The magnets associated with the pick-offs and driver have a mass of about 0.6 grams total so that the combined mass of the flow tube  102 , the affixed magnets and the process material is approximately 2 grams. Vibrating flow tube  102  is a dynamically unbalanced structure. Base  102  is massive and weighs approximately 12 pounds. This provides a ratio of the mass of the base to that of a material filledflow tube of approximately 3,000 to 1. A base of this mass is sufficient to absorb vibrations generated by the dynamically unbalanced flow tube  102  with material flow.  
         [0110]    Process connections  107 ,  108 ,  109  and  110  connect tubes  104 ,  105  and  106  to the ends of flow tube  102  and return tube  103 . These process connections are shown in detail in FIG. 4. The process connections have a fixed portion  111  that includes threads  124 . Locking holes  130  receive set screws  411  to fixably connect element  111  to base  101  as shown in FIG. 4. The movable portion of process connections  107  through  110  are threaded onto male threads  124  to connect their respective tubes to the fixed body of the process connection of which the hexagonal nut portion  111  is a part. These process connections function in a manner similar to the well known copper tubing flared process connections to connect tubes  104 ,  105  and  106  to ends of flow tube  102  and return tube  103 . Details regarding the process connections are further shown in FIG. 4. RTD is a temperature sensor that detects the temperature of return tube  103  and transmits signals representing the detected temperature over path  125  to meter electronics.  
         [0111]    Description of FIG. 2  
         [0112]    In FIG. 2 is a top view of flowmeter  100  of FIG. 1. Pick-offs LP 0  and RP 0  and driver D each include a coil C. Each of these elements further includes a magnet which is affixed to the bottom portion of flow tube  102  as shown in FIG. 3. Each of these elements further includes a base, such as  143  for driver D, as well as a thin strip of material, such as  133  for driver D. The thin strip of material may comprise a printed wiring board to which coil C and its winding terminals are affixed. Pickoffs LP 0  and RP 0  also have a corresponding base element and a thin strip fixed to the top of the base element. This arrangement facilitates the mounting of a driver or a pickoff to be accomplished by the steps of gluing a magnet M to the underside of PFA flow tube, gluing the coil C to a printed wiring board  133  (for driver D), positioning the opening in coil C around the magnet M, moving the coil C upwardly so that the magnet M fully enters the opening in coil C, then positioning base element  143  underneath the printed wiring board  133  and gluing these elements together so that the bottom of base  143  is affixed by glue to the surface of the massive base  116 .  
         [0113]    The male threads  124  of process connections  107 - 110  are shown on FIG. 2. The inner details of each of these elements is shown on FIG. 4. Opening  132  receives conductors  112 ,  113  and  114 . Meter electronics  121  of FIG. 1 is not shown on FIG. 2 to minimize drawing complexity. However it is to be understood that the conductors  112 ,  113  and  114  extend through opening  132  and further extend over path  123  of FIG. 1 to meter electronics  121  of FIG. 1.  
         [0114]    Description of FIG. 3  
         [0115]    [0115]FIG. 3 shows pick-offs LP 0 , RP 0  and driver D as comprising a magnet M affixed to the bottom portion of flow tube  102  and a coil C affixed to the base of each of elements LP 0 , RP 0  and driver D.  
         [0116]    Description of FIG. 4  
         [0117]    [0117]FIG. 4 is a sectional taken along line  4 - 4  of FIG. 2. FIG. 4 discloses all the elements of FIG. 3 and further details of process connections  108  and  109  and O-rings  430 . O-rings  430  couple flow tube  102  to base  401 . FIG. 4 further discloses openings  402 ,  403  and  404  in base  101 . The top of each of these openings extends to the lower surface of the base of pick-offs LP 0 , RP 0  and driver D. The coil C and magnet M associated with each of these elements is also shown on FIG. 4. Meter electronics  121  of FIG. 1 is not shown on FIGS. 3 and 4 to minimize drawing complexity. Element  405  in process connection  108  is the inlet of flow tube  102 ; element  406  in process connection  109  is the outlet of flow tube  102 .  
         [0118]    The fixed portion  111  of process connection  108  includes male threads  409  which screw into mating threads in receiving hole  420  located in base  401  to attach fixed portion  111  to segment  401  of base  101 . The fixed portion of process connection  109  on the right is similarly equipped and attached by threads  409  into receiving hole  420  located in element  401  of base  101 .  
         [0119]    Fixed element  111  of process connection  108  further includes a threaded portion  124  whose threads receive the movable portion  415  of process connection  108 . Process connection  109  is similarly equipped. Fixed element  111  of process connection  108  further includes on its left a conical stub  413  which together with movable element  415  acts as a flare fitting to force the right end of input tube  104  over the conical stub  413  of fixed portion  111 . This creates a compression fitting that sealably affixes the flared opening of supply tube  104  onto the conical stub portion  413  of fixed portion  111  of the process connection. The inlet of flow tube  102  is positioned in process connection fixed portion  111  and is flush with face  425  of stub  413 . By this means, the process material delivered by supply tube  104  is received by inlet  405  of flow tube  102 . The process material flows to the right through flow tube  102  to fixed portion  111  of process connection  109  where the outlet  406  of flow tube  102  is flush with face  425  of stub  413 . This sealably affixes the outlet of flow tube  102  to connector  109 . The other process connections  107  and  110  of FIG. 1 are identical to those described for the details of process connections  108  and  109  on FIG. 4.  
         [0120]    Description of FIG. 5  
         [0121]    [0121]FIG. 5 discloses flowmeter  500  as an alternative embodiment of the invention similar to that of FIG. 1 except that the base of the flowmeter  500  is not a single element and comprises separate structures  517  and  518 . Flow tube  502  and return tube  503  extend through the elements  517 ,  518  to process connections  507  through  510  which are comparable in every respect to process connections  107  through  110  of FIG. 1. Flowmeter base elements  517 ,  518  are separate and each is of sufficient mass to minimize the vibrations imparted by driver D to the dynamically unbalanced structure comprising flow tube  502 . Base elements  517  and  518  rest on surface  515  of element  516  which supports base elements  517  and  518 .  
         [0122]    All elements shown on FIG. 5 operate in the same manner as do their corresponding elements on FIG. 1. This correspondence is shown by the designation of each element which differs only in that the first digit of the part designation of the element. Thus, supply tube  104  on FIG. 1 corresponds to supply tube  504  on FIG. 5.  
         [0123]    Description of FIG. 6  
         [0124]    [0124]FIG. 6 discloses yet another alternative embodiment of the invention as comprising flowmeter  600  which is different from the embodiment of FIG. 1 in that flowmeter  600  has two active flow tubes  602  and  603  which comprise a dynamically balanced structure that does not require the massive base such as base  101  of FIG. 1. Base  601  may have significantly less mass than that of FIG. 1. Flowmeter  600  has process connections  607  through  610  comparable to process connections  107 - 110  of FIG. 1. In addition, it has process connections  611 ,  612 . Process material is received by flowmeter  600  from a supply tube  604 . The material extends via a process connection  608  to the left end of flow tube  602 . Flow tube  602  extends through leg  618  of base  601  and process connection  609  by means where it is connected to tube  615  which loops back via process connection  607  to flow tube  603 . Flow tube  603  is vibrated in phase opposition to flow tube  602  by driver D. The Coriolis response of the vibrating flow tubes  602  and  603  is detected by pick-offs LP 0  and RP 0  and transmitted via conductors not shown to meter electronics element also not shown to minimize drawing complexity.  
         [0125]    The material flow through tube  603  proceeds to the right and extends via process connection  610  to tube  606  which loops back through process connection  611  and tube  616 , process connection  612  to return flow tube  605  which delivers the material flow to the application process of the end user.  
         [0126]    Flow tube  600  is advantageous in that it comprises a dynamically balanced structure of flow tubes  602  and  603  formed of PFA material. The dynamically balanced structure is advantageous in that the massive base  101  of FIG. 1 is not required. Base  601  may be of conventional mass and vibrating PFA tubes  602  and  603  to provide output information pertaining to the material flow. The PFA flow tubes ensure that the material flow have an ultra high level of purity.  
         [0127]    Description of FIGS. 7 and 8  
         [0128]    [0128]FIG. 7 discloses a top view of a flowmeter  700  comparable to flowmeter  100  of FIG. 1. The difference between the two embodiments is that flowmeter  700  uses an optical detector for pick-offs LP 0  and RP 0 . The details of the optical detectors are shown in FIG. 8 as comprising a LED light source and photo-diode together with a flow tube  702 , with portions  720  made opaque in order to facilitate use, interposed between the LED and photo-diode. At the rest position of the flow tube, a nominal amount of light passes from the LED to the photo-diode to generate a nominal output signal. A downward movement of the flow tube increases the amount of light received by the photo-diode; an upward movement of the flow tube decreases the amount of light received by the photo-diode. The amount of light received by the photo-diode translates to an output current indicative of the magnitude of the Coriolis vibration for the portion of the flow tube  702  associated with the LED and the light source. The output of the photo-diodes are extended over conductors  730  and  732  to meter electronics not shown in FIG. 7 to minimize drawing complexity. The embodiment of FIG. 7 is otherwise identical in every respect to the embodiment of FIG. 1 and includes supply tubes  704 , exit tube  705  together with process connections  707  through  710  flow tubes  702  and exit tube  703 . The parts of flowmeter  700  and their counterparts on FIG. 1 and are designated to facilitate the correspondence with the only difference being the first digit of the designation of each element.  
         [0129]    Description of FIG. 9  
         [0130]    [0130]FIG. 9 discloses flowmeter  900  which corresponds to flowmeter  100  of FIG. 1 except that flowmeter  900  is equipped with dynamic balancers  932  and  933 . Base  901  is smaller and of less mass than  101  of FIG. 1. The dynamic balancers function to counteract the vibrations imparted to legs  917  and  918  of base  901  by the dynamically unbalanced structure comprising the material filled vibrating flow tube  902 . In the embodiment of FIG. 1, these vibrations are absorbed by the massive base  101 . In this embodiment, the material filled flow tube with the attached magnets weigh approximately 2 grams while the base weighs approximately 12 pounds. This limits the range of commercial applications for the flow tube of FIG. 1 since the upper limit on the size and mass of the material filled vibrating flow tube  102  is limited by the mass of the base that must be provided to absorb unbalanced vibrations. Using the 3,000 to 1 ratio between the mass of the base and the mass of the material filled vibrating flow tube, an increase of one pound in the mass of the material filled flow tube would require an increase of mass of 3,000 pounds for base  101 . This clearly limits the range of commercial applications in which the flow tube  100  of FIG. 1.  
         [0131]    Flowmeter  900  of FIG. 9 has a wider range of commercial applications since the dynamic balancers  932  and  933  are affixed to legs  917  and  918  to absorb much of the vibrations imparted to the legs by the dynamically unbalanced vibrating flow tube  902 . In practice, dynamic balancers (DB) may be of any type including the conventional mass and spring configuration as is well known in the art of dynamic balancers.  
         [0132]    Description of FIG. 10  
         [0133]    [0133]FIG. 10 discloses a flowmeter  1000  that is identical to flowmeter  900  except that the dynamic balancers of FIG. 10 are of the active type (ADB) and are designated  1032  and  1033 . These active dynamic balancers are controlled by an exchange of signals with meter electronics  1021  over paths  1023 ,  1024 ,  1025  and  1026 . Meter electronics  1021  receives signals over path  1023  from active dynamic balancer  1032  representing the vibrations applied by the dynamically unbalanced vibrating flow tube  1002  to leg  1017 . Meter electronics receive these signals and generates a control signal that is applied over path  1024  to active dynamic balancer  1032  to counteract the flow tube vibrations. Operating in this manner, active dynamic balancer  1032  can be controlled to reduce the vibrations of leg  1017  to whatever magnitude may be desired so that the resulting mass of base  1001  may be of an acceptable level for commercial use of flowmeter  1000 . The active dynamic balancer  1033  mounted atop leg  1018  of base  1001  operates in the same manner as described for the active dynamic balancer mounted to leg  1017 .  
         [0134]    Description of FIG. 11  
         [0135]    [0135]FIG. 11 discloses yet another alternative embodiment comprising a flowmeter  1100  having dual flow tubes  1101 ,  1102  which are substantially U-Shaped and have right side legs  1103 ,  1104  and left side legs  1105 ,  1106 . The bottom portion of the side legs are connected to form “Y” sections  1107  and  1108  which may be connected to a suitable base not shown to minimize drawing complexity. The dual flow tubes of flowmeter  1100  vibrate as dynamically balanced elements around the axes W-W and W′-W′ of brace bars  1109  and  1110 . Flow tubes  1101  and  1102  are driven in phase opposition by driver D affixed to the top portion of the U-shaped flow tubes. The Coriolis deflections imparted by the vibrating material filled flow tubes are detected by right pick-off RP 0  and left pick-off LP 0 . Meter electronics  1121  functions to apply signals over path  1123  to cause driver D to vibrate flow tubes  1101 ,  1102  in phase opposition. The Coriolis response detected by pick-offs LP 0  and RP 0  as transmitted over paths  1122 ,  1124  to meter electronics  1121  which processes the signals and derives material flow information which is transmitted over output path  1124  to a utilizations circuit not shown.  
         [0136]    Description of FIGS. 12 and 13  
         [0137]    [0137]FIGS. 12 and 13 disclose a dynamically balanced flowmeter  1200  having a pair of flow tubes  1201  and  1202  which are vibrated in phase opposition by driver D. The flow tubes receive a material flow; driver D vibrates the flow tubes in phase opposition in response to a drive signal received over path  1223  from meter electronics  1221 . The Coriolis response of the material filled vibrating flow tubes is detected by pick-offs LP 0  and RP 0  with their output being applied over conductors  1221  and  1224  to meter electronics which processes the received signals to generate material flow information that is applied over output path  1225  to a utilization circuit not shown.  
         [0138]    Description of FIG. 14  
         [0139]    [0139]FIG. 14 discloses an alternative embodiment  1400  of the invention comprising a massive base  1401  having an outer pair of upwardly extending sidewalls  1443  and  1444  as well as an inner pair of upwardly extending sidewalls  1417  and  1418 . A single flow tube  1402  extends from an input process connection  1408  on the left through the four upwardly extending sidewalls to an output process connection  1409  on the right. The flow tube  1402  is vibrated by driver D with the resulting Coriolis deflections of the vibrating flow tube with material flow being detected by pickoffs LP 0  and RP 0  which transmit signals over the indicated paths to meter electronics  1421  which functions in the same manner as priorly described or FIG. 1. Temperature sensing element RTD senses the temperature of the material filled flow tube and transmits this information over path  1425  to meter electronics  1421 .  
         [0140]    The flowmeter of FIG. 14 differs from that of FIG. 1 in two notable respects. The first is that the embodiment of FIG. 14 is only a single flow tube  1402 . The material flow extends through this flow tube from input process connection  1408 ; the output of the flow tube is applied via output process connection  1409  to output tube  1406  for delivery to a user. The embodiment of FIG. 14 does not have the return flow tube comparable to element  103  of FIG. 1.  
         [0141]    Also, the massive base  1401  has two pairs of upwardly extending walls whereas in the embodiment of FIG. 1 the massive base  101  had only the single pair of upwardly extending walls  117  and  118 . The single pair of walls in FIG. 1 performed the function of being a zero motion vibrational node as well as a mounting for process connections  107  through  110 . On FIG. 14, the inner pair of walls  1417  and  1418  function as a zero motion vibrational node for the ends of the active portion of flow tube  102 . The outer pair of upwardly extending walls  1443  and  1444  mount process connections  1408  on the left and  1409  on the right.  
         [0142]    When in use, process material is received from tube  1404  connected to process connection  1408 . The inlet of flow tube  1402  is also connected to process connection  1408 . Flow tube  1402  extends the process material flow to the right through the two pairs of sidewalls to output process connection  1409  to which is connected the output tube  1406 .  
         [0143]    The part numbers on FIG. 14 not specifically mentioned immediately above are analogous to and perform the functions identical to their corresponding elements on the previous FIGS. including FIG. 1.  
         [0144]    Description of FIG. 15  
         [0145]    [0145]FIG. 15 discloses an alternative embodiment  1500  which is similar in most respects to the embodiment of FIG. 1. The primary difference is that in the embodiment of  1500 , the rear flow tube  1503  is not dormant as is return tube  103  of the embodiment of FIG. 1. Instead, on FIG. 15, rear tube  1503  is vibrated by its driver DA with the resulting Coriolis deflections of this vibrating tube with material flow being detected by its pickoffs LP 0 A and RP 0 A. Their output signals are transmitted over paths  1542  and  1544  to meter electronics  1521  which receives these signals as well as signals from pickoffs LP 0  and RP 0  of flow tube  1502  to generate material flow information.  
         [0146]    The process material flows to right on FIG. 15 through flow tube  1502 , through tube  1500  and flows to the left through flow tube  1503 . This phase reversal of mated pickoffs can be compensated by reversing the connections to pickoffs LP 0 A and RP 0 A so that the Coriolis signals from all pickoffs received by meter electronics  1521  are additive to enhance meter sensitivity.  
         [0147]    The parts shown on FIG. 15 not specifically mentioned above are identical in function to their corresponding elements on FIG. 15.  
         [0148]    Description of FIG. 16  
         [0149]    [0149]FIG. 16 discloses an alternative embodiment  1600  that is similar to the embodiment of FIG. 14. The differences are that upwardly extending inner mounting posts  1617  and  1618  replace walls  1417  and  1418  of FIG. 14. Also upwardly extending outer mounting posts  1643  and  1645  replace walls  1443  and  1445  of FIG. 14. Outer posts  1643  and  1645  prevent flow tube  1602  from pivoting about post  1617  and  1618  as an axis. Connectors  1608  and  1609  are optional and if desired flow tube  1602  may extend outwardly through posts  1643  and  1645  and replace inlet tube  1604  and outlet tube  1402 . The extended flow tube may be connected downstream and upstream by a user to the user&#39;s equipment. When connected to users equipment the flow tube  1602  can be attached to process connection  1608  and  1609  in a similar fashion as shown in detail in FIG. 4. In addition, flow  1602  tube can be attached to process connections similar in design as described in FIG. 4. with the nipple and movable portion of the process connection being located at each end. This allows a compression fitting from flow tube  1602  to the process connection and also a compression fitting from the users equipment to the same process connection. Posts  1443  and  1445  serve as a mounting for connector  1608  and  1609  when provided.  
         [0150]    It is to be expressly understood that the claimed invention is not to be limited to the description of the preferred embodiment but encompasses other modifications and alterations within the scope and spirit of the inventive concept. For example, the flowmeter embodiments shown herein may be operated in an upside down orientation it is desired to have the driver D positioned on top of a vibrating flow tube to allow the driver heat to move upward away from the flow tube. This can better isolate the flow tube from thermal stress that might degrade the accuracy or the output data of the flowmeter. Also, the Coriolis flowmeter herein disclosed has applications other than those herein disclosed. For example the disclosed Coriolis flowmeter may be used in applications in which the flowing process material is corrosive, such as nitric acid, and incompatible for use with flow meters having a metal wetted flow path.