Helical Coriolis mass flow sensor

Abstract: This sensor for being inexpensive to manufacture, compact in that it occupies a small volume of space, for being substantially free of mechanical stress weaknesses and symmetrical, for having a rigid unitary inlet and outlet structure with inlet and outlet in line with the pipeline to which it is to be connected so as not to require pipeline offset or flow-diverting manifold features, and for having its center of mass spatially located as close as possible to the geometrical center of the sensor, comprises: an elongated, rigid junction means for coupling coaxially the pipeline ends conducting a flow of mass, the junction means having two passageways formed therein and extending axially into each end thereof and turning laterally to form an exit and an entrance port; a length of conduit (40) forming a generally helical flow tube wrapped around the junction means and having an inlet end coupled to the exit port and an outlet end coupled to the entrance port, the conduit intersecting five times an imaginary plane (P) passing vertically through the junction means and including its longitudinal axis (A), two intersections (33, 35) lying above and three intersections (32, 34, 36) beneath the junction means; two node plates (50, 52) each joining together at a point removed from and on one side of the plane a first two of the three conduit portions passing beneath the junction means and on the opposite side of the plane a second two of the three conduit portions, resp., the node plates serving to define the ends of two active loops (60, 62) of the conduit being generally parallel to each other; and driving and detecting means (70; 72, 74).

Description: The priority of the Patent Application No. 08/527 436 filed on September 13, 1995 in the United States of America is claimed. The present invention relates generally to Coriolis-type mass flow meters, and more particularly to an improved single-tube mass flow sensor for use in a Coriolis mass flow meter. The use of the Coriolis principle to measure mass flow has been known for more than fifty years. Early on, workers such as Wilfred Roth and Anatole Sipin recognized the benefits of using this principle and suggested numerous flow tube sensor configurations and measurement techniques. However, it was not until the general availability of the microprocessor in the mid-seventies that implementation of the techniques suggested by the earlyworkers became feasible. At this juncture, measurement techniques and operational principles are well known, and Coriolis mass flow sensors having tube diameters ransing from small fractions of a centimeter to more than 30 cm are in widespread use. It is no longer the motion-sensing or electronic signal-processing functions that stand in the way of progress in Coriolis flow meter technology and general availability; it is the cost and difficulty of making flow sensing structures having higher mechanical sensitivity and reliability that keeps the price up and the general acceptance of these types of meters down. One of the problems associated with existing Coriolis mass flow sensor technology is that errors are introduced into the measurement by mechanical stresses imparted to the flow tube sensor structure by the pipeline to which the sensor is connected. Attempts at isolating flow tube structures from pipeline stresses have generally followed two lines. One is to use a massive cast or machine manifold structure that forms a rigid connection between opposing pipeline ends and has flow-sensing tubes extending outwardly therefrom. Examples of such structures are disclosed in the US-A 48 91 991, US-A 49 11 020, US-A 49 57 005, US-A 50 48 350, US-A 50 50 439, US-A 50 54 326, US-A 53 43 764 and US-A 53 49 872. In particular, US-A 48 91 991, US-A 49 11 020, US-A 49 57 005, US-A 50 48 350 and US-A 50 50 439 each disclose a Coriolis mass flow sensor comprising: an elongated, rigid junction means for coupling two axially aligned but separated ends of a pipeline intended to conduct a flow of mass to be measured the junction means having a longitudinal axis for coaxial alignment with the pipeline, having a first passageway formed therein and extending axially into one end thereof and turning laterally to form two exit ports, and having a second passageway formed therein and extending axially into the opposite end thereof and turning laterally to form two entrance ports; two lengths of conduit forming two parallel flow tube means wrapped around the junction means and each having an inlet end coupled to the exit ports and an outlet end coupled to the entrance ports, the lengths of conduit each intersecting only once an imaginary plane passing vertically through the junction means and including the longitudinal axis, and touching the lower side of the junction means, a node plate means joining together in a plane less removed from the junction means the two inlet ends and the two outlet ends of the two conduits; eight means for driving the portions of the active loops toward and away from each other in oscillatory fashion; and four means for detecting Coriolis induced differences in displacement or motion of the conduits relative to the other as the conduits are moved toward and away from each other by the driving means. Further, US-A 49 57 005 corresponding to EP-A 421 812 discloses a Coriolis mass flow sensor comprising: an elongated, rigid junction means in the form of a cylindrical support structure for coupling two axially aligned but separated ends of a pipeline intended to conduct a flow of mass to be measured, the support structure having a longitudinal axis for coaxial alignment with the pipeline, having an entrance port, and having an exit port; a length of conduit forming a generally helical flow tube wrapped around the axis of the support structure, having an inlet isolation loop having a central line, fixed on its one end to an inlet end of the flow tube and on its other end to the entrance port in such a way that the longitudinal axis and the central line coincide at the entrance port, and having an outlet isolation loop fixed on its one end to an outlet end of the flow tube and on its other end to the exit port in such a way that the longitudinal axis and the central line coincide at the exit port, the length of conduit intersecting seven times an imaginary plane passing vertically through the support structure and including the longitudinal axis, four of such intersections lying above the support structure and three of such intersections lying beneath the junction means; a single node plate means joining together at a line lying in the imaginary plane and above the support structure three conduit portions; the node plate serving to define the ends of three active loops being generally parallel to each other; a means for driving the uppermost portions of the active loops toward and away from each other in oscillatory fashion; and two means for detecting Coriolis induced differences in displacement or motion of one loop relative to the other as the active loops are moved toward and away from each other by the driving means. With the exception of the Coriolis mass flow sensors disclosed in the US-A 49 57 005 just referred to sensors such as those disclosed in the other US-A documents mentioned above address not clearly the issues of simplicity, ease of manufacture, and compactness of design. US-A 49 57 005 is on the right track in that this Coriolis mass flow sensor meets most of these criteria. However, this design still does not isolate tube mechanics from flow line coupling mechanics. Other attempts to isolate the flow sensor from pipeline stresses are disclosed in the US-A 47 16 771, US-A 50 20 375, US-A 50 31 468 and US-A 53 57 811. Although each of these designs do in fact provide a degree of isolation between pipeline and active portions of the sensor tube as well as simplicity of construction, they suffer from other factors relating to vulnerability to shear force effects, out-of-line inlet and outlet, and lack of compactness. It is therefore a principal object of the invention to provide a Coriolis mass flow sensor which is relatively inexpensive to manufacture, compact in that it occupies a relatively small volume of space, is substantially free of mechanical stress weaknesses, and has the advantages associated with substantial symmetry. Another object is to provide a Coriolis mass flow sensor having a rigid unitary inlet and outlet structure with inlet and outlet in line with the pipeline to which it is to be connected so as not to require pipeline offset or flow-diverting manifold features. Still another objective is to provide a Coriolis mass flow sensor having its center of mass spatially located as close as possible to the geometrical center of the sensor. The solution of these objects by the invention is defined in the main claim and the subclaims. Briefly, a preferred embodiment of the invention includes a single connection and support structure having an inline inlet and outlet and a one-piece, generally helical sensing tube structure wound in concentric fashion about the inline axis of the support structure and supported relative thereto by tube ends affixed to ports formed in the support structure and in fluid communication with the inlet and outlet flow paths. Further, the tube extends through approximately 720° as it wraps about the centerline axis, and carries driver means at its "12 o'clock" position and detectors at the "quarter hour" positions on opposite sides of the sensor centerline. Finally, a pair of node plates are disposed at spaced-apart locations on the tube side opposite the driver and serve to couple the centermost loop section to the downstream tail and the centermost loop section to the upstream tail, respectively. An important advantage of the invention is that it can be made with a simple cast part or parts requiring a minimum of machining and a minimum of weld joints. Another advantage of the invention is that, since the sense tube is helically wrapped about the connection structure, the volume occupied by the device is minimal. Still another advantage of the invention is that its sensor tube can be made from either a single length of tubing or from a plurality of segments joined together to form a continuous length of conduit. These and other advantages of the invention will become apparent from the following detailed description of the preferred embodiment which is illustrated in the several figures of the drawing. Fig. 1 is a partially broken perspective view illustrating a Coriolis mass flow sensor; Fig. 2 is a perspective view illustrating more clearly the machining detail of the connector block of the embodiment of Fig. 1; Fig. 3 is an end view of the embodiment of Fig. 1 with the near end flange removed and illustrating connection of tube ends to center block; Fig. 4 is a top view of the Fig. 1 embodiment illustrating connection of tube to center block; and Fig. 5 is a side view of the Fig. 1 embodiment further illustrating the connection of tube to the block. Referring now to Fig. 1 of the drawing, a Coriolis mass flow sensor is depicted, including an inlet bell 10 and an outlet bell 12 rigidly joined together by a center block 14 to form a rigid junction structure for joining together two axially aligned but separated ends of a pipeline intended to conduct a flow of mass to be measured. As illustrated, the external extremities of the bells 10, 12 form flanges 16, 18, respectively, having a plurality of bolt holes 20 formed therein for use in mounting the sensor to the end flanges of a connecting pipeline (not shown). The bells 10, 12 also include a central bore 22 for receiving and discharging the mass flow stream. As revealed by the upper broken-away portion of bell 10 and as will be described in more detail below, the internal extremities of the bells 10, 12 are affixed by brazing or welding to opposite ends of center block 14. Center block 14 is typically a solid block of metallic material, either machined or cast, and includes a pair of bores 24, 26 axially aligned with each other and with the axis A of the bell bores 22. The bores 24, 26 preferably extend less than halfway into block 14 from either end. The diameter of the bores 24, 26 is substantially identical to the diameter of the bore 22 in the bells 10, 12. Extending into opposite sides of block 14 so as to intersect bores 24, 26 are laterally extending bores 28, 30. Circumscribing block 14 and having its ends weldedly affixed thereto so as to be in flow-communicating relationship with the bores 28, 30 is a length of conduit tubing (or tube) 40 which may be of a single length, deformed in substantially helical fashion about a central axis, or may include a plurality of segments suitably joined together. The length of tube 40 beginning at 31 is rather tightly bent through 180° and intersects an imaginary vertical plane P (at 32) that passes through and includes axis A. Tube 40 is then bent through another 180° before it again intersects plane P at 33. Following another 180° bend, tube 40 once more intersects plane P at 34, is bent another 180° to again encounter plane P at 35, is bent once more to intersect plane P at 36, and finally is folded back to engage block 14 at 37. Note that passing around block 14 the tubular helix includes two tube lengths 38, 39 disposed parallel to each other, and respectively extending between points 32, 34 to complete one tube loop, and points 34, 36 to complete another tube loop. Upstream and downstream tail segments respectively extend from point 31 to point 32, and from point 36 to point 37. Note also that in the lower portion of the helix three tubular portions extend substantially parallel to each other with the exception that the tails on either end are turned more tightly so that they intersect block 14 as indicated. At the bottom of the loops, as depicted, and spaced apart a suitable distance on either side of plane P, are a pair of rigid node plates 50, 52 which join remote portions of loops 38, 39 to define active loop portions 60, 62 which extend in parallel, equal-spaced relationship around block 14 from node plate 50 to node plate 52. Node plates 50, 52 are preferably welded or brazed to tube 40 and are rigid enough so as to resist bending as a result of any forces applied thereto by loop portions 60, 62. The plates 50, 52 are typically spaced apart at least one, and preferably several, times the loop-to-loop spacing between loop portions 60, 62. Disposed at the upper intersections with imaginary plane P, loop portions 60, 62 respectively carry the components of a loop driver 70 which, when actuated, serves to drive the upper extremities of the loops toward and away from each other in oscillatory fashion. Note that the resulting stresses developed at the node plates are primarily torsional as opposed to bending. Accordingly, the likelihood of weld failure at the junctions with node plates 50, 52 is substantially lower than would be expected with cantilevered U-tube designs and the like. It will also be apparent that the active part of the sensor formed by the loop portions 60, 62 is flexibly suspended from the block 14 by the tail segments 64, 66, resp., extending from point 31 to the intersection with node plate 52 at 53, and from point 37 to point 51 at node plate 50. External forces transmitted through the pipeline will in large part be transmitted across block 14 and absorbed by the tail segments 64, 66, and not extend beyond the node plates 50, 52. Moreover, it can be recognized that the only direct connection between the node plates 50, 52 is through the tube segment 54, and any torsional or other force applied to the ends thereof will be equal but opposite in direction. Accordingly, such forces will be cancelled in segment 54 and will have no adverse effect on operation of the active loops 60, 62. Appropriately positioned on opposite sides of block 14 and carried by the loop portions 60, 62 are a pair of loop stress, motion or displacement detectors 72, 74 which detect differential stress, motion or displacement of the respective loop portions relative to each other as a result of Coriolis forces arising as mass flows through the loops as driver 70 drives them to and fro. As already mentioned above, the driver 70 is arranged at the "12 o'clock" position and detectors 72, 74 at the "quarter hour" positions on opposite sides of the sensor centerline. It is of course understood that the driver 70 and detectors 72, 74 may be of any suitable design and placement so as to provide a desired degree of sensitivity for the sensor. Furthermore, any other suitable drive/detector configurations and placements can be utilized with the loop structure of the invention. Even though not specifically shown in the drawing, it will be understood that a complete Coriolis mass flow meter, in addition to the Coriolis mass flow sensor as explained, will include appropriate driving and signal detecting electronics coupled to driver 70 and detectors 72, 74, as well as signal processing and indicating means well known in the art. Although only partially depicted, it will be appreciated that a suitable multipart housing 56 enveloping the sensor components in the region between the flanges may also be provided. With respect to Fig. 2, details of the construction of block 14 will be described. Block 14 may either be machined from a solid block of suitable material or may be molded or cast and then machined as appropriate. Generally speaking, and in the case where block 14 is a machined part, the block is fabricated by boring inlet and outlet cavities 24, 26 into opposite ends of the block along the axis A, and cutting a circumscribing channel 32' around each bore so as to leave an annular sleeve 34' to which the ends of bells 10, 12 may be welded. Laterally extending passageways 28, 30 are then bored with appropriate counterbores 27, 29 to intersect bores 24, 26 respectively. The diameter of bores 24, 26 is preferably the same as the diameter of the bores 22 in bells 10, 12. The diameters of bores 28, 30 preferably match the inside diameter of tube 40. The diameter of the counterbores 27, 29 match the outside diameter of tube 40 so that the tube ends may be inserted thereinto before welding or brazing. Fig. 3 is an end view looking along the axis A with the bell 10 removed and the inlet side and outlet side of housing 56 broken away at 57, 58 respectively, to reveal various internal details. The housing 56, as illustrated, may be a two part clam-shell type structure having a parting line 59 and securing flanges 61 which may be suitably secured together by bolts 62. Housing 56 may mate with either a portion of the bell tails or as, depicted by the dash lines 63, may mate with a corner or surface groove or flange provided on opposite ends of block 14. The use of flexible seals at the junction will insure that the interior of housing is hermetically sealed. Fig. 4 is a partially broken top view further illustrating connection of end bells 10, 12 to housing 14 at 11, 13, resp., tube connections to block 14 at 31, 37, resp., and housing connection to block 14 at shoulders 63. Fig. 5 is a side view of the sensor with end bells and housing removed to further reveal the relationship of tube to block and node plates to tube. The depicted embodiment compares quite favorably with prior art designs in terms of simplicity of manufacture, safety and reliability of use, and ease of installation. It provides substantial rigidity between flow line conduit ends to which it is affixed, substantial support to all its components with no nonlinear stress paths. Since no bending stresses are applied to any welds, the integrity of all welds is less of a concern than in other designs. For example in the design illustrated in US-A 53 57 811, the ability of the device to withstand longitudinal pipeline shock and vibration is largely a function of the integrity of the tube-to-plate welds (19, 23 of Fig. 2 thereof). Note that in this design the strength of the coupling from flange-to-flange is limited by the strength of the weld lines. Although this may not be of substantial concern for small tube devices, it can be a limiting factor in larger tube designs. Furthermore, in the invention where the flow tube is of a symmetrical helical configuration, the volume of space required to accommodate the flow sensor is symmetrical about the pipeline and at an absolute minimum. Although the invention has been described above in terms of a specific embodiment, alterations and modifications become apparent to those skilled in the art. For example, as suggested by the dashed lines 64', 66' in Fig. 3, the flow tube tails may be coupled to flow exit and re-entry ports formed on a single side (as compared to opposite sides) of the block 14. It will of course also be apparent that for some applications elongated loops or oval-shaped flow tubes may be utilized without departing from the scope of the invention. Moreover, the flow sensor may be inverted as compared to the illustrated configuration.

Claims: A Coriolis mass flow sensor comprising: an elongated, rigid junction means for coupling two axially aligned but separated ends of a pipeline intended to conduct a flow of mass to be measured the junction means having a longitudinal axis (A) for coaxial alignment with that of the pipeline, having a first passageway disposed along the axis (A) and extending axially into one end thereof and turning to form a laterally extending exit port, and having a second passageway disposed along the axis (A) and extending axially into the opposite end thereof and turning to form a laterally extending entrance port; a length of conduit (40) forming a generally helical flow tube means wrapped around the junction means and having an inlet end coupled to the exit port and an outlet end coupled to the entrance port, the length of conduit intersecting no more than five times an imaginary plane (P) passing vertically through the junction means and including the longitudinal axis, two of such intersections (33, 35) lying above the junction means and three of such intersections (32, 34, 36) lying beneath the junction means; first node plate means (50) joining together at a point removed from and on one side of the plane a first two of the three conduit portions passing beneath the junction means; second node plate means (52) independent of the first node plate means and joining together at a point removed from and on the opposite side of the plane a second two of the three conduit portions, the first and second node plate means respectively serving to define the ends of two active loops (60, 62) of the conduit extending and around the junction means, the active loops being generally parallel to each other; means (70) for driving the uppermost portions of the active loops toward and away from each other in oscillatory fashion; and means (72, 74) for detecting Coriolis induced differences in displacement or motion of one loop relative to the other as the active loops are moved toward and away from each other by the driving means. A Coriolis mass flow sensor as recited in claim 1 wherein the junction means includes a metal block (14) having a first flanged end bell (10) affixed to one end of the metal block, and a second flanged end bell (12) affixed to the other end of the metal block. A Coriolis mass flow sensor as recited in claim 2 wherein the first passageway is formed by a first bore (24) extending axially into the one end and a second bore (28) extending into the metal block from the one side and in a direction transverse to the axis and intersecting the first bore, and the second passageway is formed by a third bore (26) extending axially into the opposite end and a fourth bore (30) extending into the metal block from the opposite side and in a direction transverse to the axis and intersecting the third bore. A Coriolis mass flow sensor as recited in claim 1 wherein the conduit is comprised of a helical portion having an arcuate length of less than 720° and a pair of tail portions respectively extending between the exit port and one end of the helical portion, and from the entrance port to the other end of the helical portion. A Coriolis mass flow sensor as recited in claim 1 wherein the exit port is disposed on one side of the junction means, and the entrance port is disposed on a side of the junction means opposite the one side. A Coriolis mass flow sensor as recited in claim 1 wherein the first and second node plates (50, 52) are spaced from each other at least two times the spacing between the two active loops. A Coriolis mass flow sensor as recited in anyone of claims 1 to 6 further comprising a cylindrically configured two-part housing (56) enveloping the block, the conduit, the driving means, and the detecting means.

Inventors: HOANG DANNY, YOUNG ALAN M, HOANG, DANNY, YOUNG, ALAN M.
Applicants: FLOWTEC AG, ENDRESS + HAUSER FLOWTEC AG
Application year: 1995
Main classification: G01F1
IPC codes: G01F1