Abstract:
A magnetic field coupler has a plurality of magnetic poles with respective first ends located immediately adjacent a circular path of a rotating magnet in a meter. The magnetic poles have respective opposite ends located immediately adjacent a magnetic sensor in a meter reading device. A nonmagnetic material separates each of the plurality of poles from all others of the plurality of the poles, and the nonmagnetic material is joined with the poles to form a unitary structure.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/512,363 filed on Oct. 17, 2003. 

   FIELD OF THE INVENTION 
   The present invention relates in general to fluid meters and more specifically, to a fluid meter having a magnet that rotates in response to fluid flow. 
   BACKGROUND OF THE INVENTION 
   Fluid meters, for example, those used to measure a flow of natural gas petroleum products or water, often have a shaft with one or more blades or vanes that are rotated by a flow of fluid through the meter. A magnet is often mounted on the shaft and produces a rotating magnetic field that, by mechanical, electrical, or electronic means, conveys flow information to a totalizing or rate measuring apparatus. The rotating field is often used to cause rotation of a shaft-mounted secondary magnet that, in turn, drives a mechanical totalizer or a magnetically sensitive detector generating pulses in an electrical circuit. 
   Typically, in order to be close to the rotating magnet, the magnetically sensitive detector is located in a cup approximately one-half inch in diameter, which is set into a side of a meter housing. Inside the meter, the cup is surrounded by the rotating magnet; and hence, the magnetically sensitive detector is able to a rotating magnetic field from the magnet. While a magnetically sensitive detector installed this way provides accurate fluid flow measurements, it does have some disadvantages. First, the magnetically sensitive detector is often mounted on a printed circuit board assembly that contains electrical components necessary to interface with the detector. Further, the printed circuit board assembly must be sized to fit in the cup in the meter housing; and that requirement places significant design limitations on the detector circuitry, which often leads to an increase in cost. 
   A second disadvantage is that different size fluid meters often have different size cups into which the magnetically sensitive detector is to be located; and the requirement to design, manufacture and inventory different sizes of detectors to fit the various sizes of cups is also costly. A third disadvantage relates to the construction of many meter housings. The hole in which the magnetically sensitive detector is located is capped by a metal plate inside the housing that is sealed with a gasket to prevent fluid leaks. Over time, it is possible for the gasket to fail; and the fluid then leaks into the hole, thereby exposing the detector to corrosive effects, if any, of the fluid. 
   Therefore, there is a need to provide a capability of sensing the rotation of a magnet within the meter housing, which does not have the disadvantages discussed above. 
   SUMMARY OF THE INVENTION 
   The present invention is used with fluid meters having a magnet that rotates in response to fluid flow, and the present invention provides a magnetic field coupler that eliminates all constraints on the design and size of a magnetic sensor. The magnetic field coupler of the present invention also permits a common magnetic sensor design to be used with fluid meters of many different sizes. In addition, the magnetic field coupler of the present invention permits the magnetic sensor to be better isolated from leaking fluid. The magnetic field coupler of the present invention is especially useful with rotary meters used for measuring gas flows. 
   According to the principles of the present invention and in accordance with the described embodiments, the invention provides an apparatus for coupling a magnetic field from a magnet rotating in response to fluid flow in a fluid meter to a magnetic sensor in a meter reading device. The apparatus has a plurality of magnetic poles with respective first ends located immediately adjacent the circular path of the magnet, and respective opposite ends located immediately adjacent the magnetic sensor in the meter reading device. A nonmagnetic material separates each of the plurality of poles from all others of the plurality of the poles, and the nonmagnetic material is joined with the poles to form a unitary structure. 
   These and other objects and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a magnetic field coupler interposed between a rotating magnet in the fluid meter and an external magnetic sensor in a meter reading device in accordance with the principles of the present invention. 
       FIG. 1A  is an exploded view of a portion of FIG.  1 . 
       FIG. 2  is a perspective view of a two pole embodiment of the magnetic field coupler of FIG.  1 . 
       FIG. 3  is a perspective view of another two pole embodiment of the magnetic field coupler of FIG.  1 . 
       FIG. 4  is a perspective view of a further two pole embodiment of the magnetic field coupler of FIG.  1 . 
       FIG. 5  is a perspective view of a three pole embodiment of the magnetic field coupler of FIG.  1 . 
       FIG. 6  is a perspective view of another three pole embodiment of the magnetic field coupler of FIG.  1 . 
       FIG. 7  is a perspective view of a four pole embodiment of a the magnetic field coupler of FIG.  1 . 
       FIG. 8  is a perspective view of an arrangement of a magnetic sensor and a two pole magnetic field coupler, which can be used to detect fluid flow through the meter in a forward direction. 
       FIG. 9  is a schematic representation of waveforms that are produced by magnetic sensors detecting magnetic fields from the magnetic field couplers of  FIGS. 9 and 10 . 
       FIG. 10  is a perspective view of an arrangement of magnetic sensors and a three pole magnetic field coupler, which can be used to detect fluid flow through the meter in forward and reverse directions. 
       FIGS. 11A ,  11 B and  11 C are end views of the magnetic field couplers illustrating alternative cross-sectional profiles for ends of the magnetic field couplers interfacing with the meter reading device. 
       FIG. 12  is a perspective view of another embodiment of a magnetic field coupler in accordance with the principles of the present invention. 
       FIG. 13  is a perspective view of a further embodiment of the magnetic field coupler of FIG.  12 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 and 1A , a fluid rotary meter  20  has a fluid passage  22  for conducting a fluid therethrough. A rotary shaft  24  has blades or vanes (not shown) disposed in the fluid passage. Fluid flow through the passage  22  impacts the vanes and causes a rotation of the shaft  24  in a known manner. An wall  26  of the meter  20  has a hole  28  covered by a cup  30  that is sealed against the wall  26  by a gasket  32 . The cup  30  forms a pulse well  34  extending into the meter  20 . A ring-shaped magnet  36  connected to the end of the rotating shaft  24  surrounds the pulse well  34  of the cup  30 . 
   As previously discussed, with known designs, magnetic sensors mounted on a PC board assembly are located inside the pulse well  34  to magnetically couple with the magnet  36 . The present invention permits the magnetic sensor and PC board assembly to be removed from inside the meter  20  by utilizing a magnetic field coupler  40 . The magnetic field coupler  40  is generally cylindrically shaped such that one end  41  fits within the pulse well  34  in a manner to provide a suitable magnetic coupling with the magnet  36 . A mounting plate  46  facilitates attaching a meter reading device  48  to the meter  20 . The mounting plate  46  forms one end of a housing  50  mounted to an instrument case  52  containing known electrical circuits of the meter reading device. 
   As shown in  FIG. 2 , the magnetic field coupler  40  is comprised of a plurality of poles, for example, two poles,  42  separated by a nonmagnetic material  44 . An opposite end  43  of the magnetic field coupler  40  extends into a socket  54  ( FIG. 1A ) of the mounting plate  46 , and the socket  54  has a block or key  55  that has a width equal to a spacing between the opposite ends of the poles  42 . Flat surfaces  56  ( FIG. 2 ) on the poles  42  straddle the key  55 , thereby preventing angular motion of the magnetic field coupler  40 . Thus, the coupler end  41  is angularly fixed with respect to the rotating magnet  36 , and the coupler end  43  is angularly fixed with respect to magnetic sensors  57 ,  58 . The magnetic sensors  57 ,  58  are part of a PC board assembly  60  mounted in the housing  50 . The PC board assembly  60  includes other electrical components for operating the magnetic sensors  57 ,  58  in a known manner. 
   The construction of the magnetic field coupler  40  is dependent on the meter  20 . For example, the pulse wells of different sizes of meters will have different diameters and depths. Further, the number of poles on the magnet  36  may vary. Referring to  FIG. 2 , in one embodiment, the magnetic field coupler  40  is comprised of two poles  42   a,    42   b  with the nonmagnetic material  44  interposed therebetween. The spacing between the poles  42  may be varied to optimize the transmission of magnetic fields through the magnetic field coupler  40 . Therefore, as shown in  FIG. 3 , the nonmagnetic material  44  may be thicker, thereby separating the poles  42   a ,  42   b  more. If the poles  42  have a separation greater than the width of the key  55 , the ends of the poles are formed with lips  64   a,    64   b  having flat surfaces  66  that straddle the key  55  to hold the magnetic field coupler fixed. Alternatively, as shown in  FIG. 4 , the nonmagnetic material  44  may have a greater thickness, thereby further separating the poles  42 . 
   Different numbers of poles on the magnet  36  will dictate further embodiments of the magnetic field coupler  40 . For example, as shown in  FIG. 5 , if the magnet  36  has three poles, the magnetic field coupler  40  can also have three poles  42   a ,  42   b ,  42   c  that are uniformly separated by a nonmagnetic material  44 . As shown in  FIG. 6 , in an alternative embodiment of a three pole magnetic field coupler, the nonmagnetic material  44  creates a nonuniform spacing between the poles  42   a ,  42   b ,  42   c . In a further embodiment shown in  FIG. 7 , the magnetic field coupler  40  may have four poles  42   a ,  42   b ,  42   c ,  42   d  separated by an nonmagnetic material  44 . Therefore, there is no limit on the number of poles  42  that may be utilized within the magnetic field coupler  40 ; and with known meters, the magnetic field coupler  40  can be made with six or more poles. 
   The poles  42  are made from a material that provides excellent conduction of a magnetic field, for example, a soft iron such as low carbon steel, 1008-1010. The nonmagnetic material  44  may be any nonmagnetic material, for example, a commercially available ultra-high molecular weight material. The poles  42  are attached to the nonmagnetic material  44  by an adhesive or any other means that secures the poles and nonmagnetic material into a unitary structure while minimizing interference with the transmission of the magnetic field along the coupler  40 . The distance from the bottom of the pulse well  34  to the bottom of the socket  46  determines the length of the magnetic field coupler  40 , and the diameter of the pulse well  34  determines the diameter of the magnetic field coupler  40 . 
   In use, fluid flow through the meter  20  ( FIG. 1 ) in one direction causes rotation of the shaft  24  and magnet  36  in one direction. The rotation of the magnet  36  induces magnetic fields into the coupler end  41 . The magnetic fields are detected by the magnetic sensors  57 ,  58  at the opposite end  43  of the magnetic field coupler  40 . Referring to  FIG. 8 , if a two pole magnetic field coupler  40  is used, the magnetic sensor  57  produces an output signal schematically represented by sinusoidal output waveform  70  as shown in FIG.  9 . The waveform  70  is processed by electrical circuits in the instrument case  52  ( FIG. 1 ) in a known manner to obtain a signal representing fluid flow through the meter  20  in the one direction, for example, a forward direction. In order to improve the reliability of the system, a second magnetic sensor  58  is often used and mounted in a position parallel with the magnetic sensor  57 . With this embodiment, the second sensor  58  produces an output waveform identical and in phase with the waveform  70 . 
   In many applications, it is beneficial to be able to detect and measure bidirectional fluid flows through the meter  20 , that is, a fluid flow in a forward direction and a fluid flow in an opposite, reverse direction. A sensor arrangement for detecting reverse fluid flow is shown in FIG.  10 . In this embodiment, the sensor  57  is mounted perpendicular to, that is, at a right angle with, the sensor  58 ; and the magnetic field coupler  40  has three poles  42   a ,  42   b ,  42   c . It should be noted that the poles do not have to be of an identical size and shape. Pole  42   c  is larger than the poles  42   a  and  42   b . In this embodiment, magnetic sensor  57  provides an output signal schematically represented by sinusoidal waveform  70  of  FIG. 9 ; and magnetic sensor  58  provides an output signal schematically represented by sinusoidal waveform  72 . With the sensors  57 ,  58  mounted perpendicular to each other, the output waveforms are ninety degrees out of phase. With fluid flowing through the meter  20  in one direction, for example, a forward direction, waveform  70  leads waveform  72  by ninety degrees as shown in FIG.  9 . However, if fluid is flowing through the meter  20  in an opposite direction, that is, the fluid is experience reverse flow, the waveform  72  will lead the waveform  70  by ninety degrees. The quadrature relationship between the waveforms  70 ,  72  is detectable by circuitry in the instrument case  52  in a known manner, so that the reverse flow of the fluid can be measured. If desired, another two magnetic sensors can be mounted opposite the sensors  57 ,  58  of  FIG. 10  to provide redundancy in the event of a failure of one of the sensors. 
   Referring to  FIG. 12 , a magnetic field coupler  74  is comprised of a cylindrical body  76  having a plurality of slots  78  equally spaced about the circumference of the body  76 . As will be appreciated, the body  76  can be noncircular such as a polygon that has a number of sides equal to the number of poles thereon. Conductive poles  80  are secured in the slots  78  by adhesive or other means. Active poles  81  have ends  82  that fold or bend over a sensor end  84  of the magnetic field coupler  74 . The ends  82  are sized and spaced to magnetically couple to the magnetic sensors  57 ,  58  shown in FIG.  1 A. Passive poles  85  have ends  86  that stop short of the sensor end  84 . The passive poles  85  are used to achieve a magnetic symmetry circumferentially about the magnetic field coupler  74 . A key slot  88  is used to properly angularly position the magnetic field coupler  74  within the socket  54  of FIG.  1 A. The pick up end  90  of the magnetic field coupler  74  is disposed within the cup  30  of  FIG. 1A  within the meter  20 . The active pole ends  82  are not equally spaced about the circumference, so that a direction of rotation of the shaft can be detected. However, the combination of the active poles  81  and the passive poles  85  are substantially equally spaced about the circumference to achieve the desired magnetic symmetry. The body  76  is made from a magnetically nonconductive material, for example, a plastic such as a polycarbonate, wood, etc. The poles  80  are made from a transformer laminate material or other low hysteresis steel. 
   An alternative embodiment of the magnetic field coupler  74  is illustrated in FIG.  13 . In this embodiment, a cylindrical body  92  has a central smaller diameter necked portion  94 . There is the same arrangement of active and passive poles  81 ,  85 , respectively, as shown in FIG.  12 . However, the poles  81 ,  85  descend downward into the center necked portion  94  of the body  92  and extend from the pick up end  92  to the sensor end  84 . The poles  81 ,  85  are covered by a first layer of a magnetically nonconductive material, for example, a plastic such as a polycarbonate. An outer layer  98  of a magnetically conductive material such as a transformer laminate covers the nonconductive layer  96 . The outer layer  98  has an insulating air gap  100  between its ends and the poles  81 ,  85 . 
   By permitting the magnetic sensors  57 ,  58  to be removed from the pulse well  34 , the magnetic field coupler  40  provides many advantages. First, the design constraints on the PC board assembly  60  that supports the magnetic sensors  57 ,  58  are substantially reduced; and the cost of the PC board assembly  60  can be reduced. In addition, variations in the size of the meter  20 , the pulse well  34  and the number of poles on the magnet  36  are accommodated by the use of different magnetic field couplers  40  which are relatively simple and inexpensive components to manufacture. This permits a common PC board assembly  60  to be used with a wide range of different meters  20 . The magnetic field sensor  40  further permits the PC board assembly  60  and the magnetic sensors  57 ,  58  to be mounted in a sealed chamber within the housing  50  of the meter reading device  48 . Therefore, the PC board assembly  60  is protected from any corrosive effects of the fluid in the event of a failure of the gasket  32 . In addition, the sensors can be readily arranged to detect reverse flow of the fluid through the meter. 
   While the present invention has been illustrated by a description of an embodiment, and while such embodiment has been described in considerable detail, there is no intention to restrict, or in any way limit, the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, in the described embodiment, the poles  42  are separated by a distance permitting the poles  42  to span the key  54 , thereby holding the magnetic field coupler  40  fixed with respect to the rotating magnet  36  and the magnetic sensors  57 ,  58 . As will be appreciated, in an alternative embodiment, the key  54  can be eliminated and the cross-sectional profile of the socket  46  made noncircular, for example, square, hexagonal, etc. Similarly, the opposite end  43  of the magnetic field coupler  40  is made to have a noncircular cross-sectional profile, for example, a square cross-sectional profile as shown in  FIGS. 11A-11C , so that the magnetic field coupler  40  is fixed with respect to the rotating magnet  36  and magnetic sensors  57 ,  58 . While such an embodiment provides opposed flat surfaces on the magnetic field coupler  40  and the socket for fixing the magnetic field coupler in place, in an alternative embodiment, such flat surfaces can be arcuate or curved and also function to restrain the magnetic field coupler from motion. 
   Therefore, the invention in its broadest aspects is not limited to the specific details shown and described. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims which follow.