Abstract:
An electromagnetic type fluid flow meter for measurements of conductive fluids which utilizes an interchangeable disposable electrode sensor assembly with a common magnetic drive assembly. The electrode sensor assembly includes a tubular member adapted to be connected into a flow line and which includes sensor electrodes and an electrical connector for providing external electrical connections to electrodes. An electromagnetic assembly includes a C-shaped magnetic core and a winding on the core. Parallel guide members on the electromagnetic assembly receive mating guides on either side of the tubular member in sliding engagement to hold the tubular member between the poles of the magnet with the electrodes properly oriented with respect to the flux lines. The electromagnetic assembly includes an electrical connector which engages the connector on the tubular member when it is inserted in the guides.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 700,176, filed June 28, 1976, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to electromagnetic flow meters, and more specifically relates to apparatus used in the extracorporeal measurement of blood flow or other conductive liquids. 
     BACKGROUND OF THE INVENTION 
     The use of an electromagnetic flow meter to measure blood flow is well known. The basic concept, for example, is described in U.S. Pat. No. 2,149,847. By passing blood, either in a tube or blood vessel oriented at right angles to a magnetic field, an EMF is produced in a direction mutually perpendicular to the magnetic field and the direction of blood flow, since the blood has the property of a moving conductor cutting through a magnetic field. The voltage generated is proportional to the velocity of flow and therefore directly proportional to the volume rate of flow of the fluid. The voltage can be measured by electrodes positioned at diametrically opposite points of the tube along a diameter extending perpendicular to the magnetic lines of the flux. 
     Because the electrodes, magnet structure, and fluid passage must be maintained in fixed predetermined relationship in order to maintain accurate calibration of the flow measurement, it has been the practice heretofore to assembly the tube, electrodes, and magnet structure as a unit and direct flow of blood or other conductive fluid through the tubular section in making flow measurements. Such unitary structure has several disadvantages in extracorporeal use. First, it is difficult to sterilize effectively after use. Also different size units must be provided to accommodate measurement in different size flow lines. Where measurements are to be taken at more than one point in an extracorporeal circuit, a plurality of separate complete flow meter units are required. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved electromagnetic measuring unit for use in making flow measurements in an extracorporeal circuit. The units are made into two separable parts which can be readily assembled made into two separable parts which can be readily assembled and disassembled. One part includes a tube with electrode sensors which may be made inexpensive enough to utilize it as a disposable part, or a paert which can be readily and easily changed and sterilized by conventional techniques. The other part of the assembly includes a magnet structure for generating the required magnetic field. The two parts can be easily assembled and disassembled and include quick disconnect electrical connections for the electrodes. The same magnet structure can be used in combination with tubular units of different sizes. By using a plurality of tubular parts in an extracorporeal circuit, measurements can be made at different points in the circuit by moving the magnet structure part from one tubular part to another. 
     This is accomplished, in brief, by a flow meter device having a tubular member made of nonmagnetic material adapted to be connected at either end into an extracorporeal blood flow line, such as used to connect an artifical heart and lung machine into a patient&#39;s circulatory system. The tubular member includes a central portion in which a set of electrodes extending through the walls of the tube are mounted in a common transverse plane. The central portion is surrounded by a rectangular shaped central block. Electrodes are brought out at one side of the central block to form a plurality of male plug terminals. The magnet structure includes a C-shaped magnetic core and a coil winding on the core. Parallel guide members extend along the outer ends of the core, the central block portion of the tubular member slidably engaging the guide members to hold the tubular member in fixed position within the magnetic field between the poles of the magnet. A female terminal connector mounted on the inside of the magnet structure receives the male plug terminals of the tubular member when the unit is assembled. In a modification of the invention a single magnet structure is used to provide two flowmeters by incorporating two removable tubular members positioned within the same C-shaped electromagnet. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the invention reference should be made to the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of the flow meter in disassembled condition; 
     FIG. 2 is a plan view partly in section of the flow meter; 
     FIG. 3 is a sectional view taken substantially on the line 3--3 of FIG. 2; 
     FIG. 4 is an end view of the sensor portion with a larger diameter tubular member; 
     FIG. 5 is a side view of the magnet portion of the flow meter; 
     FIG. 6 is an end view of the magnet portion; and 
     FIG. 7 is an alternative embodiment of the present invention; 
     FIG. 8 is a side elevational view of a modified arrangement with the pair of lumens using a common magnetic field; and 
     FIGS. 9 and 10 show two alternative wiring arrangements for the double lumen arrangement of FIG. 8. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, the flow meter sensor assembly comprises two separable parts, a replaceable tubular sensor member 10, and a magnet member 12. Details of the sensor member 10 are shown in FIGS. 2, 3, and 4, and details of the magnet structure 12 are shown in FIGS. 5 and 6. Sensor member 10 is designed to slidably engage and electrically plug into the magnet member 12, permitting the sensor member, which is relatively inexpensive, to be made disposable or easily removable to provide sterilization. The sensor member 10 includes a tubular member 14 having a constant diameter bore 16 providing a fluid passage therethrough. The outer ends of the tubular member 14 are tapered so as to be insertable into plastic tubing. The outer perimeter of a central section 18 of the tubular member 14 is square in cross-section and extends between a pair of spaced flange portions 20 and 22. The central section 18, which therefore takes the form of a block, with the bore 16 providing an opening therethrough, has four flat surfaces 24, 26, 28, and 30 which terminate in shoulders formed by the flange portions 20 and 22. The tubular member 14 preferably is injection molded in a single piece from suitable plastic material, such as Lexan. 
     Axially aligned holes 32 and 34 extend through the walls of the tubular portion at the center of the surfaces 30 and 26, respectively. The third hole 36 extends at right angles to the axis of the holes 32 and 34 through the center of the surface 24. The holes 32, 34, and 36 lie in a common transverse plant. Three electrodes 38, 40, and 42 are provided having ends which are inserted in the respective holes 32, 34, and 36 and terminate flush with the inner surface of the bore 16. The electrode 38 extends outwardly perpendicular to the surface 30 to form an electrical connector or first male plug or pin 43. The electrode 38 has a flange 44 which engages the surface 30 to position the electrode axially and to provide an additional surface for cementing the electrode in position. 
     The electrode 40 is J-shaped to provide an end portion extending through the hole 34, a portion terminating in a connector plug or pin 45 extending along and projecting beyond the surface 28, and a transverse portion extending along the surface 26. The electrode 42 is L-shaped providing a portion extending into the hole 36 and a portion terminating in a connector plug or pin 47 extending along and projecting beyond the surface 24. The electrodes are preferably made of stainless steel and plated with gold to form a noncorrosive low resistance contact with the fluid being measured. 
     The electrodes 40 and 42 are locked in place by a back plate 46, and by top and bottom plates 48 and 50. The back plate 46, which has a width corresponding to the distance between the shoulders formed by the flanges 20 and 22, is cemented to the surface 26 of the tubular member 14. The plate 46 has a groove 52 which receives the portion of electrode 40 extending along the surface 26, thereby securely locking the electrode 40 in position in the hole 34. The upper plate 48 similarly has a groove 54 for receiving the electrode 42. The upper plate 48 also extends between the shoulders formed by the flanges 20 and 22 and is cemented or otherwise secured to the surface 24, thereby locking the electrode 42 in position. The bottom plate 50 is provided with a groove 56 which receives the electrode 40. The bottom plate 50 is cemented or otherwise attached to the surface 28. 
     The ends of the plate 46 and the outer surfaces of the upper and lower plates 48 and 50 form a continuous guide surface, as indicated at 58 and 60, respectively. The guide surfaces 58 and 60 terminate at either end in projecting guide ridges 62, 64, 66, and 68. The ridges 64 and 68 are made higher than the ridges 62 and 66 to provide a keying effect so that the sensor section can only be inserted in one way into the magnet section. 
     Referring to FIG. 4 there is shown an end view of a sensor section having a bore of larger diameter. The top, bottom, and side plates are made thinner so that the outer dimensions of the sensor section remain the same while the tubular member 14 is made relatively larger. This results in the terminal ends of the electrodes being more widely spaced than in the smaller diameter unit described in connection with FIGS. 2 and 3. Otherwise the assembly of the sensor member of FIG. 4 is substantially identical to that of FIGS. 2 and 3. 
     Referring to FIGS. 5 and 6, the magnet section of the fluid flow meter is shown in detail. The magnet structure includes a C-shaped magnetic core having a pair of parallel end portions or legs 72 and 74 forming the poles of the magnet structure and a center connecting portion 76. The core is preferably made of laminated silicon steel and is substantially square in cross section. A coil or winding 78 is wound on the central section 76 of the core 70. The spacing or gap between the inner surfaces of the legs 72 and 74 of the core corresponds to the distance between the guide surfaces 58 and 60 of the sensor member, while the width of the core corresponds to the distance between the guide ridges 62, 64, and 66, 68. Thus the magnetic core 70 is adapted to slidably engage the central section of the sensor member 10. 
     An H-shaped pin socket plate 80 extends between the legs 72 and 74 of the core, spanning the space between the legs. A plurality of female sockets are mounted on the plate 80, including a socket 82 at the center adapted to receive a plug end 43 of the electrode 38. Two groups of three sockets each, indicated at 84 and 86, are adapted to receive the plug ends 45 and 47 of the electrodes 40 and 42. The three sockets in each group are provided to accommodate the differences in electrode spacing resulting from different tubular sizes of the sensor section, there being typically three different sizes, corresponding to FIG. 3 and FIG. 4, and to an intermediate size. 
     The magnet and coil are enclosed in a top plate 88, bottom plate 90, and end plate 92 which preferably are made of molded plastic. A pair of side plates 94 and 96 are positioned on either side of the coil. The top and bottom plates 88 and 90 form guide members and provide guide surfaces 100 and 102 on either side of the leg 72 of the core 70 which are offset by differing amounts from the inner surface of the core so as to accommodate the guide ridges 62 and 64 of the sensor section. The plates are cemented together to provide a unitary structure. 
     Because the leads from the electrical connections are positioned in the magnetic field of the magnet, the internal electrical connections from the socket 82 and socket groups 84 and 86, respectively are in the form of twisted conductor pairs 87 extending from the socket terminals toward the coil 70. The two conductors of each pair are brought out around either side of the coil and reconnected as a pair to leads in shield cable 104. The magnet leads may be brought out through the same cable but are separately shielded. The twisted pair of conductors are carefully positioned in a common plane on both sides of the coil so that no magnetic lines of flux link the conductors to induce net currents in the conductors by induction. This is essential to reduce &#34;noise&#34; in the electrode output leads that could swamp out the low level signal from the electrodes. 
     The cable 104 connects to a conventional electromagnetic flow instrument (not shown) such as the flow meter instruments presently available on the market. The signal voltage is measured between the opposing electrodes 38 and 40 while electrode 42 is connected to ground. 
     While the electrode connections are preferably made from the tubular member to terminate on the inside of the magnet member, an alternative arrangement is shown in FIG. 7. Here the tubular member 10 engages the magnet member 12 in the same manner but is rotated through 180° so that the electrode terminal plug ends project away from the magnet core. A separate socket connector 106 and shield cable 108 are used to complete electrical connections between the electrodes and the measuring instrument. Otherwise the construction of FIG. 7 is substantially identical to that of FIG. 1. 
     In an alternative arrangement shown in FIGS. 8, 9, and 10, a single magnet member 112 receives a dual tubular sensor assembly 110. The magnet member is similar to that described above in connection with FIGS. 1, 5, and 6, except that the open space between the poles of the magnet core are made wider to accommodate the dual tubular sensor assembly 110. The dual tubular sensor assembly 110 includes a pair of tubular members 114 and 114&#39;. Tubular members 114 and 114&#39; have a constant diameter bore 116. Outer central portions 118 and 118&#39; are rectangular in cross section with flat outer surfaces. Adjacent surfaces of the two central portions are preferably cemented or otherwise secured together to form the unitary non-conductive body. Opposite outer surfaces preferably slidably engage the pole faces of the magnet in the same manner as the single tubular arrangement described above. Each tubular member 114 and 114&#39; includes three electrodes which are arranged in the same manner as described above in connection with FIGS. 3 and 4. A socket plate 180 has six female sockets 182 arranged to receive the ends of the electrodes to permit removal of the dual sensor assembly 110. Six pair of electrical leads 184 extend from the sockets around either side of the electromagnet 194 to a pair of output cables 196 and 198. 
     As shown in FIGS. 9 and 10, the two tubular members and associated electrodes can be wired to provide a measure of the combined flow through the tubular members or a measure of the difference in flow. FIG. 9 shows the wiring arrangement for measuring the combined or additive flow rate and FIG. 10 shows the wiring arrangement for measuring the difference in flow rates. 
     From the above description it will be seen that a sensor assembly is provided for making extracorporeal blood flow measurements or the like which is arranged in two separable sections, one section providing the blood flow passage and associated sensor electrodes, and the other section including the electromagnet for producing the required magnetic field. The two sections provide mechanical as well as electrical connections between the two sections, permitting the magnet section to be used interchangeably with a plurality of electrode sensor sections. The electrode sections are relatively inexpensive compared to the magnet sections and therefore can be used as a disposable item or an easily replaceable item. This arrangement also permits substitution of electrode sensor sections accommodating different tube diameter sizes to be used with the same magnet structure.