Abstract:
An electromagnetic flowmeter having a flow tube wherein the electrodes leads pass through potting material forming part of the lining of the flow tube. The leads emerge at the exterior of the flow tube at three points, two of which substantially are at the electrodes, and one of which is between the two electrodes, via conduits embedded in the potting material and exiting from the flow tube at said points. The leads are accessible for repair or replacement.

Description:
FIELD OF INVENTION 
     The present invention is in the field of electromagnetic flowmeters having encapsulated internal structures, such as coils, coil boxes, etc. 
     THE PRIOR ART 
     In the prior art, the electrode leads of electromagnetic meters having internally mounted field coils, and often the coils or housings therefore, are embedded in potting material. It is therefore more or less impossible to service or replace the leads without disturbing the meter&#39;s lining and/or the potting material. 
     SUMMARY OF THE INVENTION 
     In the present invention, we provide conduits in the potting material, which conduits isolate the electrode leads from said potting material. Each electrode&#39;s one end and each said conduit&#39;s both ends exit at the exterior of the flow tube, so the leads can be fed into or out of said conduits when replacing, repairing, inspecting, or installing electrode leads. 
     The present invention has particular application to the invention of the prior application for U.S. patent Ser. No. 580,281, of Eugene Vidmantas, filed May 23, 1975, entitled ELECTROMAGNETIC FLOWMETER HAVING INTERNAL FIELD COILS, assigned to the assignee of the present invention, and now U.S. Pat. No. 3,981,190. 
     As explained in the Vidmantas application, the saddle-shaped field coils of an electromagnetic flow meter are housed inside the meter&#39;s flow tube, in sturdy saddle-shaped, non-magnetic boxes. Said boxes are secured to the inner wall of a magnetic steel pipe section forming part of said flow tube. With this sort of arrangement, the leads to the electrodes also can be located externally of the flow tube, and also connect to conventional replaceable electrodes having external ends to which connection is to be made. 
     In the present invention, however, the leads to the electrodes are still externally accessible, but actually run from the electrodes either outside or inside the flow tube to, and out through, a feed-through conveniently located, thereby providing mechanical protection for the leads. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a diametrical sectional elevation of an electromagnetic flowmeter according to the invention, taken on the plane B of FIG. 2, and FIG. 2 is the corresponding longitudinal section elevation taken on the plane A of FIG. 1. 
     FIG. 3 and 4 are enlarged partly sectional fragments of FIG. 1. 
     FIG. 5 is a diagram of the principles of an electromagnetic flowmeter. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 5 shows a flow tube 1 through which an at least slightly electrically-conductive fluid flows, generally a liquid, sometimes a slurry. Electrodes 2 are mounted in the tube wall diametrically opposite one another and in electrical contact with the fluid flowing through the tube. Field coils 3, which are to be electrically energized, are located on opposite sides of the tube so as to generate a magnetic field the direction of which is indicated by the arrow labeled FIELD. The electrodes 2 are electrically connected by leads 4 to measuring circuitry 5 which conditions the voltages sensed at electrodes 2, such as to produce a flow-representative signal for a using device 6 which records, controls or performs some other useful function in a measure determined by the rate of flow through tube 1. 
     In FIGS. 1 and 2, flow tube 1 is shown to comprise a pipe section 11, liner 8, and body 9. The pipe section 11 and liner 8 are respectively steel and rubber, say, and the body 9 is potting material or encapsulant (partially omitted in FIG. 1, to avoid obscuring structure later to be described), which fills in the space between liner 8 and section 11. The liner 8 and body 9 together define the bore of the flow tube. 
     In the space containing body 9 are also located saddle-shaped boxes 15 containing field coils 13, access to which coils is preferably provided via holes (not shown) in pipe section 11. We do not show the termination of the flow tube, but as usual suitable means such as flanges, and so on, will normally be provided for attaching the flow tube in a fluid flow line, for metering or controlling the flow therethrough. Likewise, we show no coil connections or source of coil energization as these are not germane to the present invention, although coil terminations or leads could be provided for in the manner in which we are about to describe as applied to the electrode leads 14 of the electrode 12. 
     Each lead 14 passes through a conduit 16, one end of which attaches to an electrode housing 22 having a cap 20 (which conceals the attachment in FIG. 3) and the other end of which attaches to a feedthrough 21 at the top of pipe section 11, each set of conduits 16 having its own electrode housing, but sharing a single feedthrough fitting. As will be seen from the smoothly curved shape of conduits 16, the leads 14, are necessarily flexible electrically-conductive wire of diameter somewhat narrower than the inner diameter of conduits 16, in order to provide for threading them through the conduits easily and without becoming damaged. Any suitable conduit forms or material: copper, non-magnetic stainless steel, plastic, or the like, can be used to prevent the potting material, which surrounds the conduits, from getting into the conduits and impeding or preventing removal or insertion of the leads, from or in the conduits. Obviously, the inner walls of the conduits must be smoothly curved on the whole and have a surface free of sharp or abrasive elements which could damage the wire or insulation (if any) thereon. 
     Again, in order to allow conduits 16 to pass by the upper coil box 15, without passing through it, the box may be provided with indentations 17, which form channels, externally of the box, through which channels the conduits 16 can pass. 
     As will be seen from FIG. 3, housing 22 has a right-cylindrical cup portion 23, external to section 11, and a nipple 24 between the latter and the flexible lining 8. Lining 8 has on integral nipple 25 and flange 26, the nipple being received within nipple 24, with flange 26 seating on the bottom of cup portion 23. Seated on the flange is circular collar 27 having inner and outer flexible-material O-rings 28 and 29, the former for sealingly receiving the right cylindrical stem 30 of electrode 12, and the latter for sealing the collar 27 in the cup portion 23. Collar 27 also has annular ridges 27a for sealing between it and flange 26. Electrode 12 has an enlargement 19 secured (as by threads) in the bore of the collar. Housing 22 is welded, as indicated at 31, to section 11. 
     Suitable follower means (not shown) are provided for forcing the collar 27 to the left in FIG. 3 whereby to sealingly clamp flange 26 between the housing 22 and the collar 27. The electrode is electrically conductive, so collar 27 will be made of insulating material, for example, polyvinyl chloride plastic, in order to electrically isolate the electrode from the housing 22, which would usually be of metal, and from pipe section 11, which would usually be made of steel. 
     As FIG. 3 shows, the conduits 16 exit through bores 32 in housing 22, and are sealingly fixed to the inner ends thereof, as by welds 32 or a combination of welds and epoxy sealers. The wires 14 may be fixed to the center outer end 34 of electrode 12 by any conventional electrical connecting means, such as the screw terminal 35, etc., as shown in FIG. 3. 
     FIG. 4 is largely self-explanatory (it and FIG. 3 are essentially manufacturing drawings, to life-size scale, for example). However, in addition, FIG. 4 shows tapped holes 36 for fixing the above-mentioned follower means (not shown) in the housing 22 (preferably keyed in with the help of notch 37 in the inner wall of cup portion 23). In practice, the caps 20 (not shown in FIGS. 3, 4 and 5) will provide for protectively sealing the interior of housing 23 off from the external atmosphere. 
     In use, it is obvious that either the leads 14 (singly or collectively) or the electrodes 12 (one or both) may be inserted, removed, replaced, etc., without regard for the rest of the meter (other than to prevent escape of fluid from the meter, if it is an electrode which has to be removed). 
     The apparent redundancy of electrode leads 14 provides nulling loops. When the meter is initially assembled, the conduits are symmetrically placed with respect to the diametral plane of the electrodes. For nulling, appropriate electrical means (not shown) are coupled to the loops. Thus, FIG. 2, shows one such loop, except that normally the two leads 14, from where they emerge from the feedthrough 21 to where they terminate at one terminal of circuit 5, are arranged as a twisted pair (not shown) for cancelling induced voltages arising between the feedthrough 21 and circuitry 5. There is also a second such loop and twisted pair provided for the other electrode 12, of course. 
     The foregoing is a description of our invention which will suffice to enable those skilled in the art to make and use our invention. In addition, various modifications may be made in our teachings, which modifications will fall within the scope of our claims. Thus, we have shown our invention in a form providing for nulling loops. However, such loops are not always provided, or necessary, and our invention is equally useful where there would be but a single wire 14 per electrode. 
     Likewise, our invention would be useful where more than, or fewer than, two fluid-contacting electrodes are provided, or where the electrodes are not actually in contact with the fluid but otherwise within the meter structure and electrically coupled (capacitively, for instance) to the fluid. 
     Again, the particular flow tube we have chosen for illustrating our invention is essentially a integral double-walled structure, between which walls field coils, and electrode leads and conduits, are contained. However, some times even more complex structure is used for flow tubes, in which the electrode leads (and even the field coils) would be found external to the counterpart of present pipe section 11, but nonetheless quite as inaccessible externally due to their incorporation in structure integral with, yet external to, pipe section 11. In such case, providing these leads with conduits 16 would provide accessibility just as in the present instance, and would also be regarded as being inside the flow tube, even though separated from the liner 8, etc., by structure corresponding to pipe-section 11. 
     Finally, our invention would still be useful if there were no potting material 9 and/or no coil boxes 15, or with different field coil arrangements, magnetic field sources other than coils, and so on.