Polarized Ringer

The polarized bell or ringer is, as has been stated, the device which is adapted to respond to the currents sent out by the magneto generator. In order that the alternately opposite currents may cause the armature to move alternately in opposite directions, these bells are polarized, i.e. , given a definite magnetic set, so to speak; so the effect of the currents in the coils is not to create magnetism in normally neutral iron, but rather to alter the magnetism in iron already magnetized. Western Electric Ringer. A typical form of polarized bell is shown in Fig. 79, this being the standard bell or ringer of the Western Electric Company. The two electromagnets are mounted side by side, as shown, by attaching their cores to a yoke piece 1 of soft iron. This yoke piece also carries the standards 2 upon which the gongs are mounted. The method of mounting is such that the standards may be adjusted slightly so as to bring the gongs closer to or farther from , the tapper. The soft iron yoke piece 1 also carries two bra posts 3 which, in turn, carry another yoke 4 of bra . In this yoke 4 is pivoted, by means of trunnion screws, the armature 5 , this extending on each side of the pivot so that its ends lie opposite the free poles of the electromagnets. From the center of the armature projects the tapper rod carrying the ball or striker which plays between the two gongs. In order that the armature and cores may be normally polarized, a permanent magnet 6 is secured to the center of the yoke piece 1 . This bends around back of the electromagnets and comes into close proximity to the armature 5 . By this means one end of each of the electromagnet cores is given one polarity—say north—while the armature is given the other polarity—say south. The two coils of the electromagnet are connected together in series in such a way that current in a given direction will act to produce a north pole in one of the free poles and a south pole in the other. If it be a umed that the permanent magnet maintains the armature normally of south polarity and that the current through the coils is of such direction as to make the left-hand core north and the right-hand core south, then it is evident that the left-hand end of the armature will be attracted and the right-hand end repelled. This will throw the tapper rod to the right and sound the right-hand bell. A reversal in current will obviously produce the opposite effect and cause the tapper to strike the left-hand bell. An important feature in polarized bells is the adjustment between the armature and the pole pieces. This is secured in the Western Electric bell by means of the nuts 7 , by which the yoke 4 is secured to the standards 3 . By moving these nuts up or down on the standards the armature may be brought closer to or farther from the poles, and the device affords ready means for clamping the parts into any position to which they may have been adjusted. IMG:384091999325875926_fig079_t.gif.png:Illustration_ Fig. 79. Polarized Bell Fig. 79. Polarized Bell View full size illustration. Kellogg Ringer. Another typical ringer is that of the Kellogg Switchboard and Supply Company, shown in Fig. 80. This differs from that of the Western Electric Company mainly in the details by which the armature adjustment is obtained. The armature supporting yoke 1 is attached directly to the cores of the magnets, no supporting side rods being employed. Instead of providing means whereby the armature may be adjusted toward or from the poles, the reverse practice is employed, that is, of making the poles themselves extensible. This is done by means of the iron screws 2 which form extensions of the cores and which may be made to approach or recede from the armature by turning them in such direction as to screw them in or out of the core ends. IMG:384091999325875926_fig080_t.gif.png:Illustration_ Fig. 80. Polarized Bell Fig. 80. Polarized Bell View full size illustration. IMG:384091999325875926_fig081_t.gif.png:Illustration_ Fig. 81. Biased Bell Fig. 81. Biased Bell View full size illustration. Biased Bell. The pulsating-current generator has already been discu ed and its principle of operation pointed out in connection with Fig. 77. The companion piece to this generator is the so-called biased ringer. This is really nothing but a common alternating-current polarized ringer with a light spring so arranged as to hold the armature normally in one of its extreme positions so that the tapper will rest against one of the gongs. Such a ringer is shown in Fig. 81 and needs no further explanation. It is obvious that if a current flows in the coils of such a ringer in a direction tending to move the tapper toward the left, then no sound will result because the tapper is already moved as far as it can be in that direction. If, however, currents in the opposite direction are caused to flow through the windings, then the electromagnetic attraction on the armature will overcome the pull of the spring and the tapper will move over and strike the right-hand gong. A ce ation of the current will allow the spring to exert itself and throw the tapper back into engagement with the left-hand gong. A series of such pulsations in the proper direction will, therefore, cause the tapper to play between the two gongs and ring the bell as usual. A series of currents in a wrong direction will, however, produce no effect.