Methods of Automatic Restoration

Two general methods present themselves for bringing about the automatic restoration of the drop. First, the mechanical method, which is accomplished by having some moving part of the jack or of the plug as it enters the jack force the drop mechanically into its restored position. This usually means the mounting of the drop and the corresponding jack in juxtaposition, and this, in turn, has usually resulted in the unitary structure containing both the drop and the jack. Second, the electrical method wherein the plug in entering the jack controls a restoring circuit, which includes a battery or other source of energy and a restoring coil on the drop, the result being that the insertion of the plug into the jack closes this auxiliary circuit and thus energizes the restoring magnet, the armature of which pulls the shutter back into its restored position. This practice has been followed by Bell operating companies whenever conditions require the drop to be mounted out of easy reach of the operator; not otherwise. Mechanical—Direct Contact with Plug. One widely used method of mechanical restoration of drops, once employed by the Western Telephone Construction Company with considerable succe , was to hang the shutter in such position that it would fall immediately in front of the jack so that the operator in order to reach the jack with the plug would have to push the plug directly against the shutter and thus restore it to its normal or raised position. In this construction the coil of the drop magnet was mounted directly behind the jack, the latch rod controlled by the armature reaching forward, parallel with the jack, to the shutter, which, as stated, was hung in front of the jack. This resulted in a most compact arrangement so far as the space utilization on the front of the board was concerned and such combined drops and jacks were mounted on about 1-inch centers, so that a bank of one hundred combined drops and jacks occupied a space only a little over 10 inches square. A modification of this scheme, as used by the American Electric Telephone Company, was to mount the drop immediately over the jack so that its shutter, when down, occupied a position almost in front of, but above, the jack opening. The plug was provided with a collar, which, as it entered the jack, engaged a cam on the base of the shutter and forced the latter mechanically into its raised position. Neither of these methods of restoring— i.e. , by direct contact between the shutter or part of it and the plug or part of it—is now as widely used as formerly. It has been found that there is no real need in magneto switchboards for the very great compactne which the hanging of the shutter directly in front of the drop resulted in, and the tendency in later years has been to make the combined drops and jacks more substantial in construction at the expense of some space on the face of the switchboard. IMG:384091999325875926_fig252_t.gif.png:Illustration_ Fig. 252. Kellogg Drop and Jack Fig. 252. Kellogg Drop and Jack View full size illustration. Kellogg Type:—A very widely used scheme of mechanical restoration is that employed in the Miller drop and jack manufactured by the Kellogg Switchboard and Supply Company, the principles of which may be understood in connection with Fig. 252. In this figure views of one of these combined drops and jacks in three different positions are shown. The jack is composed of the framework B and the hollow screw A , the latter forming the sleeve or thimble of the jack and being externally screw-threaded so as to engage and bind in place the front end of the framework B . The jack is mounted on the lower part of the bra mounting strip C but insulated therefrom. The tip spring of the jack is bent down as usual to engage the tip of the plug, as better shown in the lower cut of Fig. 252, and then continues in an extension D , which pa es through a hole in the mounting plate C . This tip spring in its normal position rests against another spring as shown, which latter spring forms one terminal of the drop winding. The drop or annunciator is of tubular form, and the shutter is so arranged on the front of the mounting strip C as to fall directly above the extension D of the tip spring. As a result, when the plug is inserted into the jack, the upward motion of the tip spring forces the drop into its restored position, as indicated in the lower cut of the figure. These drops and jacks are usually mounted in banks of five, as shown in Fig. 253. IMG:384091999325875926_fig253_t.gif.png:Illustration_ Fig. 253. Strip of Kellogg Drops and Jacks Fig. 253. Strip of Kellogg Drops and Jacks View full size illustration. Western Electric Type:—The combined drop and jack of the Western Electric Company recently put on the market to meet the demands of the independent trade, differs from others principally in that it employs a spherical drop or target instead of the ordinary flat shutter. This piece of apparatus is shown in its three po ible positions in Fig. 254. The shutter or target normally displays a black surface through a hole in the mounting plate. The sphere forming the target is out of balance, and when the latch is withdrawn from it by the action of the electromagnet it falls into the position shown in the middle cut of Fig. 254, thus displaying a red instead of a black surface to the view of the operator. When the operator plugs in, the plug engages the lower part of an S -shaped lever which acts on the pivoted sphere to restore it to its normal position. A perspective view of one of these combined line signals and jacks is shown in Fig. 255. A feature that is made much of in recently designed drops and jacks for magneto service is that which provides for the ready removal of the drop coil, from the rest of the structure, for repair. The drop and jack of the Western Electric Company, just described, embodies this feature, a single screw being so arranged that its removal will permit the withdrawal of the coil without disturbing any of the other parts or connections. The coil windings terminate in two projections on the front head of the spool, and these register with spring clips on the inside of the shell so that the proper connections for the coil are automatically made by the mere insertion of the coil into the shell. IMG:384091999325875926_fig254_t.gif.png:Illustration_ Fig. 254. Western Electric Drop and Jack Fig. 254. Western Electric Drop and Jack View full size illustration. IMG:384091999325875926_fig255_t.gif.png:Illustration_ Fig. 255. Western Electric Drop and Jack Fig. 255. Western Electric Drop and Jack View full size illustration. Dean Type:—The combined drop and jack of the Dean Electric Company is illustrated in Figs. 256 and 257. The two perspective views show the general features of the drop and jack and the method by which the magnet coil may be withdrawn from the shell. As will be seen the magnet is wound on a hollow core which slides over the iron core, the latter remaining permanently fixed in the shell, even though the coil be withdrawn. Fig. 258 shows the structural details of the jack employed in this combination and it will be seen that the restoring spring for the drop is not the tip spring itself, but another spring located above and insulated from it and mechanically connected therewith. IMG:384091999325875926_fig256_t.gif.png:Illustration_ Fig. 256. Dean Drop and Jack Fig. 256. Dean Drop and Jack View full size illustration. IMG:384091999325875926_fig257_t.gif.png:Illustration_ Fig. 257. Dean Drop and Jack Fig. 257. Dean Drop and Jack View full size illustration. IMG:384091999325875926_fig258_t.gif.png:Illustration_ Fig. 258. Details of Dean Jack Fig. 258. Details of Dean Jack View full size illustration. Monarch Type:—Still another combined drop and jack is that of the Monarch Telephone Manufacturing Company of Chicago, shown in sectional view in Fig. 259. This differs from the usual type in that the armature is mounted on the front end of the electromagnet, its latch arm retaining the shutter in its normal position when raised, and releasing it when depre ed by the attraction of the armature. As is shown, there is within the core of the magnet an adjustable spiral spring which pre es forward against the armature and which spring is compre ed by the attraction of the armature of the magnet. The night-alarm contact is clearly shown immediately below the strip which supports the drop, this consisting of a spring adapted to be engaged by a lug on the shutter and pre ed upwardly against a stationary contact when the shutter falls. The method of restoration of the shutter in this case is by means of an auxiliary spring bent up so as to engage the shutter and restore it when the spring is raised by the insertion of a plug into the jack. IMG:384091999325875926_fig259_t.gif.png:Illustration_ Fig. 259. Monarch Drop and Jack Fig. 259. Monarch Drop and Jack View full size illustration. Code Signaling. On bridging party lines, where the subscribers sometimes call other subscribers on the same line and sometimes call the switchboard so as to obtain a connection with another line, it is not always easy for the operator at the switchboard to distinguish whether the call is for her or for some other party on the line. On such lines, of course, code ringing is used and in most cases the operator's only way of distinguishing between calls for her and those for some sub-station parties on the line is by listening to the rattling noise which the drop armature makes. In the case of the Monarch drop the adjustable spring tension on the armature is intended to provide for such an adjustment as will permit the armature to give a satisfactory buzz in response to the alternating ringing currents, whether the line be long or short. IMG:384091999325875926_fig260_t.gif.png:Illustration_ Fig. 260. Code Signal Attachment Fig. 260. Code Signal Attachment View full size illustration. The Monarch Company provides in another way for code signaling at the switchboard. In some cases there is a special attachment, shown in Fig. 260, by means of which the code signals are repeated on the night-alarm bell. This is in the nature of a special attachment placed on the drop, which consists of a light, flat spring attached to the armature and forming one side of a local circuit. The other side of the circuit terminates in a fixture which is mounted on the drop frame and is provided with a screw, having a platinum point forming the other contact point; this allows of considerable adjustment. At the point where the screw comes in contact with the spring there is a platinum rivet. When an operator is not always in attendance, this code-signaling attachment has some advantages over the drop as a signal interpreter, in that it permits the code signals to be heard from a distance. Of course, the addition of spring contacts to the drop armature tends to complicate the structure and perhaps to cut down the sensitivene of the drop, which are offsetting disadvantages. IMG:384091999325875926_fig261_t.gif.png:Illustration_ Fig. 261. Combined Drop and Ringer Fig. 261. Combined Drop and Ringer View full size illustration. For really long lines, this code signaling by means of the drop is best provided for by employing a combined drop and ringer, although in this case whatever advantages are secured by the mechanical restoration of the shutter upon plugging in are lost. Such a device as manufactured by the Dean Electric Company is shown in Fig. 261. In this the ordinary polarized ringer is used, but in addition the tapper rod carries a latch which, when vibrated by the ringing of the bell, releases a shutter and causes it to fall, thus giving a visual as well as an audible signal. Electrical . Coming now to the electrical restoration of drop shutters, reference is made to Fig. 262, which shows in side section the electrical restoring drop employed by the Bell companies and manufactured by the Western Electric Company. In this the coil 1 is a line coil, and it operates on the armature 2 to raise the latch lever 3 in just the same manner as in the ordinary tubular drop. The latch lever 3 acts, however, to release another armature 4 instead of a shutter. This armature 4 is pivoted at its lower end at the opposite end of the device from the armature 2 and, by falling outwardly when released, it serves to raise the light shutter 5 . The restoring coil of this device is shown at 6 , and when energized it attracts the armature 4 so as to pull it back under the catch of the latch lever 3 and also so as to allow the shutter 5 to fall into its normal position. The method of closing the restoring circuit is by placing coil 6 in circuit with a local battery and with a pair of contacts in the jack, which latter contacts are normally open but are bridged acro by the plug when it enters the jack, thus energizing the restoring coil and restoring the shutter. IMG:384091999325875926_fig262_t.gif.png:Illustration_ Fig. 262. Electrically Restored Drop Fig. 262. Electrically Restored Drop View full size illustration. A perspective view of this Western Electric electrical restoring drop is shown in Fig. 263, a more complete mention being made of this feature under the discu ion of magneto multiple switchboards, wherein it found its chief use. It is mentioned here to round out the methods that have been employed for accomplishing the automatic restoration of shutters by the insertion of the plug. IMG:384091999325875926_fig263_t.gif.png:Illustration_ Fig. 263. Electrically Restored Drop Fig. 263. Electrically Restored Drop View full size illustration.