Patent GB-190901270-A (GB)
Title: Improvements in Telephone Exchanges.
IPC: H04M9/00
Filed: 1909-01-18
Granted: 1909-07-08
Abstract: 1270. Siemens Bros. & Co., [Siemens & Halske Akt.-Ges.]. Jan. 18. Exchange systems, supply and control of ringing-current in. Relates to the periodic supply of ringing.current in exchange telephone systems, in which the circuits for the ringing-relay are established in the interval between successive applications of the ringing- current. This ensures that the first application of current to a called line shall be of the proper duration, and also prevents the possibility of damage to the "busy" generator in those systems in which a " busy signal is given to the calling subscriber by inserting the connecting-plug in a special "busy" jack. The insertion of the connecting-plug VS in the jack of the called subscriber energizes the relay LR, which in turn closes (1) a circuit from the battery B<2> through the resistance w, relay UR, and armature l, back to the battery, and (2) a circuit from the batteries B<1>, B' through the resistance w, relay UR, armature l, armature h<2> of the relay HR, winding W<1> of the relay RAR, armature h, and rotary switch KV back to the battery B<1>, B<2>, as soon as the switch closes this circuit. The switch KV moves synchronously with the switch RK directly controlling the ringing-relay RR, but the switches are so constructed that the switch KV completes its circuit only when the switch RK is not completing its circuit. The attraction of the armature a<1> of the relay RAR completes the circuit of the auxiliary relay HR, which in turn completes a holding-on circuit for the relay RAR from the battery B<1> through the armature a<1>, winding W<1>, and armature h to the other pole of the battery, thereby rendering the relay RAR independent of the switch KV. The relay HR also completes a holding-on circuit for itself. The attraction of the armature a' of the relay RAR brings the ringing-relay RR under the immediate control of the switch RK, so that the calling-generator RQ is periodically connected to the line to be called. When the called subscriber replies, current is cut-off from the relay UR by shunting it in a known manner, and the armature u is released, so that, when the switch KV is next closed, current flows from the battery B' over the armatures a', u, winding W<2> of the relay RAR, and the switch KV to ground. The winding W<2> nullifies the effect of the winding W<1>, so that the armatures a<1>, a<2>, a<3> are released, thus cutting-off the ringing - current. The attraction of the armature h<2> prevents the re-establishment of current through the winding W'. When a "busy" signal is given to the calling subscriber by inserting the connecting-plug in a special "busy"-jack, "flicker" signals are given at the clearing-lamps of other operators handling the same connexion by means of current impulses transmitted over the socket leads, and in the present arrangement these impulses are used to prevent the calling-current from being switched on when the connecting-plug is inserted in a "busy"-jack SK. When the plug is inserted in such a jack the relay LR is energized as before, but since a "flicker" signal is given immediately afterwards, the armature of the relay UR falls back during this signal and prevents the calling- circuit from being closed by rendering the relay RAR inoperative.