Patent GB-190928363-A (GB)
Title: Improvements in Telephone Exchanges.
IPC: H04M3/62
Filed: 1909-12-04
Granted: 1910-02-17
Abstract: 28.363. Siemens & Halske Att.-Ges. Dec. 5, 1908, [Convention date]. Exchange systems.-In junction and trunk line working, a signal is given to the operator at the originating exchange when the operator handling the incoming call makes a double connexion. The invention is described as applied to a system having automatic means for the supply and disconnexion of ringing-current, and for disconnecting the operator's testing-receiver when the calling- plug has been inserted. The leads a", b<11> represent an incoming junction-line from the exchange I, the clearing-relay SR<1> being energized by the insertion of the calling-plug at, exchange J into the junction - line designated by the operator at exchange II. The armatures of the various relays are arranged in vertical lines, the dotted lines indicating that a certain armature belongs to a given relay. The energizing of the relay SR' supplies current to the unequal coils 5, 6 of a differential relay DR, which is temporarily energized. When the calling - plug st is inserted in the jack of a disengaged subscriber, the relay A is energized and supplies additional current to the winding 5 of the relay DR, whereupon this relay releases its armature 9, thereby suppling current over the lead 8 and armatures 3, 9 to the winding 10 of a relay C, which locks up through its armature 11 and winding 12, at the same time closing the circuit of the ringing relay G over the armatures 15, 21 and an interrupter U. The relay G by attracting its armatures 16, 17 connects the ringing-generator M to the called line, the armature 17 supplying additional battery current to the winding b<1> of the called subscriber's line-relay to prevent the operation of the latter. The relay C also cuts out at 13 the operator's testing-receiver PH, and by attracting its armature 14 earths the junction-line a" over the armatures 23, 18, and 14, thereby energizing the clearing-relay at exchange I and extinguishing its ring-off lamp. The periodic attraction of the armature 18 of the ringmg-relay G intermittently interrupts this circuit, and causes the ring- off lamp to glow periodically, thus indicating to the operator at exchange I that the required subscriber is being called. When the called subscriber replies, the relay SR' is energized and closes at 19 the circuit of a winding 20 of an auxiliary relay HR, which locks-up through its winding 22 and armature 21, at the same time breaking the circuit of the ringing-relay G. The attraction of the armatures 24, 25 connects the junction-line a", b<11> to the called subscriber, while the attraction of the armature 23 earths the lead a" during the conversation, thus extinguishing the ring-off lamp at exchange I. When the called subscriber hangs up his receiver, the relay SR<2> is de-energized, removing the ground on the lead a<11> and causing the ring-off lamp at exchange I to glow. When the calling-plug is removed at that exchange, the relay SR' is de-energized, lighting up the ring-off. lamp SL<1>, the retraction of the armature 7, together with the return of the plug st into normal position (involving the opening of a contact SS), resulting in the disconnexion of the battery from the relays DR, C, and HR. The return of the plug st also opens a contact (not shown) between the relay A and its battery, so that this relay is also deenergized. If the operator at exchange I inserts the calling-plug into the wrong junction-line, the relay SR' is not energized, so that the winding 6 of the relay DR receives no current. The insertion of the calling-plug st by energizing the relay A, sends current through the winding 5 only, so that the relay attracts its armature 9, thus preventing the energizing of the relay C and the further connexions established by it, so that the subscriber is not called. If the connexion at exchange I is correctly made, but the operator at exchange II connects up to an engaged subscriber, the testing potential at the socket of this jack strengthens the current through the winding 5 and weakens that in the winding 6, so that the relay DR is energized and prevents the excitation of the relay C and the further connexions established by it. The armature 14 being thus in its normal position, the attraction of the armature 4 connects the contact-maker F and buzzer E over the armatures 4, 14, 18, and 23 to the lead a<11>, giving the usual engaged' flicker and buzzer signals to the first operator and the calling subscriber. The commutator F and buzzer E may also be connected to a " busy " jack Bkl, in which the operator inserts the plug st if the subscriber wanted is engaged, so that flicker and buzzer signals are sent to the other operator and the calling subscriber as before. It will be seen that the operators attending to incoming calls have only to test the required line and insert the calling- plug, the supervision of incorrect connexions being allotted to the operator at the outgoing end of the junction-line.