Patent GB-190321302-A (GB)
Title: Improvements in Automatic Telephonic Installations.
Inventor: KUGELMANN BERNHARD
Filed: 1903-10-03
Granted: 1904-09-29
Abstract: 21,302. Kugelmann, B. Oct. 3. Telephone systems.-Relates to automatic telephone exchange systems of a type in which the successive insertion of two or more resistances at the subscriber's station between line and earth causes the successive balancing of corresponding Thomson bridges at the exchange, so as to deenergize relays in the cross-arms of such bridges, and close a local circuit depending on the combination of the bridges and relays affected. The closing of the local circuit effects the connection between the calling and the called subscriber. Fig. 2 shows two subscriber's stations A, B connected with the exchange apparatus. Two of the bridges x, y are shown, current normally flowing through all the relays 1, 2, &c. in the cross-arms of the bridges, and the armatures being only released when the bridges are balanced by the insertion of suitable resistances between line and earth at the subscriber's station. The bridges, of which there are 20 for a group of 99 subscribers, are all connected in parallel between the conductor 38 and earth, one only being balanced by each resistance inserted by the subscriber. The bridges control relays in two columns or rows, one for units, the other for tens. Thus to establish connection between the calling subscriber, say A, and subscriber No. 43 it is necessary to balance the bridges connected with relay 4 in the first column or row and relay 3 in the second. For this purpose subscriber A places the contacts 11 and 12 upon the points of the switch resistance R corresponding to bridge 4 of the first column or row and bridge 3 of the second, and then closes contact 13. Current now flows from the common source of current 14, of which the negative pole is earthed at 15, through the point 16, relay 18, contact 21, and line-wire 22 to earth through the contacts 23 and 13 and relay 14. This current causes the attraction of the armatures 28 and 25, but leaves the armatures 20 and 27 unattracted. The contact at 29 closes a local circuit through the relay 30, and the resulting momentary contact which occurs as the armature 31 passes over. the contact 32 causes a strong current from the battery 33 to flow through the relay 18 to earth at 34, and also through the contact 19, line 22, relay 24,. and current source 36 to earth. The armatures 20 and 27 are now attracted, so that the resistances selected by the subscriber are successively placed between the conductor 38 and earth as the successive earth contacts are made at 39, 40. If any other of the devices z had been in action at the time, the battery 14 would have been disconnected from earth by the break at 41, and the depression of the key 13 would not have produced any effect until the bridges were available for use. The successive balancing of the two selected bridges causes the armatures of relays 4 in the first row and 3 in the second row to drop, closing the contacts at 42<1>, 43<1>, 44<1>, and 45'. Current from the battery 46 now flows through 47<1>, 48', 43', and 45<1>, relay 51 of the first switch apparatus E<1> (or the next, E<2>, if the first is in use) and thence through 52, 54<1>, relay 55', contact 57', relay 58<1>, conductor 59', and contacts 44<1>, 42' to earth. At the same time, current flows in a branch circuit from 52 through the relay 55 of the calling subscriber A, contact 57, relay 58, and contact 60 to earth through the line 22 and contact 40. The relay or electromagnetic switch 51 causes contact to be made at 77 and 78 and at the same time bridges over the break at e<1> so as to put the second switch apparatus E<2> in readiness to respond to the next call. The relays 58<1>, 55<1>, and 51 remain energized by current flowing from battery 46 through 47<1>, 74<1>, 58', 57<1>, 55', 76, 77, 51, and 78, and a similar circuit through 74, 58, &c. maintains the relays 58 and 55 energized. When the calling subscriber takes his receiver T off the hook, current flows from the battery 36 through 81, 82, common speaking wire 83, contact 82<1>, conductor 81', and audible signal K', which is replaced by the called subscriber's receiver when it is litted from the hook. Branch currents also pass through the electromagnets 84, 84<1> so that their suspended armatures are attracted. When the receivers are replaced, the armatures swing back and momentarily interrupt the circuits described above, so that the relays 58, 58', 55, 55', and 51 are de-energized, and the switch apparatus resumes its normal state. For installations up to 1000 subscribers, thirty bridges are required in accordance with the above system. A division into groups is, however, preferable, each group having a calling number, and each switch apparatus having electromagnets for making connection with the leads running to the various groups. The fact that the line-wire which connects two exchanges in different towns possesses a greater resistance is utilized for effecting a control for the payment of fees. The subscriber can only balance the bridges at the distant exchange by considerably reducing his switch resistances, to allow for the increased resistance of the line-wire. This is done by connecting a resistance in parallel with his switch resistance, a relay controlling the indicator device being thereby brought into action. A time control of the conversations may be effected by the use of clockwork interrupters for the circuits.