Patent GB-190916928-A (GB)
Title: Improvements in Telephone Systems.
IPC: H04Q5/08
Filed: 1909-07-20
Granted: 1909-10-07
Abstract: 16,928. Siemens & Halske Akt.-Ges. Aug. 20, 1908, [Convention date]. Semi-automatic systems.-In telephone exchange systems having automatic sub-station switchboards with several double exchange lines, in which the subscribers are selected from the exchange by means of alternating currents of different frequencies, the subscribers are arranged in groups, and the desired group and the particular subscriber in that group are selected by alternating currents sent over the two exchange lines with an earth return. The Figure shows branch station apparatus for three pairs of exchange lines I, II, III, three sub-stations N', N', N<5> being shown. Each pair of exchange lines has associated with it two harmonic selective relays G, E responsive to the alternating currents produced by the generators X, Y, Z, and also a cut-off relay 20, 22, 23, the contacts of which are so interconnected that connexion can be made by a calling subscriber with the third exchange line only when the first and second are engaged. If the first pair of exchange lines I are idle when a calling subscriber N' removes his receiver, current flows from the exchange battery 1 through the line-relay 2, line-wire a, contacts 4, 5, winding 6 of relay RI<1>, contacts 7, 8, sub-station apparatus N<1>, and contacts 9, 10, 11 to ground. The relay RI<1> thereupon closes contacts 13, 15, connecting the subscriber to the exchange-lines I, so that current now flows from the battery 1 through the relay 2, line a, contact 13, relay RI<1>, contacts 7, 8, sub-station N', contact 15, and coil 16 to earth. The excitation of the relay 2 causes the lamp 12 to glow, and the operator then inserts the answering-plug AS so that current flows from the battery 17 over the line b, coil 19, and cut-off relay 20 to earth. The relay 20 by opening contact 4 prevents the connexion of any other calling subscriber to the exchange-lines I, and by closing contacts 21 completes a gap in the auxiliary lead H<11> of the second exchange-lines II, so that the next calling subscriber is connected to the lines II. If the exchange operator desires to call over the lines III the subscriber N<5> (assumed to be the second subscriber in the second group), she inserts the calling-plug VS in the jack VK (thus sending current from the battery 18 over the line band cut-off relay 23), moves the switch SU into the calling position, and depresses that one of the keys T which connects the second generator Y to both the a and b lines. Alternating current thus flows from the generator Y in parallel over the contacts 25, 28, condensers 26, 29, contacts 27, 30, linewires a, b, and the selective relays E<111>, G<111> to earth. The relay G<111> momentarily earths its second spring so that continuous current flows from the battery 18 over the b-line and relay ry to earth. The relay ry at once completes a locking- circuit to ground, and also connects the lead gy to the battery lead b, thus connecting one terminal of all the relays RIII in the second group to the battery. Simultaneously the selective relay E<111> earths its second contact, thereby grounding the lead ey connected to one terminal of the relays belonging to the second subscriber in each group. The relay RIII<5> belonging to the second subscriber in the second group is thus energized, and connects the subscriber N<5> to the exchangelines III over contacts 37, 38. The relay RIII<5> thus completes a locking - circuit for itself over contacts 32, 33, 34. The subscriber may be rung - up by depressing the ringing-key RT. When the subscriber removes his receiver, his microphone is fed with current from a battery 39 over the clearing-relay 41, linewire a, contact 5, winding 6, sub-station apparatus, contact 38 to earth at 50. A condenser k in the line-wire b prevents current from the batteries 17 or 18 from reaching the sub-station.