Patent GB-174837-A (GB)
Abstract: 174,837. Automatic Telephone Manufacturing Co., Ltd., (Automatic Electric Co.). Dec. 21, 1920. Automatic exchange systems; party line systems.-A party line is connected over main and intermediate distributing frames to sets of terminals (one set for each station on the party line) accessible to a connector, the supply of ring- ing current from the connector being selectively determined by conditions established at the intermediate distributing-frame. The invention is described as applied to an automatic exchange of 1000 lines in which a connection is established over a line switch, group-selector, and connector, all of which, apart from the selective ringing arrangements at the connector, are of well-known type. In the arrangement shown in Figs 2 and 3, a party line 201, 202 having four substations A<1> - - A<4> bridged across it, enters the cable side of the main distributing-frame MDF at terminals B<2> which are connected by a jumper 203 to any desired pair of terminals 1 on the switchboard side of the frame. The terminal set on this side of the main frame is connected to the individual line switch C<1> serving the party line, and to a corresponding terminal set on the vertical side of an intermediate distributing-frame IDF, from which the line is extended by a triplex jumper 204 to the upper terminal set of a vacant idler block IB, a number of which are mounted on the vertical side of the intermediate frame IDF. The four lower terminal sets 16, 33, 50, 66 on this idler block are connected on the left-hand side by jumpers 205 - - 208 to terminal sets 111, 121, 131, 141 on the horizontal side of the intermediate frame IDF, and on the right-hand side through potential modifying circuits to the upper set 1. The terminal sets 111, 121 &c. are multipled to all the contact banks in the connectors corresponding to the numbers assigned to the party line subscribers. In accordance with the wiring shown in the figures the substations A<1> - - A<4> are allotted numbers 111, 121, 131, 141 respectively, and the bells thereat are tuned to frequencies of 16, 33, 50, 66 cycles respectively. Thus a calling subscribed desiring connection with the subscriber A<1> will be connected over a line switch and group selector ( not shown) to an idle connector E, Fig. 2, which will respond in the usual manner to the last two digits 11 of the wanted number 111, and engage the first set of contacts 171, 172, 173 in the first level. If the wanted line is idle, on the de-energization of the slow-acting relay 106 a ringing current selecting circuit is completed from ground at armature 18<1> of the line switch C<1>, Fig. 3, conductors 213, 214, jumper 204, resistance 210 (1,000 ohms), jumper 205, trunk 215, armatures 121, 136, 125, 130, Fig. 2, lower windings (500 ohms each) of switching relays 109, 108, armatures 128, 122, 132, 119, contact 171, jumpers 205, 204, Fig. 3, conductor 219, to the line relay 14<1> (500 ohms) of line switch C<1>. A branch circuit also extends from a point in the above circuit between the lower windings of relays 108, 109, over the lower winding of a marginal relay 110 (500 ohms) to battery. With these resistances the current in these two circuits is so apportioned that only the switching relay 109 responds. This relay locks up over armature 147, connects up the 16-cycle ringing current generator at its armature 143, and completes a circuit for the relay 212, Fig. 3, and the switching relay 107, Fig. 2. A parallel circuit is also completed for the switching relay 13<1> (of the line switch C'), which operates halfway and disconnects the line switch C'. The switching relay 107 closes the ringing circuit at armature 136, and the ringer at substation A<1> alone responds. The relay 212 cuts the resistance 210 out of the line circuit and is made to act more slowly than the relay 107 to prevent any resistance variation being made in the selecting circuits before they are broken at armatures 130, 128. When the called subscriber removes his receiver the operation proceeds in the usual manner. If the subscriber A<2> is called the ring- ing current selecting circuits are completed as before for the switching relavs 108, 109, 110, but this time over the contacts 174, 176 and terminal sets 121, 33. In this case the resistance 210 is omitted, and the marginal relay 110 responds and locks up in addition to the relay 109, thereby connecting up the 33-cycle generator over the armatures 146, L43. When the subscriber A<3> or A<4> is called a reversal in the line connections between the 33 and 50 cycle terminal sets at the idler block IB causes the relay 108 instead of the relay 109 to actuate to connect up either the 50 or 66 cycle generator, depending upon whether the marginal relay 110 responds or not, which in turn depends upon the inclusion or not of the resistance 210 according to the terminal set (50 or 66) over which the ringing current selecting circuit is completed. The relay 110 may be provided with two lower windings to which the lower windings of the relays 108, 109 may be separately connected, two independent ringing current selecting circuits thus being formed. In a modified arrangement, Figs. 4 and 5, the ringers at stations A' and A<2> are connected from the negative side of the line to ground, which those at A<3> and A<4> are connected to earth from the positive side, the ringers at stations A<1> and A<3> being tuned to 33-cycle frequency and those at A<2> and A<4> to 50-cycle frequency. Only two ringing generators are provided at the connector E, and the switching relays 108, 109, Fig. 2, are omitted. The ringing current selecting circuit extends from earth at armature 116, Fig. 4, over the series windings of relays 107, 110, test wiper 161, the intermediate frame and idler block terminals, as determined by the number dialled, and parallel circuits including the relays 212 and 13<1>. The relay 212 short circuits the resistance 210 to make all four branches test busy and is rendered slow acting for the purpose described in the first modification. Which generator is connected up depends upon whether or not the marginal relay 110 responds in this circuit, which in turn depends upon the inclusion or omission of the resistance 210. If the subscriber A<1> is called the resistance 210 is included and the relay 110 remains inert. Current of 33- cycle frequency is thereby transmitted over the negative side of the line, 202, but the ringer at station A<1> only responds. When connection with the substation A<2> is desired the resistance 210 is omitted from the circuit of relays 107, 110, the marginal relay 110 responds and 50-cycle current is projected over the line 202, the bell at station A<2> being rung. If substations A<3> or A<4> are called ringing current is projected over the positive side of the line, 201, the frequency depending on the inclusion or not of the resistance 210 in the circuit of the relay 110. In both arrangements individual lines may be brought into the vertical side of the intermediate frame IDF and run by jumpers directly to the horizontal side.