Patent GB-138593-A (GB)
Title: Improvements in selective electric switching devices
IPC: H04M1/515
Filed: 1919-10-28
Abstract: 138,593. Allmanna Telefonaktiebolaget L. M. Ericsson. Dec. 11, 1918, [Convention date]. Electric selectors; automatic exchange systems. -Two or more line wires are each connected to a pair of polarized relays, which co-operate to select the desired circuit. The choice of circuits is increased by closing one line a moment before the other, or by sending currents of opposite polarities successively over one line. The invention is applicable to automatic telephone systems, but is described in connexion with arrangements by which ten lamp circuits 1 - - 0 are controlled by a key-set K1 - - K0 over two line wires a, b. The line relays may be of polarized construction, but in the arrangements described the relays A1, A2, B1, B2 each consist of a pair of coils with an armature C between them. The four coils of the relays A1, A2, for example, are normally energized in series in a local circuit, but when the line a is grounded at the transmitter, the current is increased in the operating-coil L1 of relay A1 and holding-coil L, of relay A2 and decreased in the operating-coil of relay A2 and holding-coil of relay A1, so that relay A1 but not A2 is operated; a battery connexion on the line a has the opposite effect. In the system shown in Fig. 1, one of the line circuits a, b is closed a moment before the other. For example, if key K1 is depressed, contact k1 connects battery to line b through the upper winding of relay LR which energizes relay TR, which, a moment later, connects battery to line a through contact k2. Consequently, at the receiver, relay B2 is first energized in series with relay O2, which energizes relay OR2, and a moment later relay A2 is energized in series with relay O1 but relay OR1 is not energized, its circuit having been opened by relay OR2. In this case, therefore, the lamp circuit I is closed through contacts of relays OR2, HR2 (energized by A2) and B2. If, on the other hand, key K6 had been depressed, battery would be connected to the line wires a, b in the reverse order, relay OR1 would be energized instead of OR2, and the lamp circuit 6 would be closed. In the .system shown in Fig. 2, eight out of the ten selections are controlled by connecting battery or ground to one or other of the two line wires, or to both simultaneously, and the remaining two selections are controlled by connecting either battery or ground to line b and both battery and ground successively to line a. For example, if key K8 is depressed, battery is connected to line b to energize relay B2 and ground is connected through relay SR to line a to energize relay A1, which energizes relay HR1, which locks itself up. Relay SR connects an interrupter RS to the circuits of relays KR1, KR2, which energize and lock up in turn, so that after an interval the relay KR2 transfers the line a from ground to bat.. tery. Relay A2 is therefore now energized and energizes relay HR2, which locks itself up and completes the lamp circuit 8. Relays KR1, KR2- HR1, HR2 are unlocked by contacts k25, k, which are opened when the selective operation is completed. The principles made use of in Figs. 1 and 2 may be used in conjunction.