Patent GB-291582-A (GB)
Title: Improved circuit arrangements for selectors in automatic and semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1927-04-21
Abstract: 291,582. Siemens Bros. & Co., Ltd., and Christian, D. A. April 21, 1927. Automatic and semi-automatic exchange systems.-In a system in which lamp flash signal is given by bringing the incoming speaking wires of a switch to the same potential, the release relay of the switch is held during lamp flash periods by a winding included in the connection from lamp flash battery to a speaking wire or to a relay which brings the incoming speaking wires to the same potential. The invention is described in connection with a group selector which moves to eleventh contacts unconnected to outgoing trunks and gives busy tone and flash signal if all outlets in a level are busy, and also in connection with a final selector in which the signal is applied to the outgoing side of a bridge and energizes a winding of an answering supervisory relay which brings the incoming wires to the same potential. Group selector, Fig. 2. Relay A at a1 closes parallel circuits for the windings 1 of release relay B and a change-over and stepping relay C, the latter being made slow to release by shortcircuiting its winding 3 at c1. C opens the circuit of the rotary magnet RM at c2 and at c3 prepares the circuit of the vertical magnet VM which operates in a circuit including winding 2 of relay C the circuit of winding 1 being opened at k1 on the first vertical step which also closes contacts k2, k3 to prepare the circuit of the rotary magnet and connect test relay H to ground. At the end of the impulse train C relapses, opens the circuit of VM at c3 and at c2 closes the circuit of RM which closes contact rm to connect winding 1 of C to test wiper C1 over back contacts h1, s1. If the outlet is busy, H is short circuited but C operates over winding 1 and at c2 opens the circuit of RM which releases and at rm opens the circuit of winding 1 of C. C releases and at c2 recloses the circuit of RM to advance the wipers another step. When a free outlet is found H operates in series with winding 1 of relay C and at h4 closes a locking circuit for itself including winding 2 of C and the vertical magnet which do not operate. If all outlets are busy, the wipers are stepped on to eleventh terminals and contacts s1 - - s3 are changed over. Relay H operates as for a free outlet when s1 changes over but A remains connected to the calling loop over the eleventh terminals. At s3 a circuit is closed from conductor BS over winding 2 of B, back contact c4 and wiper A1 to the calling subscriber. Busy tone and battery are alternately connected to conductor BS and during battery periods winding 2 of B is energized in series with winding 3 of C which operates and at c4 disconnects the grounded winding of A from the a wire and connects battery thereto over the other winding of A. The wires are thus brought to the same potential but B is held over its winding 2 during battery periods. Final selector, Fig. 1. Relay A at a1 closes a circuit for winding 1 of release relay B which, at b3 completes a circuit over w1, k1 for winding 1 of relay C which, at c3 prepares a circuit for vertical magnet VM. VM operates in series with winding 2 of relay C the circuit of winding 1 of this relay being opened at k1. At the end of the impulse train, C releases and E is energized over k3, c2, w1, b3. Circuit for winding 1 of C is closed at e5 and C closes a locking circuit for E over k3, c2, e1, b4. Relay E changes over the circuit to the rotary magnet RM at c2 and opens e3 to prevent premature operation of ring tripping relay F. Impulses are then repeated to the rotary magnet in series with winding 2 of C. At the end 'of the train, C releases and contact c1, which has been open during impulsing to prevent operation of test relay 11, falls back to complete the test circuit. If called subscriber is free, H operates over winding 1 and locks up over winding 2. Test wiper is grounded at h1, the called line is connected to the ringing circuit at h2, h3, winding 1 of F is short circuited at h7 and the line is prepared at h5 for battery reversal on operation of answering relay D, Ringing current is fed to called line over winding 2 of F and ringing signal applied to calling line from RS over f4, h6 and w2. When called subscriber replies, relay F operates over winding 2, opens short-cicruit of winding 1 at f1 and locks up over this winding, the called line being extended back to relay D at contacts f2, f3. If the called line is busy, H does not operate, C releases followed by E and at e4 a circuit is closed for winding 1 of F which disconnects ringing current and signal. Busy tone and lamp fiash battery are connected up over interrupter 1, winding 2 of B, f5, j3, h6, w2, a wire and winding 2 of D, which operates and changes contacts at d1, d2, but as relay H is not operated h5 is back and the incoming a and b wires are brought to the same potential, relay B being held over winding 2 during battery periods. The first Provisional Specification describes an alternative arrangement in which a separate relay connected in the circuit of lamp flash battery closes a holding circuit for the release relay. Attendants' supervisory arrangements. Lamp CSH, Fig. 1, is flashed at each operation of relay D during busy tone and lamp flash signal. Metering. Relay J, which energizes on seizure of the final selector, remains energized until called subscriber replies, its circuit being then broken at f6. J is slow to release and before j1 falls back D is energized and booster battery is applied over j1, d4, b1 to the incoming c wire to operate calling subscriber's meter. J also de-energizes when the called line is busy, but metering is prevented since j1 falls back and opens the metering circuit before the circuit of relay D is closed at j3.