Patent GB-474555-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1936-12-15
Abstract: 474,555. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Materiel Telephonique Soc. Anon.) Dec. 15, 1936, No. 34437. [Class 40 (iv)] A final selector controlled by marking gives access in response to a particular tens digit to a district office of 10 subscribers, the units digit being sent to that office, and the outlets thereby rendered spare provide accommodation for unmunbered P.B.X. lines, so that all the outlets from the selector are used and there are no spare numbers. The final selector shown is controlled by common apparatus which includes tens and units marking switches ST, SU. Consecutive positions of the final selector are wired to a P.B.X. group comprising numbered lines 77, 78 and unnumbered lines A, B, C, an ordinary line 79, a district office junction S denoted by the tens digit 8, and ordinary lines 90, 91. Call to an ordinary line. Common relay A energizes and connects up guard relay Ec. The switch ST moves to a position individual to the selector to bring about the operation of Fc, Cc, Rc, which lock to the test wire and disconnect A, whereupon ST advances to normal. Relay Q, energizes, bridging impulse relay B across the loop, and Gc pulls up. The tens and units digits set the switches ST, SU, series relay I being up during each train and change-over being effected by Ic. At the first step of ST, Q falls back and starts the selector, which stops in the position marked by ST due to the operation of T. After the units digit is received, P pulls up, whereupon Q reoperates and disconnects T, causing the selector to move to the position marked by SU, when T reoperates. If the wanted line is idle, Lt, Ft energize, Ct operates over the test wire and holds Ft, while Lt holds in series with I, which short-circuits Cc to bring about release of the control circuit. Ringing current is sent through Rt which energizes on reply and disconnects Rc to effect switch-through. If the wanted line is busy, I energizes and short-circuits Cc as before, and a busy signal is sent back since Ct is not operative. Call to P.B.X. The selector is set on the first line of the group in the marmer described above, and the test circuit is made by the operation of T. Relay R energizes over wiper psme and connects up Ls, but this relay is immediately disconnected by Lt if the line is idle. Relay Ls connects up Ra which connects R to the terminals of the intermediate lines of the group in bank psme, and Ls, T interact to step the switch SU and the selector in turn. Relay R falls back when the last line is reached and if this line is busy, a busy signal is sent back. A call to a numbered P.B.X. line other than the first is set up in the same manner as a call to an ordinary line. Call to district office. The tens digit takes effect as described above. Relay S however energizes in parallel with Ic, holding T and connecting up P, Q at once. in order to test the junction on which the selector is set. The loop is opened to delay sending of the units digit from the register-controller. If the junction is idle, ringing takes place and upon reply switch-through takes place and the units digit goes to the district office. If the junction is busy, a busy signal is sent back to the register-controller. If more than one junction is provided, hunting may take place as in the case of a P.B.X. call.