Patent GB-562115-A (GB)
Title: Improvements in or relating to telephone systems employing crossbar switches
IPC: H04Q3/00
Filed: 1943-03-08
Abstract: 562,115. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., GILLINGS, C., and MURRAY, L. J. March 8, 1943, No. 3717. [Class 40 (iv)] In a system in which subscribers' lines are connected to group-selecting units, e.g. of the kind described in Specification 560,732, over primary and secondary cross-bar units PSU, SSU controlled by chain circuits to guard against interference by simultaneous calls, the function of a single large chain circuit is performed by two or more smaller chain circuits to ensure that the opening of a chain contact never breaks an excessive current and so to eliminate trouble from arcing. In the system described, a group of primary switches serves from 200 to 1600 lines. In a light traffic group, there are four columns A-D of twenty 20/6 switches, the switches in a given position in all the columns sharing the six links, one of which goes to each of six 20/10 secondary switches associated individually with groupselecting units. In a heavy-traffic group, only one column of 10/6 primary switches is provided. Arrangements between these extremes are provided for intermediate traffic conditions. The columns are subdivided into sections AA ... DD, BA ... BD, &c. of five primary units. In the establishment of a connection, a relay corresponding to the primary switch in which the calling line appears is energized first, then a relay characteristic of the column and then one characteristic of the section. Each of these relays is energized over a chain of back contacts of similar relays so that only one of each kind can remain energized at a time. The circuit of the primary switch relays only includes contacts of the relays in the same section and that of the section relays only contacts of section relays in the same column so that none of the chain carries an excessive current. An arrangement for replacing a large chain by two smaller chains is described below in connection with the outlets from the secondary switches. Circuit details.-Line relay 1R completes a circuit for relay 1PA, which corresponds to the primary switch in which the line appears, over a chain of contacts of similar relays in the same section. 1PA completes a similar chain circuit for relay A which corresponds to the column containing the calling switch and A completes a similar chain circuit for AA which corresponds to the section. On the completion of the operation, a circuit is made for such of the select magnets 1PP ... 6PP of the primary switch as have available outlets. Only one can remain energized and this energizes relay SS in the control circuit of the selected secondary switch. Circuits are thus completed over two chain circuits, each of which includes back contacts of all the secondary switch select magnets SP, only five such magnets being connected to each chain. The magnets associated with idle outlets tend to pull up, but only one can remain locked. On the operation of SP, SZ completes the circuit of the secondary pull down and hold magnet SH that corresponds to the operated primary select magnet PP and the primary pull down and hold magnet that corresponds to the calling line. The latter circuit is completed over relay Z which locks temporarily and releases the column relay A ... D, whereupon the section relay AA ... AD, the primary select magnet PP, the relay SS, the secondary select magnet SP and the relays SZ and Z fall back in turn, the hold magnets being held over the private wire of the connection. Cut-off relay 1K releases the line relay 1R which releases 1PA if there are no waiting calls in this primary unit. When all the outlets of a secondary switch are busy, its relay GB falls back and energizes its relay SGB. When all the outlets of the primary switches of a particular level are unavailable because in all the secondary switches either the corresponding hold magnets are energized or all the outlets are busy, a relay PGB is energized and prevents the operation of the relay PA of the primary switch concerned.