Patent GB-302227-A (GB)
Title: Improvements in or relating to automatic switches for use in telephone or like systems
IPC: H04Q3/00
Filed: 1928-11-22
Abstract: 302,227. Associated Telephone & Telegraph Co., (Assignees of Tharp, V. S.). Dec. 12, 1927, [Convention date]. Automatic exchange systems and selectors. - A rotary connector after an unsuccessful hunt over a level operates 11th step springs which energize the ordinary release magnet and remain latched until rotary release is complete, whereupon the vertical magnet, which has previously been energized weakly to make it quick acting, operates fully and lifts the wipers to the next level. Ordinary lines and first lines of groups are marked in an extra bank by a ground connection. This ground may be used to stop the switch, if the wanted group is busy, on the terminal immediately following the last terminal in the wanted group. Alernatively, the last extra terminal of a group may be temporarily grounded through a marginal relay 123 by a relay 122 connected to the last test terminal, and a connector then stops on the last terminals of the busy group, energizing 123 which operates an overflow meter. In either case a relay such as 122 is provided for marking the last extra terminal in the 10th level. Numerical operation. Change-over relay 30 is energized by release relay 20 over double-dog springs DD which open at the first operation of the vertical magnet. At the end of the first digit 30 which has been held over a back contact of line relay 10 connects up the rotary magnet ROT over a rotary dialling relay 70. Busy test and signal. Hunting operation. If the line is busy, 80 pulls up and is followed by stepping relay 60 on the relapse of 70. If the line is a night service line, 60 releases 80 and a busy signal is sent. If it is a single line or the first of a group, 50 is operated partially over the ground encountered by the extra wiper 111 and fully, locking itself up, when 70 falls back, 80 is held at 59, and ROT is operated over 56, 57, 58. ROT interacts with 60 in the usual way. If the switch is unsuccessful on this level, springs 131 - - 136 are operated and latched, release magnet REL is operated restoring the springs DD to re-operate 30 and a weak energizing circuit is made for V. When rotary release is complete, the springs are unlatched and V is energized strongly, lifts the wipers and re-operates springs DD to release 30 which after an interval re-operates ROT to restart the hunting operation. If all the lines are busy, 60 is held energized over 111 by the ground connected over 123 to the last terminal of the group or by the ground connected permanently to the first terminal of the next group, and holds ROT. 80, which has been held over a contact of ROT, falls back after an interval. connects up busy tone and releases ROT which makes a circuit for 60 independent of that over 111 to prevent seizure of the line if it becomes idle subsequently. Completion and release of connection. If an idle line is called or when one is found, switching relay 90 pulls up, directly in the former case, or in series with a reverse winding of 60 in the latter. This is to prevent 60 from pulling up again if ROT falls before it has been permanently cut off by 90. 90 releases 50 and 80 if necessary, and connects up ringing current and ring back tone which are cut off in the usual way by 40. The connector is not released until the called party hangs up. The successive relapse of the line and release relays 10, 20 sends an impulse to 70 and releases the preceding switches. On the relapse of 70 the connector is re-guarded over 95, 71, 90 (upper) until it is released by the relapse of the back bridge and switching relays 1, 90. Construction of switch, Fig. 2. On the 11th step of the wiper shaft, the member 130 forces the long spring 131 past a latch 132, depressing the spring 135 carrying the latch, and freeing a second long spring 136 from a latch 133. The converse of these operations takes place when the shaft is restored and the member 134 engages spring 136.