Patent GB-771342-A (GB)
Title: Improvements in or relating to telephone or like systems
Inventor: GALVIN JOHN LESLIE
IPC: H04Q3/00
Filed: 1955-03-18
Abstract: 771,342. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. March 18, 1955, No. 7905/55. Addition to 766,902. Class 40 (4). In a system of the kind described in the parent Specification, the final selectors are equipped to perform P.B.X. hunting. The final selector shown is seized from a penultimate selector such as that illustrated in Figs. 1 and 2 of the Complete Specification of the parent Specification, relay H pulling up to the ground extended forward over the - wire. If the hundreds digit is odd, battery applied by the penultimate selector to the + wire brings up WS to connect up the number one set of wipers. Call to ordinary line. The tens digit is repeated over the D wire from the penultimate selector and the wipers are raised to the corresponding level, off-normal springs N3 allowing ground applied to the + wire at the end of the digit to bring up B. This relay releases H, holds over the - wire in series with BA in the penultimate selector (not shown), and transfers the impulse circuit to the rotary magnet RM, which responds to the units digit. At the beginning of the units digit the ground on the + wire is removed, and when it is re-applied at the end of the digit, G operates and brings up H to ground on the P lead. Relay H connects up the relevant wipers and releases B, which disconnects battery from the - wire and connects the high-resistance left-hand winding of G to the - wire. Relay BA in the penultimate selector thereupon relapses and releases G which switches through in the final selector. The wanted line is then tested from the penultimate selector and operation continues as described in the parent Specification. Call to P.B.X. line. P.B.X. lines are indicated by the conditions on the P2 banks of the final selector ; first lines by resistance battery, intermediate lines by a disconnection, and last lines by ground. The final selector functions as for a call to an ordinary line up to the point where G pulls up to ground on the + wire at the end of the units digit. Relay H operates as before, and, with the final selector located on the first line of a P.B.X. group, HS pulls up to the resistance battery on the P2 bank contact. HS disconnects the. rotary magnet from the D lead and provides it with an alternative operating ground, connects the right-hand winding of B to the P2 wiper, and completes a test circuit for the first P.B.X. line by connecting the left-hand winding of B to the P1 wiper. If this line is idle relay B releases and connects the left-hand winding of G to the -wire. G being slow-to-release will still be operated when B releases and will be held from the penultimate selector until BA releases, as described above. The release of B brings down HS which reconnects the D lead to the P wiper. If the first line is busy, however, the busy ground holds B, and when G relapses the rotary magnet steps the switch to the next line, B being disconnected from the P1 wiper and being held over back G. Relay G is re-operated over RMC and reconnects B to the P1 wiper to test the second line. Testing proceeds until either an idle line is found or the last line is reached. In the latter event the ground on the P2 bank contact releases the differential relay B, and the consequent relapse of G switches through the - , +, and D wires to the last line which is then tested from the penultimate selector.