Patent GB-505037-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1937-11-03
Abstract: 505,037. Automatic exchange systems. POLLAK, J. E. (Associated Telephone & Telegraph Co.) Nov. 3, 1937. No. 30150. [Class 40 (iv)] Digits transmitted by a calling party for setting up a connection are also stored in a mechanical impulse repeater to enable some or all of them to be transmitted over the connection as required. The exchange digits from the repeater may be used to determine the number or impulses for zone metering or all the digits may be transmitted to a ticket printing of punching machine, but as described, the stored digits are used for alternative routing. On all connections initiated at exchange A, Fig. 1, a mechanical impulse repeater MIR is taken into use. On local calls over certain of the first 8 levels of SR which drops back in response to a local first digit, the repeater MIR is released. On calls over direct junctions on level 9 of SR or the earlier outlets on level 10 to exchanges C and B respectively, the first digit stored in MIR, i.e. the digit used to set SR is suppressed and the remainder used to complete the setting up of the con. nection. If however on a call to B, an indirect junction over the later outlets of level 10 is taken into use, the first digit stored in MIR is also transmitted to set the incoming selector at C. The Provisional Specification describes a different lay-out in which discrimination after two digits is used and the drop-back feature is not provided. General operation of selector-repeater SR and mechanical repeater MIR. When the calling line is found, A, B in the selector pull up and an associating switch RS hunts for an idle mechanical repeater, such as that described in Specification 458,095, marked by absence of ground in bank. P. When found, HB operates in series with the magnet RSM, sends dial tone and prepares the in- and out-pulsing circuits of the mechanical repeater. The first dialled digit is repeated to VM and C of the selector and to stepping magnet R of the mechanical repeater at which relays IC, IB, IP, IS and marking magnet M also operate. At the selector, relay E operated on the 1st vertical step interacts with RM when C falls back at the end of the train, and the selector hunts until E fails to'be re-operated by busy ground whereupon switching relay HA pulls up. At the mechanical repeater, IC relapses following C and releases the marking magnet M whereupon BY pulls up and shunts IP over the pins Y, Z of the repeater. Relays IP, IS then release slowly and sending magnet S pulls up followed by IP, the first and any subsequent stored digits being sent in known manner. Discrimination. If the selector receives a local 1st digit, the holding circuit of HB is opened at NRI on the 1st rotary step and the relapse of this relay opens the pulsing circuits of the mechanical repeater and releases it. The release magnet ZM of the selector is also operated over post-springs NP3 to restore the selector whereupon it is re-set by the next train to a level in which the post springs NP are operated, and further digits are repeated by A to local switches. If however, the call is for a distant exchange over levels 9 or 10 post-springs NP3 open the release circuit, NP2 hold HB and NP1 open the local fourthwire metering circuit. Local and distant connections may be set up over different wiper-sets in accordance with the first digit. Alternative routing. Assuming that a direct junction to exchange B is seized, the mechanical repeater is ineffective in transmitting the first digit stored, that is digit O which set the selector, since the impulse springs IPS are shunted by contacts of relay DA. The second and subsequent digits stored by the mechanical repeater will however be transmitted since DA is operated over a digit counting switch CS to remove the shunt on IPS. When 4 digits have been sent, the switch CS shunts down relay HB to release the mechanical repeater. If an indirect junction over exchange C is seized, relay DA, which is polarized, pulls up due to reversed battery connections over such junction so that the first stored digit O is sent out and sets the incoming selector at exchange C to a level over which exchange B is reached. To prevent immediate operation of the supervisory relay D over indirect junctions, when HB falls back on termination of digit transmission, the reversed battery conditions on such junctions are changed to normal by one or more slow relays after the junction has been seized.