Patent GB-261859-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1925-08-31
Abstract: 261,859. Automatic Telephone Manufacturing Co., Ltd., and Saville, W. Aug. 31, 1925. Automatic exchange systems. - In a district office, means are provided for dealing with calls which are not to be completed over either the main office or the local selectors, e.g. calls to a manual operator or to a sub-office of the district office containing only line switches and connectors. In the system described a calling subscriber of either the district office itself or of its sub-office is extended non-numerically to a repeater, Fig. 1, in which line and release relays A, B pull up followed by relays L1, L2 which complete hunting circuits for the switches S1, S2 under control of relays K1, K2. In the normal position the wiper sets W1, W3 are operative and the normal test terminal is grounded. When the switch S1 finds an idle main office trunk, relay K1 switches through and releases relay L1. In a similar manner the switch S2 seizes a local selector without'however operating its line relay, the impulsing loop being open at 27, 30. Digits are repeated at 6 to the selectors and at 5 to the stepping magnet DM of the tenpoint discriminators and the sluggish relay C in parallel. At the end of each digit relay C grounds wiper 42 and certain terminals in the discriminator bank and energizes its release magnet RM. Local calls (234) and calls to the sub-office (2347). When relay C falls back at the end of the digit 2, relay DA pulls up in two steps and locks itself. Consequently at the end of the next digit 3 relay DB pulls up in a similar manner. At the end of the next digit 4, therefore, relay HA pulls up, locks itself, switches over the repeating loop from the main office trunk to the local selectors, and energizes relay HI. Relay K1 then falls back and completes a homing circuit whereby the wipers W1 are driven past the end of the bank. Relay L1 which was shortcircuited by the homing ground now pulls up and the wipers W2 hunt under control of relay KA1 for a trunk to the sub-office. When this is found relay KA1 switches through and releases relay L1. The next digit is repeated to the local selector, and if its value is anything but 7 the relapse of relay C energizes relay PCO, which locks up, disconnects the magnet DM, and unlocks relays KA1 to release the sub-office trunk and cause the restoration of switch S1 to normal. The call is then completed over the local selectors. If, however, the fourth digit is 7, HB switches over the loop from the local switches to the wipers W2, unlocks relay K2, and energizes relay PCO. Relays HA, HB. HI, KA1 remain looked up and the switch S2 is restored to normal. Long distance calls established by an operator (235). In this case relay H is operated in response to the third digit 5, locks itself and energizes relay PCO. Relay K1 is released to restore the switch S1 to normal, and in switch S2 relay H2 releases relay K2 and a homing circuit is made to drive the wipers W3 off the end of the bank. The wipers W4 then hunt for an idle operator under control of relay KA2. Main office calls. As soon as it is determined that the call is not a local one the relay PCO is energized to release relay K2 and cause the restoration of switch S2 to normal. Release. In the case of operator-calls battery is connected to the lower speaking wire, and when relay A falls back relay O pulls up and holds relay B to delay release. Modifications. The discriminating switches may be available to several repeaters in common over non-numerical switches. They need not be released after each digit and separate switches may be provided for each digit. In case there is no sub-exchange, the following arrangememt may be adopted. A subscriber sends in a preliminary impulse to a two-directional selector repeater which hunts in its first level for an idle discriminator. If the call is for the main office it is completed over the first half of the bank of the secondary switch, and if for an operator over the second half. In the case of local calls, however, the selector repeater is operated and gives access to local selectors. Metering systems. The usual current reversal when the called party answers energizes polarized relay D which grounds the meter wire.