Patent GB-628528-A (GB)
Title: Automatic telephone systems
IPC: H04Q3/00
Filed: 1945-01-26
Abstract: 628,528. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Jan. 26, 1945, No. 2088. Convention date, April 21, 1944. [Class 40 (iv)] In a telephone system wherein numbers having certain initial digits require translation for routing to other offices, an " S-link " interposed between a normal line-finder and first group selector, initiates hunting for a free register-translator while the line-finder searches for the calling line. The first digit is repeated by the register to the group selector and if the first digit is such that translation is not required the register-translator is released and the link switches the finder straight through to the group selector. If translation is required, the group selector is released and then re-set by the first of the translated digits. The S-links are connected to the register translator by " SR-links which concentrate the traffic in groups of 60 registers. The register-translator is a simplified version of that described in Specification 628,174. Seizure and setting of register. When the finder is allotted earth is sent forward on the P-wire. If the finder finds the calling line, current will be supplied to the line from the impulse relay of a normal group selector which does not carry the usual dialling tone, however. Start relay CSR, operating to the earthed P-wire, energizes all the power magnets P1 of the idle S-link finders belonging to the SR- links, and when an S-link is found, it is busied, and test relays T1R, T2R operate and check for double connection. T2R energizes power magnet P2 of the register finder which seizes an idle register and busies it, and test-relays T3R and T4R operate and check for double connection. Relay T4R operates RAR which switches brushes A-G through to the register and a dial tone circuit is completed over the E brush. Impulsing relay DR and release relay R1R operate and earth the C-wire to operate RBR and SAR, and the F- and G-wires are connected to the group selector. Relay R1R operates RCR and XR. In response to impulses DR sets the digit switches Dl ... D6 or D7 in turn, relapse of the dialling relay R2R after each digit causing the in-sequence switch P1 to step on. Relay DR1 also controls DR, which repeats the first digit to the group selector. Translation not required. If the first digit dialled is 1, 8, 9 or 0, SBR operates over wire D and locks to the P-wire now grounded by the group selector, and RBR and SAR release, the latter switching the finder through to the group selector and the former releasing RAR to release the register, which restores to normal, the digit switches being homed -by release of XR. Translation required. If the first digit is 2 ... 7, RVR and RTR1 operate when P1 goes to position 2, opening the outgoing loop to restore the selector. RTR1 initiates seizure of a twodigit translator link as described in the abovementioned Specification. Potentials characteristic of the digits are fed to the translator from brushes B of D1, D2 and maybe D3, according to whether two or three digit office prefixes are necessary. The translator then applies potentials characteristic of the routing digits to terminals 1 ... 4 of bank C of the outsequence switch PO. When the translation is complete, RTR3 operates, and RYR operates and locks and applies H.T. to gas valve GV and triodes V1, V2. RYR also closes the loop to the group selector over wires F and G through rectifier S(+) and relay PR(+). PR(+) closes a circuit for out-impulsing relay RKR through a 10 cycle interruptor. RJR operates and locks, releases PR(+) and makes a fresh circuit for RKR. When first the interrupter opens the circuit for RKR, PT steps once and removes the short-circuit on the loop over its brush B. Subsequent interruptions are repeated by RKR to the loop and counting-switch PT is stepped until the potential found on its bank A matches that on terminal 1 of bank C of PO, whereupon the gas valve GV is fired and GVR operates to disconnect RKR and RJR. Relay RKR restores PT to its home position. Relay GVR is released by means of GSR, the slow release of which provides the intertrain pause. The switch PO goes to position 2 and the circuit of RKR is re-made. The remaining routing digits are sent out similarly, PO stepping after each digit. Operation of RTR5 or RTR4 and RTR5 from the translator enables PO to skip one or two positions if there are only 3 or 2 routing digits respectively. When PO reaches positions subsequent to 4, RKR operates and characteristic digit potentials are supplied to the grid of V1 from the B brushes of the respective digit switches. When, in the case of a 6-figure number the last set of pulses have been sent out according to the setting of D6, PO goes to position 9 and the D-wire of the SR-link is grounded by brush A of. PO. Relay SBR energizes, releasing SAR and RBR. Relay SAR switches through and RBR releases RAR which frees the register. If the dialled number contains seven digits, i.e. the first three digits comprise the office prefix, RTR2 is operated, locks, and brings in a 3-digit translator link. This arranges for PO to skip position 5 since the digit on D3 is not to be transmitted as such, and operates RTR6 which transfers the release circuit on brush A of PO from terminal 9 to terminal 10 to permit the transmission of the digit registered on D7. RTR7 energizes in parallel with PO to release RTR2 as PO leaves position 5. Out trunking to a " Universal " office. At such an office the trunk wires are reversed until a register at that office is seized. The outgoing loop is completed first over rectifier S( - ) and when the reversal takes place PR(+) operates to initiate transmission of the digits. False calls. Relay TAR1 operates in the initial control loop. If the subscriber fails to dial within 20-40 seconds, TAR2 and TAR3 operate to ground terminals 1 and 2 of bank B of PO. Digit switches D1 and D2 in their initial position apply potentials characteristic of 9 and 1 (say) so that the call is automatically extended to the number 91.