Patent GB-654078-A (GB)
Title: Telecommunication switching systems
IPC: H04Q1/18
Filed: 1947-10-13
Abstract: 654,078. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Oct. 13, 1947, No. 27406. Convention date, Nov. 13, 1946. [Class 40 (iv)] In a multipotential system a control circuit is provided which responds to stop a selector switch when it encounters a - ve potential equal to a numerically set-up comparison potential, and also which responds when the switch encounters a +ve potential. This potential may be used to stop the switch at the end of a group. As shown, Fig. 1, the - ve comparison potential - PDX is applied to the grid of V1 via a biassing circuit 1 and the selector terminal potentials -PD are applied via the biassing circuit 2 to the grid of V2. When the potentials are substantially equal the anode-cathode impedance of V1, V2 rises to fire tube GV and bring up TVR which opens the drive circuit for the switch. If the switch encounters a +ve potential TRR operates over rectifier S5 to open the switch driving-circuit. The Specification as open to inspection under Sect. 91 comprises also the following description outlining the application of the circuit to a complete automatic system. This subjectmatter does not appear in the Specification as accepted. Initial test of valve circuit and group selector setting. When a subscriber 3 lifts his hand-set a start circuit 4 seizes an R-link which seizes a B-link (i.e. line-finder/1st group selector link) and also a register-controller. In the latter SCR operates over the T-wire, SER being normally operated. SFR then comes up and connects potential PDO to valve V2 while V1 is connected to potential in the first group of digit storing relays 9. This potential represents the maximum non-firing voltage difference permissible. Relay TAR comes up, followed by the anode voltage connecting relay THTR. If the valve circuit is faulty and GV fires, TUR brings up SDR. Relay SER is thereby released, opening the T-wire to release the R-link and busying the register against further seizure. Relay SDR locks up and lights an alarm lamp until manually released. If GV does not fire SCR is followed by register release relays R1R, R2R and SFR releases. Relay R2R locks up SER to prevent untimely release of the latter. Operation of the line-finder 7 and the registration of the called subscriber's number on the digit storage relay sets proceeds. When the line-finder seizes the calling line TUR, TFR1 and NAR operate temporarily to release SCR and bring up DBR (11), Fig. 4, to hold R1R. When the first digit is received XAR1 operates TAR2 and closes a series circuit over the B-wire for energizing TAR in the test circuit and relay AR2 and the clutch magnet P2 in the first group selector. Relay THTR connects up the H.T. supply to the comparison circuit V1, V2 which compares the potential applied over the A-wire from the T-terminals with the digit characterizing potentials applied from the first group digit storing relays 9. When a wanted outlet is found GV operates TVR to stop the selector and release TAR, TAR2, the latter being quick-releasing and earthing the A-wire to busy the seized selector by shunting the comparison potential on the T-terminal. When AR2 switches through the T-terminal remains grounded in the B-link. TVR brings up TCR1 and when THTR anp TVR fall back TCR2 also comes up to remove the ground from the A-wire and reconnect the reference potential for a second test. Valve GV fires and TVR operates, followed by TFR1 and TDR which releases TCR1 and momentarily applies resistance battery to the B-wire to bring up BR3 in the seized selector, so pre - paring the seized selector for subsequent similar selecting operations. TDR releases THTR, followed by TFR1, TCR2 and TDR, and the register circuit is prepared for setting the subsequent group selectors in a similar manner. Setting of final selector and final test of valve circuit. The final selector has an upper and a lower bank serving respectively lines 10-59 and 60-09, access to which are controlled by the wiper switching relay DR operated immediately on seizure by ground applied over the A-wire by the fourth group of digit storing relays. Only five potentials, different from those characterizing the units digits, are therefore required to characterize the tens positions. Relay AR4 and clutch magnet P4 are operated by ground on the B-wire and when the selector finds the required tens position GV energizes TVR to release TAR, TAR2 and stop the selector. TFR1 follows, energizing TDR in a circuit controlled over the counting relays. THTR falls away followed by TVR, TDR which causes the transfer of the selector control to the fifth set of digit storing relays. When ground is again extended over the B-wire AR4 operates to low-resistance battery on the C-terminal and locks up to the B-wire while P4 energizes to restart the selector. As usual GV fires and TVR operates TAR, TAR2 and AR4, P4 release when the wanted line is found. TFR1 brings up TDR to initiate testing of the line by a relay TBR (not shown) in the register which operates over the A-wire and the C-brush in series with the wanted party's cut-off relay if the line is free, and thereby shunts its own highresistance winding to bring up the switchthrough relay CR in the final selector. The register is released after the busy test is made, the R-link assuming control. If the called party is free and answers then the R-link releases, the call being controlled thereafter in the B-link. When the register is released DBR in the rectifier and dial pulsing relays 11 falls back followed by RIR, R3R. During the release time of the latter R4R energizes R5R which connects potential PD19 to both the grids of valves V1, V2 and energizes TAR and THTR. If GV fails to fire before R3R falls back R4R locks up so that when R3R makes its back contacts SDR operates, locks, lights the alarm lamp GL and opens the operating circuit for SER to take the register-controller out of service. Otherwise if GV fires R4R releases promptly and SDR does not operate. PBX groups. All lines in the group are given the same characteristic potential which is removed for all lines except the last by the operation of the cut-off relay. Night service lines are allotted different numbers and corresponding characteristic potentials which are, however, replaced by the PBX potential when a relay connected to the second PBX line is operated by that line being seized. Non-existing numbers. These lines have their characteristic potential removed so that the selector passes over them and ultimately reaches an " N.E." position, such positions being located after each group of ten outlets and characterized by +50 V. on their T-terminal. The polarized relay TRR operates to this potential, opens the drive circuit of the selector, and brings up TFR1, TFR2, the latter preventing TDR from operating. The A-wire is then grounded in a circuit (not shown), shunting down TRR to release TFR1 and bringing up the switching relay CR in the final selector. The cascade relays fall off in turn, applying successively potentials to V1, but as no potential is connected to the A-wire GV does not fire and eventually the register shunts down BR2 (by means not shown) to release the switch train and then applies to V1 a potential characteristic of a special service group selector to which the 1st group selector is directed. The special service selector is then controlled so as to direct the call to an operator. Overflow arrangements. A PBX line group or an ordinary subscriber's line may be followed by special N.E. positions characterized by a potential PS12 on the A terminal. The call proceeds as for an ordinary N.E. position until the cascade relays commence to release. In this case when the cascade relays cause a potential PS12 to be applied to VI, GV fires and TVR energizes TFR1 to cause changes in the counting relay circuit having the following effects:-the digit storing relays are not released; the selector train is released; the first group selector is then caused to connect to a special service second group selector which gives access to an auxiliary train of selectors which are then set according to the settings of the digit storing relays to connect with additional lines to the PBX or ordinary subscriber. False calls. On permanent loop conditions or undue delay in dialling a timed relay breaks down the call and applies a comparison potential to V1 which directs the first group selector to a false call position.