Patent GB-656132-A (GB)
Title: Telephone systems
IPC: H04Q1/18
Filed: 1947-02-04
Abstract: 656,132 Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Feb. 4, 1947, No. 3280. Convention date, Feb. 4, 1946. [Class 40 (iv)] The potential comparing means comprises two multielectrode discharge devices, one normally being used for the first test over the t wire and the second for the second test over the b wire, but when the register is controlling the final selector both devices are used simultaneously, being connected in parallel to the test wiper during the tens " and the first " units tests, and being connected respectively to the a and b wires for the second " units " test which determines the condition of the selected line. General lay-out, Fig. 1. A  call is initiated by a subscriber  actuating his line relay (Figs. 2, 2a, 2b or 2c) which operates the starting circuit (Fig. 3). B-link and register finders (Fig. 4) are operated thereupon to select an idle B-link (Fig. 5) and an idle A-register (Figs. 6 and 6a-6w). The B-link terminates in a line-finder (Fig. 7) and a first group selector (Fig. 8). Second and succeeding group selectors, thousands and hundreds selectors are wired as in Fig. 9. The tens and units selections are performed by the final selector (Fig. 10). A line to be identified is marked by the station marker (Fig. 11) to be picked up by the marker finder (Fig. 12). The station marker and the line circuits may co-operate with known identification finders (not shown). A separate translator (Figs. 13 and 13a-13d) is associated with the register when required. Party line revertive calls, and calls to a distant office, or a toll or other operator are initiated by dialling a predetermined digit to obtain access via the first group selector to a special service group selector (Fig. 9a). Permanent loop calls are extended from the first group selector over a false call trunk (Fig. 15) to the wire chief. Access to a distant office may also be obtained via the first, second or third group selector and out-trunks (Figs. 16-16d), a marker finder (Fig. 12a) identifying the number of call units to be charged, and arranging the register for multiple metering as required. Tandem connections are extended from the third group selector over a tandem out-trunk (Fig. 16b). On inter-office calls, a pulse sender (Figs. 6cc and 6dd) is associated with the A-register. An incoming call is received on an in-trunk selector (Fig. 9a) which operates as a normal third group selector if the call is for a local subscriber, or extends it to a tandem out-trunk (Fig. 16b) if it is a tandem call. All tandem calls from a distant office are handled through a tandem circuit (Fig. 17) with which a pulse repeater (Figs. 20-20d) is associated through a trunk repeater link (Fig. 19). Substation equipment. Fig. 2d shows a five-pulse rectifier key set for sending alternate positive and negative pulses, the line being fed with A.C. The subscriber moves either the brushes b1, b2 over commutator 1, or b3, b4 over commutator 2 to signal digits 1 to 5, or 6 to 0 respectively. A rectifier (S1 or S2) moves with the brushes which are pulled to a fixed stop by means of finger grips and released, whereupon they return under spring tension. When a finger grip is released contact c1 of the corresponding spring set short-circuits the transmitter and receiver, contact c2 then opens the line loop, and finally contact c3 closes so that when the finger grip has moved one space towards its home position the rectifier and commutator are connected across the line. During the return travel of the finger grip alternately poled pulses are produced to a maximum of 5, the first pulse being positive or negative according to which brushes are used. When the finger grip reaches its home position the spring set releases and the telephone set is again connected to the line. The key set is modified for use on four-party lines by the addition of a set of code contacts which sends out pulses denoting the calling station during the movement of the finger grip towards the stop when the first digit is keyed. The special code contacts are then locked out until the handset is replaced. The code used is similar to that employed in Specification 624,557. Local call. Operation is normal up to the point where the R-link selects an idle register, in which relay BR (Fig. 6g) pulls up followed by BR1 (Fig. 6d). Potentials PC1 and PC2 are assigned to unrestricted and restricted lines respectively. Relay BR connects PC1 to the register side of tube circuit No. 1 (Fig. 6d), operates R1R (Fig. 6) which brings up R2R and connects battery to both windings of KBR (Fig. 6a) (which, however, is differential and does not operate), disconnects AR (Fig. 6) and 'DR (Fig. 6i), and places potentials PS3 and PS2 respectively on front contacts of cascade relays CCR3 and CCR2 (Fig. 6j). R2R brings up CR (Fig. 4) which grounds the C brush of the B-link and the winding of ER to hold the B and R-links, and opens the start lead W, but CR1 remains down. Relay BR1 connects the switch sides of the two tube circuits in parallel, places PC2 on the register side of the second one, connects the armature of TVR1 (Fig. 6d) to the back contact of TVR2 and restricted service relay RSR1 to its front contact. Relay TAR (Fig. 6c) operates in series with relay AR and clutch magnet P (Fig. 7); and is followed by TBR (which connects H.T. to the tube circuits), and the cascade relays CCR1, CCR2 and CCR3 (Fig. 6j). AR and P (Fig. 7) of the line-finder also operate in this circuit, and the finder hunts for the calling line. Either PC1 or PC2 is extended from the test terminal of this line to the switch sides of the two tube circuits. If the calling line is unrestricted the gas tube GV1 (Fig. 6d) fires, and TVR1 opens the a-wire circuit thereby releasing TAR (Fig. 6c) and AR and P (Fig. 7). The finder T-brush is disconnected from the b-wire and connected to the t-wire (grounded at MMR3 (Fig. 6r)) to busy the calling line until COR (Fig. 2) operates later. TVR1 (Fig. 6d) brings up BR2 which releases BR1. In the case of a restricted calling line, GV2 fires instead of GV1. TVR2 opens the a-wire; and also energizes RSR1 which brings up RSR (Fig. 6g), and removes H,T. from tube circuit No. 2, thus de-energizing GV2 and releasing TVR2. RSR1 holds CCR1 (Fig. 6j) when TAR relapses; and RSR changes certain PN potentials (Fig. 6g) to divert extra-charge calls to special trunks. RSR1 also brings up BR2, and BR1 releases as above. Calling line class identification. The relapse of BR1 breaks the connection between the switch sides of tube circuits 1 and 2, connects the register side of tube circuit 2 to an armature of CCR1 (Fig. 6j) instead of to PC2, disconnects the armature of TVR1 from back TVR2, and connects front TVR2 to TDR (Fig. 6f) instead of to RSR1, thus arranging the register for the second test. One of three PS potentials is placed on the B-terminal of the line-finder by the line relay. PS1 (same as PC1) indicates a main or PBX line equipped with a rectifier key set; PS2 (same as PC2) a main or PBX line with a dial; whereas PS3 indicates a party line (Fig. 2b) equipped with rectifier key sets arranged to identify the calling station. Party lines not provided with means for station identification are treated in the same way as main lines. The relapse of TAR (Fig. 6c) after the energization of TVR1 or TVR2 in the first  test, opens the circuit of CCR1 (Fig. 6j), the first of a series of cascade relays which are slowreleasing, so that a test circuit is completed from PS1 (Figs. 2, 2a or 2d) if the line is a key set line to the grid of V4, while the same potential is still applied to the grid of V3 over front CCR1. GV2 therefore fires, and energizes TVR2 which holds CCR1 and brings up TDR (Fig. 6f). The last relay operates KAR (Fig. 6a) which disconnects KPR - and KPR+ from the calling line and connects a holding ground to RIR (Fig. 6); GR (Fig. 6i) which energizes the cut-off relay of the calling line as explained below; TER (Fig. 6f) which opens the t-wire circuit of the register and releases BR (Fig. 6g) ; and de-energizes TBR (Fig. 6c) which releases and removes H.T. from the tube circuits, thus bringing down TVR1 and TVR2. Relay BR disconnects PC1 from tube circuit 1, and PS2 and PS3 from front contacts of CCR2 and CCR3 respectively; connects PS12 to the same CCR2 front; and brings up AR (Fig. 6) and DR (Fig. 6i). AR transfers the selector side of the tube circuits from the a and b wires of the linefinder to those of the first group selector and connects KAR (Fig. 6a) across the calling line. DR transfers the right-hand front contacts of CCR1, CCR2 and CCR3 from the calling line class identification circuits to the group selector class identification circuits. If the calling line PULSE SENDER CIRCUIT TO UNIVERSAL & STROWGER NOTE . MAKES BEFORE a BREAKS  is equipped with a dial (Figs. 2 and 2a) the potential PS2 appears on the b-wire and GV2 (Fig. 6d) does not fire until CCR1 makes its back contact and places PS2 on the grid of V3. TDR comes up, as before, and CCR2 is held. In this case TDR brings up TER (Fig. 6f), GR (Fig. 6i), and FR (Fig. 6), the last of which disconnects the a and b wires from the key pulsing circuit and connects them to the dial pulsing circuit. The release of BR brings up AR and DR as before; and FR releases KAR (Fig. 6a) and brings up DAR followed by DBR (Fig. 6a) which holds RIR. When the calling line is a 4-party line with key sets, the class potential is PS3, and GV2 does not fire until CCR1 and CCR2 make their back contacts. TDR then operates XARO (Fig. 6b) of the party station pulse storing relays. BR is released, and AR and DR are operated as before, while XARO brings up GR. In each case the operation of GR brings up ER (Fig. 5) followed by the B-link release relay RR which extends ground over wire c1 to the C-brush of the linefinder (Fig. 7) and thence to the cut-off relay COR (Figs. 2, 2a or 2b). COR pulls up, disconnects the PS potentials from the B-term