Patent GB-809605-A (GB)
Title: Improvements in or relating to automatic telecommunication exchange equipment
Inventor: BRAY FREDERICK HARRY
IPC: H04Q3/00
Filed: 1956-02-09
Abstract: 809,605. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Feb. 9, 1956, No. 4028/56. Class 40 (4). In a subscriber's line circuit of the type in which a single relay LS serves both as a calling relay and as a ring-trip relay the line wires are connected to the primary winding of a transformer, the connection from the A wire being over a change-over contact of the ringing relay RR, the arrangement being such that the relay LS connected to the inner ends of the split primary winding responds when the line is looped to initiate a call, and that, with the ringing relay operated when the line is being called, the reply of the subscriber brings up LS over its lower winding in series with the ringing generator. The circuit is designed for use in the system of Specification 794,812 and its detailed operation is described below. Calling subscriber.-Operation of LS to the loop extends ground via R1, the upper winding of K (which remains down), rectifiers D2, D4 and D3, D5 in parallel, back K and front LS to the junction of R2-R3 in the calling line marker shown in the broken line box, which is common to 50 lines having the same tens and units digit combination. The circuit is controlled by timed pulses forming a 42 millisecond cycle (T10 to T41), the particular pulses employed being XA extending from T20 to T32, " no pulse " level ground, " pulse " level +, 130 volts; XB from T11 to T12, "no pulse " level - 220 volts, " pulse level - 110 volts; and XC from T10 to T33, " no pulse " level 220 volts, "pulse" " level -110 volts. Thus at T10 the anode of V1 rises to - 110 volts and at T11 the cathode of D7 rises to -110 volts so that with the ground from the line circuit present the junction of R2-R3 is at about - 100 volts and V1 fires. In the absence of the ground, R2-R3 is at - 220 volts and VI does not fine. On the firing of V1, R5 locks out all other such tubes in the exchange, and M operates, thus applying the +130 volt pulse XA (T20 to T32) to all line circuits served by that calling line marker. In that of the calling line this condition is extended via the talking wires to an inlet to an electronic switch (not shown), the potential so extended being caught at + 75 volts by D8 and D9. The outlets of the switch are pulsed during T20- T32 and when a free outlet is pulsed the switch connects the calling line to it. The resulting current flow from XA causes the marking pulse voltage to be dissipated in R6 and R7 to prevent multiple seizure. Current then flows from ground via R1, K, D2-D3 and the switch to a control relay (not shown) in the seized outlet, whereupon K and the control relay operate in series, the former connecting itself to LS1, disconnecting the line circuit from the calling line marker, and causing the operation of a further relay (not shown) in the outlet, whereupon a register is seized and reverts dial tone. LS responds to the dialled impulses and each time it releases it connects the lower winding of K in parallel with the upper, thus releasing the further relay to pass the impulse to the register. The switch is assumed to be an assembly of two-anode-one cathode tubes such as described in Specification 734,345, [Group XL (a)], giving anode-to-anode transmission paths. Called subscriber.-The called number is transferred to a called line marker (not shown)' common to the whole exchange which marks an AB lead corresponding to the thousands/ hundreds digit combination, and a CD lead corresponding to the tens/units digit combination. When both the AB and the CD leads of the line circuit shown are marked, a positive condition is extended via back LS, back K, D4 and D5 to the speech wires and thence to the inlet of the subscriber's electronic switch; The outlets are pulsed as for the calling subscriber case lent at different times in the cycle and a path is set up to a free outlet via which the subscriber is accessible. Current flows from ground over back LS, back K, ringing relay RR and D2, D3, whereupon RR pulls up, connects the ringing generator to the A wire to ring a grounded bell at the substation, and reverts ringing tone from RTT to the caller. On the reply of the called subscriber, LS pulls up in series with the ringing generator and disconnects RR which releases slowly (rectifier in shunt), thus giving time for K to operate from ground over R1 during the release time of RR to prevent re-operation of RR by the momentary release of LS. Release.-This is effected by removing the supply voltage from the cathodes of the switch tubes (not shown), the release of LS in the caller's line circuit when he hangs up initiating the process.