Patent GB-513008-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1938-03-29
Abstract: 513,008. Automatic exchange systems. POLLAK, J. E. (Associated Electric Laboratories, Inc.). March 29, 1938, No. 9581. [Class 40 (iv)] In a private automatic exchange having main exchange calls completed with the help of an operator, a subscriber wishing to make an outgoing call signals the operator by throwing a key without removing his receiver whereupon the operator plugs the junction into the subscriber's jack and his line is rung automatically. He then sets up the call in normal manner. On an incoming call, plugging in of the junction also automatically rings the line but if the line is busy this does not take 'place until it becomes idle. When the subscriber hangs up after a main exchange call, he remains connected to the junction for a short interval during which the operator is also not signalled, so that he may make a further main exchange call without assistance. After this interval his line is connected to the local equipment even if the operator does not clear the main exchange connection. The operator has a special toll-offering plug. Interim calls and transfers are provided for. Local call.-On closure of the loop over subscriber's line 1, 2, Q operates in series with LR which remains inert, locks up over its lower winding and switches through to a line circuit whereupon a line finder is started up and the call completed automatically in known manner. The busy lamp BL at the operator's position is lit. Outgoing call.-The subscriber grounds his loop by key operation without removing 'his receiver so that LR operates but Q is shortcircuited. Calling lamp CL lights and lead 14 is grounded to mark the line busy in connector banks. The operator inserts plug P1 of a main exchange junction in jack J1 whereupon G and CO operate over the sleeve, the subscriber's line 1, 2 is disconnected from the local equipment and LR is released but busy ground is maintained by CO. Relay G lights the supervisory lamp SL and starts the ringing generator GN which it connects to the calling line so that when the subscriber removes his receiver, relay F trips the ringing, stops the generator and connects the line to relay A in series with differential relay M which does not operate. Relay B pulls up and loops the junction over retard R the connection being then set up automatically in known manner, C being - operated by impulse trains to shunt R. When the subscriber replaces his receiver A and B fall back to release the junction and pendulum relay P operates N after several seconds. The subscriber may set up another main exchange call before this occurs, but if he does not, N flashes lamp SL, connects up general audible and visual signals at 22, 23 and connects P to the sleeve circuit in place of G which falls back, releases F and disconnects the plug from the junction. The high resistance of P causes CO to relapse to restore the line equipment to normal. The operator withdraws plug P1 but the subscriber may attract attention by operating the calling lamp as previously described. Incoming call.-Relay E responding to ringing current locks up, disconnects its operating circuit and lights the junction calling lamp TL. If the call is not attended to, thermal relay T operates B which releases E. The operator on throwing speaking key SK, releases E, operates D and energizes H which locks up in series with D1 in the operator's circuit, the operating circuit of H being disconnected by D1 to prevent connection of another cord circuit. The junction is now connected to the operator's set and when she has ascertained the wanted number, plugs the jack J1 of the line whereupon G and CO operate and the line is rung as previously described. Relay D has lit the supervisory lamp, looped the junction and locked over release key RK, and the operator may withdraw by restoring key SK before the wanted party replies. If the wanted party had been busy on a local call, Q would have been operated and the operation of G prevented by the addition of resistance 107 to its circuit. His line, however, is rung as soon as the local call is terminated. If the operator wishes to speak to the called party, she throws the split key PK to operate J which loops the junction across the springs of dial DS and leaves her set connected only to the called party. When the wanted party replies, ring-trip relay F pulls up followed by relays A and B and extinguishes lamp SL. Relay D releases. If there is no reply, the operator throws key SK (if she has restored it) to inform the calling party, and releases D by means of key RK. Toll-offering.-If the incoming call is a long-distance one, the operator uses plug P2 which connects her set directly with the wanted line. Relay C1 pulls up in spite of the resistance 107 in the sleeve circuit of the jack J1, and makes a self-interrupting circuit for relay B1 which thereby supplies tone over coil IC to the line. Warning subscribers if operator cuts in on a call.-The above-mentioned tone circuit is operative since C1 is operated by armature 44 of relay A in the cord circuit. Interim connection to a third party ; transferring calls.-This may be effected on an incoming or outgoing main exchange call by the key operation which grounds the loop thereby operating differential relay M while holding A. Relay K operates in two steps on operation and release of M, loops the junction to hold it, and switches the subscriber through to local connecting equipment over leads 80, 81, the interim connection being set up in normal manner. Re-connection to the junction is effected by a second operation of the key whereupon L pulls up and both K and L hold until the key is released. If the local subscriber wishes to transfer the call, he operates the key as before and hangs up. Two-step relay K pulls up. but as B has released the junction lamp TL is flashed to call the operator who speaks to the main exchange party and transfers plug P1 to the required line. When the local subscriber replaced his receiver, the afore-mentioned pendulum relay P was operated so that he could make a local call before the operator attended to the transfer. Enquiries.-A subscriber by dialling a special number obtains access to leads 120,121, relay A2 being operated by ringing current to light lamp IL. The operator responds by throwing key IK which releases A2 and operates B2 to connect the leads 120, 121 to the operator's set. Relay D1 is also operated to prevent connection to a cord-circuit. Operator connects to local party who is not entitled to main exchange calls.-Such a party has no jack and the operator may connect her set to the enquiry trunk 120, 121 by operating IK whereupon B2 pulls up and C2 connects up the dial DS when moved off-normal. Main exchange call by operator.-Movement of the dial off-normal operates the splitting relay J. Rectifiers RC are connected back-to-back across the operator's receiver to reduce clicks.