Patent GB-191319305-A (GB)
Title: Improvements relating to Telephone Exchange Systems.
Inventor: CORWIN ELMER REED
Filed: 1913-08-26
Granted: 1914-08-20
Abstract: 19,305. Corwin, E. R. Aug. 26. Semi - automatic exchange systems.-A calling subscriber is connected to an idle cordcircuit by a switch of call - finder type associated with the cordcircuit. The subscribers' lines are connected to contacts on each of a set of ten call-finders which are controlled by a common master - switch in such a way that there is always one call-finder associated with an idle cord-circuit and hunting for a calling line. Each of these ten cord-circuits is served by a different operator and each operator attends to ten cord-circuits, so that she is connectable to 1,000 subscribers. When the motor - switch 22 has connected an idle cordcircuit, the corresponding call-finder switch 8, 9 is continuously operated over a circuit extending from battery 15 over the left-hand armature contact of the energized relay 14, normal contact of relay 13, magnet 8, and interrupter 12. When a subscriber, as 120, calls, thus removing the resistance of the bell 2 from the line, the depression of the springs 5, 6 of this line by the roller 11 completes a circuit from battery 15 over relay 13, the middle armature - contact of relay 14, contacts 6, line of subscriber 120, contacts 5, impedance 16 and right-hand armature-contact of relay 14. The removal of the resistance 2 from this circuit enables the relay 13 to be energized, thus opening the circuit of the magnet 8 and stopping the switch on the terminals of this line. The armature of relay 13 brings the relay 17 into circuit, and a hold-on circuit for this relay is then made from the battery 15 over the middle contacts of the operator's switch 18, left-hand contact of relay 17, relay 17, contact 6, subscriber's line, contact 5, relay 19, and right-hand contact of relay 17. A hold-on circuit for relay 13 is also made over a right-hand contact of relay 17. A circuit for the magnet 20 of the master switch is made over a contact of the relay 17, and the switch 22 is moved on until the arm 21 reaches the contact of a cord-circuit in which the relay 17 is not energized. When the master switch arms reach the contact of an idle cord-circuit, a circuit is made from the battery 15 over the middle contacts of the switch 18, left-hand contact of relay 19, relay 14 and switch arm 23, thus causing the relay 14 to prepare a circuit for the relay 13 when the call-finder rests on a calling line. The circuit of the relay 14 is broken when the relay 19 is energized, and the relay 19 also displays a call signal to the operator. The resistances of the relays 13, 17, and 19 and the impedance 16 are arranged so that the relay 13 of a second call-finder cannot be energized by connexion with a calling line which has already obtained a connexion. A cord-circuit may be made to test busy by closing the left-hand contact of the key 18. The operator's talking set is brought into circuit by depressing the key 36, and the connexion is extended by inserting a plug 24 in a jack 7. When the ringing key 27 is depressed the hook 29 catches in the notch 31 and retains the key in this position. The ringing generator 28 is thus connected to the called line over the relay 30, but this relay is not energized to release the key until the resistance of the bell 2 is removed from the circuit. The relay 30 also completes a circuit over its upper contact, the relay 32, right-hand contact of relay 19, key 18 and battery 15, thus causing the relay 32 to extend the connexion through the cord-circuit. The relay 32 locks itself up over its middle contact. When the ringing key 27 was depressed, a circuit was made over the inductance 33, relay 35, right-hand armature of relay 19 to battery, but if the calling subscriber hangs up before the called subscriber replies, a circuit for the relay 30 is made over the contact of the relay 35 which is then de-energized. Testing potential is placed upon the jacks during ringing by the connexion through the relay 35, the test being made by means of the earthed terminal of the operator's set. The testing potential for the calling line is obtained by the connexion through the relay 13 to the contact 6. When the subscribers hang up their receivers, the relay 17 is de-energized and consequently the relays 19, 32 are de-energized and the lines and cord-circuit are cleared of battery. By moving the key 18 to close its right-hand contacts, and depressing the key 36, the operator can call and talk to a subscriber. The closing of the right-hand contact of the key 18 completes a circuit for the relay 14 over the contact of the relay 19 and middle contacts of the key 18. A circuit is then made for the relay 13 over the middle contact of the relay 14 and key 36. A further circuit is made over the contacts of relays 14, 13, relay 17, key 36, operator's set, and inductance 16 or relay 19 to ground, thus connecting the operator's set in circuit.