Patent GB-190914244-A (GB)
Title: Telephone System.
Inventor: MAY DAVID WILLIAM
IPC: H01H67/06
Filed: 1909-06-17
Granted: 1910-03-10
Abstract: 14,244. May, D. W. June 17. Semi-automatic exchange systems.-In an exchange telephone system, the sub-stations are divided into groups, and the lines of each group terminate in an automatic branch station, which is connected to the main exchange by as many trunks as are necessary to handle the traffic. Each trunk terminates at the exchange in the same manner as an ordinary line, and is provided at the automatic branch station with a selecting-switch adapted to connect the trunk automatically to any calling substation in the group, and also to enable the operator to select any desired station by stepping round the switch to the contacts of the station required. When one or more of the trunks are in use, a further call from one of the sub-stations is transferred to the next idle trunk by means of an additional switch common to all trunks. Fig. 2 shows the construction of one of the selecting- switches. The shaft 8, carrying three wipers 10, 11, 12, Figs. 2 and 6, is rotated by the ratchet 7 and spring-pawl 15 when the magnet 5 is energized by either of its two independent windings. The pawl 15 is normally held away from the ratchet by a pin 16<a>. The armature 13 engages a forked piece 17, which plays between contacts 18, 19. The detent 20 is withdrawn from the ratchet 7 and pressed against a contact 22 by a pin 23 on the armature of a magnet 6, but the ratchet is prevented from returning to its zero position as long as the magnet 6 is energized, by the engagement of the end of the armature 24 with the ratchet. When the detent 20 is moved by the pin 23 it is caught by the shoulder 28, Fig. 4, of a pivoted lever 26, so that when the magnet 6 is de-energized the ratchet returns, under the influence of a spring, to its zero position when a cam 30 on the ratchet trips the lever 26 and. allows the detent 20 to engage the ratchet. The armature 24 also controls certain contacts as will be seen from the description of Fig. 1. Sets of fixed contacts 39<a>, 40, 41, Fig. 6, connected to the sub-stations of the group are arranged in the path of the wipers 10, 11, 12, and the wiper 10 normally rests on a contact 39. Fig. 1 shows two sets of subscriber's lines 54, 55 and the switching-mechanism associated with two trunks 89, 90, 91 leading to the distant exchange. The answering-end of a cord-circuit is shown inserted in the jack of the right-hand trunk, the calling-end of the same cord-circuit being shown on the left of Fig. 1. The switch shown diagrammatically at 42 serves to transfer calls to idle trunks as will appear later. When a subscriber removes his receiver to make a call, current flows from a battery through the common call-relay 63, contact 62, armature 58, sub-station apparatus, line 54, and individual call-relay 60 to earth. The excitation of relay 60 connects the battery 61 to a lead 53 multipled to the calling-subscriber's contacts 39<a> on all the selecting-switches. The energizing of the relay 63 completes a circuit from earth over lead 67, wiper 44 of switch 42, the contact 46 on which the wiper is then resting, wire 72, contact 39 of an idle selecting-switch, wiper 10, fork 17, contacts 18, 75, winding 5, and battery to earth. The attraction of the armature 13 moves the wipers one step, and interrupts the contact 18 so that the magnet is intermittently energized and rotates the wipers until the wiper 10 engages the contact 39<a> of the calling-line when the attraction of the armature 13 closes contact 19 and completes a circuit from the battery 61 through the lead 53, contact 39<a>, wiper 10, fork 17, contact 19, winding 5<a> of the magnet 5, and magnet 6 to earth. The excitation of the magnet 6 causes its armature 24 to lock the ratchet against further movement, and at the same time closes contacts 20-22, 24-35<b>, and 33-36. The closing, of the contact 20-22 energizes relay 74, which opens the circuit of winding 5 at contact 75, and by earthing the lead 83 causes current to flow through the contact 47 and wiper 45 of the switch 42, magnet 50, and battery 61 to ground. The armature 49 automatically interrupts this circuit so that the switch is intermittently rotated until its wiper 45 rests on the ungrounded terminal of an idle selecting-switch, and is thus ready to receive a further call. The closing of contacts 24-35<b> and 33-36 completes a circuit from the battery 61 through one winding of the trunk line-relay 96, contact 101, line 91, contact 24-35<b>, wiper 12, line-wire 55, sub-station apparatus, line-wire 54, cut-off relay 56, wiper 11, contact 36-33, line 90, contact 97, and the other winding of the relay 96 to earth. The excitation of the cut-off relay 56 de-energizes the call-relay 60 and disconnects the battery from the lead 53, thus preventing the calling-line from being picked up by a second trunk. The energizing of the relay 96 causes the call-lamp 105 to glow, and at the same time causes current to pass over armature 95 and line 89 to maintain a circuit for the magnet 6. The insertion of the answering-plug completes a further circuit for the magnet 6 so that the latter is not de-energized when the cut-off relay 99 is energized by current flowing from the exchange battery 61 over the tip 108 of the plug, line 90, contacts 36, 40, cut-off relay 56, line 54, substation apparatus, line 55, contacts 41, 35<b>, line 91, cut-off relay 99, and back to the battery. The cut-off relays 56, 99 are shunted by non-inductive resistances, so that the calling subscriber and the operator may communicate over the circuit just traced. Having learnt the connexion required, the operator selects an idle trunk leading to the group in which the desired subscriber is situated, and inserts the calling-plug as shown on the left in Fig. 1. To select the desired subscriber, the operator depresses the key 129, thereby disconnecting the tip and ring of the plug from the answering-plug and connecting them to the impulse-transmitter (shown diagrammatically at 127) and to earth respectively. The grounding of the ring of the plug causes current to flow from the battery through the relay 74 at the automatic branch station, contact 35<a>, line 91, cut-off relay 99, jack ring 94, and plug ring 113 to ground at 125. The excitation of the relay 74 earths the lead 83 and causes the switch-selecting switch 42 to move, as before, on to the contacts of an idle trunk, thereby preventing the appropriation of the selected trunk by a calling subscriber. The operator now sends the required number of impulses to select the desired subscriber by depressing the key 127, the impulses flowing from the battery through the magnet 5, contacts 85, 35, line 90, tip of plug, and key 127 to earth. The magnet 5 thus moves the wipers 10, 11, 12 on to the contacts of the required subscriber, and when the operator raises the key 129 current flows from the exchange battery over wire 122, contact 123, line 89, and magnet 6 to earth. The magnet 6 trips the detent 20 and locks the ratchet 7 with its armature 24 as before, and at the same time by closing contacts 24-35<b> and 33-36 completes the talking-circuit. The operator determines whether the called subscriber is engaged by listening-in, and, if not engaged, calls him by ringing in the usual way.