Patent GB-191328291-A (GB)
Title: Improvements in Electromechanical Switching Systems for Interconnecting Telephone Lines.
Inventor: BARON HAROLD
IPC: H04Q3/00
Filed: 1913-12-08
Granted: 1915-07-15
Abstract: 28,291. Baron, H., [Aldendorff, F.]. Dec. 8. Automatic and semi-automatic exchange systems.- The selectors allotted to a group of subscribers are arranged to be available for extending a call in either direction, acting in the one case as callfinders to connect a calling-line to an outgoing trunk, and in the other case as connectors to connect an incoming trunk to a wanted line. The system involves special arrangements for metering and for the supply of ringing-current. In Figs. 2-7, which should be assembled side by side, a call is extended through a double-acting switch VS, acting as a call-finder, and through a preliminary selector HS and first and second group selectors GW<1>, GW<11> to a double-acting switch VS in the hundreds group to which the wanted subscriber belings, and this switch, acting as a connector, selects the wanted line. (The circuits of this switch are not separately shown as they are the same as in Figs. 3 and 4.) In their capacity as call-finders, the switches VS of each hundreds group are taken into action in a definite order, and the first half of them may have their outgoing circuits connected directly to group selectors while the second half have access through the switches HS to group selectors in several groups. The selectors GW<1>, GW<11> are switches of Strowger type, but the double-acting switches VS are of the type in which an auxiliary brush choosing switch is employed to bring into circuit one of a number of sets of brushes of the main switch. The means for controlling the supply of ringing-current to the wanted line are associated with the first selector GW<1>, which has also a relay set for repeating the numerical impulses to the succeeding switches. The impulses arrive as current interruptions in the incoming line and are repeated as impulses in one side of the outgoing line, followed, after each series, by a change-over impulse in the other. Operation of the selector VS as a call-finder. The energization of a calling subscriber's line relay lr12 grounds a guide-wire in each of the tens and units groups pt, p u and energizes a common relay AR. The relay AR locks the other line relays of the group out of action until the calling line has been found and sends a momentary impulse through a stirting-wire SW. The starting-impulse energizes the magnets EM, ZM, Fig. 3, of the main and brush-choosing switches of the first idle selector VS, and the relay 205, Fig. 5, of the associated preliminary selector HS, and at the termination of the impulse the magnets EM, ZM move the switches VS, Z W out of their normal positions. The starting- circuit SW is now extended at the off-normal contact 110 to the wire SW1, leading to the next selector ; the normal contact 130, Fig. 4, is opened to mark the selector non-selectable as a connector ; and the magnets EM, ZM are connected to an interrupter 168 at the off-normal contact 105. The main and brushchoosing switches VS, ZW move simultaneously under control of test-relays pr, sr, Fig. 4, which are energized over the fourth brushes pb, s<b> and the grounded guide-wires pt, pu when the proper tens and units movements are completed. When the calling line has been found, the relays pr, sr being both energized, a circuit is completed for a relay tr, which locks itself up and connects the leads va, vb, vc, to the switch HS, Fig. 5. Preliminary selector HS, Fig 5. In the meantime, the relay 205 has locked itself up and connected an interrupter 218 to the stepping-magnet 206. When the switch HS reaches an idle group selector, the relay prh energizes in series with the relay er, Fig. 6, and locks itself up, disconnecting the magnet 206 and relay 205 and connecting the incoming leads to the wipers. When both the selectors VS, HS have been set, the subscriber's cut-off relay cr12 is energized in parallel with the relay prh and disconnects the line relay lr12 and common relay AR. The consequent lowering of potential at the test wiper wc makes the selector GW<1> non-selectable to other switches HS. The calling line is at the same time rendered non- selectable to incoming calls owing to the fact that the relay er is of low resistance compared with the relay tr, Fig. 4, which acts as a test relay when the switch VS is used as a connector. First group selector GW<1>, Fig. 6. The line relay 280 energizes a release relay rr and short-circuits a relay cr. At the first line-interruption due to the subscriber's impulse-sender, the relay cr becomes energized, and as long as the scries of interruptions continues the relays cr, rr remain energized, although these relays are short-circuited when the armature of the line relay reaches the forward and backward limits, respectively, of its movement. At each interruption, the vertical magnet 246 is energized over the contacts 220, 231, 234. At the conclusion of the series, the relay cr deenergizes, causing a momentary impulse in a circuit 290, which energizes the rotary magnet 247. The selector takes its first rotary step and closes the off-normal contact 256, which connects the rotary magnet to an interrupter 257. When an idle second group selector is found, the relay 248 energizes in series with a relay 300, Fig. 7, and open-circuits the rotary magnet, at the same time short-circuiting part of its winding to mark the selected trunk non-selectable. Impulse-repeating action of the selector GW<1>. Each subsequent series of interruptions is repeated by the relay 280 as impulses over the contacts 220, 231, 234, 225, 270 and the wiper g<a>. At the conclusion of each series the relay cr deenergizes and sends a momentary impulse to the relay 249, which sends forward a change-over impulse through the contacts 252, 277 and the wiper g<b>. Second group selector GW<11>, Fig. 7. The vertical magnet 305 receives the impulses of the hundreds series, and the change - over impulse energizes the rotary magnet 306, which is then connected by the rotary off-normal contact 315 to an interrupter 314. When an idle selector VS is reached, the relay pr2 is energized and disconnects the rotary magnet. Operation of the selector VS as a connector. (The selector VS seized by the group selector GW<11>, would not, of course, in the present instance, be the one shown in Figs. 3 and 4, which connected itself to the calling subscriber, but since the circuits are the same, the operations will be described with reference to those figures) A relay SR, Fig. 4, in the incoming test lead from the selector GW<11> changes over the circuits of the switch VS from those which are necess iry as a call-finder to those which are necessary as a connector. At - the contacts 120, 122 it connects the incoming trunk from the selector GW.<1> in place of the outgoing trunk to the switch HS, Fig. 5, and at the contact 112 it extends the call-finder starting-circuit SW to the next selector. The impulses of the tens series are received through the contacts 114, 139, 1951, and operate the magnet ZM, Fig. 3, of the brushchoosing switch ZW. The change-over impulse is received through the contact 113 and energizes a relay 190, which locks itself up and connects the impure circuit to the magnet EM in place of the magnet ZM. The magnet EM is therefore operated by the units impulses and moves the main switch VS to make connexion with the wanted line. The final change-over impulse energizes a relay 193, which locks itself up and momentarily completes the circuit of the test relay tr. If the wanted line is free, the relay tr energizes in series with the line cut-off relay and switches the connexion through, at the same time short-circuiting part of its winding so as to mark the selected line non-selectable to other switches. The reduced resistance of the relay tr is still, however, approximately equal to that of the relay er in the cut-off circuit of the calling line, and is therefore high enough to, prevent the energization of the wanted subscriber's meter. Supply of ringing current. The ringing generator 268, Fig. 6, is associated with the first group selector GW<1>. In the interval between the deenergization of the relays 219, 250 at the conclusion of the second and each subsequent series of setting-impulses, the generator 288 is momentarily connected to the outgoing b-line through the contacts 254, 251, 277. Each of these momentary connexions is, however, proceeded by a change-over impulse transmitted to the b-line through the contacts 252, 277, the. effect of which is to open the b-line at the contacts 313, Fig. 7, or 152 or 149, Fig. 4, so that the ringing-current finds no path to flow through. When, however, the wanted line has been selected, tested, and found idle, the ringing-current is able to pass over the contacts 122, 142, Fig. 4, to the wanted station and back over contacts 141, 120, Fig. 4, and wipers g<1>a, Fig. 7, g<a>, Fig. 6, and contacts 270, 225, and 298 to ground, and a relay 258, Fig. 6, in the ringing-circuit is energized and cuts in a relay 299, which locks itself up and renders the supply of ringing-current independent of the temporary circuit 254, 251. Ringing current is now intermittently connected to the wanted line through an interrupter contact 265, ringing-cut-off relay 264 (which is not energized at this stage), and the right-hand winding of the relay 299, the relay 299 being kept energized during the intervals by the passage of the ringing-current in a local circuit through its left-hand winding. When the called subscriber replies, the lowered impedance of the ringing-circuit causes the energization of the relay 264, which energizes a relay 273, which locks up and cuts off the ringing-current. The called subscriber is now supplied with microphone current. through the relays 278, 279. Release. The connexion is released when either subscriber hangs up his receiver. The release magnet 215, Fig. 6, of the first group selector is energized in the one case by the de-energization of the relay 280, which short-circuits the relay