220,405. Automatic Telephone Manufacturing Co., Ltd., Mercer, R., and Tench, F. May 31, 1923. Addition to 192,036. Semi-automatic exchange systems.-In a system in which calls from a manual exchange are set up over automatic switches by operators at a tandem exchange, an idle trunk is selected by the operator, and an idle link circuit becomes associated with the operator's key set, the selected trunk and an idle impulse sender. The A operator at the manual exchange gives the wanted number over an order wire to the B operator at the tandem exchange, who assigns an idle trunk L2, Fig. 1, and presses the corresponding assignment key. The sender selector SS1 corresponding to the link circuit associated with the keyset K over a preselecting switch OF hunts to find an idle impulse sender. The B operator sets up the wanted number, which is registered in storage relay sets SR1-7 over terminals of a transfer switch TS, and upon depression of a start key or when all the digits have been registered, contacts T1, R1, Z1 are operated, so that trains of impulses are transmitted to the trunk L2 over contacts 01 controlled by the plugging in of the A operator by an impulse sender IS, which is controlled through converting relays CR. The switch OF is operated when impulse sending starts to preselect another link circuit. The Provisional Specification refers to Specifications 175,260 and 219,079. Association of link circuit with keyset and idle sender. The B operator presses the assignment key 3 corresponding to the assigned trunk 1, 2. Lead 100 is grounded over contacts such as 9, 19, and relays 109, 120 energize over wiper 113 of switch OF and the disconnect key 114 in parallel with relay 108. Relay 120 connects the stepping magnet 162 of switch SS to wiper 146 and to sluggish relay 119 to drive the switch until wiper 146 reaches an ungrounded terminal, whereupon relay 119 energizes, being no longer short-circuited, connects wipers 110 - -112 of switch OF to wipers 143- - -145 of switch SS, locks and opens the driving circuit, grounds lead 168 over wiper 146 and contacts 132, 131 and connects battery and earth to leads 102, 103 at contacts 129, 131. The guard lamp 164 lights. Relay 10 energizes, locks over busy or cancel key 25, lights assignment lamp 27 and connects the outgoing trunk 37, 38 to the impulse leads 105, 107. Registration of wanted number. Operation of a digit key connects earth or earth through a resistance 147 to one or more of three leads 169 - - 171, which are connected to relays 202 - - 206, two of which 203, 205 are marginal. The relays are selectively operated, and energize corresponding relays in the storage relay sets such as 229 - - 232, which are connected up in turn by the transfer switch TS, the stepping magnet 245 of which is connected up at each digit by relays 201, 200 and advances the switch one step when each depressed key is released. The selected storage relays remain locked over lead 168. Transmission of impulses. The start key 150 is depressed, and stepping magnet 123 is connected up to advance switch OF. Start relay 151 energizes and connects up relay 121 over resistance 141 so that it partially energizes and locks over its light armature 169<1>. When the A operator plugs in, line relay 21 lights the busy lamp 24 and energizes relay 20, completing a further circuit for relay 121 over leads 103, 104 and contact 28 so that it operates fully, connects leads 107, 105, 104 to wipers 143 - - 145, releases relay 119, and extinguishes the assignment lamp 27. Relay 260 energizes over leads 167, 104, 103, connects leads 165, 166 to the impulse contact 270, energizes relay 253, and connects lead 168 to earth at contact 259. Relay 253 connects up the release magnet 246 to rotate switch TS to normal and operates relay 256, which initially attracts its light armature 257 to shunt its upper winding. Relay 207 energizes over contacts 248 in normal position of switch TS, locks, connects up impulse relay 280 and connects the converting relays 272 - - 275 over the first terminals, of switch TS to contacts of the first set of storage relays. One or more converting relays energize corresponding to the first digit and ground a terminal in the lower bank of the impulse control switch IS. Relay 253 is thereby released and removes the short-circuit from the upper winding of relay 256, which energizes fully. Lead 168 is now grounded at contact 254. Relay 280 energizes intermittently to operate the stepping magnet 293 of switch IS, and relay 292 energizes over the second terminal of the upper bank to place the impulse circuit under sole control of contact 270, so that an impulse is sent at each de-energization of relay 260 over trunk 37, 38 by way of leads 105, 107. Relay 291 energizes over the grounded terminal, locks, opens the impulse circuit and completes a restoring circuit for magnet 293 over wiper 289. Magnet 245 of switch TS operates momentarily in parallel with relay 2.91 and advances one step. Relays 292, 2,91 fall back when switch IS is restored to normal, and further trains of impulses are sent in a similar way. A special impulse may be sent over wiper 225 and the 8th terminal of switch TS to indicate in the case of a call going to a call indicator position that the call comes from a tandem exchange : if the call goes direct to automatic switches, this impulse is merely absorbed. Relay 253 energizes at the end of impulse sending, completes the release circuit for switch TS and removes earth from lead 168 to release the operated relays. Relays 121, 10 fall back and lamp 164 is extinguished. On the reply of the called subscriber, polarized relay 23 energizes and substitutes choke coil 33 for the high resistance winding of relay 21 to give the A operator answering supervision. Wiping out incorrect registrations. If the start key has not been operated, this is done by pressing the cancel key 149, which energizes sluggish relay 159 for an interval until released after the energization of relay 157. Earth at contact 131 is thus removed from lead 168 and the impulse sender is released. If the start key has been operated, the operator presses the busy or cancel key 25 associated with the trunk, thereby releasing relays 20, 10, which disconnect the outgoing trunk 37, 38 and at contact 28 remove earth at contact 254 from lead 167, so that relay 260 falls back and the impulse sender is released. Trunk or link circuit out of order. A defective trunk is marked by pressing the busy or cancel key 25, and a lamp 35 is lighted. A defective link circuit is marked by pressing the disconnect key 114, which opens the energizing circuit of relay 120 and grounds the corresponding terminal' of switch OF. The guard lamp 164 is lighted,. and the energizing circuit of relay 10 is opened. Sender selector finds all impulse senders busy- In this case, relay 118 energizes over lead 142 and chain contacts of the first sets of storage relays, and causes the switch OF to be advanced. Similar action takes place if all the impulse senders become busy while the sender selector is hunting. In a modification, the switches OF, SS are provided with five wipers, and the storage relays are operated directly instead of through relays 202-206 by means of ground on one or more of four wires. A relay is provided which energizes after seven digits have been registered over wiper 225 and the 8th terminal of switch TS, and wipers of switches OF, SS. and performs the functions of the start key. This feature is claimed in Specification 221,175. If the wanted number comprises less than seven digits however, the start key must be operated. The assignment lamp flashes until the A operator plugs in, and then glowssteadily. An additional key is associated with each trunk to enable it to be used as an order wire if necessary. To obviate the possibility of two operators seizing the same impulse sender, an individual relav is energized when an assignment key is pressed, and a control switch rotates when two such relays are energized. Series relay 119 is connected up normally over a front contact of the corresponding relay to one terminal and overback contacts of the remaining relays in series to the other terminals of the control switch, so that when two relays are energized, the latter circuit is broken and impulse senders are taken into use in turn.