291,510. Pollak, J. E., (Associated Telephone & Telegraph Co.). March 1, 1927. Automatic and semi-automatic exchange systems.-A test clerk is provided with a test cord and a special single-ended cord for setting up connections when acting as a zero operator. The clerk's calling device is connected automatically to his test-cord when the device moves offnormal, and at the same time, if the listening key is thrown, his head-set is disconnected from the test cord; by throwing special keys, the clerk can connect his calling device and head-set to the single-ended cord. The test cord can be plugged into (a) jacks J<2>, Fig. 2, connected to test distributors (b) jacks J<5>, Fig. 5, connected to trunks reached by trouble men who dial a special number (c) jacks J<4>, Fig. 4, connected to general service trunks. All the connections can be maintained by a holding circuit if the test-plug is withdrawn so that the clerk can return to a busy line or deal with several trouble men at intervals. In setting up a test connection, busy condition is signalled bv reversal of current in the line, thus sending back busy tone and lighting a lamp; these signals are cut off, when the listening key is thrown for verifying the busy condition. The head-set. receiver circuit includes a condenser for preventing " click " when switching in. Tests for setting up a connection from a sub-station through automatic switches, and for foreign battery or earth on the line are described. After testing one substation, the clerk can reach the next line on the test connector level by dialling a single impulse, but for getting to another connector level, he throws key CRK, and dials the required two digits to re-set the connector. For outgoing calls through jack J<4>, a relay 403 energizes in a holding circuit, while incoming calls it energizes in series with a condenser 417 in response to ringing current. When acting as zero operator, the clerk sets up the required connection over trunk 621, 622, which is temporarily disconnected from plug P<6>. The answer of the called subscriber extinguishes a lamp L<8> and talking connection is now established between the subscribers. Setting up of test connections. When plug P<1> is inserted into jack J<2>, relay 204 operates over contacts 218, and relay 201 operates [earth, armature 38, resistance 41, contacts 55, 57, 52, relay 201, upper winding of relay 202, battery], connecting up the test conductors 223, 224. Line relays 302, 303 of the test distributor switch TD now operate over the loop closed at armature 207, and release relay 304 then pulls up. Setting of the impulse sender S closes off-normal springs 19 therein to energize relay 4, which in turn energizes relay 32. Armature 38 is operated to release relay 201 and to energize relay 31 which disconnects the apparatus to the left of armatures 35, 36. The conductors 221, 222 are now connected to the test cord and the relays 302, 303 remain operated in a circuit over the tip and ring of the plug and jack, polarized relay 5, which does not operate, and the sender S. The first set of impulses operate the vertical magnet 311 in series with relay 305, first over contacts 339. and then over off-normal contacts 339<1> and armature 323. When the sender S returns to normal, relays 4, 32, 31 de-energize in turn, but before the latter releases, relay 201 again operates to maintain the switch TD operated. The next set of impulses operate rotary magnet 312 in parallel with relay 306, which closes a circuit for relay 307, disconnecting the wires 223, 224. If the selected connector TC is busy, earth on the contact 353 operates busy relay 308, immediately relay 306 de-energizes, in a circuit including relay 307 which remains energized. Relay 301 energizes to reverse the current in the wires 221, 222, so that relay 5 operates to connect the busy tone machine B to the test clerk's receiver, maintain relay 32 operated, and to light the lamp L'. If the test clerk temporarily removes the plug P', relay 201 will de-energize, while relay 203 will now operate in series with relay 204 which remains energized. The holding bridge is maintained across the wires 221, 222 at armature 211 and relays 5, 32, 31 release. Upon re-insertion of plug P<1>, relay 203 de-energizes slowly since it is short-circuited, while relay 201 operates to maintain the holding bridge. When the connector TC becomes idle, if not already idle, relays 308, 307 de-energize in turn, and switching relay 309 energizes before relay 307 releases and locks up over armature 337. Relays 5, 32, 31 release cutting out busy tone and the lamp L<1>. Line relay 361 operates over wipers 344, 345 and armatures 338. 320, and closes the circuit of the release relay 362. The next two digits are repeated at armature 320 to relay 361, which operates the vertical magnet. 365 and the rotary magnet 366 in turn to bring the wipers 374 - - 376 on to the wanted line. Wanted line test busy. Relays 306, 307 operate without result during the last set of impulses, and when relay 306 releases, relay 301 energizes [battery, relay 301, armatures 324, 327, 335, wipers 342, 375, armature 384, earth] and forms a holding circuit over armature 314 when relay 307 releases. Busy tone is fed back as before, and the lamp L' is lighted. To test the busy condition of the line, the clerk throws the listening key TK to break the circuits of relay 32 and lamp L<1> at contacts 59 so that relays 32, 31 release, to energize relays 3, 201 [earth, armature 13, relay 3, contacts 8, contacts 56, 57, 52, sleeves of plug and jack, relay 201, upper winding of relay 202, battery]. Relay 2 then operates, locks up over armature 8 to the above circuit and cuts out relay 3. The telephone, set is now connected to the tip and ring conductors of the test cord C, relay 3 being slow to release, the receiver circuit is not closed until the condenser 29 has had time to charge, so preventing click in the receiver. Line busy. If the clerk hears conversation, he may unplug, in which case relay 203 operates in series with relay 204, forming a holding loop at armature 211, and energizing relay 202 over the substation. A lamp L<2> now lights. When the sub-station A becomes idle, relays 202, 301 deenergize, cutting out lamp L<2>, and forming a circuit to energize relay 382 in the subscriber's line switch [earth, armatures 317, 314, contacts 327, wipers 342, 375, relay 382, magnet 383, battery] so that the subscriber's set is disconnected. Faulty busy condition; test operations. If no conversation were heard, various tests would be made to ascertain the condition of the line. To test the called line in the direction of the automatic switch-board, key BCO is operated, releasing relay 31 at contacts 58, and locking relay 32 at contacts 61. Direct ground at contacts 62 allows relay 202 to operate in series with relay 201, breaking the holding bridge at armature 210, but connecting earth to the wire 22, so that relay 303 holds up, while relay 302 releases. Earth is therefore disconnected at armature 317 from the private wire so that the relay 382 of the line switch LS de-energizes. A dialling test may now be made, and by operating key TK, the progress of the connection can be followed by the test clerk. To test for foreign battery on the subscriber's line, ground key GRD, first with, then without the reversing key REV, is thrown. the voltmeter reversing key VMR being used if required. Testing for ground is made by key GRD, with either high scale or low scale voltmeter key HS or LS. and in turn with and without the key REV thrown. Wanted line idle. If the substation A had been idle, relay 382 would have energized immediately relay 307 had released. Changing test connections. By dialling a single impulse after being in connection with a substation A, the wipers 374 - - 376 rotate to the next line in the connector level, which can then be tested. To obtain connection to another connector level, the key CRK is thrown to release the connector and the last two digits of the wanted line dialled. By throwing the connector release key CRK, earth is disconnected from the plug sleeve at contacts 52 so that relay 201 deenergizes and removes the holding loop so that relay 303 de-energizes. Relay 302 holds up over wire 221, the plug and jack tip contacts and contacts 60 of the key CRK to battery, and maintains relay 304 energized, thus keeping the distributor release circuit open. Armature 320 falls back so that relays 361, 362 de-energize, and the release circuit for the connector is completed to restore it to normal. Release of connection. When the plug P<1> is withdrawn, relays 203, 204 operate in series to maintain the connection. By operating key K, these relays are shorted so that the holding bridge is broken and the switches TD, TC, LS return to normal. Operation of impulse sender with talking key TK thrown. As described above, when the key TK is thrown, relays 201, 2 are in operation. When the impulse sender is moved off-normal, relay 4 operates, cutting out the receiver at armature 15, and shorting the relay 2 to disconnect the telephone set. When the sender returns to normal, relay 4 releases and relays 3, 2 pull up in turn as before to re-establish the talking connection. Connection of trouble man to test clerk. After repairing a subscriber's line, the trouble man connects his set across the line and dials a special number which connects him to a trunk, e.g. 523 - - 525, Fig. 5, terminating at the test clerk's position. Relay 503 operates, lights lamp L<5>, sends ring-back tone over armature 513 and operates relay 504. When the clerk plugs in, relays 501, 502 operate in series over the sleeve of the plug, disconnecting relay 503, the ring- back tone, and lamp L<5>. Relay 504 remains operated over armature 511 and relay 501 locks up over armatures 507, 516. By operating key TK and key BC1 which provides talking current to the