214,529. Western Electric Co., Ltd., (Polinkowsky, L.). Aug. 4, 1923. Automatic excahnge systems having a capacity of several hundred lines comprise a connecting circuit terminating in a number of connectors. The hundreds digit controls the setting of a register which operates a group of relays in various combinations to select the stepping magnet of the appropriate connector. The register is then restored to normal and is again operated by the tens digit and, after restoration to normal, by the units digit to put a marking potential firstly on the first. of a group of ten terminals in the connector and then on the wanted terminal. The connectors are 50-point rotary hunting switches and have two sets of wipers, one set being used when the tens digit is odd, and the other when it is even. The connector wipers move simultaneously with those of the register when hunting for a tens group. The other end of the connecting circuit terminates in a call-finder which is controlled by a relay which subsequently controls the connector and tests the wanted line. On release the connectors are tested in succession and those off normal are restored, their wipers being first disconnected from the calling line to prevent interference with other calls. Dialling of a non- existant number causes the switches to be held up until released. Means are provided to break down a local in favour of a preferred call. Pro. vision is made for connecting to an idle line of a private branch exchange group. The system described has a capacity of 700 lines, but certain parts of it may be omitted when fewer lines are to be served. Call-finder. The subscriber T, on calling, energizes his line relay 1 which connects the cut-off relay 2 to test terminals in a group of call-finders and energizes their starting relay 3. The stepping magnets SM thereupon drive the call-finders until one of the test wipers d engages the calling terminal, when relay 2 energizes in series with the test relay 5 and releases relay 1. Relay 5 stops the successful switch and energizes relay 6. Relay 1 releases relay 3 to stop the other switches. Relay 6 disconnects the high-resistance winding of relay 5, connects the subscriber's loop to the stepping relay 7 and energizes the power magnet 8 of the sequence switch which is then driven to its 2nd position. The relay 5 is designed so that it cannot be maintained energized over its low resistance winding in series with a cut-off relav if it is shunted by another relav 5. If two call-finders are successful simultaneously therefore, relav 5 falls back on the energization of relay 6 and before the release of relay 1 and both the switches are stepped on, the call being picked up later by another switch. Relay 7 energizes relay 10 which prevents release of relay 5 when the sequence switch breaks its original circuit. In position 2 the sequence switch energizes relay 4 over both windings in parallel, the circuit for the right hand winding being 4, u, Ub, 13, battery. Relay 4 locks up in series with a winding in the dialling tone circuit (not shown) connected to wire 34 in a circuit: left hand winding of 4, Ed, Ec, 4c, Rd, h, 34. Dialling tone is now sent back from the lead 33. Hundreds selection. Relay 7 repeats the impulses to the stepping magnet RSM of the register RS. Slow release relay 11 energizes on the first impulse and prevents the release of relay 4 when the register moves out of normal. If the digit is 1, the terminal engaged by wiper h is dead and relay 4 releases when relay 11 falls back, and energizes the power magnet 8 in a circuit 8, Bc, 4h, Gb, so that the sequence switch moves into position 3. If the digit is 2, relay 14 energizes in series with relay 4 and locks up, thereby shunting the left-hand winding of relay 4 by a low resistance 13 so that relay 4 falls back and operates the sequence switch. Relay 14 also disconnects the stepping magnet SM<1> of the first connector and prepares a circuit for the magnet SM<2> of the second. Other digits cause the energization of relays 14 - - 17 singly or in pairs. The combination locks up, releases relay 4 and prepares a circuit for one of the stepping magnets SM3 - - SM7 and the sequence switch moves into position 3. If a connection is wanted with the main exchange, the digit O is dialled. Relay 4 remains energized in series with a line lamp in a circuit : left-hand winding of 4, Ed, Ec, 4c, Rd, Rc, h, c (of call-finder) and a lamp (not shown). The sequence switch therefore remains in position 2 in which relay 4 is shunted by a non-inductive resistance to lessen the inductance and an attendant connects up to the main exchange. In moving from position 2 to position 3, the sequence switch disconnects relay 5 at Dd and replaces it by relay 18 in a circuit 2, d, 10c, 18, Db, 6a. Relay 6 is prevented from releasing during the change at contact Dc and is then held under control of relay 18. In position 3 the sequence switch completes a circuit for the magnet RSM through its self-interrupting contact to restore the register to normal RSMa, Kd, 4f, 5b. When the wipers reach normal, relay 5 energizes in a circuit 13, W, Ud, t<1>, Nd, M, 5, Ga, H, opens the driving circuit of magnet RSM and energizes the power magnet 8 which drives the sequence switch into position 4.. During the movement, relay 4 is energized over contact Fd, and locks up in a circuit including wiper t, 4, Ed, 4c, Rd, Rb, t, ground over normal contact. A locking circuit is made for the right-hand winding also, but this is short-circuited at contact 5a. Connector. In response to the tens digit, the relays 7, 11, 4, and magnet RSM are operated as in the case of hundreds selection and the register RS is stepped to the desired position. The wiper t<1> now puts a selectable potential on the first terminal of the wanted tens group co-operating with wiper k<1> of the connector FS, and the wiper k<1> is connected to the test relay 5, over 5, M, Na, 4a, k<1>. As soon as the register leaves normal, relay 5 falls back and energizes the previously selected stepping magnet, e.g. SM1, which drives the connector until relay 5 again energizes when the marked terminal is reached. The wiper t of the register controls the relay 20 to select which set of wipers is to be used in completing the connection. If the tens digit is even the wiper el - g<1> remain connected, but if it is odd, relay 20 energizes in a circuit Hc, 20, l, Rb, Rd, 4c, Ed, Ec, 4 and connects up the other set. Relay 20 locks up, thereby short-circuiting the left-hand winding of relay 4 which is then held over its right-hand winding until relay 5 short-circuits it on the seizing of the marked terminal. On falling back, relay 4 releases relay 5 and the restoring circuit for the register is completed. When the register is restored, relay 5 pulls up and energizes magnet 8 to drive the sequence switch into position 5. whereupon relay 4 again energizes in a circuit 13, W, Ub, u, 4. The register is set in response to the units digit in the same way as for the other digits, but in this case the wiper u supplies the marking potential and relay 4 releases as soon as relay 11 releases. The hunting circuit is not completed until the end of the digit, this circuit being over SM<1>, 15d, 14d, Lc, Ld, 4f, 5b. When the wanted terminal is reached, relay 5 energizes, stops the magnet SM<1> and completes a circuit for magnet 8 which drives the sequence switch to position 6. When the units digit is zero, the connector remains stationary as relay 5 pulls up as soon as the wiper u reaches the zero terminal, which is connected to relay in this position. Busy test and signal. In position 6, the test relay 5 is controlled by the selected wiper g<1>, j<1>. Relay 12, which replaces relay 5 in position 6 of the sequence switch, energizes and completes a circuit to drive the sequence switch from position 6 to position 7 in which relay 12 is released. If, owing to the wanted line's being busy, relay 5 does not energize in position 6, busy tone is sent back from lead 30 in position 7. Supply of ringing current. If the wanted line is idle, the test relay energizes in position 6, in series with the wanted cut-off relay and energizes relay 4 which short-circuits the high resistance winding of relay 5. As in the case of controlling the call-finder, the relay 5 does not energize if another connector is testing at the same instant. Relay 4 energizes the power magnet 8 and the sequence switch is driven into position 8. In this position a circuit is completed over lead 31 to the starting relay of the ringing apparatus, and ring- ing current from lead 32 is sent out over the lefthand winding of relay 12, the right-hand winding of which is short-circuited to make it slow acting. On reply of the called party, relay 12 energizes and causes the sequence switch to move to position 9, which is the talking position. Release. When the calling party hangs up, relay 7 falls back and releases relay 10, which deenergizes relays 18, 2.. Relay 6 releases and energizes magnet 8 which drives the sequence switch out of the 9th into the 11th position. Relay 5 is thus disconnected from the connector and falls back, completing the restoring circuit for magnet RSM. The register on reaching normal re-energizes relay 5 which causes the sequence switch to be driven to position 12. In positions 12-18, relay 5 tests the connectors in succession, and if the connector being tested is in the normal position, relay 5 energizes and causes the sequence switch to be driven to its next position. If the connector is out of normal, a circuit is completed for restoring it to its normal position in which relay 5 is energized and causes the advance of the sequence switch. Assuming the connector chosen by magnet SM7 to be off normal, relay 5 does not energize in position 12 and magnet SM7 is energized in a self-interrupting circuit SM7, 17g, 16c (relays 16, 17 being