150,072. Automatic Telephone Manufacturing Co., (Automatic Electric Co.). May 27, 1919. Automatic exchange systems and apparatus.- In a system in which selecting impulses are repeated from one exchange to another, the impulserepeating relay is provided with an operating- winding controlled by the selector line relay and with a de-energizing winding carrying the impulses sent over the trunk line in order that the length of the impulses may be varied in accordance with the length and consequently the resistance of the trunk line over which they are sent. Preliminary selector. The removal of the receiver at the substation A, Fig. 1, energizes the line relay 2 the contact 11 of which completes the circuit of the rotary magnet 6 of the selector C if the private wiper 10 is upon a busy trunk, or energizes the magnet 6 and switching relay 5 if the trunk is not busy. The relav 5 operates to disconnect the relay 2 and ground from the substation A and to connect the station A to the line relay 12 of the group selector D through the wipers 8 and 9 and springs 13, 14 and 15, 16. Group selector. The line relay 12 closes a circuit for a relay 17 and a circuit for a relay 20. The relay 17 establishes a grounded holding circuit for the switching relay 5 over the wiper 10 before the de-energized relay 2 has disconnected ground therefrom. The operation of the calling- device CD in accordance with the first digit of the called number interrupts the line relay 12 a number of times, and upon each de-energization of this relay the vertical magnet 22 and a slow-acting relay 23 are energized over the lower contacts of the relay 17. The armatures of the slow-acting relay 23 remain attracted during the operation of the vertical magnet 22, and as soon as the wipers 24, 25 and 26 take their first step, the off normal springs 27 and 28 close to complete the circuit of the rotary interrupter relay 30 and to prepare the circuit of the release magnet 29 respectively. The relay 30 prepares the circuit of the rotary magnet 31 and completes a ground for itself and a relay 34 at the contacts 33. The relav 34 is short-circuited, during the operation of the vertical magnet 22, at the springs 38, 39 of the relay 23. When the impulses of the first digit cease, the relay 23 is de-energized and the rotary magnet 31 will be energized periodically by its operation and that of the relay 30 until an idle trunk line leading to the connector E, Fig. 2, is found. Under this condition the relay 30 is energized in series with a relay 34 and will not operate. The relay 34 opens the circuit of the vertical magnet 22 and closes a locking circuit for itself over the private wiper 26 independent of the ground from the relay 17. The relay 34 also closes springs 46 to connect the trunk conductor 51, Fig. 2, to station A. The line relay 47 of the connector E, Fig. 2, is energized from ground over its lower winding, springs 48, 49, trunk conductor 50, wiper 25, Fig. 1, springs 45. lower windings of relays 20 and 55, springs 46, wiper 24, trunk conductor 51, Fig. 2, springs 56, 57 and upper winding of relay 47 to battery. The relay 47 operates to close the circuit of a slow acting relay 58, the contacts 60, 61 of which close a circuit to hold the magnet 34, Fig. 1. of the group selector D energized. Repetition of selecting impulses to distant exchange. When the subscriber at station A, Fig. 1, operates the calling-device CD in accordance with the next digit of the called number, the relay 20 controlled by the line relay 12 repeats these impulses to the line relay 47 of the connector E, Fig. 2, and the slow-acting relay 23, Fig. 1, controlled by the relay 12 operates to short-circuit the upper winding of the relay 55 and the lower winding of the relay 52 during the transmission of the impulses. The current impulses, as described above, pass through the lower winding of the relay 20 which is wound to oppose its upper winding so that according to the length of the trunk line between the selector D and the connector E the current in this winding will vary to give a long or short impulse to the relay 47. The relay 20 therefore automatically adjusts itself to the length of the trunk lines. Connector. The relay 47, Fig. 2, controls the energization of the vertical magnet 63 and a slow relay 64 through the spring 68, but as soon as the wipers 65, 66 and 67 step off the normal the springs 68 are opened and springs 69 are closed to establish a new circuit for the magnet 63 and relay 64. After the impulses of the second digit cease, the magnet 64 is de-energized to open its own circuit and close a circuit for the rotary magnet 73 at the springs 70, 72. The impulses of the next digit control the rotary magnet 73 and a relay 79 through the operation of the repeater relay 20 and relay 47. Busy test. If the called line be busy the wiper 67 is grounded and the busy relay 84 energized to disconnect the rotary magnet 73 of the connector E and to connect the busy signal to the calling line. If the called line be idle, the deenergization of the relay 79, establishes a circuit from ground at relay 58, through the springs of relay 84, lower winding of relay 85, springs 86, 81 of relay 79, private wiper 67, relay 87 and magnet 88 to battery. The relay 85 closes its springs 89 and 90, and the relay 87 disconnects the operating magnets of the preliminary selector C<1> of the called subscriber. Ringing current. The closure of the springs 89, 90 of the relay 85 completes the ringing circuit and the circuit of the upper winding of the ringing cut-off relay 91. When the called subscriber at station B removes his receiver, the relay 91 operates in the usual manner to disconnect the signalling circuit. Release. The operation cf the relay 91 connects the called line to the back bridge relay 97 which operates to prepare certain release circuits and to reverse the connexions of the line relay 47 to the conductors 50, 51. The current flowing in the relays 20, 52 and 55 will be reversed and the relay 55 operates to close the operating circuit of the relay 98. The relay 98 reverses the battery connexion in the calling line and energizes the upper winding of the relay 52 in series with its lower winding in the holding circuit of the connector E, so that as soon as conversation is completed the connexion will be released in the usual manner. In the modification shown in Fig. 3, the lower winding of the relay 20 is not included in the holding circuit after the calling party answers, and this arrangement may be used with a repeater having no trunk-selecting functions.