500,737. Exchange systems; electric switches. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Aug. 19, 1937, No. 22793. Convention date, Nov. 7, 1936. [Class 40 (iv)] [Also in Groups XXXVII and XL] In a system comprising a number of automatic exchanges, supervisory and calling and clearing signals are given by means of single impulses of voice frequency current modulated at a lower frequency. These signals produce their characteristic effect with the aid of counting arrangements in the repeater circuits. Selecting impulses are transmitted in the form of unmodulated currents of the same frequency. The invention is described with reference to the system shown in Fig. 1 which comprises an automatic step-by-step, exchange at Sao Paulo comprising several automatic offices and a semi-automatic toll office, other step-bystep exchanges at Campinas and Santos, a power-driven rotary exchange at Rio de Janeiro comprising several offices one of which includes a toll board, and manual exchanges at Campos and Jundiahy. A call incoming to Rio de Janeiro over one of the junctions TL-4 takes into use a coder which responds to the digits dialled by the distant toll operator and transfers its record to one of a group of register senders RS-2, Fig. 3, which are. controlled from the operator's key set PE-2 to extend calls arriving over the manual junctions TL-5. Calls are set up by the Rio de Janeiro operator over the junctions TL-4 with the aid of a further set of register senders RS-1. These are so arranged that they will register and transmit any number of digits up to six, transmitting a signal to the' operator when sending is complete, and then register and transmit further digits. Use is made, in several of the circuits described of relays, e.g. 1109 .. 1111, Fig. 13, which are differentially wound and provided with a shunt resistance so that they merely store energy when their circuit is first made and pull up when it is broken, locking over a different circuit and disconnecting the shunt. Specification 260,048, [Class 40 (iv)], is referred to. Supervisory-signalling arrangements for calls involving only one operator. In all cases of calls to automatic offices the idle condition of a wanted line is signalled to the originating operator, this " line " signal causing the supervisory lamp to light and the subsequent " answer" signal putting it out until the reception. of the " disconnect " signal or hookswitch signals. " All trunks busy " causes the lamp to flash at one rate and a busy subscriber's line at twice that rate. The repeaters at the step-by-step offices for converting direct current supervisory signals into modulated alternating current and vice-versa are like that shown in Figs. 12 .. 16. Whenever a supervisory signal is to be sent, 1127, Fig.'15, is operated and then 1128 .. 1131 in succession. 1128, 1129 cause the tone unit to generate modulated tone current, split the talking circuit and send the tone currents over the junction and 1131 releases 1127 to terminate the impulse. The signals sent are counted by a chain of relays 1109 .. 1111 of the stored energy type. 1109 operates when the " line " signal is about to be sent and 1110 is energized by the pulsecontrolling relays operating to send the signal. The " answer " signal is accompanied by the operation of 1111 which energizes 1112 and this releases 1110, 1111. The " disconnect "signal re-operates 1110. The same chain is used to count supervisory signals received and repeated by 1123, 1109 operating on the " line," 1110 on the " answer " and 1111 on the " disconnect " signal, and controlling the supervisory lamp 509 over the wire EC. Similar functions are exercised by the sending relays 1427 .. 1431, counting relays 1409 . . 1411 and signal repeating relay 1423 in the repeaters at Rio de Janeiro. At this end, however, the supervisory lamp is controlled over the sleeve of the answering or calling jack J1, J2. Hook switch and busy signals are repeated in the same way. Local subscribers in outgoing calls signal the Sao Paulo operator by means of current reversals in the trunks such as T1 Fig. 4, and polarized relay 303 repeats the signal by varying the sleeve current and so controlling relay 504 and lamp 507. Supervisory signals are given by current reversals and interruptions in the case of calls to Sao Paulo subscribers established over switches such as TOS-1, Fig. 10. Polarized relay 906 pulls up over the loop when the wanted line is found to be idle and connects up 907, which pulls up over the loop, and 905 which locks up. When the subscriber replies, the loop current is interrupted, and when he hangs up it is restored and 907 responds and controls lamp 509 or supervisory relay 1122 in the repeater circuit over the wire EC according to the nature of the call. In the case of a busy condition, the current is reversed and interrupted at an appropriate rate and 907 repeats the impulses. Hook switch impulses are repeated in a similar way. In the Rio de Janerio exchange supervisory &c. signals from local subscribers are given. to control the lamps 2001, 2003, Fig. 33, or the supervisory relay 1422 in the repeater, Figs. 18 .. 21 and 32, by varying the current in the sleeve circuits S, the signals being repeated in a similar form by marginal relays such as 2022, 2012. In the case of calls in which two automatic toll .lines in tandem are involved, e.g. Rio de Janeiro to Campinas and vice versa the two repeater units at Sao Paulo do not respond effectively to supervisory impulses. This result is brought about by relays 1108 which are operated with the lower winding of that in the incoming repeater in series with the upper winding of that in the outgoing repeater. This causes the release of 1115, energization of 1109, 1117. 1119 and release of 1116 in the incoming repeater and the operation of 1109 in the outgoing one. Supervisory arrangements in calls involving two or more operators. (1) Jundiahy to or through Sao Paulo and Sao Paulo to Jundiahy. After the connection has been established, 409 in the junction circuit TC-1 is energized and 408 released. The Jundiahy operator signals the Sao Paulo operator by again projecting ringing current over the junction. 408 is momentarily operated to release the relay 504 and light lamp 507. In the case of established calls in the other direction ringing current from Jundiahy operates 408 as before, but in this case 408 locks in series with the lamp 609. (2) Rio de Janeiro to Jundiahy. For this kind of call no tandem operator is needed supervisory relay 1122 is operated when the switch TLS-1 finds an idle junction and is released shortly afterwards because the loop test relay 1119 finds no battery source across the junction. " Line " and " answer " signals are thus sent back automatically. To bring in the Rio do Janeiro operator after the call has been established the Jundiahy operator intermittently rings the junction and 408 sends an impulse over the wire EC. 1122 pulls up and falls back at each impulse and two signal impulses are thus sent back for each operation of the ringing key. The originating operator can attract the Jundiahy operator by operating her ringing key. This causes a signal to go forward to cause a temporary operation of relays 1116, 1115, 1114, and application of potential to the talking circuit to actuate the polarized relay 403 which sends ringing current over the junction. (3) Sao Paulo to Campos. In this case it is necessary first to call the Rio do Janeiro operator. As the result of a signal from Sao Paulo, the relay 1902 is energized to operate 1422 to send. a dummy " line " signal at the same time as the line lamp 1907 is lit to call the Rio de Janeiro operator. When the operator plugs in, 1422 is released to give the " answer " signal. After plugging in to the Campos junction the Rio de Janeiro operator leaves tho connection but she can be recalled by a signal from Sao Paulo which causes a temporary operation of 1415, 1414 to remove ground from wire RR. 1904 then operates and locks in series with 1905 and lamp 2001 which glows. The Rio de Janeiro operator attracts the Sao Paulo operator by operating her ringing key to actuate 1426. This energizes 1427 which initiates the transmission of a signal pulse and such pulses continue to be sent until the key is restored, the counting relays 1410, 1411 ensuring that the total number sent is always an even one. Sao Paulo toll board called by local subscriber. Operation of finder F-1, Fig. 6. On its tenth level the office selector gives access over a trunk circuit TC, not shown in detail, to the circuit CLR-1, Fig. 4. Line relay 304 pulls up, marks the line calling to the finders F-1, polarizes supervisory relay 303 energizes and start relay 301. This grounds the wire 511 at an operator's position through a distributer or at all the positions. The next cord circuit to be used has its talking key K-3 operated and consequently its relays 504, 503 energized. The starting ground thus energizes 501 which lights busy lamp 508, polarizes switching relay 502 and makes a self interrupting circuit for the driving magnet 510. When the calling trunk is found, the switching relay 502 pulls up in series with cut-off relay 302, marks the line busy over the low-resistance upper winding of 504 and lights the group lamp 306. In the circuit CLR-1, 301 falls shunting the high resistance winding of 304 to increase the current over the trunk and so cause the class tone to be disconnected after a suitable interval and the release control to be transferred to the operator. Relay 305 under the operator's control can be made to remove the shunt and so cause the class tone to be re-applied. The operator's headset is now connected to the trunk through contacts of 503. Sao Paulo toll board called by Jundiahy. Ringing current received over the junction TL-1, Fig. 5, energizes 407 which brings down a normally energized relay 406, and start relay 408 causes an idle cord