Patent GB-174332-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1921-12-23
Abstract: 174,332. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Ray, A. J.). Jan. 21, 1921, [Convention date]. Automatic exchange systems.-In systems comprising main and branch exchanges, and in which connections between subscribers on the same branch exchange are made without tying up trunks to the main exchange, selector repeaters at the branch exchange are organized so that by jumpering certain pairs of terminals the switch-over which determines whether a call shall be extended to the main exchange or not can be made to take place after a variable number of digits. This enables the same selector-repeator to be used in branch exchanges of different sizes, or when the capacity of the whole system is expended from four digits to five. The invention is descibed in relation to a 5-digit area comprising 9 automatic main exchanges of 10,000 subscribers the digit 0 being allotted for calls to trunk operators. A call from a subscriber A, Fig. 1, belonging to a branch exchange of one hundred lines, is taken by his line switch C to a selectorrepeater D, Fig. 2, with which is associated a switch E, Fig. 1, which picks out an idle trunk 138, 139 to the main exchange. If the call is to another subscriber in the same branch exchange it will be characterized by a particular combination of the first three digits, say 345xx. The first two digits are repeated by the line relay 35, Fig. 2, over wires 101, 105 and trunk 138, 139 to the main exchange and also raise and rotate the switch D, bringing the upper test wiper 251, Fig. 3, on to a directly-grounded terminal 255, whereby the release magnet 48 is energized to restore the switch D to normal position and a relay 42 is locked up to prevent subsequent digits from affecting the rotary magnet 46. The third digit 5 is repeated to the main exchange and raises the switch D to its fifth level. The circuit of a stepping relay 41 was closed at contact 80 by the energization of relay 42, so that the switch D now hunts over its fifth level to find an idle local connector, represented by an ungrounded terminal in the path of the lower test wiper 252. The energization of the switching relay 45 enables the local connector to complete the wanted connection in response to the two final digits and causes the de-energization of the line relay 35, which results in the release of the main exchange trunk 138, 139 by the switch E. If the call is to a main exchange subscriber this fact may be aparent after either the first, second or third digit. If the first digit is other than 3 a contact 97 in the circuit of the rotary magnet 46 is not closed so that the switch D is prevented from actuation by further digits, acting merely as a repeater to repeat them to the main exchange. If the first digit is 3 but the second digit is other than 4 the wiper 251 is brought on to a terminal such as 263 which is grounded through a resistance R<1>. This resistance prevents the energization of the marginal release magnet 48 but permits the energization of the relay 42, which locks itself up and opens the circuit of the rotary magnet 46, so that the switch D is unaffected by further digits and acts merely as a repeater. If the first two digits are 34 but the third digit is'other than 5, the first step in the rotary hunting movement of the switch D brings the lower test wiper 252 on to a dead terminal such as 262, so that the switch D rotates no further, and the wiper 261 arrives on a live terminal 261 so as to energize reday 43, which opens the circuit of the switching relay 45. The switch D then acts merely as a repeater for the remaining digits. If the number characterizing the branch exchange is such that the first and third digits are the same, for example, 343xx, the test terminal bank of the switch D is modified as shown in Fig. 4, the upper terminals of the third row being grounded through a wire 27' and a back contact of relay 42, so that these terminals are dead during the rotary hunting movement of the switch; otherwise the relay 43 would become energized and would open-circuit the switching relay 45. The contact 97, Fig. 2, and the test terminal bank, Fig. 3, may be arranged to meet the case of a branch exchange having several hundred lines, the first digit of local calls having either of several values. In the case of a branch exchange belonging to a system in which the subscribers are numbered only to four digits, the branch exchange would be characterized by two digits only, for example, 45xx. When the switch D is to be used in such a system the terminals 90 are jumpered together, the spring 97 is put out of action, and the test terminal bank is wired as shown in Fig. 5. The terminals 90 are in parallel with contact 80 of relay 42 in the circuit of the stepping relay 41, so that the switch D takes a rotary step immediately on the termination of the first digit If the first digit is 4 the wiper 251 arrives on the directly grounded terminal 273, causing the release of the switch D, and the second digit operation is the same as the third digit operation in the case previously described. If the first digit is other than 4 the wiper 251 arrives on a terminal grounded through a resistance R<4>, so that the switch D is not released but the relay 42 becomes locked up and prevents further action of the switch except as a repeater. If the two digits characterizing the branch exchange are the same, for example, 55xx, the test terminal bank is modified as shown in Fig. 6. If the branch exchange is a very large one it may be characterized by the first digit unly, for example the branch exchange subscribers may be numbered 4xxx and 5xxx. In this case the terminal bank is arranged as shown in Fig. 7 and the terminals 89 are jumpered together, so that the relay 42 becomes energized immediately the switch D is seized. If the first digit is 4 or 5 the switch D hunts to find a .local group selector, and the energization of the switching relay 45 causes the release of the main exchange trunk, but if the first digit is other than 4 or 5 the first rotary step brings the wiper 252 on to a dead terminal, so as to stop the switch, and the wiper 251 arrives on a live terminal causing the energization of relay 43 which open-circuits the switching relay 45. Other features of the invention relate to the provision in systems of this kind of means for giving dialling and busy tones, and discriminating tones for enabling a trunk operator to tell whether a calling subscriber is entitled to trunk service. The operations in setting up a 5-digit local call 345xx are as follows. Operation of the switch E to find a trunk to the main exchange. When a line switch C extends a call to the selector-repeater D, relays 35, 36 are energized and the winding of relay 38 is bridged across wires 101, 105 to energize the line relay 119 of the switch E. Relay 36 also closes a circuit over wire 102 for the stepping magnet 117, which rotates the switch E until the wiper 132 comes to the ungrounded terminal of an idle trunk, whereupon the switching relay 118 becomes energized, extending connection to the trunk 138, 139, locking relay 119, and energizing relay 120. Contrary to the usual practice the armatures of the line and switching relays 119, 118 are not interlocked, this being possible because the extended connection includes contacts of both these relays in series. Operation of the selector-repeater D in response to the first three digits. The first digit 3 is repeated by relay 35 at contact 93 to the mainexchange trunk and at contact 57 to the vertical magnet 47 and series relay 40 of the switch D, the impulses subsequent to the first being transmitted over contact 69 of a relay 39 which is energized whenever the switch D is off normal. On its third level the switch D closes the contact 97 so that the second digit 4 is repeated to the main exchange and also over contacts 69, 74, 97, 99 to the rotary magnet 46. At the termination of the digit a relay 37, which is energized whenever impulses are passing, relapses and connects a relay 43 over wire 95 to the upper test wiper 251, Fig. 3. The relay 43 connects the lower winding of relay 42 and the release magnet 48 to the wiper 251, and since this wiper is on the directly grounded terminal 255 the relay 42 is short-circuited but the marginal release magnet 48 becomes energized and restores the switch D. (If the wiper 251 stood on a terminal such as 263 grounded through the resistance R<1> the relay 42 would be energized and not the release magnet). The release magnet closes a locking circuit for itself and for the relay 43, which is opened by relay 39 at contact 70 when the switch regains its normal position. The magnet 48 then relapses and opens the circuit of relay 43, but in the instant before, the de-energizing of relay 43, a circuit is closed through relay 42 and magnet 48. The current in this circuit is insufficient to energize magnet 48, but relay 42, being no longer short-circuited at the locking armature of magnet 48, responds and locks itself to the release wire 32, The third digit 5 is repeated by relay 35 to the main exchange and to the vertical magnet 47, and at the termination of the digit, since the relay 42 is now energized, a circuit is closed for the stepping relay 41 over contacts 80, 85, 72, 50 and a back contact of the rotary magnet 46. Relay 41 energizes the rotary magnet 46, and a rotary hunting movement takes place to find an idle local connector, represented by an ungrounded terminal in the path of the lower test wiper 252, and switching relay 45 then becomes energized, disconnecting the line relay 35 and extending the connection through the wires 91, 92 to the connector. Release of the main-exchange trunk by the switch E. The de-energization of relay 36 disconnects the wire 102 and leads to the de-energization of relays 118, 119, 120. In the momentary interval between the relapse of relay 118 and that of the other two relays t