Patent GB-355820-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1930-05-30
Abstract: 355,820. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., WRIGHT, E. P. G., and HARKER, R. A., Columbia House, Aldwych, London. May 30, 1930, No. 16765. [Class 40 (iv).] In a small partially equipped exchange employing single-motion switches with common by-path control circuits, the switches at the first numerical stage are adapted to serve either as group selectors or as connectors for local calls or as outgoing selectors for main exchange calls, the discrimination being dependent on the value of the first dialled digit. Local calls are designated by three digits, the first having no numerical effect when only a single switching stage is necessary. The control circuit includes a marking switch having two sets of wipers which is arranged to hunt over both sets for trunks to a further switching stage and for main exchange junctions and over a selected set for idle P.B.X. lines. Main exchange calls. These are designated by the initial digit 9 or 0. When a call is initiated, relay STR, Fig. 1, energizes over the common start wire ST and causes a line finder to make connection with the calling line. Line relay A of the control circuit energizes and connects up relays B, BB. The first train of dialled impulses are repeated at contact a2 to the magnet of the switch RA in series with dialling relay C, and as soon as this switch moves off-normal, a self-interrupting circuit is completed for the switch RB over wiper RA5 and is subsequently maintained over wiper RB4, until wiper RB1 reaches the terminal marked by wiper RA5, when relay M energizes, opens the stepping circuit and connects up relay EH, which in turn connects up relay E. A self-interrupting circuit is now closed to step the switch RA into engagement with the conversation switch which is marked by relay E, and relay T energizes. Meanwhile, since relay M falls back when the switch RA resumes stepping, the switch RB hunts for an idle main exchange junction, test relays P, Q being connected to wipers RB5, RB6. If relay P operates, relay H energizes, while if relay Q operates, relay J energizes and connects up relay H. If the last junction tests busy, a circuit is completed over wiper RB1 for relay M, which stops the switch RB and connects up relay G, and release relay B relapses, connecting ground to wire ML to send busy tone. Relay H upon operation, locks, marks the junction busy and disconnects relays EH and P or Q. A circuit is now closed over wiper RA4 and wire N for driving the conversation switch S until the preselected junction is reached, when relay M energizes over wiper RB2 or RB3. If two common control circuits are provided, the battery and ground connections of relay M in the other control circuit are reversed. Relay M extends ground over wipers RA2, RA3 to energize relay GS in the conversation switch to extend the connection to the junction. Battery applied over wiper RB7 or RB8 energizes relay G, which effects release of the operated relays in the control circuit and the switches RA, RB are restored to normal. Local calls involving a second switching stage. These are designated by the initial digit 3 or 4. In this case the switch RB hunts for an idle trunk to the next switching stage under control of relays P, Q, and the second and third digits are repeated at contact a1 over wiper RB7 or RB8 and a wire such as T to the control circuit, Fig. 2, of the next switching stage. The switch RA associates itself with the preselected conversation switch as before. Upon operation of relay H, impulse relay A, Fig. 2, energizes over wire T in series with relay G, Fig. 1 (inoperative) and repeats the second digit to the switch RA, whereupon the switch RB moves to the position marked by the switch RA under control of relay T. Dialling relay C upon relapse connects up relay E, which releases relay T, and the switch RA advances automatically to associate itself with the selected conversation switch, and relay T re-energizes, The conversation switch S now moves to the position marked by wiper RB2 or RB3 under control of relay N. If the second digit is even, relay J energizes over wiper RA5 and remains locked in series with relay E. If two control circuits are provided, a common marking multiple arranged in two halves is employed. Relay X energizes when the control circuit is seized and is normally disconnected by relay E, but should the required half-multiple be in use by the other control circuit, relay X remains locked therein and holds up the setting of the conversation switch S until the other control circuit is released. The final digit is repeated directly to the switch RB and the conversation switch S again moves in accordance with the fresh marking into engagement with the wanted line. Dialling relay C upon relapse connects up relay G and relay N upon operation connects up relay TT, thereby connecting test relay P over wiper RA3 to wiper S3 of the conversation switch. If the wanted line is idle, relay P energizes, connecting up relay H, and switching relay HS energizes. Relay G falls back and connects low resistance battery to wire to energize relay G, Fig. 1, which effects release of the control circuit at the preceding stage, whereupon ground is disconnected from relay A to effect release of the control circuit at the final stage. Upon release of the control circuit, Fig. 1, a relay in the conversation switch operates over test wire H1 and connects holding ground thereto. If the wanted line is busy, relay P is inoperative, and relay W energizes in series with relay V (inoperative) and disconnects relay G, which initiates release and busy tone is sent. P.B.X. hunting. The first line of a P.B.X. group is marked by ground in one of banks RB4-7, and when relay TT energizes relay V pulls up, relay W being short-circuited, and if this line tests busy, the switches RB, S step together under the control of relay N until an idle line is found, when test relay P energizes. Battery is connected to the last line in one of banks RB4-7, and if all the lines are busy, relay W energizes as in the case of a single line being found busy. Local calls requiring only a single switching stage. These are designated by the initial digit 2. When the switch RB, Fig. 1, stops in the position marked by the switch RA, relay W energizes over wipers RA3, RB4 and locks and the switch RA steps in a self-interrupting circuit completed over wiper RA5 to its second normal position, while the switch RB resumes stepping and takes up the fresh marking. The switch RA responds to the second digit, marking a new position for the switch RB, and with dialling relay C released and relay M operated, relay R or relays J, R energize according as the digit is odd or even. Relay E energizes and causes the switch RA to associate itself with the conversation switch, while the third digit is repeated to the switch RB. Dialling relay C on energizing disconnects relay W, and on release connects up in turn relays RR, EH, thus connecting test relay P to wiper RB5 or RB6. If the wanted line is busy, relay P is inoperative, and relay G pulls up, releasing the control circuit and causing busy tone to be sent. If the wanted line is idle, relay P. operates and connects up relay H, which closes a self-interrupting circuit for stepping the conversation switch S to the called line under control of relay M, which on operation connects up relay G in parallel with relay GS to release the control circuit. P.B.X. hunting. The first line of a P.B.X. group is marked by ground in bank RB7 or RB8 and when relay RR energizes relay V pulls up, and if this line is busy the switch RB steps until an idle line is found, when test relay P energizes. Battery is connected to the last line in bank RB7 or RB8, and if all the lines are busy, relay M energizes and connects up relay G as in the case of a single line being found busy.