Patent GB-694915-A (GB)
Title: Improvements in or relating to automatic exchange systems
IPC: H04M15/10
Filed: 1951-06-04
Abstract: 694,915. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES, Inc. June 4, 1951 [June 21, 1950], No. 13222/51. Class 40 (iv). In a multi-exchange system, each exchange comprises a timer for operating a meter to assess local calls, another timer for assessing toll calls, and common means for operating the timers and for varying the charge according to the time of day. As shown, a branch exchange, Figs. 1, 2, 3, 6, 7, comprises a meter 150, local timer cams A1, B1 driven by a motor magnet 160, and toll timer cams A2, B2, C2 driven by a motor magnet 395, both timers being controlled by cams A-L driven by a motor magnet 665 whose rate of stepping is determined according to the time of day by means of a cam B3 having a 24-hour period of revolution. Local call. A calling subscriber X is connected to a called subscriber Y in known fashion through line circuit 170, line finder 171, and selectors 175, 180. Polarized relay 120 operates on the reversal of current when Y answers. Meanwhile cams A-L are being stepped and cam A, by means of its hump 693, sends a pulse to operate relay 110. Cam B at hump 688 sends a pulse to operate relay 140, which shunts the left-hand winding of relay 120 to improve transmission and releases relay 110. Cam A at hump 694 now sends a further pulse, which is repeated by local meter relay 100 to meter 150 and to local timer motor magnet 160 which advances cams A1, B1 by one step. Cam B1 opens the pulsing circuit from cam A to relay 100 and completes a circuit over which cam C sends one pulse in each revolution to the magnet 160. After a predetermined time, local timer cam A1 applies a momentary warning tone to the connection. If the call continues, the local timer soon reaches its home position, cam A once more sends a pulse to relay 100 to operate the meter 150 as before, and the timing and metering cycle continues until the end of the call when the local timer goes home by self-interruption of magnet 160. Early or late in the day, cam B3 causes slower pulses to be sent to magnet 665, thereby lengthening the metering periods. During the night, cams A3 and B3 are both operative and cam A3 prevents local calls from being metered at all. Short distance toll call. In this case X calls a subscriber Z on another branch exchange comprising a repeater 585 and selectors 590, 595, the connection passing through a main exchange, Figs. 4, 5. The first digit dialled steps selector 175 to the " automatic toll" level, say level 1, where normal post springs 176 are closed to bring up relay 130 and prevent the operation of local meter relay 100. Selector 175 seizes an idle junction, Figs. 2, 3, to the main exchange, and relays 250, 260, 230 are operated. The dial impulses of the second digit are repeated by relay 250 to the receiving magnet R of a mechanical impulse regenerator of the type described in Specification 458,095, which closes its off-normal contact 218, and to a relay 270, which slightly pre-energizes relay 250 to improve impulsing and also repeats the impulses to a magnet 385. This steps wipers 356, 357 to select the charge rate for the call, in accordance with the second digit dialled. Relays 280, 300, 310 and marking magnet M of the impulse regenerator are energized during the impulsing, releasing at the end of the digit to bring up relays 320, 340. Magnet S is energized and causes the impulse regenerator to send the stored digit to selector 400 at the main exchange which now seizes an idle junction to the called branch exchange. Relays 450, 460, 440 are operated. The called branch exchange has a repeater 585 which is a mirror image of that at the main exchange, Figs. 4, 5. Relay 570 at the main exchange operates in series with the relay corresponding to 550 at the branch exchange, bringing up relay 580 at the main exchange and relays 540, 500 at the branch exchange. The remaining dialled digits complete the connection through selectors 590, 595 to the called subscriber Z. When Z answers, the reversal of current operates polarized relays 510 at the called branch exchange and 330 at the calling branch exchange. Relay 560 at the called branch exchange is energized to release relay 570 at the main exchange which brings up relays 430, 410, thereby reversing the current back to the calling branch exchange to start the cams A-L rotating. Relay 330 brings up relays 210, 220, 240, and relay 230 releases slowly. Now cam E sends a pulse to operate relay 360, and cam D similarly energizes relay 350. Cam J, which was selected by wiper 356 in response to the second dialled digit, sends four pulses to toll meter relay 200 which repeats them to the right-hand winding of the meter 150 while cam L immediately sends four pulses of reverse potential to the left-hand winding of the meter to make it restore quickly. Cam C at each revolution sends a pulse to motor magnet 395 to advance the toll timer cams A2, B2, C2 by one step. After a predetermined time, cam A2 applies a momentary warning tone to the connection. If the conversation continues, cam B2 soon brings up relay 370 to energize relay 380 which switches the pulse circuit for the toll timer motor magnet 395 from cam C to cam F. By means of its second hump 663, cam F sends a pulse to step the toll timer to its home position, whereupon relay 380 is released. Relay 370 having connected relay 200 to wiper 357 instead of wiper 356, cam K now sends two pulses to relay 200 which repeats them to the meter 150 to register the first overtime charge. Cam C again advances the toll timer by one step so that relay 380 reoperates and cam F, by means of its second hump 663, advances the toll timer by a second step. On each subsequent revolution, cam F sends two pulses and the toll timer advances twice as fast as during the initial period. Thus, each overtime period is half as long as the initial period. Long distance toll call. The calling subscriber X dials " 0 " to call an operator over the tenth level of selector 175 where normal post springs 176 are closed to prevent the operation of the local meter relay 100 as in a short distance toll call.