Patent GB-365637-A (GB)
Title: Improvements in or relating to telephone exchange systems
IPC: H04M3/28
Filed: 1930-10-23
Abstract: 365,637. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. and HARTLEY, G. C., Columbia House, Aldwych, London. Oct. 23, 1930, No. 31848. [Class 40 (iv).] A routine-testing equipment for subscribers' line circuits performs the following functions : (1) If a line is busy when seized for testing the routiner waits until it becomes idle but if it remains busy for more than a predetermined time an alarm is given. (2) If the routiner seizes a dead-number line, the test is stopped, the test-controlling sequence switch returns to normal, and the test is recommenced on the next line. (3) The leakage resistance of the line conductors to ground and to one another is tested by connecting up the conductors in turn as part of a potentiometer which controls the potential of the grid of a thermionic valve. (4) The bell-condenser discharge is tested at a rate such that the bell is not disturbed. (5) A low-resistance loop across the line conductors causes a line to simulate a calling condition but this is replaced by a high-resistance loop after extension to an outgoing trunk to prevent seizure of the trunk. (6) Two timing arrangements are provided, one giving an alarm if the test sequence switch remains in any position for more than three minutes. The second operates, for the majority of the tests, after a much shorter time and causes the test sequence switch to return to normal and a second test to be made on the same line. This provides for the case of a subscriber initiating a call during a test and if the repeated test is successful no alarm is given. The invention is described with reference to a system in which the routiner distributing switch FM has access to a final bye-path and to a finalselector switch, the latter being a special test switch or a combined conversational and test switch. Specification 324,982, [Class 40 (iv), Telephones &c.], is referred to. Detailed operation. The start key SK operates relays B, SB, BB, and relay B is locked over wiper fm6 as long as the bye-path is in use. When B releases, relay H operates over wiper fm6 if the final-selector switch is free. Interrupted ground is now connected to relay SA controlling relay SZ and in the interval between the release of these two relays an impulse is sent over wiper fm7 to the bye-path. Two impulses are thus sent causing the selection of line 11 after which relay K operates, releasing H, SB, and the bye-path. Relay TS operates over wiper tsm8, energizing relay CA which connects interrupted ground to magnet TSM of the test sequence switch to move the switch to position 1 in which CA releases. If the selected line is busy, relay KT operates over wiper fm1 to ground on the test wire, but if or when the line becomes free relay CA operates over contacts kt3 to move the switch to position 2. If the selected line is a dead-number line, characterized by a disconnected a-wire and low-resistance battery on the b-wire, relay LN (operated in position 1 over tsm7) will release and DN will hold energizing relays DZ, Z, which release TS restoring TSM to normal and transmitting an impulse to the final-selector over wiper fm5. If the line is not a deadnumber line the operation of LN advances switch TSM to position 3 in which the line relay connections are tested. If correct, relay LA is short-circuited by ground on the a-wire and LB operates in series with the line relay advancing switch LSDZ to position 4. Relay P should now operate over low-resistance battery on the test wire and the switch LSM moves to position 5. From positions 5 to 15 the cut-off relay is energized over wipers tsm1, fm1, disconnecting the line relay, and if this is correctly performed relay LB does not operate in position 5 and TSM moves to position 6. In positions 6 and 7 the b-wire over wiper fm3 is connected to battery over resistance R and to the grid of a thermionic valve V. If the leakage resistance of the b-wire to ground is less than a predetermined amount relay LT operates and stops the test. In positions 8 and 9 the insulation between the a- and b-wires is similarly tested, the a-wire being directly grounded. In position 10, earth on the b-wire and battery on the a-wire discharge the bell condenser, and in positions 11 and 12, the leakage resistance between the a-wire and ground is tested. In position 13 the bell condenser is charged and in position 14 discharged through resistance R and inductances in the leads to wipers fm2, fm3. This discharge should cause the operation of relays LT, BC to advance switch TSM to position 15 from which movement continues to position 17, the subscriber's cut-off relay being released. A low-resistance loop is now connected across the a- and b-wires causing a finder switch associated with a first by-path to hunt for the subscriber's line. When this is found relay KT operates over ground on the third wire opening the low-resistance loop and closing a highresistance loop over relay LB to prevent operation of the bye-path line relay. Relay LB operates to drive switch TSM to position 18 in which relay Z energizes, releasing TS and restoring switch TSM to normal. Relay Z also transmits an impulse to switch LSM which indicates on banks lsm1, lsm2, the tens and units digits of the line being tested, and an impulse over wiper fm5 to advance the finalselector switch. When the last line of a group has been tested relay AS energizes over wiper lsm3 to advance FM one step. Timing and alarm arrangements. If the switch TSM remains in any position for more than three minutes timed impulses operate successively relays AP, AL. A shorter timing control is provided by a slow-release relay SZ energized over contacts ca1, and if this relay releases during a testing cycle a circuit is completed from wiper tsm8 for relay AL which energizes Z and restores switch TSM to normal, relay DA being locked up. The test is now repeated on the same line and if AL operates again, relay AG is energized to give an alarm. If the second test is successful, relay DA is short-circuited in position 17 and the test proceeds on the next line.