Patent GB-158910-A (GB)
Abstract: 158,910. Relay Automatic Telephone Co., Ltd., (Assignees of Betulander, G. A.). Fob. 11, 1920, [Convention date]. Automatic and semi-automatic exchange systems.-The numerical switching operations are governed by code impulses, which are transmitted by a series of relays forming part of an operator's keyboard set or of a register controlled by a calling subscriber. The code impulses may consist of alternating currents of different frequencies, but in the semi-automatic system described each digit is represented by two direct current impulses transmitted in succession, each impulse being sent over one or other or both of the a and b speaking wires. Relays are used exclusively to effect all connections. In general outline the operation is as follows :-A trunk FL1, Fig. 1, can be connected through link lines ML, Fig. 2, to any of the trunks GL, which are divided into groups G0L, G1L, &c. leading to numerically different sections of the next switching stage. When the trunk FL1 is seized by a calling subscriber, it is connected to an operator's position and to a common selector GV, Fig. 3. The wanted number is set up on a key-set KS and one of the relays CR0 - - CR9, corresponding to the depressed key of the first-digit row, sends two successive impulses over the a and b wires of the trunk to energize a particular combination of the relays SR2, SR3, SR5, SR6, Fig. 3, thereby energizing a relay GR corresponding to the de. pressed key. The relay GR connects the test wires of all the trunks GL of the selected numerical group to a testing-device PS, which tests the trunks two at a time and energizes the appropriate connecting relays for connecting the first idle trunk to the trunk FL1 through a link line ML. The selector GV is then released and the selected trunk GL is connected to a corresponding selector in the next switching stage, where the process is repeated under control of the depressed key of the second-digit row, and so on. The different rows of keys are brought into action at successive stages by the successive energization of relays FR1, FR2, &c. When the selecting operations are completed the operator's. circuits are disconnected. Specification 141,006 is referred to. Connection of trunk FL1 to operator's circuits and to selector GV. A disengaged operator's position is found by known means and is connected to the trunk FL1 by a relay DR, which locks itself up and causes the energization of relays BR1, BR2. The operator, observing the lighted lamp ARL, enquires the wanted number and writes it on the key-set KS. She then presses the starting-key SK, energizing relay NR1 in series with relay TR1, which disconnects the operator's telephone TT and locks itself up in series with relay BR3. The relay NR1 closes a circuit 15 for relay V1R1, Fig. 2, which locks itself up, connecting the a and b wires of the trunk to the selector GV, Fig. 3, and energizing relays ER1, ER2. The relay ER2 open-circuits the other relays V1R so as to render the selector GV inaccessible to other calling trunks. The relay ER1 energizes relay HR1, Fig. 3. Operation of the selector GV by code impulses from the key-set KS. Assuming that the first digit is O, which is represented by two successive impulses over the a wire, the relay BR3 closes a circuit 19 through relays FR1, CR0, and relay CR0 closes a circuit 20 through relay OR1, the a wire, and relay SR2, Fig. 3, which energizes relays SR1, SR5. Relay SR5 locks itself up and shortcircuits relay HR1, which opens the impulse circuit and energizes relay SR4, which locks itself and removes the short-circuit from relay HR1, which again becomes energized. Thus the effect of the first impulse has been to lock up relays SR4, SR5. If the impulse had been in the b wire it would have energized relay SR3 and locked up relays SR4, SR6, and if it had been in both a and b wires it would have locked up relays SR4, SR5, and SR6.) The opening of the impulse circuit by the momentary de-energization of relay HR1 has the effect of de-energizing relay OR1, Fig. 1. A circuit was closed through relay OR, in series with relay OR2 when relay OR1 was energized, but as long as relay OR5 remained energized it short-circuited relay OR6 and only the relay OR2 was energized. Now however the relay OR6 becomes energized and switches over the a and b wires from the upper to the lower contacts of the relays CR0 - - CR9, and a circuit 32 is closed through relay OR3, the a wire, and relay SR2, Fig. 3. The relays SR1, SR4 being energized, the relay SR2 now, in combination with the previously-energized relay SR5, closes a circuit 33 through the relays G0R and M2R1, Fig. 2. In the case of certain numerals a resistance is inserted in one or other of the impulse circuits so that the relay SR2 or SR3 is not energized by the impulse, which is only effective for change-over purposes. Operation of the testing device PS; completion of the first-digit switching operations. The relay G0R connects the test wires of all the trunks of the selected 0 group G0L to the testing device PS, and the relay M2R1 closes a circuit 34 for the first testing relay KR1, which connects the test circuits of the first pair of trunks to relays PR1, PR2. If the first two trunks are busy, neither of these relays is energized, but the relay KR1 energizes relay KR2 which closes test circuits for the next pair of trunks. If the third trunk G0L3 is idle, relay PR1 now becomes energized and locks itself up in a circuit 38 in series with relays A2R3, M1R3, and relay M1R3 energizes relay A1R1. The conjoint action of these relays and of relay M2R1 in known manner closes contacts K1G13 and K2G31 to connect the trunk FL1 through the link line ML3 to the trunk G0L3. The relay A1R1 de-energizes relay V1R1 so as to release the selector GV, and a relay V2R3, Fig. 3, connects the trunk G0L3 to a similar selector in the next switching stage. Subsequent digit operations; release of the operator's circuits. The release of the selector GV interrupts the second impulse and de-energizes relay OR3. The relay OR4, which was perviously energized by relay OR3, remains energized over its own locking contact, so that a circuit is now closed for relay IR, which energizes the second relay FR2 in series with the relay CR corresponding to the depressed key of the second row. The relay FR2 locks itself up and energizes a relay UR, which restores the relay set OR1 - - OR6 to a currentless condition and de-energizes relay IR, which in turn de-energizes relay UR and unlocks relay FR1. These operations are repeated after each digit, the relays FR3, FR4, &c. being successively locked up and preceding relays unlocked so as to bring the different rows of keys successively into action. At the conclusion of the selective operations, the relay IR closes a circuit 49 for relay BR4, which unlocks the relays BR2, BR3, TR1 NR1, DR, so as to release the operator's circuits.