Patent GB-302441-A (GB)
Title: Improved circuit arrangements in automatic or semi-automatic telephone systems
IPC: H04Q1/24
Filed: 1927-10-12
Abstract: 302,441. Siemens Bros. & Co., Ltd., and Caswell, A. E. Oct. 12, 1927. Automatic and semi-automatic exchange systems.-When a wanted line is found to be busy, the test relay of the selector is momentarily applied again at periodic intervals to the test circuit during the release period of a slow release relay. The invention is described in its application to a test distributor and a test connector without relays controlled from the distributor. Establishment of connection to the wanted line. When the test clerk plugs into the jack of the distributor, a loop is closed over wires x, y, and line relay A energizes in series with relay PC, connecting up release relay B. Relay C(1) energizes and connects up relay (El), which on operation leaves relay C(1) dependent on off-normal contact n3. The first train of dialled impulses are repeated by relay A to the vertical magnet V over relays C(2), E(2), and at the end bf the digit, relay C falls back, slowly followed by relay E. Relay C(1) now re-energizes over contacts e2, e3, but relay E(1) is short-circuited over off-normal contact n1, and change-over relay EA energizes and locks over contact c4. The second digit is therefore repeated to the rotary magnet R. relays C(2), E(2) being in series as before. Relays C, E fall back in turn, disconnecting relay EA, and relay C(1) then re-energizee. If the test connector is idle, change-over (relay H(1), energizes, locks, transfers the impulse circuit to wipers X. Y and marks the connector busy by connecting battery to wiper Z. If, however, the test connector is in use, busy relay G operates over battery on wiper Z, connecting busy tone to wire x at contact g6, reversing the connections to wires x, y to give a lamp signal, and opening the circuit y of relay H at contact g5. Assuming the test connector to be idle, the third digit operates the vertical magnet VM of the connector, and when relay C falls back, relay EB energizes and locks. On the re-operation of relay C after the release of relay E, change-over relay EA energizes and locks, and the last digit is repeated to the rotary magnet RM. Testing arrangements. Between the relapse of relay C and that of relay E, relay RC energizes, locks, releases relay EA and connects test relay T to wiper C over contacts c5, e5. If the wanted line is idle, relay T energizes, locks, switches through and disconnects relay G at contact t5. If the wanted line is busy, on the re-operation of relay C, relay G energizes over contacts; t5, c3 and locks. The connections of wires x, y are reversed to give a lamp signal, and relay C(1) is connected to an interrupter over wire I at contact g<7>. At each connection of earth to wire I, relay energizes, and relay E operates when a short-circuit is removed by the removal of earth from wire]. Relays C, E fall back in succession and connect test relay T momentarily to wiper C. Testing lines in succession. The digit 1 is dialled after each test, and is repeated to the rotary magnet RM over relay S, which energizes, connects up relay C(1) and holds until relay EB falls back. Relay E pulls up, and the test of the line is made as before after the relapse of relay C. Setting up a connection over a subscriber's line switch. The test clerk by depressing a key earths both wires x, y, releasing relay PC by short-circuiting. Holding earth is thus removed from wiper C, and the test clerk is in the position of a calling subscriber and may set up a connection by 'dialling over wires a, b. Release. Relays RC, H are disconnected when release relay B falls back, but since relay H is slow to release, a circuit is closed for the release magnet ZM of the connector in series with relay H(2), which relapses when the connector has restored, and connects up the release magnet Z of the distributor. Specification 266,037 is referred to.