Patent GB-213417-A (GB)
Abstract: 213,417. Coventry Automatic Telephones, Ltd., and Cornell, W. March 13, 1923. Automatic and semi-automatic exchange systems provided with a set of connectors available to both trunk operators and test clerks over separate distributor switches and with means for giving trunk operators preference over test clerks, are characterized by the feature that the connectors are tested and controlled over a single wire additional to the talking wires and private wire so that the distributors need have only four wipers. Trunk operator's distributor. A trunk operator at A takes the distributor switch B into use by inserting a plug in jack 1 to energize relays 2 and 3. Relay 3 locks up and cuts the wires through to the line relay 60 which energizes relay 62. Relay 62 energizes relay 64. The operator now dials the thousands digit and relay 60 delivers impulses from ground at 65 to the vertical magnet 54. Off normal contacts 57 change over and render the holding up of relay 64 dependent on impulses from the contacts 68 of the vertical magnet. At the end of the digit, relay 64 falls back, energizing relay 69 which energizes relay 76, and switches over the impulse circuit to rotary magnet 55. Relay 76 energizes relay 78. Rotary off normal springs 58 open so that relay 69 is held up only by impulses from the springs 74 of the rotary magnet. At the end of the digit, relay 69 releases relay 76 which opens the circuit of slow release relay 78. In the interval between the relapse of relays 76, 78, relay 79 is connected to wiper 53. If the wanted connector is busy, relay 79 pulls up, holds up relay 78 and sends back busy tone and flash from wire 84. The operator may now wait until the freeing of the connector releases relay 79 and relay 78 falls back. On falling back, relay 78 grounds wiper 53 and energizes relay 85 to cut the line through. Connector C. Relay 101 energizes from ground on wiper 53 and energizes relay 103 which energizes relay 106. The tens digit is repeated by relays 60, 101 to the vertical magnet 109. The change-over of springs 107 causes relay 106 to release at the end of the digit and energize relay 112. The units digit is thus repeated to rotary magnet 115. The opening of springs 113 causes relay 112, to release at the end of the digit, and springs 104 insert resistance 118 to prepare relay 103 to release more quickly. The wanted party may now be informed of the waiting call. Release. When the plug is withdrawn, relays 2, 3, 60 fall back followed by relay 62 which energizes the release magnet 56 and relay 76, the latter releasing relay 85. The removal of ground from wiper 53 releases relay 101 so that relay 103 falls back and energizes release magnet 123. Test clerk's equipment and distributor. The test clerk at D takes the distributor F into use by plugging into jack 151. Relay 152 energizes and lights lamp 176 at the position E of another test clerk to show the switch F is engaged. Relay 201 pulls up and energizes relay 203 which energizes relay 205. Thousands and hundreds digits are now sent, the distributor F being operated in the same way as the distributor B. At the end of the hundreds digit, rotary springs 214, 229, having changed over, relay 215 falls back and releases relay 217. In the interval between the relapse of these two relays, relay 222 tests the wanted connector over wiper 229. If it is idle, relay 217 on falling back connects low-resistance relay 227 over wiper 229 in series with relay 101 of the connector. Relay 227 is not energized, but relay 101 is, and the test clerk controls the connector in the same way as the trunk operator. The wanted line is now connected to jack 156, and key 157 is thrown, lights lamp 160 and puts ground on wiper 241 to operate the wanted cut-off relay. At the same time, a circuit is made over resistance 179 for relay 152 to prevent release of the distributor if the plug is taken from jack 151. If the connector is busy, relay 222 is energized over wiper 229 and the relay 227 of the distributor holding the connector in the case of a test clerk or from ground at 72 in the case of a trunk operator. Relay 222 locks up over its contact 240, opens the operating circuit, and lights the lamp 155. Arrangements for giving preference to a trunk operator. When a trunk operator's distributor tests a connector already in use by a test clerk, relay 79 pulls up in series with relay 227 of the test clerk's distributor. Relay 227 locks up over resistance 235 and energizes the release magnet 237. The connector and relay 79 are thus released and the trunk operator can now dial the remaining two digits.