Patent GB-212985-A (GB)
Abstract: 212,985. Automatic Telephone Man ufacturing Co., Ltd., Gillings, C., and Passmore, W. O. Dec. 19, 1922. Automatic and semi-automatic exchange systems.-In a multi-exchange system, when a call is extended to an operator's position, release of the connection is placed under the control of the operator. Fig. 9 shows a system of five exchanges X, X1-X4 in which a repeater is associated with the outgoing end of each trunk line, which may extend to a selector or direct to an operator's position. When the operator plugs in, a relay such as 105, Fig. 3, energizes, places an additional earth on the incoming test wire and completes a simplex circuit over the trunk wires to operate a relay such as 47, Fig. 2, at the preceding repeater, which acts in the same way and operates a relay such as 19, Fig. 1. If a busy condition is found at any stage of the connection, a busy signal is repeated back at each repeater by the same relays over one trunk wire. Call to an automatic subscriber; repeater R1. The line relay 3 and sluggish relay 8 energize, earthing the test wire 10, connecting up the upper winding of polarized relay 13, and connecting the upper windings of relays 18, 19 to the line relay at the succeeding selector. Relay 18 energizes, short-circuiting relay 19 at 24 and closing a bridge across the trunk over its upper winding and the lower winding of relay 13, which does not operate. Impulses are repeated over the trunk at armature 6, and slow relay 15 is energized at this time, completing a direct bridge across the trunk at 21, while relay 20 also energizes and locks itself. Relay 13 is energized by the reversal of current upon reply of the called subscriber, connecting through the speaking leads independently of relays 3, 15, releasing relay 20 and energizing relay 37, which reverses the current over the calling loop and brings in additional condensers to improve transmission. Relay 37 also removes short-circuits round relay 19 and lower winding of relay 18 at 39, 40, and completes the metering circuit which is momentarily connected to booster battery until sluggish relay 20 falls back. Release is initiated in the usual way by the calling party. The repeater R2 is similar to the repeater R1, but an additional relay 53 is provided to permit seizure by local selectors at the exchange X1, and separate line relays 41, 42 are connected up over contacts of relay 53. Pairs of relays may be used in place of the double-winding relays 19, 47. Call to operator's position at exchange X3; repeaters R2 and R3. The line relays 103, 104 energize when the previous selector switches through, and relay 104 earths the test wire 101 while relay 103 connects ring back tone to the upper wire 100 to indicate that the operator is being signalled, and energizes relay 112 in series with the lower winding of relay 105 which does not operate (the manual exchange battery being only of half the voltage of that at the automatic exchange in opposition thereto). Relay 112 lights the calling lamp and connects an impedance across the jack line springs, and when the operator plugs in, cut off relay 114 connects relay 115 to the upper wire 100, so that relay 105 energizes over both its windings, putting a further earth on the test wire and connecting battery instead of earth to line relay 104. Relay 46 which is shunted across the trunk at the repeater R2 falls back, and parallel circuits are closed over the trunk wires, one over relay 103 and upper windings of relay 46, 47, the other as soon as relay 47 operates over relay 104 and lower windings of relay 46, 47. Relay 46 is inoperative since its windings are in opposition. Relay 47 puts a further earth on the test wire 52 and connects battery instead of earth to line relay 42, operating the preceding repeater R1 in a similar manner. Relays 19, 47, 105 are held energized over one winding only, so that release by the calling party is prevented until the operator takes down, a disconnect signal being given by the relapse of relays 103, 112. The calling party can recall the operator before she takes down by moving his switchhook up and down. When the repeater R2 is seized bv a local selector at the exchange X1. the test wire 72 is earthed over the upper winding of relay 53 which energizes upon relapse of the release relay at the selector, locks and prepares an alternative circuit for line relay 42 so that battery is not connected to the lower wire by relay 47. The repeater R4 used for calls from the exchange X2 has an ordinary doublewinding line relay since it is not necessary to connect battery to the lower wire, but is otherwise similar to the repeater R3. Call to operator's position at exchange X4. The position 01 has a line relay 143 and release relay 144, and when the operator plugs in, the cut-off relay 147 prepares a second earth for the test wire 142, and connects relay 145 to the lower wire 141 in place of the lower winding of line relay 143, operating as before the relay similar to 47 at the repeater R5, which is identical with the repeater R2. For a local call at the exchange X4. the corresponding position 02 has merely a sluggish line relay and a cut-off relay which disconnects the line relay and puts a second earth on the test wire. Busy signal. Busy tone and busy flash battery are connected alternately to the lower wire and repeated at each repeater to give an audible signal to a calling subscriber or a visual signal to a calling operator. At the repeater R2, for example, busy flash battery establishes the simplex circuit and energizes relay 47 as before, earthing the mid-point of relay 78 which partially operates and earths itself at 74. Busy tone releases relay 47 and relay 78 energizes fully, connecting busy tone and busy flash battery to the lower wire.