Patent GB-196018-A (GB)
Abstract: 196,018. Coventry Automatic Telephones, Ltd., (McBerty, F. R.). Dec. 9, 1921. Automatic and semi-automatic exchange systems.-A connecting trunk is provided with tens and units relays at both ends for connecting calling and wanted lines. Marking wires which determine the energization of the appropriate relay of each series are selected in the case of calling lines bv the line relav and in the case of wanted lines by a relay counting chain which responds to the two called digits. The counting chain is disconnected by the energization of a marginal test relay if the wanted line is idle, the test relay at the same time completing the talking circuits. The invention is described in connection with a private branch exchange system. If a P.B.X. subscriber calls the digit O, the local connecting trunk first seized is disconnected and the subscriber is connected to the first idle line to the main exchange. These lines, which serve for incoming as well as outgoing calls, are each provided with tens and units relays for connecting them with the local lines, the appropriate relays being energized in the case of outgoing calls by the calling subscriber's line relay, and in the case of incoming calls by keys depressed by the P.B.X. operator. Connection of calling line to idle trunk A, Fig. 1. Each trunk such as A is equipped with tens relays 130 and units relays 140 controlled by the line relays 109 through contacts of a relay 120. If there are more than 100 subscribers in a calling group, more than one relay 130 may be provided. The energization of a line relay 109 energizes a common relay 110 in series with relay 120, which completes the circuits of the appropriate relays 130, 140. A relay 114 is now energized over the calling line and locks the relays 130, 140, at the same time energizing relays 112, 107. The relay 107 cuts out the line relay 109, which de-energizes relays 110, 120. Relay 112 extends the starting circuit to the relay 120<a> of the next idle trunk and energizes relay 151, which connects the calling line to relays 201, 202, Fig. 2, over the wire 157. Operation of the counting relays, Fig. 2, and completion of the connection under their control. The relays 202, 201 respectively energize selflocking relays 203, 211 by connecting them to the battery wire 156. At the first impulse of the tens digit, relay 201 relapses and energizes relay 210, which locks itself. At the termination of the impulse, the re-energization of relay 201 energizes relav 213, which locks itself and unlocks relay 211. Similarly the next impulse energizes relays 212, 215. which lock themselves and unlock relays 210, 213. and so on. The relay 202 is also de-energized at the first impulse and energizes relay 204, which locks itself up, but relay 202, being slow to energize, does not become energized again until the termination of the tens impulses. Relay 202 then energizes relay 205, which locks itself and energizes relay 190, which energizes the appropriate tens relay 170 over a circuit 183 closed by the counting relay, such as 219, which was energized by the last impulse. Relay 170 locks itself independently of the counting relays. Relay 190 also energizes relay 208, which unlocks the relay 190 and the relays of the counting chain and then relapses, but a relay 209 energized by relay 208 remains locked up. The units impulses now arrive and operate the counting chain in the same way. At the first impulse, relay 202 relapses and energizes relay 206, and after the last impulse, relay 202 is re-energized and energizes relay 207, which energizes relay 180, which energizes the appropriate units relav 160 over a circuit 183<a> closed by the counting relay, such as 213, which was energized by the last impulse. The relay 160 looks itself in a local circuit. Busy test and signal. If the wanted line is idle, its cut-off relay 107<x> is energized in series with a marginal test relay 179, which locks itself through a low-resistance winding, to mark the line busy, and de-energizes relay 151 to disconnect the counting relays. If the line is busy. relay 179 is not energized and a busy signal is transmitted to the calling subscriber over contact 182 and a front. contact of relay 151. The. calling subscriber may wait until the line becomes available. Supply of ringing current. If the line is idle or when it becomes idle, relay 179 energizes relav 159, which completes the circuit of the ring- ing generator 159<a>. When the called subscriber replies, a relay 153 in the ringing circuit responds, de-energizing relay 159 and energizing a relay 152, which locks itself up. Release. If the calling subscriber is the first to disconnect himself, the relapse of relay 114 unlocks relays 130, 140, but relays 160, 170 are kept energized by relays 152, 153 until the called subscriber hangs up. If the called subscriber is the first to disconnect himself, the relapse of relay 153 energizes relay 154, which unlocks relays- 160, 170, but the relays 130, 140 are not released until the calling subscriber hangs up, Call from P.B.X. to main exchange. A connection of this kind is made by calling the digit 0 (ten impulses) to energize the connecting relay 231, which closes a circuit 115 to energize relay 113, which causes the de-energization of relays 112, 114, 151, 130, 140 to release the trunk A and the counting relays. Relay 113 now relapses, but in the meantime it has closed a starting circuit 500 to energize relay 350, which energizes self-locking relays 301, 302, 360, 370. Relays 360, 370 are tens and units relays, corresponding to 130, 140, and connect the calling line to an idle main exchange trunk. Relay 302 extends the starting circuit 500 to the relay 350<a> of the next idle trunk, ready to deal with the next main exchange call. Relay 303 is now energized over the calling test circuit and locks itself through a lowresistance winding to mark the calling line busy. Relays 306, 311 are energized over the calling line. Relay 306 energizes relay 307 and bridges the outgoing trunk 321, 322 through a relay 323 to light the call lamp at the main exchange. The operator answers and completes the connection in the ordinary way. A P.B.X. operator can listen in by throwing a key 324, or, if she desires to talk with the P.B.X. subscriber only, can do so by throwing a key 325, which energizes a relay 312 to interrupt the talking circuit while connecting her head-set 355 to the P.B.X. side. The P.B.X. subscriber can call the P.B.X. operator by. momentarily opening his line circuit (e.g. by his impulse dial) to de-energize the relay 311 but not the sluggish relay 306. Relay 311 energizes relay 308 which locks itself and lights a call lamp 330. When the P.B.X. subscriber disconnects himself, the relapse of relay 306 energizes relay 309, which releases the connection. Call from main exchange to P.B.X. Ringing current from the main exchange energizes the A.C. relay 323, which energizes relav 312 to light the call lamp 330. The P.B.X. operator, having ascertained the connection wanted, presses a corresponding group key 333 and tens and units keys 340, 341 to energize relays 380, 360; 370, 302. If the wanted line is idle, test relay 303 is energized and energizes relay 304, which energizes relay 305, bridges relay 323 metallically across the main exchange trunk, lights a ringing lamp 331 and closes the circuit of a ringing generator 320. A tell-tale ringing tone is sent back through a resistance 356. When the subscriber replies, a relay 310 in the ringing circuit responds and deenergizes relays 304, 305. Relay 305 de-energizes relay 310, but relay 304 is not re-energized because relays 311. 306 are now energized over the called line. If the line is busy, the test relay 303 is not energized, and the glowing of a lamp 334 informs the operator, who may either press the key 332 to energize the release relay 309 or may wait for the line to become idle. In the latter case she throws the key 325 to energize relay 312 to prevent the calling main exchange subscriber from over-hearing the conversation of the engaged party.