Patent GB-122047-A (GB)
Title: Machine Switching Telephone Systems.
IPC: H04Q3/00
Filed: 1918-01-19
Abstract: 122,047. Western Electric Co., Deakin, G., and Polinkowsky, L. Jan. 19, 1918. Automatic and semi-automatic exchange systems; manual exchange systems.-Calls from a trunk position A are extended manually by an operator at a manual-switching section B of a machine-switching exchange to a subscriber's line C without disturbing a local connexion already existing. The trunk operator may listen in on the existing connexion by the depression of the listening-key 256, and may release this connexion by the depression of her ringing-key 257. After an interval timed by a set of relays operating in succession, ringing-current is applied to the wanted line and is cut off when the called subscriber replies. The operator at the position B receives a call over the order wire, tests the wanted line, assigns the junction to be used, and inserts the plug of this junction in the jack of the wanted line. The cut-off relay 207 energizes in series with a relay 211 and the secondary of a tone coil 212, thus indicating to other testing operators that the subscriber is engaged in a trunk call. The relay 211 energizes a relay 214 which (1) lights the supervisory lamp 220 over a resistance 221, (2) energizes a relay 217 over the plug switch 218, and (3) extends the subscriber's line to the repeater 215, the circuit including a condenser 216 of such small capacity that the trunk operator may listen in without disturbing an existing conversation. When the trunk operator inserts the toll plug in the jack of the assigned junction, a relay 253 is energized and connects a relay 265 over the third wire of the junction through the low-resistance winding of a relay 222 and the armature of a relay 231 to the battery. Relay 222 shunts out the lamp 220, and relay 265 shortcircuits the high-resistance winding of relay 253 and permits the relay 254 to light the supervisory lamp 252. When the trunk operator is ready to establish the through connexion, she depresses the ringing-key 257, thereby energizing a relay 223, which in turn energizes a relay 224. The relay 224 (1) energizes a relay 225 to bridge a comparatively large condenser 226 and a supervisory relay 231 across the wanted line, (2) directly earths the test lead of the wanted line over the normal contact of relay 219 to release the local call if necessary, and (3) by opening its normal contact closes a holding-circuit through its lefthand winding and a slow-acting relay 227. The direct earthing of the test lead is maintained for a time sufficient to release the local automatic connexion by the set of relays 227, 217, 219, of which the slow-acting relay 227 short-circuits the relay 217, which releases slowly and then closes the circuit of the slow-acting relay 219, which then earths the test lead over the right winding of relay 211 and the tone coil 212. The relay 219 also energizes relay 229, which connects ringing- current to the wanted line. Repeated depressions of the ringing-key 257 by the trunk operator energize the relays 223 and 229. In the first non- ringing interval after the called subscriber replies, the supervisory relay 231 is energized, throwing the high-resistance left-hand winding of relay 222 in series with relay 265, which in turn brings the high-resistance winding of relay 253 in series with relay 254 and thus cuts off the lamp 252. When the subscriber replaces his receiver, relay 231 is de-energized, whereby relays 265, 254 are again energized and the lamp 252 lights up. The withdrawal of the plug by the trunk operator deenergizes relays 253, 222, causing the lamp 220 to glow until the operator at the automatic exchange removes the second plug. If the trunk operator inserts the toll plug in the wrong junction, the lamp 220 of that junction is lighted continuously over the armature of relay 222, resistance 230, and back contact of relay 214 of that junction.