Patent GB-215557-A (GB)
Abstract: 215,557. Siemens Bros. & Co., Ltd., and Patterson, W. G. May 1, 1923. Automatic and semi-automatic exchange systems.-Hunting switches such as line switches are controlled as to stopping, starting, and restoration to normal, by a single relay. The test circuit of this relay goes over the calling loop so that in the event of a premature release no outgoing line is seized and the line switch is returned to normal. In the case of incoming calls the line switch is moved one step and disconnects the relay but does not give access in this position to an outgoing line. Two arrangements are described. First arrangement, Fig. 1, in which idle lines are marked by full battery potential. Outgoing call. When a call is made, relay T energizes over its winding 1 and normal contacts engaged by wipers da, xa, and energizes the stepping magnet D over wipers aa, da. The wipers move to their first contacts which are not connected to outgoing lines and release relay T which again energizes magnet D. Outgoing lines are now tested over the circuit ca, 3, 2, calling loop xa, and when an idle one is reached, relav T pulls up, extends the loop, cuts out the high resistance winding 2, and locks up over contact t<1>. Release of the first selector releases relay T, which energizes magnet D to step the wipers on to their normal position. If the calling party abandons the call before an idle line is found the test circuit is interrupted, and since relay T cannot energize the switch is stepped on to normal. Busy signal. The last terminals of the line switch are not associated with outgoing lines, and the last c-terminal is connected to batterv over winding 1 so that relay T energizes, connects busy tone over wiper ba, and locks up over the loop to the busy wire. Incoming call. Relay T energizes over its high resistance winding 1, wiper xa, and the connector test wiper, and energizes the stepping magnet. Wipers aa - - ca move on to dead terminals but relay T remains energized over wiper xa. When the connector releases relay T releases, and provided the called party hangs up, causes the stepping magnet to drive the switch on to normal. Second arrangement, Fig. 2, in which busy lines are marked bv a direct ground. When a call is made, relay T energizes over da, loop, xa, 2, and energizes stepping magnet RM over ba, t<3>, da. On the first step wiper da releases relay T, which completes another driving circuit over da, t<4>, rcm. While the switch is engaging busy lines, relay T is short-circuited over wiper ca, but when an idle one is encountered relay T pulls up over a circuit 2, xa, loop, t<3>, and extends the loop. Relay T is held during the connection by the ground returned from contact b of the usual release control relay, but before relay A energizes,. relay T is held in a circuit T, 2, ca, k, d<1>, loop, A2. Premature release prevents relay T from operating as in the first arrangement. Busy signal. When there are no idle lines the wipers move to an extra set of terminals of which the c-terminal is dead. Relay T pulls up and locks itself over the loop to the busy wire. Incoming calls. Relay T energizes and wipers aa-ca move to dead terminals. Relay T locks up over both its windings and the connector c-wiper. Release of relay T causes wipers aaxa to be moved to normal provided the called party has replaced his handset.