Patent GB-253254-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q1/26
Filed: 1925-03-27
Abstract: 253,254. Siemens Bros. & Co., Ltd., and Peters, C. L. March 27, 1925. Automatic exchange systems.-Fault or other special conditions occurring at an unattended exchange are signalled to an attendant or operator at a main exchange over a previously-assigned one of the trunks which are normally used for conversation, the transmission of the signal taking place as soon as the assigned trunk, if busy, becomes free. Provision may be made for repeating the signal through an intermediate exchange. When the signal has been acknowledged at the main exchange, a checking signal is sent back to the originating exchange and the trunk is freed for ordinary traffic. A further signal is transmitted in a similar manner when the original fault is cleared. If desired, two trunks may be employed for fault signalling, one for faults requiring prompt attention, the other for faults requiring less urgent treatment . For certain special conditions, e.g. the necessity for recharging the battery at the unattended exchange, the return checking signal may start up a charging machine which may similarly signal that it is in operation. In the system shown, the occurrence of a fault at an originating exchange (on the left of Fig. 1) is signalled over a two-wire trunk to an intermediate exchange (on the right of Fig. 1) at which the signal is repeated over a further two-wire trunk to a main exchange, Fig. 2. The first trunk is an incoming trunk to the originating exchange, normally terminating in the wipers of a group selector GW, and when the trunk is busy, relay ES is energized and holds open the circuit of a relay CP. When a fault occurs, the operation of a fault relay N completes a circuit for relay B which if, or as soon as, the trunk is free, closes a circuit for relay CP. This relay disconnects the trunk from the selector GW and connects signalling battery over contact c3 to the b-wire of the trunk. Relav L at the intermediate exchange, over this battery connection, opens the test circuit to mark the trunk busy to the outgoing selector GW<1> and energizes relay CQ (if or as soon as the trunk to the main exchange is free), which repeats the signal by connecting battery to the outgoing b-wire. At the main exchange, relay LL operates and completes a circuit over contacts e1, s4, j3 for lamp AL and alarm relay P at an attendant's position. The depression of key K to acknowledge the signal energizes relay J, and, on the subsequent release of the key, relays JA, S operate. Relay S lights lamp RL and extinguishes lamp AL and sends back a check signal by connecting battery to the a-wire which causes the operation of relays F, C at the originating exchange. Relay C removes the battery connection from the b-wire releasing relays L, LL, the latter in turn releasing relay F. Relay C remains locked, but relay CP releases and frees the trunk. At the main exchange, relay S and lamp RL remain operated. When the fault is cleared, relay B releases and battery connection over contact b4 transmits a signal over the b-wire in the same way as before, and the resultant operation of relay LL unlocks relay S and extinguishes lamp RL. During the interval before relay S releases, a battery connection to the a-wire again operates relay F which releases relay C and results in all the apparatus returning to normal. If the attendant's position is vacant, the fault signals may be received at a manual operator's position (shown in the upper dotted rectangle of Fig. 2) by the throwing of key KK. Key X is provided for use when the manual operator does not know whether key KK has been thrown or not. If it has, the operation of key X energizes relav PP. thus sounding the audible alarm. If the key KK has not been thrown, the operation of key X to the left energizes relay E which has the same effect as the throwing of key KK. A switch M, Fig. 1, may disconnect the fault signalling apparatus and connect up local signalling apparatus at times when the originating exchange is attended.