Patent GB-474980-A (GB)
Title: Improvements in electric remote indicating systems
IPC: H02J13/00
Filed: 1936-05-06
Abstract: 474,980. Electric signalling systems. STANDARD TELEPHONES & CABLES, Ltd., and McWHIRTER, E. M. S. May 6, 1936, No. 12803. [Class 40 (i)] [Also in Group XXXIX] In an electric supervisory system, the supervisory signals are sent over the normal telephone lines, a transmission from the sub-station being initiated in response to the normal telephone call signal and being transmitted without appreciable delay. The signal may take the form of ring-back tone, the pulses first identifying the connected station and then indicating the condition or position of the various equipments thereat. In addition, the sub-station may initiate a telephone call to the main station if a unit at the sub-station changes its position. In the embodiment shown in Figs. 1 and 2, when the station is left unattended the telephone lines L1, L2 are connected to the ringing relay RR. The receipt of ringing current energizes relay RR so that relays GA, GAA, GB, GBA, GC, GCA and RP energize quickly in turn and then commence to fall away slowly. When relay GA falls away battery is connected over relay A to the supervisory switch of circuit breaker X1. If this is in the upper position the 1m.f. condenser shown is charged and a surge occurs in the lower winding of A so that a noise or acoustical bang is heard at the receiver. If the circuit breaker had been open, the switch would have been in the lower position and relay A would have energized to complete a self-interrupting circuit for relay TR and a tone frequency would have been connected to line. The circuit to relay A is broken when relay GAA falls away. After an interval relay GB releases connecting relay B to allow the condition of circuit breaker X2 to be indicated in a similar manner to that described for circuit breaker X1. The condition of each circuit breaker is transmitted in turn and when the last indication has been transmitted relay GCA falls away but during the slow period of relay RP relay GAAGCA re-energize. No circuits are however completed for relays GA and RP. The indications are now sent a second time in a manner similar. to that described above and when relay CCA finally releases the circuit returns to normal condition ready for another call. An alternative arrangement is shown in Fig. 3 in which the line is a party line connected to a private automatic exchange. When a call to the sub-station is made the battery connection is reversed and relay HR responds. The pendulum vibrator RV is energized and relays PA and PB interact to step switch SM. As wiper sm3 passes over the earthed contacts in its bank, relay RN is energized and the sub-station bell is rung in the normal way. Relay S is energized and as wiper sm1 engages earthed terminals relay TR induces ringing tone in the line, the wiring to bank sm1 being such that the code number of the sub-station (35 as shown) is transmitted. When wiper sm4 reaches its last terminals, relay SW is energized so that the ring-back circuit is changed over from sm1 to sm2. Contacts bra2, brb2 &c. are controlled by circuit breakers, so that the ring back signals now comprise either 2 dots or a dash for each circuit breaker thus indicating whether the breaker is in or out. When wiper sm4 reaches its penultimate contact the second time relay S is short-circuited so that relays S and SW release in turn. Relay S then re-operates and the cycle is repeated. If the call is not answered, the cycle is repeated until the calling party clears. If the call is answered relays F and FF pull up. Relay HR is replaced by a low resistance loop at 12 and the battery feed is reversed at the far end so that Q energizes and switches the line through. Relays HR, RV, PA, PB, SM, S and SW release and the circuit returns to normal. If a switch changes over a signal is sent to the main station. When contacts such as bra1 change over relays FA and FB energize as described in Specification 460,903 and relay FR energizes and locks. Relays F and FF pull up to connect relay Q across the line and relay Q operates. Relay F releases and L energizes. Relays PA and PB interact to step switch S. Relay S operates. When the switch reaches positions 6, 8, 10, 12 and 14 relay IS is energized over sm4 and a train of five impulses is sent to the main office. The battery feed at the main office is then reversed and D energizes to open the circuit of PA so that the switch stops. This is to allow the valves at the main office to warm up. After a predetermined time the battery feed is returned to normal so that D releases and S continues to step. A train of nine impulses is now sent by relay IS to give a continuous ring signal at the central office. When switch S reaches position 41 relay Z energizes and all the energized relays except X and FR release. The attendant must now ring each station in turn and when he rings the station which sent the alarm, contact fr4 being closed, a long burst of tone follows the transmission of the code number. Key RK must be released before relay FR falls away.