Patent GB-325530-A (GB)
Title: Improvements in or relating to electrical signalling systems
IPC: G08B25/00
Filed: 1928-10-18
Abstract: 325,530. Automatic Telephone Manufacturing Co., Ltd., and Burns, G. A. Oct. 18, 1928. Fire, police, and like alarm systems.-Relates to an electric signalling system wherein alarm call stations are connected in loop circuits which are connected to district stations serving a single central station. Hunting switches provided at the central and district stations facilitate the use at those stations of common registering apparatus for recording any particular call. Fig. 1 shows a district station serving two loop circuits LP1, LP2 in which are connected a plurality of alarm stations e.g. a - - h. Fig. 2 shows the central station apparatus. Alarm call stations. Each station on an alarm loop employs transmitting apparatus of known type wherein when a signal is transmitted the normal loop circuit is interrupted in accordance with the characteristic code. Electromagnets normally short-circuited are switched into the loop circuit and prevent interference. when several alarm call boxes are operated simultaneously. District station apparatus. Each district station has a hunting switch HS, the contacts of which are associated with the various loop circuits entering the station. When a call box is operated, the switch HS hunts for the contacts associated with the operated alarm loop and associates the common registering apparatus PR with the line relay of that loop to effect a record of the transmitted signal. Central station apparatus, Fig. 2. The district stations are connected to the central station by individual loop circuits e.g. 122, 123 which are associated with a hunting switch CHS, which when an alarm is transmitted hunts for the effected district loop and thereby connects the common registering apparatus CPR to a repeater in the district station. The central station also may cater for ordinary alarm loop circuits e.g. CLP1. Signalling to a district station. In the normal condition each loop forms a closed circuit e.g for the loop LP1, from battery BT1, relay AL1, alarm boxes a - - h, Delays T1 L1 back to the battery over contacts i1, 16, 12. In the event of operation of an alarm box, the loop circuit is broken and the line relay L1 is de-energized to operate a delay-anting relay S provided no call is being transmitted from another loop e.g. LP2. Relay T1 also is de-energized to operate an alarm bell relay AT1. Relay S at its contacts 114 closes the circuit of the stepping magnet DM of the switch HS, over wiper 119 and stepping proceeds under the control of the self-interrupted contacts 116 until the wiper engages a contact associated with the calling loop and from which potential is removed owing to the de-energization of the corresponding line-relay. The contacts of the wiper 119 are marked by the various loop circuits over contacts, such as 61 of the line relay L2, and stepping proceeds until the wiper co-operates with the dead contact of the calling loop. When the calling loop is found a short-circuit for the relay K over contact of wiper 119 is removed and the relay operates in series with the stepping magnet DM which deenergizes owing to the high resistance of the relay K. During the progress of the call, the relay K maintains open the circuits of relay S and stepping magnet to prevent interference due to the initiation of a call in another loop. Relay K also energizes relays I, A, SO and illuminates a line supervisory lamp LS1 over wipers 119, 117. Relay I controls the operation of the district station register PR and gong G under the control of the contact 24 of the line relay L1 so that line interruptions in accordance with the code transmitted are recorded. Relay I also operates contacts i1, i2 individual to the various loops so as to open the unaffected loop circuits and thereby prevent the transmission of calls therein during transmission in the effective loop, the contact i1 of which is bridged over the wipers 120, 121 of the switch HS. Relay A causes operation of relays B, C which provide a locking circuit for relay K. Relay SO is slow acting and is operative only upon faulty operation of the system. Operation in the event of breakage of an alarm loop circuit. In the event of a break, e.g. in loop LP1, line relay L1 is de-energized and the switch HS is driven to find the affected loop. The relay SO is energized in the manner previously described and since relay L1 remains de-energized relay SO becomes operative and energizes relay LBR1 over wiper 118. Relay LBR1 locks up and operates individual " line break " lamp LBL1, and common lamp GLBL. Relay SO also energizes relay ER1 which earths over terminals of the battery BT1 and connects the other terminal to both ends of the broken loop. Relay LBR1 die-energizes relays SO, A, B, C to restore the common equipment to normal ready to receive a call from any loop. If a call is transmitted from a box to the 'right of a break, the signals are transmitted over the unbroken portion of the line and earth return to energize relay T1, L1. Relay L1 releases relay LBR1 and the signals are recorded by contact 24 in a manner similar to that previously described. When the call is completed relay L1 remains de-energized to allow relay 80 to again operate relay LBR1. Signals transmitted from boxes on the left of the break, operate relay AL1 which controls a register APR. In order to prevent battery wastage due to continued operation of relays ER1, LBR1 in the event of a breakage, the key LBE1 may be operated to release those relays and effect circuit changes which still facilitate signalling. The key comprises contacts 11 - - 15, 28 - - 37. The contacts 11 - - 15 earth the battery and deenergize the relay ER1, whilst contact 37 opens the locking circuit of relay LBR1. As soon as relay L1 is operated in response to a signal over the broken loop relay LBR1 is operated over contact 25 and locks up. Due to the operation of the key similar marking conditions for the switch HS are ensured although the effective condition of the line relay L1 is energization instead of de-energization for normal working. When the hunting switch engages the appropriate contact, a circuit is completed for relays I &c. over the operated contacts of the relay LBR1 and key LBK1 and registering is effected due to the intermittent operation of contact 24 in a manner similar to that for normal operation. Repeating signals to central station. The loop circuit from the district station, Fig. 1, to the central station is normally closed from battery CBT2, relays RAL1, PP, contacts 94, 99, relays DT, RT1, RL1. The code signal from the operated alarm box is, repeated by relay I which at contact 94 interrupts the district loop. The initial interruption of the loop causes de-energization of the line relay RL1 which operates relays CS to cause the switch CHS to hunt for the contact associated with the calling district loop. These operations are similar to those described in connection with the switch HS. The initial loop interruption also effects operation of alarm relay RAT1 and allows contact 99 of relay DT to open and insert resistance R in the line circuit to prevent re-operation of relay DT when the loop is again closed. Due to the intermittent closure of the loop circuit the relays RL1 operates relay CI, in a manner similar to that of relay I, to control the register CPR and gong CG. When the calling loop is found, relay CK is energized and a relay KR is operated to mark the hunting switch contacts corresponding to alarm loops directly entering the central station e.g. the loop CLP1, to provide supervision in the case of a further call while a call is incoming over loop 122, 123. In such an event operation of a relay, such as CL1, closes a circuit for relay TO over lamp CLS1, the relay TO being effective only provided a parallel circuit is completed over lamp RLS1 and wiper 319 of a loop which is already effective. Relay TC operates a " twocall " lamp TCL. In order to prevent repetition of signals from a district station to other district stations a relay SC is operated to shunt the contacts ci1 &c. of relay C1 in the district loops at contacts 331, 332, 333. Repeating signals of alarm loops local to central station to district station. Upon operation of relay CI in the central station in response to an alarm in the loop CLP1, contact ci1 interrupts the district loop and intermittently operates relay PP which operates the recorder PRC. Interferenoe with this signal by an alarm originated in loops, such as LP1, is prevented by contact 95 of relay RC which remains de-energized if the loop 122, 123 is in use when relay S operates. Breakage of district loop. The operations which take place at the central station when a break occurs in a district loop are similar to those described in connection with Fig. 1.