629,314. Fire, burglar and like alarm systems. ERICSSON TELEPHONES, Ltd., DRYSDALE, L. H., and STEVENS, J. R. H. Feb. 28, 1947, No. 5809. [Class 40 (i)] In a burglar, fire or like alarm system comprising a plurality of stations connected over a common line to a control point, each station is adapted to transmit to the control point alarm and non-alarm signals of a plurality of different kinds, and means are provided for recording the kinds of signals sent and the particular stations sending them. A distinctive operation at any one of the plurality of stations causes an alarm signal to be sent to the control point if the operation occurs during a particular period, but not otherwise, and means are provided for sending non-alarm signals indicative of the said particular period for a particular station from the latter over the common line to the control point. The apparatus at the control point is arranged to ignore any non-alarm signals while any alarm signal awaits attention. The invention is described with reference to a system in which a number of sub-stations are connected in parallel to a central station. Figs. 1 to 5 represent the circuits at the central station and Figs. 6 to 10 the circuits at one (No. 4) of the sub-stations. General operation. In the system described, in which a number of sub-stations share a two-wire line, each sub-station is provided with a fire alarm circuit, a burglar alarm circuit and a hold-up alarm circuit, these circuits being associated with a particular position of a uniselector V, the position being different for each sub-station. Each alarm circuit has two signalling conditions, one for giving an alarm and the other concerned with setting or re-setting. When any circuit is in a signalling condition, a uniselector Z at the central office is stepped simultaneously with the switches V at all the sub-stations. If any circuit is in an alarm condition, this operation proceeds until the position of a station giving an alarm signal is reached, whether or no earlier stations are giving non-alarm signals. If there are no alarm signals, the switches stop when the position of a station giving an ordinary signal is reached. A further uniselector Y then interacts with a couriting chain PA ... PE at the selected sub-station to ascertain the nature of the signal and finally lamp signals are given identifying the station and the signal and a printed record is made of these particulars. Setting sub-station circuits. A momentary operation of key KA, Fig. 8, leaves FA locked over a fire protection circuit and holding a sluggish relay AF and a momentary operation of key KB, Fig. 9, leaves AL locked over a hold-up protection circuit and holding a sluggish relay AC. This is the normal day and night condition of the circuit. Completion of a burglary protection circuit BCD, Fig. 10, energizes LA, which energizes AA. When the main door is locked, CY is operated, leaving LA dependent on its holding circuit over the protection circuit BCD, and AA dependent on its holding circuit over the main door contact BCA and on LA. CT also energizes AB, which energizes and is then held by S which also grounds wire L1, Figs. 6 and 7, to signal the central station. The latter, as explained below, energizes CB, whereupon S falls and a lamp LPD outside the main door, which was lit on the initiation of the signal to the central station, is extinguished. Signalling an alarm condition. If the protective contacts BCA, BCD are opened, AA is unlocked, directly or by the relapse of LA, an releases AB. Similarly, if the fire protection circuit is interrupted FA releases AF and if the hold-up circuit is broken AL releases AC. In all cases S is energized and grounds L1 to signal the central station, and EX is energized and ground is connected to L2 in the even positions of a uniselector V which as a result of the signal over L1 is stepped on under control of the central station, as described below. The central station subsequently releases CB or energizes CC or CE to release S, EX. Identifying calling sub-station. The grounding of L1 by relay S whenever a signal is sent unbalances DR at the central office, Fig. 5, to energize MC which, provided the switches X, Y, Z are normal, as indicated by the fact that N is operated, energizes CO which locks, releases MC and energizes XS, Fig. 4, which energizes TA, Fig. 3. Ground and battery are thus connected to lines L1, L2 to operate the central office line relay ZA, and all the substation line relays A. ZA is followed by ZC, ZB, the latter operating in series with stepping magnet Z and relay PZ, which are unable to operate in this circuit, and the relays A are followed by their relays C, B. PU also operates, locks-up and reverses the feed to the line so that A, ZA (which are polarized by rectifiers) fall back. As a result, the stepping magnet V at each sub-station operates, releases C and falls back to drive its wipers and the stepping magnet Z at the central office operates, releases ZC and then falls back to drive its wipers. ZC, on falling, energizes the stepping magnet X of a further switch which moves one step by selfinterruption and substitutes TB for TA. PU is thus unlocked and CA is connected to line wire L1, which is still grounded at the calling sub-station, and energizes stepping-magnet X which drives its wipers by self-interruption to position 3, in which TC is substituted for TB. TC connects AS, which is connected to reverse battery, to wire L2, which is grounded (if the signal is an alarm signal) by EX at the substation so that AS operates and locks up. In any event, X is stepped on to position 4 either by the operation of AS or the relapse of TB. In this position, TA again operates the central station and substation line relays ZA, A and the switch Z and all the switches V take another step as before. The relapse of ZC as before initiates the stepping of X which in position 5 energizes YS. TE is thus operated and connects LL to line L1. Each sub-station has its signalling wire W5 connected to a characteristic position in its bank V1 and accordingly if the sub-station represented by the present position of switches Z, V is calling, ground is connected to L1 over a high or low resistance according as the condition of the station is merely signalling (set or reset) or alarm signalling. If this station is not calling, LL remains inert and the relapse of PU when TA falls initiates a new cycle of 5 steps by X controlling 2 steps by Z, V, to test the next sub-station. When the calling sub-station is reached. LL pulls up, energizing LR, and the relapse of PU does not cause X to step unless another station has priority. Z remains in its set position and indicates the calling sub-station by lighting a lamp LPP ... LPQ. Priority of alarm signals. If any of the sub-stations is in the " alarm " condition, AS is energized. When LR pulls up in the position of a calling sub-station, it substitutes the marginal relay H for the sensitive relay LL, Fig. 2, and if that sub-station is in an alarm condition H pulls up and the stepping of X is prevented. If, however, H fails to pull up when AS is energized the relapse of PU starts a new cycle of X and Z. Identifying nature of signal. The operation of LR if AS is not operated or the operation of H if AS is operated, steps a third switch Y off normal to release TE and energize TD which connects reverse battery over KO to line wire L2 to energize XA, Fig. 7, at the sub-station over high and low resistance windings in series. XA energizes the first relay PA of a counting chain PA ... PE and PA locks up and shunts the high resistance winding of XA to enable KO to operate at the central station and cause Y to take an automatic step to its 3rd position in which TD is disconnected and TF is operated, and connects LC to line L1. L1 should be disconnected at this time and if LC operates, further stepping of Y is prevented and an alarm is given as referred to below. On the relapse of TD, Y makes an automatic step, KO is disconnected and the distant relay XA falls operating ST which locks up and removes the shunt from the high resistance winding of XA. In position 4 of Y, TD re-operates, the next counting relay PB is energized, releases PA and causes Y to take an automatic step to position 5 in which TE re-operates and connects LL to the wire L1. If the fire alarm circuit is signalling, L1 is grounded over resistance YLA or YKA according as the signal is an alarm or re-set signal, and LL pulls up, energizing LR which substitutes the marginal relay H for LL. FH or FL is thus energized according as H does or does not pull up, locks itself, selects a characteristic lamp and causes Y to step on to position 6. If neither relay operates, Y is stepped on in a circuit over Y3. In position 6, TD reoperates, the next counting'relay PC is operated and switch Y is stepped to position 7 in which the condition of the hold-up circuit is tested in the same way. If it is signalling, CH or CL is energized. In any event, Y is stepped on to position 8 in which PD operates and then to position 9 in which the burglar alarm circuit is tested in the same way as the other circuits. If it is signalling, BH or BL is operated and if not, OF is operated. In any event Y steps on to position 10, the last counting relay PE is energized and Y is stepped to position 11. If the fire alarm circuit is in the alarm condition (AF de-energized) the operation of PE energizes CE. If it is in the re-set signal condition (AF and CE both energized), the operation of PE shunts out CE to complete the re-setting. A similar action takes place with relay CC of the hold-up circuit. In the case of the burglar circuit CB is energized if the circuit is in the " on " signal condition and de-energized if it is in the " off " signal or alarm condition. As a result, S falls back and again shunts the high resistance winding of XA to cause Y to step to position 11 in which SF is