453,699. Fire, police, and like alarm systems. DENZLER, F. F., Pomona, California, U.S.A. Dec. 8, 1934, No. 34230. Convention date, Dec. 8, 1933. [Class 40 (i)] In a fire or burglar alarm system wherein operation of a protection circuit at a substation operates a signal transmitter at a central station for sending a signal of the locality of the affected substation to a fire or police station, the circuit between the substation and the central station for controlling the signal transmitting means comprises a pair of line conductors bridged at the substation by a protection loop and being associated at both the substation and central station with transfer means which upon a break occurring in either line conductor transfers the protective loop into an earth return circuit including the sound conductor. Fig. 1 shows a layout of the entire system, protection loops L being provided at a plurality of premises, each of which is connected to a central station CS by a separate pair of lines SL. A code transmitter T is provided for each of the premises and is associated with a line finder LF which is adapted to hunt for a free line HL connecting the central station to alarm apparatus AR at a fire or police station SD. The protection loops L at the premises are normally energized so as to facilitate the indication of faults. Fire-alarm system, Fig. 2. The protection loop 11, 12 at the premises includes a resistance 24 and relays 0, 1, 2 and is connected in series over the line wires X, Y with relays 3, 4, 8, 7 at the central station. Relay 7 is slow to release and maintains relay 6 operated to prevent operation of the code transmitter T. Relay 2 is slow releasing and relays 0, 3, 4 are marginal. Fire responsive contacts 13 are connected across the loop 11, 12 and upon operation, resistance 24 is short-circuited to increase the current strength and operate relay 0 which is locked up at the latch 17 and opens the loop circuit. Relay 8 is released and at its back contacts connects battery over relay 7 to the line conductors X, Y in parallel but as relay 0 is locked up the circuits over X, Y remain open and relay 7 is allowed to fall back to release relay 6 and thereby initiate operation of the code signal transmitter T. Operation of system under fault conditions. (1) In the event of an accidental opon-circuit in either line X or Y, relays 1, 8 are released, the latter applying battery at the central station to the XY lines in parallel and the former connecting earth from the back contacts of 0 to the sound line so as to maintain the relay 7 operated and thereby prevent operation of the transmitter. Operation of an alarm contact, however, brings about the operation of marginal relay 0 so as to open the sound circuit and effect the release of 7. (2) If an open-circuit occurs in either leg of the premises loop 11, 12, relays 1, 8 are released, the relay 1 at contacts T<1>, B<1>, T2, B<2> providing short-circuit paths across each leg of the loop. Thus an auxiliary loop is formed including resistance 24. (3) A short-circuit across the line wires X, Y brings about operation of relay 3. Line Y is thus isolated at both ends while the release of 8 maintains a circuit over relays 7, 4, 2 over line X and loop 11, 12 to the earth at the back contacts of 0 to facilitate signalling. If inadvertently relay 4 pulls up on this short-circuit an alternative circuit round the relay 4 is provided at the contacts T<3>, F3 of relay 3. (4) In the event of an earth on lines X or Y, relays 1, 8 or 8 are shunted out so as to cause a normal current flow over the unearthed line and thereby facilitate operation of the transmitter T if necessary. (5) Signals may also be transmitted under fault conditions brought about by an earth on either loop wire 11, 12. (6) In the event of open-circuits on both line wires X, Y, a fire alarm is transmitted. Earths on both line wires, however, maintain relay 7 operated to prevent release of the transmitter. Upon occurrence of a fault a trouble relay 10 normally energized over back contacts of relay 8 operates a buzzer 20 and alarm lamp B. A lamp L is lighted in addition to B when a fire alarm is transmitted. Restoration of equipment to normal. The relays at the central station and the premises are reset upon operation of keys A, Z respectively. Modified fire-alarm system. In a modified loop circuit, the marginal relay 0 is connected directly to the loop conductor 12 and the shortcircuit paths around each conductor 11, 12 are completed respectively at back contacts of relays 1, 2. Burglar-alarm system. In a system adapted for burglar-alarm purposes, the loop 11, 12 is opened instead of being short-circuited, the relay 0 is omitted and an additional marginal relay, connected in the lead between battery 18 and relay 4, is provided at the central station. The system operates in a manner similar to that previously described except that an alarm is given upon the occurrence of a fault. The additional relay at the central station effects the release of the transmitter upon the occurrence of a short-circuit on the loop conductor or earth upon both line conductors. Under certain circumstances, viz. a short on lines X, Y, an open-circuit or earth of either line wire the system will give a trouble indication and restore the line into condition to transmit a bona fide alarm. If it is desired to render the system proof against the surreptitious connection of a resistance bridge across the line with the object of maintaining relay 8 operated whilst the loop circuit is opened, a slow release relay is used instead of the resistance 24 to effect the release of the alarm transmitter. Restoration to normal of burglar alarm system. The relays at the central station are restored by a special key and a further key is provided which is adapted to connect alternating current alternately to the line wires X, Y to pull up the relays 2, 1 at the premises. Burglar alarm system. Day and night operation. The protection loop is divided into two sections, one of which may be cut out of circuit during the day bv a key which when operated maintains the alarm relays operated to prevent transmission of an alarm and inserts into the loop signalling circuit a relay which is released to give an alarm when a key at the premises is operated to open the circuit. Alarm code transmitter and line finder action, Fig. 9. The code transmitter is driven through gearing by a spring motor 50 and is released for operation when relay 6 is released to deenergize magnet 65 which allows the armature 66 to drop back and remove the detent 63. The code cam 56 is rotated through a plurality of turns for each revolution of a cam 52 which controls contacts 86, 87 which short-circuit the signalling contacts 56B, 56T when the follower 85 is on the depression of the cam 52. This period of short-circuit allows time for the line-finder to hunt for a free line leading to the fire or police station. The line-finder is normally inactive but hunts when the circuit through the transmitter is completed, hunting taking place until the test wiper 93, Fig. 8, engages a free (unearthed) line contact 90. A coding relay 96 individual to the fire station line is in series with a battery 99 and following the opening of the short-circuit at 86, 87 code impulses are transmitted to operate relay 96 which operates the alarm recorder relay 105 at the headquarters. After a plurality of revolutions, a pin 82 in the cam 52 opens contact 83, 84 to insert a relay 73 into the loop. Relay 73 attracts armature 72 which through lever 68 operates contacts T<2>, B<2> to open the circuit and release 73. Armature 70 is retained by latch 75 and when the projection 77 engages 76 the latter is moved to the right and operates bellcrank 81 into the path of projection 62 to stop the mechanism. When the protection loop circuits are restored and relay 6 is re-energized, magnet 65 is operated to attract armature 66 and allow 70 to drop. This causes the restoration of 81 and the mechanism moves through a short distance into its starting position. Faults on fire station transmission loop. Normally a loop circuit is closed over recorder relays 103, 105, marginal relay 102 and sensitive relay 101. In the event of a short, open circuit or accidental earth on line wires 106, 107, relay 102 causes operation of alarms 110, 111 and applies a " busy " earth potential to the test contact 90.