377,437. Fire and like alarm systems. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. July 29, 1931, No. 21686. Convention date, July 30, 1930. [Class 40 (i).] Relates to a signalling system more particularly a fire alarm system wherein the impulse transmitters of a plurality of substations are connected by a common loop circuit to a central station and are arranged so that in the event of simultaneous operation of two transmitters, the separate signals are transmitted over opposite sides of the circuit and earth return, and furthermore if a third transmitter is operated during a simultaneous transmission the signal is automatically withheld ready for sending when the prior signalling is completed. Fig. 6 shows code transmitters M<1> .. M<5> connected in a loop line circuit to a central station provided with receiving devices 77, 78 and a battery 79, the midpoint of which is automatically earthed in known manner when a signal is received. Construction of code sender, Figs. 1, 2 and 3. Figs. 1 and 3 show the apparatus mounted on each side of a common baseplate, Fig. 2, showing only the elevational view of the gearing shown in Fig. 1. The transmitter is driven by a spring 1, Fig. 3, which is wound by hand through a spindle 2. During winding a toothed wheel 5 is moved to bring a pin 6 into engagement with one arm of a lever 7 the other arms of which co-operate respectively with a notch 30 in a wheel 29 on a spindle 24 which carries the impulse wheel and a notch 17 in the locking disc 13 of a gear train 8 .. 11 which by means of escapement mechanism 14, 15 effects regulation of the running down of the spring 1. The disc 13 is normally locked by the engagement of one end of a lever 19 with a notch 16, the other end of the lever being controlled by a release electromagnet 22 and adapted to co-operate with a notch 26 on a disc 25 on the shaft 24. A pivoted sector 27 is arranged to rotate and prevent re-engagement of the lever 19 in the notch 26 after the lever is depressed by the armature 23 of the magnet 22 and thus ensures release of the apparatus even though the excitation of the magnet 22 is not sustained. When the apparatus is released by operation of the magnet 22, the spring 1 drives differential gearing 31, which effects the driving of the shaft 24 through a wheel 32 and a wheel 34, Fig. 2, through a gear 33. A locking-disc 35 is mounted on the shaft of the gear wheel 34 and co-operates with a lever 36, Fig. 1, controlled by a pin 39 on a disc 40 mounted on the spindle 24. The gear wheel 34 drives wheels 41, 42 which, through a change-over gear 45, effects the rotation of one or other of the discs 48, 49. The wheel 45 is mounted on a pivoted lever 52, Fig. 1, having a pin 57 normally engaged by the armature 55 of an electromagnet 56 which is adapted to control the operation according to whether other. transmitters are already in operation in the line circuit. The disc 48, which is spring controlled, controls a lever 58 which closes a contact 60 when the lever drops into a notch 61 to lock the disc, the lever being reset by a pin 62 on the disc 40. The disc 49, also spring controlled, controls a lever 63 which norma,lly locks the wheel 40 and impulse wheel 70, unlocking being effected when the step 66 engages the lever. Simultaneously with unlocking by the step 66, a step 67 operates contact 68. Operation of system upon release of single transmitter. The transmitter is released by operation of electromagnet 22 which rocks lever 19 and unlocks the gear train 8 .. 13 and thereby releases the driving spring to effect the drive of gear wheel 34. Lever 19 also opens contact 21 which removes the shortcircuit across electromagnet 56 to switch the latter into the line circuit. Magnet 56 is consequently energized and the lever 52 is released to bring the change-over gear wheel 45 into engagement with wheels 44, 47. The disc 49 is then rotated counterclockwise and after an interval step 66 releases the impulse wheel 70. Contact 68 is simultaneously closed to earth the impulse contact 71. After small rotation of the impulse wheel pin 39 releases lever 36 which drops into a notch in a disc 35 to lock the wheel 34 against further rotation but allow further operation of the impulse wheel. During rotation of the impulse wheel, a characteristic code of impulses is transmitted over the line 75 by interruptions of contact 72. Upon the first interruption magnet 56 is deenergized and wheel 45 restores to normal, the disc 49 being restored under spring-control. The earth connection which is removed by restoration of contact 68 is maintained by contact 81 controlled by the impulse wheel until one revolution thereof is completed, whereupon one arm of the lever 7 drops into the notch 30 of disc 29, Fig. 3, and allows the other arm to engage notch 17 in locking disc 13 to prevent further operation. When the mechanism is reset for further operation by manually winding the spring 1 the toothed wheel 5 re-engages the pin 6 with the lever 7 to remove the locking arm and thus prepare the apparatus for further release by the magnet 22. Simultaneous signalling by two transmitters. When two transmitters are released, individual codes are transmitted over the corresponding sides of the line circuit and earth return since contacts 68 are operated substantially simultaneously at both transmitters to provide the necessary earth returns. Operation when more than two transmitters are operated. In the event of the operation of a transmitter intermediate of two operative transmitters, the operating mechanism is released in the manner previously described, but the magnet 56 remains de-energized by reason of the short-circuit produced by the other two transmitters and the upper disc 48 is driven until lever 58 co-operates with notch 61 to lock the disc against further rotation. The impulse disc remains locked but the contact 60 is closed to prepare the signalling circuit. When one of the operative transmitters ceases sending the contact 81 is opened and the shortcircuit is removed to allow energization of winding II of magnet 56 to the prepared earth at contact 60 of the third transmitter. The gear 45 is thus moved into engagement with the wheel 44, 47 and the control disc 49 is driven to effect release of the impulse wheel 70. If a third transmitter located nearer the central station is released during the simultaneous transmission of two transmitters, the magnet 56 is intermittently energized by the signalling impulses to oscillate the gear wheel 45 at a rate sufficient to render the discs 48, 49 ineffective and thus prevent release of the impulse wheel until signalling is completed and the line circuit is re-established. Specification 5623/15, [Class 40 (i), Electric signalling systems &c.], is referred to.