300,927. Jackson, L. Mettersh-, (Siemens & Halske Akt.-Ges.). May 18, 1927. Fire-alarm systems and apparatus.-Relates to fire-alarm systems in which means are provided for preventing interference when several alarms are set in action simultaneously or in short succession after one another and in which an earth connection is made at each alarm before its code signal is transmitted. Fig. 1 shows the circuit arrangement for ten alarm boxes, (one of which is shown in detail) connected by a common loop line to each side of the central station battery, the mid point of which is earthed. Construction of alarm box. A code wheel 52, adapted to control the signalling contacts 44, 45 is driven by clockwork through a train of wheels, the wheel 9 of which is normally locked by a stop 6 on a lever 2 held in locking position by a release lever 4 which may be operated manually or electromagnetically. The lever 2 is under the influence, of electromagnets 70 - - 73 which are adapted to be inserted in the line circuit after the release of the alarm and is operated thereby only upon the transmission of an increased current upon termination of an alarm. The lever 2 carries a projection 68 and a pivoted and spring controlled angle-shaped member 32, Fig. 4, having a pin 31, the pins 31, 68 being adapted for co-operation with a cam 42, a channel 50 and an annular cam surface 56 on a control disc 51 which is rotated simultaneously with the code wheel. A lever 2a, adapted to be operated by the electromagnets 70, 71 upon passage of current of normal strength and also by the magnets 70 - - 73 when excited by current of normal or increased strength, co-operates with the pin 31 to facilitate stopping the alarm in the event of the signalling line being busy or to allow the alarm to deliver its signal. The lever 2<a> also controls the position of a pivoted lever 23 which carries a pin 22 operated by a cam surface 24 having a depression 39 and in turn controls the position of a pivoted lever 16 which controls contacts 18, 19, 20 adapted upon normal operation of an alarm firstly to insert into the line circuit the electromagnets 70, 71 and secondly to insert the magnets 72, 73 and simultaneously connect the alarm to earth. The lever 16 also is controlled by cam surfaces 17, 40 on a segment 35. Normal condition of line circuits.-If the loop is intact, current from the central station battery flows over a circuit including resistance 84, line relay 85 at the central station line 86 contact 18 of the first alarm, line 74, contacts 18 in alarms 1 - - 9, line 76, and relay 82, rest current instrument 104 and resistance 83 at the central station. Normal operation of one alarm. When the release lever 4 is operated the lever 2 is raised by spring 48 and the projection 6 releases the pin 7 of the wheel 9. The clockwork is thus released to drive the code wheel and the associated control discs. The release lever is locked in its operated position by a lever 10, 55. As the segment 35 is rotated the pin 15 drops on to surface 40 and allows contact 18 to open, the contacts 19, 20 being maintained in their normal conditions i.e. " closed " and " open " respectively. The contact 18 thereby removes the short-circuit and inserts the coils 70, 71 in the line circuit. The lever 2a is attached and comes to lie with its surface 30 in engagement with the pin 31 to lock the angle-shaped member 32 against rotation. Simultaneously the pin 32 on the lever 23 drops into the recess 39 and allows the lever 23 to assume a vertical position with its pin 26 under the pin 27 on the lever 16 to prevent for a time further falling of the lever 16. Upon further rotation the surface 37 of the cam 42 engages the pin 31 and depresses the lever 2 so far that the stopping projections 6, 8 are moved below the pin 7 and further rotation is allowed and the lever 23 is again moved to the left to allow the lever 16 to drop and thereby remove the short-circuit of the magnets 72, 73 at the contact 19 and close the earthing contact 20. The pin 31 continues to engage the outer surface of the cam 42 and finally engages projection 41a at which time the pin 68 is beyond the gap 49 and is allowed to fall on to the external rim of surface 56 thereby allowing the code wheel to complete its rotation and send its signal. The signalling impulses are transmitted over both sides of the loop from earth to the alarm box. Near the completion of rotation the arm 54 operates the levers 10, 55 to unlock the release lever 4 and the pin 68 moves off the surface 56 and allows the lever to rise and stop the clockwork. Preventing interference. - In the event that several alarms are released simultaneously, the levers 2a of the operated alarms will at first be operated. Earthing at the extreme alarms i.e. the alarms nearest the central station, causes short-circuiting of the intermediate alarms and therefore the release of the levers 2a on those alarms. According to the time at which an intermediate alarm, relative to an extreme alarm, is released the intermediate alarm is stopped in one or other of two positions. If the lever 2a on such an alarm is released prior to the establishment of the earth connection at this alarm, the mechanism is stopped when the pin 36 of the lever 23 is below the pin 27 on the lever 16. This is accomplished by the action of the cam 42 on the pin 68 to depress the lever 2 so that the projection 8 lies in the range of movement of the pin 7. The pin 31 on the -member 32 is rotated by the cam 42 and thus remains ineffective owing to the release of the lever 2a. If however the lever 2a is released after the earth connection is already established, removal of the lever 2a from engagement with the pin 31, allows the member 32 to pivot and the pin 68 is allowed to move into engagement with the cam 42 and the clockwork is stopped by the engagement of the pin 7 with the projection 8. When the lever 23 is vertical and the alarm is locked in the first position a pivoted hook 36 is moved beneath a pin 60 on the lever 2a to prevent operation by current impulses from other running down alarms. At the termination of the previous signal an impulse of strengthened current is transmitted to cause operation of the lever 2 until the pin 68 is beyond the gap 49. This lever releases the pin 7 and the alarm is operated to deliver its signal. If an alarm in a short-circuited group is pulled the lever 2a remains unattracted. A pin 29 on the lever co-operates with a pin 28 on the lever 23 to prevent the lever 23 from assuming a vertical position. In this manner the alarm is earthed and is locked in the first stopping position. In the event of the operation of two alarms in quick succession, the subsequently operated alarm is stopped in an unearthed position. If after the transmission of the first signal and the subsequent release of the second alarm, the latter is short-circuited by another alarm, the pin 68 is moved through the gap 49 and runs in the groove 50, the lever 2 being held so that the pin 7 is below the stop 6 to permit rotation. The alarm thus rotates without transmitting its signal until the pin 68 slides out of the proove 50 and is lowered to stop the clockwork. Upon termination of the third signal the second alarm is again released and its signal is sent. When the pin 68 runs in the groove 50, the release lever 4 remains ineffective at the end of the rotation and the lever 2 after leaving the groove assumes the same position that it occupies after the . first release of the mechanism. Operation in the event of wire breakage. In the event of wire breakage the signalling circuit extends from earth and through the uninterrupted part of the loop circuit. When an alarm is released, the lever 2a is attracted to permit running when the alarm is earthed. When several alarms situated to one side of a wire breakage are released interference, between the signals is prevented in a manner similar to that previously described. Central station apparatus. A momentary increase in the line current is produced to release subsequently operated alarms by the operation of a slow-acting relay, such as 118, which is responsive to a final long impulse transmitted by the alarm in action. During impulsing the relay 119 is operated and locked and upon the transmission of the final impulse the relay 118 is operated to short-circuit momentarily the resistance 84 and thereby increase the line current. Similar apparatus is associated with the line relay 82.