Patent GB-630734-A (GB)
Title: Improvements in or relating to burglar and fire alarm systems
IPC: H04M11/04
Filed: 1946-07-25
Abstract: 630,734. Burglar and fire alarms. SAGAR, E. N. July 25, 1946, No. 22214. [Class 40 (i)] [Also in Group XXXIX] In a burglar and fire alarm system wherein the alarm switches at a premises are series connected in a normally energized two-wire circuit extending to a supervisory station, a fire alarm causes a recurrent visual and, or aural signal at the station in contradistinction to a burglar alarm which produces a steady signal, and the location on the premises of the alarm point is indicated selectively by the recurrence frequency for fire and the steady current intensity in case of burglar alarms. Protected premises circuit arrangements, Fig. 2. The line 1 from the supervisory station extends serially over a spring-loaded calling switch 56, a visual indicator 59, fire alarm switches 65, terminals 66, 69, 68 and burglar alarm switches 67 this series circuit being normally energized from the supervisory station in the sealed condition. Should a fire alarm switch 65 between terminals 60, 66 be actuated, the normally short-circuited relay 70 is connected in the line circuit, and by self-interruption at contacts 72 produces a recurrent signal in line 1, the signal frequency depending on the value of condenser 74. Further fire alarm switches connected in the series circuit, e.g. across terminals 66, 69 or 69, 68 in place of the straps shown, may have similar relays, arranged to self-interrupt at different frequencies, connected in parallel therewith, the signal frequency then being indicative of the location on the premises of the alarm. The burglar alarm switches 67, upon operation switch various resistances 83, 84, 85, &c. into the line circuit dependent on the location of the alarm so that the steady line current intensity is indicative of the location. For telephonic communication with the supervisory station the transmitter 64 is switched into line 1 in place of the alarm circuits by operating switch 56. 54 is a polarised ringer. The burglar alarms may be cut-out of circuit, e.g. during daytime by a short-circuiting switch 89. Supervisory station, Fig. 1. The subscriber's line 1 is energized from a battery 6 or other D.C. source in series with a jack 10 and normally energized relay 13. In the event of an alarm the line current drop is sufficient to release relay 13, whereby a shutter relay 24 and pilot lamp 25 are energized from battery 6, the relay operating a bell 29 and signal lamp 30. These visual and aural signals are oscillatory or steady depending on whether a fire or burglar alarm has been actuated. To determine the location of the alarm the supervisory operator inserts a plug 45 into jack 10 to connect a meter 47 directly in the line circuit, the current intensity in which is indicative of the alarm location. In the case of fire alarms the meter reading is dependent on the frequency and the make-to-brake time ratio of the operative relay-condenser combination 70, 74, Fig. 2. These ratios differ for the various combinations to produce different responses of the meter 47 indicative of the alarm location. In a modification, Fig. 3 (not shown), a frequency meter may be switched into circuit by a press-button switch in lieu of the meter 47 to serve as a fire alarm location indicator. Telephone arrangements. By inserting. a plug 31, Fig. 1, in the jack 10 and a plug 42 in jack 36 the telephone set 41 is connected in the line to the subscriber, ringing being effected by the generator 37 which is normally shortcircuited, but when operated throws contacts to connect it in line in place of the transmitter 41. At the subscriber's the ringer 54 responds. A ringing generator is not provided at the subscriber's since the operation of push-button 62 thereat to connect the telephone set into line draws attention at the supervisory station, in the sealed or unsealed condition, by operating the visual and aural signals 25, 29. Manual operation of a switch 35 disconnects the telephone and connects the meter 47 in the line 1. Miscellaneous. The aural and visual alarms 29, 30, Fig. 1, may be common to a plurality of subscribers and switches 20, 44, Fig. 1, and 86, 87, 88 are provided for testing the various circuits.