Patent GB-688117-A (GB)
Title: Improvements in or relating to burglar or like alarm systems
IPC: G08B13/26
Filed: 1949-05-11
Abstract: 688,117. Burglar alarm systems. CLAESSON, P. H. E., and JOHANSSON, K. L. May 11, 1945 [June 22, 1948], No. 12599/49. Class 118 (i). In a capacity-operated burglar or like alarm system having a plurality of antenna units co-operating with a central indicating station, the variation in current from an antenna unit due to the entry of a foreign body into the field of an antenna unit or the occurrence of a fault in such a unit are indicated at the central indicating station in different ways by means which are not restored automatically when the current from the antenna unit returns to normal. Local circuits. In the normal state two valves E (Fig. 1) oscillate with less than maximum amplitude and each draws anode current through one winding I of a corresponding polarized relay Re1 or Re2. In each case the other winding II carries an equal opposing 'current and the relay remains unoperated. When a body comes within the field of an aerial A the anode current of the associated valve E increases and the winding I therefore moves the relay armature to its "alarm" position in which it drops a suitably marked shutter (see below). If owing e.g. to bad joints or dirty contacts the anode current falls. the current in winding II of the relay Re1 will predominate and move its armature to the opposite "fault" position to drop a second shutter, the relay being locked in the operated position by its contacts 4 or 3 respectively. A complete current failure can be indicated by giving the armature of the relay Re1 a mechanical bias toward its fault position. The H.T. potential is derived from the mains via a rectifier network Li1 and the rectified output also keeps operated a relay Re4. If the mains voltage drops by, say, 15 per cent. relay Re4 releases, releasing Re3 in turn. At contacts 3, and 5 of the latter the anodes and cathodes of the valves E are switched from the mains to a local battery B. At contact 2 of Re3 a resistor R4 is connected across the mains as an artificial load, and at contact 1 a resistor R5 in series with the relay Re4 is short-circuited to ensure that this relay will re-operate as soon as the mains voltages reaches its normal value again. A time constant circuit R3, C3, holds the anode potential fairly constant during a switch-over. The indicators Re1, Re2 may be situated at a central position in the area to be protected and transmit warning signals to a distant station. Signalling to distant station. In the normal condition a fault relay Re5 and an alarm relay Re6 are both energized and their contacts 1 complete a circuit over resistor R6 and leads a, b to the distant station equipment shown in Fig. 2. The resistor R6 is of such a value that relay Re7 remains energized but Re8 releases and completes the circuit to a green lamp Lgr to indicate that the local apparatus is in order. When an alarm condition occurs the alarm relay Re6 releases, putting a blocking rectifier L13 into series with the lamp relays Re7 and Re8 which both release, lighting a red lamp Lr as well as the green lamp Lgr. When a fault condition occurs the fault relay Re5 releases and similarly lights the red lamp Lr. In order to determine whether the lighting of the red lamp indicates a fault or an alarm condition, the switch 02 at the distant station is closed. If the alarm relay Re6 has released the line current, of reverse polarity, flows via a resistor R7 to record an indication on a test meter J. If the fault relay Re5 has released, the test current flows over contact 2 of Re6 and bypasses the resistor R7, to record a different indication on the test meter J. If after a fault indication a further switch 03 is closed and the test switch 02 is opened the connection of the rectifier L13 is reversed and the relays Re7 and Re8 operate, extinguishing the red lamp Lr and allowing asubsequent alarm condition to re-light it. By providing additional contacts on switch 03 a different indication (e.g. on a further lamp) may be given when the fault or alarm condition is removed and Re7 operates again. When the test switch 02 is operated an electromagnet in series with rectifier L13 is energized and may be used to transmit any desired reply signal or indication to the local end. Indicator construction. The polarized indicator relays Re1, Re2 are constructed as shown in Figs. 3 and 4. The armature I moves to the left or right (Fig. 4) as the result of a fault or alarm condition respectively and thus drops a weighted shutter 6 or 7 so that it becomes visible through a transparent window 5. The shutters are restored by turning a button 26 which has a coarse thread 27 on its spindle and is thus advanced to press the shutter member 11 into its vertical position. Each shutter may be individually restored by its own button, or a button may move a, strip 21 and thus restore both shutters. Signalling to distant station; several local stations on one line. In order that three local stations Ca, Cb and Cc (Fig. 6) may each signal to its own particular receiver M1, M2 and M3 respectively over the single channel a, b, each station is identified by a different frequency f1, f2, and f3 respectively. When a fault relay Re5 releases it operates a further relay Re9 over contact 1 and this relay in turn re-operates relay Re5. The relay Re9 thus continues to vibrate and sends pulses of its corresponding frequency (say, f1) over the line a, b, to operate a tuned receiver relay M, which in turn flashes an alarm lamp La. If instead an alarm relay Re6 releases corresponding relay Re9 still vibrates but 'with a slower repetition rate because of the condenser C8. At the distant station the indicator lamp therefore flashes at this different rate.