Patent GB-277362-A (GB)
Title: Improvements in or relating to fire alarm systems
IPC: G08B17/06
Filed: 1927-09-09
Abstract: 277,362. Telefonaktiebolaget L. M. Ericsson, (Assignees of Ekman, O. I. H.). Sept. 11, 1926, [Convention date]. Fire, police, and like alarm systems.-In a fire alarm system of the type employing normally closed protective loop circuits, each loop is formed by two conductors extending side by side through the localities to be protected. heat sensitive switches being located in each conductor at each locality. Fig. 1 shows a complete alarm system employing two protective loop circuits A<1>, A<2>. The relay R in each loop is normally energized over the back contacts K<1>. Upon the operation of a thermostatic switch T. the relay R is de-energized and a slow acting relay TR is operated to short-circuit a relay BR which normally is energized in series with a. relay' HBS, which however remains inoperative. Release of the relay BR causes the operation of bells AK and a lamp AL to indicate the outbreak of fire. A lamp SL energized upon release of the relay R indicates the loop affected. The relay HBS is operated when the relay BR is shortcircuited to close further alarm circuits. When a breakage occurs in one of the lines L', L<2>, the relay R is released to close a circuit for the relay FR over the other line. The relay FR operates a fault lamp FL and a bell FK, and also opens the short-circuit path for the relay BR so that upon the energization of the relay TR after a time interval the relays BR, HBS still remain inoperative. The alarms FL, FK are also operated when a short-circuit occurs a resistance FM being connected in series with the battery to 'limit the short-circuit current. A relay JR is energized to operate the lamp JL when an earth develops upon one or other of the inductors L<1>, L<2>. In a further modification, fault alarm relays individual to each line of a loop are arranged in shunt with the line. The Specification as open to inspection under Sect. 91 (3) (a) comprises also further modified systems, examples of which are shown in Figs. 1 and 4 (Cancelled). As shown in Fig. 1 (Canceled), a single protective loop comprises conductors L<1>, L<2> connected in series with a battery B and line relays R<1>, R<2> at the central station. Thermostatic switches T<1>, T<2> having normally closed contacts in each line circuit maintain the relays R<1>, R<2> energized. Upon the occurrence of a fire, both line circuits are opened and the relays R<1>, R<2> are de-energized to cause the operation of the ,alarm bells K<1>, K<2> and the fire alarm relay S. The loop circuit is earthed at each end so that in the event of a breakage in one of the lines L<1>, L<2> one of the relays R<1>, R<2> only is de-energized to cause operation of the corresponding alarm K<1>, K<2>. the fire alarm relay S remaining inoperative. In a modification wherein provision is made for the operation of an alarm in the event of a shortcircuit occurring between the lines L', L<2>, the relays R<1>, R<2> are arranged in the loop at the end remote from the battery. The earth return may be replaced by a wire connection. Fig. 4 (Cancelled) shows a modified system wherein provision is made for the operation of an alarm when an earth fault develops on one or both of the conductors L', L<2>. A resistance M and additional alarm relays JR<1>, JR<2> are included in the loop circuit. Normally the current is not sufficient to cause the operation of the relays JR<1>, JR<2>, but when one of the line wires is earthed the current in that line is increased to operate the corresponding alarm relays. The relays JR<1>, JR<2> may be replaced by a singe relay having two windings, and the relays R'. R<2> may take the place of the resistance M. That Specification also states that the systems may be applied to automatic sprinkling plants, and that the thermostats may be replaced by manually operated switches, and describes a further modification wherein a fire alarm relay is normally energized over the contacts of the control relay and is adapted to be maintained operated to prevent an alarm upon the de-energization of the control relay if the release of the latter relay is due to a fault. This subject-matter does not appear in the Specification as accepted.