GB1389607A - Electric lamp assembly - Google Patents

Abstract

1389607 Visible-signalling apparatus PLESSEY CO Ltd 31 May 1973 [25 Sept 1972] 44298/72 Heading G4F [Also in Division H4] In a battery-electric lamp assembly a series circuit comprises a lamp L, an interrupter t 5 and a repeater switch t 2 , and a control circuit comprises a first control terminal T1 connectable to the battery B and a second control terminal T2 connected in a circuit leading to a control input (the base of a transistor t 3 ), of the repeater switch; the repeater switch, which repeats the action of a local switch k 2 when a remote switch is actuated, acts to complete the series circuit. The interruptions are effected by an astable multivibrator one side of which includes a timing capacitor c 2 , transistors t 5 , t 6 and a diode d 4 ; the other side includes a timing capacitor c 5 , a transistor t 8 and a diode d 5 . To ensure multivibrator start-up with t 5 always the first to conduct, a circuit comprises a capacitor c 3 , resistors r 19 , r 20 , a diode d 6 and a transistor t 7 . The invention is applied to a mine lamp; the remote control is via a cable passing only a small current. Resistor r 22 limits the current in the cable to a safe value under fault conditions. The cable may be tapped for connecting several devices. A key k 1 permits a different flashing rate. The device may be operated, with contacts k 1 , k 2 ganged, from a methane detector actuating the remote control switch, the flashing rate being dependent on concentration with the quickest rate corresponding to danger. It can be arranged that continuous earthing of, or continuous contact between, the cable conductors disables the multivibrator by utilizing terminal T3 instead of T2: a transistor t 1 , normally non-conductive, is rendered conductive by the closure of tho remote control switch and consequent charging of capacitor c 1 and remains so until after the lamp L extinguishes on multivibrator changeover. When the remote control switch is opened capacitor c 1 discharges through resistor r 1 and diode d 1 ; when a cable fault occurs earth or negative potential thus appearing at resistor r 4 enables capacitor c 1 to charge and a single flash of the lamp ensues. Contact k 2 may be combined with a lock. Integrated circuit construction may be used and the repeater switch be an electromagnetic relay. Visually indicating incoming telephone calls, Fig. 2.- A is a telephone station connected to an exchange via conductors a, b and the aforementioned device is connected thereto via a circuit 3 in which capacitor c 6 isolates D.C. in the conductors from rectifying network d 7 -d 10 and relay E. A.C. ringing current is rectified and contact E1 closes and lamp L, Fig. 1, flashes according to the manner in which the aforementioned device is set up.