Device for the remote detection of a failed lamp in a lighting system with a plurality of lamps connected in parallel

Claim 1

Device for the remote detection of a failed lamp in a lighting system with a plurality of lamps connected in parallel to a power line feeding the lamps with a voltage of predetermined characteristics supplied by an a.c. voltage source, the device comprising: means associated with each lamp for isolating the lamp from the power line and comprising a pair of input terminals connected to the power line and a first pair of output terminals connected to the lamp, said isolating means supplying the lamp with the voltage present on the power line when said voltage has said predetermined characteristics, and isolating the lamp from the power line when the line voltage is different from the voltage with predetermined characteristics, said isolating means further comprising rectifying means emitting at a second pair of output terminals of the isolating means a low d.c. voltage proportional to the voltage present at input terminal; a timer connected to said second pair of output terminals of the isolating means and emitting, after a predetermined time corresponding to the lamp lighting time, the voltage present across said second pair of output terminals of the isolating means; a light sensitive element, fed with said low d.c. voltage through said timer and located so as to be illuminated by the lamp, said element supplying a voltage which is substantially zero when it is illuminated by the lamp and is substantially equal to the low d.c. voltage when it is not illuminated; a threshold comparator, fed by said low d.c. voltage through the time and connected to the light sensitive element, said comparator emitting an output signal with a first voltage level when the output voltage of said light sensitive element is substantially zero and a second voltage level when the output voltage of said light sensitive element is substantially equal to the low d.c. voltage; means for releasing a movable unit connected to the threshold comparator output and to an output terminal of said second pair of output terminals of the isolating means and operable to allow displacement of the movable unit from a first position to a second position when the comparator output voltage is at said second level, the movable unit being associated with a signalling device, arranged to indicate, in the second position of the movable unit, that the lamp has not lit up and with an electric contact that in said second position connects a predetermined resistance across the line, said predetermined resistance being manually disconnected when the failed lamp has been replaced; resistance measuring means connected to a power line section common to a number of lamps of the lighting system, for the remote detection of the connection across the line section of at least a resistance, said resistance measuring means being operative after the disconnection of said line section from the a.c. source.