Electric lamp and discharge devices: systems – Automatic substitution of the load device or electrode – With current shifting switch
Patent
1976-04-14
1977-07-05
La Roche, Eugene
Electric lamp and discharge devices: systems
Automatic substitution of the load device or electrode
With current shifting switch
240 371, 307 39, 315 88, 315 90, H05B 3704
Patent
active
040342590
ABSTRACT:
A control circuit for a light projection system for energizing a spare lamp when the circuit detects failure of a main lamp. A pair of input lines apply an alternating-current voltage source to the circuit, to the main lamp and to a spare lamp which is substantially in parallel connection with the main lamp. A switch is in series connection with the main and spare lamp for selectively energizing one of the lamps. Current sensing means, generally a resistor, in series connection with the switch and the lamps, senses the current through the main lamp thereby dropping a small portion of the voltage source. A pair of opposite polarity voltage references are established by rectifying the voltage dropped across the current sensing resistor and by rectifying the voltage across the input lines of the voltage source. A tracking voltage reference, proportionally tracks voltage variations on one of the input lines to distinguish between operation of the system at reduced voltages and failure of the main lamp, and is provided by summing and dividing the voltages of the opposite polarity voltage references. A voltage comparator monitors the voltage reference, and has an output adapted to control the switch. Failure of the main lamp causes the voltage across the current sensing resistor to collapse, thereby causing the tracking voltage reference to differ significantly from the potential on one of the input lines, further causing the voltage comparator to change its output and the switch to change position such that the spare lamp is energized. The output of the voltage comparator generally controls an electromechanical device for changing positions of the switch. A second switch, in series with the circuit between the input lines, is controlled by the electromechanical device. The second switch assumes an open state after the first switch energizes the spare lamp, thereby interrupting energization of the electromechanical device and the circuit.
REFERENCES:
patent: 2197700 (1940-04-01), MacGregor
patent: 3809917 (1974-05-01), Vore
Audio Visual Innovators Corporation
La Roche Eugene
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