An Automatic Voltage Regulator
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The Paper describes a method by which automatic voltage regulation to 0.15 per cent. may be obtained for such purposes as the operation of photometric standard lamps on an ordinary outside supply varying by as much as 10 per cent. The lamp is placed a cross an unbalanced Wheatstone bridge of which two opposite arms are composed of tungsten filament lamps. The increase of resistance of these lamps, due to the extra current passing through them when the outside voltage rises, causes a shift in the balance of the bridge such that the voltage across the photometer lamp remains unaltered if the values of the resistances in the arms be properly proportioned. The power taken is about 40 times that used in the regulated circuit.