High-temperature warning system

Claim 1

A thermal warning system comprising a tungsten filament lamp, a sensor thermistor device, and a direct current voltage source connected with said lamp and said device in series circuit relationship, wherein: said lamp filament is of such a thermal mass relative to said device that its thermal time constant is longer than that of the thermistor device; the thermistor device comprises a body having a negative thermal coefficient of resistance, a pair of conductive wires, said wires terminating at opposite faces of said body, a hard solder connection forming a bond between the terminal end of a said wire and its adjacent body face, there being one such connection for each said wire terminal, and a conductive resistance film on said body between said connections at each of two opposite faces of the body; the thermal masses of the lamp and the thermistor device being such that, as thermistor resistance decreases with increasing temperature, the lamp filament heats and increases in resistance thereby reducing power dissipation in the thermistor device and eventually switching the thermistor device back to its initial condition in which the resistance of the thermistor device again decreases as its temperature increases, thereby providing cyclic heating and cooling and consequent alternately bright and dull glowing of the lamp filament to indicate when the thermistor device is at or above a specified temperature.