Temperature responsive circuit having a high frequency output signal

Claim 1

A temperature sensing circuit for producing a high frequency output signal, the frequency of which is indicative of the level of the ambient temperature comprising: a temperature sensitive circuit impedance element responsive to an ambient temperature and having a large change in impedance over a predetermined small change in temperature of said element, said element being a thin resistance film thus having a relatively small mass, switching circuit means for providing an output signal when said switching circuit switches back and forth between one state and a second state of operation, circuit means connecting said impedance element to said switching circuit means whereby a predetermined level of temperature of said impedance element causes said switching circuit means to be in said one state, a feedback heating element associated with said temperature impedance element for artificially changing the said predetermined level of said temperature of said impedance element, said heating element being a thin coating on said thin resistance film, said coating having a small mass, means connecting said feedback element to said switching circuit to energize said feedback element when said switching circuit is in said one state whereby the level of said temperature of said sensitive element changes by said small change from said predetermined level of said temPerature to produce said large change in impedance to operate said switching circuit means from said one state to said second state to deenergize said feedback heating element thereby by a repetition of the operation providing a pulsing signal having a frequency indicative of the ambient temperature.