Temperature control circuitry

Claim 1

Control circuitry for controlling the application of electrical power to heating electrodes for rapidly heating and for sustaining a constant preselected elevated temperature of a member having a surface which, when heated, emits radiation, said circuity comprising: photodetector means positioned to observe the radiation produced at the surface of the member to be heated; adjustable threshold circuitry coupled to the output of said photodetector means, said threshold circuitry being adjustable to generate an output signal when the radiation from said member reaches a level corresponding to a first predetermined threshold temperature of said member which is in the range of said preselected elevated temperature; voltage controller means for controlling the voltage supplied to said heating electrodes; first input means, including switching means, for inputting into said voltage controller means a first signal indicative of the voltage supplied to said heating electrodes when said switching means is in a first position and for discontinuing said first signal when said switching means is in a second position; said switching means being switchable from its second position to its first position by the output signal from said threshold circuitry; second input means for inputting an adjustable command signal into said voltage controller means corresponding to the preselected elevated temperature of the member; said voltage controller means providing a high heating first output voltage to said heating electrodes in the absence of said first input signal, and in the presence of said first input signal shifts into an automatic control mode of operation in which a second output voltage to said heating electrodes is provided corresponding to a comparison of said first input signal and said command signal.