Abstract: Multiple heaters are calibrated and controlled by a microcomputer, and a multiplexer for this system. The heaters are sequentially sampled and resistance calculated from voltage and current measurements. The operator enters a temperature for the calculated resistance to establish a calibrated resistance value. During run, the computer energizes and samples each heater to calculate its resistance. The calculated resistance if divided by the calibrated resistance to determine a resistance ratio. A look-up table is stored in the computer having resistance ratios for corresponding temperature. The computer compares the calculated ratio to that of the look-up table to determine actual heater temperatures. Based upon heater temperatures, the computer controls energization of the heaters until set points are achieved. Negative temperature coefficient and positive temperature coefficient transistors and semiconductors can be utilized.

Abstract: Multiple heaters are calibrated and controlled by a microcomputer, and a multiplexer of this system. The heaters are sequentially sampled and resistance calculated from voltage and current measurements. The operator enters a temperature for the calculated resistance to establish a calibrated resistance value. During run, the computer energizes and samples each heater to calculate its resistance. The calculated resistance is divided by the calibrated resistance to determine a resistance ratio. A look-up table is stored in the computer having resistance ratios for corresponding temperatures. The computer compares the calculated ratio to that of the look-up table to determine actual heater temperatures. Based upon heater temperatures, the computer controls energization of the heaters until set points are achieved.

Abstract: Integral sensor controller for an electrical resistance heater, where the heater is constructed from materials such as nickel, balco, platinum, alumel, or like materials which have an appreciable, positive temperature coefficient of resistivity. The resistance versus temperature characteristic of the heater acts as the temperature sensor. A low level D.C. current provides a sensor voltage which is compared to a set point voltage for switching the heater power through a transistor. The relationship of the sensor voltage to the set point voltage is compared by a comparator which is subsequently used to toggle flip flops for switching of the heater power. Circuitry is provided for protection against heater short circuits.