US Patent 8197123 Thermistor circuit calibration

Temperature detection circuitry is selectively coupled to a thermistor and one of two sources representing the impedance at respective ends of the expected range of temperature to which the thermistor is to be exposed. The offset of an amplifier and a scale factor to account for gain set of the amplifier are determined in an automatic calibration process while coupled to the source(s), and thereafter temperature readings are taken from the thermistor. During the calibration process, if the gain or scale factor are outside of expected ranges, a failure is determined and an alarm given and/or a heater is disabled.