Self-calibrating thermometer

A calibration system for an electronic thermometer comprising:

• a reference temperature element having a characteristic that varies as a function of temperature;
• a reference temperature sensing circuit, responsive to said reference element, for providing a reference signal representative of the temperature sensed by said reference element;
• a temperature-sensitive probe having a characteristic that varies as a function of temperature;
• a probe temperature sensing circuit responsive to said probe for providing a probe signal representative of the temperature sensed by said probe;
• means for releasably interconnecting said probe and said probe temperature sensing circuit;
• comparator means for comparing said probe signal representative of the temperature sensed by said probe and said reference temperature signal representative of the temperature sensed by said reference element;
• said probe temperature sensing circuit being responsive to said comparator means for adjusting said probe signal representative of the temperature sensed by said probe to match said reference signal representative of the temperature being sensed by said reference element;
• and
• fault detector means including means for monitoring the output of said comparator means and means responsive to said means for monitoring for indicating that output from said comparator means has not dropped to zero within a predetermined time to indicate that a said probe cannot be calibrated.