A first heater is attached to a sensor capable of emitting thermal radiation toward an object to be sensed. Electrical energy provided to the heater, required to maintain the sensor at a predetermined temperature when it is radiating energy toward the object is monitored by a circuit which provides a...http://www.google.com.au/patents/US5054936?utm_source=gb-gplus-sharePatent US5054936 - Sensor for active thermal detection
