Heated exhaust oxygen sensors

Electrical heating of the sensor plays an important role in exhaust-gas sensors because almost all sensor principles work only at high temperatures, and the efficiency of the heater determines the time from engine start to control readiness (light-off time). Two types of heaters are used in oxygen sensors. 

Takami, A. (1988), Development of titania heated exhaust-gas oxygen sensor. 

Fig. 7. Exhaust gas oxygen sensor responds sharply to change in engine air to fuel ratio. HEGO, heated exhaust gas oxygen.

This modern sensor is referred to as the HEGO (heated exhaust gas oxygen)-type sensor. Because the control system utilizes feedback, there is a time lag associated in adjustment to the A/F ratio, resulting in a perturbation around the control set point. The amplitude of the A/F ratio and the response frequency (in Hz) characterize this perturbation. 

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