Oxygen Sensor: Description and Operation

Oxygen Sensor:

This sensor is used to determine the oxygen content of the exhaust gases. The oxygen sensor is basically a galvanic battery consisting of a cylindrical electrolyte element of zirconium dioxide which is coated inside and out with platinum. The outer platinum electrode is exposed to atmosphere, while the inner is exposed to the hot exhaust gases. A porous ceramic coating protects the platinum against damage by the exhaust gases.

The air from the atmosphere acts as one conductor of the battery, the exhaust gases act as the other, and the zirconium dioxide acts as the electrolyte. The higher the oxygen content in the exhaust, the less dissimilarity, thus yielding a low voltage output (.45 volts or less). When the oxygen content is low (rich mixture), the greater the dissimilarity between the outside air and the exhaust gases, this dissimilarity causes a higher voltage output (.45 to 1 volt).

The MCU uses the voltage value from the oxygen sensor and other input signals to adjust the air/fuel mixture and to determine the proper time for switching from open to closed loop operation.