Characteristics of Limiting Current‐Type Oxygen Sensor

Characteristics of oxygen sensors based on limiting current behavior of zirconia pumping cells have been investigated. To limit oxygen transport from ambient gas to the cathodes of the zirconia pumping cells, a drilled cover and a porous layer were examined. For the sensor with a diffusion hole of the drilled cover, the limiting current showed a considerable nonlinearity to oxygen concentration in a high oxygen concentration and a temperature dependence as in oxygen‐nitrogen mixtures. This behavior is in good agreement with that expected from a model in which the oxygen transport rate is limited by the diffusion hole. For the sensor with the porous layer, the sensor output indicated a weak temperature dependence and good linearity to oxygen concentration compared with the former sensor. These characteristics can be explained by taking into account the fact that the oxygen diffusion in the porous layer involves both the Knudsen and ordinary molecular diffusion mechanisms.