The active layer of the dynamic oxygen sensor is made up of porous platinum and the oxygen ionic conductor YSZ, i.e. with yttrium (Y) stabilized (S) zirconium dioxide (Z).
Platinum catalyses the reduction of oxygen to oxygen anions, which diffuse through the zirconium dioxide. Subsequently, platinum catalyses the oxydation of the oxygen anions to oxygen. Four electrons are needed for the reduction, four electrons are released during the oxydation.
See Fig. 1: Voltage probe
Current flows along this so-called voltage probe only until the same concentration of oxygen prevails on both sides. In order to obtain a dynamic measuring process, a current probe was integrated. In this way, a hermetically sealed chamber was obtained, in which the current probe alternately pumps oxygen ions in or out. A gradient in oxygen concentration is generated artificially; the diffusion process and, hence, the current flow along the voltage probe are maintained.
See Fig. 2: Dynamic oxygen probe
The measuring cycle starts at an electromotive force of 40 mV. The pump is started and evacuates the chamber until an electromotive force of 90 mV is reached. Afterwards the pump reverses direction: oxygen is transported into the chamber until an electromotive force of 40 mV prevails again. The time required for this depends on the oxygen content of the gas mixture to be measured.
