We explain the physical background, operating principle and construction of non-consumptive zirconium dioxide oxygen sensors

Physical background

Nernst voltage

Two different ion concentrations on either side of an electrolyte generate an electrical potential known as the Nernst voltage. The larger the difference in the ion concentration ratio, the greater the voltage.

Zirconium dioxide

At high temperatures >650 °C zirconium dioxide (ZrO₂) exhibits two mechanisms:

1. ZrO₂ partly dissociates to produce oxygen ions which can be transported through the material when a voltage is applied.
2. ZrO₂ behaves like an solid electrolyte for oxygen. If two different oxygen pressures exist on either side of an ZrO₂ element a voltage (Nernst voltage) can be measured across that element.

Sensor function

Sensor construction

First Sensors XYA oxygen sensors consist of two zirconium dioxide (ZrO₂) discs coated with thin porous layers of platinum which serve as electrodes. The two discs are attached to a platinum ring, forming a hermetically sealed chamber. At the outer surfaces of the ZrO₂ discs there are two further platinum rings to provide for the sensors electrical contacts. The first disc is connected to a reversible current source, at the second disc a voltage (Nernst voltage) can be measured. Two outer alumina elements prevent any ambient particulate matter from entering the sensor and also remove any unburnt gases.

Pumping disc

The first ZrO₂ disc (pumping disc) works as an electrochemical oxygen pump, evacuating or pressurising the sealed chamber. Depending on the direction of the connected reversible constant current source the oxygen ions move through the disc from one electrode to the other thus changing the oxygen concentration and therefore the pressure (p₂) inside the chamber.

Sensing disc

This Nernst voltage is sensed and compared with two reference voltages. Each time either of these two references is reached the constant current source is reversed and the Nernst voltage approaches its other reference value.

Now read our complete application note „Operating principle and construction of XYA zirconium dioxide oxygen sensors“ and …

1. … understand the physical background, operating principle and construction of non-consumptive zirconium dioxide oxygen sensors.
2. … get practical advice for the implementation of a measurement.
3. … find out more about cross sensitivity and fail safe operation.