The design of an OXITEC^® Zirconia Cell
with the gastight seal

The zirconia measuring principle is basically very simple

A process gas (A) with unknown oxygen (O₂)-concentration flows over a measuring probe, which is sealed against 
the process gas with a heated zirconia cell (B).

The reference gas air (C) with its known and constant O₂-concentration contacts the cell from the inside.

At high temperatures a  voltage V is generated between the two surfaces of the cell, which, at constant cell temperature, depends
only on the ratio of the oxygen concentrations (partial pressures) in A and C.

With air (oxygen content constant 20,95%) as reference gas the measured voltage is a direct measure for the oxygen concentration in the process gas A, as long as the seal between process and reference gas is absolutely and perfectly gas tight and therefore any influence to the measuring results are eliminated for ever!

The Nernst equation and the gas tight fraction line

V Measured voltage		With a "leak proof" fraction line and air as reference gas all values of the Nernst equation except P2 are constant! This means the  voltage output depends only on partial pressure P2 (process  gas) and calibration is not  required.
K Natural constant
T Temperature, is kept constant
P1 Partial pressure of reference gas; is      constant, if air is used as reference gas      and mixture prevented with process       gas.
C Constant offset

Calibration?

Other oxygen measuring methods require a two point calibration, which in practice has been transferred to 
zirconia measuring principle. This is not necessary, as the Nernst equation is a mathematical linear function
and with air as a known reference gas the only parameter P1 is constant. Therefore calibration is not required!

Only one condition must be fulfilled:
The measuring cell must have a totally gas tight seal between the process gas side and the reference gas side.

Any leakage at the cell will cause a migration of process and reference gas that will make regular calibrations
necessary.