<9. Calibration>
9-1
IM 11M12G01-02EN 1sh Edition : Mar. 25, 2021-00
9. Calibration
9.1 Calibration Briefs
9.1.1 Principle of Measurement with a zirconia oxygen
analyzer
This section sets forth the principles of measurement with a zirconia oxygen analyzer before
detailing calibration.
A solid electrolyte such as zirconia allows the conductivity of oxygen ions at high temperatures.
Therefore, when a zirconia-plated element with platinum electrodes on both sides is heated up
the action of the concentration cell. In other words, the electrode in contact with a gas with a
higher oxygen partial pressure acts as a negative electrode. As the gas comes in contact with the
become ions. Moving in the zirconia element, they eventually arrive at the positive electrode on
the opposite side.
There, the electrons are released and the ions return to the oxygen molecules. This reaction is
indicated as follows:
Negative electrode: O
2
+ 4e 2 O
2-
Positive electrode: 2 O
2-
O
2
+ 4 e
The electromotive force E (mV) between the two electrodes, generated by the reaction, is
E = -RT/nF ln Px/Pa
........................................
where, R: Gas constant
T: Absolute temperature
n: 4
F: Faraday’s constant
Px: Oxygen concentration in a gas in contact with the positive zirconia
electrode (%)
Pa: Oxygen concentration in a gas in contact with the negative zirconia
electrode (%)
E =
log
Px
Pa
.................................
Equation
(2)
−50.74
sample gas in contact with the positive electrode and the electromotive force of the sensor (cell),
where a comparison gas of air is used on the negative electrode side.
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