# Nernst equation (%O2 calculation)

## Calculation of oxygen concentration from SIRO2 sensor signal

Please enter the operating temperature (500 – 1700 deg C) and the measured mV (0 – 1200 mV) signal. The corresponding oxygen concentration is calculated. If it is very low, it is displayed in scientific notation.

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The Nernst equation is **E = (RT/nF)ln(pO _{2}/pO_{2}‘)**

Where:

E = sensor electromotive force, (mV)

R = gas constant

T = temperature, (Kelvin)

n = number of charges per reactant species

F = Faraday constant

p = partial pressure (mole fraction)

This equation describes the electromotive force (emf) developed when there are different concentrations of a reactant on each side of an electrolyte.

If oxygen is to be measured, using a zirconia ceramic electrolyte and atmospheric air, with pO_{2} = 0.209, as a reference, this equation simplifies to:

**pO _{2} = 0.209 exp(-46.421 E/T)**

The equation may be re-arranged, to allow calculation of the emf from a known reference concentration and a measured oxygen concentration:

**E = 0.0496 T log(pO _{2}/0.209 )**

## Calculation of Nernst voltage from oxygen concentration

Note that the oxygen concentration can be entered either as a decimal fraction (so that 1% would be entered as 0.01) or in power of 10 notation ( so that 0.001% would be 1.00*10^-5).

**ECONOX supplies a range of industrial, scientific and pottery probes for the measurement of oxygen at high temperature**