The above process causes the internal electrode to lose electrons, becoming positively charged, while the external electrode gains electrons, becoming negatively charged, creating a potential difference (electromotive force - EMF). This forms a primary cell, generating an open-circuit potential difference.

The magnitude of this potential difference is determined by the Nernst equation:

　　EMF (mV) = (RT)/(4F) * ln(P_ref / P_sample)

R: Ideal Gas Constant (8.314 J/mol·K)

T: Zirconia Temperature (Operating Temperature, measured by thermocouple, unit: K)

Faraday's constant (96485 C/mol)

ln: natural logarithm

P_ref: Reference Oxygen Partial Pressure (constant, known)

P_sample: Oxygen partial pressure of the measured atmosphere (to be measured)