Eaton Crouse-Hinds Z130 Instruction Manual

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Eaton Crouse-Hinds Z130 Instruction Manual Manual pdf 16 page image

12INM MTL 130-0200 Rev 47 TECHNICAL DESCRIPTION OF SENSORThe zirconia oxygen sensor (see sketch below) is an impervious tube-shaped zirconia (zirconiumoxide) element with a closed end coated externally and internally with porous metal electrodes,typically platinum. At high temperatures, typically above 400°C, the zirconia becomes anoxygen ion conductor, which results in a voltage being generated between the electrodesdependent upon the differences between the partial pressures of the oxygen in the sampleand the oxygen in a reference gas (generally air). The voltage generated is determined by theNernst equation:-Cell output = 2.303RT log P14F P2where:-R = molar gas constantT = absolute temperature of cell in °KF = Faraday constantP1 = partial pressure of oxygen in thereference (air in most cases)P2 = partial pressure of oxygen in the sample.Thus, with air on both sides of the cell, the output is zero (log1=0).The reference electrode is negative with respect to the sample electrode for sampleconcentrations of oxygen higher than that of air and positive for concentrations less thanthat of air. Depending on the application either the internal or external electrode is used asthe reference.The output voltage is processed electronically to provide signals suitable for display or forprocess control purposes.