A NOVEL MINIATURE ZIRCONIA GAS SENSOR WITH PSEUDO-REFERENCE - AMPEROMETRIC OPERATION PROVIDING UNAMBIGUOUS DETERMINATION OF AIR-TO-FUEL RATIO

The problem of ambiguity of the output of a single-chamber amperometric zirconia oxygen sensor with the possible confusion of lean and rich operation of a combustion system is well known. The solution previously proposed entails the addition of a second chamber containing a piped reference gas such as air. In this paper the novel solution proposed is to generate a pseudo-reference gas, which always contains excess oxygen, in the second chamber so eliminating the need for a piped reference gas. The detailed theory of the device in one particular mode is developed and confirmed by experimental tests in O2-N2 and CO-CO2-N2 mixtures. The device was also operated in the flue of a gas-burning system over a wide range of air-to-fuel ratios from rich to lean. The output changed monotonically over the whole range switching sign as stoichiometry was traversed. An amperometric zirconia gas sensor with such a characteristic has previously only been described for a sensor with supplied reference gas of fixed composition.