Solid electrolyte sensor for monitoring combustibles in an oxygen containing environment

Claim 1

A combustible sensor for measuring the concentration of a combustible in an excess oxygen gas environment, comprising a first and a second resistance element, each of said resistance elements being of a material which conducts electrical current at elevated temperatures on the basis of a vacancy mechanism involving doubly charged oxygen ions, said resistance elements having a resistance characteristic which varies exponentially with the inverse of the resistance element temperature, and a pair of electrodes disposed on opposite surfaces of each of said first and second resistance elements, said pair of electrodes associated with said first resistance element being catalytic electrodes, heater means associated with said first and second resistance elements to maintain said resistance elements at desired operating temperatures, said heater means maintaining said first resistance element at a temperature corresponding to the temperature of combustion of the combustibles constituent of interest, said catalytic electrodes combusting said combustibles constituent and the heat of combustion causing an increase in the temperature of said first resistance element and a corresponding decrease in the resistance of said first resistance element, the surface to volume ratio of said first resistance element being such as to minimize dissipation of heat in said first resistance element, and an electrical bridge circuit, said first and second resistance elements each forming one leg of said bridge circuit such that changes in the resistance of said first resistance element in response to said heat of combustion produces an electrical imbalance, the electrical imbalance of said bridge circuit being an indication of the concentration of said combustibles constituent in said gas environment.