Oxygen concentration detector

An oxygen concentration detector for detecting oxygen concentration in gases, comprising:

• a plurality of resistive bodies, each of said resistive bodies including a number of portions with a negative temperature coefficient of electric resistance and high-resistance substance layers separating said portions one from the other, and at least two separate electrodes contacting each of said plurality of resistive bodies, each of said resitive bodies being located between said at least two separate electrodes, at least one of said plurality of resistive bodies being a solid electrolyte, thereby forming an oxygen concentration cell, at least another of said plurality of resistive bodies being a solid electrolyte other than said oxygen concentration cell;
• an AC power source connected to said at least two separate electrodes contacting said oxygen concentration cell, said AC power source applying an AC current to said oxygen concentration cell so as to heat said cell, said AC power source being arranged to supply an AC voltage at a frequency sufficiently high that an impedance between said at least two electrodes to which AC voltage is applied is largely independent of interface capacitances between said electrodes to which AC voltage is applied and a surface of said concentration cell;
• a DC source, said DC source applying a DC current to said electrolyte, for controlling oxygen partial pressure around at least one electrode contacting said oxygen concentration cell;
• and
• means for measuring a DC potential difference of the oxygen concentration cell.