Planar polarographic probe for determining the .lambda. value of gas mixtures

Planar polarographic probe for determining the lambda value of gas mixtures, particularly of exhaust gases of internal combustion engines, comprising

• a pumping cell (A),
• a diffusion unit (B) with a diffusion resistance preceding a pumping electrode (6) of the pumping cell (A) and
• a heater unit (C),
• made of at least three solid electrolyte foils, namely,
• a first solid electrolyte foil(1) forming the pumping cell (A) and having
• an outer and an inner pumping electrode (6),
• of which the inner pumping electrode is arranged
• on the solid electrolyte foil (1)
• in a diffusion zone (10) for the gas being measured and
• conductive tracks for the pump electrodes;
• a second solid electrolyte foil (9) having a diffusion zone and forming the diffusion unit (B);
• and
• a third solid electrolyte foil (14) forming said heater unit (C);
• the diffusion zone (10) being defined exclusively by an aperture, formed near the inner pumping electrode, in the second solid electrolyte foil (9) laminated together with the first solid electrolyte foil (1) and the third solid electrolyte foil (14), into which aperture a porous sintered body (11), formed during a probe sintering process, is embedded;
• and further comprising a Nernst cell (N) having first and second electrodes,
• said first electrode being exposed to exhaust gas by being located adjacent the pumping electrode behind the preshaped bodies (11) which becomes porous on sintering and forms the diffusion resistance,
• said second electrode being exposed to a reference medium.