Abstract: A measuring sensor is described for determining a physical property of a measured gas, especially for determining the oxygen concentration or the pollutant concentration in the exhaust gas of internal combustion engines, which has a sensor element that is exposable to the measured gas which is at least partially coated with a protective layer that protects against harmful components in the measured gas. In order to achieve producing a “contamination protection”, that is cost-effective from a manufacturing technology point of view, particularly against silicon compounds and phosphorus compounds, the protective layer (26) is made of highly active ?- or ?-aluminum oxide (Al2O3) having additives of compounds of the alkaline metals group, the alkaline earths group, the IV B subgroup or the lanthanides group.

Abstract: A measuring sensor is described for determining a physical property of a measured gas, especially for determining the oxygen concentration or the pollutant concentration in the exhaust gas of internal combustion engines, which has a sensor element that is exposable to the measured gas which is at least partially coated with a protective layer that protects against harmful components in the measured gas. In order to achieve producing a “contamination protection”, that is cost-effective from a manufacturing technology point of view, particularly against silicon compounds and phosphorus compounds, the protective layer (26) is made of highly active ?- or ?-aluminum oxide (Al2O3) having additives of compounds of the alkaline metals group, the alkaline earths group, the IV B subgroup or the lanthanides group.

Abstract: An unheated planar sensor element for determining the concentration of a gas component in a gas mixture, in particular the oxygen concentration in the exhaust gas of an internal combustion engine, has a sensor foil made of a solid electrolyte with an outer electrode exposed to the measuring gas, and an inner electrode exposed to a reference gas, as well as a reference-gas channel, which is covered by the sensor foil on one side and accommodates the inner electrode. To produce a small-volume, cost-effective unheated sensor element for use in small combustion engines having low power output yet sufficiently satisfactory measuring accuracy, the reference-gas channel is sealed on the underside by an additional sensor foil made of a solid electrolyte, and covered by an inner electrode lying inside the reference-gas channel and an outer electrode exposed to the measuring gas.