Oxygen concentration sensor

An oxygen concentration sensor comprising:

• a solid electrolyte member including two portions, one portion being exposed to a gas of interest and the other portion being exposed to the atmosphere;
• an inner cover member formed with a first space communicating portion arranged to communicate with said other portion of said solid electrolyte member;
• a water-proof cover member enclosing said inner cover member and defining with said inner cover member a ventilating passage, said water-proof cover member being formed with a second space communicating portion maintaining said first space communicating portion of said inner cover member in communication with the atmosphere through said ventilating passage, said second space communicating portion of said water-proof cover member being axially spaced apart from said first space communicating portion of said inner cover member;
• a housing formed of metal caulked at one end portion for securing said inner cover member thereto and supporting said solid electrolyte member, said second space communicating portion of said water-proof cover member being defined by a clearance partially defined between said caulked one end portion of said housing and an end portion of said water-proof cover member;
• and
• means, disposed in said ventilating passage between said first and second space communicating portions and spaced axially from said first space communicating portion, for impeding the flow of water through said ventilating passage.