Method and apparatus for inspecting airtightness of gas sensor

A method of inspecting the airtightness of a gas sensor including a gas sensor element, a sub assembly, and an atmosphere-side cover, the gas sensor element having a reference gas chamber and being disposed in the sub assembly, the atmosphere-side cover covering a base end side of the sub assembly and defining an atmosphere chamber extending outward of the sub assembly, the sub assembly having a measurement gas chamber therein, the gas sensor element being exposed in the measurement gas chamber, the atmosphere chamber communicating with the reference gas chamber, the atmosphere chamber and the measurement gas chamber being airtightly isolated from each other, the method being of inspecting the airtightness of the isolation between the atmosphere chamber and the measurement gas chamber, the method comprising the steps of:

• supplying high-pressure air to a distal end side of the sub assembly to introduce the high-pressure air into the measurement gas chamber;
• applying a low pressure to the base end side of the sub assembly to supply the low pressure to the atmosphere chamber, the low pressure being lower than a pressure of the high-pressure air introduced into the measurement gas chamber;
• and
• monitoring a variation in a pressure in the atmosphere chamber to detect an air leakage from the measurement gas chamber into the atmosphere chamber.

An apparatus for inspecting the airtightness of a gas sensor including a first chamber for containing a reference gas during actual use of the gas sensor, and a second chamber for containing a measurement gas during actual use of the gas sensor, the apparatus comprising:

• a pressure source generating a first predetermined pressure;
• first means for connecting the first chamber with the pressure source to subject the first chamber to the first predetermined pressure;
• second means for disconnecting the first chamber from the pressure source after the first means connects the first chamber with the pressure source;
• third means for applying a second predetermined pressure higher than the first predetermined pressure to the second chamber;
• and
• fourth means for monitoring a difference between a pressure in the first chamber and the first predetermined pressure to detect an air leakage from the second chamber into the first chamber after the second means disconnects the first chamber from the pressure source and when the third means applies the second predetermined pressure to the second chamber.