Seal means for isolated grounded o.sub.2 sensor

Abstract

A sensor (24) having a metal shell (30) joined to a sleeve (96) to locate a heater (92) in a thimble of an electrolyte member (72). A sealed joint is produced between the sleeve (96) and metal shell (30) to define a sealed reference chamber (118). A porous filter (112) in the sleeve (96) prevents water in environmental air from entering the reference chamber (118). Leads (106') and (106') which pass through a seal (123) adjacent the porous filter (112) are connected to terminals (164 and 164'). Terminals (164 and 164') located in a terminal member (120) position a heater (92) within chamber (118) and the electrolyte member (72). Leads (106 and 106.sup.n) which pass through the porous filter are connected to contact rings (142 and 144). Contact rings (142 and 144) are connected to an external and internal coating (80 and 82) on the electrolyte member (72). In response to a signal from a controller (26) electrical current is supplied to the heater (92) to maintain the temperature in chamber (118) above present limits such that changes in the ion conduction through the electrolyte member (72) is accurately measured. The changes result from a difference in the oxygen content of air in the reference chamber (118) as compared with oxygen in an exhaust gas supplied to the external surface (80). The seal (123) and filter (112) are free to move axially within the sleeve (96) while still maintaining radial engagement to assure that only dry environmental air is presented to the reference chamber (18).