Heated 0.sub.2 sensor having isolated ground

Abstract

An oxygen sensor (24) having an electrolyte member (72) with a thimble that is held in a metal shell (30) by an insulating member (56). The thimble has an external surface (80) and internal surface (82) that are coated with a conductive material. A sleeve (96) is attached to the metal shell (30) by spot welds (108) and a seal is established therebetween. A terminal member (120) located in sleeve (96) includes a first contact ring (142) that is connected by a spring (148) and cylinder (152) to the external surface (80) and a second contact ring (144) that is connected by a coil spring (146) to the internal surface (82). Terminals (164 and 164')carried by terminal member (120) hold a tubular housing (90) of a heater member (92). Tubular housing (90) has an end (94) that is located in the thimble of electrolyte member (72). When electrical current is supplied to heater member (92) the temperature of the thimble is maintained above a minimum operating temperature of the electrolyte member (72). The external surface (80) of member (72) is subjected to exhaust gases while a reference gas is transmitted to internal surface (82). Changes in ion flow are carried by leads (106 and 106') to a controller (20) to provide an indication of the oxygen in the exhaust gases.