Oxygen sensor

An oxygen sensor of the immersion type for measuring the active oxygen content in a bath of molten metal comprising a measuring head adapted to fit on the end of a carrier, said head having a portion which supports an electro-chemical cell, said cell including an oxygen ion conductive solid electrolyte projecting from said head, a solid reference material juxtaposed to one surface of said oxygen ion conductive solid electrolyte, means for reducing the thermal shock to which said oxygen ion conductive solid electrolyte is subjected after initial immersion including a shield, said shield cooperating with said head to envelop said oxygen ion conductive solid electrolyte, said shield having its inner periphery juxtaposed to and in thermal contact with the opposite surface of said oxygen ion conductive solid electrolyte, said shield being constructed of a metal which melts below 2800.degree. F. whereby the shield will be consumable by a bath of molten steel for exposing said oxygen ion conductive solid electrolyte to the bath, and a second shield supported by said head for protecting said first mentioned shield and said cell during passage through slag.