A sensor assembly for an electric power generation, transmission, and distribution equipment, wherein the equipment comprises a mounting flange on the equipment providing access to the interior of the equipment provided with a plurality of bolt receiving apertures arranged on the mounting flange in a first pattern; the sensor assembly comprising: a) a first flange having at least one or more openings and an outer periphery, and a plurality of bolt receiving holes within the outer periphery of the first flange which are arranged in a pattern corresponding to said first pattern; b) a sensor comprising: (a) a semiconductor element for measuring hydrogen concentration in an insulating fluid in the equipment; (b) a tubular housing support member having one end received in one of the openings; (c) a housing body having one end thereof connected to the tubular housing support member and disposed among the bolt receiving holes, and spaced therefrom a sufficient distance to allow access to bolts disposed in the openings for inserting and removing bolts from the openings and further having a substantially uniform cross-section extending from the tubular housing support member; (d) at least one wire receiving opening extending into the housing body; and (e) a cover closing an end of the housing body distal from the one end; c) a first seal disposed between the first flange and the tubular housing support member; d) a second seal disposed on the first flange for engaging the mounting flange; characterized in that e) the outer periphery of the first flange contains the opening in which the tubular housing support member is mounted and another opening in which a sampling and bleeding valve is mounted, said sampling and bleeding valve extending into the first flange in communication with the interior of the equipment and oriented so that when opened trapped gas will exit the valve. a) a first flange having at least one or more openings and an outer periphery, and a plurality of bolt receiving holes within the outer periphery of the first flange which are arranged in a pattern corresponding to said first pattern; b) a sensor comprising: (a) a semiconductor element for measuring hydrogen concentration in an insulating fluid in the equipment; (b) a tubular housing support member having one end received in one of the openings; (c) a housing body having one end thereof connected to the tubular housing support member and disposed among the bolt receiving holes, and spaced therefrom a sufficient distance to allow access to bolts disposed in the openings for inserting and removing bolts from the openings and further having a substantially uniform cross-section extending from the tubular housing support member; (d) at least one wire receiving opening extending into the housing body; and (e) a cover closing an end of the housing body distal from the one end; (a) a semiconductor element for measuring hydrogen concentration in an insulating fluid in the equipment; (b) a tubular housing support member having one end received in one of the openings; (c) a housing body having one end thereof connected to the tubular housing support member and disposed among the bolt receiving holes, and spaced therefrom a sufficient distance to allow access to bolts disposed in the openings for inserting and removing bolts from the openings and further having a substantially uniform cross-section extending from the tubular housing support member; (d) at least one wire receiving opening extending into the housing body; and (e) a cover closing an end of the housing body distal from the one end; c) a first seal disposed between the first flange and the tubular housing support member; d) a second seal disposed on the first flange for engaging the mounting flange; characterized in that e) the outer periphery of the first flange contains the opening in which the tubular housing support member is mounted and another opening in which a sampling and bleeding valve is mounted, said sampling and bleeding valve extending into the first flange in communication with the interior of the equipment and oriented so that when opened trapped gas will exit the valve.