The invention provides a sensor assembly for determining the concentration of hydrogen in an insulating fluid in electric power generation, transmission, and distribution equipment. The assembly includes a housing having an opening therein communicating with the fluid, a hydrogen sensor disposed in the housing and responsive to the concentration of hydrogen in the fluid and generating a signal related to the concentration of hydrogen, and a pressure sensor disposed in the housing responsive to the fluid and generating a second signal indicative of the pressure of the fluid in the equipment. The assembly further includes a signal processor disposed in the housing and connected to the hydrogen sensor and the pressure sensor and responsive to the first and second signals for generating a third signal representing the concentration of hydrogen in the fluid.