Abstract: A self-cleaning thermal conductivity sensor comprises: a bellows coupled to a support structure; a pneumatic or hydraulic cylinder; a sensor configured to measure a thermal conductivity of a fluid and extending from the pneumatic or hydraulic cylinder, wherein the sensor comprises an exposure end configured to contact the fluid during sensing by the thermal conductivity sensor, a temperature sensor, and a heat source; sensor wires connected with the thermal conductivity sensor and extending to a control system; a self-cleaning system comprising: a hood having walls extending radially outward and defining a volume; and a cleaning brush integrated with or adjacent the bottom of the support structure. In a retracted configuration, the exposure end of the sensor is positioned at a retracted position a distance from cleaning brush, and, in an extended configuration, the exposure end of the sensor extends a distance along the central axis away from the retracted position.