Methods and systems for preventing degradation of a sensor exposed to a harsh fluid, such as one that might corrode or be exposed to radioactive contaminants, live pathogens, freezing temperatures, overheating, particle deposition or condensable vapors is disclosed. An auxiliary purge stream of comparatively clean fluid or purge fluid is utilized, which flows past the sensor in opposition to the harsh fluid, thereby preventing the harsh fluid from contacting and degrading the sensor. The clean fluid itself may comprise a purge gas, such as clean, dry air, or a liquid that is compatible with the composition of the harsh fluid. The flow and pressure of the clean fluid can be adjusted utilizing one or more supply regulator valves.