Determining separation distance of two surfaces in a hostile environment

This invention relates in general to casting molds or other equipment and in particular to a method and apparatus for monitoring separation distance of two surfaces such as casting molds in a hostile environment such as high heat, smoke, dirt, oil mist, and sprays. A sensor for measuring the distance between two surfaces injects pressurized fluid (e.g., air) between the surfaces. The pressurized fluid passes through two flow restrictors prior to reaching the surfaces to be measured. The fluid pressures between the flow restrictors and between the downstream flow restrictor and the surfaces are compared to yield the distance between the two surfaces. An accurate distance measurement can be obtained even where the surfaces to be measured are located in a hostile environment which would destroy many other types of sensors.