High-temperature rotor bore dilatometer unit

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Abstract
The instrument measures optically the dilation due to centrifugal stresses of the bore of a steam turbine rotor under running conditions. The measurements are independent of vibration of the rotor. Light from an illuminated pinhole within an autocollimator is collimated on to a system of three mirrors supported kinematically inside a cylindrical cartridge, which is pushed into the rotor bore of the turbine. Two of the mirrors are fixed to the cartridge, and the third is hinged and connected to a feeler which is spring loaded against the rotor bore. With all three mirrors mutually at right angles, the light is reflected back to the autocollimator in exactly its own path, independent of any relative movement between the dilatometer and the autocollimator. On expansion of the rotor bore, the third mirror is displaced, tilting the returned beam of light. Since the turbine rotor is rotating, the image seen in the autocollimator appears as a circle, the diameter of which gives a measure of the dilation. The preparation of the mirror surfaces enabling them to withstand the conditions inside the turbine is discussed.

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