Optical probe

Abstract

An optical probe is particularly for use as part of the viewing system of a radiation pyrometer, e.g. for measurement of temperatures of turbine blades in a gas turbine aeroengine. Although the objective end of the probe lies flush with the outer wall of the turbine gas passage in order to avoid disturbance of the gas flow and is angled away from the blade by virtue of its conformity with the geometry of the outer wall of the gas passage, the probe's field of view nevertheless includes locations on the turbine blades which are considerably axially upstream from the probe's position. This is achieved by providing the probe with an objective prism whose front and rear faces are inclined with respect to each other, so that, for rays of a preselected wavelength, the prism refracts into the probe and along the internal optical path of the probe only those rays from a preselected location on the blade. Since the blade radiates at a number of wavelengths, a filter is included in the viewing system so that the pyrometer is presented with radiation at a single wavelength, and therefore with a single image from the single preselected location on the blade. The probe also includes an image centralizing prism in order to centralize the optical path within the probe, and glare stops in order to collimate the rays after they have passed through the objective prism and the image centralizing prism. The objective prism may be made of sapphire in order to withstand the heat of the turbine gases.