Abstract: Monitor signals are produced which are qualitative or quantitative measures of the shape, size or position of a light spot on an optical head relative to fibre-optic receptors in the optical head. One pair or two pairs of receptors may be used. Production of the monitor signals involves modulating the incident light forming the light spot at a predetermined frequency, delaying the light signals in one or more of the fibre-optic receptors relative to the light signals in one or more of the other receptors by, say half a wavelength of the predetermined frequency, combining the outputs of the fibre-optic receptors to produce a compound light signal, producing an equivalent compound electrical signal by means of a photodiode, and processing the compound electrical signal in electronic processors to extract one or more of its components to act as the monitor signals.

Abstract: Simplification in manufacture and use of an optical triangulation probe is achieved by providing it with a T-shaped optical path. The cross-bar of the T-shape extends between a light source comprising a laser diode and a light detector comprising a photodiode array, while the stem of the T-shape contains a rod-shaped lens and prism arrangement. The cross-bar of the T-shape is occupied by a solid optical bar-shaped assembly comprising a number of blocks cemented together and providing reflective surfaces for directing outgoing and return light through the T-shape. The lens and prism arrangement focusses outgoing light from laser diode onto the surface of an object whose distance is to be measured and focusses reflected return light onto the photodiode array as a light spot. Position of the light spot as monitored by the output signal of a photodiode array is a measure of distance D between the object and the probe.

Abstract: An optical device for monitoring variations in the distance between an object and a datum is particularly useful for monitoring running clearances in the demanding environment of a gas turbine engine. The device depends upon the principle that an image focussed by an astigmatic lens system changes shape as it passes through the focus. To monitor variations, e.g., in the working clearance between a turbine blade tip and a turbine casing, light from a light source is projected through an astigmatic lens system, onto the blade tip. Reflected light from the astigmatic image on the blade tip is passed back through the lens system and re-projected onto an image shape monitor which includes photo-cells. The photo-cells may be mounted in the main optical assembly or probe, or they may be distant from the probe and fed by light guides. Signals from the cells are combined to produce a monitor signal, the magnitude of which is a measure of the shape of the image on the blade tip, and hence of the clearance.