Temperature compensated fiber optic vibration sensor

Abstract

A light beam altering grid (20), having a graded slit density pattern (22), is mounted on a temperature responsive support structure (23) to traverse a light beam (28). The slit density (slit per unit length) of the grid (20) is greater at one end of the grid (20) and gradually reduces towards the opposite end of the grid (20). The grid (20) is disposed on a thermally responsive support (23) such as a bimetallic cantilever (23). The thermally responsive support (23) operates to bend by an amount dependent upon the temperature of the environment in which it operates. In this manner, the grid (20) disposed on the thermally responsive support (23) is positioned in dependence upon the environmental temperature. The grid (20) may be arranged, for example, such that at higher environmental temperatures, when the natural frequency of the support (23) is reduced, the grid (20) will be positioned such that the change in density of slit graduations intersecting the light beam (28) compensates for change in the vibration amplification factor of the bimetalic cantilever (23) caused by the elevated environmental temperature.