Fiber optic sensor probe

Abstract

A fiber optic sensor probe system comprises an electromechanical arrangement system which enables a fiber optic probe to lock onto a null point relative to a target which null point represents an in focus condition for the probe relative to the target. A servomechanism feedback circuit maintains the probe in an in focus condition relative to the target if the target moves. A dithering motion is provided to the probe such that, when the electrical output of the probe has a frequency component which is the same frequency as that of the dither, an out of focus condition of the probe relative to the target exists and the servomechanism feedback system operates to correct it. A monochromatic light source is used to eliminate the problem of different spectral components of light having slightly different focal lengths. A second dither or oscillation of the servomechanism's motor drive voltage causes the motor to oscillate and thus enables it to avoid becoming stuck by static friction, therefore enabling the system to achieve its proper null point. Finally, the geometry of the probe is such that the lens face is not parallel to the target, so that flat regions in the area of the null response point of the output curve of the probe which might cause the probe to hunt excessively for the null point are eliminated.