An axial bearing unit made up of a cage and races is in which the collar located at the outer peripheral edge of the race is extended by a first flange and a protruding rib is formed in an area made up of the collar and the flange. The fiber-optic sensor device is capable of sensing a change in physical quantity by using two fiber Bragg grating units arranged within an optical fiber and a fiber-optic sensor unit arranged therebetween, thereby implementing a low cost fiber-optic grating sensor having a simple structure without requiring a reference FBG. The outer sleeve has a distal anchor engaging end, a proximal end, and a central passage extending from the distal end to the proximal end. Connecting a filter network with an inductor and a capacitor to the output of the comparator and deriving the feedback signal from the filter network, results in an output of the comparator which is a DC output with a superimposed ripple. The methodology includes calibration of a known pattern to the area array image sensor, equations to map the physical points to the image sensor, algorithms to determine a best estimate of the coordinates of occluded points, and techniques to merge the computed coordinates from different sections of the object. These characteristics include the spectral emission characteristics of the plasma, the spectral absorption characteristics of the plasma, the physical dimensions of the plasma, the angular distribution of the light emitted from the plasma on the coating and the geometry of the coated surface.