An optical comparator is a device that applies the principles of optics to the inspection of manufactured parts. In a comparator, the magnified silhouette of a part is projected upon the screen, and the dimensions and geometry of the part are measured against prescribed limits.
The optical comparator is widely used to precisely measure external size of workpiece by comparison with a gauge block or standard part. It is applicable for examining 5-grade gauge blocks, cylinder gauges and external sizes of precision parts such as parallel planes, spheres and cylinders.
Optical comparators can provide more information than just simple dimensions. Length and width measurements of the part shown above, for example, can be quickly obtained from two separate measurements by using a micrometer. These superficial measurements, however, might not reveal burrs, scratches, indentations or undesirable chamfers. Such imperfections are best detected on a comparator. In addition, a comparator’s screen can be simultaneously viewed by more than one person and provide a medium for discussion, just as a white board might facilitate a conference.
Another advantage of comparators is their ability to measure in 2-D space. Unlike micrometers and calipers, which measure one dimension at a time, comparators measure length and width simultaneously. To do this, the operator lines up the lower left-hand corner of the image with the screen centerline to establish a zero point, as illustrated above, and then checks the upper right-hand corner to get a simultaneous reading of both length and width. The straight-line distance from corner to corner can be obtained with a single keystroke.