A profile projector is an optical measurement tool that
magnifies a sample’s surface features to allow
measurement on a linear/circular scale. A profile
projector is also referred to as an optical comparator, or
even known as a shadowgraph. A profile
projector projects a magnified profile image of an area or
feature of a work piece onto a screen most commonly
using diascopic illumination. Dimensions can be measured
directly on the screen or compared to a standard reference
at the correct magnification. For accuracy, it is important
that the magnification does not change with perspective,
i.e. its position or the view point of the operator.
Telecentric lenses are, therefore, highly desirable. The
screen often has a grid and this grid can often be rotated
through 360 degrees to align with an edge as displayed on
the screen. Point positions, measurements, and
calculations may also be performed using a simple digital read out device. A computer may be
added to a profile projector system for edge detection, thereby eliminating some human error.