Comparators are more appropriate for flat surfaces than for highly contoured forms. Making cross-sectional measurements often requires cutting a sample in half and fixturing it for inspection. Because a camera does not measure height, these systems work best on relatively flat objects or features. Laser-triangulation sensors measure only z, and therefore are used when height measurements are required. Combined with x and y measurement stages, 3-D data can be obtained.
Triangulation sensors have resolutions in the micrometer to submicrometer range.
Applications requiring nanometer resolutions require laser interferometry. Most triangulation sensors do not provide the operator with a visual image of the inspection site, but sensors with that capability are available. There are practical limits to the technology. Optical restrictions force a trade-off between measuring range and resolution, i.e., increasing resolution reduces sensor range. A sensor cannot reliably measure features smaller than the sensor's spot size.