Optical comparators (profile projectors) magnify part profiles onto a screen for dimensional inspection using shadow or surface illumination. Calibration verifies the magnification accuracy, screen alignment, and linear measurement system. Optical comparators are widely used for inspecting complex profiles, radii, and angles in precision manufacturing.
Inspect the optical system for scratched lenses, dirty screens, and burned-out lamps. Verify the stage moves smoothly in X and Y axes. Check that the protractor (angular measurement) functions correctly.
Using a calibrated test reticle, verify that the projected image is square to the screen crosshairs. Check that the horizontal and vertical screen axes are perpendicular.
Using a calibrated stage micrometer or certified gage block, verify the magnification at each available lens setting (e.g., 10x, 20x, 50x, 100x). Measure a known dimension on the screen and compare to the expected magnified value.
Verify the X and Y stage micrometer or digital readout accuracy using gage blocks at a minimum of five points across each axis. Record the error at each point.
Using a calibrated angle standard or precision polygon, verify the protractor accuracy at multiple angles (e.g., 30°, 45°, 60°, 90°). Record the error at each angle.
Record all data including magnification errors, stage travel errors, angular errors, and lamp condition. Issue the calibration certificate and apply the calibration label.
Magnification error must not exceed ±0.1% at each lens setting. Stage travel (linear) error must not exceed ±(2 + L/100) µm where L is travel in mm. Angular measurement error must not exceed ±2 arc minutes.
12 months
Place a calibrated stage micrometer on the comparator stage and measure a known length on the projected image. The measured screen dimension divided by the actual dimension should equal the stated magnification within ±0.1%.
Lamps should be replaced when they darken, produce uneven illumination, or when edge definition deteriorates. Most labs replace lamps proactively every 12-18 months. Lamp condition should be assessed and documented at each calibration.
An optical comparator can verify profiles, radii, and angles of gages when its measurement uncertainty is adequate. However, for linear dimensions, gage blocks or CMMs typically provide lower uncertainty. Comparators excel at profile and form measurements.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
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