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Laser Micrometers – Theory of Operation
Laser scan micrometers use a laser light source to measure diameter, gap, position, width,
and other dimensions. The light source is focused onto the facets of a rotating mirror that
reflects the laser beam into a collimating lens. The lens refracts the beam so that all paths
of light from the mirror through the lens emerge parallel to each other. A "focal" lens on
the other side of the measurement field focuses the incoming light onto a photocell,
generating an analog voltage. When an object is placed in the measurement field, it
obstructs the laser beam. When the beam is obstructed, the photocell output voltage is at
its lowest level; when unobstructed, the voltage is at its highest level. As the mirror
rotates, the beam scans the measurement field from one side to the other. An object in
the field obstructs the laser beam, casting a shadow that causes a low output voltage for a
period of time that is proportional to the size of the object. Using the speed at which the
beam is traversing the measurement field as a reference, the shadow time is converted to
an accurate measurement of the object's size.
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