Optical Comparators
Optical Comparator
There is no pure optical comparator but large
magnification is obtained by use of optical principle in optical comparators. A
mechanical instrument also contributes quite a lot for the overall
magnification. Hence sometimes it is referred as ‘Mech-optical comparator’. Magnification
in case of optical comparators is obtained with the help of light beams which
has an advantage of being straight and weightless. Optical comparators have
their own built in light source.
Principle of Working:
The optical principle adopted in the optical
comparators is ‘optical lever’ and is shown in Fig. If a ray of light AC
strikes a mirror, it is reflected as ray CO such that, ∠ACN =∠NCO
Now, if the mirror is tilted through an angle a, the
reflected ray of light has moved through an angle of ‘2a’. In optical
comparators, the minor is tilted by the measuring plunger movement and the
movement of reflected light is recorded as an image on a screen. Figure shows
the working principle of an optical-mechanical comparator in which both
mechanical and optical levers are used.
Magnification:
The magnification of optical comparator is defined as
“the ratio between distance moved by the indicating pointer (beam) and the
displacement of plunger”.
The Magnification of optical comparators is usually
1000:1, with measuring range of plus and minus 0.075 mm.
Advantages:
High Accuracy
High Range
High Magnification
Light beam has No Inertia
No Parallex Eerror
Disadvantages:
Costly
Large Size
Need Source of Light - Electrical supply to operate
light source
Heating of Instrument affects the accuracy of the
measurement
Need of Dark Room
Reading not Convenient
