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Comparators

Unit 7

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Comparator

Comparator are one form of linear measurementdevice which is quick and more convenient forchecking large number of identical dimensions.

Normally it will not show the actual dimensions of the

work piece. It will show only deviation in size duringmeasurement.

It cannot be used as an absolute measuring device butcan only compare two dimensions.

Comparator are designed in several types to meetvarious conditions.

All types are incorporate with some kind ofmagnification devices.

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The advantages of comparators are

1) that not much skill is required on the part of operator

in its use 2) the calibration of instrument over full range is of no

importance as comparison is done with a standard endlength.

3) Zero error of instrument also does not lead to anyproblem

4) Since range of indication is very small, being thedeviation from set value, a high magnification resulting

into great accuracy is possible

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USE OF COMPARATOR

MASS PRODUCTION.

LABORATORY STANDARDS- CORRELATED.

ATTACHED WITH SOME MACHINES-ASWORKING GAUGES.

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Types of comparator

According to principles comparators can be

classified into 3 types

Mechanical comparators

Electrical comparators

Optical comparators

Pneumatic comparators

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Mechanical Comparator

It employs mechanical means of magnifying smalldeviation.

The method of magnifying small movement of theindicator in all mechanical comparators are

effected by means of levers, gear trains or acombination of these element.

Its are available having magnification from 300 to

5000 to 1. Mostly used for inspection of small parts

machined to close limits.

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Dial indicator

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HOW TO USE ?

LET US ASSUME THAT THE REQUIRED HEIGHT OF THECOMPONENT IS 32.5mm.

INITIALLY, THIS HEIGHT IS BUILT UP WITH SLIPGAUGES .

THE SLIP GAUGES BLOCKS ARE PLACED UNDER THESTEM OF THE DIAL GAUGE .

THE POINTER IN THE DIAL GAUGE IS ADJUSTED TOZERO THE SLIP GAUGES ARE REMOVED .

NOW , THE COMPONENT IS TO BE CHECKED ISINTRODUCED UNDER THE STEM OF THE DIALGAUGE.

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FRICTION IS MORE ACCURACY LESS.

SLACKNESS IN MOVING PARTS REDUCE THE

ACCURACY.

MECHANISM CAUSE THE INSTRUMENT

SENSITIVE TO VIBRATION.

RANGE IS LIMITED.

PARALLAX ERROR IS POSSIBLE.

DISADVANTAGES OF COMPARATORS

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ELECTRICAL COMPARATOR

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