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MECHANICAL COMPARATORS AND ITS WORKING

 A Mechanical comparator employs mechanical means for magnifying the small movement of the measuring stylus brought about due to the difference between the standard and the actual dimension being checked.

Mechanical comparators operating essentially on the same principle are available in different designs. They are : Sigma,  Mercer, Mikrokator, etc. The method of  magnifying small movement of the stylus in all mechanical comparators is effected by means of levers, gear-trains or a combination of these elements. Mechanical comparators are available having magnifications from 300 to 5000 to 1, and used mostly for inspection of  small parts machined to close limits. 

Dial Indicators may be classified as mechanical comparators as they have multiplying mechanism which greatly magnifies on the dial any movement of the indicator. 

    

mechanical comparators


Dial Indicators . The essential parts of the instrument is like a small clock with a plunger projecting at the bottom. Very slight upward pressure on the plunger moves it upward and the movement is indicated by the dial pointer. The dial is graduated into 100 divisions. A full revolution of the pointer about this scale corresponds to 1  mm travel of the plunger. Thus, a turn of the hand by the one scale division represents a spindle travel of 0.01mm. A revolution counter or a small dial to indicate the travel of the plunger through whole millimeters is sometimes incorporated in the gauge on the big dial. 

Movement of  stem 1 is transmitted by means of  an toothed rack through a compound gear train 2 and  3 to a pointer 4, which moves around a dial face. The required measuring pressure is provided by small spring incorporated in the mechanism. 

The Indicator is adjusted to zero by either turning the rim of the dial, or turning the head of the plunger while holding the dial stationary. 

Dial Indicators are available for ranges of measurement of 0 to 3 , 0 to 5  and 0 to 10 mm. These measurements indicate total movement "lift" of the plunger.

Dial gauges or dial indicators are used to true and align machine tools , fixtures and work , to test and inspect the size and trueness of a finished work to an accuracy of 0.01 mm. In English measurement dials are graduated in 0.001 in and some in 0.0001 in. They are also used in conjunction with other measuring instruments , e.g. inside calipers, depth gauges, etc, to measure inside and outside dimensions, errors in parallelism, flatness, etc. 


Other Common Types of  Comparators :

* Electrical Comparators. 

* Optical comparators. 

* Pneumatic Comparators. 

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