Comparator Comparator

Introduction :Introduction : A comparator is a precision A comparator is a precision

instrument employed to compare the instrument employed to compare the dimension of a given component with dimension of a given component with a working standard (usually slip a working standard (usually slip gauges).gauges).

It thus does not measure the actual It thus does not measure the actual dimension but indicate how much it dimension but indicate how much it differs from the basic dimension. differs from the basic dimension.

In mass production identical In mass production identical component parts are produced on a component parts are produced on a very large scale.very large scale.

To produced interchangeability these To produced interchangeability these parts produced very close parts produced very close dimensional tolerance.dimensional tolerance.

As a result, inspection is often more As a result, inspection is often more concerned with the dimensional concerned with the dimensional variation from the standard parts.variation from the standard parts.

The micrometer and vernier calliper The micrometer and vernier calliper are not more feasible because skill are not more feasible because skill involve and time required to involve and time required to measure the dimension.measure the dimension.

In such case comparator is more In such case comparator is more suitablesuitable

for the measurement. for the measurement.

Basic principle of operationBasic principle of operation

The comparator first adjust on zero on The comparator first adjust on zero on its dial gauge with a gauge block in its dial gauge with a gauge block in position.position.

The gauge block is of dimension The gauge block is of dimension which the work piece should have.which the work piece should have.

The work piece to be checked is then The work piece to be checked is then placed in position and comparator placed in position and comparator gives the difference in dimension in gives the difference in dimension in relation to the gauge block.relation to the gauge block.

Dimension may be greater, less or Dimension may be greater, less or equal than the standard dimension.equal than the standard dimension.

If the dimension greater or equal than If the dimension greater or equal than the standard gauge its indicate on dial the standard gauge its indicate on dial gauge.gauge.

Thus comparator does not give the Thus comparator does not give the dimension of the work piece but just dimension of the work piece but just give the difference b/w work piece give the difference b/w work piece and standard gauge. and standard gauge.

Mechanical optical Mechanical optical comparatorcomparator

Sigma comparatorSigma comparator

It is mechanical It is mechanical comparator comparator providing providing magnification in the magnification in the range of 300 to range of 300 to 5000.5000.

It consist of a It consist of a plunger mounted on plunger mounted on two flat steel string.two flat steel string.

This provide This provide frictionless linear frictionless linear movement.movement.

The plunger carries The plunger carries the knife edge the knife edge which bear upon the which bear upon the face of mounting face of mounting blocks of cross strip blocks of cross strip hinge.hinge.

The moving block The moving block carries a light metal carries a light metal y- forked arms and y- forked arms and wrapped around the wrapped around the smalldrum.smalldrum.

A thin phosphors A thin phosphors bronze ribbon is bronze ribbon is fastened to the end fastened to the end of the forked arms of the forked arms and wrapped and wrapped around the small around the small drum, mounted on drum, mounted on the spindle the spindle carrying the carrying the pointer.pointer.

Any vertical movement movement of Any vertical movement movement of the plunger and hence that of the the plunger and hence that of the knife edge makes the moving block knife edge makes the moving block of the cross strip lever to pivot.of the cross strip lever to pivot.

This cause the rotation of the y-arms.This cause the rotation of the y-arms. The metallic band attached to the The metallic band attached to the

arms makes the driving drum hence arms makes the driving drum hence the pointer to rotate.the pointer to rotate.

Total magnification of the instrument Total magnification of the instrument isis

L/a = l/rL/a = l/r