Comparator Introduction : Introduction : A comparator is a precision instrument employed to compare the dimension of a given component with a working standard (usually slip gauges). A comparator is a precision instrument employed to compare the dimension of a given component with a working standard (usually slip gauges). It thus does not measure the actual dimension but indicate how much it differs from the basic dimension. It thus does not measure the actual dimension but indicate how much it differs from the basic dimension.

In mass production identical component parts are produced on a very large scale. In mass production identical component parts are produced on a very large scale. To produced interchangeability these parts produced very close dimensional tolerance. To produced interchangeability these parts produced very close dimensional tolerance. As a result, inspection is often more concerned with the dimensional variation from the standard parts. As a result, inspection is often more concerned with the dimensional variation from the standard parts.

The micrometer and vernier calliper are not more feasible because skill involve and time required to measure the dimension. The micrometer and vernier calliper are not more feasible because skill involve and time required to measure the dimension. In such case comparator is more suitable In such case comparator is more suitable for the measurement.

Basic principle of operation The comparator first adjust on zero on its dial gauge with a gauge block in position. The comparator first adjust on zero on its dial gauge with a gauge block in position. The gauge block is of dimension which the work piece should have. The gauge block is of dimension which the work piece should have. The work piece to be checked is then placed in position and comparator gives the difference in dimension in relation to the gauge block. The work piece to be checked is then placed in position and comparator gives the difference in dimension in relation to the gauge block.

Dimension may be greater, less or equal than the standard dimension. Dimension may be greater, less or equal than the standard dimension. If the dimension greater or equal than the standard gauge its indicate on dial gauge. If the dimension greater or equal than the standard gauge its indicate on dial gauge. Thus comparator does not give the dimension of the work piece but just give the difference b/w work piece and standard gauge. Thus comparator does not give the dimension of the work piece but just give the difference b/w work piece and standard gauge.

Mechanical optical comparator

Sigma comparator

It is mechanical comparator providing magnification in the range of 300 to It is mechanical comparator providing magnification in the range of 300 to It consist of a plunger mounted on two flat steel string. It consist of a plunger mounted on two flat steel string. This provide frictionless linear movement. This provide frictionless linear movement.

The plunger carries the knife edge which bear upon the face of mounting blocks of cross strip hinge. The plunger carries the knife edge which bear upon the face of mounting blocks of cross strip hinge. The moving block carries a light metal y- forked arms and wrapped around the smalldrum. The moving block carries a light metal y- forked arms and wrapped around the smalldrum.

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

Any vertical movement movement of the plunger and hence that of the knife edge makes the moving block of the cross strip lever to pivot. Any vertical movement movement of the plunger and hence that of the knife edge makes the moving block 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 arms makes the driving drum hence the pointer to rotate. The metallic band attached to the arms makes the driving drum hence the pointer to rotate.

Total magnification of the instrument is Total magnification of the instrument is L/a = l/r