Page 63 - CITS - Fitter - Trade Theory

FITTER - CITS

LESSON 10 : Precision measuring instrument

Objectives

At the end of this lesson you shall be able to
• explain various types of precision measuring instruments like vernier caliper, vernier height gauge, micrometers
etc.
• working principles of various precision measuring instruments
• state the safety precautions and care and maintenance while using

Universal Vernier Caliper (Metric)

• Definition of universal vernier caliper
It is the precision measuring instruments by which we can measure external internal and depth of a job with
0.02 mm accuracy
Parts
1 Fixed jaw
2 Movable jaw

3 Thumb grid thumb rest
4 Depth bar
5 Beam
6 Nibs
7 Locking screw

8 Find adjusting unit
1 Main scale: The main scale is a graduated scale marked in millimeters (or inches) along its length. It is fixed
to the caliper body and serves as the primary reference for measurement.

2 Vernier scale: The vernier scale is a secondary scale that slides along the main scale. It contains divisions
that are slightly smaller than those on the main scale. The vernier scale allows for more precise measurement
readings by providing additional subdivisions beyond the main scale divisions.
3 Measuring jaw: The measuring jaw is the stationary upper jaw of the caliper, against which the object
being measured is placed. It typically has an inside and outside measuring surface for different types of
measurements.
4 Sliding jaw: The sliding jaw is the lower movable jaw of the caliper, which moves along the main scale and
vernier scale. It is adjusted to contact the opposite side of the object being measured, allowing the caliper to
accurately measure the distance between the jaws.

5 Depth bar: Many vernier calipers also feature a depth probe or rod attached to the lower end of the sliding jaw.
This probe extends perpendicular to the measuring jaws and allows for depth measurements of holes, slots,
and other recessed features.
6 Locking screw: Some vernier calipers are equipped with a locking screw or clamp mechanism to secure the
sliding jaw in position once the measurement has been taken, preventing accidental movement and ensuring
measurement accuracy.
• Principal of universal vernier caliper
The difference between two sliding scale i.e.main scale division & vernier scale division

Least count of universal vernier caliper
value of 1 main scale division = 1mm hence 49 main scale division = 49mm

48