Vernier caliper
This is a linear measuring instrument and it is used to measure the dimension to second decimal. The vernier caliper is shown in fig.
Main parts of vernier caliper -:
1. Main scale A -: It is the fixed beam scale having a fixed jaw at left end and is graduat-ed in millimetre. This is called a metric scale .
2. Vernier scale B -: It consist of sliding jaw and this scale slides over the main scale A . These scale is also graduated in 10 , 20 and 25 divisions.
3. Jaw C-:These jaw are used to measure the dimensions such as inner radius of inside of the hollow cylinders.
4. Jaw D -: These jaw are used to measure the outside diameter of the object like width, thickness etc.
5. Thumb screw E -: It is provided with the vernier scale and used to lock the position of the vernier scale.
6. Blade F -: The blade is used for measuring depth of the slots.
Least count -:
( 1 ). If there are 10 divisions on the vernier scale, and the smallest division on the main scale is of 1.0 mm.
Then, Least count = Smallest division on main scale no. of division on vernier scale = 1.0 = 0.1 mm. 10
(2). If there are 25 divisions on vernier scale and the smallest division on the main scale is 0.5 mm. Then ,
Least count = 0.5 = 0.02 mm. 25
Procedure -: Fix the jaw on the workpiece and then lock the jaw with the help of thumb screw. Then note the reading on main scale angaist zero on vernier scale. Count the no. of division on vernier scale which co-insides with a division on main scale. Multiply this number by least count and add to the main scale reading.
Hence , Total reading = Reading on the main scale + ( Least count × no. of division on vernier scale which co-inside with division on main scale ).
Very useful
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