Measurement II

 Measuring Length Using Vernier Callipers

-Vernier callipers is used when higher accuracy in measurement is required and this cannot be done using a metre rule.
– Vernier callipers has two scales; main scale and vernier scale. Outside jaws are used to measure both lengths and external diameters, inside jaws for measuring internal diameters while the tail is used for measuring depths of cavities.
– main scale is divided into cm and mm.
– The vernier scale is divided into 10 equal divisions of 0.9 mm each. The accuracy of vernier callipers is 0.10 mm.

The reading is taken in two steps:

1. The main scale is read at zero mark of the vernier scale. The values given in cm.
2. The vernier is read at the position where a mark on the vernier scale is exactly lined up with a mark on the main scale. The values are given as a two decimal of a cm.

Practice Example 1

Give the reading in the following diagram

Solution

Main scale reading: – 2.7 cm
Vernier scale reading: – 0.04 cm
Adding both we get 2.74 cm

Practice Example 2

What is the reading of the vernier callipers shown below?

Solution

Main scale reading – 7.6 cm
Vernier scale reading – 0.04 cm
Adding both readings we get 7.64 cm

Micrometer screw gauge

– It is a device used to measure small lengths. It has an accuracy of 0.01 mm.
– It has two scales; the sleeve scale and thimble scale.
– The sleeve scale is divided into upper and lower scales with the upper division in mm and lower divisions in 0.5 mm.
– Thimble scale is divided into 50 equal divisions each division consisting of 0.01 mm.

The reading is taken in two steps:
a) The reading on the sleeve scale is read ta the point where it touches the edge of the thimble in mm and half mm.
b) The thimble scale is read at the point where the centre line of the sleeve is parallel to the thimble scale division.

Practice Example 1

Give the reading in the following.

Solution

Sleeve reading – 3.5 mm.
Thimble reading – 0.45 mm.
Adding up we get 3.95 mm.

Practice Example 2

What is the reading in the following micrometer screw gauge?

Solution

Sleeve scale reading – 4.0 mm.
Thimble scale reading – 0. 32 mm.
Adding up the two we get 4.32 mm.