VERNIER CALLIPER

What is vernie calliper?

A vernier calliper is defined as a measuring device that is used for the measurement of linear dimensions. It is also used for the measurement of diameters of round objects with the help of the measuring jaws.

French mathematician Pierre Vernier invented the vernier scale in 1631. The main use of the vernier calliper over the main scale is to get an accurate and precise measurement.

Least Count of Vernier Calliper

The least count of vernier callipers is also known as the vernier constant. It is defined as the difference between one main scale division and one vernier scale division.

It is mathematically given as :

VC=1MSD-1VSD

When there are n divisions on the vernier scale, which coincides with (n-1) division on the main scale, then the least count of vernier calliper is:

$\begin{array}{l}LC=(1-\frac{n-1}{n})MSD\end{array}$

Therefore, the least count of vernier calliper is 0.1 mm.

■ VC is the vernier constant

■ MSD is the main scale division

■ VSD is the vernier scale division

■ LC is the least count

What Is Zero Error?

Zero error is defined as the condition in which the measuring device registers a reading when there should not be any reading.

The zero error of the vernier calliper is calculated as:

☆ Actual reading = Main scale + Vernier scale – (Zero error)

There are two types of zero error:

● Positive zero error: When the jaws of the vernier calliper are closed, the reading is positive and away from the actual reading of 0.00 mm. For instance, if the reading is 0.08 mm, then the zero error is +0.08 mm.

● Negative zero error: When the jaws of the vernier calliper are closed, the reading is negative and away from the actual reading of 0.00 mm. For instance, if the reading is 0.10 mm, then the zero error is -0.10 mm.

How to Read Vernier Calliper?

● The first step is to measure nothing through which we can check if the main and the vernier scales are aligned.

● When the main scale reading and the vernier scale reading are at zero, it means there is no zero error.

● Now, place a ball between the two jaws of the vernier scale.

● Look at the 0 mark on the vernier scale lining with the main scale.

● That gives the main scale reading.

● Next, look for the point on the vernier scale, which is aligned with the main scale, which gives the vernier scale reading.

● It is important to note that the readings will most of the time be in decimals.

● The number before the decimal point is the main scale reading, while the number after the decimal point is the vernier scale reading.

Main Scale

It is a large scale that runs along the body of the vernier calliper. Depending on the usage, the reading on the main scale could be either in centimetres or millimetres. 1 mm is the lowest main scale division according to the SI units. The main scale is stationary.

Vernier Scale

This is the smaller scale attached to the main scale, moving along the main scale. The vernier scale’s movement depends on the jaws’ opening. The main function of the vernier scale is to provide accuracy to the main scale reading by dividing the reading into smaller increments. The vernier scale in a metric calliper can have divisions up to 50 increments, each of which measures 0.02 mm.

Lower Jaws

These jaws are considered one of the most prominent features of vernier calliper. One of the jaws is fixed and attached to the main scale. While the other jaw is movable and is attached to the vernier scale. These jaws are designed mainly to grip the objects firmly. The main function of the lower jaw is to measure the outer dimensions such as diameter, width and length.

Upper Jaws

These jaws are similar to the lower jaws but are smaller than, the lower jaws. These jaws are attached to the upper part of the vernier scale. One of the jaws is fixed, while the other jaw is movable. The main function of the upper jaw is to measure the inner dimensions of the objects. The jaws are opened until they touch the objects’ edges before taking the reading. The inside diameters of objects such as hollow pipes and jars can be measured using upper jaws.

Depth Rod

The depths of the jars can be measured using the depth rod. It is a thin rod located at the end of the main scale. Using a depth rod for measuring is simple. The edge of the main scale is placed on the object’s top surface. Then the jaws are slowly opened. The opening of the jaws results in the extension of the depth rod. The jaws need to be opened until the depth rod reaches the bottom of the object.

Thumb Screw

This screw is located at the bottom of the vernier scale. The main function of the thumbscrew is to provide grip to the users so that the sliding of the jaws becomes easy.

Lock Screw

The main use of the lock screw is to fix the position of the jaws once the object is firmly fixed between the jaws. This also makes it easy to take proper readings.

Applications of Vernier Callipers

● Medical usages

● Science labs

● Industries such as steel and aerospace

● Educational sectors