Vernier Callipers

Definition of Callipers

A visual aid invented by Pierre Vernier, a vernier calliper, uses mechanical interpolation to measure between two graduation lines on a linear scale accurately. We use this instrument to compute the inner and outer diameters of hollow cylinders. 

We can also measure the diameters of circular objects using the measuring jaws of the vernier calliper. For instance, by putting the calliper’s jaws on each side of the circumference, the vernier calliper calibrates the diameter of round and cylindrical objects.

The vernier calliper is a highly accurate measurement device in the toolkit. It provides precise linear measurements, such as the straight linear distance between two places.  

The Least Count of Vernier Calliper

The least count of vernier callipers means the vernier constant. We can define it as the difference between one main scale division and one vernier scale division.

We can denote it as: 

VC = 1 MSD – 1 VSD

When there are n divisions on the vernier scale that overlap with (n-1) divisions on the main scale, the vernier calliper with the lowest count is:

LC = 1 – [(n-1) /n] MSD

Here, the smallest vernier calliper count is 0.1 mm.

• The least count is LC.

• The major scale division is MSD.

• The vernier scale division is VSD.

• VC denotes the vernier constant.

What is Zero Error?

The situation in which the measuring equipment registers a reading when there should be no reading is known as zero error.

We can compute the vernier calliper’s zero error as follows:

Actual reading = Main scale multiplied by Vernier scale – (Zero error)

Types of Zero Error

• Error with a positive zero: When the vernier calliper’s jaws are closed, and the reading is positive away from the 0.00 mm reading, it is an error with a positive zero. For example, if the measurement is 0.08 mm, the zero error is +0.08 mm.

• Error with a negative zero: When the vernier calliper’s jaws are closed, the reading is negative away from the true reading of 0.00 mm. For example, if the reading is 0.10 mm, the zero error is -0.10 mm.

Applications of Vernier Calliper

We can use vernier callipers for a range of tasks, due to which several engineering sectors make the best use of this instrument. The following are some of the most common applications for a vernier calliper:

• Medical applications

• Scientific laboratories

• Steel industry 

• Aerospace industry

• Education sectors

Medical Industry

Vernier callipers are used in the surgical tools of the medical sector because the healthcare professionals must measure the dimensions of medical instruments with extreme accuracy for medical usage.

Scientific Laboratories

Scientific laboratories use vernier callipers for various tasks. For example, to investigate the influence of heat fluctuations on multiple metals with varying chemical characteristics. 

These labs also use vernier callipers to accurately measure things needed to combine two sections of two objects, requiring great skill accuracy.

Steel Industry

Vernier callipers are an essential tool in the steel industry. 

The industry uses them to determine the interior and outside dimensions of steel-made items along with the thickness of steel items of various forms.

Aerospace Industry

The aerospace industry needs very high accuracy. Even little changes in an object’s dimensions can cause significant damage to it and its surroundings. Thus, the industry uses vernier callipers of various types with high precision reading.

Education Industry

In engineering research classes, students learn how to utilise vernier callipers. The instrument helps intermediate and high school physics students take accurate measurements of various items.

How to Use a Vernier Calliper?

Typically, a vernier calliper is useful to measure the diameter of circular objects. The vernier calliper’s round jaws exactly match the circumference of round objects. 

A vernier calliper has two scales: a fixed main scale and a movable vernier scale. The main scale displays measurements in millimetres. Unlike normal scales, a vernier calliper can precisely measure values up to 0.001 cm. We use a vernier scale with a vernier calliper for precise measurement. 

Range of Vernier Callipers

The difference between the smallest and the largest measurement readings states the range of vernier calliper. Usually, the main scale is the whole length of the vernier calliper. Its range is usually 300 mm. 

Vernier Reading: A vernier reading is the shortest quantifiable distance that a vernier calliper can capture. It is also known as a vernier calliper’s “Resolution.” 

The resolution of an imperial vernier calliper is typically 0.001 inch, while the resolution or shortest detectable distance of a metric vernier calliper ranges between 0.02 mm to 0.05 mm. 

Tolerance: Tolerance, also known as instrument error, refers to the precision of a Vernier calliper’s readings. We often use vernier callipers to calculate measurement readings with limited tolerance. 

Because the chance of error is low, measurement readings with low tolerance produce accurate and dependable findings. Typically, they have a tolerance of +/- 0.03mm (+/- 0.0015 in).

Conclusion

Invented by Pierre Vernier, s vernier calliper takes an accurate measurement reading on a linear scale between two graduation lines via mechanical interpolation. We use it to calculate the inner and outer diameters of hollow cylinders and measure the diameters of circular objects using the measuring jaws. 

When n divisions on the main scale overlap with (n-1) divisions, the vernier calliper with the lowest count is: 

LC = 1 – [(n-1) /n] MSD

As a result, the vernier calliper count is as low as 0.1 mm. There is no zero inaccuracy when both the main and vernier scale readings are zero.