How To Use Vernier Calliper? & How To Read A Vernier Calliper? - SKengineers

 

HOW TO USE VERNIER CALLIPER?

Vernier callipers are measuring tools used mainly for measuring linear dimensions. These callipers come handy in measuring the diameter of circular objects. Their circular jaws fit securely on either side of the circumference of round objects. Vernier callipers have two types of scales- a fixed main scale and a moving Vernier scale. The main scale is normally in millimetres or 1/10th of an inch. Vernier callipers score well over standard rulers because they can measure precise readings up to 0.001 inches. Vernier scales is used along with the Vernier calliper for accurate measurements.

Instructions on use -

The Vernier calliper is an extremely precise measuring instrument; the reading error is 1/20 mm = 0.05 mm.

Close the jaws lightly on the object to be measured.

If you are measuring something with a round cross section, make sure that the axis of the object is perpendicular to the calliper. This is necessary to ensure that you are measuring the full diameter and not merely a chord.

Ignore the top scale, which is calibrated in inches.

Use the bottom scale, which is in metric units.

Notice that there is a fixed scale and a sliding scale.

The boldface numbers on the fixed scale are centimeter.

The tick marks on the fixed scale between the boldface numbers are millimeter.

There are ten tick marks on the sliding scale. The left-most tick mark on the sliding scale will let you read from the fixed scale the number of whole millimeter that the jaws are opened.

Example 1 -

In the example above, the leftmost tick mark on the sliding scale is between 21 mm and 22 mm, so the number of whole millimeter is 21.

Next we find the tenths of millimeter. Notice that the ten tick marks on the sliding scale are the same width as nine ticks marks on the fixed scale. This means that at most one of the tick marks on the sliding scale will align with a tick mark on the fixed scale; the others will miss.

The number of the aligned tick mark on the sliding scale tells you the number of tenths of millimeter. In the example above, the 3rd tick mark on the sliding scale is in coincidence with the one above it, so the calliper reading is (21.30 ± 0.05) mm.

If two adjacent tick marks on the sliding scale look equally aligned with their counterparts on the fixed scale, then the reading is half way between the two marks. In the example above, if the 3rd and 4th tick marks on the sliding scale looked to be equally aligned, then the reading would be (21.35 ± 0.05) mm.

On those rare occasions when the reading just happens to be a "nice" number like 2 cm, don't forget to include the zero decimal places showing the precision of the measurement and the reading error. So not 2 cm, but rather (2.000 ± 0.005) cm or (20.00 ± 0.05) mm.

Range of Vernier Callipers -

General Vernier Calliper Range -

The maximum capacity of a Vernier calliper is the difference between the smallest and largest measurement reading. Usually, it is the total length of the main scale. Vernier callipers, generally, have a range of 300 mm. Vernier callipers of smaller ranges are also widely available in the marketplace.

Vernier Reading -

Vernier reading is the smallest measurable distance captured by a Vernier calliper. It is also termed as "Resolution" of the Vernier calliper. Imperial Vernier callipers have a resolution of 0.001 inches. The resolution of metric Vernier callipers varies from 0.02mm to 0.05mm. The resolution is normally indicated at the end of the Vernier scale.

Vernier Callipers Reading Scale

Tolerance -

Tolerance or instrument error refers to accuracy of Vernier calliper readings. Vernier callipers are generally used for low tolerance measurement readings. Low tolerance measurement readings are accurate and reliable because there is a minimal chance of error. The tolerance of Vernier callipers is +- 0.03mm (+- 0.0015 in). Callipers with quadri feature are used to take step measurements.

How To Read A Vernier Calliper -

Vernier calliper -

A quick guide on how to read a Vernier calliper. A Vernier calliper outputs measurement readings in centimetres (cm) and it is precise up to 2 decimal places (E.g. 1.23 cm).

Note - The measurement-reading technique described in this post will be similar for Vernier callipers which output measurement readings in inches.

Measurement Reading Technique For Vernier Calliper -

In order to read the measurement readings from Vernier calliper properly, you need to remember two things before we start. For example, if a Vernier calliper output a measurement reading of 2.13 cm, this means that:

The main scale contributes the main number(s) and one decimal place to the reading (E.g. 2.1 cm, whereby 2 is the main number and 0.1 is the one decimal place number)

The Vernier scale contributes the second decimal place to the reading (E.g. 0.03 cm)

Calliper 1 -

Let’s examine the image of the Vernier calliper readings above. We will just use a two steps method to get the measurement reading from this -

To obtain the main scale reading: Look at the image above, 2.1 cm is to the immediate left of the zero on the Vernier scale. Hence, the main scale reading is 2.1 cm

To obtain the Vernier scale reading: Look at the image above and look closely for an alignment of the scale lines of the main scale and Vernier scale. In the image above, the aligned line correspond to 3. Hence, the Vernier scale reading is 0.03 cm.

In order to obtain the final measurement reading, we will add the main scale reading and Vernier scale reading together. This will give 2.1 cm + 0.03 cm = 2.13 cm.

In a nutshell -

Use the following formula -

Obtained reading

=

Main scale reading

+

Vernier scale reading

Let’s go through another example to ensure that you understand the above steps:

calliper 2 -

Main scale reading: 10.0 cm (Immediate left of zero)

Vernier scale reading: 0.02 cm (Alignment of scale lines)

Measurement reading: 10.02 cm

Compensating For Zero Error

In a nutshell

Use the following formula:

Correct reading

=

Obtained reading

–

Zero error

where

zero error

 can be either negative (the “0” of Vernier scale is left of the “0” of the main scale) or positive (the “0” of Vernier scale is right of the “0” of the main scale)

Explanation -

Now, we shall try with zero error. If you are not familiar on how to handle zero error for Vernier callipers, I suggest that you read up on Measurement of Length.

 calliper 3 -

The reading on the top is the measurement obtained and the reading at the bottom is the zero error. Find the actual measurement. (Meaning: get rid of the zero error in the measurement or take into account the zero error)

Measurement with zero error: 3.34 cm

Zero error: – 0.04 cm (negative because the Vernier scale is to the left)

Measurement without zero error -

3.34

–

(

–

0.04

)

=

3.38

 cm

If you do not understand the subtraction of the negative zero error from the measurement, please read on. Since the zero error is -0.04 cm, this means that all measurements taken by the Vernier callipers will be SMALLER by 0.04cm. Hence, you will have to ADD 0.04 cm to ALL measurements in order to get the TRUE measurement. The subtraction is done in the above case is to have an elegant way of obtaining a resultant addition -

3.34

+

0.04

=

3.38

and to make it COMPATIBLE with positive zero error. This means that once you have determined the nature of the zero error (positive or negative), you can just subtract the zero error and be sure that your final answer is correct.

Consider a zero error of +0.04 cm. With my method,

3.34

–

(

+

0.04

)

=

3.30

 cm.

 Normal method - Since the zero error is +0.04 cm, this means that all measurements taken by the Vernier callipers will be larger by 0.04 cm. Hence, you will have to SUBTRACT 0.04 cm from ALL measurements in order to get the true measurement. The final calculation will be -

3.34

–

0.04

=

3.30

 cm, which is the same as my method.