VERNIER CALIPER

By Aditya Abeysinghe

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Like the micrometer screw gauge, the vernier caliper is used to take measurements that are accurate to within .001 of an inch or .02 of a millimeter or in other words it’s used to make very precise measurements which cannot be accurately measured from a meter scale

INTRODUCTION

PARTS OF A VERNIER CALIPER

Fixed jaw Movable jaw

Outer jaws

Fixed jaw Movable jaw

Inner jawsFor internal measurements

For external measurements

Vernier scale

Main or meter scale

Fine adjustment screw

Lock

Depth rod (to measure depth)

Least count- Least Count refers to the smallest distance that can be measured using an instrument. Most of the vernier Calipers have a least count of 0.1mm.

Least Count = Length of 1 MSD – Length of 1 VSD

Where MSD and VSD refer to Main Scale Division and Vernier Scale Division respectively

Generally N divisions on main scale coincide with N-1 divisions on vernier scale

1 VSD is equivalent to (N-1)/N main scale divisions

Using the formula for Least Count, we get

LC = 1 MSD – 1VSD

= 1 MSD – (N-1)/N MSD

= 1/N MSD

SPECIAL DEFINITIONS ON CALIPER MEASUREMENTS

E.g.:

A vernier scale has the length of 9 main scale divisions and is divided into 10 divisions.

Since 9 divisions of the vernier scale coincide with 10 divisions of the main scale

VSD = 9 / 10 mm = 0.9 mm

MSD= 1 mm (the least length that can be measured from the main scale – 1/10 cm)

Least Count= 1 MSD- 1VSD = 1mm - 0.9mm = 0.1mm

*The least count may vary between different vernier calipers.

Although the least count may vary between different calipers, the length formula for any caliper is as follows:

Length = MSR + (VSR * LC)

Where MSR, VSR and LC refer to Main Scale Reading, Vernier Scale Reading and Least Count respectively.

LENGTH FORMULA FOR A VERNIER CALIPER

0

0

Any vertical caliper may have two types of errors:

1.Positive zero error

2. Negative zero error

Positive zero error –

Occurs when the zero of the vernier scale is to the right of the vernier scale when the two jaws are in contact.

To take the precise value for the measurement we are taking, we have to substract the value of the positive zero error from the obtained measurement.

ERROR IN A VERNIER CALIPER

Negative zero error –

Occurs when the zero of the vernier scale is to the left of the vernier scale when the two jaws are in contact.

To take the precise value for the measurement we are taking, we have to add the value of the negative zero error to the obtained measurement.

0

0

0

0

Positive Zero Error

Negative Zero Error

No zero error is the precise arrangement of the meter scale and the vernier scale so that the zeros of both scales fit each other as follows:

To take precise measurements, we have to ensure that the caliper we are using is of no zero error.

NO ZERO ERROR

0

0

1. First find whether there’s an error on the caliper.

2. Second find its least count(LC)

3. Place the object between the appropriate jaws (outer/inner) or on the depth rod according to the measurement.

4. The reading of the main scale (MSR) which is to the left of the zero of the vernier scale is the Main Scale Reading

5. Now look up for the no. of divisions on the vernier scale which exactly coincides with any of the main scale reading. This is the Vernier Scale Reading(VSR)

6. The length of the object is calculated using the formula: Length = MSR + (VSR * LC)

7. If there’s an error in the caliper add or substract depending on the type (positive error/negative error)

TAKING A MEASUREMENT

There are three types of measurements that can be measured with a vernier caliper.

They are:

1. Measuring the external width/external diameter of an object with outer jaws

2. Measuring the internal width/internal diameter of an object with inner jaws

3. Measuring the depth of an object with the depth rod

E.g.: Measuring the length of a test tube.

TYPES OF MEASUREMENTS

1. First find whether there’s an error on the caliper.

2. Second find its least count(LC)

3. Place the object between the outer jaws

4. The reading of the main scale (MSR) which is to the left of the zero of the vernier scale is the Main Scale Reading

5. Now look up for the no. of divisions on the vernier scale which exactly coincides with any of the main scale reading. This is the Vernier Scale Reading(VSR)

6. The length of the object is calculated using the formula: Length = MSR + (VSR * LC)

7. If there’s an error in the caliper add or substract depending on the type (positive error/negative error)

MEASURING WITH OUTER JAWS

1. First find whether there’s an error on the caliper.

2. Second find its least count(LC)

3. Place the object betweenthe inner jaws

4. The reading of the main scale (MSR) which is to the left of the zero of the vernier scale is the Main Scale Reading

5. Now look up for the no. of divisions on the vernier scale which exactly coincides with any of the main scale reading. This is the Vernier Scale Reading(VSR)

6. The length of the object is calculated using the formula: Length = MSR + (VSR * LC)

7. If there’s an error in the caliper add or substract depending on the type (positive error/negative error)

MEASURING WITH INNER JAWS

1. First find whether there’s an error on the caliper.

2. Second find its least count(LC).

3. Keep the object in contact with the brim of the vernier caliper. Extend the depth rod until it meets the

depth to be measured.

4. The reading of the main scale (MSR) which is to the left of the zero of the vernier scale is the Main Scale Reading.

5. Now look up for the no. of divisions on the vernier scale which exactly coincides with any of the main scale reading. This is the Vernier Scale Reading(VSR).

6. The length of the object is calculated using the formula: Length = MSR + (VSR * LC).

7. If there’s an error in the caliper add or substract depending on the type (positive error/negative error).

MEASURING WITH DEPTH ROD

Vernier caliper

Object whose depth is to be measured

Depth rod