Vernier caliper: Types of Vernier Caliper [Complete Guide]

Vernier Caliper and Types of Verier Caliper [Complete Guide]

Introduction to Vernier caliper and types of Vernier caliper:

A vernier caliper is an instrument which is most commonly used for a variety of exact measurements, which was not necessarily related to the engineering manufacturer.

There are three types of vernier caliper used in the physics laboratory to measure lengths of small objects accurately which could not have been possible with a metre scale.

  • Type A
  • Type B
  • Type C.

The main use of the vernier caliper is to measure the internal and external diameters of an object.The word caliper means any instrument with two jaws which is used to determine the diameters of objects.

In ancient China, the caliper was born without the beginning of scale as the Qin Dynasty (AD 9). In 1631, French Pierre Vernier introduced a device to obtain accurate measurements required for scientific experiments.

The principle of the vernier caliper is that when two scales or divisions slightly different in size are used, then the difference between them is used to increase the accuracy measurement.

Construction and Parts of Vernier Caliper

Vernier-calliper-parts-discription

The main elements of the vernier caliper are the

  • Main Scale
  • Vernier scale
  • Thumbscrew
  • Lock screw
  • Depth Rod
  • Fixed jaw, and
  • Sliding jaw

Vernier Caliper Part Description

Vernier-calliper-part-discription

Vernier caliper consists of two steel rules and they can slide along with each other.

  • One is a long rectangular metal strip which has a fixed jaw on one end. It is graduated in inches at its upper end and centimetre at its lower end which is called the main scale.

The main scale is marked on solid L shape frames, on which cm graduates are divided into 20 parts so that a small division is equal to 0.05 cm. This allows improvements in the commonly used measuring techniques, over direct measurement with line graduated method.

  • There is another small rectangular metal strip which is graduated with a special relation to that of the main scale, which is called the vernier scale which slides over this long metal strip it has a jaw similar to that of the main scale.

There are two jaws on vernier caliper upper jaw and lower jaw. These jaws together are used to hold the object firmly while measuring its length which is not possible with a metre scale.

The external or lower jaws which are generally used to measure the diameter of a sphere or a cylinder. The internal jaws or upper jaws which are generally used to measure the internal diameter of a hollow cylinder.

There is also a metal strip attached at the back of the vernier calipers which is used to measure the internal depth of a cylinder.

The Principle Of Vernier Caliper

A scale cannot measure objects which are smaller than 1mm but a vernier caliper can measure objects up to 1mm. As already know that vernier caliper has two scales the main scale and the vernier scale together this arrangement is used to measure very small lengths like 0.1mm.

Here the main scale has least count of 1mm and vernier scale has least count of 0.9mm. So therefore 10 unit of the main scale is 1cm whereas 10 unit of vernier scale is 0.9mm.

The unit of the vernier scale is 9mm. So this difference between the main scale and vernier scale which is 0.1mm is the working principle of vernier caliper.

Vernier Caliper Least Count:

The difference between the value of one main scale division and the value of one Vernier scale division is known as least count of the Vernier.

Least count of vernier caliper is the smallest value that we can measure from this device. To calculate the least count of vernier caliper is the value of one main scale division divided by the total number of division on the vernier scale.

Let’s assume if the value of one main scale division is 1mm and the total number of division on vernier scale 10mm then the least count will be 0.1mm. Thus least count is defined as the smallest distance that can be measured from an instrument.

Vernier Caliper Zero Error 

Zero error in the vernier caliper is a mathematical error due to which, The zero of the vernier scale does not coincide with the zero of the main scale.

In other words, if the zero mark on the vernier scale doesn’t coincide with the zero mark on the main scale, then the error that occurs is called zero error. They are of 2 types.

  1. No zero error
  2. Positive zero error
  3. Negative zero error

No Zero Error 

vernier-calliper-zero-error

In no zero error, when we bring two jaws together. You will see zero of the Main scale is coinciding with the zero of the vernier scale. they are exactly in a straight line so this vernier caliper is free from zero error or you can say there is no zero error in this vernier caliper.

Positive Zero Error

In positive zero error, Let’s bring these jaws together. you see, the zero of vernier scale is ahead of main scale zero. Or you can say zero of vernier scale is at the right side of main scale zero.

vernier-calliper-positive-error

In both cases either it is ahead of main scale zero or it is the right side of main scale zero. this is called as zero error and it is positive

Negative Zero Error

In negative zero error,  we will bring the two jaws together. Here you can see zero of vernier scale is the back side of main scale zero. Or to the left of main scale zero.

Vernier-calliper-negative-error

So if vernier scale zero is either backside or to the left of main scale zero, in both cases, zero error is the negative error.

Working of Vernier Caliper

The sliding jaw runs on the main scale with the guiding surface, which is accompanied by a vernier scale, in which it has a measuring tip on the left side.

When two measuring tip surfaces are in contact with each other, the scale shows zero reading.

how to use vernier calliper
By Lookang many thanks to Fu-Kwun Hwang and author of Easy Java Simulation = Francisco Esquembre – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=15912813

The finer adjustment of the movable jaw can be done by adjusting screw.

First, the whole movable jaw assembly is adjusted so that the two measuring tips just touch the part to be measured. Then lockout B is tightened.

Final adjustment depending upon the sense of correct feeling is made by adjusting screw, which makes the part containing locking nut A and sliding jaw to move, as the adjusting screw rotates on a screw which is in a way fixed to the movable jaw.

After all, the final adjustment has been done, the locking nut has also been tightened and the reading has been noted. Measuring tips are designed so that they can be used to measure external dimensions as well as internal dimensions.

Types of Vernier Caliper

Vernier calipers are classified based on international standard IS 3651-1974, according to this standard three types of vernier calipers have been specified to meet external and internal measurement requirements of up to 2000mm with the accuracy of 0.02, 0.05 and 0.1 mm. Types of vernier caliper are termed as type A, type B and type C.

Type A

  • This is made with only one scale on the front of the beam for direct reading.
  • It has jaws on both sides for external and internal measurements.
  • It is also having a blade for depth measurements.
  • The calipers are made of good quality steel and the measuring faces hardened to 650 HV. minimum.
Types of vernier caliper - Type A

The beam is made flat throughout its length to within the tolerances of

  • 0.05mm for nominal lengths up to 300mm,
  • 0.08mm from 900 to 1000mm and
  • 0.15 for 1500 and 2000mm sizes.

The guiding surface of the beam is made straight to within 0.01mm for measuring the range of 200mm and 0.01mm every 200mm measuring range or larger size.

As per IS 3651-1974 nominal sizes for measuring are

0-125, 0-200, 0-250, 0-300, 0-500, 0-750, 0-1000, 750-1500 and 750-2000mm.

The scale serves for both external and internal measurements.

The fixed jaw is made an integral part of the beam and the sliding jaw is made a good sliding fit along with the beam and made to have seizure free movement along the bar.

Type B

  • It is made only one scale on the front of the beam for direct reading.
  • It is provided with jaws on one side for external and internal measurement.

The beam is made flat throughout its length to within the tolerances of

  • 0.05mm for nominal lengths up to 300mm,
  • 0.08mm from 900 to 1000mm and
  • 0.015mm for 1500 and 2000mm sizes.
    Types of vernier caliper - type B
    The guiding surfaces of the beam are made straight to within
  • 0.01mm for measuring the range of 200mm and
  • 0.01mm every 200mm measuring range of large size.

The main scale serves for external measurements and internal measurements are made by adding the width of the internal measuring jaws to the reading on the scale.

As per IS 3651-1974 nominal sizes for measuring are

0-25, 0-200, 0-250, 0-300, 0-500, 0-750, 0-1000, 750-1500 and 750-2000mm.

The scale serves for both external and internal measurements.

The measuring surfaces are given a fine ground finish and the portion of the jaws between the beam and the measuring faces are relieved.

The fixed jaw is made an integral part of the beam and the sliding jaw is made a good sliding fit along with the beam and made to have seizure free movement along the bar.

Type C

  • It is made only one scale of the front of the beam for direct reading.
  • It has jaws on both sides for making the measurements and for marking operations.

The beam is made flat throughout its length to within the tolerances of

  • 0.05mm for nominal lengths up to 300mm,
  • 0.08mm from 900 to 1000mm and
  • 0.15mm for 1500 and 2000mm sizes.
    Types of vernier caliper - type C

The guiding surface of the beam is made straight to within 0.01mm for measuring the range of 200mm and 0.01mm every 20mm measuring range of large size.

As per IS 3651-1974 nominal sizes for measuring are

0-125, 0-200, 0-250, 0-300, 0-500, 0-750, 0-1000, 750-1500 and 750-2000mm.

The scale serves for both external and internal measurements.

The measuring surfaces are given a fine ground finish and the portion of the jaws between the beam and the measuring faces are relieved.

The fixed jaw is made an integral part of the beam and the sliding jaw is made a good sliding fit along with the beam and made to have seizure free movement along the bar.

General Errors In Measurement With Vernier Caliper

The errors occurred in vernier caliper due to its incorrect handling of the jaws on the workpiece.

In measuring outside diameter, it must be ensured that the caliper bar and the plane of the caliper jaws are truly perpendicular to the workpiece.

To avoid error you must be ensured that caliper is not tilted or twisted. But it happens because of relatively long extending the main bar of the average vernier calipers.

The accuracy depends on the greater extent on the condition of the jaws of the caliper.

The accuracy and the natural wear, warping of vernier caliper jaws should be tested frequently by cooling them together tightly or setting them to the 0.0 point of the main and vernier scale.

In above position when it is held against a light source, in case of wear, spring or warp, a knock-kneed condition observed and of measurement error is greater than 0.005mm the instrument should not be used and sent for repair.

Whenever the wear or wrapping of sliding jaw frame place it does not slide squarely and snugly on the main caliper beam, then jaws will appear.

The jaws of vernier caliper may become bowlegged or its outside edges are worn down while measuring inside diameter.

Advantages and Disadvantages of Vernier Scales

Advantages

  • Amplification is achieved by design and it is not dependent on the parts that can go out of wear or calibration.
  • No interpolation is possible in reading, let alone required.
  • Zero setting adjustment is easy.
  • There is no theoretical limit to the scale range.

Disadvantages

  • The main disadvantages lie in the instruments on which verniers are used.
  • The reliability of reading depends more upon the observer that must instruments.
  • No way to adjust for any errors other than zero setting.
  • The discrimination is limited.

How To Use Vernier Caliper In Right Way Step-by-Steps

  1. Clean both the part and the calliper completely so that it is free from burrs and other obstacles.
  2. Loose clamping screws on both of sliding jaws. Set the sliding jaw slightly larger than measurable features.
  3. Clamp nut carries to the beam. Snug up but do not lock the clamping screw on the movable jaw.
  4. Place the fixed jaw in contact with the reference point of the part feature.
  5. Align the beam of the caliper in both planes to be almost parallel to the line of measurements as much as possible.
  6. Turn the adjusting nut so that movable jaw just touches the part.
  7. Tighten clamp screw on the movable jaw without disturbing the feel between the caliper and the part.
  8. Read in place without disturbing part of a caliper, if possible, otherwise remove the caliper.
  9. Record the reading on paper, mark on the part, or part drawing.
  10. Repeat the measurement steps a sufficient number of times to rule out any obviously incorrect reading and average the others for the desired measurement.
  11. Loosen both clamps, slides movable jaw open, remove work, if not already done.
  12. Clean, lubricate and replace instrument in its box.
  13. Check yourself, what errors may remain in my measurement.

Precautions In The Use Of Vernier Caliper

Often during experiments or in the industry, there is a very small margin of error. Some of that error is due to the environmental conditions or inherent in the procedure which we cannot control.

The other part is due to human error and errors in the system. These errors lie within our control and can be eliminated if the proper measures are taken otherwise the measurements can be significantly inaccurate which is obviously undesirable.

The following precautions should be considered while using a vernier caliper. These precautions are necessary to minimize any errors which can affect the accuracy of the measurement.

Number 1

The most common form of error is the parallax error. This means “alteration”. This error occurs when an object is observed from an angle. This makes the object appear at a slightly different position than it really is and can lead us to take a wrong reading on a measuring scale. To eliminate this error the observer should position his eyes directly above the scale when taking the Main Scale reading and the Vernier Coincidence.

Number 2

Make sure you to take all the readings in the same unit system while measuring. for example,

  • MKS units metre, kilogram and second for measurement of length, weight and time.
  • CGS system which uses the units of a centimetre, gram and second.

If any measurements are taken in a unit in another system it should be converted to the appropriate units before being used in any calculations.

Number 3

Avoid excessive force on the jaws, while gripping the object to be measured. The object should always be gripped gently between the jaws. This is extremely important while measuring objects which are easily deformable e.g wires.

Number 4

As we discussed above, Before taking any measurements, make sure the vernier caliper does not have a zero error. If there is zero error the appropriate corrections should be applied.

Number 5

The accuracy of measurement primarily depends on two senses:

  1. Sense of sight
  2. Sense of touch

Number 6

The surface of the object and instrument cover should be cleaned and dried with a cloth soaked in cleaning oil.

Number 7

Loosen the locking key of the vernier caliper and make sure there is no friction between the scales while moving the jaws of the vernier caliper.

Number 8

In the case of a digital vernier caliper the following additional steps should be taken: Bring the jaws in contact with each other and then press the on/off button.

  1. Check the reading and make sure it is zero.
  2. Move the slider and check whether all the buttons and the LCD display are working properly.

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