e.g.s. pillay engineering college rev.0 nagore post, nagapattinam 611...

E.G.S. PILLAY ENGINEERING COLLEGE (An Autonomous Institution, Affiliated to Anna University, Chennai)

Nagore Post, Nagapattinam – 611 002, Tamilnadu.

Rev.0 COE/2019/QB

1702ME402 MEASUREMENTS AND METROLOGY

Academic Year : 2019-2020 Question

Bank

Programme : B.E – Mechanical

Year / Semester : II / IV Course Coordinator: Dr. J. Jeevamalar

Mr.S. Murugesh

S.No Questions COs Marks BTL

UNIT – III LINEAR AND ANGULAR MEASUREMENTS

1 What are the various types of linear measuring instruments? CO3 2 K1

Vernier caliper

Micrometer

Slip gauge or gauge blocks

Comparator

2 Give the advantages of digital Vernier caliper. CO3 2 K1

They provide long measurement ranges (6 to 80in) and fare economical.

One pair of Vernier caliper can substitute for many outside and inside micrometers, but

they cannot replace them.

They are very important in tool rom, die-making, model-making and similar condition.

3 List down the errors when Vernier caliper is used in

measurements CO3 2 K1

Error may arise in manipulation of Vernier caliper

Jaw movement should be perpendicular to the scale readings. Otherwise, measurement

will not be correct.

During internal measurements, the jaws may become bowlegged. It should be checked

frequently.

The contact position of jaws should be good conditions. So, the wear and tear, and

wrapping of Vernier caliper jaws should be tested frequently. At the same time, when

we close the jaws, it should be tightly together.

4 Why are sine bars not used for measuring large angles? CO3 2 K1

The sine bar is physically clumsy to hold in position.

The body of the sine bar obstructs the gauge block stack even if relieved

Slight errors of the sine bar cause large angular errors

5 Describe the precautionary measures to be taken at various

stages of using slip gauge. CO3 2 K1

The blocks are removed from the set, cleaned of their protective coating (petroleum jelly or

oil) and wrung together to from a stack of the required dimensions, with the minimum number

of blocks. The wear pieces are included at each end of the stack whenever possible as they

provide protection against damage to the lapped faces of the main pieces. After use the blocks

are reoiled or greased to protect their faces from corrosion.

6 Classify the comparator according to the principles used for

obtaining magnification. CO3 2 K1

The common types are: (i) Mechanical comparators. (ii) Electrical comparators. (iii) Optical

comparators. (iv) Pneumatic comparators



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7 How the mechanical comparator works? CO3 2 K1

The method of magnifying small movement of the indicator in all mechanical comparators are

effected by means of levers, gear trains or a combination of these elements.

8 State “Taylor’s principles of gauge design. CO3 2 K1

It states that GO gauge should check all related dimensions. Simultaneously; NOGO gauge

should check only one dimension at a time.

9 List out any four angular measuring instrument used in

metrology. CO3 2 K1

1. Angle gauges

2. Sine bar with slip gauge

3. Autocollimator

4. Angle dekkor

10 State any four advantages of mechanical comparator. CO3 2 K1

i. It is usually robust, compact and easy to handle.

ii. There is no external supply such as electricity is required.

iii. It has very simple mechanism and is cheaper when compared to other types.

iv. It is suitable for ordinary workshop and also easily portable.

11 What are the constructional requirements of a good sine bar? CO3 2 K1

Two rollers must have equal diameter and equal cylinders.

The rollers should be placed to each other and also to the upper face.

The accurate center to center of rollers must be known.

The top surface of the bar must be flat with high degree of accuracy.

12 What are the sources of errors in using sine bar? CO3 2 K1

Error in distance between two rollers

Error in slip gauge combination

Error in parallelism of roller axes with each other.

Error in flatness of the upper surface of the sine bar.

13 What is comparator? CO3 2 K1

Comparator is the one form of linear measurement devices which is quick and more

convenient for checking the large numbers of identical dimensions by comparing to actual

dimensions with standard dimensions.

14 What are the advantages of pneumatic comparator? CO3 2 K1

• The wear of measuring heads is avoided due to absence of direct contact.

• Friction is less due to less number of moving parts.

• Work piece is cleaned by supplying of all during the measurement.

• High magnification is possible.

15 Define least count and mention the least count of a mechanical

comparator. CO3 2 K1

The least value that can be measured by using any mechanical instrument is known as least

count.

Least count of a mechanical comparator is 0.01mm.



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PART – B

S.No Questions COs Marks BTL

UNIT – III LINEAR AND ANGULAR MEASUREMENTS

1 Explain with a neat sketch how a vernier caliper is used for

linear measurements. CO3 12 K2

Vernier Caliper – Construction & Working (6)

The principle of Vernier caliper is which has two scales of different sizes used to measure the

dimensions in high accuracy. The Vernier caliper has two steel rules which slide each other.

One of the longer scales is named as main scale which is graduated on a solid L-shaped frame.

The graduation is done for 20 parts in which one small division is equal to 0.05cm. The Vernier

caliper consists of three elements such as beam, fixed jaw and sliding jaw or movable jaw. The

movable jaw slides over the main scale according to the dimension of the specimen to be

measured. Before starting the measurement, we should ensure, the scale is checked for zero

reading when two measuring jaws are in contact with each other. During measurement, the fine

adjustment of the movable jaw is done by adjusting the adjustment screw. At that same time,

both jaws should touch the part to be measured during measurement. After doing the fine

adjustment, the lock nut B is tightened. Final adjustment depends on the correct feel of the

operator which is based on the experience of an operator. After the final adjustment has been

done, the locknut A is also tightened to note down the readings. Vernier calipers have two

scales namely, mains scale and Vernier scale. The Vernier scale moves along the main scale.

Vernier is used to measure both internal and external dimensions.

The caliper is placed on the object to be measured and fine adjustment screw is rotated until the

jaws fit tightly against the work piece. The readings from the main scale and the Vernier scales

are taken.

Diagram (6)



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2 Explain with a neat sketch explain the types of micrometer. CO3 12 K2

1. OUTSIDE MICROMETER (4)

It consists of a C-shaped frame with a stationary anvil and a movable spindle. The spindle

movement is controlled by a precision ground screw. The spindle moves as it is rotated in a

stationary spindle nut. A graduated scale is engraved on the stationary sleeve and the rotating

thimble. The zeroth mark on the thimble will coincide with the zeroth division on the sleeve

when the anvil and spindle faces are brought together. The movement of the screw conforms to

the sets of graduations. The locknut enables the locking of the spindle while taking a reading.

The ratchet ensures a ‘feel’ while taking a reading and prevents application of excessive force

on the job.

2. INSIDE MICROMETER (4)

The axis of an inside micrometer is also its line of measurement. It is useful for measuring the

inside diameter of cylinders, rings, and other machine parts. The inside micrometer set has

several accessories, which have to be assembled together for taking the readings. The main unit

is the measuring head, which has a thimble that moves over a barrel, same as in the case of an

outside micrometer. Graduated scales are provided on the barrel and thimble, which give

readings up to an accuracy of 0.01 mm, but with a limited range.

3. MICROMETER DEPTH GAUGE (4)

An alternative to vernier depth gauge is the depth micrometer. In fact, most shop floor

engineers vouch for its superiority over vernier depth gauges because of its greater measuring

range, better reliability, and easier usability. One peculiarity of this instrument is that it reads in

reverse from other micrometers. Looking from the ratchet side, a clockwise rotation moves the

spindle downwards, that is, into the depth of the job being measured. Therefore, the entire

barrel scale is visible when the tip of the measuring rod is in line with the bottom surface of the

base. As the measuring rod advances into the depths, the thimble will move over the barrel



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scale. Reliable measurements of up to 0.01 mm are possible with this instrument. Figure

illustrates the parts of a depth micrometer. The bottom flat surface of the base butts over the

reference plane on the job, and the micrometer scale directly gives the depth of the measuring

rod tip from the reference plane.

3 Explain the working of universal Bevel Protractor with a neat

sketch. CO3 12 K2

Construction & Working (6) The universal bevel protractor with 5’ accuracy is commonly found in all tool rooms and metrology

laboratories. Figure illustrates the construction of a universal bevel protractor. It has a base plate or

stock whose surface has a high degree of flatness and surface finish. The stock is placed on the

workpiece whose angle is to be measured. An adjustable blade attached to a circular dial is made to

coincide with the angular surface. It can be swiveled to the required angle and locked into position

to facilitate accurate reading of the circular scale that is mounted on the dial. The main scale on the

dial is graduated in degrees and rotates with the rotation of the adjustable blade. A stationary

vernier scale mounted close to the dial, as shown in Fig. 5.1, enables measurements to a least count

of 5' or less. An acute angle attachment is provided for the measurement of acute angles. The main

scale on the dial is divided into four quadrants, each measuring 90°. Each division on this scale

reads 1°. The degrees are numbered from 0 to 90 on either side of the zeroth division. The vernier

scale has 24 divisions, which correspond to 46 divisions on the main scale. However, the divisions

on the vernier scale are numbered from 0 to 60 on either side of the zeroth division.

Diagram (6)



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4 Explain with the help of neat sketch, the principle and

construction of an auto-collimator. CO3 12 K2

Definition (2)

Auto-collimator is an optical instrument used for the measurement of small angular difference,

change or deflection, plane surface inspection etc. for small angular measurements, the

autocollimator provides a very sensitive and accurate approach. An autocollimator is essentially

an infinity telescope and a collimator is combined into one instrument.

Diagram (5)

Working (5)

There are three main parts in autocollimator

1. Micrometer microscope

2. Lighting unit

3. Collimating lens

A target graticule is positioned perpendicular to the optical axis. When the target graticule is

illuminate by a lamp, rays of light diverging from the intersection point reach the objective lens

via beam splitter.

A flat reflector is placed in front of the objective and exactly normal to the optical axis reflect

the parallel ray of light back along the original paths. They are then brought to the target

graticule and it exactly co-insides with its intersection. A portion of the return light passes

through the beam splitter it is visible to the eye-piece.

If the reflector is tilted to the small angle, the reflector beam will be changed is path at twice the

angle. It can also be brought to target graticule linearly displaced from the actual target by the

amount 2f. linear displacement of the gratitude imaging the plane is tilted angle of eyepiece

therefore directly proportional to the reflector. It can be measured by an optical micrometer.

The photoelectric autocollimator is particularly suitable for calibrating polygons, for checking

angular indexing and for checking small linear displacement.



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5 Discuss the working principle of Angle Dekkor with a sketch. CO3 12 K2

Working (6)

It is the type of auto collimator. There is an illuminated scale in the focal plane on the

collimating lens this illuminated scale in the parallel beam by the collimating lens which after

striking a reflector below the instrument is refocused by the lens in the field of eye-piece.in the

field of view of microscope, there is another datum scale fixed across the centre of screen.

Reflected image of the illuminated scale is received at right angle to the fixed scale. Thus, the

changes in angular position the reflector n two planes are indicated by changes in the point of

intersection of the two scales. One division of the scale is calibrated to read one minute.

The whole optical system is enclosed in a tube which is mounted on an adjustable bracket.

Adjustable bracket is attached to a flat lapped reflective base.

Diagram (6)

6 Explain working of sine bar and also write its advantage,

disadvantage and limitations. CO3 12 K2

Definition (6)

A sine bar is used to measure angles based on the sine principle. Its upper surface forms the

hypotenuse of a triangle formed by a steel bar terminating in a cylinder near each end. When

one of the cylinders, called a roller, is resting on a flat surface, the bar can be set at any desired

angle by simply raising the second cylinder. The required angle is obtained when the difference

in height between the two rollers is equal to the sine of the angle multiplied by the distance

between the centres of the rollers. Figure illustrates the construction details of a sine bar. Sine

bars are made of corrosion-resistant steel, and are hardened, ground, and stabilized. The size is

specified by the distance between the centres of the cylinders, which is 100, 200, or 300 mm.

The upper surface has a high degree of flatness of up to 0.001 mm for a 100 mm length and is

perfectly parallel to the axis joining the centres of the two cylinders. The parallelism of upper

surface with the datum line is of the order of 0.001 mm for a 100 mm length. Relief holes are

sometimes provided to reduce the weight of the sine bar. This by itself is not a complete

measuring instrument. Accessories such as a surface plate and slip gauges are needed to

perform the measurement process.



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Working principle of sine bar (6)

The working of sine bar is based on the trigonometry principle. To measure the angle of a given

specimen, one roller of the sine bar is placed on the surface plate and another one roller is

placed over the surface of slip gauges. Now, ‘h’ be the height of the slip gauges and ‘L’ be the

distance between roller centers , then the angle is calculated as

sin=h/L

=sin-1(h/L)

Limitations of sine bar

1. Sine bars are fairly reliable for angles less than 15º.

2. It is physically difficult to hold in position.

3. Slight errors in sine bar cause larger angular errors

4. A difference of deformation occurs at the point of roller contact with the surface plate

and to the gauge blocks.

5. The size of parts to be inspected by sine bar is limited.

PART – C

Questions COs Marks BTL

1 Describe the working of electrical comparator and Mechanical

comparator with a neat sketch. CO3 20 K2

i. Electrical Comparator (10)

Construction:

A electrical comparator consists of the following three major parts such as

1. Transducer

2. Display device as meter

3. Amplifier

Working principle

If the armature is centrally located between coils, the inductance of the both coils will be

equal but in opposite direction with the sign change. Due to this, the bridge circuit A.C.

Wheatstone bridge is balanced. Therefore, meter will read zero value. But practically it not

possible. In real cases, the armature may be lifted up or lowered down by the plunger during

measurement .it would upset the balance of the Wheatstone bridge circuit. Due to the effort



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the change in current or potential will be induced correspondingly. On the time the meter

will indicates some value as displacement. This indicated value may be either for larger or

smaller component.as the induced in current is too small, it should be suitably amplified

before being displayed a meter.

ii. Mechanical comparator (10)

Dial indicator mechanical comparator,

The dial indicator or dial gauge is used as a mechanical comparator. The essentially part of

the instrument the small clock with a plunger projecting at the bottom.

Very slight upward movement on the plunger moves it upward and the movement is indicated

by the dial pointer. The dial is graduated into hundred divisions. Full revolution of the pointer

about the scale corresponds to 1mm travel of the plunger. Thus a turn of the pointer by one

scale division represents the plunger travel of 0.01mm.

2 Explain the types of pneumatic comparator with a sketch. CO3 20 K2

i. Free Flow Air Gauge (10)

This uses a simple pneumatic circuit. Compressed air with a pressure in the range 1.5–2 bar is

passed through a tapered glass column that contains a small metal float. The air then passes

through a rubber or plastic hose and exits to the atmosphere through the orifice in the gauging

head. Since the gauging head is inserted inside the work part that is being inspected, there is a

small clearance between the gauging head and the work part. This restricts the flow of air,

thereby changing the position of the float inside the tapered glass column. The set-up is



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illustrated in Fig. Compressed air from the factory line is filtered and reduced to the required

pressure. A shut-off valve is provided to ensure shut-off of air supply when not in use. Air

bleed and zero adjustment screws are provided to facilitate calibration of the gauge. The

gauge head is mounted onto a handle, which provides a convenient way of handling the

gauge head during inspection. As mentioned, the amount of clearance between the gauge

head and the work part determines the rate of air flow in the glass column, which in turn

regulates the position of the float.

ii. Solex Pneumatic Gauge (10)

This air gauge has been developed and marketed by Solex Air Gauges Ltd, USA, and is one

of the most popular pneumatic comparators in the industry. The Solex pneumatic gauge is

generally used for the inspection of internal dimensions, although it is also used for external

measurements with suitable attachments. Figure 6.24 illustrates the construction details of

this

comparator. Compressed air is drawn from the factory air supply line, filtered, and regulated

to a pressure of about 2 bar. Air will now pass through a dip tube immersed in a glass water

tank.

The position of the dip tube in terms of depth H will regulate the effective air pressure in the

system at the input side. Extra air, by virtue of a slightly higher supply air pressure, will leak

out

of the water tank in the form of air bubbles and escape into the atmosphere. This ensures that

the air moving towards the control orifice will be at a desired constant pressure. The air at a

reduced pressure then passes through the control orifice and escapes from the measuring

orifice in the measuring head. Based on the clearance between the work part and the

measuring orifice, a back pressure is created, which results in the head of water being

displaced in the manometer tube. As we have already seen, within a limited measuring range,

change in pressure varies linearly with change in internal dimension of the work part.

Therefore, the change in linear dimension can be directly read from a linearly calibrated

scale. The Solex comparator has a high degree of resolution, and variation in dimension up to

a micrometer can be determined easily.



Rev.0 COE/2019/QB

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