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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
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
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.
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
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)
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
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
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
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)
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
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.
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
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.
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
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
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
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
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
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.
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