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S.K.P. Engineering College, Tiruvannamalai VI SEM

Mechanical Engineering Department 1 Metrology and Measurements

SKP Engineering College

Tiruvannamalai – 606611

A Course Material

on

Metrology and Measurements

By

Mr.K.Venkatesh, Mr.R.Susenthirar, Mr.R.Manjunathan,

Mr.E.Ravindarsingh

Assistant Professor

Mechanical Engineering Department



Quality Certificate

This is to Certify that the Electronic Study Material

Subject Code: ME6504

Subject Name: Metrology And Measurements

Year/Sem: III / VI

Being prepared by Mr.K.Venkatesh, Mr.R.Susenthirar, Mr.R.Manjunathan,

Mr.E.Ravindarsingh and it meets the knowledge requirement of the University

curriculum.

Signature of the Author

Name: Mr.K.Venkatesh, Mr.R.Susenthirar, Mr.R.Manjunathan, Mr.E.Ravindarsingh

Designation: Assistant Professor

This is to certify that the course material being prepared by R.Susenthirar,

Mr.K.Venkatesh is of the adequate quality. He has referred more than five books and

one among them is from abroad author.

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Name: Dr.J. Kuberan Name: Dr.V.Subramania Bharathi

Seal: Seal:



SYLLABUS UNIT I CONCEPT OF MEASUREMENT 9

General concept – Generalized measurement system-Units and standards-measuring instruments: sensitivity, stability, range, accuracy and precision-static and dynamic response-repeatability-systematic and random errors-correction, calibration - Introduction to Dimensional and Geometric Toleranceing - interchangeability UNIT II LINEAR AND ANGULAR MEASUREMENT 9 Definition of metrology-Linear measuring instruments: Vernier, micrometer, Slip gauges and classification, - Tool Makers Microscope – interferometer, optical flats, -Comparators: limit gauges Mechanical, pneumatic and electrical comparators, applications. Angular measurements: -Sine bar, Sine center, bevel protractor and angle Decker. UNIT III FORM MEASUREMENT 9 Measurement of screw threads: Thread gauges, floating carriage micro meter measurement of ear tooth thickness: constant chord and base tangent method-Gleason gear testing machine – radius measurements-surface finish: equipment and parameters, straightness, flatness and roundness measurements UNIT IV LASER AND ADVANCES IN METROLOGY 9

Precision instruments based on laser-Principles- laser interferometer-application in measurements and machine tool metrology- Coordinate measuring machine (CMM): need, construction, types, applications.- computer aided inspection. UNIT V MEASUREMENTOFMECHANICALPARAMETERS 9

Force, torque, power:-mechanical, pneumatic, hydraulic and electrical type-Pressure measurement - Flow: Venturi, orifice, rotameter, pitot tube –Temperature: bimetallic strip, thermocouples, pyrometer, electrical resistance thermistor.

TOTAL: 45 PERIODS CONTENT BEYOND SYLLABUS

Fit and tolerance

Multiple operation

LEARNINGRESOURCES: TEXT BOOKS: 1. Jain R.K., ―Engineering Metrology‖, Khanna Publishers, 2005



2. Alan S. Morris, ―The Essence of Measurement‖, Prentice Hall of India, 1997 REFERENCES

1. Gupta S.C, ―Engineering Metrology‖, Dhanpatrai Publications, 2005 2. Jayal A.K, ―Instrumentation and Mechanical Measurements‖, Galgotia Publications 2000 3. Beckwith, Marangoni, Lienhard, ―Mechanical Measurements‖, Pearson Education, 2006. 4. Donald Deckman, ―Industrial Instrumentation‖, Wiley Eastern, 1985. WEB RESOURCES:

1. www.redoaksys.com (for animations) 2. www.boschrexroth.com 3. www.eaton.in (Vickers) 4. www.compair.com/products/compressor_training_animations.aspx

ADDITIONAL RESOURCES :

1. NPTEL Tutorials (Internal Server) 2. Online Objective Questions 3. YouTube



CONTENTS

S.No Particulars Page

1 Unit – I 6

2 Unit – II 17

3 Unit – III 40

4 Unit – IV 62

5 Unit – V 80



Unit I

BASICS OF METROLOGY

PART-A

1. Define tolerance and zero line. (ODD 2015)

The basic dimension say 25 mm is the zero line. Any variation to this basic

dimension is the tolerance towards upward or downward limits.

2.Define interchangeable system. (ODD 2015)

Interchangeability means ease of replacement in the event of failure. Any

one component selected at random should assemble correctly with any other mating

component, that too selected at random.

3. Differentiate the terms reproducibility and repeatability. (EVEN 2015)

Reproducibility is the degree of closeness between measurements of the same

quantity where the individual measurements are made under different conditions.

Repeatability is the closeness between successive measurements of the same quantity

with the same instrument by the same operator over a short time span.

4. What is the difference between allowances and tolerance? (EVEN 2015)

Tolerance is the limit of random deviation of a dimension from its nominal value.

Allowance is the amount of designed deviation between two mating dimensions

in a fit, which, in combination with their respective tolerances, results into a

maximum and minimum clearance or interference.

5. What is meant by static response? (ODD 2014)

The static characteristics of an instrument are considered for instruments

which are used to measure an unvarying process conditions

6. Define tolerance and zero line. (ODD 2014)

The basic dimension say 25 mm is the zero line. Any variation to this basic

dimension is the tolerance towards upward or downward limits.



7.What is measurement? Give its types. (EVEN 2014)

Measurement is a process of comparing the input signal (unknown

magnitude) with a pre-defined standard and giving out the result. Its types are : Direct

comparison method, Indirect comparison method, Primary measurement, Secondary

measurement and Tertiary measurement.

8.What do you mean by sensitivity of a measuring instrument? (EVEN 2014)

Sensitivity may be defined as the following relation:

Sensitivity = Change in the output signal / Change in the input signal.

9. Distinguish between relative error and random error. (EVEN 2013)

a) Relative error: Relative error is defined as the results of the absolute error and

the value of comparison used for calculation of that absolute error. The comparison

may be true value or conventional true value or arithmetic mean for series of

measurement.

b) Random errors: This type of errors occurs randomly and reason for this type of

errors cannot be specified.

10. What is the relationship between sensitivity and range? (EVEN 2013)

Sensitivity: The ratio of the change in output of the instrument to a change of

measured variable is termed as sensitivity.

Range: It is the minimum and maximum values of a quantity for which an

instrument is designed to measure.

PART-B

1. Explain the need of standards of measurements in modern industrial system

and describe the term traceability in connection with standards. (ODD 2015)

Standards The term standard is used to denote universally accepted

specifications for devices. Components or processes which ensure conformity and

interchangeability throughout a particular industry. A standard provides a reference for

assigning a numerical value to a measured quantity. Each basic measurable quantity

has associated with it an ultimate standard. Working standards, those used in

conjunction with the various measurement making instruments.



The national institute of standards and technology (NIST) formerly called

National Bureau of Standards (NBS), it was established by an act of congress in 1901,

and the need for such body had been noted by the founders of the constitution. In order

to maintain accuracy, standards in a vast industrial complex must be traceable to a

single source, which may be national standards.

The following is the generalization of echelons of standards in the national

measurement system.

1. Calibration standards

2. Metrology standards

3. National standards

1. Calibration standards: Working standards of industrial or governmental

laboratories.

2. Metrology standards: Reference standards of industrial or Governmental

laboratories.

3. National standards: It includes prototype and natural phenomenon of SI (Systems

International), the world wide system of weight and measures standards. Application of

precise measurement has increased so much, that a single national a large country with

high technical development. It has led to the establishment of a considerable number of

standardizing laboratories in industry and in various other areas. A standard provides a

reference or datum for assigning a numerical value to a measured quantity.

Classification of Standards To maintain accuracy and interchangeability it is

necessary that Standards to be traceable to a single source, usually the National

Standards of the country, which are further linked to International Standards. The

accuracy of National Standards is transferred to working standards through a chain of

intermediate standards in a manner given below.

•National Standards

•National Reference Standards

•Working Standards



•Plant Laboratory Reference Standards

•Plant Laboratory Working Standards

•Shop Floor Standards Evidently, there is degradation of accuracy in passing from the defining standards to the shop floor standards. The accuracy of particular standard

depends on a combination of the number of times it has been compared with a standard

in a higher echelon, the frequency of such comparisons, the care with which it was

done, and the stability of the particular standards itself.

2. Explain the sources of errors in precision measurement with suitable

illustrations. (EVEN 2015)

It is never possible to measure the true value of a dimension there is always

some error. The error in measurement is the difference between the measured value

and the true value of the measured dimension.

Error in measurement = Measured value - True value

The error in measurement may be expressed or evaluated either as an absolute error or

as a relative error.

Absolute Error

True absolute error: It is the algebraic difference between the result of measurement

and the conventional true value of the quantity measured.

Apparent absolute error: If the series of measurement are made then the algebraic

difference between one of the results of measurement and the arithmetical mean is

known as apparent absolute error.

Relative Error: It is the quotient of the absolute error and the value of comparison use

or calculation of that absolute error. This value of comparison may be the true value, the

conventional true value or the arithmetic mean for series of measurement. The accuracy

of measurement, and hence the error depends upon so many factors, such as: -

Calibration

-standard



-Work piece

-Instrument

-Person

-Environment etc

Types of Errors

1. Systematic Error These errors include calibration errors, error due to variation in

the atmospheric condition Variation in contact pressure etc. If properly analyzed,

these errors can be determined and reduced or even eliminated hence also

called controllable errors. All other systematic errors can be controlled in

magnitude and sense except personal error.

These errors results from irregular procedure that is consistent in action. These errors

are repetitive in nature and are of constant and similar form.

2. Random Error These errors are caused due to variation in position of setting

standard and work-piece errors. Due to displacement of level joints of instruments, due

to backlash and friction, these error are induced. Specific cause, magnitude and sense

of these errors cannot be determined from the knowledge of measuring system or

condition of measurement. These errors are non-consistent and hence the name

random errors.

3. Environmental Error These errors are caused due to effect of surrounding

temperature, pressure and humidity on the measuring instrument. External factors like

nuclear radiation, vibrations and magnetic field also leads to error. Temperature plays

an important role where high precision is required. e.g. while using slip gauges, due to

handling the slip gauges may acquire human body temperature, whereas the work is at

20°C. A 300 mm length will go in error by 5 microns which is quite a considerable error.

To avoid errors of this kind, all metrology laboratories and standard rooms worldwide

are maintained at 20°C.

3. What are the various elements of metrology? With example. Explain how these

elements influence the accuracy of measurements? (ODD 2014)

Elements of measuring system:



1) Measuring Instruments

2) Calibration Standards

3) Work piece

4) Person (who is carrying out the measurement)

5) Environment

The above said five elements composed into the acronym ―SWIPE‖.

Where,

S — Standard

W — Work piece

I — Instrument

P — Person

E — Environment

The factors affecting these five elements:

1. Standard : Affected by Temperature, time, thermal expansion and

elasticity.

2.Workpiece :Surface finish, cleanliness, supporting elements, and elastic

Properties.

3. Instrument : Friction, error, mechanical parts.

4. Person : Ability to measure, training, cost estimation.

5. Environment : Light, Temperature, Humidity.

An example for the elements influence the accuracy of measurements

A generalized measurement system consists of the following components:

1. Primary Sensing Element

2. Variable Conversion Element

3. Variable Manipulation Element



4. Data Processing Element

5. Data Transmission System

6. Data Presentation Element

In addition to the above components, a measurement system may also have a data

storage element to store measured data for future use. As the above six components

are the most common ones used in many measurement systems, they are discussed in

detail below

Block diagram of generalized measurement system:

1. Primary Sensing Element:

The primary sensing element receives signal of the physical quantity to be

measured as input. It converts the signal to a suitable form (electrical, mechanical or

other form), so that it becomes easier for other elements of the measurement system, to

either convert or manipulate it.

2. Variable Conversion Element:

Variable conversion element converts the output of the primary sensing element

to a more suitable form. It is used only if necessary.

3. Variable Manipulation Element:



Variable manipulation element manipulates and amplifies the output of the

variable conversion element. It also removes noise (if present) in the signal.

4. Data Processing Element:

Data processing element is an important element used in many measurement

systems. It processes the data signal received from the variable manipulation element

and produces suitable output.

Data processing element may also be used to compare the measured value with

a standard value to produce required output.

5. Data Transmission System:

Data Transmission System is simply used for transmitting data from one element

to another. It acts as a communication link between different elements of the

measurement system. Some of the data transmission elements used to cables, wireless

antennae, transducers, telemetry systems etc.

6. Data Presentation Element:

It is used to present the measured physical quantity in a human readable form to

the observer. It receives processed signal from data processing element and presents

the data in a human readable form. LED displays are most commonly used as data

presentation elements in many measurement systems.

4.With suitable example explain the difference between precision and accuracy.

(EVEN 2014)

Precision

The terms precision and accuracy are used in connection with the performance

of the instrument. Precision is the repeatability of the measuring process. It refers to the

group of measurements for the same characteristics taken under identical conditions. It



indicates to what extent the identically performed measurements agree with each other.

If the instrument is not precise it will give different (widely varying) results for the same

dimension when measured again and again. The set of observations will scatter about

the mean. The scatter of these measurements is designated as σ, the standard

deviation. It is used as an index of precision. The less the scattering more precise is the

instrument. Thus, lower, the value of σ, the more precise is the instrument. Accuracy

Accuracy is the degree to which the measured value of the quality characteristic agrees

with the true value. The difference between the true value and the measured value is

known as error of measurement. It is practically difficult to measure exactly the true

value and therefore a set of observations is made whose mean value is taken as the

true value of the quality measured.

Accuracy is very often confused with precision though much different. The

distinction between the precision and accuracy will become clear by the following

example. Several measurements are made on a component by different types of

instruments (A, B and C respectively) and the results are plotted. In any set of

measurements, the individual measurements are scattered about the mean, and the

precision signifies how well the various measurements performed by same instrument

on the same quality characteristic agree with each other. The difference between the

mean of set of readings on the same quality characteristic and the true value is called

as error. Less the error more accurate is the instrument. Figure shows that the

instrument A is precise since the results of number of measurements are close to the

average value. However, there is a large difference (error) between the true value and

the average value hence it is not accurate. The readings taken by the instruments are

scattered much from the average value and hence it is not precise but accurate as there

is a small difference between the average value and true value.



5. Distinguish between (i)Repeatability and reproducibility. (EVEN 2013)

Repeatability: Repeatability is defined as the variation of scale reading and is random in

nature. It is the closeness between successive measurement of the same quantity, with

the same instrument by the same operator over a short time span.

Reproducibility: it is the degree of closeness between measurement of the same

quantity where the individual measurements are made under different conditions like at

different locations, with different measuring instruments, by different operators.

6. Explain detail in static and dynamic response. (ODD 2015)

The static characteristics of measuring instruments are concerned only with the steady-

state reading that the instrument settles down to, such as accuracy of the reading. The

dynamic characteristics of a measuring instrument describe its behavior between the

time a measured quantity changes value and the time when the instrument output

attains a steady value in response. As with static characteristics, any values for dynamic

characteristics quoted in instrument data sheets only apply when the instrument is used

under specified environmental conditions. Outside these calibration conditions, some

variation in the dynamic parameters can be expected. In any linear, time-invariant



measuring system, the following general relation can be written between input and

output for time (t) > 0:

where qi is the measured quantity, qo is the output reading, and ao...an, bo... bmare

constants. If we limit consideration to that of step changes in the measured quantity

only, then Equation (2) reduces to

UNIT-2



LINEAR AND ANGULAR MEASUREMENTS

PART-A

1. State any two limitation of sine bar. (ODD 2015)

i.It is physically difficult to hold the position.

ii.slight errors in sine bar cause larger angular solutions.

2. What are the constructional requirements of a good sine bar? (ODD 2015)

i) The sine bar is physically clumsy to hold in position.

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

iii) Slight errors of the sine bar cause large angular errors.

iv) Long gauge stacks are not nearly as accurate as when compared with shorter gauge

blocks.

v) Temperature variation affects the accuracy.

3. What is a comparator? (EVEN 2015)

i) It has less number of moving parts.

ii) Magnification obtained is very high.

iii) Two or more magnifications are provided in the same instrument to use various

ranges.

iv) The pointer is made very light so that it is more sensitive to vibration.

4. Mention the various applications and needs of comparators. (EVEN 2015)

The following are some of the ways in which the comparators used :i) In mass production, where components are to be checked at a very fast rate. ii) As



laboratory standards from which working or inspection gauges are set and correlated. iii) For inspecting newly purchased measuring gauges and iv) Comparators can be used as working gauges to prevent work spoilage and to maintain required tolerances at all stages of manufacturing by attaching with the machines.

5. Differentiate between sine bar and sine centre. (ODD 2014)

Sine bar is used for locating any work to a given angle and to change unknown angle.The conical work is difficult to mount on sine bars, to overcome this sine centre is used. In this two blocks are mounted on top surface of sine bar at each end, these block have centres and can be clamped at any position.

6. Write any two precaution to be followed when using gauge blocks? (ODD 2014)

The following precautions must be taken.

• Use the minimum number of blocks.

• Wipe the measuring faces clean using soft clean chamois leather.

• Wring the individual blocks together by first pressing at right angles, sliding & then twisting.

7. Why are lasers used in metrology? (EVEN 2014)

The photon emitted during stimulated emission has the same energy, phase and frequency as the incident photon.

This principle states that the photon comes in contact with another atom or molecule in the higher energy level E2 then it will cause the atom to return to ground state energy level E, by releasing another photon.

8. State the working principle of an electronic comparator. (EVEN 2014)

In an electronic comparator, transducer induction or the principle of application of frequency modulation or radio oscillation is followed.

9. What are the advantages of electrical and electronic comparator? (EVEN 2013)

i) It has less number of moving parts.

ii) Magnification obtained is very high.



iii) Two or more magnifications are provided in the same instrument to use various

ranges.

iv) The pointer is made very light so that it is more sensitive to vibration.

10. Write the constructional requirements of the sine bar for accurate measurement.

(EVEN 2013)

i) The rollers must have equal diameter and equal cylinders.

ii) The rollers must be placed parallel to each other and also to the upper face.

iii) The accurate center to center of rollers must be known.

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

PART-B 1. Explain the working principles of tool maker‟s microscope with neat sketch.

Also list out its applications. (ODD 2015)

Working:

i. Worktable is placed on the base of the instrument



ii. The optical head is mounted on a vertical column and it can be moved up

and

down.

iii. Work piece is mounted on a glass plate

iv. A light source provides horizontal beam of light which is reflected from a

mirror

by 90O upwards towards the table

v. Image of the outline of contour of the work piece passess through the

objective of

the optical head.

vi. The image is projected by a system of three prisms to a ground glass

screen.

vii. The measurement are made by means of cross line engraved on the

ground glass

screen.

viii. Thescreencan be rotated through 360O

ix. Different types of graduated screens and eyepieces are used.

Application:

-Linear measurement, measurement of pitch of the screw.

-Measurement of pitch diameter.

2. What is comparator? Discuss the different types of comparators and its

applications.

(EVEN 2015)

Comparators are one form of linear measurement device which is quick and more

convenient for checking large number of identical dimensions. Comparators normally



will not show the actual dimensions of the work piece. They will be shown only the

deviation in size. i.e. During the measurement a comparator is able to give the deviation

of the dimension from the set dimension. This cannot be used as an absolute

measuring device but can only compare two dimensions. Comparators are designed in

several types to meet various conditions. Comparators of every type incorporate some

kind of magnifying device. The magnifying device magnifies how much dimension

deviates, plus or minus, from the standard size. The comparators are classified

according to the principles used for obtaining magnification.

The common types are:

1) Mechanical comparators

2) Electrical comparators

3) Optical comparators

4) Pneumatic comparators

MECHANICAL COMPARATORS Mechanical comparator employs mechanical means

for magnifying small deviations. 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. Mechanical comparators are available having

magnifications from 300 to 5000 to 1. These are mostly used for inspection of small

parts machined to close limits.

1. Dial indicator A dial indicator or dial gauge is used as a mechanical comparator.

The essential parts of the instrument are like a small clock with a plunger projecting at

the bottom as shown in fig. Very slight upward movement on the plunger moves it

upward and the movement is indicated by the dial pointer. The dial is graduated into

100 divisions. A full revolution of the pointer about this scale corresponds to 1mm travel

of the plunger. Thus, a turn of the pointer b one scale division represents a plunger

travel of 0.01mm.

Experimental setup The whole setup consists of worktable, dial indicator and vertical

post. The dial indicator is fitted to vertical post by on adjusting screw as shown in fig.

The vertical post is fitted on the work table; the top surface of the worktable is finely

finished. The dial gauge can be adjusted vertically and locked in position by a screw.



Procedure Let us assume that the required height of the component is 32.5mm. Initially

this height is built up with slip gauges. The slip gauge blocks are placed under the stem

of the dial gauge. The pointer in the dial gauge is adjusted to zero. The slip gauges are

removed

Now the component to be checked is introduced under the stem of the dial gauge. If

there is any deviation in the height of the component, it will be indicated by the pointer.

Mechanism The stem has rack teeth. A set of gears engage with the rack. The pointer is

connected to a small pinion. The small pinion is independently hinged. I.e. it is not

connected to the stern. The vertical movement of the stem is transmitted to the pointer

through a set of gears. A spring gives a constant downward pressure to the stem.

2. Read type mechanical comparator.



In this type of comparator, the linear movement of the plunger is specified

by means of read mechanism. The mechanism of this type is illustrated in fig. A spring-loaded pointer is pivoted. Initially, the comparator is set with the help of a known dimension eg. Set of slip gauges as shown in fig. Then the indicator reading is adjusted to zero. When the part to be measured is kept under the pointer, then the comparator displays the deviation of this dimension either in ± or— side of the set dimension.

Advantages

1) It is usually robust, compact and easy to handle.

2) There is no external supply such as electricity, air required.

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

4) It is suitable for ordinary workshop and also easily portable.

Disadvantages

1) Accuracy of the comparator mainly depends on the accuracy of the rack and pinion

arrangement. Any slackness will reduce accuracy.

2) It has more moving parts and hence friction is more and accuracy is less.



3) The range of the instrument is limited since pointer is moving over a fixed scale. 2

ELECTRICAL COMPARATOR: An electrical comparator consists of the following three

major part such as

1) Transducer

2) Display device as meter

3) Amplifier

Transducer An iron armature is provided in between two coils held by a lea spring at

one end. The other end is supported against a plunger. The two coils act as two arms of

an A.C. wheat stone bridge circuit.

Amplifier The amplifier is nothing but a device which amplifies the give input signal

frequency into magnified output Display device or meter The amplified input signal is

displayed on some terminal stage instruments. Here, the terminal instrument is a meter.

Working principle If the armature is centrally located between the coils, the inductance

of both coils will be equal but in opposite direction with the sign change. Due to this, the

bridge circuit of A.C. wheat stone bridge is balanced. Therefore, the meter will read zero

value. But practically, it is not possible. In real cases, the armature may be lifted up or

lowered down by the plunger during the measurement. This would upset the balance of

the wheat stone bridge circuit. Due to this effect, the change in current or potential will

be induced correspondingly. On that time, the meter will indicate some value as

displacement. This indicated value may be either for larger or smaller components. As



this induced current is too small, it should be suitably amplified before being displayed

in the meter.

Checking of accuracy

To check the accuracy of a given specimen or work, first a standard specimen is placed

under the plunger. After this, the resistance of wheat stone bridge is adjusted so that the

scale reading shows zero. Then the specimen is removed. Now, the work is introduced

under the plunger. If height variation of work presents, it will move the plunger up or

down. The corresponding movement of the plunger is first amplified by the amplifier

then it is transmitted to the meter to show the variations. The least count of this

electrical comparator is 0.001mm (one micron).

ELECTRONIC COMPARATOR

In electronic comparator, transducer induction or the principle of application of

frequency modulation or radio oscillation is followed

Construction details

In the electronic comparator, the following components are set as follows:

i. Transducer

ii. ii. Oscillator



iii. iii. Amplifier

iv. iv. Demodulator

v. v. Meter

(i) Transducer

It converts the movement of the plunger into an electrical signal. It is connected with

oscillator.

(ii) Oscillator

The oscillator which receives electrical signal from the transducer and raises the

amplitude of frequency wave by adding carrier frequency called as modulation.

(iii) Amplifier

An amplifier is connected in between oscillator and demodulator. The signal coming out

of the oscillator is amplified into a required level.

(iv) Demodulator

Demodulator is nothing but a device which cuts off external carrier wave frequency. i.e.

It converts the modulated wave into original wave as electrical signal.

(v) Meter

This is nothing but a display device from which the output can be obtained as a linear

measurement.

Principle of operation The work to be measured is placed under the plunger of the

electronic comparator. Both work and comparator are made to rest on the surface plate.

The linear movement of the plunger is converted into electrical signal by a suitable

transducer. Then it sent to an oscillator to modulate the electrical signal by adding

carrier frequency of wave. After that the amplified signal is sent to demodulator in which

the carrier waves are cut off. Finally, the demodulated signal is passed to the meter to

convert the probe tip movement into linear measurement as an output signal. A

separate electrical supply of D.C. is already given to actuate the meter.



Advantages of Electrical and Electronic comparator

1) It has less number of moving parts.

2) Magnification obtained is very high.

3) Two or more magnifications are provided in the same instrument to use various

ranges.

4) The pointer is made very light so that it is more sensitive to vibration.

5) The instrument is very compact.

Disadvantages of Electrical and Electronic comparator

1) External agency is required to meter for actuation.

2) Variation of voltage or frequency may affect the accuracy of output.

3) Due to heating coils, the accuracy decreases.

4) It is more expensive than mechanical comparator.

3. Explain how the measurements are made with optical bevel protactor. (ODD

2014)

1. Vernier bevel protractor is the simplest angle measuring instrument. It consists of

main body, base plate stock, adjustable blade, circular plate containing vernier

scale and acute angle attachment. A universal bevel protractor is used to

measure angles between two planes. The blade can be moved along throughout



its length and can also be reversed. It is about 150 or 300m long, 13mm wide and

2mm thick. Its ends are beveled at angles of 45˚ and 60˚. The acute angle attachment can be readily fitted into the body and clamped in any position. The

bevel protractors are tested for flatness, squareness, parallelism, straightness,

etc. The main scale is graduated in degrees of arc. The vernier scale has 12

divisions each side of the center zero. These are marked 0-60minutes of arc, so

that each divisions equals 1/12, of 60, that is 5minutes of arc. These 12 divisions

occupy the same space as 23 degrees on the main scale. Therefore, each

divisions of the vernier scale is equal to 1/12 of 23˚ or

12

111

. Since two divisions on

the main scale equals 2 degrees of arc, the difference between two divisions on

the main scale equals 2 degree of arc, the difference between two divisions on

the main scale and one division on the vernier scale is 2˚-

12

111

=

12

1

or 5

minutes of arc.

Procedure

1. First clean the blade of the bevel protractor and fix it over the body of it in the

groove.

2. Then place the specimen to which we have to determine the angle.

3. By adjusting the blade and the stock to slide over that two adjacent side of the

given

specimen, so that we can read the reading from main scale and vernier scale

reading.

4. Hence the angle of the given specimen was determined

4. Write the applications of auto collimeter. (EVEN 2014)

Auto-collimators are used for

1) Measuring the difference in height of length standards.

2) Checking the flatness and straightness of surfaces.



3) Checking square ness of two surfaces.

4) Precise angular indexing in conjunction with polygons.

5) Checking alignment or parallelism.

6) Comparative measurement using master angles.

7) Measurement of small linear dimensions.

8) For machine tool adjustment testing

5. With a neat diagram explain the working of angle dekkor . (EVEN 2013)

Alignment telescope is used for aligning of bores, surfaces and check

squareness, straightness, flatness, parallelism, vertically and level.

One of the important type of alignment telescope is

Taylor-Hobson alignment telescope.

This instrument can be used to measure angular alignment as well as lateral

displacement and for this purpose the sighting target is mounted in a collimating

unit.

The telescope has an internal-focusing optical system, similar in principle to that of the

surveyor’s level built into a robust unit having a precisely ground external diameter.he focusing knob can be clearly seen in the optical system is shown in fig.



The collimating unit consists of another steel tube, ground to the same diameter

as the telescope and containing an illuminating system, a graticule G2, a

collimating lens and another graticule G3.

The graticule G2 is graduated with central cross lines, surrounded with scales

and concentric circles and lies exactly at the principal focus of the collimating

lenses.

The graticule G3 contains a central pattern of converging Vee and several

graduated scales lying in two directions at right angles.

The use of telescope with the collimator is given in fig.

If the telescope is aligned with the collimator and sighted on it with its focus

adjusted to infinity target graticuleG2 will appear in the field of view, since rays

from this target will emerge parallel beams from the collimating lens.

Purely lateral displacements of telescope and target will therefore not register,

but any angular misalignment will show as a displacement of the image of the

target.



If the telescope is now refocused until the target G3 appears in the field, only

lateral displacements of the collimator will be indicated, the parallel beams from

the target G2 being out of focus.

Lateral displacements of the collimator unit will therefore be measured in

thetelescope by means of the scales on graticuleG3.

The ground bores of the telescope and collimator make the instrument

particularly suitable for the alignment of two or more bores, such as bearings of

large engines.

The two units can be located centrally in each bore, using ground bushes where

necessary and both lateral and angular alignment can be measured.

Accurate optical alignment of the telescope with its ground diameter is ensured

by careful centering of the lenses and accuracy of the draw table of the focusing

lens.

The use of the optical micrometer and the accuracy obtainable by rotation of the

telescope are only available for the measurement of lateral displacement of the

target.

The instrument is not equipped for a similar accuracy or angular measurent

without any reason; a micrometer eyepiece would provide the means of doing

this.

6. Calculate the limits for a hole shafts pair designated 25 H8/d9 .Show

graphically the disposition of tolerance zones with reference to the zero line . The

lower deviation for a H, Type hole is zero.25 mm lies in the diameter range 18 mm

to 30 mm . Standard tolerance for IT 8 is 25 I and IT 9 is 40 I,where i is the

standard tolerance unit in microns and given as I (µm)= D+0.001D (Disin mm)

the upper deviation for “d” shaft is -16d ^o.44. (ODD 2015)

Solution:

Using calculations we proceed as under:

D =



= 23.2379 mm

= 0.45 + 0.001 (23.2379)

= 1.307 microns

IT 8 is 25 i

Limits 25 H 8: 25 + 0.044 mm

- 0.00 mm

Tolerance on Hole = 0.044 mm

Since the tolerance on hole is less than 0.1 mm, no wear allowance will be

provided on the Go gauge.

Taking gauge tolerance to be 10% of work tolerance, tolerance on Go gauge =

0.0044 mm. similarly tolerance on Not-Go gauge is also 0.0044 mm. Disposition of

gauge tolerance with respect to work tolerance is shown in figure.

Fig: Disposition of workshop gauge tolerance

Upper limit of GO gauge = 25.000 mm

Lower limit of GO gauge = 25.0044 mm

Upper limit of Not-GO gauge = 25.044 mm



Lower limit of Not-GO gauge = 25.025 mm.

IT 9 is 40 i

Limits 25 H 8: 25 + 0.044 mm

- 0.00 mm

Tolerance on Hole = 0.044 mm

Since the tolerance on hole is less than 0.1 mm, no wear allowance will be provided on

the Go gauge.

Taking gauge tolerance to be 10% of work tolerance, tolerance on Go gauge = 0.0044

mm. similarly tolerance on Not-Go gauge is also 0.0044 mm. Disposition of gauge

tolerance with respect to work tolerance is shown in figure.

Fig: Disposition of workshop gauge tolerance

Upper limit of GO gauge = 25.000 mm

Lower limit of GO gauge = 25.0044 mm

Upper limit of Not-GO gauge = 25.044 mm

Lower limit of Not-GO gauge = 25.025 mm.

7. Explain the working principle of AC laser interferometer and explain how the

the straightness is measured? (EVEN 2015)



Ac Laser Interferometer

It is possible to maintain the quality of interference fringes over longer distance

when lamp is replaced by a laser source:

Laser interferometer uses AClaser as the light source and the measurements to

be madeover longer distance.

Laser is a monochromatic optical energy, which can be collimated into a

directional beamAC.

Laser interferometer (ACLI) has the following advantages.

High repeatability

High accuracy

Long range optical path

Easy installations

Wear and tear

Two-frequency Zeeman laser generates light of two slightly different

frequencies with opposite circularpolarizations. These beams get split up by

beam splitter B1 One part travels towards B2 and from there to external cube

corner here the displacement is to be measured. This interferometer uses cube

corner reflectors which reflect light parallel to its angle of incidence. Beam

splitter B2optically separates the frequency f1 which alone is sent to the

movable cube corner reflector.

The second frequencyf1 from B2is sent to a fixed reflector which then rejoins f1

at thebeam splitter B2to produce alternate light and dark interference flicker at

about 2 Megacycles per second. Now if the movable reflector moves, then the

returning beamfrequency will be Doppler-shifted slightly up or down by (∆f1).

Thus the light beams moving towards photo detector P2have frequencies

f2and(f1± ∆f1)andP2changes these frequencies into electrical signal. (Photocells

convert light-intensity variations into voltage pulses which can be processed by

electronic instruments to give the amount and direction of position change.)



Photo detector P1 receive signal from beam splitter B1 and changes the

reference beamfrequencies f1and f2into electrical signal.

An AC amplifier A1 separates frequency difference signal (f2 – f1)and A2

separates frequency difference signal [f2- (f1±∆f)]. The pulse converter extracts ∆f, one cycle per half wavelength of motion. The up-down pulses from the pulse

converter are counted electronically and displayed in analog or digital form on

indicator. It may be noted that output in case of ACLI is in the form of pulses,

whereas in D.C systems, the output is in the form of a sinusoidal wave, the

amplitude (intensity) of which depends upon laser aging, air turbulence or air

pollutant and thus the change of amplitude leads to improper triggering and

counting errors.

8. Explain the following angular measurement methods using rollers. (ODD 2014)

(i) Measurement of angle by using rollers.

Rollers are precisely manufactured with high accuracy for metrological

applications. It is used to determine both linear and angular dimensions in

conjunction with gauge blocks. These are made of good quality steel and are

hardened and tapered. The length of the roller is equal to the diameter. The use

of precision rollers for determining both linear and angular dimensions is

explained with the help of following examples.



1. Measurement of angle by using rollers

Angle of the right-tapered piece can be measured by using two rollers of different

sizes, slip gauges and a dial indicator. The two rollers whose diameters are known

and slip gauges are placed on a surface plate as shown in fig. 2.117. The rollers

may be clamped in position against an angle plate by C-clamps. The work is then

placed on top of rollers clamped against the angle plate by C-clamp, if the angle of

the piece all right, then the top edge will be parallel to surface plate. The di indicator

will show no variation when traversed along its surface.

From fig., the triangle 02A 01

Where, 1 = Length of slip gauge pile and

d1 and d2 = Diameters of rollers

From the above equation,



Thus, initially the length of the slip gauges is calculated by ikabove equation and

the rollers are placed in contact with the slip gauges

(ii) Checking the angle of taper plug guage using rollers

Method of checking the angle of a taper plug gauge using rollers, micrometer and

slip gauges is illustrated by fig. A taper plug is placed on a surface plate. First, two

rollers of equal diameters are placed touching on the opposite sides of the lower

surface of the plug on the slip gauge combination of equal heights.

The distance (M1) between the ends of the roller is measured with a micrometer.

Then the rollers are placed on slip gauge combination of height (112) touching on

the opposite sides of the top portion of the plug. The distance (M2) between the

ends of the rollers in this new position is again measured by means of micrometer.

9. Explain Measuring of included angle of an interval dovetail. (EVEN 2014)



Dovetail slides are widely used in machine tools as a guide ways. The sloping side

of the dovetail slide acts as guide and prevent the lifting of the female mating part

during sliding operation. This angle can be measured by using two rollers of equal

size, slip gauges and a micrometer similar to the previous case of taper plug gauge.

The two rollers of equal diameters are placed one each at the two corners and

distance 11 is measured across the rollers with a micrometer.

Then the rollers are placed on two sets of equal size slip gauge blocks and the

distance, is measured. It should be noted that the rollers do not extend above the

top surface of dovetail. Let the height of slip gauges be h, then from fig.

Dovetail slides are widely used in machine tools as a guide ways. The sloping side

of the dovetail slide acts as guide and prevent the lifting of the female mating part

during sliding operation. This angle can be measured by using two rollers of equal

size, slip gauges and a micrometer similar to the previous case of taper plug gauge.

The two rollers of equal diameters are placed one each at the two corners and

distance 11 is measured across the rollers with a micrometer.



10. Explain in detail Measuring interior angle of a profile guage. (EVEN 2013)

Fig. shows the setup for measuring the interior angle of a profile gauge. Two balls

of different diameters and a vernier height gauge are required for measurement.

The small ball of diameter di is first placed in the slot of a profile gauge and the

height hi is measured using vernier height gauge. Then the ball of bigger diameter

d2 is placed after removing smaller one in the slot and the height h2 is measured

using vernier height gauge. The angle of a profile gauge 0 is given by the relation.



UNIT-3

ADVANCES IN METROLOGY

PART-A

1. Differentiate between straightness and flatness. (ODD 2015)

A line is said to be straight over a given length if the variation of the distance

between the two points on the two planes perpendicular to each other and

parallel to the direction of a line remaining within the specified tolerance limits.

2. Give the advantages of co ordinate measuring system. (ODD 2015)

-Geometric errors in individual components of CMM cause errors. These errors

can be eliminated by compensation.

-Quick and accurate inspection is possible

-Automatic online processing of measured data is possible, even when the

component bring analyzed is still on the work table of CMM

3. State any two applications of laser in machine tool technology. (EVEN 2015)

* Straightness and flatness of guide ways and slide ways of machine tool.

* Flatness of machine tables

* Parallelism, equidistance and alignment of the slide ways.

* True running and alignment of shaft and spindle.

* Lead of lead screw or error in pitch

4. Name the four types of machine vision system. (EVEN 2015)

Image formation

Processing of image

Analysing the image

Interpretation of image.

5. What are touch trigger probes? (ODD 2014)



A type of contact probe that detects a feature on a part and generates an

electronic signal to record its dimension. Touch trigger probes are the most

accurate and commonly used probes on the CMM.

6. What are diffraction gratings? (ODD 2014)

Diffraction grating are strips of glass or metal ruled with fine equally spaced lines

to from the grating. If the gratings are set at a small angle across the glass and

positioned so that the lines are angled to cross each other, a series of

interference type fringes known as moiré fringes would be produced.

7. Define degree of fullness and degree of emptiness in form factor. (EVEN 2014)

Degree of fullness is defined as the ratio between the area of metal present and

the area of the enveloping portion.

8. What are the advantages of Laser in interferometry? (EVEN 2014)

Laser provides a source of coherence and truly monochromatic light. The

property of clearance enables it to be projected in a narrow pencil of beam

without any scatter.

9. Write the features of CMM. (ODD 2013)

i) In faster machines with higher accuracies, the stiffness to weight ratio has to be

high in order to reduce dynamic forces.

ii) All the moving members, the bridge structure Z-axis carriage and Z-column are

made of hollow box construction.

iii) Errors in machine are built up and fed into the computer system so that error

compensation is built up into the software.

iv) All machines are provided with their own computers and the CMM is able to

measure three-dimensional object from the variable datums.

10. Mention the various geometrical checks made on machine tools. (ODD 2013)

The geometrical checks made on machine tools are :



* Straightness and flatness of guide ways and slide ways of machine tool.

* Flatness of machine tables

* Parallelism, equidistance and alignment of the slide ways.

PART-B

1. Explain the gear tooth thickness and base tangent length is measured using

vernier gear tooth caliper and flange micrometer. (ODD 2015)

Tooth thickness is generally measured at pitch circle and also in most cases the

chordal thickness measurement is carried out i.e. the chord joining the intersection

of the tooth profile with the pitch circle. The methods which are used for measuring

the gear tooth thickness is

a) Gear tooth vernier caliper method (Chordal thickness method)

b) Base tangent method.

c) Constant chord method.

d) Measurement over pins or balls.

a) Gear tooth vernier method In gear tooth vernier method the thickness is

measured at the pitch line. Gear tooth thickness varies from the tip of the base

circle of the tooth, and the instrument is capable of measuring the thickness at a

specified position on the tooth. The tooth vernier caliper consists of vernier scale

and two perpendicular arms. In the two perpendicular arms one arm is used to

measure the thickness and other arm is used to measure the depth. Horizontal

vernier scale reading gives chordal thickness (W) and vertical vernier scale gives

the chordal addendum. Finally the two values compared.

The theoretical values of W and d can be found out by considering one tooth in the

gear and it can be verified. In fig noted that w is a chord ADB and tooth thickness is

specified by AEB. The distance d is noted and adjusted on instrument and it is

slightly greater than addendum CE.



Vernier method like the chordal thickness and chordal addendum are dependent

upon the number of teeth. Due to this for measuring large number of gears different

calculations are to be made for each gear. So these difficulties are avoided by this

constant chord method.



2. Discuss the need, types and constructional features of co ordinate

measuring machine. (ODD 2015)

CO-ORDINATE MEASURING MACHINES

Measuring machines are used for measurement of length over the outer surfaces of

a length bar or any other long member. The member may be either rounded or flat

and parallel. It is more useful and advantageous than vernier calipers, micrometer,

screw gauges etc. the measuring machines are generally universal character and

can be used for works of varied nature. The co-ordinate measuring machine is used

for contact inspection of parts. When used for computer-integrated manufacturing

these machines are controlled by computer numerical control. General software is

provided for reverse engineering complex shaped objects. The component is

digitized using CNC, CMM and it is then converted into a computer model which

gives the two surface of the component. These advances include for automatic

work part alignment on the table. Savings in inspection 5 to 10 percent of the time is

required on a CMM compared to manual inspection methods

Types of Measuring Machines

1. Length bar measuring machine.

2. Newall measuring machine.

3. Universal measuring machine.

4. Co-ordinate measuring machine.

5. Computer controlled co-ordinate measuring machine.

Constructions of CMM

Co-ordinate measuring machines are very useful for three dimensional

measurements. These machines have movements in X-Y-Z co-ordinate, controlled

and measured easily by using touch probes. These measurements can be made by

positioning the probe by hand, or automatically in more expensive machines.

Reasonable accuracies are 5 micro in. or 1 micrometer. The method these



machines work on is measurement of the position of the probe using linear position

sensors. These are based on moiré fringe patterns (also used in other systems).

Transducer is provided in tilt directions for giving digital display and senses positive

and negative direction.

Types of CMM

(i) Cantilever type The cantilever type is very easy to load and unload, but

mechanical error takes place because of sag or deflection in Y-axis.

(ii) Bridge type Bridge type is more difficult to load but less sensitive to mechanical

errors.

(iii) Horizontal boring Mill typeThis is best suited for large heavy work pieces.



Working Principle :

CMM is used for measuring the distance between two holes. The work piece is

clamped to the worktable and aligned for three measuring slides x, y and z. The

measuring head provides a taper probe tip which is seated in first datum hole and

the position of probe digital read out is set to zero. The probe is then moved to



successive holes, the read out represent the co-ordinate part print hole location with

respect to the datum hole. Automatic recording and data processing units are

provided to carry out complex geometric and statistical analysis. Special co-

ordinate measuring machines are provided both linear and rotary axes. This can

measure various features of parts like cone, cylinder and hemisphere. The prime

advantage of co-ordinate measuring machine is the quicker inspection and accurate

measurements.

Causes of Errors in CMM

1) The table and probes are in imperfect alignment. The probes may have a degree

of run out and move up and down in the Z-axis may cause perpendicularity errors.

So CMM should be calibrated with master plates before using the machine.

2) Dimensional errors of a CMM is influenced by

Straightness and perpendicularity of the guide ways.

Scale division and adjustment.

Probe length.

Probe system calibration, repeatability, zero point setting and reversal error.



Error due to digitization.

Environment

3) Other errors can be controlled by the manufacture and minimized by the

measuring software. The length of the probe should be minimum to reduce

deflection.

4) The weight of the work piece may change the geometry of the guide ways and

therefore, the work piece must not exceed maximum weight.

5) Variation in temperature of CMM, specimen and measuring lab influence the

uncertainly of measurements.

6) Translation errors occur from error in the scale division and error in straightness

perpendicular to the corresponding axis direction.

7) Perpendicularity error occurs if three axes are not orthogonal.

3. What is coordinate measuring machine ? What are the its basic elements ?

(EVEN 2015)

Coordinate measuring machine is one type of measuring machine. For

measurement of large dimensions CMM is used. These machines can take up work

of varied nature.

CMM are used for 3 dimensional measurements. These machines have movement

in 3 coordinates namely x-y-z coordinates. The movement of each coordinate can

be controlled and measured.

CMM has three slides. Each slide is fitted with an accurate and precise linear

measuring transducer to sense both in the positive and negative directions. The

transducer output is obtained digitally.

The work table of the machine is suspended on 3 point suspension

For master guide ways and probe location, principles of kinematic design are used.

Systematic errors in the machine are compensated by the soft wave.



CMM has its own computer.

Measurement of the three dimensional objects from different datum is possible

using computers

Advantages of CMM

Geometric errors in individual components of CMM cause errors. These errors can

be eliminated by compensation.

Quick and accurate inspection is possible

Automatic online processing of measured data is possible, even when the

component bring analyzed is still on the work table of CMM

4. List out the various probes used in CMM and explain the working principle of

touch trigger probe. (EVEN 2015)

The various probes used in CMM are

Touch trigger probe (Reinshaw probe)

Touch scanners

Laser probers

Vision probes

Touch trigger probe (ieRenishaw probe)

The buckling mechanism is a three point hearing the contacts which are

arranged at 1200 around the circumference. These contacts act as

electrical micro switches.

When being touched in any probing direction one or f contacts is lifted off

and the current is broken, thus generating a pulse, when the circuit is

opened, the co-ordinate positions are read and stored.

After probing the spring ensures the perfect zero position of the three-

point bearing. The probing force is determined by the pre stressed force of



the spring with this probe system data acquisition is always dynamic and

therefore the measuring time is shorter than in static principle.

5. Explain the working principle of a DC laser interferometer with a neat diagram ?

(ODD 2014)

Single Frequency DC Interferometer System:

DC laser interferometer is much improved system over the Michelson

simple interferometer. It uses a single frequency circular polarized laser

beam. On reaching the polarizing beam splitter, the beam splits into two

components. The reflected beam is being vertically polarized light. And,

the transmitted beam is being horizontally polarized light. These two

beams referred to as reference are and measurement are respectively

travel to their retro reflectors and are then reflected back towards the

beam splitter.

The recombined beam at beam splitter consists of two superimposed

beams of different polarization; one component vertically polarized having

traveled around reference arm and other component horizontally polarized

having traveled around the measurement arm. These two beams being

differently polarized do not interface. The recombined beam then passes

through a quarter wave plate which causes the two beams to interfere with

one another to produce a beam of plane polarized light. The angular

orientation of the plane of this polarized light depends on the phase

difference between the light in the two returned beams.

The direction of plane of polarization spin is dependent on the direction of

movement of the moving retro reflector. The beam after quarter wave

plate is split into three polarization sensitive detectors. As the plane of

polarized light spins, each detector produces a sinusoidal output wave



form. The polarization sensitivity of the detectors can be set so that their

outputs have relative phases of 0, 90, and 180.

The output of the detectors can be used to distinguish the direction of movement and

also the distance moved by the moving retro reflector attached to the surface whose

displacement is to be measured.

For linear measurements (positional accuracy of velocity), the retro reflector is attached

to the body moving along the linear axis. For angular measurement, pitch and yaw), the

angular beam splitter is placed in the path between the laser head and the angular

reflector. In this way it is possible to measure flatness, straightness, rotatory axis

calibration. Arrangements also need to be made for environmental compensation

because the refractive index of the air varies with temperature, pressure and humidity.

Heterodyne interferometer, an A.C. device avoids all the problems encountered in



above D.C. device, i.e. effect of intensity level change of source, fringe contrast

changes and D.C. level shifts which can cause fringe miscounting.

Interferometer is now an established and well developed technique for high accuracy

and high resolution measurement.

6. Write briefly about the various stages involved in machine vision. (ODD 2014)

A Vision system can be defined as a system for automatic acquisition and

analysis of images to obtain desired data for interpreting of controlling an activity. It is a

technique which allows a sensor to view a scene and derive 3 numerical or logical

decisions without further human intervention.

Machine vision can be defined as a means of simulating the image recognition

and analysis capabilities of the human system with electronic and demo mechanical

techniques. Machine vision system are now a day’s used to provide accurate and in

expensive 100% inspection of work pieces. They are used for functions like gauging of

dimensions, identification of shapes, measurement of distances, determining orientation

of parts, quantifying motion-detecting surface shading etc. It is best suited for high

production. These systems function without fatigue. This is suited for inspecting the

masks used in the production of microelectronic devices. Standoff distance up to one

meter is possible. Accuracy of ± 3p is achieved.

Vision System

The schematic diagram of a typical vision system is shown in fig.

This system involves image acquisition; image processing Acquisition requires

appropriate lighting. The camera and store digital image processing involves

manipulating the digital image to simplify and reduce number of data points.

Measurements can be carried out at any angle along the three reference axes x. y and

z without contacting the part the measured values are then compared with the specified

tolerance which stores in the memory of the computer.



The main advantage of vision system is reduction or tooling and fixture costs,

elimination of need for precise part location for handling robots and integrated

automation of dimensional verification and defect detection.

Principle:

Four types of machine vision system and the schematic arrangement is shown in fig.

(i) Image formation.

(ii) Processing of image in a form suitable for analysis by computer.

(iii) Defining and analyzing the characteristic of image.

Interpretation of image and decision-making



For formation of image suitable light source is required. It consists of incandescent light.

Fluorescent tube fiber optic bundleandarc lamp. Laser beam is used for triangulation

system for measuring distance. Ultraviolet light is used to reduce glare of increase

contrast. Proper illumination back lighting. Front lighting, structured light is required.

Back lighting is used to obtain maximum image contrast.

The surface of the object is to be inspected by using front lighting. .

For inspecting three-dimensional feature structured lighting is required. An image

sensor vidicon camera. CCD camera is used to generate the electronic signal

representing the image. The image sensor collects light from the scene through a lens,

using photosensitive target converts into electronic signal.

Vidicon camera:

Image is formed by focusing the incoming light through a sense of lenses onto the

photoconductive faceplate of the vidicon tube. The electron beam scans the

photoconductive surface and produces an analog voltage proportional to the variation in

light intensity for each scan line of the original scene.

Solid-stale camera:

The image sensors change coupled device (CCD) contain matrix of small away,

photosensitive elements accurately spaced and fabricated on silicon chips using

integrated circuit technology. Each detector converts in to analog signal corresponding

to light intensity through the camera lens.

Image processor:



A camera may form an image 30 times per sec at 33 m see intervals. At each time

interval the entire image frozen for processing by an image processor. An analog to

digital converter is used to amen analog voltage of each detector in to digital value.

If voltage level for each pixel is given by either 0 or 1 depending on threshold value. It

is called binary system on the other hand grey scale system assigns upto 256 different

values depending on intensity to each pixel. Thus is addition to black and white many

different shades of grey can be distinguished.

Grey scale system requires higher degree of image refinement, huge storage

processing capability. For analysis 256 x256 pixels image array up to 256 different pixel

values will require 65000-S bit storage locations at a speed of 30 images per second.

Techniques windowing and image restoration are involved.

Windowing:

Processing is the desired area of interest and ignores non-interested part of image.

Image restoration:

Preparation of image during the pre-processing by remove the degrade.

Blurring of lines, poor contrast between images, and presence of noise are the

degrading.

The quality may be improved

(i) By improving the contrast by brightness addition.

(ii) By increasing the relative contrast between high and low intensity

elements.

(iii) By Fourier domain processing.

(iv) Other techniques to reduce edge detection and run length encoding.

Image Analysis:

Digital image of the object formed is analyzed in the central processing unit of the

system. Three important task performed by machine vision system are measuring the



distance of an object from a vision system camera, determining object orientation and

defining object position.

The distance of an object from a vision system camera can be determined by

triangulation technique. The object orientation can be determined by the methods of

equivalent ellipse.

The image can be interpreted by two-dimensional image. For complex three-

dimensional objects boundary locations are determined and the image is segmented

into distinct region.

Image Interpretation:

This involves identification of an object.

In binary system, the image is segmented on the basis of white and black pixels.

The complex images can be interpreted by grey scale technique and algorithms.

The most common image interpretation is template matching.

FUNCTION OF MACHINE VISION

Block diagram of machine vision is shown.

Lighting and presentation of object to evaluated.

It has great compact on repeatability, reliability and accuracy.

Lighting source and projection should be chosen and give sharp contrast.

Images sensor compressor TV camera may be vidicon camera and state. The vidicon

camera low cost, greater resolution. Solid state cameras have greater accuracy, no

image tat and longer life. Image digitizer is a six to eight bit analog to digital AD

convener which is designed to keep up with the flow of video information from camera

and store the digitized image in memory.



For simple processing, analog comparator and a computer controller to convert the

video information to a binary image is used Data compactor employs a high speed away

processor to provide high speed processing of the input image data. System control

computer communicates with the operator and make decision about the pan being

inspected. The output and peripheral devices operate the control of the system.

The output enables the vision system to either control a process or provide caution and

orientation information MU a robot. etc. These operate under the control of the system

control of computer.

7.Explain how V-Block and three point probe are used for measurement of

Roundness.Whatare the limitations of V-Block?

The fig. shows three probes with 120° spacing is very, useful for determining

effective size they perform like a 60° V-block.

60° V-block will show no error for 5 or 7 lobes magnify the error for 3-lobed parts

show partial error for randomly spaced lobes.



7. Explain the following Direct Instrument measurements. (ODD 2013)

STYLUS PROBE TYPE INSTRUMENT:

Principle:

When the stylus be moved over the surface which is to be measured, the

irregularities in the surface texture is measured and it is used to assess the

surface finish of the work piece.

Working:

The stylus type instruments consist of skid, stylus, amplifying device and

recording device.

The skid is slowly moved over the surface by hand or by motor drive. The

skid follows the irregularities of the surface and the stylus moves along with skid.

When the stylus moves vertically up and down and the stylus movements’

are magnified, amplified and recorded to produce a trace.



Then it is analyzed by automatic device.

Advantage:

Any desired roughness parameter can be recorded.

Disadvantages:

Fragile material cannot be measured.

High Initial cost.

Skilled operators are needed to operate.

8. Explain the Tomlinson surface meter. (ODD 2013)

This instrument uses mechanical-cum-optical means for magnification.

Construction:

In this the diamond stylus on the surface finish recorder is held by spring

pressure against the surface of a lapped cylinder. The lapped cylinder is supported one

side by probe and other side by rollers.The stylus is also attached to the body of the

instrument by a leaf spring and its height is adjustable to enable the diamond to be

positioned and the light spring steel arm is attached to the lapped cylinder and carries at

its tip a diamond scriber which bears against a smoked glass.



Working:

When measuring surface finish, body is traversed across the surface by a screw rotated

by a synchronous motor. Any vertical movement of the stylus caused by the surface

irregularities causes the horizontal lapped steel cylinder to roll. By its rolling, the light

arm attached to its end provides a magnified movement on a smoked glass plate. This

vertical movement coupled with the horizontal movement produces a trace on the glass

magnified in vertical direction and there being no magnification in horizontal direction.

The smoked glass trace is then, further projected at 50 and 100 magnification for

examination. Finally the movement of scriber together with horizontal movement

produces at race on the smoked glass plate and this trace is magnified by an optical

projector.



UNIT-IV

FORM MEASUREMENT

PART-A

1. What is floating carriage micrometer? (ODD 2015)

2.List the equipments needed for computer aided inspection. (ODD 2015)

i.micrometer

ii.screw gauge

iii.vernier caliper

iv height gauge

3.What is meant by best size wire in screw thread measurement? (EVEN 2015)

Best size of wire is the diameter of the wire in such a way that it makes

contact with the flanks of the thread on the pitch line.

4.Name the devices used for measurement of roundness. (EVEN 2015)



The roundness is measured by,

Diametral gauge, Circumferential conferring gauge

Rotating on centre, Three point probe and Accurate spindle

5.Name the various stylus probe instruments used for surface finish

measurement. (ODD 2014)

1. Tomlinson surface meter.

2. Profilometer.

3. Taysurf-surface roughness meter.

6. How is roundness measured in the least squares circle method? (ODD 2014)

A circle is fitted to the measured profile such that the sum squares of the

departure of the profile data from this circle is a minimum. The roundness error is

the difference between the maximum departures of the profile from this circle.

7.Define machine vision. (EVEN 2014)

Machine vision is defined as the means simulating the image recognition and

analyse the capabilities of the human system with electronic and

electromechanical techniques.

8. Define straightness of axes. (EVEN 2014)

Is a geometrical shape.

Straightness measuring instrument:

– Collimator

9. Name the four reference circles used in measurement of roundness. (ODD

2013)

i) Least squares circle

ii) Minimum zone or minimum radial separation circles

iii) Maximum inscribed circle and



iv) Minimum circumscribed circle

10. Derive the expression for „Best size of wire‟ in screw thread measurement. (ODD 2013)

Db=2AP sec x

Where , Db= wire diameter, X= included angle

AP=P/4, Therefore, Db=2(P/4)*sec x, Db=P/2*sec x

PART-B

1. Explain how to use laser interferometer to predict machine tool accuracies.

(ODD 2015)

i. Leveling of the machine

ii. Time running of locating cylinder of main spindle

iii. Axial ship of main spindle and tune running of shoulder face of spindle

nose.

iv. Time running of head stock center

v. Parallelism of main spindle to saddle movement

vi. True running of taper socket in main spindle

vii. Movement of upper slide parallel with main spindle in vertical plane.

viii. Parallelism of tailstock guide ways with the movement of carriage.

ix. Parallelism of tail stock sleeve taper socket to saddle movement.

x. Pitch accuracy of lead screw.

xi. Alignment of lead screw bearings with respect to each other.

2. How major and minimum diameters are measured? (ODD 2015)



Pitch It is the distance measured parallel to the screw threads axis between the

corresponding points on two adjacent threads in the same axial plane. The basic pitch is

equal to the lead divided by the number of thread starts.

Minor diameter: It is the diameter of an imaginary co-axial cylinder which touches the

roots of external threads.

Major diameter: It is the diameter of an imaginary co-axial cylinder which touches the

crests of an external thread and the root of an internal thread.

Lead: The axial distance advanced by the screw in one revolution is the lead.

Pitch diameter: It is the diameter at which the thread space and width are equal to half

of the screw thread

Helix angle: It is the angle made by the helix of the thread at the pitch line with the axis.

The angle is measured in an axial plane.

Height of thread: It is the distance measured radially between the major and minor

diameters respectively

Addendum: Radial distance between the major and pitch cylinders for external thread.

Radial distance between the minor and pitch cylinder for internal thread.

Dedendum: It is the radial distance between the pitch and minor cylinders for external

thread. Also radial distance between the major and pitch cylinder for internal thread.



3. How is the straightness of straight edge measured? (EVEN 2015)

A straight edge is a measuring tool which consists of a length of a length of a

steel of narrow and deep section in order to provide resistance to bending in the plane

of measurement without excessive weight. For checking the straightness of any surface,

the straight edge is placed over the surface and two are viewed against the light, which

clearly indicate the straightness. The gap between the straight edge and surface will be

negligibly small for perfect surfaces. Straightness is measured by observing the colour

of light by diffraction while passing through the small gap. If the colour of light be red, it

indicates a gap of 0.0012 to 0.0075mm. A more accurate method of finding the

straightness by straight edges is to place it in equal slip gauges at the correct point for

minimum deflection and to measure the uniformity of space under the straight edge with

slip gauges.

Test for straightness by using spirit level and Autocollimator

The straightness of any surface could be determined by either of these instruments by

measuring the relative angular positions of number of adjacent sections of the surface

to be tested. First straight line is drawn on the surface then it is divided into a number of

sections the length of each section being equal to the length of sprit level base or the

plane reflector’ s base in case of auto collimator. The bases of the spirit level block or

reflector are fitted with two feet so that only feet have line contact with the surface and

the surface of base does not touch the surface to he tested. The angular division

obtained is between the specified two points. Length of each section must be equal to

distance between the centerlines of two feet. The special level can be used only for the

measurement of straightness of horizontal surfaces while auto-collimator can be used

on surfaces are any plane. In case of spirit level, the block is moved along the line equal

to the pitch distance between the centerline of the feet and the angular variation of the



direction of block. Angular variation can be determined in terms of the difference of

height between two points by knowing the least count of level and length of the base.

In case of autocollimator the instrument is placed at a distance of 0.5 to 0.75m from the

surface to be tested. The parallel beam from the instrument is projected along the

length of the surface to be tested. A block fixed on two feet and fitted with a plane

vertical reflector is placed on the surface and the reflector face is facing the instrument.

The image of the cross wires of the collimator appears nearer the center of the field and

for the complete movement of reflector along the surface straight line the image of cross

wires will appear in the field of eyepiece. The reflector is then moved to the other end of

the surface in steps equal to. The center distance between the feet and the tilt of the

reflector is noted down in second from the eyepiece.

4. Explain the principle and working of an electrical torsion meter with a sketch.

(EVEN 2015)



Due to the applied torque, there is a relative displacement between the two slotted

discs. Due to this relative displacement of the slotted discs, a phase shift exists between

the pulse generated by the transducers. When these pulses are connected to an

electronic unit, it will show a time lapse between the two pulses. This time lapse

between the two pulses is proportional to the twist of the shaft and the torque of the

shaft.

The teeth produce voltage pulses in the transducers.

When torque is not applied on the shaft, the teeth of the both the discs perfectly align

with each other and hence he voltage pulses produced in the transducers will have zero

time difference.

But when torque is applied on the shaft, there is a relative displacement of the slotted

discs due to twist experienced by the shaft and hence the teeth of both the discs will not

align with each other and hence the voltage pulses produced in the transducer will have

a time difference (that is , time lapse).

This time lapse between the pulses of the two discs is proportional to the twist of the

shaft and hence the torque of the shaft.

A measure of this time lapse becomes of torque when calibrated.

5. How is the tooth thickness of a gear measured in the base tangent method ?

Derive the expression for tooth thickness of a gear in this method. (ODD 2014)

The measurement is done by using micrometer with anvils or by the david brown

tangent computer.



Two anvils, one is fixed and another immovable.

Fixed anvil is used to set the distance by adjusting locking ring and setting tubes.

6. With a neat diagram explain the working principle of any one stylus type

surface finish measuring instruments. (ODD 2014)

The accuracy of manufactured parts depends on the accuracy of machine tools.

The quality of work piece depends on Rigidity and stiffness of machine tool and its

components. Alignment of various components in relation to one another Quality and

accuracy of driving mechanism and control devices. It can be classified into Static tests

Dynamic tests. Static tests If the alignment of the components of the machine tool are

checked under static conditions then the test are called static test. Dynamic tests If the

alignment tests are carried out under dynamic loading condition. The accuracy of

machine tools which cut metal by removing chips is tested by two types of test namely.

Geometrical tests o Practical tests Geometrical tests In this test, dimensions of

components, position of components and displacement of component relative to one

another is checked. Practical tests In these test, test pieces are machined in the

machines. The test pieces must be appropriate to the fundamental purpose for which

the machine has been designed.

7. How is surface finish indicated in an engineering drawing .What are the various

elements indicated in the symbol? (EVEN 2014)

This instrument uses mechanical-cum-optical means for magnification.



Construction:

In this the diamond stylus on the surface finish recorder is held by spring

pressure against the surface of a lapped cylinder. The lapped cylinder is supported one

side by probe and other side by rollers. The stylus is also attached to the body of the

instrument by a leaf spring and its height is adjustable to enable the diamond to be

positioned and the light spring steel arm is attached to the lapped cylinder and carries at

its tip a diamond scriber which bears against a smoked glass.

Working:

When measuring surface finish, body is traversed across the surface by a screw rotated

by a synchronous motor. Any vertical movement of the stylus caused by the surface

irregularities causes the horizontal lapped steel cylinder to roll. By its rolling, the light

arm attached to its end provides a magnified movement on a smoked glass plate. This

vertical movement coupled with the horizontal movement produces a trace on the glass

magnified in vertical direction and there being no magnification in horizontal direction.

The smoked glass trace is then, further projected at 50 and 100 magnification for

examination. Finally the movement of scriber together with horizontal movement

produces at race on the smoked glass plate and this trace is magnified by an optical

projector.



8. With a neat sketch explain the dimensional measurement using

Scanning Laser Guage. (EVEN 2014)

Laser telemetric system is a non-contact gauge that measures with a

collimatedlaser beam. It measures at the rate of 150 scans per second.It

basically consists of three components, a transmitter, and a receiver and

processorelectronics. The transmitter module produces a collimated parallel

scanning laserbeam moving at a high constant, linear speed.

The scanning beam appears a red line. The receiver module collects and photo

electrically senses the laser light transmitted past the object being measured.



The processor electronics takes the received signals to convert them to

aconvenient form and displays the dimension being gauged.

The transmitter contains a low power helium-neon gas laser and its power

supply, a specially designed collimating lens, a synchronous motor, a multi-

facetedreflector prism, a synchronous pulse photo detector and a protective

replaceable window.

The high speed of scanning permits on line gauging and thus it is possible to

detect changes in dimensions when components are moving on a continuous

product such as in rolling process moving at very high speed.There is no need

of waiting or product to cool for taking measurements. This system can also be

applied on production machines and control then with closed feedback

loops.Since the output of this system is available in digital form, it can run a

process controller limit alarms can be provided and output can be taken on

digital printer. It is possible to write programs for the microprocessor to take care

of smoke, dust and other airborne interference around the work piece being

measured.

(ii)Name the alignment tests performed on milling machine.

(4)

Alignment Tests on Milling Machine:

Machine tools are very sensitive to impact or shock, even heavy cast inn

standards are not always solid and rigid enough to withstand stresses due to

falling during transportation, and deformations may be set up.

Although the machine is always carefully adjusted and aligned when on the test

stand or in the assembly department of the manufacturer, it is well known from

experience that erection in the workshop of the user is not always done with

sufficient care and thus inaccuracies of the work may result from the faulty

erection of the machine.



So the machine should be carefully levelled up by means of a spirit level before

starting with the actual trial tests. Each trial measurement is based on the correct

erection of the machine. No upright, base etc. can be made so rigid that it will be

thoroughly free from deformation resulting from faulty erection.

Machine tools for the workshop must be able to produce workpieces of given

accuracy within prescribed limits, consistently and without requiring artistic skill

on the part of the operator.

For acceptance test of a machine, its alignment test is performed and to see its

dynamic stability, which may be poor though alignment tests are right, certain

specific jobs are prepared and their accuracy check.

The relative alignment of all parts of machine and the accuracy of the control

devices and driving mechanisms are measured under no load condition. The

result of these measurements must lie within the prescribed limits given by the

manufacturer depending upon the grade of the machine tool

A specification for the alignment tests must comply with the following general

requirements:

The procedure for testing standard machine tools must not require more than 6

to 8 hrs of work provided allthe tooling and measuring equipment are readily

available.

The permissible limits of accuracy of individual measurements must be wide

enough to make economical manufacture possible while on the other hand the

cumulative error of number of superimposed details should not be excessive.



The various tests performed on the milling machine are shown in (Fig. 16.16) and

described below.

1. Cutter Spindle Axial Slip or Float.

We have to distinguish between axial (or end) play and axial slip of the spindle.

End play means the indispensable freedom of a spindle moving in the axial

direction to prevent it from seizing by heating. This end play is especially

important on high speed machines and it should be within the prescribed limits.

Axial slip is denned as the axial spindle movement which may repeat positively

with each revolution as a consequence of manufacturing errors. It is only this

axial sliding movement which is to be tested, and the specified tolerance applies

only to this movement.

When testing the axial slip of a spindle the feeler of the dial gauge rests on the

face of the locating spindle shoulder and dial gauge holder is clamped to the

table. The locating spindle shoulder is rotated and change in reading is noted.

This is done at the two spots diametrically opposite to each other. The total error

indicated by the movement of the pointer includes three main sources of errors.

(i)Axial slip due to error in bearing supporting the locating shoulder.

(ii) Face of the locating shoulder not in a plane perpendicular to axis of rotation.

(Hi)

Irregularities of front face. Effects of this will be that in cutting spirals, the pitch

will not be constant and we will get irregular pitch helix. If the feeler touches at

the same spot where the turning tool on the emery wheel has machined the

spindle collar in the assembled machine, then the feeler will not show any

deviation. Therefore axial slip must always be tested at two points 180° apart on

the collar of the spindle.

2. Eccentricity of External Diameter.



The feeler is placed on the cylindrical surface of the shoulder. The locating

shoulder is rotated and any deviation in reading of dial gauge is noted. It is due to

eccentricity of the spindle in the hole in which it fits.

Due to it, vibrations are produced and the cutter will float sideways and cut over,

or under-size. Face mills may dig in when leading edges cease to cut.

3. True Running of Internal Taper.

The table is set in its main position longitudinally and the mandrel 300 mm long is

fixed in the spindle taper. A dial gauge is set on the machine table and feeler

adjusted to touch the lower surface of the mandrel.

The mandrel is then turned and the dial readings at two points are noted i.e., one

at the place nearest to spindle nose and other at about 300 mm from it. For

shifting the position of dial gauge from A to B cross-slide of the machine is

operated to bring the dial gauge at the bottom of the end of mandrel.

There are can be two errors :

a. Axis of the spindle and the axis of taper may not be parallel.

b. Eccentricity of the taper hole which, if present, should indicate same error

at both the places. The error in first case will give different readings at two

places. Due to this error, cut will not be shared equally between teeth of

cutters, and therefore vibrations and poor finish will result.

4. Table surface parallel with arbor rising towards overarm.

In selecting the permissible errors of horizontal milling machines, care is taken to

the fact that in the direction parallel to the cutter spindle, the work table extends

towards the front face of the knee only, and never slopes down. While working,

the table tends to incline downwards under the influence of the weight of work

and cutting pressure, while the cutter arbor tends to deflect upwards. Great

importance, therefore, has always been attached to the necessity of having the



direction of table tolerance opposite to the deformation expected under cutting

conditions.

Parallelism between table face and the axis of the main spindle is checked as

follows:

A dial gauge is set on the machine table. A mandrel 300 mm long is fitted in the

spindle taper. The feeler of dial gauge is made to touch the lower surface of the

mandrel. With mandrel in position (mean) the readings at the maximum travel of

the table surface are observed. The stand of the dial gauge is moved and not the

table itself remains stationary. Effect of this error will be that the milled surface

produced will not be square to the base and parallel cross ways.

5. Surface Parallel with Longitudinal Movement.

For this test the dial gauge is fixed to the spindle. Feeler is directed upon the

surface the machine table and latter moved longitudinally. The deviations from

parallelism between the table surface and longitudinal motion are noted down. If

the table is uneven, a straight edge may be placed on the surface.

Due to this error the surface of the table will fluctuate up and down and cutter will

not take equal cuts on the job which is clamped on the table and the milled

surface will not be parallel to the base.

6. Traverse Movement Parallel with Spindle Axis.

(a) In horizontal plane; (b) In vertical plane. The table is set in its mean position and

dial gauge fixed on the table. The table is moved crosswise and any deviation on

reading of dial gauge is noted with feeler on one side of mandrel in horizontal plane and

under the mandrel for error in vertical plane.Due to this error, depth of cut will vary when

cross slide is moved.

7. Central T-Slots Parallel with Longitudinal Movement.

The T-slot, particularly the central one should be well machined on the internal

vertical surface throughout its length because jigs and fixtures are located by T-



slots. The general parallelism of the central slot with the longitudinal movement

of the table is checked by using a bracket 150 mm long with a tension which

enters the T-slot.

Against the upper surface of the bracket in vertical plane the feeler of the dial

gauge is located. Having fixed the dial gauge to the spindle and adjusting its

feeler to the surface of the bracket the table is moved longitudinal while

thetension block is held stationary by hand and deviations from parallelism are

noted from dial gauge. During the process the tension slides along the slot, thus

eliminating the effects of local error.

Due to this error, the depth of cut will not remain constant as the job will be

inclined according to inclination of T-slots with longitudinal movement and the

axis of job held between tail stock and index head will not be perpendicular to

cutter.

8. Centre T-slot Square with the Arbor.

If the central T-slot is not perpendicular to the arbor, the key way etc. cut on the

machine will not be parallel to the axis of job.

For this test table is adjusted in the middle portion of its longitudinal movement

and a tension block 160 mm long inserted in the central T-slot. A dial gauge is

fixed on the mandrel, the feeler being adjusted to touch the vertical face of the

bracket.

Observe the reading on the dial gauge when the bracket or tension block is near

one end of table. Then swing over the dial gauge and move the tension block so

that the corresponding reading can be taken near the other end of the table.

Generally two tension blocks are used.

9. Tests on Column.

(a) Column ways of knee square with table, inclination front to rear (b) Side

inclination.



Arrange table is its central position and fix a square with an arm about 300 mm

long (Angle iron type bracket placed on the surface), on the table surface and

attach a dial gauge to the spindle mandrel in such a way that the feeler rests on

the arm (vertical face) of the surface near the bottom edge. Observe the reading

of the dial gauge.

Move the table upwards about 300 mm and again observe the dial gauge. The

difference in readings is a direct indication of the error of perpendicularity of the

table surface (from guiding surface) and knee support or side guiding support.

The above test is conducted for two positions of the square and in first position

the dial gauge touches the square in front and in second position it faces the

side of the square i.e. at 90° to the first position (for testing side inclination).

If column-ways for knee are not square with the table, as the table is fed

upwards in facing operation or end milling, the surface produced will not be

square with the table surface.

10. Overarm parallel with spindle.

(a) In horizontal plane, (b) in vertical plane.

To check the parallelism of the overarm and the spindle, fix the dial gauge on the

table and its feeler under the mandrel. Move the table crosswise and note any

change in the reading.

For error in the horizontal plane, repeat above readings so that feeler is under

overarm and compare the two sets of readings. For vertical plane compare the

readings on mandrel and side of overarm.16.4.10.

Alignment of the main spindle with bore of the bracket of the overarm.

With the mandrel (parallel) in the bore of the overhanging bracket and gauge

holder in the mandrel fitted to the spindle taper, the feeler is adjusted so that it

touches the mandrel in thebore.



The main spindle is turned slowly and reading of the dial gauge is noted at four

points (opposite ends in horizontal and vertical planes i.e. 90° apart).

The difference between two 180° opposite readings and other two is twice the

eccentricity of the mandrel in the vertical and horizontal directions respectively.

It the axis of the bearing of the supporting bracket is not co-axial with the spindle

axis, the axis of the arbor which is held in spindle and supporting bracket will not

be parallel with table surface and hence the cutter mounted on the arbor will take

more cut on supporting bracket side if the bearing axis is somewhat lower than

spindle axis and less cut if the bearing axis is above.



UNIT-5

MEASUREMENT OF POWER, FLOW AND TEMPERATURE

PART-A

1. List any two methods employed for measuring torque. (ODD 2015)

Mechanical torsion meter

Electrical torsion meter

2. What are the physical characteristics of temperature measuring sensor? (ODD

2015)

Resistance Temperature Detectors are the sensors used to measure the

temperature by correlating the resistance of the RTD element with temperature.

3. What is the function of load cell? (EVEN 2015)

When the strain gauge – elastic member combination is used for weighing it is

called a load cell. Load cells utilize an elastic member as the primary transducer and

strain gauge as secondary transducer.

4. Name any four instruments used for measuring temperature. (EVEN 2015)

1. Thermocoulping.

2. Electrical thermal resistance.

3. Thermostats.

4. Pyrometers.

5. Define the principle of electrical resistance thermistor. (ODD 2014)

Electrical Resistance thermometers, also called resistance temperature detectors

(RTDs), are sensors used to measure temperature by correlating the resistance of the

RTD element with temperature. Most RTD elements consist of a length of fine coiled

wire wrapped around a ceramic or glass core. The element is usually quite fragile, so it

is often placed inside a sheathed probe to protect it. The RTD element is made from a

pure material, typically platinum, nickel or copper. The material has a predictable



change in resistance as the temperature changes and it is this predictable change that

is used to determine temperature.

Advantages

• High accuracy

• Low drift

• Wide operating range

• Suitability for precision applications.

6. Name the instrument used for low pressure measurements. (ODD 2014)

Low pressure-Manometer

7. Why are measuring instruments calibrated? (EVEN 2014)

Laser interferometer system can be used to determine linear positioning and

straightness errors in machine axes, to improve performance through targeted

maintenance and correction for linear positioning errors using error compensation

(using sensors for measurement of air and material temperature, air humidity and air

pressure).

8. What is the working principle behind strain gauges? (EVEN 2014)

When force is applied to any metallic wire its length increases due to the strain. A strain

gauge consists of a foil of resistive characteristics, which is safely mounted on a

backing material. When a known amount of stress in subjected on the resistive foil, the

resistance of the foil changes accordingly. Thus, there is a relation between the change

in the resistance and the strain applied. This relation is known by a quantity called

gauge factor. The change in the resistance can be calculated with the help of a

Wheatstone bridge.

9. What is a bimetallic strip? Name its types. (ODD 2013)



A bimetallic strip is made of two thin strips of metal which have different thermal

co-efficients of expansion. The two metal strips are joined together by brazing,

welding or riveting so that the relative motion between them is arrested.Different

common forms of bimetallic sensors are: * Helix type * Spiral type * Cantilever type

and * Flat type.

10. What is the principle used in thermocouples? (or) What is “Principle of thermo electricity”? (or) What is seebeck effect? (ODD 2013)

The principle states that ― When two conductors of two different metals A

and B are joined together at one end to form a junction, and this junction is heated to a

higher temperature with respect to the free ends, a voltage is developed at the free

ends and if these two conductors of metals at the free ends are connected, then the emf

setup will establish a flow of current‖.

PART-B

1. Explain in briefly any one method of torque measurement. (ODD 2015)

Measurement of applied torques is of fundamental importance in all rotating

bodies to ensure that the design of the rotating element is adequate to prevent failure

under shear stresses.

wer transmitted by

rotating shafts.

The four methods of measuring torque consist of

Measuring the strain produced in a rotating body due to an applied torque

An optical method

Measuring the reaction force in cradled shaft bearings

Using equipment known as the Prony brake.



Measurement of Induced Strain Measuring the strain induced in a shaft due to an

applied torque has been the most common method used for torque measurement in

recent years. The method involves bonding four strain gauges onto a shaft as shown in

Figure, where the strain gauges are arranged in a d.c. bridge circuit. The output from

the bridge circuit is a function of the strain in the shaft and hence of the torque applied.

It is very important that positioning of the strain gauges on the shaft is precise, and the

difficulty in achieving this makes the instrument relatively expensive. This technique is

ideal for measuring the stalled torque in a shaft before rotation commences. However, a

problem is encountered in the case of rotating shafts because a suitable method then

has to be found for making the electrical connections to the strain gauges. One solution

to this problem found in many commercial instruments is to use a system of slip rings

and brushes for this, although this increases the cost of the instrument still further.

2. How is the pitot tube used for flow measurements? (ODD 2015)

An obstruction type primary element used mainly for fluid velocity measurement is the

Pitot tube.

Principle

Consider Figure which shows flow around a solid body. When a solid body is held

centrally and stationary in a pipeline with a fluid streaming down, due to the presence of

the body, the fluid while approaching the object starts losing its velocity till directly in



front of the body, where the velocity is zero. This point is known as the stagnation point.

As the kinetic head is lost by the fluid, it gains a static head. By measuring the

difference of pressure between that at normal flow line and that at the stagnation point,

the velocity is found out. This principle is used in pitot tube sensors

Pitot tube

A common industrial type of pitot tube consists of a cylindrical probe inserted into the air

stream, as shown in Figure. Fluid flow velocity at the upstream face of the probe is

reduced substantially to zero. Velocity head is converted to impact pressure, which is

sensed through a small hole in the upstream face of the probe. A corresponding small

hole in the side of the probe senses static pressure. A pressure instrument measures



the differential pressure, which is proportional to the square of the stream velocity in the

vicinity of the impact pressure sensing hole. The velocity equation for the pitot tube is

given by,

Advantages

1. No pressure loss.

2. It is relatively simple.

3. It is readily adapted for flow measurements made in very large pipes or ducts

Disadvantages

1. Poor accuracy.

2. Not suitable for dirty or sticky fluids and fluids containing solid particles.

3. Sensitive to upstream disturbances.

3. Explain the working of bimetallic strip type temperature measuring system.

(EVEN 2015)

Two dissimilar metals are bonded together into what is called a bimetallic strip, as

sketched to the right.

As temperature increases, metal B expands more than does metal A, causing the

bimetallic strip to curl upwards as sketched.



bimetallic strip is used as the arm of a switch between electrical contacts. As the room

temperature changes, the

bimetallic strip bends as discussed above. When the bimetallic strip bends far enough, it

makes contact with electrical leads that turn the heat or air conditioning on or off.

perature indicates over-current,

which shuts off the circuit.

thermometers. These thermometers consist of a bimetallic strip wound up in a spiral,

attached to a dial that is calibrated into a temperature scale.

4. What are the thermocouples?State its applications. (EVEN 2015)

Thomas Johan Seeback discovered in 1821 that thermal energy can produce

electric current. When two conductors made from dissimilar metals are connected

forming two common junctions and the two junctions are exposed to two different

temperatures, a net thermal emf is produced, the actual value being dependent on the

materials used and the temperature difference between hot and cold junctions. The

thermoelectric emf generated, in fact is due to the combination of two effects: Peltier

effect and Thomson effect. A typical thermocouple junction is shown in fig. 5. The emf

generated can be approximately expressed by the relationship



Where, T1 and T2 are hot and cold junction temperatures in K. C1 and C2 are

constants depending upon the materials. For Copper/ Constantan thermocouple,

C1=62.1 and C2=0.045.

Thermocouples are extensively used for measurement of temperature in industrial

situations. The major reasons behind their popularity are:

(i) They are rugged and readings are consistent

(ii) They can measure over a wide range of temperature

(iii) Their characteristics are almost linear with an accuracy of about 0.05%.

However, the major shortcoming of thermocouples is low sensitivity compared

to other temperature measuring devices (e.g. RTD, Thermistor).

5.With a sketch explain the torque measurement using Strain Guages. (ODD 2014)

Measuring the strain induced in a shaft due to an applied torque has been the

most common method used for torque measurement in recent years. Torque

transducers based on strain measurement are normally made by applying strain gauges

to a shaft to measure the shear strain caused by torsion. The shear stress causes

strains to appear at 45° to the longitudinal axis of the shaft. So, the strain gauges must

be placed precisely at 45° to the shaft axis as shown in fig.



(ii) Otherwise, the arrangement is sensitive to bending and axial stress in

addition to those caused by torsion. The output is increased by using four

gauges so that the adjacent arms have strains of opposite nature. Also this

arrangement provides complete thermal compensation. For taking signals in

and out of the rotating shaft, slip rings and brushes are used. The

arrangement of slip rings and brushes are shown on fig .

(iii) It is easier to measure bending strains rather than strains due to torque at 45°

and so an arrangement using beams may be employed, in which the



transmitted torque results in bending the beams. This arrangement is shown

in fig.

(iv) A slip ring arrangement results in noise due to change in contact resistance

also slip rings and brushes wear out and hence it needs to be renewed. A

non-contacting type of arrangement as shown in fig 5.24.is preferred. This

bridge supply and output signals are transmitted between the rotating and

stationary member through transformers. Through AC supply of the bridge, an

amplitude modulated AC voltage proportional to the torque is obtained as the

output of the bridge. The AC voltage necessary for supply, the strain gauge

bridge and the measurement signal can be transmitted via rotating

transformer.

6. Explain the different types of torque measurements techniques with example.

(ODD 2014)

Measurement of applied torques is of fundamental importance in all rotating bodies to

ensure that the design of the rotating element is adequate to prevent failure under shear

stresses.



Torque measurement is also a necessary part of measuring the power transmitted by

rotating shafts.

The four methods of measuring torque consist of

1.Measuring the strain produced in a rotating body due to an applied torque

2.An optical method

3.Measuring the reaction force in cradled shaft bearings

4.Using equipment known as the Prony brake.

1.Measuring the strain induced in a shaft due to an applied torque has been the

most common method used for torque measurement in recent years.

The method involves bonding four strain gauges onto a shaft as shown in Figure, where

the strain gauges are arranged in a d.c. bridge circuit. The output from the bridge circuit

is a function of the strain in the shaft and hence of the torque applied. It is very

important that positioning of the strain gauges on the shaft is precise, and the difficulty

in achieving this makes the instrument relatively expensive. This technique is ideal for

measuring the stalled torque in a shaft before rotation commences. However, a problem

is encountered in the case of rotating shafts because a suitable method then has to be

found for making the electrical connections to the strain gauges. One solution to this

problem found in many commercial instruments is to use a system of slip rings and

brushes for this, although this increases the cost of the instrument still further.

2. Optical Torque Measurement



Optical techniques for torque measurement have become available recently with the

development of laser diodes and fiber-optic light transmission systems. One such

system is shown in Figure. Two black-and-white striped wheels are mounted at either

end of the rotating shaft and are in alignment when no torque is applied to the shaft.

Light from a laser diode light source is directed by a pair of fiber-optic cables onto the

wheels. The rotation of the wheels causes pulses of reflected light, which are

transmitted back to a receiver by a second pair of fiber-optic cables. Under zero torque

conditions, the two pulse trains of reflected light are in phase with each other. If torque

is now applied to the shaft, the reflected light is modulated. Measurement by the

receiver of the phase difference between the reflected pulse trains therefore allows the

magnitude of torque in the shaft to be calculated. The cost of such instruments is

relatively low, and an additional advantage in many applications is their small physical

size.

3. Reaction Forces in Shaft Bearings

Any system involving torque transmission through a shaft contains both a power source

and a power absorber where the power is dissipated. The magnitude of the transmitted

torque can be measured by cradling either the power source or the power absorber end

of the shaft in bearings, and then measuring the reaction force, F, and the arm length, L,

as shown in Figure. The torque is then calculated as the simple product, FL. Pendulum

scales are used very commonly for measuring the reaction force. Inherent errors in the



method are bearing friction and windage torques. This technique is no longer in

common use.

4. Prony Brake

The Prony brake is another torque-measuring system that is now uncommon. It is used

to measure the torque in a rotating shaft and consists of a rope wound round the shaft,

as illustrated in Figure. One end of the rope is attached to a spring balance and the

other end carries a load in the form of a standard mass, m. If the measured force in the

spring balance is Fs, then the effective force, Fe, exerted by the rope on the shaft is

given by

Fe = mg - Fs If the radius of the shaft is Rs and that of the rope is Rr, then the effective radius, Re,

ofthe rope and drum with respect to the axis of rotation of the shaft is given by

Re = Rs+ Rr The torque in the shaft, T, can then be calculated as

T= FeRe



While this is a well-known method of measuring shaft torque, a lot of heat is generated

because of friction between the rope and shaft, and water cooling is usually necessary.

Prony brake

7. Explain any one type of pyrometer for measuring temperature.

Pyrometers(Thermocouple

8. Describes with neat sketches thermocouples.

INTRODUCTION:



The most common method of temperature used the thermocouples. It is based on setback effect. The thermocouple temperature measurement is based on creation of an electromotive force. BASIC PRINCIPLE: The basic principle of thermocouple ―when two dissimilar metals are joined together an e.m.f will exist between the two points A and B which is primarily a functions of the junction temperature. The above said to be principle is see-back effect.

CONSTRUCTION: The thermocouple consists of one hot junction and the cold junction. The hot junction will be introduced into the place where temperature it be measured. The other cold junction is maintaining at constant reference temperature. Also one voltage-measuring instrument is connected to the free ends of the thermocouple. OPERATION: In thermocouple, the known temperature is called reference temperature. The temperature which is to be measured is introduced in the thermocouples hot junction. A common arrangement for establishing the reference temperature is lath. The reference temperature is controlled to be at a constant temperature of 00c The temperature difference between the ice bath and the hot junction temperature will an e.m.f. this e.m.f production is measured in the millivoltmeter. So, this



change in e.m.f rate will give the measure of temperature. The output voltage is, Where T is the temperature in 0c and A, B and c are constant depending upon the thermocouple material. THERMOCOUPLE LAWS:

o Law of intermediate metals.

o Law of intermediate temperature. LAW OF INTERMEDIATE METALS If a third metal is introduced into a thermocouple circuit, as shown in fig. the net e.m.f of the circuit is no affected as long as the new connections are at the same temperature.

9. With a neat diagrams explain the working of bimetallic strip and thermometer.

(EVEN 2014)

The bimetallic strip temperature measurement is based on change in dimension of the metal. A very widely used method of temperature measurement is the bimetallic strip. Already discussed the basic principle in bimetallic temperature measurement is based on the change in dimension of metals i.e., expand or contract when there is a change in temperature.



The expansion or contraction is based on the thermal expansion coefficient. It changes from metal to metal contact.

WORKING: Two pieces of metal with different coefficient of thermal expansion are bonded together to form the bimetallic strip as shown in fig. it is in the form of a cantilever beam. When the strip is subjected to a temperature higher than the bonding temperature. It will be bent in one direction. Suppose, it is subjected to a temperature lower than the bounding temperature, it will be bent in the other direction. The radius of curvature `r` may be calculated as [ ]

Where,

T=combined thickness of the bonded strip mm.

1=Lower coefficient of expansion peroc

2=Higher coefficient of expansion per0c.

m=Ratios of thickness of low to high expansion material.

n=Ratio of modulus of elasticity of low to high expansion material

T=Temperature in 0c



T0=Initial bounding temperature in 0c

While selecting the bimetallic trip materials, it should have high coefficient of expansion, high ductility, high modules of elasticity, high electrical conductivity. There properties are very important. The various material used in bimetallic strip and their mechanical properties are given below. MATERIAL THERMAL COEFFICIENT OF

EXPANSION PER0C MODULUS OF ELASTICITY(GN/m2)

YELLOW BRASS 2.02 x 10-5 96.5

INVAR 1.7 x 10-5 147

STAINLESS STELL 1.6 x 10-5 193

MONEL 400 1.35 x 10-5 179

INCONEL 702 1.25 x 10-5 217

APPLICATIONS:

Bimetallic strips are frequently used in simple ON-OFF switches. The bimetallic strips are also used in control witches.

ADVANTAGES:

The cost is low when compared to other temperature measuring instruments. It has neglible maintenance expense. Stable operation over extended periods of time Accuracy of this type of instruments is between 2 to 5% of the scale.

DISADVANTAGES:

It is not suitable for more than above 4000c The permanent deformation of metallic strip may occur.

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