Mm ppt

Mechanical Engineering Department
PPT on Measurement and metrology
Prepared by
Assistant Professor :Mahesh Kumar
12/31/2016 Mahesh Kumar(ME) Asst.Prof. 1

Unit-1
Measurement and measuring instrument

Introduction to measurement and metrology
Measurement to ensure that the part to be measured
conforms to the established standard.
.
Metrology is the name given to the science of pure
measurement. Engineering Metrology is restricted to
measurements of length & angle.

Need for Measurement
1.To ensure that the part to be measured conforms to the
established standard.
2.To meet the interchange ability of manufacture.
3.To provide customer satisfaction by ensuring that no faulty
product reaches the customers.
4.To coordinate the functions of quality control, production,
procurement & other departments of the organization.
5.To judge the possibility of making some of the defective parts
acceptable after minor repair.
12/31/2016 4Mahesh Kumar(ME) Asst.Prof.

Precision & Accuracy of Measurement
Precision : It is the degree which determines how well
identically performed measurements agree with each other. It is
the repeatability of the measuring process. It carries no meaning
for only one measurement. It exists only when a set of
observations is gathered for the same quantity under identical
conditions. In such a set, the observations will scatter about a
mean. The less is the scattering, the more precise is the
measurement.

Accuracy : It is the degree of agreement between the
measured value and it’s true value. The difference between
the measured value & the true value is known as ‘Error of
measurement’. Accuracy is the quality of conformity. To
distinguish the Precision from Accuracy, the following simple
example can be said. A repaired needle-watch will give
Precision readings (same time)all the times, but will give
Accurate readings (correct time) only 2 times in a day.

Factors affecting the accuracy of measuring system
a)Factors affecting the standard of measurement:
 co-efficient of thermal expansion
elastic properties
stability with time
geometric compatibility
b)Factors affecting the work piece to be measured:
co-efficient of thermal expansion
elastic properties
arrangement of supporting work piece
hidden geometry
surface defects such as scratches, waviness, etc.

c) Factors affecting the inherent characteristics of instrument:
repeatability & readability.
calibration errors.
effect of friction, backlash, etc.
inadequate amplification for accuracy objective.
deformation in handling or use.
d) Factors affecting person:
 improper training / skill.
 inability to select proper standards / instruments.
less attitude towards personal accuracy measurements.

Measurement and measuring instruments
The following quantise are are typically within the scope of
mechanical measurements:
1.Pressure
2.Temprerature
3.Displacement
4.mass,length,time etc.

The fundamental measuring process
The word measured is used to designate the particular physical
parameters being observed and quantified; that is, the input
quantity to the measuring process.
Input
signal
Measurement
system
Output
signal

Instrumentation
Instrumentation is a technology of using instrument to
measurement and control the physical and chemical properties
of materials is known as instrumentation.
 When the instrument are used for the measured and control of
industrial manufacturing conversion or treatment process, is
process instrumentation.
 When the measuring and controlling instruments are
combined so that measurement provide impulses for remote
automatics action, the result is called control system.

Standards of measurement
1. Primary standards: The highest standard of either a base
unit or a derived unit is called primary standards.
2. Secondary standards: the secondary standards are the
reference calibrated standards, designed and calibrated
from the primary standards.
3. Working standards: these standards have an accuracy of
one order lower than that of the secondary standards.

S.I units and conversion factors
The international system of units is divided into three classes:
1. Base units
2. Derived units
3. Supplementary units

Mechanical mesurements
Mainly the fallowing two types of measurement are involved
in the mechanical engineering field:
1. Mechanics type (or self operated type) measurements.
a) The empirical method
b) The rational method
c) The experimental method
2. Power type mesurements.

Method of mesurements
The broad classification of methods of mesurements is follows:
1. Direct comparison methods: directly compared with either a
primary or a secondary standards. Direct comparison is quite
commonly used for mesurements of length.
2. Indirect comparison methods: In this method the comparison is
done with a standards through the use of a calibrated system.

Modes of mesurements
1. Primary mesurements
Example: mesurements of time by counting the number of stokes
of a clock
2. Secondary mesurements
Example: the pressure measurement by manometers.
3. Tertiary mesurements
Example: the speed mesurements by tachometer.

Generalised measurement system and its
functional element
It is important to have systematic organization and analysis of
measurement system .Most of the the mesurements system
contain three main functional element .they are:
1. Primary sensing element
2. Variable conversion element
3. Data presentation element
4. Data transmission element
5. Manipulation element

fig. Generalised measurement system.
Physical
system
sensor transducer manipulation
controller
indicator
recorder

Application of measurement system
Instrument and Measurement system are used for different
application are as under:
1. Monitoring of process and operations: These type of instrument
simply indicate the value or condition of parameter under study
and do not serve any control function.
2. Control of processes and operation: there has been a very strong
association between measurement and control.
3. Experimental engineering analysis: the engineering problem
can be solved by theoretical as well as experimental method;
several application require the use of both the methods.

Statics and dynamics characteristics
measurement system
Statics characteristics : measurement of application in which
parameter of interest is more or less constant or vary slowly with
time are called statics measurements. A set of criteria(Example:
accuracy, errors, reproducibility, drift, sensitivity dead zone.) that
provide meaningful description of measurements under statics
condition are called statics characteristics.

The main statics characteristics may be summed up as follows:
1.Accuracy
2. Sensitivity
3.Reproducibility
4.Drift
5.Static error
6.Dead zone
7.Precision
8.Linearity & non linearity
9.Thresold and resolution

Dynamics characteristics: When a instrument is required to
measure a time varying process variable, one has to be
concerned with dynamics characteristics . The characteristics
quantify the dynamics relation between the input and output.
Dynamics response: the evaluation of the ability of a system to
faithfully transmit and present all the pertinent information
included in the input signal and to exclude all else, is called the
response.
The behaviour of the system when inputs vary with time and
so does the output , is called dynamics response.

Dynamics characteristics of a measurement system
1. Speed of response ........Desirable
2. Measuring lag ........Undesirable
3. Fidelity ........Desirable
4. Dynamics error ........Undesirable

Dynamics analysis of measurement system
The dynamics behaviour of mesurements system is studied in
the following two domain:
1.Time domain analysis
i) Step input
ii) Parabolic input
iii) Impulse input
2.Frequency domain analysis
i) Linear function
ii)Step function

calibration
Instrument calibration is one of the primary processes used to
maintain instrument accuracy. Calibration is the process of
configuring an instrument to provide a result for a sample
within an acceptable range. Eliminating or minimizing factors
that cause inaccurate measurements is a fundamental aspect of
instrumentation design.

The calibration of the instrument is done to find its accuracy.
Before using an instrument, particularly a new one, in a
measurement system, it is required to calibrate it to find the
accuracy, precision or uncertainty of the instrument. It can be
done by comparing its performance with
(a) a primary standard instrument,
(b) a secondary standard instrument having high accuracy, and
(c) a known input source.

For example, a flow meter might be calibrated by
(a) comparing it with a standard flow measurement facility of
the National Bureau of Standards,
(b) comparing it with another flow meter of known accuracy
(c) direct calibration with a primary measurements such as
weighing a certain amount of water in a tank and
recording the time elapsed for the quantity of flow
through the meter.

Errors
In measurement system the errors could originate from several sources.
These may be classified as follows:
1. Gross errors: these errors occurs human mistakes in reading
instruments and recording and calculating result of
measurement.
2. Systematic errors: the systematic errors are replaced
consistently with the repetition of experiment and are caused
by such effect as sensitivity shift, known non linearity.
i) Instrumental errors
ii) Environmental errors
iii) Observational errors
3. Random errors: the random errors accidental , small and
independent.

Errors in measurement
Error in measurement is the difference between the measured
value and true value of measured dimension.
Errors in measurement = measured value – true value
The error in measurement may be expressed as an absolute
error or as a relative error.
1) Absolute error: It is the algebraic difference between the
measured value and the true value of the quantity measured.

It is further classified as;
i) True absolute error
ii) Apparent absolute errors
2. Relative error: It is the quotient of the absolute error and the
value of comparison (which may be true value, conventional
true value or arithmetic mean value of a series of
measurements)used for the calculation of that absolute error.

The most common causes of these errors are:
1) Friction in instrument movement
2) Backlash in the movement
3) Parallax errors between pointer and scale
4) Hysteresis in elastic member.
5) Mechanics vibration

SOURCES OF ERRORS
Source of errors found in physical and mechanical in nature and
the errors which necessarily result from the faulty calibration of
measuring system.
The errors arises from the following sources also:
1. Noise : it is defined as any signal that does not convey useful
information.
2. Response time: it is defined as he time taken by the
instrument to show 63.2% change in a reading to a step input.

3. Design limitation: in the design of the instrument certain
inevitable factors such as a friction and resolving lead to
uncertainty to measurements.
4. transmission: during the transmission information from the
primary sensing element to the indicator.
The signal may be attenuation due to any of the reason:
i)It may suffer loss through leakage.
ii) It may be absorbed consumed in communication channel.
iii) It may be distorted by resonance.

5. Deterioration of measuring system: the example of some type
of deterioration which occurs in measuring system and result
in as a source of errors in measurement are:
1) Change in resistance of circuit element through strain relief.
2) Weakening of a permanent magnet.
3) Alteration of thermocouple.
6. Ambient influence on measuring systems.
7. Errors of observation and interpretation.

Statistical Analysis
It is important to define some pertinent terms before
discussing some important methods of statistical analysis of
experimental data.
Arithmetic Mean : When a set of readings of an instrument is
taken, the individual readings will vary somewhat from each
other, and the experimenter is usually concerned with the mean
of all the readings. If each reading is denoted by xi and there
are n readings.
Variance :The square of standard deviation is called variance.
This is sometimes called the population or biased standard
deviation because it strictly applies only when a large number
of samples is taken to describe the population.

Geometrical mean: It is appropriate to use a geometrical mean
when studying phenomena which grow in proportion to their
size. This would apply to certain biological processes and
growth
When an experiment is performed and some data are obtained,
then it is required to analyze these data to find error, precision
and the general validity of the experimental measurements.
The error analysis of the experimental data can be done by
various methods, such as common sense basis, uncertainty
analysis, statistical analysis, probability error analysis, limiting
error analysis rate in financial resources.

SENSOR AND TRANSDUCER
SENSORS convert energy information One energy form must
be converted into the same or another energy form with exactly
the same information content as the originating energy form.
It is defined as an element which produces signal relating to the
quantity being measured .According to the Instrument Society
of America, sensor can be defined as “A device which provides
a usable output in response to a specified measured.” Here, the
output is usually an ‘electrical quantity’ and measured is a
‘physical quantity, property or condition which is to be
measured'.

 It is defined as an element when subjected to some physical
change experiences a related change or an element which
converts a specified measured into a usable output by using a
transduction principle.
 It can also be defined as a device that converts a signal from
one form of energy to another form. A wire of Constant an
alloy(copper-nickel 55-45% alloy) can be called as a sensor
because variation in mechanical displacement (tension or
compression) can be sensed as change in electric resistance.
 This wire becomes a transducer with appropriate electrodes
and input-output mechanism attached to it. Thus we can say
that ‘sensors are transducers.

Mechanical detector transducer element
The various mechanical detector-transducer element may be
discussed as fallows:
1. Elastics member/elements.
2. Mass sensing element.
3. Thermal detectors.
4. Hydro-pneumatics elements.

Transducer
Transducer
Excitation
Electrical outputPhysical quantity

Classification of transducer
Transducer are broadly classified into two group as fallows:
1. Active transducer: they are also known as self – generating
type transducer. These transducers develop their own voltage
or current. The energy required for production of an out put
signal is obtained from the physical phenomenon being
measured.
Example: thermocouple. and thermopiles, photovoltaic cell
2. Passive transducers: they are known as externally-powered
transducer. They may absorb some energy from the physical
phenomenon under study.
Example: resistance thermometers and thermistors.

3. Analogue transducer. These transducer convert the input
physical phenomenon into an analogous output which is a
continuous function of time.
Example: strain gauge, a thermocouple
4. Digital transducers. These transducer convert the input
physical phenomenon into an electrical output which may be i
form of pulse.

Analog and digital modes of operation
Analog mode: signal that vary in a continuous fashion and take
on an infinite number of values in any given range are called
analog signal. The device which produce these signal are
called analog device.
Digital modes: the signal which vary in discrete steps and thus
take up only finite different value range are called digital
modes. the device that produce such signal are called digital
device.

Classification of instruments
The instrument may be classified as follows:
1.Absolute and secondary instruments.
2. Analog and digital instruments.
3.mechanical,electrical and electronic instruments
4. Manual and automatic instruments.
5.Deflection and null output operated instruments

Basic units
For Length : Metre
For Mass: Kilogram (kg)
For time : second (s)
For current: ampere (A)
For temperature: Kelvin(k)
For luminous intensity : candela (cd)
For amount of substance: mole (mol)

Units of measurements
a) FPS System: In this system, the units of length,
mass,time,temperature are Foot (or Yard), Pound (or Slug,
Second, Rankin (or Fahrenheit) respectively. It is common
in English speaking countries and is developed by Britain.
b) Metric System: It is a decimal system of weight
&measurement is based on the Metre as the unit of length.
It was first used in France. Its basic unit is Metre.CGS
prescribes Centimetre, Gram, Second for length, weight &
time respectively.
c) Cgs system

Supplementary SI units:
For plane angle: radian (rad)
For solid angle: steradian(sr)
for Frequency: Hertz (Hz)

TYPE OF SENSOR
 Temperature Sensor
 Accelerometer
 Light Sensor
 Magnetic Field Sensor
 Ultrasonic Sensor
 CO2 Gas Sensor

A device which provides a usable output in response to a
specified measured.
A sensor acquires a physical parameter and converts it into
a signal suitable for processing (e.g. optical, electrical
mechanical)
Sensor
Input Signal Output Signal

Physical Principles
1.Amperes' Law. A current carrying conductor in a magnetic
field experiences a force (e.g. galvanometer)
2.Curie-Weiss Law. There is a transition temperature at
which ferromagnetic materials exhibit paramagnetic
behavior.
3.Faraday’s Law of Induction. A coil resist a change in
magnetic field by generating an opposing voltage/current
(e.g. transformer)
4.Photoconductive Effect. When light strikes certain
semiconductor materials, the resistance of the material
decreases (e.g. photo resistor)

Temperature Sensor
 Temperature sensors appear in building, chemical process
plants, engines, appliances, computers, and many other devices
that require temperature monitoring
 Many physical phenomena depend on temperature, so we can
often measure temperature indirectly by measuring pressure,
volume, electrical resistance, and strain

Temperature Sensor
i) Bimetallic Strip
ii)Application.
Thermostat (makes or breaks electrical connection with deflection)
Metal A
Metal B
δ
)]T-(T1[ 00  LL

Temperature Sensor
Resistance temperature device.









0
11
0
00 )]T-(T1[
TT
eRR
RR



Accelerometer
Accelerometers are used to measure along one axis and is
insensitive to orthogonal directions
Applications :
i) Vibrations, blasts, impacts, shock waves
ii) Air bags, washing machines, heart monitors, car alarms
Vibrating Base
m
k b
Position Sensor

Light Sensor
• Light sensors are used in cameras, infrared detectors, and
ambient lighting applications
• Sensor is composed of photoconductor such as a photoresistor,
photodiode, or phototransistor.
p n
I
+ V -

Magnetic Field Sensor
• Magnetic Field sensors are used for power steering, security,
and current measurements on transmission lines
• Hall voltage is proportional to magnetic field
x x x x x x
x x x x x x
x x x x x x
+ + + + + + + + + + + + + + +
- - - - - - - - - - - - - - -
I (protons) +
VH
-
B
tqn
BI
VH




Ultrasonic Sensor
• Ultrasonic sensors are used for position measurements
• Sound waves emitted are in the range of 2-13 MHz
• Sound Navigation And Ranging (SONAR)
• Radio Diction And Ranging (RADAR)

Photogate
 Photogates are used in counting applications (e.g. finding
period of period motion).
 Infrared transmitter and receiver at opposite ends of the
sensor.
 Time at which light is broken is recorded

CO2 Gas Sensor
• CO2 sensor measures gaseous CO2 levels in an environment.
• Measures CO2 levels in the range of 0-5000 ppm
• Monitors how much infrared radiation is absorbed by CO2
molecules
Infrared Source IR Detector

Type of transducer
There are a variety of transducer types like:
1. Temperature transducer
2. Piezoelectric transducer
3. Pressure transducer
4. Ultrasonic transducer

Temperature Transducer
Temperature transducer is an electrical device that is used to
convert the temperature of a device into another quantity like
electrical energy or pressure or mechanical energy, then the
quantity will be sent to the control device for controlling the
temperature of the device.
Application of Temperature Transducer
 Temperature transducer is used to measure the temperature of
the air such that to control the temperature of several control
systems like air-conditioning, heating, ventilation, and so on.

Piezoelectric transducer
Piezoelectric transducer is a special kind of sensor, and the main
function of this transducer is to convert mechanical energy into
electrical energy. In the same way, electrical energy can be
transformed into mechanical energy.
Piezoelectric Transducer Applications
This transducer is mainly used to detect the sticks drummer
impact in electronic drum pads.
 Also used to detect the movement of the muscle, which can be
named as acceleromyography.
The load of the engine can be determined by calculating diverse
absolute pressure,

Pressure Transducer
Pressure transducer is a special kind of sensor that alters the
pressure forced into electrical signals. These transducers are
also called as pressure indicators, manometers, piezometers,
transmitters, and pressure sensors.
Application of Pressure Transducer
Pressure transducer is used to measure the pressure of the
specific quantity like gas or liquid by changing the pressure
into electrical energy.
The different kinds of these transducers like an amplified
voltage transducer, strain-gage base pressure transducer.

Ultrasonic Transducer
The main function of the ultrasound transducer is to convert
electrical signals to ultrasound waves. This transducer can also
be called as capacitive or piezoelectric transducers
Application of Ultrasonic Transducer
This transducer can be used to measure the distance of the
sound based on reflection.
This measurement is based on a suitable method compared
to the straight methods which use different measuring scales.
 The areas which are hard to find, such as pressure
areas, very high temperature

65
Analog signal and digital signal
A digital signal is superior to an analog signal because it is more
robust to noise and can easily be recovered, corrected and
amplified. For this reason, the tendency today is to change an
analog signal to digital data. In this section we describe two
techniques, pulse code modulation and delta modulation.
 Pulse Code Modulation (PCM)
 Delta Modulation (DM)
12/31/2016 Mahesh Kumar(ME) Asst.Prof.

Pulse Code Modulation
PCM consists of three steps to digitize an analog signal:
1. Sampling
2. Quantization
3. Binary encoding
 Before we sample, we have to filter the signal to limit
the maximum frequency of the signal as it affects the
sampling rate.
 Filtering should ensure that we do not distort the signal,
i.e. remove high frequency components that affect the
signal shape.

Sampling
with analog (non integer) value Analog signal is sampled
every TS sec.Ts is referred to as the sampling interval. fs =
1/Ts is called the sampling rate or sampling frequency.
There are 3 sampling methods:
 Ideal - an impulse at each sampling instant.
 Natural - a pulse of short width with varying amplitude.
 Flattop - sample and hold, like natural but with single
amplitude value.
The process is referred to as pulse amplitude modulation
PAM and the outcome is a signals.

Delta Modulation
• This scheme sends only the difference between pulses, if
the pulse at time tn+1 is higher in amplitude value than the
pulse at time tn, then a single bit, say a “1”, is used to
indicate the positive value.
• If the pulse is lower in value, resulting in a negative value,
a “0” is used.
• This scheme works well for small changes in signal values
between samples.
• If changes in amplitude are large, this will result in large
errors.

Delta modulation components

Unit-2
Time related measurement

Stroboscope
A Stroboscope also known as a strobe, is an instrument
used to make a cyclically moving object appear to be
slow-moving, or stationary. In its simplest form, a marker
is placed to the rotating shaft and a lamp capable of
emitting brief and rapid flashes of light is used. The
frequency of the flash is adjusted so that it equals to the
shaft’s cyclic speed, at which point the object is seen to be
either stationary or moving backward or forward,
depending on the flash frequency

A stroboscope also known as a strobe, is an instrument used
to make a cyclically moving object appear to be slow-moving,
or stationary. It consists of either a rotating disk with slots or
holes or a lamp such as a flashtube which produces brief
repetitive flashes of light

Measurement of torque
There are many ways of measuring torque, out of which the two
most important ones are
 strain gauges
 balancing motors

Frequency measurement
 A direct comparison power measurement system has been
developed to measure power sensor effective efficiency in the
100 kHz to 18 GHz frequency range.
 This system is capable of measuring thermistor and
thermoelectric based power sensors.
 the sensitivity of the power meter and digital volt meter to
extraneous signals, and the effect of compensation beads, if
there were any, in the sensors.

Measurement of displacement
Measurement of linear displacement
Linear displacement may be measured by following transducers:
1. Resistive potentiometer
2. Strain gauge
3. Variable inductance transducer
4. Linear variable differential transducer(LVDT)
5. Capacitive transistor
6. Digital transducer

Measurement of velocity
Measurement of linear velocity
The following type of transducer are used for measurement of
linear velocity.
1.electro-magnetic transducer
i) Moving magnet type
ii) Moving coil type
2. Seismic type transducer

Tachometer
An instrument which either continuously indicate the value of
rotary speed or continuously display a reading of average
speed over rapidly operated short-intervals of time.
Classification of tachometer:
1.Mechanical tachometer
i) Hand speed indicator
ii) Tachoscope
iii) Centrifugal tachometer
iv) Vibrating reed tachometer

2. Electrical tachometer
i)D.C. Tachometer generator
ii) A.C. Tachometer generator
iii)Photoelectric tachometer
iv)Capacitive tachometer
v)Stroboscopic tachometer

PRESSURE MEASUREMENT
Pressure (P ) expresses the magnitude of normal force (F-N)
per unit area (A-m2) applied on a surface.
A
F
Por
A
F
P



gageatmabs PPP 
Where Pabs : Absolute pressure
Patm : Atmospheric pressure
Pgauge : Gage pressure

Pressure Measuring Devices
Bourdon Gauge:
Applications: tire pressure, pressure at the top or along the
walls of tanks or vessels.

Strain Gauge
Applications: Sensors for internal combustion engines,
automotive, research etc.
Principles: ∆ P  ∆ Resistance  ∆ Voltage

Applications: measurements with high accuracy, good
repeatability, high resolution e.g. Quartz Clock
Principles: ∆ Pressure  ∆ Charge  ∆ Voltage
http://www.ransohoff.com/images/systems/transducerlgr.jpg
Quartz gaugeransducers

Applications: Very accurate for small pressure differentials
e.g. Difference between indoor and outdoor pressure
Principles: ∆Pressure = ∆Charge = ∆Resistance = ∆Voltage
Digital Manometer

Elastic and indirect type pressure transducers
Mechanical pressure measurement devices are large and
cumbersome. Not suited for automated control loops typical
in industry.
Mechanical devices:
– U-tube Manometer
– Bourdon tube
– Diaphragm and Bellows element

 Flexible element used as sensor.
 Pressure changes cause change in element position.
 Element connected to pointer to reference pressure.
 Similar concept to Bourdon type.
 Widely used because they require less space and can be made
from materials that resist corrosion.

 Measures deflection of elastic diaphragm due to pressure
difference across diaphragm.
 Widely used in industry.
 Used for small pressure ranges.
 Measurements tend to drift.

Measures changes in capacitance of electrically charged
electrodes from movement of metal diaphragm due to pressure
difference across diaphragm.

Measurement of very low pressures
Main characteristics of manometers are pressure range,
accuracy, sensitivity and speed of response. Pressure range of
manometers varies from almost perfect vacuum to several
hundreds of atmosphere. The conventional instruments used
for pressure measurement are divided into the following
groups.
1)Liquid column manometers
2)Pressure gauges with elastic sensing elements
3)Pressure transducer

For amplifying the deflection in a liquid column manometer,
liquids with lower density could be used or one of the limbs of
the manometer may be inclined. Commonly used manometric
liquids are mercury, water or alcohol.
Some of the important and desirable properties of the manometric
liquids are:
1.Low viscosity
2.Low capillary constant
3.Low coefficient
4. thermal expansion
5.Low volatility
6.Low vapour pressure

Micro manometer
For accurate measurement of extremely small pressure
differences micro manometers are used In the Figure. The
instrument is initially adjusted such that p1= p2

Mechanical manometers
Mechanical manometers provide faster response than
liquid column manometers. In liquid column
measurements, lag is due to the displacements of the
liquid. In elastic sensing element type of manometers the
time lag is due to the time required for equalisation of
pressure to be measured with that in the sensing chamber.
The deformation of elastic sensing elements is measured
with the aid of kinematic, optical or electrical systems.

Strain Gauge circuit
As a consequence of strain two physical qualities are of particular interest:
(1) the change in gauge resistance and
(2) the change in length. The relationship between these two
variables expressed as a ratio is called the gauge factor.
Where
K = the gauge factor
R = the initial resistance in ohms (without strain)
= the change in initial resistance in ohms
L = the initial length in meters (without strain)
= the change in initial length in meters
LL
RR
K
/
/



L
R

Stress is defined as the internal force per unit area. The stress
equation is
Where
S = the stress in kilograms per Square meter
F = the force in kilograms
A = the area in square meters
A
F
S 

The constant of proportionality between stress and strain
for a linear stress-strain curve is known as the modulus of
elasticity of the material. E or Young's modulus. Hooke's
law is written as
Where
E =Young's modulus in kilograms per square meter
S = the stress in kilograms per square meter
G = the strain (no units)
G
S
E 

For strain gauge applications, a' high degree of sensitivity is
very desirable. A high gauge factor means a relatively large
resistance change for a given strain. Such a change is more
easily measured than a small resistance change. Relatively
small changes in strain can be sensed.

Semiconductor strain gauges are often used in high-output
transducers as load cells. These gauges are extremely
sensitive, with gauge factors from 50 to 200. They are
however, affected by temperature fluctuations and often
behave in a nonlinear manner. The strain gauge is
generally used as one arm of a bridge. The simple
arrangement shown in Fig. (2-a) can be employed when
temperature variations are not sufficient to affect accuracy
significantly, or in applications for which great accuracy
is not required.

The resistance of this dummy gauge is not affected by the
deformation of the material. Therefore, it acts like a passive
resistance with regard to the strain measurement. Since only one
gauge responds to the strain, the strain causes bridge unbalance
just as in the case of the single gauge.
Basic gauge bridge circuits.

Strain gauge rosettes
Rosette gauge are used for measuring strain in complex parts.
These gauge have three or four separate grid with various
angular orientation and they can be cemented to the part with no
particular attention being paid to the overall gauge orientation .
The resultant strain on each of the grid can then be recorded and
the true magnitudes and directions of the significant surface
strain in the parts can be calculated from these data.

To meet the foregoing requirements, the Micro-Measurements
Division manufactures three basic types of strain gauge
rosettes (each in a variety of forms).
1. Rectangular (0-45-90 degree):Three grids, with the second and
third grids angularly displaced from the first grid by45 degrees
and 90 degrees, respectively.
2. Delta (0-60-120 degree):Three grids, with the second and third
grids 60 degrees and 120 degrees away, respectively, from the
first grid.

3.Stacked: Co-location of the gauges requires mounting each
individual gauge on top of the others in what is called a
“stacked” rosette, but this leads to a complicated and often
inaccurate type of gauge.

All three types of rosettes (tee, rectangular, and delta) are
manufactured in both planar and stacked versions. As
indicated (for the rectangular rosette) below, the planar rosette
is etched from the strain-sensitive foil as an entity, with all
gauge elements lying in a single plane. The stacked rosette is
manufactured by assembling and laminating two or
three properly oriented single-element gauges.

When strain gradients in the plane of the test part surface are
not too severe, the normal selection is the planar rosette.
This form of rosette offers the following advantages in such
cases:
 Thin and flexible, with greater conformability to curved
surfaces.
 Minimal reinforcing effect.
 Superior heat dissipation to the test part.
 Available in all standard forms of gauge construction, and
generally.
 Accepts all standard optional features.
 Optimal stability.
 Maximum freedom in lead wire routing and attachment.

Force: It is defined as the reaction between the two bodies or
components. The reaction can be either tensile force (Pull) or it
can be Compressive force (Push).
Measurement of force can be done by any two methods:
1.Direct Method: This involves a direct comparison with a
known gravitational force on a standard mass. Example:
Physical Balance.
2.Indirect Method: This involves the measurement of effect of
force on a body. E.g. Force is calculated from acceleration due
to gravity and the mass of the component.
Measurement of force torque and pressure

Unequal arm balance:

• For balance of moments,
Ft * a = Fg * b
or test force,
Ft = Fg * (b / a)
Therefore, the test force is proportional to the distance ‘b’ of the mass
from the pivot.

Platform Balance: (Multiple Lever System)

Torque Measurement:
Torque: Force that causes twisting or turning moment.
E.g. the force generated by an internal-combustion engine
to turn a vehicle's drive or shaft. Torque measuring
devices are called as dynamometers.
The torque may be computed by measuring the force ‘F’
at a known radius ‘r’, given by the formula
in N - m

Torque Measurement:
Torque measurement is usually associated with determination of
mechanical power, either power required to operate a machine or
to find out the power developed by the machine.
Where,
N = Speed in rpm.
T =Torque developed due to load “W”, (N-m)
R = Radius from the center to the point of application of force (m)
kw
NT
power
1000*60
2


Types of Dynamometers:
Absorption dynamometers: They are useful for measuring
power or torque developed by power source such as engines
or electric motors.
Driving dynamometers: These dynamometers measure power
or torque and as well provide energy to operate the device to
be tested. These are useful in determining performance
characteristics of devices such as pumps and compression.
Transmission dynamometers: These are the passive devices
placed at an appropriate location within a machine or in
between the machine to sense the torque at that location.

Hydraulic and Pneumatic Systems
A continuously variable transmission is possible Most of
this lecture will be about hydrostatic systems (in common
language it is also called simply hydraulics)

Power train
• Mechanical Mechanical power transmission:
1.Gears
2.Belt drive
3.Friction drive
4.Rigid couplings
5.Clutches
Prime mover
AC Motor
DC Motor
Diesel Engine
Otto Engine
Power
transmission
system
Machine
(linear or
rotational
motion)
Mi, ωi M0, ω0
F0, v0

Structure of a hydrostatic drive
Aggregate
Control
elements
Actuator
Valves, determining the
path, pressure, flow rate
of the working fluid
Elements doing work
• Linear
• Rotational
• Swinging
Pump, motor
Fluid reservoir
Pressure relief valve
Filter
Piping

A typical hydraulic system

1 – pump
2 – oil tank
3 – flow control valve
4 – pressure relief valve
5 – hydraulic cylinder
6 – directional control valve
7 – throttle valve

Good lubrication characteristics
 Viscosity should not depend strongly on temperature and
pressure
 Good heat conductivity
 Low heat expansion coefficient
 Large elasticity modulus
Economic
 Low price
 Slow aging and thermal and chemical stability  long life
cycle

Structure of a hydrostatic drive
Aggregate
Control
elements
Actuator
Valves,
determining the
path, pressure,
flow rate of the
working fluid
Elements doing
work
• Linear
• Rotational
• Swinging
Pump, motor
Fluid reservoir
Pressure relief valve
Filter Piping

Hydraulic fluids
They have the following primary tasks:
 Power transmission (pressure and motion transmission).
 Signal transmission for control.
Secondary tasks:
 Lubrication of rotating and translating components to avoid
friction and wear.
 Heat transport, away from the location of heat generation,
usually into the reservoir.
 Transport of particles to the filter.
 Protection of surfaces from chemical attack, especially
corrosion.

Good lubrication characteristics
 Viscosity should not depend strongly on temperature and
pressure
 Good heat conductivity
 Low heat expansion coefficient
 Large elasticity modulus
Economic
 Low price
 Slow aging and thermal and chemical stability  long life
cycle

Temperature measurements
1. Liquid-in-glass thermometers
2. Biomaterial thermometers
3. Electrical thermometers
4. IR-thermometer
5. Pyrometers

Functionning method
Method is based on the expansion of a liquid with
temperature. The liquid in the bulb is forced up the capillary
stem.
Thermal expansion:
)1(0 TVV 

Structure

Bimaterial thermometres
Method based on different thermal expansions of different
metals.
– Other metal expands more than other: twisting
– Inaccurary ± 1 ° C
– Industry, sauna thermometers

Electrical thermometres
Resistive thermometres
Resistivity is temperature dependent
Materials: Platinum, nickel
)1()( 0 TRTR 

Cavity effect
• Emissivity of the cavity increases and approaches unity
• According to Stefan-Boltzmann’s law, the ideal emitter’s
photon flux from area a is
• In practice:
4
0 Ta
0 r

Detectors
hole in a valence band serves as a current carrier
Reduction of resistance
Photon’s energy= hE 
Thermal detectors
1.Response to heat resulting from absorption of the sensing
surface.
2.The radiation to opposite direction (from cold detector to
measured object) must be taken into account.

Pyrometres
Two-color pyrometer
.Since emissivities are not usually known, the measurement
with disappearing filament pyrometer becomes impractical.
In two-color pyrometers, radiation is detected at two separate
wavelengths, for which the emissivity is approximately equal
The corresponding optical transmission coefficients are γx and
γy .

Pyrometers
Displayed temperature
1
5
5
ln
11



















yx
xy
xy
c CT




Measurement
Stefan-Boltzmann’s law with manipulation:
Magnitude of thermal radiation flux, sensor surface’s
temperature and emissivity must be known before
calculation.
Other variables can be considered as constants in calibration
4
4
s
c
A
TT




Thermistor
A thermistor is a type of resistor with resistance varying
according to its temperature. The resistance is measured by
passing a small, measured direct current through it and
measuring the voltage drop produced.
There are basically two broad types
1. NTC-Negative Temperature Coefficient: used mostly in
temperature sensing
2.PTC-Positive Temperature Coefficient: used mostly in
electric current control.

Types
 A NTC thermistor is one in which the zero-power resistance
decreases with an increase in temperature
 A PTC thermistor is one in which the zero-power resistance
increases with an increase in temperature

Assuming, as a first-order approximation, that the relationship
between resistance and temperature is linear, then:
ΔR = kΔT
where
ΔR = change in resistance
ΔT = change in temperature
k = first-order temperature coefficient of resistance
For PTC k is positive while negative for NTC

Advantages and Disadvantages
 Thermistors, since they can be very small, are used inside
many other devices as temperature sensing and correction
devices.
 Thermistors typically work over a relatively small temperature
range, compared to other temperature sensors, and can be very
accurate and precise within that range

 PTC thermistors can be used as current-limiting devices for
circuit protection, as replacements for fuses. Current
through the device causes a small amount of resistive
heating. This creates a self-reinforcing effect that drives the
resistance upwards.
 PTC thermistors can be used as heating elements in small
temperature-controlled ovens. As the temperature rises,
resistance increases, decreasing the current and the heating,
resulting in a steady state.
 NTC thermistors are regularly used in automotive
applications.
 Thermistors are also commonly used in modern digital
thermostats and to monitor the temperature of battery packs
while charging.
Applications

Characteristics of vibration signal
Amplitude
Frequency
Phase
Orbit
VIBRATION

Types of vibration pick up
Proximity probe
Velocity pick up
Accelerometer

Proximity probe
Shaft vibration measurement
Key phaser marker
Shaft centre line position
Best suited for 1 to 500 hz

Velocity pick up
For bearing and structural vibration
Best suited for 10 to 1000 hz
Accelerometer
For high frequency range
Best suited for 1000 hz onwards

(A) displacement
Microns, peak to peak
Microns, 0 to peak
Microns, rms
(B) velocity
Mm/sec, 0 to peak
Mm/sec, rms

(C)ACCELERATION
M/SEC2, PEAK
M/SEC2, RMS
G, PEAK
G, RMS

Average
RMS 0 - Peak
Peak - Peak
RMS = 0.707 x (0-Peak)
Average = 0.637 x (0-Peak)
Peak to Peak = 2 x (0-Peak)

Reasons of vibration
Shaft bow
Oil / steam whirl
Deviated operating parameters
Defective bearing / assembly of bearing
Vibration transmission from other source
Gear inaccuracies
Casing distortion
Cavitations

Accelerometers
Accelerometers can be used to measure vehicle
acceleration. Accelerometers can be used to measure
vibration on cars, machines, buildings, process control
systems and safety installations. They can also be used to
measure seismic activity, inclination, machine vibration,
dynamic distance and speed with or without the influence of
gravity. Applications for accelerometers that measure
gravity, wherein an accelerometer is specifically configured
for use in gravimetry, are called gravimeters

Capacitive MEMS accelerometer
 High precision dual axis accelerometer with signal conditioned
voltage outputs, all on a single monolithic IC.
 Sensitivity from 20 to 1000 mV/g.
 High accuracy.
 High temperature stability .
 Low power (less than 700 uA typical) .
 5 mm x 5 mm x 2 mm LCC package .
 Low cost ($5 ~ $14/pc. in Yr. 2004)

Accelerometer

Accelerometer
Piezoresistive MEMS accelerometer
 Operating Principle: a proof mass attached to a silicon
housing through a short flexural element. The implantation
of a piezoresistive material on the upper surface of the
flexural element. The strain experienced by a piezoresistive
material causes a position change of its internal atoms,
resulting in the change of its electrical resistance.
 low-noise property at high frequencies.

vibrometer
A vibrometer is generally a two beam laser interferometer that
measures the frequency (or phase) difference between an
internal reference beam and a test beam. The most common
type of laser in an LDV is the helium–neon laser, although
laser diodes, fiber lasers, and Nd:YAG lasers are also us.

The test beam is directed to the target, and scattered light from
the target is collected and interfered with the reference beam
on a photo detector, typically a photodiode. Most commercial
vibrometers work in a heterodyne regime by adding a known
frequency shift (typically 30–40 MHz) to one of the beams.
This frequency shift is usually generated by a Bragg cell, or
acousto-optic modulator.

• Single-point vibrometers – This is the most common type of
LDV.It can measure one directional out of plane movement.
• Scanning vibrometers – A scanning LDV adds a set of X-Y
scanning mirrors, allowing the single laser beam to be moved
across the surface of interest.
• 3-D vibrometers – A standard LDV measures the velocity of
the target along the direction of the laser beam.
• Rotational vibrometers – A rotational LDV is used to measure
rotational or angular velocity.

Unit-3
Metrology and Inspection

Measurement and inspection
1. Metrology
2. Inspection Principles
3. Conventional Measuring Instruments and Gages
4. Measurement of Surfaces
5. Advanced Measurement and Inspection Techniques

Measurement
 Procedure in which an unknown quantity is compared to
a known standard, using an accepted and consistent
system of units.
 The measurement may involve a simple linear rule to
scale the length of a part.
 Or it may require a sophisticated measurement of force
versus deflection during a tension test.
 Measurement provides a numerical value of the quantity
of interest, within certain limits of accuracy and
precision.

Inspection
Procedure in which a part or product feature, such as a
dimension, is examined to determine whether or not it
conforms to design specification.
Many inspections rely on measurement techniques, while
others use gagging methods
 Gaging determines simply whether the part characteristic
meets or does not meet the design specification.
 Gaging is usually faster than measuring, but not much
information is provided about feature of interest .

Metrology
Defined as the science of measurement Concerned with seven
fundamental quantities (standard units shown in parentheses):
 Length (meter)
 Mass (kilogram)
 Time (second)
 Electric current (ampere)
 Temperature (degree Kelvin)
 Light intensity (candela)
 Matter (mole)

Metrology
From these basic quantities, most other physical quantities are
derived, such as:
 Area
 Volume
 Velocity and acceleration
 Force
 Electric voltage
 Heat energy

Manufacturing Metrology
In manufacturing metrology, we are usually concerned with
measuring a length quantity of a part or product.
 Length and width
 Depth
 Diameter
 Straightness, flatness, and roundness, etc.
 Surface roughness

Types of Inspection
Inspection involves the use of measurement and gaging
techniques to determine whether a product, its components,
subassemblies, or materials conform to design specifications.
Inspections divide into two types:
1. Inspection by variables - product or part dimensions of
interest are measured by the appropriate measuring
instruments.
2. Inspection by attributes – product or part dimensions are
gaged to determine whether or not they are within
tolerance limits.

Manual Inspection
 Inspection procedures are often performed manually .
 The work is boring and monotonous, yet the need for precision
and accuracy is high .
 Hours may be required to measure the important dimensions
of only one part .
 Because of the time and cost of manual inspection, statistical
sampling procedures are often used to reduce the need to
inspect every part.

Measuring Instruments and Gages
Conventional measuring instruments and gages include:
 Precision gage blocks
 Measuring instruments for linear dimensions
 Comparative instruments
 Fixed gages
 Angular measurements

Linear / Angular measuring instrument
1.Linear or (length) measuring instrument:
2.Angular or (angle) measuring instrument:
Measuring instrument can be divided based on their metrological
properties, such as
 range of measurement scale graduation value
 scale spacing
 sensitivity,
 and reading accuracy.

Depending on the accuracy
1. Most accurate group includes light interference instruments.
2. Second group includes: optimeters, dial comparators.
3. Third group includes: dial indicator, vernier calipers.

Range of measurement
It indicated the size values between which measurements can be
made on the given instrument.
Example: micrometers are available for the following ranges. (0
to 25, 25 to 50, 50 to 75, 75 to 100, 100 to 125, 125 to 150)mm
Scale division value
It is the measured value corresponding to one division of the
instrument scale.
Example: the scale division value of a micrometer is 0.01mm.
.

Sensitivity
 It is also called “ amplification factor” or “gearing ratio”
 It is the ratio of scale spacing to the scale division value.
 Example: on a dial indicator the scale spacing is 1.5 mm and
the scale division value is 0.01 mm then the sensitivity is
150mm.

Types of length standards
The distance may be expressed as the distance between two
lines or the distance between two faces.
The instruments used for the direct measurement if the linear
dimensions fall into two categories:
1. Line standards.
2. End Standards.

Line Standards / End standards
In the Line Standards:
The measurement is made between two parallel lines engraved
across the standard.
In the End Standard:
The measurement is made between two flat parallel faces.

Steel Rule
Type: This is a low-resolution line-measuring instrument
Operating principle: comparing an unknown length to a
previously calibrated one.

Steel Rule
Type: This is a low-resolution line-measuring instrument
Operating principle: comparing an unknown length to a
previously calibrated one
Construction: It consists of a strip of hardened steel having
line graduations etched or engraved at intervals of fraction of
standard unit of length. These graduations may not be uniform
all throughout its length. This allows for multiple use for
particular range as per accuracy required.

Basic desirable qualities:
(1) Clearly engraved lines.
(2) Minimum thickness.
(3) Good quality spring steel.
(4)Graduations on both sides.
(5) Low coefficient of thermal expansion.

Calipers
 Calipers are used to pick off diameters or distance from a work
piece.
 This setting is then measured with a scale, vernier caliper, or
micrometer.
 They are known as “ transfer measuring instruments”.

Limit, fits &tolerance
Limits: These Are two extreme permissible sizes of dimension
between which actual size of dimension iscontained.The greater Of
these two is called high limit and the smaller low limit.
Fits: this is relation between two mating parts interference which is
present when they are assembled to gether.
Tolerance: A tolerance is an acceptable amount of dimensional
variation that will still allow an object to function correctly.

Terminology
Nominal size: It is the size of a part specified in the drawing.
Basic size: It is the size of a part to which all limits of variation
are determined.
Actual size: It is the actual measured dimension of a part.
Nominal and basic size are often the same.

Limit of sizes
 There are two extreme possible sizes of a component.
 The largest permissible size for a component is called upper
limit and smallest size is called lower limit.

Positional tolerances
Two types of positional tolerances are used:
1. Unilateral tolerances
2. Bilateral tolerances
When tolerance is on one side of basic size, it is called
unilateral and if it is both in plus and minus then it is known
as bilateral tolerance.

Fits
The degree of tightness or looseness between two mating
parts is called a fit.

Types of fits
Clearance fit: There is a clearance or looseness in this type of fits.
These fits maybe slide fit, easy sliding fit, running fit etc
Interference fit: There is an interference or tightness in these type
of fits. E.g. shrink fit, heavy drive fit etc.
Transition fit: In this type of fit, the limits for the mating parts are
so selected that either a clearance or interference may occur
depending upon the actual size of the mating parts.

Circles are divided into 360 equal parts, each being a degree.
Each of these degrees can be evenly divided into 60 equal parts.
These parts are called minutes.
These minutes can be evenly divided into 60 equal parts. These
parts are called seconds.

Linear measurement
linear measurement includes the measurement of lengths,
diameters, heights and thickness. The basic principle of
linear measurement (mechanical type) is that of comparison
with standard dimensions on suitably engraved instrument or
device. Linear measuring instruments are categorized
depending upon their accuracy.
Some liner measuring devices:
1) Steel rules
2) Calliper
3) divider

Angular mesurements tools
• Most common tools:-
 i)Simple Protractor
 ii)Multi-Use Gauge
 iii)Combination Set
 iv)Universal bevel protractor

• used accuracy of angle must be checkeUsed when accuracy of
angle must be checked to less than 5 minutes Consists of steel
bar with two cylinders of equal diameter fastened near ends
Centers of cylinders exactly 90º to edge Distance between
centers usually 5 or 10 inches and 100 or 200 millimeters.
Centers of cylinders exactly 90º to edge.

Comparators
Comparators are the instruments calibrated by means of end
standards to measure unknown dimensions. The purpose of a
comparator is to detect and display the small differences
between the unknown linear dimensions and the length of the
standard. The difference in lengths is detected as a
displacement of a sensing probe. The important and essential
function of the instruments is to magnify or amplify the small
input displacement so that it is displayed on an analogy scale.
Comparators are classified on the basis of type of the
amplification method used. Accordingly comparators are of
following types or hybrid thereof.

(a)Mechanical comparators: Conventional mechanical methods
to obtain magnification are not suitable in construction of
mechanical comparators as it causes backlash and friction. Also
they require a large input force. Let us understand the
mechanical comparators by studying a reed comparator which is
strictly a mechanical comparator.
(b)Optical Comparators. Optical comparators are based on the
principle of projection of image. A simple optical comparator
for measurement of linear dimension . The arrangement consists
of mechanical system which causes a plane reflector to tilt
about an axis so that the image of an index is projected on scale
on the inner surface of a ground glass screen. The actual
difference x between the two dimensions is amplified by a lever
to give an angular displacement of a pivoted mirror.

c)Pneumatic comparators: Pneumatic comparators are the widely
used precision instruments which use the principle of
obstructed nozzle.
(d)Electrical comparators: Electrical comparators are used as a
means of detecting and amplifying small movements of a work
contacting elements. It may use any of the following
transducers for magnification. They are
(a)strain gauges,
(b)variable inductance transducers, and
(c)variable capacitance transducers.

The transducer converts the displacement into a corresponding
change in current and a meter recorder connected in the circuit
to indicate the electrical change calibrated to show in terms of
displacement. Generally, an amplifier is used to provide the
requisite sensitivity and to match the characteristics of
different parts of the circuit. There are different types of
electrical comparators

Johansson Mikrokator
A Johansson Mikrokator (also called Abramson's movement) is
a mechanical comparator used to obtain mechanical
magnification of the difference in length as compared to a
standard. It works on the principle of a button spinning on a
loop of string. A twisted thin metal strip holds a pointer, which
shows the reading on a suitable scale. Since there is no friction
involved in the transfer of movement from the strip to the
pointer.

A metallic strip is twisted and fixed between two ends as
shown. Any longitudinal movement (in either direction) will
cause the central portion of the strip to rotate. One end of the
strip is fixed to an adjustable cantilever and the other end is
fixed to the spring elbow. The spring elbow, in turn, is
connected to a plunger, which moves upwards or downwards.
The spring elbow, which consists of flexible strips and a stiff
diagonal acts as a bell crank lever and causes the twisted strip
to change length whenever there is a movement in the plunger.
This change in length will result in a proportional amount of
twist of the metallic strip. The magnification can be varied by
changing the length of the spring elbow.

The instrument is initially calibrated to the standard, and the
zero is set to this value. Then, the test specimen are placed on
the measuring table and are slid below the plunger of the
instrument. Any difference in the measured dimension of the
specimen will result in either the lowering or rising of the
plunger. The lowering or rising of plunger will make the bell
crank lever to move in forward or backward direction, and in
turn, will twist or untwist the metallic strip. The centre line of
strip is perforated in order to prevent excessive stress.

Classification of Limit Gauges
 Production gauges are of various types, but there is a little
doubt that the majority are in the form of limit gauges.
 These are designed to cover a very wide range of work.
 The general form of limit gauges is of the fixed type. That is to
say, gauging contact elements remain fixed during the gauging
process.
 Gauging elements, however, may be provided with means for
size adjustment

Following gauges are the most commonly used in production
work. The classification is principally according to the shape
or purpose for which each is used.
1. Snap gauges 5. Form Comparison Gauge
2. Plug gauges 6. Thickness Gauges
3. Ring gauges 7. Indicating Gauges
4. Length gauge 8. Pneumatic Gauges

9. Electric Gauges
10. Electronic Gauges
11. Projecting Gauges
12. Multiple Dimension Gauges

Description of some commonly used
gauges
1. Snap Gauges:
a. A Snap gauge is used in the measurement of external
dimensions,
b. It consist of a U-shaped frame having jaws equipped with
suitable gauging surfaces.
c. A plan gauge has two parallel jaws or anvils which are
made to some standard size & cannot be adjusted
d. They may be either single-or double -ended

2. Snap Gauges:
e. Special forgings & stampings are available
commercially for their manufacture, or they may be
constructed from gauge plate
f. Special snap or gap gauges may have to be used for
checking the recessed diameters & other features

Description of some commonly
used
1.Plug Gauges:
 A plain plug gauge is an accurate cylinder used as an
internal gauge for size control of holes.
 It is provided with a suitable handle for holding & is
made in a variety of styles.
 These gauges may be either single or double ended.
 Double ended plain gauges have “GO” and “NOT GO”
members assembled on opposite ends, where as
Progressive gauges have both gauging sections combined
on one side

2.Plug Gauges:
a. Solid Type (Double ended)
b. Solid Type (Single ended)
c. Renewable-end type (Double ended)
d. Progressive Type
e. Shell form type (Double ended)
f. Shell form type (Single ended)
g. Bar end Type
h. Special Types

3. Ring Gauges:
Used to gauge outside diameters.
 Used in Pairs as “Go” & “Not Go”
4. Taper Gauges:
Taper gauges are not dimensional gauges but rather a
means of checking in terms of degrees.
Their use is a matter more of fitting rather than measuring

5. Thickness or Feeder Gauge:
It consist of a number of thin blades & is used in checking
clearances & for gauging in narrow places.
6. Dial Gauge:
Dial gauges or Dial Test Indicators are used for checking
flatness of surfaces & parallelism of bars & rods.
They are also used for testing the m/c tools.
They can also be used for measurement of linear
dimensions of jobs which require easy readability &
moderate precision

Gauges
 Gauges are used for dimensional control of the component
parts , their function being to establish whether or not surface
levels lie within the zone specified by the designer.
 Gauges must be manufactured & checked with reference to
standard of length, which in turn is related to a fundamental
length standard. The standard of length is then transferred
through the gauge to the component

Gauges
 The true value of a gauge is measured by its accuracy &
service life which, in turn, depends on the workmanship &
materials used in its manufacture. Since all gauges are
continually subject to abrasive wear while in use, the
selection of the proper material is of great importance.
 High carbon steel & alloy tool steels have been the principal
materials for manufacture of such gauges

The Taylor principle
Taylor’s Principle lays it down:
1. A GO Gauge will check all the dimensions of the work piece
in what is called the maximum metal condition (indicating
the presence of the greatest amount of material permitted at a
prescribed surface).
2. That NOT GO Gauges shall check only one dimension of the
work piece at a time, for the minimum metal conditions
(indicating the presence of the least amount of material
permitted at a prescribed surface) size.

The Taylor principle
 In case of hole, the maximum metal condition obtains when
the hole is machined to the low limit of size, & minimum
metal condition results when the hole is made to the high limit
of size.
 in case of shaft the limits taken would be inverse of hole.

Unit- 4
Measurement and geometric form

Straightness
A line is said to be straight over a given length, if the variation
of the distance of its points from two planes perpendicular to
each other and parallel to the general direction of the line
remains within the specified.
The tolerance on the straightness of a line is defined as the
maximum deviation in.

Measurement of straightness
The straightness can be measured by fallowing method :
1.Straighy edge method
2.The wedge method
3.The level method
4. The autocollimator method

Flatness
The flatness may be defined as the minimum distance between
two planes which coverall the irregularities of the surface
under examination.
The following method may be used for flatness measurement:
1.Direct composition
2.Dial gauge
3.Level or autocollimator method
4.Flate comparators
5.Interference method

Circularity and roundness
Roundness is a condition of a surface of revolution (like
cylinder, sphere) where all point of the surface intersected by
any plane perpendicular to a common axis in case of cylinder
and cone are equidistant from the axis and the circular contour
is the characteristics form of the entire periphery of a plane .
The errors of circularity at a cross-section can be of the
fallowing nature:
1.Ovality
2.Lobbing
3.Irregularities of no specific form

Toolmakers microscope
A toolmakers microscope is a measuring device that can be used
to measure up to 1/100th of an mm. It works on the principle of a
screw gauge, but a few changes were added to it to make its
operation more easier.
It needs application of optics too. A light focuses on the object
and through lens we can see the shadow of the object, which
resembles the object. More clear shadow would be enhance the
accuracy of measurement.

TMM (toolmakers microscope) has got a robust and strong base
such that it can bear and withstand sudden loads. A column with a
track is present to carry lens, along with illuminating source in
certain TMM’s. Lens has two perpendicular straight lines marked
that act as reference lines. Object to be measured is placed on
glass table. Glass table is provided with 3 scales on it .
Two scales are meant for measuring in X and Y directions and
the movement of table the respective direction.

An autocollimator is an optical instrument that is used to
measure small angles with very high sensitivity. As such, the
autocollimator has a wide variety of applications including
precision alignment, detection of angular movement,
verification of angle standards, and angular monitoring over
long periods.

Type of collimator
 Digital Autocollimator
 Visual Autocollimators

Principles of Operation
The autocollimator projects a beam of collimated light.
An external reflector reflects all or part of the beam back
into the instrument where the beam is focused and
detected by a photo detector. The autocollimator measures
the deviation between the emitted beam and the reflected
beam. Because the autocollimator uses light to measure
angles, it never comes into contact with the test surface.

Interferometer
Most interferometers use light or some other form of
electromagnetic wave. Typically ( The well-known Michelson
configuration) a single incoming beam of coherent light will
be split into two identical beams by a beam splitter (a partially
reflecting mirror).

mirror
Coherent light
source
detector
mirror
halfmirror

The light path through a Michelson interferometer. The two
light rays with a common source combine at the half-silvered
mirror to reach the detector. They may either interfere
constructively (strengthening in intensity) if their light waves
arrive in phase, or interfere destructively (weakening in
intensity) if they arrive out of phase, depending on the exact
distances between the three mirrors.

Application of iterferometry
There are following application of interferometry:
1.Physics and astronomy
2. Engineering and applied science
3. Biology and medicine

Optical flat
An optical flat is an optical-grade piece of glass lapped and
polished to be extremely flat on one or both sides, usually
within a few millionths of an inch (about 25 nanometres).
They are used with a monochromatic light to determine the
flatness of other optical surfaces by interference.
Optical flats are sometimes given an optical coating and used
as precision mirrors for special purposes.

wedgeair
flatoptical
lighticmonocromat

Screw thread measurements
A screw thread is helical ridge formed on uniform section
round the curved surface. the shape of the normal section of
the thread depends upon the shape of he tool which produces
its groove .
The screw thread applied to many devices for various purpose
as fallows:
1.To hold parts together as in the case of fastening.
2.To transmit power
3.To control movement as in micrometer

Classification of threads
The may be classified as fallows:
1.According to the surface o which the treads are cut:
i) External treads . Cuts into the surface of a cylindrical bar.
ii) Internal treads. Cuts in to hole of the cylindrical bar.
2. According to the direction of rotation of the threaded cylinder:
i) Right handed thread
ii) Left handed thread

Types of gear
The different type of gear used are:
1. Spur gear
2. Helical gear
3. Bevel gear
4. Worm gear
5. Rack and pinion

Gear measurement
A gear is a wheel provided with teeth which mesh with the
teeth on another wheel , or on to a rack, so as to give a positive
transmission of motion from one component to other.
Most commonly used for power transmission or for changing
power speed ratio in a power system.
In the gear measurement is necessary to differentiate between
the measurement of the individual parameters of a gear , i.e..
Their individual errors and the measurement of accumulative
errors.

Spur gear fig . 1 bevel gear fig.2

Surface texture
Surface finish, also known as surface texture or surface
topography, is the nature of a surface as defined by the three
characteristics of lay, surface roughness, and waviness. It
comprises the small local deviations of a surface from the
perfectly flat ideal (a true plane).
“the characteristic quality of an actual surface due to small
departure from its general geometry form which , occurring at
regular or irregular intervals, tend to form a pattern or texture
on the surface”

Primary and secondary texture
Primary texture :
Included irregularities of small wavelength of a cause by
direct action of the cutting element on the material or by some
other disturbance such as friction ,wear or corrosion.
Secondary texture:
Irregularities of considerable wavelength of a periodic
character resulting from mechanical disturbance in the
generating set up.

Method of measuring surface
finish
The surface finish of machined part can measured by fallowing
two methods:
1.Surface inspection by comparison method:
i) Touch inspection
ii) visual inspection
iii) scratch inspection
iv) microscopic inspection
v)surface photograph
vi) micro-interferometer

2.Direct instrument measurements:
i)Intersection method
ii)Interface method
iii)Stylus method
iv) Pneumatics measuring method
iv) Perthen condenser method

Limit gauging
Gauging is the method by which it is determined quickly
whether or not the dimensions of the checking parts, in the
production, are within their specified limits. The tools which
are used for the same are called gauges
 These are also called „go‟ and „no go‟ gauges. These are made to
the limit sizes of the work to be measured.
 One of the sides or ends of the gauge is made to correspond to
maximum and the other end to the minimum permissible size.
 The function of limit gauges is to determine whether the actual
dimensions of the work are within or outside the specified limits

comparator
A comparator works on relative measurements, i.e. to say, it
gives only dimensional differences in relation to a basic
dimension. So a comparator compares the unknown dimen-
sions of a part with some standard or master setting which
represents the basic size and dimensional variations from the
master setting are amplified and measured.

The various comparators may be classified as follow:
(1) Mechanical comparators
(2) Mechanical-optical comparators
(3) Electrical and Electronic comparators
(4) Pneumatic comparators
(5) Fluid displacement comparators
(6) Projection comparators
(7) Multi-check comparators
(8) Automatic gauging machines.

Feature inspection
 In order to determine the fitness of anything made, man has
always used inspection. But industrial inspection is of recent
origin and has scientific approach behind it. It came into being
because of mass production which involved interchangeability
of parts.
 The inspection process can be made by traditional methods. If
the dimensions are not within the given tolerance zone, a
correction can be made to the next parts.

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