UNIT-I PPT EMM.ppt

Basics of metrology
 Metro-Measurement, Logy-Science.
 Important parameter is length.
 Metrology of length and metrology of time.
 IMPORTANCE
 Errors of measurement and developing new methods.
 Researching the causes of measuring error.
 Industrial inspection in various techniques.
 Design and manufacturing and testing in various
guages.

Need and importance of
metrology
 Metrology is solving for all technical
problems of engineering field.
 The design engineer not only checked
from design and production point of view
dimensions also measured.
 To achieve quality of production.
 To reduce rejection rate in quality unit.
 To develop inspection procedure and cost,
and instrument measuring time.

TYPES OF METROLOGY
 Scientific metrology - Development of measurement standards.
 Industrial metrology- proper measuring instrument are used.
 Legal metrology - NSLM ( National service of legal measurement).
 A) industrial measurement b) Commercial transaction c) Public
health and human safety.
 Fundamental metrology - scientific measurement.
 Dynamic metrology - measurement of small variation electronic
equipment ( CADD OPTIC FIBER LASER INSTRUMENT).
 Deterministic metrology - Replace measurement of CNC control
system.

MEASUREMENT
 Measurement is comparison of a given unknown
quantity with one of its predetermined standard
values adopted as a unit.
 The standard are used and accurate of
accepted internationally.
 The apparatus and process used for comparison
is proved.

Metrology:
Metrology is defined as the science of measurement.
Metrology divided into two types:
1.Industrial Metrology
2.Medical Metrology
Metrology Mainly Concerned with:
Unit of Measurement and their standards
Errors of measurement
Ensuring the uniformity of measurements
Developing new methods of measurements
Analyzing this new methods and their accuracy
Gauges design and manufacturing
Researching the causes of measuring errors.
Industrial Inspection

Legal Metrology:
Is the part of Metrology and it is directed by National organization
which is called" National service of legal metrology”
Main objective of Legal Metrology:
To maintain uniformity of measurement in a particular country.
Functions of NSLM:
To ensure conversation of industrial standards
Guarantee their accuracy by comparison with
International standards
To organize training in this field
Regulate, Supervise and control the manufacturer
Giving advice to repair of measuring instruments
To inspect and detect guilty of measurement.

Applications of Legal Metrology:
Industrial Measurement
Commercial Transactions
Public health and human safety ensuring
Dimensional Measurements:
Very common measurement is that of a dimension,i.e length,
Width or height of an object.
Depending on the quality of requirement the instruments
are classified into the following type.
oLow Resolution
oMedium Resolution
oHigh Resolution

Low Resolution Devices(upto 0.25mm):
Steel rule
Steel rule with the assistance of calipers, dividers
and surface gauges
Thickness gauges
Medium Resolution Devices(upto 0.0025mm):
Micrometers
Vernier
Dial indicators
Measuring Microscope

High Resolution Devices(Less than microns):
Gauge Blocks
Gauge blocks with
Mechanical Comparators
Electrical Comparators
Pneumatic Comparators
Optical Flats

Linear Measuring Instruments:
It Includes the Measurement of
Length
Diameter
Heights
Thickness
Basic Principal of Linear Measuring Instruments:
Comparison with standards Dimensions on a suitably
engraved instrument or device.

Various Devices Used for Measuring the
Linear Measuring Instruments:
1. Vernier Caliper
2. Micrometers
3. Slip gauge or gauge blocks
4. Comparators
Vernier Caliper:
The Vernier Caliper is a precision instrument that can be
used to measure internal and external distances extremely
accurately.

Least count (L.C):
The least count of the vernier can be measured by
using the formula stated below.
Least count (L.C) = 1 M.S.D - 1 V.S.D
Example;
vernier scale is constructed by taking 49 main scale
divisions
dividing them into 50 divisions
i.e.. 49mm divided into 50 parts
therefore
1 Vsd=49/50 mm=0.98mm
1 MSD=1mm
substituting in formula
L.C = 1 M.S.D - 1 V.S.D
L.C=1-0.98=0.02mm

MATHEMATICAL METHOD
A. The main metric scale is read first and this shows that there
are 13 whole divisions before the 0 on the hundredths scale.
Therefore, the first number is 13.
B. The’ hundredths of mm’ scale is then read. The best way to do this
is to count the number of divisions until you get to the division that
lines up with the main metric scale. This is 21 divisions on the
hundredths scale.
C. This 21 is multiplied by 0.02 giving 0.42 as the answer
(each division on the hundredths scale is equivalent to 0.02mm).
D. The 13 and the 0.42 are added together to give the final
measurement of 13.42mm (the diameter of the piece of round section steel)

Types of Vernier Calipers: TYPE A
Accuracy – 0.02mm
Jaws are provided on both sides for internal and External measurements
One blade is fitted to measure the depth of the part

TYPE B
Accuracy - 0.05mm
Jaws are provided on only one side for internal and External measurements

TYPE C
Accuracy - 0.1mm
Jaws are provided on both sides for internal and External measurements

Errors in measurements with vernier calipers:
Errors may arise in manipulation of vernier caliper.
Jaw movement should be perpendicular to the scale readings.
Contact portions of measuring jaws should be good conditions
During internal measurements, the jaws may be bowlegged

Care and Precautions:
Jaws should not be used as wrench or hammer Because vernier is not
a rugged instrument
Instrument should be kept in box and not suddenly dropped and turned up
and down
Vernier caliper should not be used in oil, grit and chip area
One hand should be used for stationary jaw and the other hand for
Supporting Movable jaw
Operator should wear eye glass and magnifying glass during measurements

Micrometer:
is a device incorporating a calibrated screw used widely for precise
measurement of small distances in mechanical engineering.

Parts:
1.Frame:
The C-shaped body that holds the anvil and barrel in constant relation to each other.
It is thick because it needs to minimize flexion, expansion, and contraction,
which would distort the measurement.
The frame is heavy and consequently has a high thermal mass, to prevent substantial
heating up by the holding hand/fingers.
It is often covered by insulating plastic plates which further reduce heat transference.
2.Anvil:
 The fixed anvil of the micrometer protrudes for 3mm form frame to support the part
at the end
 The measuring face of the anvil should be strong enough to reduce wear and tear
 The face of the anvil is tipped with tungsten carbide.

3.Spindle:
The spindle is placed inside the barrel to slide freely
Bush is placed in the space between barrel and spindle to ensure free running of spindle
Light non corrosive oil is used to lubricate the spindle and screw.
4.Ratchet driver:
Wear resistant material is used to make ratchet
5.Thimble and barrel:
 Graduations are made on both barrel and thimble
 Parts are made by using high wear resistant material
6.Adjusting nut:
 Adjusting nuts are used to get zero reading
 Accuracy of the measurement is depends on original accuracy and function of
lock nut

Types of Micrometer:
1.Outside Micrometer:
It consists of two scales, Main scale and thimble scale
While the pitch of barrel screw is 0.5mm,the thimble has graduation of 0.01mm
The least count of this micrometer is 0.01mm

2.Inside Micrometer:
Used for measuring internal dimensions.
It consists of mainly four parts such as measuring head, extension rods,
spacing collars and handle.
The range of measurement can be varied by using different lengths of extension
rods and spacing collars

3.Stick Micrometer:
Inside micro meters can be used to measure only smaller lengths
A Micrometer to measure longer lengths is known as stick micrometer
These Micrometers are formed by connecting 150mm or 300mm micrometer unit

4.Micrometer depth gauge:
Mainly used to measure depth of holes, slots and recesses
Shoulder act as a reference surface
While measuring reference surface slides up and down
It is held tightly perpendicular to the axis of the hole

5.Thread Micrometer:
Thread micrometer is used to measure threads within certain range of thread pitches
The end of the spindle is pointed to the ‘V’ thread form with a corresponding Vee - reces
in the fixed anvil.

Advantages:
The only method is to show the variation in drunken thread
Limitations:
It must be set to a standard thread plug
When setting standard plug gauge the reading is not exactly zero

6. V-anvil micrometer caliper:
The running error can be checked quickly by V-anvil micrometer caliper in grinding
and other special machines.
The accuracy is high because all parts involved in this caliper are highly precision.
But error may become due to incorrect handling of micrometer caliper, inadequate
aligning wear and tear etc.

7. Blade type Micrometer:
This is best suitable for measuring circular formed tools, diameter of narrow grooves
Slots and key ways.
It has non-rotating spindle.
The rate of measurement is fast.

8. Micrometer for measuring thickness of cylindrical walls:
The anvil of thickness micrometer is in spherical form
The axis of spindle is perpendicular to the spherical surface

9.Dial Micrometer caliper:
oDial indicator is connected with the movable anvil.
oThe slight movement of this anvil is directly indicated on the dial of the dial indicator
oThis type of micrometer is very much useful for statistical quality work for different
size variation

10.Bench micrometer:
All parts of the micrometer are mounted on the bench.
Fixed anvil is fitted at the one end of the micrometer.
Movable anvil along with dial is fitted on the other end of the bench
Slight movement of the movable anvil will be indicated correspondingly
on the dial as deflection.

11.Taper screw operated internal micrometer:
Taper screw threads are formed at the end of the main spindle
The screw threads are just made to the feeler
For measurement the same procedure is followed as that of conventional type.
When he ratchet is revolved, the vibration will be adjusted itself in the bore.
Due to this the sense of feel is sensed by the operator quickly

12. Groove Micrometer:
Specially designed for grooves, recess and shoulders which are located centrally
These are stain chrome finished throughout to ensure high precision
Not only used to measure thickness and spacing but also to measure the distance
between Edge to land.

13.Digital Micrometer:
All the measurements will be indicated as numerical values
Interpolations can be avoided when the measurements is in between to divisions
Accuracy will be higher
Spindle can be locked at any desired position
Zero setting is done by pressing push button

14.Differential screw micrometer:
Micrometer is designed in such a way that to get differential movement
Spindle advancement is larger when compared to conventional micrometer.
Measurement obtained is very high accuracy
Theoretical value of accuracy is 0.002mm

Interval of measurement:
Slip Gauges:
Slip gauges are blocks of steel that have been hardened and stabilized
by heat treatment.
Surface of slip gauges are made to a high degree of accuracy
Distance between two opposite faces indicates the size of the gauge
The accuracy and finish is so high that two or more slip gauges may be
wrung together

Classification of slip gauges:
Based on their use classified into the following:
1. Grade 2
2. Grade1
3. Grade 0
4. Grade 00
5. Calibration Grade

Grade2:
It is a workshop grade
Used for setting tools
Cutters and
Checking dimensions roughly
Grade 1:
Used for precise work in tool rooms
Grade 0:
This is Inspection grade, Used in Inspection Department

Grade 00:
Used in high precision works in the form of error detection in instruments.
Calibration Grade:
Actual size of the slip gauge is calibrated on a chart supplied by the
manufacturers.

Checking of Slip gauges for Surface Quality:

Inferometers are used to check the surface quality of the slip gauges
Instruments consists essentially of a mercury - vapour lamp
Whose Radians are passed through a green filter
Thus removing all other colour, and leaving green mono-chromatic light
Wavelength is very closer to 0.5µm.
Light is focused into a pinhole
This gives intense point source of monochromatic light which is in the
focal plane Beam of the light.
The beam is directed onto the gauge to be tested via an optical flat so that
Interference are formed across the face of the gauge.
Fringes being viewed from directly above the face of the gauge
The glass plate semi reflector set at 45° to the optical axis.

Advantage:
We can test parallelism between two gauge surface
Two methods are used:
1.For gauges below 25mm in length
2.For gauges greater than 25mm in length
When shorter gauges are used ,interference fringes will be focused
Both on the gauge surface and the base plate.
As the gauge is wrung on the base plate, its underside is parallel with its base plate
It means the gauges are parallel.

If the gauge is more than 25mm in length the fringe pattern on the
base plate is difficult to observe but the base plate is rotary and its under side
is lapped Truly parallel with its working surface.
If it is non parallel, If the table is turned through 180°, the surface is now less paralle
With the optical plate, and a greater number of fringes are observed.

Application of Limit gauges:
Thread Gauges
Form Gauges
Screw pitch Gauges
Radius and fillet gauges
Feeler gauges
Plate gauge and wire gauges
Indicating gauges
Air gauges

Thread Gauge:
Threads are checked with the help of thread gauges
Internal Thread - Plug thread gauges are used
External Thread - Ring thread gauges are used

Form Gauge:
To be used to check the contour of a profile
of a work piece
Form gauges are nothing but template gauges
Made of steel sheet.

Screw pitch Gauge:
Used to Check the pitch of the thread immediately.
It is very much in every day tool used to pick out a
required screw

Radius and fillet gauges:
Radius of curvature can be measured by using
these gauges.
Radius may be either inner or outer
For inner radius end of the blade made in convex
For outer radius end of the blade made in concave

Feeler Gauge:
Used for checking the clearance between mating surfaces
Mainly used in adjusting the valve clearance in automobiles
They are made from 0.03mm to 1.0mm thick of 100mm long
The blades are pivoted in a holder

Plate Gauge and Wire gauge:
Thickness of sheet metal is checked by plate gauge
Diameter of wire is checked by wire gauge

Indicating Gauge:
Mainly designed for measuring errors in geometrical
Form and size, and for testing surfaces for their true
position with respect to one another.
Run out of toothed wheels,pullyes and various revolving
parts

Air Gauge:
Primarily used for determining the inside characteristics
of a hole by means of Compressed air.

Comparators:
Comparators is a precision instrument employed
to compare the dimension of a given Component
with a working standard (usually slip gauges).
Comparators will not show the actual dimension
This will shown only the deviation in size
Types of Comparators are:
Mechanical Comparators
Electrical Comparators
Optical Comparators
Pneumatic Comparators

Mechanical Comparators:
It Employs mechanical means for Magnifying small deviations
Method of magnifying small movement of the in all mechanical comparators
are effected by means of levers, gear trains or combinations of these elements.
Mainly used for inspection of small parts machined to close limits

Dial gauge is used as a mechanical Comparators
Essential parts are Small clock with a plunger projecting
at the bottom
Very Slight Upward movement on the plunger moves it upward
and the movement is indicated by the dial pointer.
The Dial is graduated into 100 divisions
A full revolution of the pointer about this scales corresponds
to 1mm travel of the plunger
Thus, a turn of a pointer by one scale division represents a plunge
travel of 0.01mm

The setup consists of work table, dial indicator and vertical post
Dial indicator is fitted to a vertical post by on adjusting screw
Vertical post is fitted on the work table
Surface of the work table is fine finished
Dial gauge can be adjusted vertically and locked in position
by a screw
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 plunger has rock teeth
Set of gears engage with the rocks
The pointer is connected to a small pinion
Small pinion is independently hinged
(i.e. It is not connected to the plunger)
Vertical movement of the plunger is
transmitted to the pointer through a
set of gears
Spring gives constant downward pressure
to the plunger

Electrical Comparators:
Construction Details:
1.Transducer
2.Display device or meter
3.Amplifier

Transducer:
An iron armature is provided in between two coils held by a leaf 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:
Is nothing but a device which amplifies the given input signal frequency into
magnified output.
Display device or meter:
The amplified signal is displayed on some terminal stage instruments.
Here the terminal instrument is meter.

Working principle:
Since the armature is centrally located between the coils, the inductance
of both the coils Will be equal but in opposite direction with the sign change.
Due to this, Wheatstone bridge is balanced
Therefore the meter will read zero value
But practically it is not possible
In real time, the armature may be lifted up or lowered down by the plunger
during measurement.
This would upset the balance of the Wheatstone circuit
Due to this change in current is introduced correspondingly
On that time the meter will indicate some value as displacement

Optical Comparator:
In Optical Comparators, a small plunger displacement is amplified by
both mechanical and Optical System.
The Amplification is first done by a pivoted lever and then by simple optical
system.

Construction Details:
It Consists of the following parts,
Pivoted Lever, Objective Lens,scale,Plunger,Table and Base, and Mirror
Pivoted lever:
The Pivoted lever amplifies the plunger movement mechanically
It is pivoted near the plunger
One end is fitted with the plunger and the other end is fitted with a mirror.
Objective Lens:
Main Function is to convert the incoming light rays from the source
into Parallel Beams.

Screen and scale:
This is a final display device from which the readings can be obtained.
This is nothing but a semi-transparent glass.
Plunger:
It is a reciprocating member.
During the measurement, the plunger actuates
Table:
The work is placed on the table to carry our task.

Base:
It is a rigid support over which the table is mounted
Mirror:
It reflect the incoming light rays
from the source which is hinged at the other
end of the lever.

Working Principle:
During the measurement, the vertical displacement of the plunger is magnified
by the ratio of the lever arm
The lever tilts the mirror about its hinge to again magnify.
The light rays from the lamp are condensed by a condensing lens.
Then the condensed light falls on the objective lens
Here the light rays are converted into parallel beams
Again the parallel beams of light ray fall on the mirror.
The mirror reflects the light rays on a screen.
AS the screen is a semi-transparent glass, the image of the work placed over
the screen.
Now the projected image is compared with the master drawing
This type is used for to inspect small thread gear teeth, cutting tools,needles,cam profile
etc.,

Pneumatic Comparators:
The pressurized air is used as the working medium in pneumatic comparator
Classified into two types:
1.Flow or Velocity type
2.Back pressure type

1.Flow or Velocity type:
Parts:
Compressor,Filter,Shut-off valve,Pressure
regulator,Glass Column,Float,Gauging Head.

Principle of working:
The readings are obtained by sensing and indicating the rate of
airflow through a tapered glass tube.

The glass tube is already calibrated to the required dimensions by
a suitable device called Slip Gauges
Then the Compressed air from the Compressor is passed through the filter and
Pressure regulator.
Then it is passed through a tapered glass tube from which the air is passed through
A plastic tube to the measuring head.
The measuring head has a orifices through which the air escapes to the atmosphere
The position of float depends on the gap between the internal dimensions and the
Gauging head.
If more displacement for the float requires with high amplification, the following
Modification has to implement.
The plastic tube is extended to supply air through the bottom of the glass tube.
Thus higher magnification can be obtained.
The bleed valve is fitted in the top to rest the float at any required position
(i.e Setting Zero reading).

A bleed valve is the valve through which air can be escaped to the atmosphere
Without passing to measuring head.
In measuring head, the orifices are recessed to avoid the direct contact of air wit
Work piece.
Hence, Surface wear will not occur on the specimen.

Back Pressure Type:
In this type, the air flows to the atmosphere
at a constant pressure through orifices.
When the orifice O2 is fully Closed, the
pressure Ps and Pi will be equal.
The Pressure Ps ans Pi are equal to zero
when the Orifice O2 is in full opening
Condition.
Pressure Ps and Pi varies when the distance d Varies.
If there is any variation in pressure of Ps and Pi which can be measured by suitable
measuring device.
This type is mainly used in backpressure type pneumatic Comparators.
Ex:Solex air gauge.

Sine Bar:
Sine bars are always used along with slip gauges
Used to:
 Measures angles very accurately
 Locate the work piece to a given angle with very high precision.

Sine bars are made from high corbon,high chromium, and corrosion steels
Materials are highly hardned,ground and stabilized
Two Cylinders of equal diameters are attached at the ends with its axis mutually
parallel to each other
Also at equal distance from upper surface of the sine bar.
Sine bar Ranges 100mm,200mm and 300mm
Cylindrical holes are provided to reduce the weight of sine bar

Most preferred sine bar, Since the distance between rollers can be adjusted exactly.
Also it is easy to set on steep angle without the slip gauges.

Most commonly used form of sine bar
Rollers are arranged in such a way that their outside surface on one side is level wit
the plane top surface of the sine bar.

Hollow rollers are integral with the sine bar and the outside diameter of the rollers
Is equal to the width of the sine bar

Special form of sine bar
This type is used where ordinary type cannot be used on the top surface due to
interruption

Working is based on trigonometry principle
To measure the angle of the given specimen, one roller of the sine bar is placed on the
Surface plate and another one roller is placed over the surface of the slip gauges.
h – Height of the slip gauge
L- Distance between roller centers

Accuracy Requirement of a sine bar:
Rollers must have equal diameter and equal cylinders
Rollers should be placed parallel to each other and also to the upper surface
The accurate center to center of rollers must be known
The top surface of the bar must be flat with high degree of accuracy

Classification of sine bars:
Classified into two Categories:
According to accuracy of centre distance:
1.Grade A
2.Grade B
According to availability of different designs
 Type 1
 Type 2
 Type 3
 Type 4

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