Measurement Standards and Design of gauges

Matoshri College of Engineering and Research Center
Nashik
Department of Mechanical Engineering
Subject:- Metrology And Quality Control
Class:-TE Mechanical
Unit: I Measurement Standards and Design of gauges
Semester:-V
2020-21
By
Prof R.S.Patil
(Assistant Professor MCOERC )

What is metrology?
• The science of measurement
• Greek Word Metro – Measurement Logy – Science
• Examples: distance, time, mass, temperature, voltage, values
of physical and chemical constants
Matoshri College of Engineering and
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Career in Metrology
 Scientific Metrology – Organization and development of
measurement standards and their maintenance (highest level)
 Industrial Metrology –Adequate functioning of measurement
instruments used in industry as well as production and testing
processes
 Pharmaceutical Industry-Metrology laboratories test weights and
volume standards for pharmaceutical companies Products include
medicines like aspirin, antibiotics, vaccines, insulin, & vitamins
 Space Station- Satellite Metrology laboratories test standards for
many companies that provide parts of the space shuttle
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Course Objectives
Students are expected to :-
1. Select suitable instrument / gauge / method of inspection for determining geometrical and
dimensional measurements.
2. Calibrate measuring instruments and also design inspection gauges.
3. Understand the advances in Metrology such as use of CMM, Laser, Machine Vision System for
Metrology etc.
4. Select and apply appropriate Quality Control Technique for given application.
5. Select and Apply appropriate Quality Management Tool and suggest appropriate Quality
Management System (QMS).
Course Outcomes
The student should be able to :-
1. Understand the methods of measurement, selection of measuring instruments / standards of
measurement, carryout data collection and its analysis.
2. Explain tolerance, limits of size, fits, geometric and position tolerances and gauge design
3. Understand and use/apply Quality Control Techniques/ Statistical Tools appropriately.
4. Develop an ability of problem solving and decision making by identifying and analyzing the
cause for variation and recommend suitable corrective actions for quality improvement.

Course Contents
Unit – I Measurement standards and Design of gauges
Introduction: Principles of Engineering metrology, Measurement standards, Types and
sources of errors, Accuracy and Precision, Calibration: Concept and procedure,
traceability
Geometric Form Measurement: Straightness, Flatness, Roundness - Straight edge, use
of level beam comparator, autocollimator testing of flatness of surface plate.
Design of Gauges: Tolerances, Limits and Fits [IS 919-1993], Taylor’s principle, Types of
gauges, Wear allowance on gauges, Types of gauges-plain plug gauge, ring gauge,
snap gauge, limit gauge and gauge materials, Considerations of gauge design
(numerical).
Reference books:
1. Jain R.K., Engineering Metrology, Khanna Publication.
2. I. C. Gupta, Engineering Metrology, Dhanpath Rai.

Content
• Principles of Engineering metrology
• Measurement standards
• Types and sources of errors
• Accuracy
• Precision
• Calibration
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Standard of Measurement
• Metrology is science of measurement involve measurement of
Dimensions.
• Measurement is process of comparison with standard instrument.
• A standard is defined as “something that is set up and established
by an authority as rule of the measure of quantity, weight, extent,
value or quality”.
• Necessary to give standards to avoid confusion during interchanging
Measurement.
• In India, Bureau of Indian Standards(BIS) responsible for
metrological standards.

Standard of Measurement(cont.)
• Two standard system for linear Measurement used
Throughout the world English and Metric( Yard and meter)
• Most country used metric System
• Various standard for Linear Measurement
 Line standard
 End Standard
 Wavelength Standard

1) Line Standard
• Line standard in which distance is measured between two line.
• Yard :- The Imperial Standard Yard is a bronze bar of 1 inch square
cross-section and 38 inches long. It is distance between two flat
parallel line of plug at 17 ͦC
• METRE :- This is the distance between the centre portions of two
lines engraved on the polished surface of a bar of pure platinum-
iridium alloy (90% platinum and 10% iridium).

2) End Standard
• Is expressed as the distance between two surfaces, this is referred
to as end standard.
• For all the important works in the shop, the users prefer end
standards e.g. slip gauges, length bars, the ends of micrometer
anvils, gap gauges, and so on.
• Dimensional tolerance as small as 0.0005 mm can be obtained.
• They are not subjected to parallax effect as their use depends on
“feel”.
• Well suited to measurements of close tolerance.

3) Wavelenth Standard
• A meter is defined as equal to 1670763.73 wavelength of red-
orange radiations of Krypton isotope 86 gas .
• Length of path travelled by light in vacuum in 1/299792458
second.
• Higher Accuracy
• Environment-friendly
• Reproducible
• No Wear and Tear

Comparison of Standard

Error
• It is Difference between true value and indicated value.
• Error= True value- Indicated Value
• Ex-Thermometer
• Sources of Error
 Defect in Instrument.
 Observation Error.
 Method of Location of Instrument
 Manufacturing defects in Instruments

Types of Error
(1) Gross Error
(2) Systematic Error
(3) Instrument Error
(4) Environmental Error
(5) Observation Error
(6) Alignment Error
(7) Elastic Deformation
(8) Dirt Error
(9) Contact Error
(10) Parallax Error
(11) Random Error
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Types of error
GROSS ERROR :
• These errors occur due to human mistakes such as careless
reading, mistake in recording observation, incorrect
applications of a correction, improper application of
instruments.
• These errors can not be treated mathematically.
• They can be avoided only by taking care in reading and
recording the measurement data.

Types of error
INSTRUMENT ERROR :
• These errors are due to design and construction of
instruments that limits the accuracy of measurements.
• Example : Improper selection of instruments, poor
maintenance, loading effects, etc.
• Can be avoided by : Selecting suitable instruments, applying
correction factors, etc.

Types of error
ENVIRONMENTAL ERROR :
• An environmental error is an error in calculations that are
being a part of observations due to environment.
• Any experiment performing anywhere in the universe has its
surroundings, from which we cannot eliminate our system.
• The environmental errors have different causes, which are
widening with the passage of time, as the research works
telling us, including; temperature, humidity, magnetic field,
constantly vibrating earth surface, wind and improper
lightening.

Types of error
OBSERVATION ERROR :
• When human factors involved in measurement, the
capabilities of individual observers effects the accuracy of
measurement.
• The observation errors occur due to poor capabilities and
carelessness of operators.
• Example : Wrong reading, wrong calculations, wrong
conversion, wrong recording data, etc.
• These errors eliminates by using modern instrument having
digital display.

Types of error
ALIGNMENT ERROR
• This error based. on Abbes principle of alignment which states that
the line of measurement of the measuring component should
coincide with the measuring scale or axis of the measuring
instrument.
• Cosine errors will be developed generally while measurement of a
given job is carried out using dial gauge or steel rule

Types of error
ELASTIC DEFORMATION :
• Long bars due to improve support or due to self weight may
undergo deflection or may bend. As shown in fig due to less
or high distance between the support, A long bar tends to
deform.

Types of error
DIRT ERROR
• Sometimes, dirt particles can enter in the inspection room
through the door and the windows.
• These particles can create small dirt errors at the time of
measurement.
• These errors can be reduced by making dust proof
laboratories.

Types of error
CONTACT ERROR
• The ring as shown in fig whose thickness is to be measured.
• If the jaws of the instrument are placed as shown in fig, the
error developed, which is because of poor contact only.

Types of error
PARALLAX ERROR
• Parallax is a displacement or difference in the apparent
position of an object viewed along two different lines of sight,
and is measured by the angle or semi-angle of inclination
between those two lines.

Types of error
RANDOM ERROR
• These errors are caused due to variation on position of setting
standard and work piece.
• Due to Displacement of level joints of instrument, due to
backlash and friction, these error are induced.
• Random errors in experimental measurements are caused by
unknown and unpredictable changes in the experiment.
These changes may occur in the measuring instruments or in
the environmental conditions.

Contents
Unit – I Measurement standards and Design of gauges (06 hrs)
• Accuracy and Precision
• Calibration: Concept and procedure & traceability
• Geometric Form Measurement
• Straightness
• Flatness, Roundness - Straight edge
• Use of level beam comparator
• Autocollimator testing of flatness of surface plate

Accuracy
 Closeness of measured value to the true value
 For ex if true value of Component is 4.25 and measured values are
4.15,4.18 and 4.20 so on then they are not accurate as Compared to 4.25
Precision
 How finely tuned your measurements are or how close they can be to
each other
 Depends on the measuring tool
 Determined by the number of significant digits

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Calibration
• Process of Checking the accuracy of the measuring
instrument or a gauges.
• Comparison with Standard
• Periodic Checking of instrument
• Need of calibration
• Requirement of Calibration
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Assignment
Q1) Write short notes on-
i) Types of standards.
ii) Accuracy and Precision
iii) Error
Q 2) What are different types of error Explain in Brief
Any Question
patil.roshaneng@gmail.com
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Measurement Standards and Design of gauges

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