UNIT 1 BASICS OF METRO LOGY

METROLOGY AND
MEASUREMENTS
PREPARED BY
L. DEVAKUMAR
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL ENGINEERING
KNCET
1

UNIT-I BASICS OF METROLOGY
Introduction to metrology-Need-
Element Work piece, Instruments-
Persons-Environment-Their effect on
precision and accuracy-Errors-Errors in
measurement-Types-Control-Types of
standards.
3

GENERAL APPLICATIONS
• Design and drawing
• Production planning
• Manufacturing
• Assembly section
• Research and
development
• Prizing
• Packaging
• Marketing
• Surveying
• Banking
• Medical metrology
• Food factory's
• Oil industry’s
• Piping
• Textile industry's
• Environment
• Austhetic
4

INTRODUCTION TO METROLOGY
• Science of measurement
• Ensuring uniformity of measurement
• Developing new methods of measurement
• Analyzing new methods
• Gauges design, manufacturing and testing
• Changing units in the form of standards
• Researching cases and industrial inspection
5

NEED FOR METROLOGY or
MEASUREMENT
• To determine true dimensions
• To ensure public health and human safety
• To evaluate the performance of a system
• To study the basic laws of nature
• To check the limitations of theory in practical
situation
• To design and finding new data
6

TYPES OF METROLOGY
• SCIENTIFIC METROLOGY (Organization and
development)
• INDUSTRIAL METROLOGY (used in a wide variety of
industries)
• LEGAL METROLOGY
• FUNDAMENTAL METROLOGY (Industrial and Scientific)
• DYNAMIC METROLOGY (continuous measurements)
• DETERMINISTIC METROLOGY (3D Error, Comparison
with CNC)
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INTRODUCTION TO MEASUREMENT
• Predetermined standard values adopted as a
unit.(mm, cm,)
Elements
• Measurand (Physical Quantity) - length, angle
diameter, thickness)
• Reference (Unknown quantity is compared with
the available standard quantities such as length,
mass and time to produce)
• Comparator (Monitoring in Power plant,
temperature, pressure)
8

METHODS OF MEASUREMENT
• Direct Method or Primary measurement
(length, mass, time are Not accurate)
• Indirect Method (Comparing with another
quantity)
• Absolute or Fundamental method
• Comparative (using comparators)
mechanical, electrical, hydraulic,
pneumatic types) Petrol Diesel
9

METHODS OF MEASUREMENT
• Substitution (quantity = quantity – same
values)
• Coincidence
• Deflection
• Complementary (Solid by Liquid)
• Methods of null (Measuring by
potentiometer) (stop watch – running)
10

DEFLECTION TYPE COINCEDENCE
11

Methods of Measurements
1. Direct Method:
 This is the simplest method of measurement in which the value of
the quantity to be measured is obtained directly without any
calculations, e.g. measurements by scale, calipers & micrometers.
 It involves contact or non contact type of inspections.
2. Indirect Method:
 The value of the quantity to be measured is obtained by measuring
other quantities, which are related to required value.
 E.g. density calculation by measuring mass & volume.
3. Absolute Method:
 Also called fundamental method & is based on the measurement of
the base quantities used to define a particular quantity.

4. Comparison Method:
 The value of quantity to be measured is compared with a known value of
a same or related quantity to it.
 E.g. dial indicators & other comparators.
5. Substitution Method:
 The quantity is measured by direct comparison on an indicating device
by replacing the measurable quantity with another which produces the
same effect on the indicating device.
6. Coincidence Method:
 There is a very small difference b/w the value of the quantity to be
measure & the reference.
 It is also called differential method of measurement.

8. Deflection Method:
 The value of the quantity to be measured is directly indicated by
the deflection of a pointer on a calibrated scale.
 e.g. dial indicator.
9. Complementary Method:
 The value of the quantity measured is combined with a known
value of the same quantity.
 E.g. determining volume of solid by liquid displacement.
10. Method of Null Measurement:
 It is a method of Differential measurement.
 In this method the difference b/w measured & known value is
brought to zero.
 E.g. measurement by potentiometer. (Voltage limit)

IMPORTANT TERMS USED IN
MEASUREMENTS
 Range: The capacity with in which the instrument is capable of
measuring.
 Span: Span = Maximum value of input – minimum value of input
 Error: The indication of measuring instrument output minus the
true value of the input quantity.
 Accuracy: The closeness of agreement between a test result & the
accepted reference value.
 Precision: The closeness of agreement b/w independent test results
obtained under stipulated conditions.
16

MEASUREMENTS
• Sensitivity: The smallest change in the value of the measured variable to
which the instrument responds.
• Stability: The ability of measuring instrument to constantly maintain its
metrological characteristics with time.
• Scale interval: Difference between two successive scale marks (Vernier)
• Hysteresis: Difference in the output for the given input value (Elastic)
• Threshold: No output changed when given input (Zero)
• Resolution: The smallest change of the measured quantity which
changes the indication of a measuring instrument.
17

MEASUREMENTS
• Calibration: The set of operations that establish the relationship b/w
values indicated by instruments & the corresponding values given
by standards, under specified conditions.
• Dead zone and dead time: Largest Range of values of a measured
values engine does not respond. Time taken to instrument response
that is dead time
• Backflash: Lost motion or free play of the mechanical elements.
(Gears, linkages)
• Bias: The difference B/w the expectation of the test result & an
accepted reference value.
18

MEASUREMENTS
• Tolerance: Maximum allowable error
• Drift: A slow change of metrological characteristics of a measuring
instruments.
• Un certainity:
 It is a parameter associated with the result of a measurement
that characterizes the dispersion of the values that could
reasonably be attributed to the Measurand.
 It can also be expressed as an estimate characterizing the
range of values with in which the true value of a Measurand
lies.
 When specifying the uncertainty it is necessary to indicate the
principle on which the calculation has been made.
19

MEASUREMENTS
• Zero drift: Change when occurs in output is zero input is
known as zero output
• Over shoot: Maximum amount by which moving parts
beyond the steady state
• Response Time: Indicate the values when differ from
(true vale to error value)
20

ELEMENTS OF GENERALIZED
MEASUREMENT SYSYTEM
• A number of measuring instruments used in
practice. Therefore it is necessary to identify
the common features or the basic elements of
a generalized system
21

1. Primary sensing element (receives energy
as input signal)
2. Variable conversion element (without
changing)
3. Variable manipulation element
(magnification)
4. Data transmission element
5. Data processing element (modify)
6. Data presentation element (monitoring)
22
GENERALIZED MEASURING ELEMENT
SYSTEM

1. Primary Sensing Element: The primary sensing element receives signal of
the physical quantity to be measured as input. It converts the signal to a
suitable form (electrical, mechanical or other form), so that it becomes easier
for other elements of the measurement system, to either convert or
manipulate it.
2. Variable Conversion Element: Variable conversion element converts the
output of the primary sensing element(Detector) to a more suitable form. It
is used only if necessary.
3. Variable Manipulation Element: Variable manipulation element
manipulates and amplifies the output of the variable conversion element. It
also removes noise (if present) in the signal.
4. Data Processing Element: Data processing element is an important element
used in many measurement systems. It processes the data signal received
from the variable manipulation element and produces suitable output.
24

5. Data Transmission System: Data Transmission System is
simply used for transmitting data from one element to
another. It acts as a communication link between different
elements of the measurement system. Some of the data
transmission elements used are cables, wireless antennae,
transducers, telemetry systems etc.
6. Data Presentation Element: It is used to present the
measured physical quantity in a human readable form to the
observer. It receives processed signal from data processing
element and presents the data in a human readable form. LED
displays are most commonly used as data presentation
elements in many measurement systems.
25

EXAMPLE OF MEASUREMENT SYSTEM
• Liquid or gas filled temperature bulb act as a
primary sensing element and variable
conversion element.
• It sense the temperature and it converts into
temperature built up within the bulb.
• Pressure transmitted to the capillary tube
(Which act as a data transmission element) to
a spiral bourdon type pressure gauge
26

• Bourdon tube act as a variable conversion. It
convert pressure in to displacement..
• The displacement is manipulated by linkage
and gearing arrangement to give a larger
pointer deflection.(Variable manipulation
element).
• The pointer and scale indicate the
temperature (Data presentation Elements)
27

ELEMENTS OF
MEROLOGY/MEASUREMENT SYSTEM
• Standard - S
• Work piece - W
• Instrument - I
• Person - P
• Environment - E
30

STANDARD
• Physical representation of unit of
measurement
• The term standard is used to denote
universally accepted specifications for devices.
• Components or processes which ensure
conformity and interchangeability throughout
a particular industry.
• A standard provides a reference for assigning a
numerical value to a measured quantity.
31

TYPES OF STANDARD
• International standards (Internationally
accepted)
• Primary standards ( National Physical
Laboratory at New Delhi)
• Secondary standards(Basic reference
standard)
• Working standards(To check the components)
32

WORKPIECE
• Once standard is chosen a work piece is
selected on which experiment will be
performed.
• Variations of geometry and surface finish of
the measured part directly affect a measuring
system’s repeatability.
33

INSTRUMENTS
• It is a device with the help of which the
measurement will be done.
• A gauge is selected based on the tolerance of
the parts to be measured, the type of
environment and the skill level of operators.
• Also remembered that what type of
instrument the customers will use to measure
the parts.
34

UNITS
• M.K.S,CGS &S.I
• System International
Fundamental units-Length, Mass, Time,
Temperature, Electric current & Luminus
intensity.
Supplementary units-radian, steradian
Derived units-A,V,Density,v,a,F,P,W,p
35

PERSONS
• Some person or mechanism to carry out the
measurement.
36

ENVIRONMENT
• The measurement should be perform under
the standard environment. (Temperature, Rain
etc.,)
37

Measuring Instruments & Their
Selection
i. On the basis of Function:
a. Length Measuring Instruments
b. Angle Measuring Instruments
c. Surface Roughness Measuring Instruments
d. Shape Checking Instruments
ii. On the basis of Accuracy:
a. Most Accurate Instruments
b. Moderate Accurate Instruments
c. Below Moderate Accurate Instruments
iii. On the basis of Precision:
a. Precision Measuring instruments
b. Non Precision Measuring Instruments

Factors Affecting Accuracy of Measuring
Instruments
1. Standards of Calibration for Setting Accuracy
2. Work piece control during Measurement
3. Inherent Characteristics of measuring instruments
4. Inspector (Human Factor)
5. Environmental Conditions

PRECISION AND ACCURACY
Accuracy: Accuracy is how close a measured
value is to the actual (true) value.
It refers how closely the measured value agrees
with the true value.
Precision: Precision is how close the measured
values are to each other.
40

STABILITY AND REPEATABILITY
42

RELIABILITY AND READABILITY
43

TYPES OF ERRORS
• STATIC ERROR
Characteristic error
Reading error
Environmental error
• LOADING ERROR
• DYNAMIC ERROR
Systematic error
Random error
44

Errors in
Measurement
Error in Measurement=Measured value-True Value
Error may be Absolute or Relative.
Absolute Error:
It is divided into two types:
a. True absolute Error:
 It is defined as the algebraic difference b/w the result of measurement & the
conventional true value of the quantity Measured.
b. Apparent Absolute Error:
 It is defined as the algebraic difference b/w the arithmetic mean & one of the
results of measurement when a series of measurements are made.
 Absolute Error = |Actual Value-Approximate value|
If, absolute value = x & approximate value = x+dx, then
Absolute Error = dx

Errors in
Measurement
Relative Error:
 It is the quotient of the absolute error to the true/ actual value
(may be true or arithmetic mean of a series of measurements)
Relative Error = |𝐴𝑐𝑡𝑢𝑎𝑙𝑉𝑎𝑙𝑢𝑒−𝐴𝑝𝑝𝑟𝑜𝑥𝑖 𝑚𝑎𝑡𝑒 𝑉𝑎𝑙𝑢𝑒|
|𝐴𝑐𝑡𝑢𝑎𝑙𝑉𝑎𝑙𝑢𝑒|
Relative Error = dx/x
Percentile Error (Ep) = Relative Error * (100)

ERRORS IN MEASUREMENT
• Gross Error – It is a parasitic error.
• Systematic Error – Errors occurs fault in
equipment
• Static Error - Physical Nature of various error
48

Errors in
Measurement
• Environmental Error:
 The error arising from the effect of the surroundings like pressure,
temperature, humidity, magnetic & electric fields etc.
 It can be controlled by controlling the atmospheric factors.
4. Loading error:
 If the datum surface is not flat or if foreign matters like dirt, chips
etc. get entrapped b/w the datum & work piece then there will be
Loading error.
 Also poor contact b/w instrument & work piece can cause this.
 To avoid such errors an instrument with wide area of contact should
not be used.
5. Dynamic error:
 It is caused by time variation in the Measurand. It is the result of
incapability of the system to respond reliably to time varying
measurement.
 Inertia, damping & friction are causes of dynamic error.

• Dynamic Error – Instrument not responding
» Instrumental Error
• Error of a physical measure
• Characteristics error
• Zero Error
• Calibration Error
• Complementry error
• Error of indicating of a measuring instrument
• Error due to temperature
• Error due to friction
• Error due to inertia
50

Errors in
Measurement
Observation Error:
 These errors are introduced by observer
 They are further classified as:
a. Reading Error:
 Errors when the line of sight is not perpendicular to the measuring
scale.
 Error = X tan θ
b. Parallax Error:
 It is the deviation of the system output from
the theoretical predicted performance.
 Linearity, repeatability, hysteresis & resolution
error are its types.
C. Interpolation Error
Reading error (Graph)

Errors in
Measurement
b. Random Error:
 These errors are accidental, non consistent in nature.
 As they occur randomly they cannot be eliminated since no
definite cause can be located.
 Small variation in the setting standards & the work piece can
cause such errors.

SOURCES AND CAUSES OF ERRORS
• Errors due to deflection
53

• Errors due to misalignment
54

• Error due to contact pressure or stylus
pressure error:
55

• Error due to poor contact:
56

• Error due to vibrations
• Error due to dirt
• Error due to wear in gauges
• Error due to loosens
• Error due to parallax effect
57

END STANDARD
• End bars (Carbon steel – larger steels
measuring)
• Slip gauges (Standard of measurement in
practically every precision engineering works
in industry)
59

• CALIBRATION
Process of determining and adjusting the
instruments accuracy to make sure its
accuracy is within the manufacture’s
speciation.
• Primary calibration: Primary calibration most
often takes a laser interferometer and
provides an absolute calibration by comparing
the dynamic vibration to the wavelength of
the laser light.
• Secondary calibration
61

EFFECTS OF ELEMENTS OF METROLOGY
ON PRECISION AND ACCURACY
• Factors affecting the standard of
measurement
• Factors affecting the work piece to be
measure
• Factors affecting the inherent characteristics
of an instrument
• Factors affecting the person
• Factors affecting environment
62

SENSITIVITY
• It is an instrument is defined as the ratio of
the magnitude of output signal to the
magnitude of input signal.
63

UNIT 1 BASICS OF METRO LOGY

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UNIT 1 BASICS OF METRO LOGY