Basic concepts and standards of Metrology

1.  INTRODCTION TO SUPPLY CHAIN
MANAGEMENT
&
ROLE OF LOGISTICS
POWER POINT PRESENTATION
ON
Metrology concepts and standards
Presented by
Md Tayab Ali
Lecturer (Sr. Scale)
Dept. of Mechanical Engineering
H.R.H. The POWIET, Jorhat
6/13/2021 1

2. Meaning of Metrology
The word metrology is derived from two Greek words
Metro = measurement
Logy = science
Thus metrology is the science of measurement.
Metrology may be defined as, “Comprehensive study
of different measuring instruments for finding
precision, accuracy, possible sources of errors, and
methods for elimination of errors”.
Engineering Metrology is restricted to measurement
of length and angles and other quantities which are
expressed in linear or angular terms.
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3. Significance of Metrology
 In addition to linear and angular measurements, “Metrology” covers
the following aspects:
 (a)Manufacturing: Metrology is concerned with the manufacturing of
various instruments.
 (b)Range and capabilities: Metrology is used to find the ranges and
capabilities of various instruments used for measurements.
 (c) Calibration: Metrology is used to calibrate the measuring
instruments according to the prescribed standards with a high degree
of accuracy.
 (d) Method of measurements: Metrology is concerned with the
different methods of measurements, essential to obtain precise
measurements.
 (e) Maintaining and defining the standards: For accurate
measurements, metrology is concerned with defining and maintaining
the standards.
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4. Activities of Metrology
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5. Objectives or Necessity of Metrology
 To provide the required accuracy at a minimum cost.
 To standardize the measuring methods.
 To find out sources of errors.
 Useful in selection of proper measuring instruments and
gauges.
 To have good accuracy and precision.
 To reduce cost of inspection by effective and efficient use of
available facilities.
 To evaluate newly developed products.
 To enhance consumer satisfaction.
 To reduce rework and rejections through application of
statistical quality control techniques.
 To prepare design for all gauges and special inspection
fixtures.
 To maintain the accuracies of measurement.
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6. Types of Metrology
 Scientific Metrology-This form of metrology deals
with the establishment and development of
measurement standards with their maintenance.
 Industrial Metrology-Industrial metrology’s purpose
is to ensure the ‘adequate functioning of measuring
instruments’ used in ‘Industry’ as well as in
‘production and testing’ processes.
 Legal Metrology- Legal metrology is directed by a
national organization which is called National Service
of Legal Metrology. Legal metrology is concerned, to
maintain uniformity of measurement throughout the
world
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7. Functions of Legal Metrology
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8. Inspection
Inspection means checking of all materials, products
or component parts at various stages during
manufacturing.
 It is the act of comparing materials, products or
components with some established standard.
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9. Need of Inspection
The need of inspection can be summarized as:
 To ensure that the part, material or a component conforms
to the established standard.
 To maintain customer relation by ensuring that no faulty
product reaches the customers.
 Provide the means of finding out shortcomings in
manufacture.
 It also helps to purchase good quality of raw materials,
tools, equipment which governs the quality of the finished
products.
 It also helps to co-ordinate the functions of quality control,
production, purchasing and other departments of the
organization.
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10. PROCESS OF MEASUREMENTS
 The sequence of operations necessary for the execution of
measurement is called process of measurement.
 Three important elements of measurements are:
(i)Measurand: It is the physical quantity or property like length,
angle, diameter, thickness etc. to be measured.
(ii) Reference: It is the physical quantity or property to which
quantitative comparisons are made.
(iii) Comparator: It is the means of comparing measurand with
some reference.
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Example: Measuring the length of a M.S. flat by a steel rule.
Here the length of M.S. flat is a measurand,, Steel rule is the
reference and Observer’s eye can be considered as a comparator

11. METHODS OF MEASUREMENTS
The methods of measurement can be classified as:
 1.Direct Method
 2. Indirect Method
 3. Absolute or Fundamental Method
 4.Comparative Method
 5. Transposition Method
 6. Coincidence Method
 7. Deflection Method
 8. Complementary Method
 9. Contact Method
 10. Contactless method
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12. 1.Direct Method of Measurement
Measurements are directly obtained without any
calculations.
Example: Measurements by using scales, Vernier
calipers, micrometers & bevel protractors etc .
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13. 2.Indirect Method of Measurement
The value of the quantity to be measured is obtained
by measuring other quantities, which are related to
required value.
Example: Weight of a substance is measured by
measuring the length, breath and height of the
substance directly and then by using the relation
Weight = Length x Breadth x Height x Density
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14. 3. Absolute or Fundamental Method
It is based on the measurement of the base quantities
used to define the quantity.
Example: Measuring a quantity directly in accordance
with the definition of that quantity,
OR measuring a quantity indirectly by direct
measurement of the quantities linked with the
definition of the quantity to be measured.
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15. 4.Comparative Method of Measurement
The value of the quantity to be measured is compared
with known value of the same quantity or other
quantity practically related to it. So, in this method
only the deviations from a master gauge are
determined.
Example: Dial indicators, or other comparators.
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16. 5. Transposition Method of Measurement
Quantity to be measured is first balanced by an initial
known value and then balanced by another new
known value.
Example: Determination of mass by means of a
balance and known weight.
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17. 6. Coincidence Method of Measurement
Measurements coincide with certain lines and signals.
Example: Measurement by Vernier calliper,
micrometer.
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18. 7. Deflection Method of Measurement
The value of the quantity to be measured is directly
indicated by a deflection of a pointer on a calibrated
scale.
 Example: Measurement of Pressure.
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19. 8. Complementary Method of Measurement
The value of quantity to be measured is combined with
known value of the same quantity.
Example: Determination of the volume of a solid by
liquid displacement.
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20. 9.Contact Method of Measurement:
In this method the sensor or measuring tip of the
instrument actually touches the surface to be
measured.
Example: Measurements by micrometer, Vernier
caliper, dial indicators etc.
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21. 10. Contactless method of Measurement
There is no direct contact with the surface to be
measured.
Example: Measurement by optical instruments such
as tool makers microscope, projection comparator etc.
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22. Basic elements of measuring system
1. Standard: The most basic element of measurement
is a standard without which no measurement is
possible.
2. Work piece: Once the standard is chosen select a
work piece on which measurement will be performed.
3. Instrument: Then select an instrument with the
help of which measurement will be done.
4. Person: There must be some person or mechanism
to carry out the measurement.
5. Environment: Lastly, the measurement should be
performed under standard environment.
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23. Terminologies used in measuring instruments:
 Precision Accuracy
 Sensitivity Readability
 Calibration Magnification
 Repeatability Reproducibility
 Range Threshold
 Hysteresis Backlash
 Resolution
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24. Precision
 Precision is the repeatability of the measuring process.
(i.e. how closely individual measurements agree with
each other)
 It refers to the group of measurement for the same unit
of product taken under identical conditions.
 It indicates to what extent the identically performed
measurements agree with each other.
 If the instrument is not precise it will give different
(widely varying) results for the same dimension when
measured again and again.
 The set of observations will scatter about the mean
value.
 The less the scattering more precise is the instrument.
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25. Accuracy
 The agreement of the measured value with the
true value of the measured quantity is called
accuracy.
 The term accuracy denotes the closeness of the
measured value with the true value.
 The difference between the measured value and
the true value is the error of measurement.
 The lesser the error, more is the accuracy
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26. Precision Vs Accuracy
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Fig.-1

27.  Several measurements are made on a component by
different types of instruments (A, B and C
respectively) and the results are plotted.
 Fig.-1 (a) shows that the instrument A is precise since
the results of number of measurements are close to the
average value. However, there is a large difference
(error) between the true value and the average value
hence it is not accurate.
 The readings taken by the instruments B as shown in
Fig.-1(b) are scattered much from the average value
and hence it is not precise but accurate as there is a
small difference between the average value and true
value.
 Fig.-1(c) shows that the instrument C is accurate as
well as precise.
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28. Difference between Accuracy and Precision
Accuracy Precision
1. Accuracy is the agreement of
measured value with the true value of
measured quantity.
1. Precision is the repeatability of the
measuring process. It shows, how well
identically performed measurements
agree with each other.
2. Accuracy is concerned with true
value.
2. Precision is concerned with mean
value. Precision has no concern with
true value. Precision has no meaning
for only one measurement, but exists
only when numbers of measurements
are carried out for measuring same
quantity under identical conditions.
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29. Difference between Accuracy and Precision
Accuracy Precision
3.If true value is 10 mm, then measured
dimension of 9.99 mm is more accurate
than 9,91 mm.
3. If true value is 10 mm, and readings
obtained are 10.001, 10.002, 10.003,
10.004 and 10.005 mm, the mean value of
readings will be 10.003 mm. Therefore,
The measurements are said to be precise,
because all the obtained readings are very
close to their mean value (10.003 mm).
4. It is difficult and expensive to have good
accuracy.
4. It is much easier and cheaper to
achieved precision than to achieve great
accuracy.
5. High accuracy cannot be obtained with
low precision.
5. High precision cannot be obtained with
low accuracy.
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30. Sensitivity
 Sensitivity refers to the ability of a measuring device to
detect small variations in a quantity being measured.
 In other words, sensitivity is the ratio of the change in
output of the instrument to a change of input or measured
quantity.
 i.e. Sensitivity = Change in output/Change in input.
 Higher the ability of such detection of an instrument, more
sensitive it is.
 Example-1: If on a dial indicator, the scale spacing is 1.0
mm and the scale division value is 0.01 mm, then sensitivity
is 100.
 Example-2: Sensitivity of thermometer means that it is the
length of increase of the liquid per degree rise in
temperature.
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31. Readability
 Readability refers to the ease with which the readings
of a measuring instrument can be read.
 Fine and widely spaced graduation lines improve the
readability.
 To make the micrometers more readable they are
provided with vernier scale or magnifying devices.
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32. Calibration
Calibration is a pre-measurement process, generally
carried out by the manufacturer.
It is the process of framing the scale of the measuring
instrument by applying some standards”.
It is carried out by making adjustments such that the
read out device produces zero output for zero input.
The accuracy of the instrument depends on the
calibration.
If the output of the measuring instrument is linear
and repeatable, it can be easily calibrated.
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33. Magnification: Magnification is the process of
enlarging magnitude of the output signal of
measuring instrument many times to make it
more readable.
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34. Repeatability:
It is the ability of the measuring instrument to
repeat the same results for the measurements for
the same quantity, when the measurements are
carried out:
-by the same observer,
- with the same instrument,
- under the same conditions,
- without any change in location,
- without change in the method of measurement,
- the measurements are carried out in short intervals
of time.
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35. Reproducibility
Reproducibility is the closeness of the agreement
between the results of measurements of the same
quantity, when individual measurements are
carried out:
- by different observers,
- by different methods,
- using different instruments,
- under different conditions, locations, times etc.
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36. Range
 The upper and lower limits an instrument can
measure a value or signal such as amps, volts and
ohms.
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37. Threshold
The min. value below which no output change can be
detected when the input of an instrument is increased
gradually from zero is called the threshold of the
instrument.
Threshold may be caused by backlash.
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38. Hysteresis
It is defined as the magnitude of error caused in the
output for a given value of input, when this value is
measured from opposite direction, i.e from ascending
order and then descending order.
This is caused by backlash , elastic deformation but is
mainly caused due to frictional effects.
Hysteresis effects are best eliminated by taking
observation in both the direction i.e. in ascending and
then descending order values of input and then taking
the arithmetic mean.
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39. 6/13/2021 39
Hysteresis of a stretched rubber band. The gap between the load and
unload is the tendency of the rubber not to return to its original shape
due to friction.

40. Resolution
Resolution is the smallest measurement that can be
measured by a measuring instrument.
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The gauge on top has finer resolution. Notice that there are more tick
marks between 280 and 290 on the top gauge than on the bottom one. Finer
resolution reduces rounding errors, but doesn't change a device's accuracy.
However, resolution that is too coarse may add rounding errors.

41. Backlash
In Mechanical Engineering, backlash, is clearance
between mating components, sometimes described as
the amount of lost motion due to clearance or
slackness when movement is reversed and contact is
re-established.
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42. System of Measurement
The following systems of measurement are in use
in different countries.
1.F.P.S. System
2.MKS system
3.S.I. System
1.F.P.S. System: In this system, unit of length is
yard, unit of mass, weight of force is pound, unit of
time is seconds and unit of temperature is degree
Fahrenheit.
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43. 2.MKS system: Metric system is the predominant
system in the world. It is based on metre as a unit
of length, kilogram as the unit of mass and
kilogram force as the unit of weight or force, unit
of temperature is degree centigrade (°C).
S.I. System: This S.I. (International System of
Units) provides only one basic unit for each
physical quantity. It is comprehensive because its
seven units cover all disciplines. For example: The
units of length, mass, time, temperature, electric
current, luminous intensity, quantity of substance
are m, kg, s, k, a cd, and mole respectively.
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44. Derived S.I. units
Units that are a combination of two or more
quantities and which usually requires a compound
word to name them are called compound or
derived units.
Example: Unit of Force is Newton.
1 N = kgm/sq.sec
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45. STANDARDS
A standard is physical representation of a unit of
measurement.
A known accurate measure of physical quantity is
termed as a standard.
These standards are used to determine the values of
other physical quantities by the comparison method.
The standards of measurements are very useful for
calibration of measuring instruments.
They help in minimizing the error in the measurement
systems.
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46. Standard systems of linear measurement
There are two standard systems of linear measurement
commonly in practice:
1.English System
2.Metric system
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47. 1.English System
It is also known as British System of linear
measurement.
This system is based on the “Imperial Standard Yard”.
The yard in its current form was first setup in 1855 in
England.
An imperial standard yard, shown in fig, is a bronze
(82% Cu, 13% tin, 5% Zinc) bar of 1 inch square section
and 38 inches long.
Yard is defined as the distance between the two central
transverse lines on the two golden plugs at 62° F, and is
equal to 36 inches.
Now-a-days, English system is limited in use.
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48. Imperial Standard Yards
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49. 2. Metric system
 Also known as international standard system.
 Based on the “International prototype meter”.
 This meter was setup in the year 1872 and is maintained by
the International Bureau of Weights and Measures in
France.
 The prototype meter is made of pure platinum-iridium
alloy (90% platinum & 10% iridium) of 1020 mm total
length and having a cross section as shown in fig.
 One meter is defined as the distance between the two fine
lines engraved over upper surface of the web, when
measured at a temperature of 0°C.
 This system has been adopted in India.
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50. International Prototype Meter
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51. Disadvantages of Material Standards
 1. Material standards are affected by changes in
environmental conditions such as temperature, pressure,
humidity, and ageing, resulting in variations in length.
 2. Preservation of these standards is difficult because they
must have appropriate security to prevent their damage or
destruction.
 3. Replicas of material standards are not available for use
at other places.
 4. They cannot be easily reproduced.
 5. Comparison and verification of the sizes of gauges pose
considerable difficulty.
 6. While changing to the metric system, a conversion factor
is necessary.
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52. Wave Length Standard
 The 11th General Conference of Weights and Measures,
which was held in Paris in 1960, recommended a new
standard of length, known as wavelength standard, which
is highly accurate and is very small unit of measure.
It was decide that Krypton 86 is used in a hot cathode
discharged lamp maintained at 68 °K temperature
generates orange radiation can be used as ultimate
wavelength standard.
 According to this standard, metre is defined as 1,650,763.73
× wavelengths of the red–orange radiation of a krypton 86
atom in vacuum.
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53. Advantages of Wave Length Standard
It is not a material standard and hence it is not
influenced by effects of variation of environmental
conditions like temperature, pressure and
humidity.
 It need not be preserved or stored under security and
thus there is no fear of being destroyed as in case of
meter and yard.
 It is not subjected to destruction by wear and tear.
 This standard is easily available to all standardizing
laboratories and industries.
 Used for comparison with high accuracy.
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54. Wave Length Standard
Disadvantages:
 Maintenance cost is high.
 Requires accurate wavelengths of spectral radiation.
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55. Subdivision of standards
Depending upon the degree of accuracy required
for the work, the standards are subdivided into
four categories or grades:
 1. Primary standards
 2. Secondary standards
 3. Territory standards
 4. Working standards.
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56. 1. Primary standards
 They are material standard preserved under most careful
conditions.
 These are used once in 10 to 20 years for calibration and
verification of secondary standards.
These are maintained at the National Standards
Laboratories in different countries.
For India, it is National Physical Laboratory at New
Delhi.
 The primary standards are not available for the use out side
the National Laboratory.
 Example: Imperial Standard Yard, International prototype
meter, and international prototype of the kilogram (IPK)
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57. 2. Secondary standards
Secondary standards are made as nearly as possible
exactly similar to primary standards as regards design,
material and length.
They are compared with primary standards after long
intervals and the records of deviation are noted.
These standards are kept at number of places for safe
custody.
They are used for occasional comparison with tertiary
standards whenever required.
 e.g: voltmeter, a glass thermometer and pressure
gauge are examples of secondary instruments.
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58. 3. Territory standards
The primary and secondary standards are applicable
only as ultimate control.
Tertiary standards are the first standard to be used for
reference purposes in laboratories and workshops.
They are made as true copy of the secondary
standards.
They are used for comparison at intervals with
working standards.
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59. 4. Working standards.
These standards are similar in design to primary,
secondary and territory standards.
But being less in cost and are made of low grade
materials they are used for general applications in
Metrology Laboratories.
Both line and end working standards are used.
For example, manufacturing of mechanical
components such as shafts, bearings, gears etc, use a
standard called working standard for checking the
component dimensions.
Example: Plug gauge is used for checking the bore
diameter of bearings.
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60. Some times standards are also classified as:
1. Reference standards- Used for reference
purposes.
2. Calibration standards - Used for calibration of
inspection and working standards.
3. Inspection standards - Used by inspectors.
4. Working standards - Used by operators, during
working.
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61. Types of Measurement Standards
A length may be measured as the distance between
two lines or at the distance between two parallel
faces.
So, the instruments for direct measurement of
linear dimensions fall into two categories.
1. Line standards.
2. End standards.
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62. 1. Line standards
When the length is measured as the distance between
centers of two engraved lines, it is called line standard.
Both material standards yard and meter are line
standards.
Example: Steel rule with divisions shown as lines
marked on it.
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63. 2. End standards.
When length is expressed as the distance between two
flat parallel faces, it is known as end standard.
 Examples: Measurement by slip gauges, vernier
calipers etc.
 The end faces are hardened, lapped flat and parallel to
a very high degree of accuracy.
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64. Comparison between Line and End Standard
SL
No
Line Standard End Standard
1 Length is expressed as the
distance between two lines.
Length is expressed as the distance
between two flat parallel faces
2 They are accurate up to ±0.2 They are accurate up to ±0.001
3 Measurement is quick and easy Requires skill and is time-consuming.
4 Less costly More costly
5 Parallax error can occur They ate not subjected to parallax
error
6 Scale markings are not subject to
wear. However, significant wear
may occur on leading ends.
These are subjected to wear on their
measuring surfaces
7 Manufacturing is simple Manufacturing is complex
8 E.g. Steel rule E.g. Micrometer
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65. ERRORS IN MEASUREMENTS
 It is never possible to measure the true value of a
dimension there is always some error. The error in
measurement is the difference between the
measured value and the true value of the
measured dimension.
 Error in measurement = Measured value – True
value
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66. Classification of Errors
Generally errors are classified into two types:
systematic errors, random errors but they are broadly
classified as :
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67. Gross errors
Instrumentation misuse, calculation errors and other
human mistakes (i.e. mistakes in reading, recording data
results) are the main sources of Gross errors.
Gross error mainly occur due to carelessness or lack of
experience of a human being or incorrect adjustments of
instruments.
Example: A person may reads a pressure gauge indicating
1.01 N/m2 as 1.10 N/m2 .
Elimination: These errors can be minimized by
 1.Taking great care while taking reading, recordings and
calculating results.
 2. Taking multiple readings preferably by different
persons.
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68. Measurement errors: The measurement error is
the result of the variation of a measurement of the
true value. Usually, Measurement error consists of
a random error and systematic error.
Example: The best example of the measurement
error is, if electronic scales are loaded with 1000
grams standard weight and the reading is 1002
grams, then
The measurement error is = (1002 grams-1000
grams) = 2 grams
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69. Blunder
Blunders are final source of errors.
These errors are caused by faulty recording or due
to a wrong value while recording a measurement,
or misreading a scale or forgetting a digit while
reading a scale.
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70. Systematic Error
The Systematic errors (controllable error) are of
constant or similar forms that occur due to fault in the
measuring device or environmental condition etc.
These errors can be removed by correcting the
measurement device.
Systematic errors can be classified as:
 Instrumental Errors
 Environmental Errors
 Observational Errors
 Theoretical Errors
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71. Instrumental Errors:
 These errors are mainly due to following four reasons:
 Shortcoming in the instrument-these are because of the
mechanical structure of the instruments, e.g. friction in the
bearings of various moving parts, irregular spring tensions,
gear backlash etc.
 Elimination
-Selecting proper instruments for the measurements
-Recognize the effect of such errors and apply the proper
correction factors.
-Calibrate the instrument carefully against standard.
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72. Environmental Errors(due to the external
condition)
 External conditions mainly include: Temperature
changes, Pressure, Vibration, Humidity, Dust, External
magnetic fields, Aging of equipments etc.
Elimination
 Using proper correction factors and using the
instrument catalogue.
 Using the Temperature & Pressure control methods
etc.
 Reducing the effect of dust, humidity on the
components in the instruments.
 The effect of external fields can be minimized by using
the electrostatic shields of screens.
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73. Observational Errors
 This errors are produced by observer
 Few sources are:
1. wrong observations or reading in the instruments
2.Parallax error while reading the meter.
2.Inaccurate estimate of average reading.
3.Wrong scale reading and wrong recording the data.
4.Incorrect conversion of units between consecutive
readings.
Elimination
 Taking two or more readings repeatedly.
 Instrument having digital display.
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74. Theoretical Errors
 Theoretical errors are caused by simplification of
the model system.
 For example, a theory states that the temperature
of the system surrounding will not change the
readings taken when it actually does, then this
factor will begin a source of error in measurement.
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75. Random Errors (Uncontrollable Error)
Random errors are caused by the sudden change in
experimental conditions and noise and tiredness
in the working persons.
An example of the random errors is during
changes in humidity, unexpected change in
temperature and fluctuation in voltage.
These errors may be reduced by taking the average
of a large number of readings.
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76. Comparison between Systematic Errors and Random Errors
Systematic error Random error
1.These errors are repetitive in nature
and are of constant and similar form.
1.These are non-consistent. The sources
giving rise to such errors are random.
2.These errors result from improper
conditions or procedures that are
consistent in nature
2. Such errors are inherent in the
measuring system or measuring
instruments.
3. Except personal errors, all other
systematic errors can be controlled in
magnitudes and sense.
3. Specific causes, magnitudes and sense
of these errors cannot be determined
from the knowledge of measuring
system or condition.
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77. Comparison between Systematic Errors and Random Errors
Systematic error Random error
4. If properly analyzed these can be
determined and reduced or
eliminated.
4.These errors cannot be
eliminated, but the results obtained
can be corrected.
5.These include calibration errors,
variation in contact pressure,
variation in atmospheric conditions,
parallax errors, misalignment errors
etc.
5.These include errors caused due to
variation in position of setting
standard and work-piece, errors due
to displacement of lever joints of
instruments, errors resulting from
backlash, friction etc.
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78. Factors in selecting the measuring instruments
 The following are factors considered while selecting
measuring instrument:
 1. The important factor to be considered in selection of
measuring instrument are its measuring range,
Accuracy and Precision.
 2. For better results instruments with higher accuracy
is selected.
 3. Precision is also very important feature for any
measuring instrument because it provides repeatable
readings.
 4. The sensitivity of that instrument should remain
constant through the range of its measurement.
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79. Factors in selecting the measuring instruments
 5. Minimum inertia in the moving parts of the mechanism.
The effect of inertia is to make the instrument sluggish
(slow moving).
 6. The time taken to display the final data. (as less as
possible).
 7. The type of data displayed. (Analog or digital or
photograph)
 8. The cost of measuring instrument.
 9. Type of quantity to be measured constant or variable.
 10. Nature of quantity being measured hot or cold
 11. Resistance to environmental disturbance.
 12. Simplicity in calibration when needed.
 13. Safety in use.
 14. Adoptability to different sizes.
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80. THANK YOU
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