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Metrology Metrology
MEEG 219
How much sand?
Module I : General Measurement Concept
Lecture 1 : Introduction to Measurement Pressure?
Bijendra Shrestha Furnace Temperature? Height?
Lecture 1: Measurement 2
Metrology Metrology
What is Metrology?
• Science of measurement
• Purpose:
– To establish means of
determining physical
quantities, such as
dimensions, temperature,
force, etc.
But what is Measurement?
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General Measurement Concept General Measurement Concept
What is Measurement? What is Measurement?
• Act or the result of a
Quantitative Comparison Predetermined Standard
between a
predetermined standard
and an unknown
magnitude.
Unknown magnitude
-Obtain the qualitative information about a physical object
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General Measurement Concept
Element of Measurement
• “ A is longer than B” – Statement incomplete, 1. Measurand : Physical quantity or property like
until and unless we answer how much length, angle, diameter, thickness etc to be
measured.
• Must be able to express this difference in 2. Reference : Physical quantity or property to
quantitative terms i.e, in terms of numbers. which qualitative comparisons are made.
3. Comparator : means of comparing measurand
with some reference.
Note: Measuring device/process need to be calibrated against a Standard Calibration
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General Measurement Concept
Standard
Primary Standard
• Basic element of measurement without which no • Highest standard
measurement is possible.
• Copies of international
• Standard is something that is set up and prototypes
established by authority as a rule for the
measurement of quantity, weight, extent, value • Kept throughout world
or quality etc. in National
• standard laboratories
– Primary • Eg: International
– Secondary Prototype Kilogram One kilogram mass of a
platinum-iridium alloy
– working (IPK) as in fig maintained by Bureau
International des Poids et
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General Measurement Concept General Measurement Concept
Secondary Standard Working Standard
• Calibrated from • Standard one order
Primary Standard less than Secondary
• References kept standards
measurement • Used by workers and
laboratories & technicians for actual
industrial measurement
organizations One kilogram mass of a One kilogram mass of a
platinum-iridium alloy platinum-iridium alloy
maintained by Bureau maintained by Bureau
International des Poids et International des Poids et
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General Measurement Concept General Measurement Concept
Primary Standard
What about Errors?
• Difference between the true value of
(National Standard)
measurand and measured value
Secondary Standard • Error = True value – Measured value
(Industrial Reference)
Working Standard
(Worker Reference)
Each standard should be 10X accurate than the next standard
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General Measurement Concept
Types of Errors
• Gross Errors
• Systematic Errors
• Random Errors
To be cont….
Lecture 1: Measurement 15
