This document provides an overview of measurement and instrumentation concepts for a mechanical engineering course. It defines key terms like variable, parameter, measurement system, and experimental test plan. It describes the four main elements of a measurement system: the sensing element, signal conditioning element, signal processing element, and data presentation element. Specifically, it gives examples of common sensors, transducers, and ways of presenting measurement data. The overall purpose is to introduce students to the fundamental principles and components involved in taking mechanical measurements.
1. University of Engineering and Technology Taxila
Mechanical Engineering Department
Lecture No: 01
Course Title: Measurement and Instrumentation
(ME-314)
Tutor: Khalid Masood Khan
3. Variable
• Variable is the quantity targeted for
measurement
• It can be independent or dependent,
continuous or discrete
• Engineering variables such as displacement,
pressure, strain, or temperature are
continuous
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4. …continued
• A variable is controlled if it can be held
at a constant value or at some prescribed
condition during a measurement
• Variables that are not or cannot be
controlled during measurement but
affect the value of the variable measured
are called extraneous variables
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5. Parameter
It is a functional relationship between variables.
Example is a fan flow coefficient (C1).
C1 = Q / (nd3) = f (Q, n, d)
Where
Q = flow rate
n = fan rotational speed
d = fan diameter
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6. Measurement
• The process of quantifying a parameter
• An act of assigning a specific value to a
physical variable
• Objective is to establish the value or
the tendency of some variable
• Determination of amount/extent of a
physical variable
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7. Mechanical Measurement
• Every thing that exists is related to the
practice of mechanical engineering
• The determination of the amount/extent
constitutes the subject of mechanical
measurement
• The means to achieve the measurement
may or may not be mechanical
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8. Significance of Mechanical Measurement
• An essential activity in every branch of
science and technology
• Allows monitoring and control of processes and
operations
• Temperatures, flows, pressures, and vibrational
amplitudes monitored by measurement to
ensure proper system performance
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9. • Allows experimental engineering analysis
• Measurement is one of the important basic
subjects for engineers and scientists
• Measurement and the correct interpretation
thereof are necessary parts of any engineering
and development program
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10. …continued
• All research, design and development is
based on measurement
• The experimental element of a product/process
development is based on measurement
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11. Experimental Test Plan
• Conceptualize the factors that influence the test
• Plan the experiment around these factors
• Define test objectives
• Identify process variables, parameters,
and means for their control
Continue…
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12. …continued
• Define tolerances for errors
• Select measurement technique, equipment,
and test procedure
• Plan in advance on how to analyze,
interpret, and present the expected data
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13. True Value and Measured Value
• The input to the measurement system
is the true value of the variable called
measurand
• Output is the measured value
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14. Act/Process of Measurement
• Obtaining a quantitative comparison between
a predefined standard and a measurand
• The act of measurement produces a result
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15. System
A system is composed of components
that work together to accomplish a
specific task.
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16. Measurement System
• A measurement system is an information system
which presents an observer with a numerical
value corresponding to the variable being
measured.
• Measurement system is meant to include
all components in a chain of hardware
and software that leads from the measured
variable to processed data.
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17. Measurement System Elements
There are four types and, in a system, one type
of element may be missing or may occur more
than once.
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19. 1. Sensing Element (The Sensor)
The sensor is a physical element that uses some
natural phenomenon to sense the variable being
measured.
Examples:
• Energy exchange between the liquid (the
sensor) contained in the bulb of a
thermometer and the surrounding air is the
input signal
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20. …continued
• Thermocouple is the sensing element
that measures temperature
• Load cell in a strain gauge is the sensing
element that is used to measure mechanical
strain
• Orifice plate is the sensing element
that is used to measure the flow rate
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21. 2. Signal Conditioning Element (The
Transducer)
• The transducer takes output from the sensing
element and converts it into a form more
suitable for further processing. The transduced
signal form might be electrical, mechanical,
optical, etc.
Continue…
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22. • Transducer may include both sensing and
signal processing units. Each element in
the measurement system may itself be a
system made up of simpler components.
Continue…
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23. Examples:
• Thermal expansion forces the liquid into the
narrow capillary (transducer) of the bulb
thermometer. It transforms thermal information
into a mechanical displacement.
• Deflection Bridge converts an impedance
change into a voltage change
Continue…
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24. …continued
• Amplifier amplifies millivolts to volts
• Oscillator converts an impedance change
into a variable frequency voltage
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25. 3. Signal Processing Element
Takes the output of the conditioning element/
transducer and converts it into a form more
suitable for presentation.
Example:
• Analogue-to-Digital-Converter takes
analogue signal as input and converts it to
digital form for input to a computer.
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26. 4. Data Presentation Element
Presents the measured value in a form which
can be easily recognized by the observer.
Examples:
• A simple pointer-scale indicator
• Chart recorder
• Alphanumeric display
• Visual display unit
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