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Information
Course : “ME-308 - Measurements and Instrumentation”
Location: SE-210
Course Credits: 2+0
Time table: As circulated by Course Coordinator
Tuesday : 9:30-10:25
Wednesday: 10:35 – 11:30
Semester: Jan 27, 2014 till May 16, 2014
Text Book:
“Measurement and Instrumentation Principles” Alan S.
Morris
\\172.30.10.2\learning material\ Javaid Khurshid Dr.\
Introduction
Why do we need measurement?
If I cultivate “Oranges” How many do I need to give
to get clothes / Goat etc?
How can I seek an advice from a doctor?
What should be the standards of interconversion?
Why need measurement?
To understand an event or an operation.
To monitor an event or an operation.
To control an event or an operation.
To collect data for future analysis
To validate an engineer design.
Measurement Methods
Direct comparison method
We have a standard and we compare to measure
Length of a bar (using ruler)
Weight of rice (measuring bots)
Indirect comparison method
We measure the quantity by converting it into another
form
Measurement of temperature using expansion of liquid in
a glass tube
Earlier measurement methods Earlier:
Length
Unit of Hand
Foot
Cubit
Weight
Grain of wheat
Time
Temperature
Problems:
Measured using body parts.
All measurements were imprecise
Standards vary from one place to other
Standards even vary from one person to other
Units : Today
There are many units which had to be defined with
the development in technical fields.
Units should be standardized
New units must be incorporated
Unit conversion should be possible
Now we have the units as
Basic Units (Length, Time etc)
Derived Units (Speed, Acceleration etc)
Standardization in Units
SI (System International) Unit
Length (m), Weight (gm)…
British System (Foot, Pound, Second)
Length (ft), Weight (lb)…
MKS system (Meter, Kilogram, Second)
Any other system
Need interconversion methods
Some Standard Units
Fundamental Units
Supplementary Fundamental Units
De
rive
d U
nits
Unit Conversion
Applications of Measuring Systems
Present day applications of measuring instruments
are classified in three categories.
1. In regulating trade, by measuring physical quantities
such as length, volume and mass in terms of standard
units.
2. Monitoring functions
3. Automatic feedback control systems
Simple Temperature Control System
Elements of a simple closed loop control system
Elements of a measurement system
A measuring system provides information about the physical value of some variable being measured.
The system can consist of a single unit that gives an output signal/reading.
In complex case, the system consists of several separate elements as shown below
Elements of a measurement system
1. Sensor
2. Variable Conversion Element
3. Signal Processing Element
4. Signal Display / Recording Element
Optional Elements
1. Signal Transmission
2. Utilization of measured signal (e.g. Control part of a
system)
1- Sensor
Gives an output that is a function of the measurand.
Measures the physical quantity
Mostly the output is approximately linear
Examples:
Liquid in glass thermometer
Thermocouple
Strain gauge
2 – Variable Conversion Element
Output of the primary sensor is in inconvenient form.
It has to be converted for convenient form.
Example (Temperature using expansion of liquids)
change of resistance of thermocouple with change in
temperature
The resistance change has to be converted into voltage
using bridge circuit etc.
3 – Signal Processing Element
The output of a sensor is very weak that has to be
identified correctly
There is noise in the sensors output
Example (ECG data)
Amplification of the signal
Filtration of the required signal
4 – Signal Transmission Element
Signal transmission is needed when the observation
of the measurement system is far from the primary
sensor.
Example:
Measurement of temperature of a volcano
Measurement of radiation from a nuclear accidental
location
5 – Signal Display / Recording
Signal has to be displayed
Example: Display temperature on LEDs / display monitor
Signal may be recorded
Example: Recording of temperature for analysis and
prediction of rain, storm etc
Selection of Measurement System
The suitable instrument for measuring a particular
quantity depends on many parameters like
Cost
Resolution
Sensitivity
Dynamic performance
Ruggedness
Durability
Maintenance requirement etc
Example: Measuring temperature of a plant,
environment, Volcano need different type of
temperature sensitive devices
Assignment
Dead line (Feb 12m 2014) in Power point format Definition of the unit
Basic / Derived Unit
Name in different systems of units including the ancient/old systems (Indian, British, Roman, Arabic, Japanese etc)
Unit symbols
Length, Mass, Volume, Time, Temperature,
Current, Voltage, Inductance, Resistance, Capacitance,
Force, Pressure, Torque, Force, Frequency,
Electric Charge, Electric Flux, Power, Luminance, Gravity
Paper sizes (A4, A3,…etc), Radiation dose, Metal thickness gauge, wind speed, monitor resolution
Internet speed, Energy, Karat, earthquake intensity, Viscosity
