Instrumentation and Electrical Measurements
EE 300
Lecture 1
INTRODUCTION TO MEASUREMENT
Dr. Fahad Alsunaydih
System of Units
• The unit of measurements can be expressed as a standard quantity
used to describe a physical quantity.
Example : meter
• It can be defined by convention or by law.
• Unit is the basic quantity in a given system of measurement.
• Any other value of the physical quantity is expressed as a simple
multiple of the unit of measurement.
System of Units
• Two types of units are used in science and engineering
• Fundamental units (Primary)
length
mass
time
• Fundamental units (Auxiliary)
Current
Thermodynamic temperature
Amount of a substance
Luminous Intensity
( meter)
(kilogram)
(second )
(Ampere)
(Kelvin)
(Mole)
(Candela)
• Derived units All units which can be expressed in terms of fundamental units
Every derived unit originals from some physical law defining that unit.
• E.g. The volume of a substance is proportional to its length (l), breadth (b) and height (h), or V= l x b x h.
• So, the derived unit of volume (V) is cube of meter (m3).
System of Units
The international system of units (SI) or MKSA (meter kelvin second
ampere) system contains the units of 6 fundamental quantities from
which the units of all quantities can be derived.
System of Units
The English system of units uses foot(ft), pound.mass(lb) and second(s)
as three fundamental units of length, mass and time respectively.
System of Units
System of Units
An example of determining the dimensions of units.
It is clear that all the fundamental units have one dimension,
now you can easily find out the fundamental units from the
table!
Scientific Notation and Metric Prefixes
• Numbers can be rewritten in different forms rather than the normal
way of writing them.
• Scientific notation is very useful to represent large numbers or small
numbers.
Scientific Notation and Metric Prefixes
Measurements standards:
• Measurement standards are considered as physical representation of the
units.
• The measurement instruments used Measurement standards as a reference
for calibration.
• The classification of standards of measurement are:
1. International standards.
2. Primary standards/national standards.
3. Secondary standards.
4. Working standards.
Measurements standards:
1- International standards.
• It is an international agreement.
• These standards are maintained at the international bureau of weight
and measures in Paris (BIPM).
• They are not available to the ordinary users for the calibration purpose.
International Prototype Metre bar
International Prototype Kilogram
Measurements standards:
2- Primary standards/national standards.
• These are highly accurate absolute standards (Reference Standards).
• They are held at national standard laboratories.
• They are not commonly in use.
• It is used for the calibration and verification of secondary standards.
Measurements standards:
3- Secondary standards.
• They are mostly as accurate as the primary standards (calibration
standards).
• Each industry has its own secondary standard.
• Each laboratory periodically sends its secondary standard to the
National standards laboratory for calibration and comparison against
the primary standard.
• After comparison and calibration, the National Standards Laboratory
returns the secondary standards to particular industrial laboratory with
a certification of measuring accuracy.
Measurements standards:
4- Working standards.
• Working standards are the primary tools that can be used to calibrate
the accuracy and the performance of the instruments used in lab.
Definition of Measurement
• It is the process of determining the amount of a quantity or a variable
by comparing them with reference standard.
• Measurement tell us about property of something.
• Measurement provide us with a means of describing various
phenomena in quantitative terms and meaningful numbers.
• In order to distinguish between the meaningful numbers, we use
UNITS to differentiate between different phenomena.
Elements of a measurement system
• The measuring system can consist of only a single unit that gives an
output reading or signal according to the magnitude of the unknown
variable applied to it.
• In more complex measurement situations, a measuring system consists
of several separate elements.
• These components might be contained within one or more boxes, and
the boxes holding individual measurement elements might be either
close together or physically separate.
Elements of a measurement system
• The first element in any measuring system is the primary sensor: this gives an output that is a function of the
measurand (the input applied to it).
• For most cases, this function is at least approximately linear.
Elements of a measurement system
• If output variable of a primary sensor is in an inconvenient form and has to be converted to a more convenient
form.
• For instance, the displacement-measuring strain gauge has an output in the form of a varying resistance. The
resistance change cannot be easily measured and so it is converted to a change in voltage by a bridge circuit.
Elements of a measurement system
• If the primary sensor and variable conversion element are combined, and the
combination is known as a transducer
Elements of a measurement system
• Signal processing elements exist to improve the quality of the output of a
measurement system in some way.
• A very common type of signal processing element is the electronic amplifier, which
amplifies the output of the primary transducer or variable conversion element, thus
improving the sensitivity and resolution of measurement.
Elements of a measurement system
• This element of a measuring system is particularly important where the primary
transducer has a low output.
• For example, thermocouples have a typical output of only a few millivolts. Other
types of signal processing element are those that filter out induced noise.
Elements of a measurement system
• Signal transmission is needed when the observation or application point of the
output of a measurement system is some distance away from the site of the primary
transducer.
Elements of a measurement system
• The final stage is to store the received data and present it at any required form
(LCD display, meter etc.).
Measurement system applications
• Present-day applications of measuring instruments can be classified into three major areas.
1- Applying instruments that measure physical quantities such as length, volume and mass in terms of standard units.
2- The second application area of measuring instruments is in monitoring functions as they provide information that
enable human beings make decisions. Whilst there are thus many uses of instrumentation in our normal domestic lives,
but majority of the monitoring functions exist to provide information necessary to allow us to control some industrial
operation or process. Another important use of monitoring instruments is in calibrating the instruments used in the
automatic process control systems described below.
Measurement system applications
3- Use as part of automatic feedback control systems forms the third application area
of measurement systems.
Ta is the room Temperature
Td is the reference Temperature
References :
1- A. S. Morris, Measurement and instrumentation: Theory and application,
Waltham, MA: Academic Press, 2001.
2- D. A. Bell, Electronic instrumentation and measurements. Oxford: Oxford
University Press, 1997.