NAME : MOHD ZULKIFLI RAMLI
ROOM : Power Electronics and Drives Research
lab
EMAIL : mohd.zulkifli@utem.edu.my
Principles of Instrumentation &
Measurement
BEKG 1233
Learning Outcomes (chapter 1)
Able to define various measurement and instrument principles,
application, terms and standards.
Able to define and explain the following types of errors that
occur in measurements: gross, systematic, random.
Able to use basic statistical methods for analyzing
measurement errors, accuracy, precision and limiting error.
Able to describe types of noise occur in measurement, effects
and reduction techniques.
Introduction
Instrument is a device or mechanism used to determine
the value or magnitude of a quantity under observation.
Electronic instrument is based on electrical or electronic
principles for its measurement functions.
Instrumentation system is a physical system, which is
collection of physical objects connected in such a way to
give the desired output response. May be defined as an
assembly of various instruments and other components
interconnected to measure, analyze and control the
electrical, thermal, hydraulic and other non-electrical
physical quantities.
Introduction
An instrument may serve three basic functions:
Indicating-Indication of the value parameter under
observation. (e.g. Oscilloscope, Instrument with a scale
and moveable pointer or maybe digital instrument)
Recording- To provide a permanent graphic record of
variation in value of the parameter under observation with
respect to time. (e.g. Strip chart recorders )
Controlling- To provide control of the system being
monitored. (e.g. An automatic control system)
Introduction
Measurement is the process of determining the amount,
degree or capacity by comparison with the accepted standards
of the system units being used.
The physical embodiment of the unit of measurement as well
as that of its submultiple or multiple value is called a
Standard.
The device used for comparing the unknown quantity with the
unit of measurement or a standard quantity is called A
Measuring Instrument.
Measurement
Indirect measurement methods
the unknown quantity is determined by measuring other
functionally related quantities and calculating the desired
quantity rather than measuring it directly with an
instrument
Used of formula
eg:- resistance of a conductor may be determined by
measuring voltage across the conductor, V and current
flowing through the conductor, I and calculating by Ohm’s
law :
Measurement
Direct measurement methods
Deflection methods
the value of unknown quantity is determined by means of
measuring instrument having a scale graduated to the quantity
under measurement directly such as measurement of current
with an ammeter.
Measurement
Direct measurement methods
Comparison methods
the unknown quantity is determined by direct comparison with
a standard of the given quantity such as measurement of emf by
comparison with the emf of a standard cell.
Include null method, differential method etc.
Measurement
Null measurement method: measuring current and voltage
more accurately by balancing the circuit so that no current
flows through the measurement device (using potentiometer
and Wheatstone bridge).
Standard measurements of voltage and current alter circuits,
introducing numerical uncertainties. Voltmeters draw some
extra current, whereas ammeters reduce current flow. Null
measurements balance voltages, so there is no current flowing
through the measuring device and the circuit is unaltered.
Null measurements are generally more accurate but more
complex than standard voltmeters and ammeters. Their
precision is still limited
SI Units
Nature of units
In engineering quantities of different kinds are involved
including physical, chemical, mechanical, thermal, electrical,
physiological and etc.
In order to record or to compare magnitude of quantities, some
one magnitude of each kind must be taken as basis or unit.
Each unit either must be represented by a physical standard of
some kind, natural or artificial or must be derived from a
combination of other units represented by such standards.
SI Units
Fundamental quantities of the SI system
SI stands for “Systeme International d’ Unites” in French.
This abbreviation is now adopted by the International
Standardizing Organization as the abbreviated name of
this new system of units in all languages.
The SI system is a comprehensive, logical and coherent
system, designed for use in all branches of science,
engineering and technology.
SI system consist of 28 units :- 7 base units, 2 addition
units and 19 derived units.
SI Units
This system derives all the units from the following base
units:
Dimensions
Dimensions
A derived unit is recognized by the dimensions and can be
defined as the complete algebraic formula for the derive unit.
Dimension equation help:
In conversion from on system of units to another one
In derivation of equations for physical quantities
In checking the accuracy of an equation
For convenience, some derived units have been given new
names such as the derived unit of force in the SI system is
called Newton (N) instead of dimensionally correct name kg-
m/s2.
Dimensions
Example:
Find the dimension of derived units below:
Dimensions
Standards of Measurements
A standard of measurement is a physical representation of a
unit of measurement. A unit is realized by reference to an
arbitrary material or to natural phenomenon including physical
and atomic constant.
A standard is a known accurate measure of physical quantity.
Standards are used to determine the values of other physical
quantities by the comparison method.
Four categories of standard:
International Standard
Primary Standard
Secondary Standard
Working Standard
Categories of Standards
International Standards
Defined by international agreement and they represent
certain units of measurement to the closest possible
accuracy that production and measurement technology
allow. These standards are periodically evaluated and
checked by absolute measurements in terms of
fundamental units. These standards are maintained at the
International Bureau of Weight and Measures in Paris.
Categories of Standards
Primary Standards
Main function of primary standards is the verification and
calibration of secondary standards. These standards are
maintained at national standards laboratories in different
countries. These are calibrated independently by absolute
measurements at each of the national laboratories. The results
of such measurements are compared against each other, leading
to a world average figure for the primary standards. Primary
standard are not available for used outside the national
laboratories.
For example in Malaysia, this function is carried out by SIRIM.
Categories of Standards
Secondary Standards
These standards are the basic reference standards used by
measurement and calibration laboratories in the
industry to which they belong. Each laboratory
periodically sends its secondary standards to the primary
standards in national standard laboratories. After calibrate
the secondary standards are returned to the industrial
laboratory with certification of measuring accuracy in
term of a primary standard.
Categories of Standards
Working Standards
The principle tools of a measurements laboratory. They are
used to check and calibrate the instruments use in the
laboratory or to make comparison measurements in industrial
application.
For example, manufacturers of electronic components such as
capacitors, resistors and many more use a standard called a
working standard for checking the component values being
manufactured.
Categories of Standards
Summary
Standard of Electrical Measurements
SI Electrical Units can be divided into five (5) :-
Current Standard
Voltage Standard
Resistance Standard
Inductance Standard
Capacitance Standard
Standard of Electrical Measurements
Current Standard
Electric current (I) is known as a flow of charge carriers.
Therefore, current could be defined as the quantity of
electricity (Q) that passes a given point in a conductor during
a time of 1 second.
Coulomb (C) is refer to unit of electrical charge or quantity of
electricity. It was the fundamental electrical unit from all other
units were derived.(1 coulomb ~ 6.24 x 1018 electrons)
Since, to measure current accurately is much easier than to
measure charge, the unit of current is now become the
fundamental electrical unit in the SI system.
Standard of Electrical Measurements
Unit of electric current ~ ampere (A)
The Ampere is defined as constant current when flowing in each of
two infinitely long parallel conductors 1 meter apart, exerts a force
of 2 x 10-7 Newton per meter of length on each conductor.
While, the coulomb is defined as the charge which passes a given
point in a conductor each second, when a current of 1 ampere flows.
Hence, the coulomb could be termed an ampere-second, or the
ampere can be describe as a coulomb per second
Standard of Electrical Measurements
Voltage Standard
The volt (V) is defined as the potential difference between two
points on a conductor carrying a constant current of 1 ampere
when the power dissipated between these points is 1 watt. Volt
(V) is the unit of electromotive force (emf) and potential
difference.
(1 Watt = 1 Joule/s)
Volt = Watt / Ampere
Watt = J/S = Power
Joule = N/m = Work / Energy
Newton = kg.m/s2
Standard of Electrical Measurements
1 joule of work is consider done when 6.24 x 1018
electrons (1 coulomb) are move through a potential
difference of 1 V. One electron carries a charge of
1/(6.24 x 1018 ) coulomb. When only 1 electron moved
through 1V, the energy involved known as electron volt
(eV).
eV is used in the case of very small energy level
associated with electrons in orbit around the nucleus of an
atom.
Standard of Electrical Measurements
Resistance Standard
The ohm (Ω) is the unit of resistance. Ohm is defined as
the resistance which permits a current flow of 1 ampere
when a potential difference of 1 volt is applied to the
resistance.
Resistance (R) = Voltage (V) / Current (I)
Standard of Electrical Measurements
Inductance Standard
The henry (H) is the unit of inductance. The inductance of a
circuit is 1 henry, when an emf of 1 volt is induced by the
current changing at the rate of 1 A/s.
The weber (Wb) is the unit of magnetic flux. Weber defined
as the magnetic flux which, linking a single-turn coil, produces
an emf of 1 V when the flux is reduced to zero at a constant
rate in 1s.
While Tesla (T) is the unit of magnetic flux density. Tesla is
the flux density in a magnetic field when 1 weber of flux
occurs in a plane of 1 square meter. Tesla ~ 1 Wb/m2.
Standard of Electrical Measurements
Therefore,
1 H = 1 Wb / 1 A
1 Wb = 1V x 1 s
Hence, Inductance , L = (4π2 x 10-7N2r2) / l
Where :
N is no. of wire turn
r is solenoid radius in meter
l is length of solenoid in meter
Standard of Electrical Measurements
Capacitance Standard
The farad (F) is the unit of capacitance. The farad is the
capacitance of a capacitor that contains a charge of 1
coulomb when the potential difference between its
terminal is 1 volt.
1 Farad = 1 Coulomb / 1 volt
where
1 Q = 1 Ampere x 1 s
Note* Q is refer to the charge carried by one electron
What’s next?
Performance characteristics
Accuracy, precision, sensitivity, errors etc
Error in measurement
Absolute error, relative accuracy, precision
Types of errors
Gross error/human error, Systematic Error, Random Error
Statistical analysis
Arithmetic mean, deviation, average deviation, standard deviation
Limiting error
