Dr.

/ Abdelhady Ghanem

Electrical Measurements
ELE243
Prepared by Dr./ Abdelhady Ghanem
Presented by Dr./ Mohamed Elgohary

Lec. №: (1)
 Dr./ Abdelhady Ghanem

Department: Electrical Engineering

Name: Dr. Mohamed Elghary
Mobile: +2 01144272186
E-mail: mohamedyae1919@mans.edu.eg
 ‫‪Dr./ Abdelhady Ghanem‬‬

‫محظورات المحاضرة‬

‫‪ -1‬اآلراء السياسية‬

‫‪ -2‬اآلراء الدينية‬

‫‪ -3‬اآلراء الرياضية‬

‫‪ -4‬الكالم الجانبي‬

‫‪ -5‬استخدام الهاتف‬

‫‪3‬‬
 Dr./ Abdelhady Ghanem

Course Description
 Dr./ Abdelhady Ghanem

Course Description (cont’)

– Points:
➢ Attendance
➢ Reports
➢ Sheets
➢ Quiz + Random Quiz
➢ Mid-Term Exam
➢ Final Exam
 Dr./ Abdelhady Ghanem

Chapter (1)

Introduction
 Dr./ Abdelhady Ghanem

Introduction

Measuring is basically used to monitor a process or operation, or as well as

the controlling process.

For example, thermometers, barometers, anemometers are used to indicate

the environmental conditions.

Similarly, water, gas and electric meters are used to keep track of the
quantity of the commodity used, and also special monitoring equipment are
used in hospitals.
 Dr./ Abdelhady Ghanem

What is Measurement?
Measurement
➢ Measurement (also called metrology) is the science of determining values
of physical variables.
➢ Comparison between a standard and what we want to measure (the
measurand).
➢ Two quantities are compared the result is expressed in numerical values.
Instrumentation
➢ Devices used in measurement system

Basic requirements for a meaningful measurement

➢ The standard used for comparison purposes must be accurately defined
and should be commonly accepted.
➢ The apparatus used and the method adopted must be provable (verifiable).
 Dr./ Abdelhady Ghanem

Examples of Standard Bodies

➢ International Organization for Standardization (ISO).

➢ International Electro-technical Commission (IEC).

➢ American National Standards Institute (ANSI).

➢ Standards Council of Canada ( SCC).

➢ British Standards (BS).

➢ Institute of Turkish Standards (TSE)

 Dr./ Abdelhady Ghanem

SI Units: Systems Internationales Units

Two different units are defined:

➢ Fundamental Units.
➢ Derived Units Fundamental Units
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SI Units: Systems Internationales Units

Derived Units
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Elements of The Measuring Instruments

Primary Sensing Unit

➢ Detects the physical measured quantity (measurand).

➢ It helps in transferring the measurand to a variable

conversion unit for further processing. For
example, liquid or mercury in glass thermometer acts as
a primary sensing unit. Displacement or voltage is the
output of the primary sensing unit.
 Dr./ Abdelhady Ghanem

Elements of The Measuring Instruments

Variable-conversion Unit
➢ Converts primary sensing unit output to more
suitable variables, e.g. Analogue to digital
conversion.

➢ In some cases, the primary sensing unit and the

variable-conversion unit are combined to form a single
unit called a transducer.
 Dr./ Abdelhady Ghanem

Elements of The Measuring Instruments

Variable-manipulation Unit

➢ Numerical value of the signal gets modified i.e., it

manipulates the signal presented to this unit without
affecting the original nature of the signal.

➢ It helps in improving the output quality of the

measurement system by removing the random
signals like noise.
 Dr./ Abdelhady Ghanem

Elements of The Measuring Instruments

Data-Transmission Unit

➢ It acts as a communication link for transmitting

the signals from one unit to another. This unit is
mandatory when the system is operated remotely.

➢ Some of the common data-transmission units used are

cables, wireless antennae, transducers, telemetry
systems and so on.
 Dr./ Abdelhady Ghanem

Elements of The Measuring Instruments

Data Processing Unit

➢ It used to produce suitable output to be presented

to the experimenter.

➢ In addition, it is used to compare the measured

value with the standard value to produce the
required output.
 Dr./ Abdelhady Ghanem

Elements of The Measuring Instruments

Data Presentation Unit

➢ This unit is used for communicating the

measured quantity to the experimenter, which
could be used for controlling and analyzing
purposes.
 Dr./ Abdelhady Ghanem

Classification of Instruments
a) Mechanical
Basic Classifications: b) Electrical
c) Electronic Instruments.
Mechanical:
➢ These instruments are very reliable for static and stable conditions. But
their disadvantage is that they are unable to respond rapidly to
measurements of dynamic and transient conditions.
Electrical:
➢ It is faster than mechanical, indicating the output are rapid than
mechanical methods. But it depends on the mechanical movement of the
meters. The response is 0.5 to 24 seconds.
Electronic:
It is more reliable than other system. It uses semiconductor devices and weak
signal can also be detected.
 Dr./ Abdelhady Ghanem

Classification of Instruments
Other Classifications: 1- Methods of Measurement

Direct Methods:
➢ In these methods, the unknown quantity (called the measurand ) is directly
compared against a standard.
➢ Such as measurement of current by an ammeter, voltage by voltmeter,
resistance by ohmmeter, power by wattmeter etc.

Indirect Method:
Quantity is determined by measuring other functionally related
quantities and calculating the desired quantity rather than measuring it
directly such as resistance of a conductor may be determined by measuring
voltage across the conductor, V and current flowing through the conductor, I
and then calculating it by Ohm's law i.e., R=V/I.
 Dr./ Abdelhady Ghanem

Classification of Instruments
Other Classifications: 1- Methods of Measurement
Direct methods can be classified in to:
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, and pressure by pressure gage.

➢ They are most widely used in electrical engineering practice, being the most simple
and least time consuming, though their accuracy is not more than 0.2 to 10%.

Comparison methods:
➢ The unknown quantity is determined by direct comparison with standard of the
given quantity (same quantity or other quantity practically related to it) such as
measurement of emf by comparison with the emf standard cell.
 Dr./ Abdelhady Ghanem

Classification of Instruments
Other Classifications: 1- Methods of Measurement
Comparison methods can be classified in to:
Complementary method:
➢ Determination of the volume of a solid by liquid displacement.

Null method:
➢ In this method the difference between the value of the quantity to be measured and
the known value of the same quantity with which it is compared is brought to zero.
Such as: determination of a mass by means of a balance and known weights.
➢ Null-type instruments are more accurate and highly sensitive as compared to
deflection-type instruments
 Dr./ Abdelhady Ghanem

Classification of Instruments
Other Classifications: 2- Absolute or primary instruments

➢ Gives the magnitude of the measurement quantity in terms of physical

constants of the instrument and deflections.

➢ Do not require any comparison with the standard instrument

➢ The time required to determine the magnitude of the measuring quantity is high.

➢ Do not used in laboratories and are seldom used by electricians and engineers.

Example: Tangent galvanometer which gives the measured current in terms of the
tangent of the deflected angle, the radius, and the number of turns of the
galvanometer.
 Dr./ Abdelhady Ghanem

Classification of Instruments
Other Classifications: 3- Secondary instruments

➢ Gives the magnitude of electrical quantity to be measured directly.

➢ Takes less time to compute the output.

➢ Generally used in laboratories.

Some of the widely used secondary instruments are: ammeters, voltmeters, wattmeters,
energy meters (watt-hour meters), ampere-hour meters and so on.
 Dr./ Abdelhady Ghanem

Classification of Instruments
Other Classifications: 3- Secondary instruments
Secondary instruments can be classified in to:

A- Based on various effects used to measure electrical quantity:

❑ Magnetic effect: Used in ammeter, voltmeter, wattmeter etc.

❑ Thermal effect: Used in ammeter and voltmeter
❑ Chemical effect: Used in DC ampere-hour meter
❑ Electrostatic effect: Used in voltmeter
❑ Electromagnetic induction effect: Used in AC ammeter, voltmeter, wattmeter etc.
 Dr./ Abdelhady Ghanem

Classification of Instruments
Other Classifications: 3- Secondary instruments
Secondary instruments can be classified in to:

B- Based on nature of the instrument operation:

❑ Indicating instrument: Indicate the quantity to be measured using a pointer, which
moves over a scale. E.g: ammeter, voltmeter and so on
❑ Recording instruments: Record the quantity that is continuously varying with
respect to time. It can make a permanent record of the indication.
❑ Integrating instruments: Record the consumption of total quantity of electricity,
energy and so on.
❑ Displaying instruments: These instruments measure the electrical quantities in the
form of waves on the screen. E.g: Oscilloscope
 Dr./ Abdelhady Ghanem

Classification of Instruments

The indicating instruments are of different types, as listed below:

➢ Moving-iron instruments
The two different types of moving-iron instruments are:
o Moving-iron instrument–attraction type
o Moving-iron instrument–repulsion type

➢ Moving-coil instruments
The different types of moving-coil instruments are:
o Permanent magnet moving-coil instrument (PMMC): used for DC
o Dynamometer type: used for both AC and DC
 Dr./ Abdelhady Ghanem

Classification of Instruments
Other Classifications: 3- Secondary instruments
Secondary instruments can be classified in to:

C- Based on nature of quantity that can be measured:

❑ DC instruments: Measure only DC quantities

❑ AC instruments: Measure only AC quantities

❑ Both DC and AC instruments: Measure both DC and AC quantities

 Dr./ Abdelhady Ghanem

Classification of Instruments
Other Classifications: 3- Secondary instruments
Secondary instruments can be classified in to:

D- Based on methods used:

❑ Direct measuring instruments: Convert the energy of the measured quantity
directly into a form, which actuates the instrument and the value of the unknown
quantity, is indicated or measured or recorded directly.

❑ Comparison measuring instruments: Measure the unknown quantity with the help
of comparison with the standard quantity. Example: AC Bridge.
 Dr./ Abdelhady Ghanem

Classification of Instruments
Other Classifications: 3- Secondary instruments
Secondary instruments can be classified in to:

D- Based on analog and digital technologies:

❑ Analog instruments: it presents the physical variables in form of continuous or
stepless variations with respect to time. They generally cost less and are easy to
maintain and repair.

❑ Digital instruments: the physical variables are represented by digital quantities

which are discrete and vary in steps.