unit-5 eee
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UNIT -5: Communication Systems
Introduction to Communication Systems
Every day, in our work and in our leisure time, we come in contact with and use a variety of modern
communication systems and communication media, the most common being the telephone, radio, television, and
the Internet. Through these media we are able to communicate (nearly) instantaneously with people on different
continents, transact our daily business, and receive information about various developments and events of note
that occur all around the world. Electronic mail and facsimile transmission have made it possible to rapidly
communicate written messages across great distances.
Can you imagine a world without telephones, radio, and TV? Yet, when you think about it, most of these modern-
day communication systems were invented and developed during the past century. Here, we present a brief
historical review of major developments within the last two hundred years that have had a major role in the
development of modern communication systems.
2. Types of Communication
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Verbal Communication:
1. Oral Communication: Oral communication is information spoken by mouth; the use of speech. Some of the
examples of Oral Communication are: Face to face communication,Telephonic Communication, Public Address
System (Speech), Informal rumor mill (Grape Wine), Audio & Visual Media(Radio, TV), Lectures, Conference-
Interchange of views, Meetings, Cultural Affairs.
2. Written Communication: Communication by means of written symbols (either printed or handwritten). Some
of the examples are: Orders, Instructions, Letters, Memos, Reports, Policy manuals, Information Bulletin,
Complaint System, Suggestion System, etc
Nonverbal Communication:
1. Body Language includes facial expression, eye contact, postures, gestures, touch.
2. Para Language is the way we say something rather than what we say, is another nonverbal code.
3. Space and Time Space Language includes surroundings (Design & Language). It communicates social status also.
4. Sign Language: A sign language is a language which, instead of conveyed sound patterns, uses visually
transmitted sign patterns.
3. IEEE Spectrum for Communication Systems:
4.MODULATION: Radio signals can be used to carry information. The information,
which may be audio, data or other forms, is used to modify (modulate) a single frequency known
as the carrier. The information superimposed onto the carrier forms a radio signal which istransmitted to the receiver. Then “THE PROCESS OF SUPERIMPOSITION A LOW
FREQUNCY SIGNAL ON ONE OF THE VARIBLES OF A HIGH FREQUNCY WAVE
(CARRIER)”.
There are many different varieties of modulation but they all fall into three basic categories, namely amplitude
modulation, frequency modulation and phase modulation.
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(1)Amplitude modulation: Amplitude modulation (AM) is a technique used in electronic communication,
most commonly for transmitting information via a radio carrier wave. Amplitude Modulation occurs when a
voice signal's varying voltage is applied to a carrier frequency. The carrier frequency's amplitude changes in
accordance with the modulated voice signal, while the carrier's frequency does not change.
When combined the resultant AM signal consists of the carrier frequency, plus UPPER and LOWER sidebands. This
is known as Double Sideband - Amplitude Modulation (DSB-AM), or more commonly referred to as plain AM.
Another type of analog modulation is known as Vestigial Sideband. Vestigial Sideband modulation is a lot like
Single Sideband, except that the carrier frequency is preserved and one of the sidebands is eliminated through
filtering. Analog bandwidth requirements are a little more than Single Sideband however.
Vestigial Sideband transmission is usually found in television broadcasting. Such broadcast channels require 6 MHz
of ANALOG bandwidth, in which an Amplitude Modulated PICTURE carrier is transmitted along with a Frequency
Modulated SOUND carrier.
(2)Frequency Modulation (FM)
Frequency Modulation occurs when a carrier's CENTER frequency is changed based upon the input
signal's amplitude. Unlike Amplitude Modulation, the carrier signal's amplitude is UNCHANGED. This
makes FM modulation more immune to noise than AM and improves the overall signal-to-noise ratio of the communications system. Power output is also constant, differing from the varying AM power
output.
The amount of analog bandwidth necessary to transmit a FM signal is greater than the amount
necessary for AM, a limiting constraint for some systems.
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Q.1What is the difference between Amplitude modulation and frequency modulation?
ANS1.
1. In case of frequency modulation the change in amplitude may be due to noise. If we make use of amplitude
limiters in FM receivers then we can completely vanish this noise effect.
2. FM waves are waves having constant amplitude. These are independent of the modulation. So, due to this the
power transmission of these waves is also constant. The power transmission of FM waves is better than that of the
AM signals.
3. In FM signals, all the transmitted power can be used, but in AM wave the transmission carriers contain most of
the power. So, complete use of power is not possible.
4. In FM wave’s noise can be controlled by increasing the deviation up to some amount. This is impossible in case
of AM waves.
5. VHF and UHF are the bands of FM broadcasting. In these bands noise effect is very less. But on the other hand
bands of AM broadcasting such as MF and HF has higher effects.
6. Co-channel interference can be reduced by using some space wave in FM broadcasting.
The major disadvantages of FM are:
1. Complex apparatus is used to transmit and receive the FM wave.
2. FM waves needs 10 times larger channel width than that of the AM waves.
3. The reception area of FM waves is less than that of AM waves. Due to this wide area communication using the
Fm waves is not possible.;
Instrumentation & Control
(1)Introduction to Transducers: Transducers play an important role in the field of
instrumentation and control engineering. Any energy in a process should be converted from one form into
another form to make the communication from one rectification sector to another. Transducer is a device which converts one form of energy into another form i.e,. the given non-electrical
energy is converted into an electrical energy.
Types of transducers :There are two types of transducers, they are:
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(1)Active transducers:
Active transducer is a device which converts the given non-electrical energy into electrical energy by itself.
Thermocouple, Photovoltaic cell and more are the best examples of the transducers
(2)Passive transducers:
Passive transducer is a device which converts the given non-electrical energy into electrical energy by external
force. Resistance strain gauge, Differential Transformer are the examples for the Passive transducers.
(2) Thermocouple: A thermocouple is a device consisting of two different conductors
(usually metal alloys) that produce a voltage, proportional to a temperature difference, between
either ends of the two conductors. Thermocouples are a widely used type of temperature sensor
for measurement and control
[1] and can also be used to convert a temperature gradient into electricity. They are inexpensive,
[2] interchangeable, are supplied with standard connectors, and can measure a wide range of
temperatures. In contrast to most other methods of temperature measurement, thermocouples are
self powered and require no external form of excitation. The main limitation with thermocouples
is accuracy, specifically, system errors of less than one degree Celsius (C) can be difficult to
achieve
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A thermocouple measuring circuit with a heat source, cold junction and a measuring instrument.
(2)RTD - RTDs - Resistance Temperature DetectorsWhat is a Resistance Temperature Detector? Resistance Temperature Detectors (RTD), as the name implies, are
sensors used to measure temperature by correlating the resistance of the RTD element with temperature. Most
RTD elements consist of a length of fine coiled wire wrapped around a ceramic or glass core. The element is
usually quite fragile, so it is often placed inside a sheathed probe to protect it. The RTD element is made from a
pure material whose resistance at various temperatures has been documented. The material has a predictable
change in resistance as the temperature changes; it is this predictable change that is used to determine
temperature.
Common Resistance Materials for RTDs:
Platinum (most popular and accurate)
Nickel
Copper
Balco (rare)
Tungsten (rare)
RTD Styles and Types:
(a)RTD Elements
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The RTD element is the simplest form of RTD sensor. It consists of a piece of wire wrapped around a ceramic or
glass core. Because of their compact size, RTD elements are commonly used when space is very limited
(b) RTD Surface Elements
A surface element is a special type of RTD sensor. It is designed to be as thin as possible thus providing good
contact for temperature measurement of flat surfaces.
(c ) RTD Probes:
The RTD probe is the most rugged form of RTD sensors. A probe consists of an RTD element mounted inside a
metal tube, also known as a sheath. The sheath protects the element from the environment. OMEGA offers a
wide variety of probes in various configurations
(3 ) Strain gauge: A strain gauge (also strain gage) is a device used to measure the strain
of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of
strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The
gauge is attached to the object by a suitable adhesive, such as cyanoacrylate.
The strain gauge has been in use for many years and is the fundamentalsensing element for manytypes of sensors, including pressure sensors,load cells, torque sensors, position sensors, etcThe
majority of strain gauges are foil types, available in a wide choiceof shapes and sizes to suit a variety
of applications. They consist of apattern of resistive foil which is mounted on a backing material.
Theyoperate on the principle that as the foil is subjected to stress, the resistance of the foil changes
in a defined way.
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( Typical foil strain gauge. The gauge is far more sensitive to strain in the vertical direction than in the horizontal
direction. The markings outside the active area help to align the gauge during installation.)
(1)The strain gauge is connected into a Wheatstone Bridge circuit with a combination of four active gauges (full
bridge), two gauges (half bridge), or, less commonly, a single gauge (quarter bridge). In the half and quarter
circuits, the bridge is completed with precision resistors.
(1) Gage facter:
LOAD CELL:The basic definition of a load cell will come in the form of a transducer. This is a
device that is used to convert a specific force into a signal that is electrical.
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FIG(1) :How Do Load Cells Work
If you are not specifically working with load cell devices, this information may not be very important. However, for
those that work with a force on a consistent basis, this information will be quite beneficial. By converting force into
a measurable amount of deformation or strain, this will provide an individual with the ability to measure
consistencies or inconsistencies in a conversion. Not only can that force be measured, it can also be used in
separate phases.
Q.1:How Do Load Cells Work?
Ans.1:It’s important to realize that a load cell can consist of more than one strain gauge. Sometimes they will
consist of one, two, or even four different strain gauges depending on the type of cell that has been created. The
strain gauge is the actual item that is used to measure deformation or resistance of the electrical wire receiving the
current. Now, it’ll be important to understand that there are different types of cells. They use fiber optics,
pneumatic, washer, button, and hydraulics instead of strain gauges. Depending on the type of cell that has been
created will determine the type of output that particular cell will provide.
Bimetal:Bimetallic strip is made by bonding strip of two metal with different of thermal thermal coefisien
together.When the strip is heated, it tends to bend to the side that has a smaller coefisient of thermal
expantion.When it is cooled, it tend to bend to the biger coefisient of thermal expantion.
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5. Integrated circuit:
An integrated circuit or monolithic integrated circuit (also referred to as IC, chip, or microchip) is an electronic
circuit manufactured by lithography, or the patterned diffusion of trace elements into the surface of a thin
substrate of semiconductor material. Additional materials are deposited and patterned to form interconnections
between semiconductor devices.
Fig. 5.8: Integrated circuits
These are have been two types:
1. Analog integrated circuits
2. Digital integrated circuits
Generations: vlsi, SSI, MSI and LSI
(1)vlsi: Main article: Very-large-scale integration
Upper interconnect layers on an Intel 80486DX2 microprocessor die
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The final step in the development process, starting in the 1980s and continuing through the present, was "very
large-scale integration" (VLSI). The development started with hundreds of thousands of transistors in the early
1980s, and continues beyond several billion transistors as of 2009.
FIG:5.9 Upper interconnect layers on an Intel 80486DX2 microprocessor die
In 1986 the first one megabit RAM chips were introduced, which contained more than one million transistors.
Microprocessor chips passed the million transistor mark in 1989 and the billion transistor mark in 2005.[15] The
trend continues largely unabated, with chips introduced in 2007 containing tens of billions of memory transistors.
BY: SHUBHAM KHANDELWAL
(FARRE.IN)