SCADA IMPLIMENTATION

134
PROJECT REPORT ON “SCADA” IMPLEMENTED OVER POWER TRANSFORMER WITH REMOTE MONITORING SYSTEM

description

SCADA of wtreless communication system

Transcript of SCADA IMPLIMENTATION

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PROJECT REPORT

ON

“SCADA” IMPLEMENTED OVER POWER TRANSFORMER WITH REMOTE

MONITORING SYSTEM

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CONTENTS

1. SYNOPSIS

2. INTRODUCTION

3. BLOCK DIAGRAM AND ITS BRIEF DESCRIPTION

4. CIRCUIT ANALYSIS

5. DETAILS ABOUT WIRELESS COMMUNICATION

6. THEORY RELATED TO DISTRIBUTION TRANSFORMER

7. DETAILS ABOUT ANALOG TO DIGITAL CONVERTERS

8. DETAILS ABOUT MICROCONTROLLERS

9. HARDWARE DETAILS

10.MICROCONTROLLER SOFTWARE

11.COMPUTER SOFTWARE

12. FABRICATION DETAILS

13. CONCLUSIONS AND REFERENCES

14. COMPLETE CIRCUIT DIAGRAM WITH LIST OF COMPONENTS

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CHAPTER – 1

SYNOPSIS

The aim of the project work is to protect the distribution transformer or any other

power transformer, burning due to the overload, over temperature and input high voltage.

Normally most of the transformers are burning because of these three reasons; hence by

incorporating this type of monitoring and control circuits, life of the transformer can be

increased. In addition to the monitoring and control, information about these three

parameters can be transmitted to the nearest electrical office where the maintenance staff of

the electrical department can monitor the transformer continuously without going nearer to

the transformer. For this purpose, radio communication is utilized in this project work, so

that, due to what reason the transformer has been failed, at what time, when the power is

resumed etc., can be monitored and this information can be stored in a computer at the

receiving station. With the help of this kind of system, the maintenance staff of the

department can have a continuous vigilance over the transformer.

This is a innovative project work introduced in the field of wireless communication,

in this project work micro-controller is used at the transmitting side, and computer is utilized

at the receiving end. The advantage of using micro-controller is, efficient control of each

parameter can be achieved. Similarly the advantage of using computer is, the received

information can be stored effectively.

In this project work, for the demonstration purpose a small step-down transformer of

12V, 2amps rating at secondary is considered and these three parameters are carried over this

small transformer. This transformer is known as TUT (Transformer under Test).

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The transducers used in this project work is for monitoring the various parameters

are, a) CT (Current transformer) is used for measuring the load current at transformer

secondary. b) PT (potential transmitter) for measuring the line voltage at transformer

primary. c) SL100 (semiconductor) is used as a temperature sensor for measuring the

transformer body temperature or oil temperature.

The micro-controller used in this project work is INTEL/ATMEL 89C51 chip, which

functions according to the program written and stored in it. The program is made in

assembly language. Similarly at the receiving end, for the computer, the program is written

in ‘C’ language and with the help of associated hardware, the information received through

the A/D converter can be stored and facilitates the display of failure parameter at the

transmitting end. The output of the computer, through the latch is used to drive the alarm,

which energizes automatically, whenever the receiver receives failure information.

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CHAPTER – 2

INTRODUCTION

This project report describes on the design, development and fabrication of one

demonstration unit of the project work “SCADA” IMPLEMENTED OVER POWER

TRANSFORMER WITH REMOTE MONITORING SYSTEM”.

Nowadays, with the advancement of technology, particularly in the field of computers

as well as micro-controllers, all the activities in our day to day living have become a part of

information and we find computers and micro-controllers at each and every application.

Thus, the trend is directing towards computer based project works. However, in this project

work the basic signal processing of temperature, load current and input high voltage

parameters related to the distribution transformers are monitored with analog electronics

only. For measuring various parameters values, various transducers are used, and the output

of these transducers are converted to control the parameters. The control circuit is designed

using micro-controller. The outputs of all the three parameters are fed to the analog to digital

converter for converting the analog information in to the digital information and this digital

information is fed to micro-controller. The output of the micro-controller is used to drive the

digital display, so that the value of each parameter can be displayed. In addition to the digital

display micro-controller outputs are also used to drive four relays independently. These

relays energize and de-energizes automatically according to the condition of the parameter.

Out of four relays one relay is treated as common relay and energizes automatically

whenever any parameter exceeds its preset value. This relay contact is used to break the

supply to the transformer primary. The remaining three relays are used for the three different

parameters, to transmit the information about the failure parameter. For example, if the load

is more than the rated load, then immediately the micro-controller energizes one relay out of

these three relays and this relay contact is used to provide supply to the low frequency

oscillator, which produces a perfect square wave of 1 KHz approximately. This low

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frequency is fed to transmitter as a modulating wave, which is super imposed over the carrier

and transmitted as a modulated wave. Like wise for other two parameters, two different low

frequencies are generated. The idea of generating three different low frequencies is to

identify the failure parameter and to transmit the failure information.

In the receiver, the received information in the form of low frequency as a modulated

wave is demodulated, amplified and converted into proportionate DC voltage using

frequency to voltage converter. The output of this F/V converter is again converted into

digital pulses, which are essential for the computer. Here the computer is used at receiving

end, where the receiver is installed; generally the receiving part of the system can be installed

at electrical office.

In this project work the micro-controller is playing a major role. Micro-controllers

were originally used as components in complicated process-control systems. However,

because of their small size and low price, Micro-controllers are now also being used in

regulators for individual control loops. In several areas Micro-controllers are now

outperforming their analog counterparts and are cheaper as well.

Micro-controllers are also being used increasingly as tools for analysis and design of

control systems. The control engineer thus has much more powerful tools available now than

in the past. Digital computers are still in a state of rapid development because of the

progress in very large-scale integration (VLSI) technology. Thus substantial technological

improvements can be expected in the future.

Because of these developments, the approach to analysis, design, and implementation

of control systems is changing drastically. Originally it was only a matter of translating the

earlier analog designs into the new technology. However, it has been realized that there is

much to be gained by exploiting the full potential of the new technology. Fortunately,

control theory has also developed substantially over the past 35 years. For a while it was

quite unrealistic to implement the type of regulators that the new theory produced except in a

few exotic mostly in aerospace or advanced process control. However, due to the

revolutionary development of microelectronics, advanced regulators can be implemented

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even for basic applications. It is also possible to do analysis and design at a reasonable cost

with the interactive design tools that are becoming increasingly available.

The purpose of this project work is to present control theory that is relevant to the

analysis and design of Micro-controller system with an emphasis on basic concept and ideas.

It is assumed that a Microcontroller with reasonable software is available for computations

and simulations so that many tedious details can be left to the Microcontroller. The control

system design is also carried out up to the stage of implementation in the form of controller

programs in assembly language.

Micro-controllers are "embedded" inside some other device so that they can control

the features or actions of the product. Another name for a micro-controller, therefore, is

"embedded controller". Micro-controllers are dedicated to one task and run one specific

program. The program is stored in ROM (read-only memory) and generally does not change.

Micro-controllers are often low-power devices. A battery-operated Microcontroller might

consume 50 milli watts. A micro-controller has a dedicated input device and often (but not

always) has a small LED or LCD display for output. A micro-controller also takes input from

the device it is controlling and controls the device by sending signals to different components

in the device.

Radio transmission technique is incorporated in the design. There are number of

mechanisms by which Radio waves may travel from a transmitting to a receiving Antenna.

The terms, GROUND WAVES, SKY WAVES, and SPACE or TROPOSHERIC WAVES

designates the more important of these.

The ground wave can exist when the transmitting and receiving are close to

the surface of the Earth and are vertically polarized. The sky wave represents energy that

reaches receiving antenna as a result of a bending of the wave path introduced by the

ionization in the upper atmosphere. The space wave represents energy that travels from the

transmitting to the Receiving Antenna in the Earths troposphere. The radio transmission at

frequencies above about 30MHz is normally the space wave propagation. The transmitter

that is frequency modulated find extensive use at frequencies above 40MHz.

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In this project work, 100MHz carrier is considered and 100MHz F.M

transmitter is designed. The signals transmitted from the transmitter to the receiver are over

load, over Temperature and over voltage information.

Coming to the computers, the technology is so much advanced. Initially the PC era

started with Intel 8088/8086, then PC-XT with Intel 80286 and PC-AT with 80386 SX and

80386 DX, then with Intel 80486. Subsequently the new generation of Intel series has come

with ‘PENTIUM’ processors. In Pentium series, variety of devices have come i.e., (Pentium

– I) P – I, P – II, P – III, P – IV, P – Celeron, P – Pro etc. Today we are getting P- 4 or

power of 4 processors are available in the Market. Thus the need come to develop PC Based

project works in the field of monitoring and control system, which will serve the need of the

Industry.

The purpose of this project work is to present control theory that is relevant to the

analysis and design of computer controlled systems, with an emphasis on basic concepts and

ideas. It is assumed that a digital computer with reasonable software is available for

computations and simulations so that many tedious details can be left to the computer. The

control system design is also carried out up to the stage of implementation in the form of

computer programs in a high level language. One can view computer-controlled systems as

approximations of analog control systems, but this is a poor approach because the full

potential of computer control is not used. At best the results are only as good as those

obtained with analog control circuit.

The computer-controlled system contains essentially four parts, i.e., the process, the

analog to digital converter, the control algorithm, and the clock. The times when the

measured signals are converted to digital form are called the sampling instants; the time

between successive samplings is called the sampling period and is denoted by ‘h’. The output

from the process is a continuous time signal. The output is converted into digital form by

the A – D converter. The A – D converter can be included in the computer or regarded as a

separate unit, according to ones preference. The conversion is done at the sampling times.

The computer interprets the converted signal, as a sequence of numbers, processes the

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measurements using an algorithm, and gives a new sequence of numbers. This sequence is

converted to an analog signal by a digital to analog converter. Notice that the system runs

open loop in the interval between the A – D and the D – A conversion. The real time clock in

the computer synchronizes the events. The digital computer operates sequentially in time and

each operation takes sometime. The computer-controlled system contains both continuous

time signals and sampled, or discrete time, signals such systems have traditionally been

called sampled data systems, and this term will be used here as a synonym for computer

controlled systems.

Now a days, we find lot of transformers are burning because of over loads,

voltage variations and transformer body temperature rising. The body temperature of a

transformer rises due to overloads and continuous long run, because of these reasons the

transformer may shutdown automatically. Particularly, in the rural areas we find shutdown

of transformers due to agricultural pump-sets, and we know it takes lot of time to repair and

it involves lot of cost. Hence, the transformer failure prevention is become essential for

smooth transmission and distribution.

For simulation of the faults in the demonstration unit a step-down transformer

of 2 amps current rating is used, and above parameters are carried over this transformer and

the corrective action is initiated when the parameters crosses its limits.

For over voltage parameter monitoring, the input voltage to the transformer primary

is fed through autotransformer and the over voltage is checked. Normally the transformer

primary is designed to operate at 230V AC, but, if the voltage is more than 250V AC, then

there is a chance that the transformer primary winding may burn due to over voltage, to

protect from this, supply to the primary is provided through the relay contact, which in turn

breaks the supply to the transformer primary when the primary voltage exceeds more than

250V AC. Similarly for other two parameters, if the limits are crosses, the high logic signal

from the microcontroller energizes the relay and breaks the supply to the primary and

prevents from burning the transformer.

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For monitoring the transformer body temperature or oil temperature (most of the

distribution transformers are oil cooled transformers) SL100 NPN transistor is used as a

temperature sensor and this transducer is wired with operational amplifier. Similarly for

monitoring the load current, the current transformer (CT) is used which gives the secondary

voltage proportional to the current flowing in the primary. The primary of the CT is

connected in series with the load (The details of these parameters will be described in detail

in later chapters).

Thus, this project work simulates the substation environment and any transformer

crosses any of these parameters, then the input to the transformer is disconnected and

prevents from burning the transformer. By implementing this kind of “SCADA” system

everywhere at the distribution transformer end, failures of the transformer can be minimized

and lot of revenue can be saved.

Now coming to the transformers, a transformer is a static piece of apparatus by means

of which AC power in one circuit is transferred to AC power of the same frequency in

another circuit. This transformation of Electric power usually takes place with a change in

voltage level. When the transformer raises the voltage i.e., output voltage is higher than the

input voltage, it is called a step-up transformer, on the other hand, when it lowers the voltage,

it is called a step-down transformer.

Electric power is almost exclusively generated, transmitted and distributed in the

form of alternating current. In order that electric power may be transmitted economically

over larger distances, high voltages must be used, but in order that electric power may be

safely distributed; low voltages are necessary. This is accomplished by means of

transformers; step-up transformers being used to raise the voltage and step-down

transformers for lowering down the voltage.

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A transformer works on the principle of mutual induction between the two circuits

linked by a common magnetic flux. The first coil, in which the electric energy is fed from

the AC supply mains, is called primary winding, and the other, from which the energy is

drawn, is called secondary winding. If the primary is connected to AC supply an alternating

flux is set up in the laminated core. The flux links with the turns of both primary and

secondary windings, there by inducing e.m.fs, in these windings. The e.m.f induced in the

primary is self-induced e.m.f, and opposes the supply voltage. The e.m.f induced in the

secondary is the mutually induced e.m.f and is expanded in producing current in it. Thus the

electric energy is transformed electro magnetically from first coil to the second coil by virtue

of magnetic coupling. The magnetic coupling between the two circuits plays an important

part in the action of transformer.

Distribution transformer failures have been an expensive problem for the State

Electricity Departments, mainly in rural networks. Research centers and consultants have

done particular diagnosis studies and punctual solutions in order to reduce transformer

failures and improve network performance. Transformer failures have many causes and

variables involved, like natural phenomena (lightning, wind, and forest), no natural

phenomena (human errors), design, build (manufacturing problems, materials defects) and

transformers and networks (lines, protection equipment, and structures) maintenance.

Distribution transformers account for the majority of losses in an electric power

network. Of these losses, core heating accounts for the substantial portion. They can be

considered constant so long as a transformer is in service. By contrast, winding losses are

only significant under higher load conditions. On a daily basis, the transformer may

experience these conditions only briefly. Also, distribution transformers are often over-rated

for their requirements, as load growth and variation may mean an installed capacity much

greater than what is actually being used. This means that the winding losses may be well

below the nominal short circuit value.

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CHAPTER – 3

BLOCK DIAGRAM AND BRIEF DESCRIPTION

The block diagram of the project work “Implementation of wireless communication

in supervisory control and data acquisition system of a distribution transformer using

microcontroller & computer” is explained. For better under standing, the total block diagram

is divided into various blocks and each block explanation is provided in this chapter. The

complete block diagram of this project work is provided at the end of this chapter. The

complete block diagram consists the following blocks:

1. Load Monitoring Circuit

2. High Voltage Monitoring Circuit

3. Temperature Sensing Circuit

4. Analog to Digital Converter

5. Micro-controller

6. Digital Display

7. Signal Generators

8. Transmitter

9. Receiver

10. Signal Amplifier

11. Frequency to Voltage Converter

12. A/D Converter (RX)

13. Clock Generator

14. Computer

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LOAD MONITORING CIRCUIT:

For monitoring the load current continuously, Current Transformer (CT) is used.

The current transformer is used with its primary winding connected in series with load

carrying the current to be measured and, therefore, the primary current is dependant upon the

load connected to the system and is not determined by the load (burden) connected on the

secondary winding of the current transformer. The primary winding consists of very few

turns and, therefore, there is no appreciable voltage drop across it. The secondary winding of

the current transformer has larger number of turns, the exact number being determined by the

turn’s ratio. The ammeter, or wattmeter current coil, are connected directly across the

secondary winding terminals. Thus a current transformer operates its secondary winding

nearly under short circuit conditions. One the terminal of the secondary winding is earthed so

to protect equipment and personnel in the vicinity in the even of an insulation breakdown in

the current transformer.

The output of the CT is rectified, filtered and it is fed to A/D converter for converting

the analog information of current flowing through the CT primary into digital information,

which is accepted by the Micro-controller.

HIGH VOLTAGE MONITORING CIRCUIT:

Transformer failures have many causes and one of the main causes is over voltage.

The primary of the distribution transformer or any other transformer primary is designed to

operate at certain specific voltage, if that voltage is more than the rated voltage, then

immediately the transformer primary may burn because of over voltage. To protect the

transformer, burning due to over voltage, this voltage monitoring and control circuit is used

in this project work.

In this project work for generating high voltage, autotransformer is used so that the

line voltage can be increased to more than 240V. For monitoring the line voltage, a step-

down transformer of 6V-0-6V center-tapped secondary is used as a line voltage sensor. As

this transformer primary voltage increases, according to that secondary voltage also raises,

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and this secondary voltage is rectified, filtered and it is applied to the analog to digital

converter for converting the analog information in to the digital information.

TEMPERATURE SENSING CIRCUIT:

The methods of temperature measurement may be divided into two main classes

according as the exchange of heat between the testing body and the hot system takes place by

contact or by radiation across a space. In the contact methods, thermometers or

thermocouples are used and they are immersed in solids or liquids. The thermodynamic

equilibrium between the hot body and the testing body is established by material contact. In

the non-contact methods, the thermodynamic equilibrium is established by the radiation

emitted as excited atom and molecules in the hot body return to the ground state.

For monitoring the transformer body temperature, SL100 general purpose NPN

switching transistor is used and it is having ‘TIN’ metal body, so that it can absorb the heat

properly. This transistor can be placed over the transformer body, where the transformer

radiates maximum heat. The exact location where the transistor is to be installed using

suitable clamp should be determined on the ease of access and the degree of accuracy

obtainable at the given point.

As the transistor body temperature raises, the base-emitter junction resistance

decreases and this resistance variation is monitored with the help of op-amp IC, whose feed

back resistor is nothing but the transistor. This differential amplifier output is further

amplified using another op-amp IC and the output of this 2nd amplifier is fed to analog to

digital converter for converting the analog information to digital information.

ANALOG TO DIGITAL CONVERTER:

As the peripheral signals usually are substantially different from the ones that micro-

controller can understand (zero and one), they have to be converted into a pattern which can

be comprehended by a micro-controller. This task is performed by a block for analog to

digital conversion or by an ADC. This block is responsible for converting an information

about some analog value to a binary number and for follow it through to a CPU block so that

CPU block can further process it.

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This analog to digital converter (ADC) converts a continuous analog input signal, into

an n-bit binary number, which is easily acceptable to a computer.

As the input increases from zero to full scale, the output code stair steps. The width

of an ideal step represents the size of the least significant Bit (LSB) of the converter and

corresponds to an input voltage of VES/2n for an n-bit converter. Obviously for an input

voltage range of one LSB, the output code is constant. For a given output code, the input

voltage can be any where within a one LSB quantization interval.

An actual converter has integral linearity and differential linearity errors. Differential

linearity error is the difference between the actual code-step width and one LSB. Integral

linearity error is a measure of the deviation of the code transition points from the fitted line.

The errors of the converter are determined by the fitting of a line through the code

transition points, using least square fit, the terminal point method, or the zero base technique

to provide the reference line.

A good converter will have less than 0.5 LSB linearity error and no missing codes

over its full temperature range. In the basic conversion scheme of ADC, the un-known input

voltage VX is connected to one input of an analog signal comparator, and a time dependant

reference voltage VR is connected to the other input of the comparator.

In this project work ADC 0809 (8 Bit A/D converter) is used to convert an analog

voltage variations (according to the condition of the parameters) into digital pulses. This IC

is having built in multi-plexer so that channel selection can be done automatically.

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MICRO-CONTROLLER:

Micro-controller unit is constructed with ATMEL 89C51 Micro-controller chip. The

ATMEL AT89C51 is a low power, higher performance CMOS 8-bit microcomputer with 4K

bytes of flash programmable and erasable read only memory (PEROM). Its high-density

non-volatile memory compatible with standard MCS-51 instruction set makes it a powerful

controller that provides highly flexible and cost effective solution to control applications.

Micro-controller works according to the program written in it. The program is

written in such a way, so that the output from the ADC will be converted into its equivalent

voltage and based on the magnitude of the voltage, it calculates the parameter value. Now

this magnitude is again digitalized and fed to 7-segment display unit through the latch.

Micro-controllers are "embedded" inside some other device so that they can control

the features or actions of the product. Another name for a micro-controller, therefore, is

"embedded controller". Micro-controllers are dedicated to one task and run one specific

program. The program is stored in ROM (read-only memory) and generally does not change.

Micro-controllers are often low-power devices. A battery-operated Microcontroller might

consume 50 milli watts. A micro-controller has a dedicated input device and often (but not

always) has a small LED or LCD display for output. A micro-controller also takes input from

the device it is controlling and controls the device by sending signals to different components

in the device.

DIGITAL DISPLAY:

The output of the micro-controller is used to drive the digital display, for this purpose

four 7-segment common anode displays are used for measuring the line voltage, transformer

body temperature and load current. These displays are used to display the data received from

the Microcontroller through the latches. The segments of each display are called A, B, up to

G. In order to reduce the numbers of connections needed to address each of the LED’s (Light

Emitted Diode), the anodes of the LED’s of each seven-segment display have been connected

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together. The common anode for the first seven-segment display is called A1, A2 for the

second display, etc. In addition, the cathode pins from each display have been connected

together to form seven common terminals, called A, B, C, D, E, F and G, corresponding to

the seven-segments. In addition to the seven segments, decimal point is also arranged in this

common anode display.

SIGNAL GENERATORS (LOW FREQUENCY OSCILLATORS):

For the three different parameters, three different tone frequencies are generated.

Supply to these three-tone generators, provided through three different relay contacts, and

these relays energizes automatically, if that particular parameter output exceeds its limit.

Three 555 timer IC’s are used for generating 1 KHz, 2 KHz and 3 KHz

separately. These IC’s are designed in ‘Astable Multi-vibrator’ Mode (self oscillators). The

outputs of all the three oscillators are clubbed together and fed to carrier oscillator as

modulating waves.

F.M. TRANSMITTER:

This block generates a continuous frequency of 100MHz, which is used to form a

permanent link between the transmitter and receiver, and this is known as carrier frequency.

The outputs of 1 KHz, 2 KHz and 3 KHz Tone generators are combined and are fed to this

F.M radio transmitter. This is a frequency modulated radio transmitter. The radiating power

of the transmitter is 20mw, and it is designed using BC 494 B high frequency switching

transistor. The detailed description is provided in the next chapter

FM RECEIVER:

The FM receiver is designed with IC TDA5591A, which is AM/FM Radio receiver

IC, operates at a local oscillator of 100MHz and is tuned with the transmitter. This IC

consists of built in RF amplifier, a double balanced mixer, local oscillator, a two stage IF

amplifier, a quadrature demodulator for a ceramic filter and an automatic frequency control.

The built in RF amplifier, a part from the amplification of received RF signal, it also reduces

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the Noise figure, which could other wise be a problem because of the large band widths

needed for FM. It also matches the input impedance of the radio receiver with the antenna.

SIGNAL AMPLIFIER:

The received signal or detected signal from the radio receiver, which is audio tone

signal of 1 KHz, 2 KHz and 3 KHz, is amplified with the help of a transformer coupled

amplifier. This amplifier can be used in the following three applications.

(a) As an input stage, usually driven by a micro-phone

(b) As an output stage, feeding the load impedance

(c) As an intermediate stage

The transformer coupling provides the facility of impedance matching and thus

results in increased power gain. Further this method of coupling isolates the load impedance

circuit of the amplifier from the DC bios stabilization network of the succeeding stage.

FREQUENCY TO VOLTAGE CONVERTER:

This circuit is designed to generate DC voltage according to the input frequency, i.e.,

input frequency is proportional to the output voltage. In this block IC 4046 and IC 4053 are

used and the brief description about these two ICS is as follows:

IC 4046 phase locked loop IC; the phase locked loop (PLL) is an important building

block of linear system. The output from a PLL system can be obtained either as the voltage

signal VC (t) corresponding to the error voltage in the feed back loop, or as a frequency

signal at VCO output terminal. The voltage output is used in frequency discriminator

application whereas the frequency output is used in signal conditioning, frequency synthesis

or clock recovery applications.

Consider the case of voltage output, when PLL is locked to an input frequency, the

error voltage VC (t) is proportional to (fs – fo). If the input frequency is varied as in the case

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of FM signal, VC will also vary in order to maintain the lock. Thus the voltage output serves

as a frequency discriminator, which converts the input frequency changes to voltage changes.

IC4053 MULTIPLEXER; the multi-plexer is a special combinational circuit that is

one of the most widely used standard circuits in digital design. The Multi-plexer (or data

selector) is a logic circuit that gates one out of several inputs to a single output. The output

selected is controlled by a set of select input. The following figure shows the block diagram

of a multi-plexer with ‘n’ input lines and one output line. For selecting one out of n inputs

for connection to the output, a set of ‘m’ select input is required where 2m=n.

Depending up on the digital code applied at the select inputs one out of n data sources

is selected and transmitted to a single output channel. Normally a strobe (or enable) input (G)

is incorporated which helps in cascading and it is generally active-low, which means it

performs its intended operation when it is low.

ANALOG TO DIGITAL CONVERTER (RX):

An analog to digital converter (ADC) converts a continuous analog input signal, into

an n-bit binary number, which is easily acceptable to a computer.

As the input increases from zero to full scale, the output code stair steps. The width

of an ideal step represents the size of the least significant Bit (LSB) of the converter and

corresponds to an input voltage of VES\2n for an n-bit converter. Obviously for an input

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voltage range of one LSB, the output code, the input voltage can be anywhere within a one

LDB quantization interval.

An actual converter has integral linearity and differential linearity errors.

Differential linearity error is the difference between the actual code-step width and one LSB.

Integral linearity error is a measure of the deviation of the code transition points from the

fitted line.

The errors of the converter are determined by the fitting of a line through the code

transition points, using least square fit, the terminal point method, or the zero base technique

to provide the reference lien.

A good converter will have less than 0.5 LSB linearity error and no mission codes

over its full temperature range. In the basic conversion scheme of ADC, the un-known input

voltage VX is connected to one input of an analog signal comparator, and a time dependant

reference voltage VR is connected to the other input of the comparator.

In this project work ADC 0809 (8bit A/D converter) is used to convert an analog

voltage of frequency to voltage converter output in to an output binary word that can be used

by a computer.

PC BLOCK:

For monitoring and displaying of temperature and load current parameters ‘C’

language is used. This is custom built software. The advantage of using ‘C’ is, while there

are around 250 languages existing in the world of computers, today the software

professionals are showing increasing performance for ‘C’. According to one survey as much

as 75% of total software developed in the world today, is written in ‘C’ or C++. What makes

‘C’ such a success and popular is because it is simple, reliable, capable and easy to use. The

compactness of ‘C’ language is mainly due to the fact that it is a one-man language rather

than a product of the committees. “DENNIS RITCHIE” developed it at AT & T bell lab,

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USA. The software details are provided in chapter – 6. Program for the project work copied

from ‘C++’ and converted into ‘C’.

This program is for reading 8 – channel ADC and two different parameters output is

converted into analog signal and it is fed to channel ‘O’ in the ADC i.e., the program is made

to read the frequency to voltage converter output.

CLOCK GENERATOR:

The clock generator circuit is designed using 555 Timer IC. This IC is configured in

Astable Mode of operation (free running oscillator). The frequency can be adjusted using

external resistor and capacitor. The required frequency is more than 100 KHz. The output of

this IC is fed to the A - D converter.

The complete block diagram of the project work is shown in the next page.

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CHAPTER – 4

CIRCUIT ANALYSIS

The detailed circuit description of the project work ““SCADA”

IMPLEMENTED OVER POWER TRANSFORMER WITH REMOTE MONITORING

SYSTEM” is explained in section wise. For better understanding the total circuit diagram is

divided into various sections and each section explanation along with circuit diagram is

provided in this chapter.

LOAD MONITORING CIRCUIT:

The current transformer used in this project work is designed for 5Amps i.e., the

current flowing through the primary is restricted for 5Amps. But in practical a higher rating

transformer can be used according to the rated power of the distribution transformer. Most

common industrial CT’s have 5 to 10 Amp current outputs and can generate high voltage

levels when not connected to a burden resistor.

The CT used in this project work is nothing but a step-up transformer. This

transformer is designed in 1:50 ratio, so that the voltage developed across the secondary is 50

times more than the voltage induced at primary. The voltage induced at primary is

proportional to the load current. The CT secondary when it is open circuited, the voltage

developed across the open terminals may be very high because of the step-up ratio, and

therefore, the secondary winding of the CT should always be connected to a burden resistor.

The secondary AC signal, which is proportional to the current flowing through the primary,

due to transformer action, is rectified with the help of a diode (Half wave rectification) and

then filtered by a filter Capacitor This DC voltage is a variable voltage, which varies

according to the load current. The variable voltage from the CT secondary is fed to analog to

digital converter for converting the analog information into digital information. The output of

the A/D converter is fed to Micro-controller unit for taking the necessary action. The current

flowing through the CT primary can be measured, for this purpose, digital display is provided

at the output of the Micro-controller Chip. The following is the circuit diagram of load

sensing circuit.

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In the above circuit, with the help of a 470 resistor connected across the CT

secondary, the ripple can be suppressed and real value can be obtained at the output of CT.

This voltage can be adjusted to the required level, for this purpose 2K variable resistor is

used and the final output taken from mid point of the preset. Since it is a protype module, in

this project work for the demonstration purpose, a small transformer of 12V secondary at

1amp rating is considered, and it is treated as distribution transformer. This transformer

secondary is used to drive the lamp load through the current transformer primary. For this

purpose two No.s of 12V 10W AC lamps are used, one lamp is treated as nominal load and

the other one is used to create a fault, i.e., the transformer secondary is designed to drive only

one amp load, if the load is more than one amp then the transformer may burn because of

over load, to protect the transformer burning due to the over load, the output of the load

monitoring circuit is used to drive the relay through the A/D converter and microcontroller.

This relay contact is used to break the supply at the primary side of the transformer; so that

once the transformer is overloaded automatically primary supply can be disconnected.

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HIGH VOLTAGE MONITORING CIRCUIT:

The Line voltage-sensing circuit used in this project work is capable to measure up to

250V AC. For this purpose a step-down transformer of 6V-0-6V, 500mA, Center tapped

secondary is used for monitoring the line voltage continuously. In the prototype module, the

line voltage can be increased through the autotransformer, the output of the line voltage

sensing circuit is fed to micro-controller unit through the A/D converter, so that according to

the received digital information form the ADC, the micro-controller energizes relay. This

relay contact is used to break the supply to the feeder cable. In practical, the distribution

transformers primary is designed to operate at very higher voltage of 11KVA or 33KVA,

because, the output of the power generating station is very high. According to the main grid

voltage, the step-down transformer primary (for Monitoring the line voltage) can be

designed.

The output of the line voltage-sensing transformer is rectified and filtered for

obtaining pure DC voltage. The final output is taken from the mid point of 2K variable

resistor (Preset), so that the voltage applied to the A/D converter can be controlled. As the

line voltage varies, according to that output voltage also varies. This variable voltage from

the potential transformer (PT) is applied to the A/D converter. The applied voltage to the

ADC should not exceed more than 5V, so that the output voltage is clamped at +5V DC, for

this purpose, 1W, 5V zener is used. This circuit is designed such that, the voltage applied to

the transformer primary, if it is more than 245V AC then immediately the microcontroller

energizes the relay and breaks the supply to the primary, by which the transformer can be

protected burning due to the over voltage. Since it is a prototype module, the output of the

transformer is restricted for lower voltages for the demonstration purpose, but when it is

implemented for the real time applications, at that time the output of the distribution

transformer will be around 220V AC, and with the help of this kind of voltage control circuit,

the household electrical gadgets like TV, Fridge, Tube, Motor etc., can be protected burning

due to the over voltage.

The following is the circuit diagram of the High voltage Sensing

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TEMPERATURE SENSING CIRCUIT:

In this block, two op-amps are used to form two different stages, the first stage is

configured as differential amplifier and the second stage is configured as gain amplifier. In

the first stage an ‘NPN’ General purpose transistor (SL100) is used as a temperature sensor

and this transistor is having ‘TIN’ metal body so that it can absorb the heat properly. This

transistor is connected in feed back loop (input to output). This first stage is designed in such

a way so that, as the transistor body temperature rises, according to the temperature, the base-

emitter or base-collector junction resistance decreases. This first stage is designed to generate

2mv/0C which is not sufficient for the calibration. Hence, using 2nd stage this voltage is

amplified, and the gain of the 2nd stage is 10, so that (2x10) 20mv per degree centigrade can

be obtained at the output of the second stage. This variable voltage (according to the

temperature) from the output of second stage is fed to the analog to digital converter for

converting the analog information in to the digital information and this digital information is

fed to the microcontroller for taking the necessary action.

The circuit design consists a basic transducer, which converts temperature in to

equalent voltage. For this, transistor ‘SL100’ is used as a sensor. The transistor junction

(Base & emitter or Base & collector) characteristics are depends upon the temperature. For a

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transistor, the maximum average power that it can dissipate is limited by the temperature that

collector - base junction can with stand. Therefore, maximum allowable junction temperature

should not be exceeded. The average power dissipated in collector circuit is given by the

average of the product of the collector current and collector base voltage. At any other

temperature the de-rating curves are supplied by the manufacturer to calculate maximum

allowable power (Pj).

Where TC is case temperature, Tj is junction temperature and Qj is the thermal

resistance. The entire circuit design of the temperature sensing circuit is given below.

In the above circuit diagram with the help of 2K preset (variable resistor) connected

at the input of first stage, the initial room temperature corresponding output voltage can be

adjusted for the easy calibration. The output of the second stage is clamped with 5V zener

and the same output is fed to the A/D converter. For better understanding the following is the

further description along with formulas and equations.

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For sensing the transformer body temperature, a sensor has to chosen based on the

following requirements.

1. Sensitivity and accuracy

2. Temperature Range

3. Desired life of Sensor

4. Budget

In the prototype module for the simulation purpose, ‘SL100’ NPN Transistor is used

as sensor because semiconductor Temperature sensor are best suited for embedded

applications as they tend to be electrically and mechanically more delicate than other

temperature sensor types.

In general silicon temperature sensors resistance is given by the equation

R = Rr (1+a (T - Tr) + b (T - Tr) 2 - c (T - Ti) d); where

Rr → Resistance at temperature Tr;

a, b, c→ constants.

Ti→ Inflection point temperature resistance, such that c=0 for T < Ti Also

resistance is dependent to some extent on the excitation current.

In the present module, as the resistance property of the transistor cannot be used

directly for interfacing, this transistor is employed as a feedback element in the following

configuration

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Let Rf be the resistance offered by the sensor under normal conditions(i.e. at S.T.P). The first stage is configured in Non-inverting amplifier mode, whose output voltage is given by

The second stage is designed as summing amplifier whose output is given by (Using superposition Principle)

Substituting the value of V01 from eq (1) in eq (2) we get

As Temperature increases Rf decreases and so from above equation (2) it can be

concluded “V0 increases with Temperature”. After fabricating the circuit as per above

configuration and with the resistor values as specified in list of components, it is

experimentally observed that the output voltage is increasing by 20mv for each degree rise in

temperature, after room temperature the initial output voltage can be set to desired value by

varying rest ‘P’.

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ANALOG TO DIGITAL CONVERTER:

The output of the various parameters is fed to A/D converter. The channel selection

depends upon the address selection sent by the Micro-controller. This ADC is having three

address inputs to select one out of eight channels of the ADC. This ADC 0809 is a successive

approx. Analog to digital converter and the clock rate at which the conversion is fed from the

IC 555 timer configured as astable multi-vibrator. The digital output after conversion is fed

to Micro-controller

For ADC to start converting the data after selecting the channel by sending the

address inputs, the start conversion signal is to be sent by Micro-controller. Then ADC starts

converting the analog signals voltage into corresponding digital data. For Ex: The following

table shows the digital data corresponding to analog input.

After conversion, the ADC generates EOC (End of conversion). This indicates to

Micro-controller that the conversion is completed and takes the digital data corresponding to

analog input. The following is Circuit diagram of A/D Converter along with its clock

generator:

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In the above circuit diagram 555 timer IC is used for generating the required clock pulses.

CLOCK GENERATOR:

The required clock for the ADC is generated using 555 Timer IC that is configured as

Astable multi-vibrator (Self Oscillator). In this mode of operation the required frequency can

be adjusted using two external components i.e., resistor and capacitor. Keeping capacitor

value constant where as by varying the value of resistor the frequency can be adjusted from

1Hz to 500KHz. Here the required frequency is 100 KHz approximately.

In the above circuit diagram 555 timer IC is used for generating the required clock

pulses. Frequency can be adjusted using variable resistor 100K (RB). In this circuit, the

external capacitor charges through RA+RB and discharges through RB. Thus the duty cycle

may be precisely set by the ratio of these two resistors. In this mode of operation, the

capacitor charges and discharges between 1/3 VCC and 2/3 VCC. As in the triggered mode,

the charge and discharge times, and therefore the frequency are independent of the supply

voltage. Here the timing resistor is now split into two sections, RA and RB, with the

discharge transistor (Pin 7) connected to junction of Ra and Rb. When the power supply is

connected, the timing capacitor C charges towards 2/3 VCC through Ra and Rb. When the

capacitor voltage reaches 2/3 VCC, the upper comparator triggers the flip-flop and the

capacitor starts to discharge towards ground through Rb. When the discharge reaches 1/3

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VCC the lower comparator is triggered and a new cycle is started. The capacitor is then

periodically charged and discharged between 2/3 VCC and 1/3 VCC respectively. The output

state is high during the charging cycle for a time period t1, so that

The output state is LOW during the discharge cycle for a time period t2, given by

t2 = 0.693 RbC

Thus, the total period charge and discharge is

T = t1 + t2 = 0.693 (Ra + 2Rb) C (Seconds)

So that the output frequency is given as

MICRO-CONTROLLER:

Circumstances that we find ourselves in today in the field of micro-controllers had

their beginnings in the development of technology of integrated circuits. This development

has made it possible to store hundreds of thousands of transistors into one chip. That was a

prerequisite for production of microprocessors, and adding external peripherals such as

memory, input-output lines, timers and other made the first computers. Further increasing of

the volume of the package resulted in creation of integrated circuits. These integrated circuits

contained both processor and peripherals. That is how the first chip containing a

microcomputer, or what would later be known as a micro-controller came about.

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MEMORY UNIT:

Memory is part of the micro-controller whose function is to store data. The easiest

way to explain it is to describe it as one big closet with lots of drawers. If we suppose that we

marked the drawers in such a way that they cannot be confused, any of their contents will

then be easily accessible. It is enough to know the designation of the drawer and so we will

know its contents for sure.

Memory components are exactly like that. For a certain input we get the contents of a

certain addressed memory location and that’s all. Two new concepts are brought to us:

addressing and memory location. Memory consists of all memory locations, and addressing

is nothing but selecting one of them. This means that we need to select the desired memory

location on one hand, and on the other hand we need to wait for the contents of that location.

Besides reading from a memory location, memory must also provide for writing onto it.

Supplying an additional line called control line does this. We will designate this line as R/W

(read/write). Control line is used in the following way: if r/w=1, reading is done, and if

opposite is true then writing is done on the memory location. Memory is the first element,

and we need a few operation of our micro-controller.

CENTRAL PROCESSING UNIT:

Let add 3 more memory locations to a specific block that will have a built in

capability to multiply, divide, subtract, and move its contents from one memory location onto

another. The part we just added in is called “central processing unit” (CPU). Its memory

locations are called registers.

Registers are therefore memory locations whose role is to help with performing

various mathematical operations or any other operations with data wherever data can be

found. Look at the current situation. We have two independent entities (memory and CPU)

that are interconnected, and thus any exchange of data is hindered, as well as its

functionality. If, for example, we wish to add the contents of two memory locations and

return the result again back to memory, we would need a connection between memory and

CPU. Simply stated, we must have some “way” through data goes from one block to another.

BUS:

That “way” is called “bus”. Physically, it represents a group of 8, 16, or more wires.

There are two types of buses: address and data bus. The first one consists of as many lines as

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the amount of memory we wish to address, and the other one is as wide as data, in our case 8

bits or the connection line. First one serves to transmit address from CPU memory, and the

second to connect all blocks inside the micro-controller.

INPUT-OUTPUT UNIT:

Those locations we’ve just added are called “ports”. There are several types of ports:

input, output or bi-directional ports. When working with ports, first of all it is necessary to

choose which port we need to work with, and then to send data to, or take it from the port.

When working with it the port acts like a memory location. Something is simply

being written into or read from it, and it could be noticed on the pins of the micro-controller.

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The following is the Circuit diagram of Digital Display Driven by the micro-controller

In the above circuit diagram, four common anode 7-Segment displays are used for

displaying the motor speed. The output of the Micro-controller is fed to digital display

through the latches, for this purpose IC 74573 is used, this is an octal transparent D-type

latches IC. To drive the displays independently 547 transistors are used. A seven segment

LED is a device for display of numbers and letters. It contains seven LED bars, which can be

turned on by placing the appropriate signals on the appropriate pins.

In order to produce a specific number, we must light the correct segments of the LED.

For example, to display the number 3, we must light segments a, b, c, d and g. By which we

understand that the pattern of lit and unlit segments can be formed into a binary number.

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F.M TRANSMITTER:

The following is the circuit diagram

In the above circuit design, the instantaneous frequency of the carrier is varied

directly in accordance with the base band signal by means of a device known as VCO

(Voltage controlled oscillator) one way of implementing such a device is to use a sinusoidal

oscillatory having a relatively high – Q frequency. Determining network and to control the

oscillator by symmetrical incremental variation of the reactive components. Thus the tone

signal modulated at 100 MHz carriers.

To understand how radio wave are generated and radiated into space, consider

alternating currents of suitable frequency fed into conductor or wire of suitable length called

the antenna. Fast moving alternating currents produce a moving electric field around the

antenna. This field in turn produces a magnetic field at right angles to it. This combination of

electric and magnetic fields constitutes the radio wave or electro magnetic wave, which is a

form of radiant energy.

F.M RECEIVER:

The FM receiver is located at the remote end. The first stage of this remote end unit is

the F.M. Radio Receiver, which is designed with Phillips IC TEA 5591A. In the circuit

diagram an LED indicator is connected at Pin No.7 of 5591 IC, which glows brightly, if the

receiver is tuned perfectly with the transmitter.

The F.M. receiver, which operates at 100 MHz, will have an intermediate frequency

of 10.7 MHz and bandwidth of 200 KHz. This IC consists of a built in RF amplification

circuit. It matches the input impedance of the antenna. This IC consists of F.M. Detector

including amplifier of modulated signal (RF amplification). Two sections of LC are provided

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and a ceramic filter is used to filter the IF of 10.7 MHz. The FM demodulator is basically a

frequency to amplitude converter, which converts the frequency deviation of the incoming

carrier into an AF (Audio frequency) amplitude variation identical to that of modulating

signal. In demodulation any change in amplitude of the signal fed to the FM demodulator is a

spurious signal. Therefore it must be removed, if distortion is to be avoided. A limiter is a

form of clipping device. It is quite possible for the amplitude limiter to be described to be

inadequate to its task, because signal strength variations may easily take average signal

amplitude outside the limiting range. As a result, further limiting is required. In practice, two

amplitude limiters are used in cascade. This arrangement increases the limiting range

satisfactory. To ensure that the signal fed to the limiter is within its range regardless of input

signal limiting range strength and also to prevent overloading of the amplifier, the AGC

(Automatic Gain Control) is used. Instead of designing a double limiter, the better

performance is obtained by using one limiter and AGC. The frequency-modulated signal is

fed to a tuned circuit whose resonant frequency is to one side of the center frequency (CF) of

the FM signal, the output of this tuned circuit will have an amplitude that depends on the

frequency deviation of the input signal. The following is the circuit diagram of F.M.

Receiver.

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SIGNAL AMPLIFIER:

For maximum power output and impedance matching the audio frequency driver

transformer is used in the signal amplifier circuit. The design equation of a driver transformer

is

When n = Ratio of the transformer

Where N1 = Primary winding and N2 = Secondary winding. The following is theCircuit diagram of signal amplifier.

The signal, which is detected by the receiver, is further amplified with the help of

above audio amplifier. In this circuit, the input capacitor 0.1 MF permits complete input

power to flow into the base circuit. It also blocks the DC component to flow into the base

circuit. The 330K resistor works as a biasing resistor. The purpose of this biasing is as

follows.

A study of the transistor characteristics shows that the transistor function is most

linear when the transistor operates in its active region. The operating point may then be

suitably placed in this region by proper selection or dc potentials and currents through use of

external energy sources. With a properly selected operating point, the time varying

component of the AC input signal. Say base current in common emitter amplifier, results in

output signal of the same waveform. An improperly selected operating points results in an

output signal, which differs in waveform from the input signal, such an operative point is

unsatisfactory and should be rejected. The selection of suitable operating point is vital for

linear amplification. The 100 and 330K forms as a input resistance of the transformer

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primary. For securing maximum transfer of power from the amplifier to the load, the source

impedance should match with the input impedance of the amplifier transferred to the primary

of the transformer. Similarly for maximum transfer of power from the amplifier to the load,

the output impedance of the amplifier is matched with the load impedance. To get large

output the two secondary signals are cascaded and output is taken for further processing. In +

VC half cycle, the top transistor circuit enables and in the –VC half cycle, the bottom

transistor circuit enables and total cycle gets amplified output signal.

The output of this signal amplifier is fed to the F/V converter.

FREQUENCY TO VOLTAGE CONVERTER:

The output of the signal amplifier is converted into DC voltage in proportion to the

tone frequency, with the help of phase locked loop IC 4046 and Multi-plexer IC 4053. The

amplified signal is fed to the in signal (Pin NO.14) of the device, which is the input of the

phase comparator. The other input of the phase comparator is fed from the internally

generated voltage controlled oscillator (VCO), whose frequency is set with the help of

external capacitor connected between Pin 6 and 7, here PLL is used for synchronization. The

output of the PLL is fed to the Multiplexer. The signals of the phase comparator – I and

phase comparator – II are fed so that the output is multi-plexed with the hlp of IC4053. The

output of the F/V converter is fed to the Analog to digital converter circuit for converting the

Analog information into digital pulses. The circuit design of phase locked loop with

multiplexer and its associated circuitry is shown below.

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ANALOG TO DIGITAL CONVERTER:

The A/D Converter used in the receiving module is similar to the A/D converter used

in the transmitter. The difference is the transmitter converter is interfaced with the Micro-

controller where as the receiver converter is interfaced with computer. The following is the

circuit diagram of A/D converter along with latches and buffer used in the receiving module.

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CHAPTER – 5

DETAILS ABOUT WIRELESS COMMUNICATION

Model of a communication system:

The overall purpose of the communication system is to transfer information from one

point to in space and time, called the source to another point, the user destination. As a rule,

the message produced by a source is not electrical. Hence an input transducer is required for

converting the message to a time varying electrical quantity called a message signal. At the

destination point another transducer converts the electrical waveform to the appropriate

message.

The information source and the destination point are usually separated in space. The

channel provides the electrical connection between the information source and the user. The

channel can have many deferent forms such as a microwave radio link over free space a pair

of wires, or an optical fiber. Regardless of its type the channel degrades the transmitted

single in a number of ways. The degradation is a result of signal distortion due to imperfect

response of the channel and due to undesirable electrical signals (noise) and interference.

Noise and signal distortion are two basic problems of electrical communication. The

transmitter and the receiver in a communication system are carefully designed to avoid signal

distortion and minimize the effects of noise at the receiver so that a faithful reproduction of

the message emitted by the source is possible.

The transmitter couples the input message signal to the channel. While it may

sometimes be possible to couple the input transducer directly to the channel, it is often

necessary to process and modify the input signal for efficient transmission over the channel.

Signal processing operations performed by the transmitter include amplification, filtering,

and modulation. The most important of these operations is modulation a process designed to

match the properties of the transmitted signal to the channel through the use of a carrier

wave.

Modulation is the systematic variation of some attribute of a carrier waveform such as

the amplitude, phase, or frequency in accordance with a function of the message signal.

Despite the multitude of modulation techniques, it is possible to identify two basic types of

modulation: the continuous carrier wave (CW) modulation and the pulse nodulation. In

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continuous wave (CW) carrier modulation the carrier waveform is continuous (usually a

sinusoidal waveform), and a parameter of the waveform is changed in proportion to the

message signal. In pulse modulation the carrier waveform is a pulse waveform (often a

rectangular pulse waveform), and a parameter of the pulse waveform is changed in

proportion to the message signal. In both cases the carrier attribute can be changed in

continuous or discrete fashion. Discrete pulse (digital) modulation is a discrete process and is

best suited for messages that are discrete in nature such as the output of a teletypewriter.

However, with the aid of sampling and quantization, continuously varying (analog) message

signal can be transmitted using digital modulation techniques.

Modulation is used in communication systems for matching signal

characteristics to channel characteristics, for reducing noise and interference, for

simultaneously transmitting several signals over a single channel, and for overcoming some

equipment limitations. A considerable portion of this article is devoted to the study of how

modulation schemes are designed to achieve the above tasks. The success of a

communication system depends to a large extent on the modulation.

The main function of the receiver is extracting the input message signal from the

degraded version of the transmitted signal coming from the channel. The receiver performs

this function through the process of demodulation, the reverse of the transmitter’s modulation

process. Because of the presence of noise and other signal degradations, the receiver cannot

recover the message signal perfectly. Ways of approaching ideal recovery will be discussed

later. In addition to demodulation, the receiver usually provides amplification and filtering.

Based on the type of modulation scheme used and the nature of the output of

the information source, we can divide communication systems into three categories:

1.analog communication systems designed to transmit analog information using

analog modulation methods

2. Digital communication systems designed for transmitting digital information using

digital modulation schemes and

3. Hybrid systems that use digital modulation schemes for transmitting sampled and

quantized values of an analog message signal.

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Other ways of categorizing communication systems include the classification based

on the frequency of the carrier and the nature or the communication channel.

With this brief description of a general model of a communication system, we will

now take a detailed look at various components that make up a typical communication

system using the digital communication system as an example. We will enumerate the

important parameter of each functional block in a digital communication system and point

out some of the limitations of the capabilities of various blocks.

ELEMENTS OF A DIGITAL COMMUNICATION SYSTEM:

The overall purpose of the system is to transmit the messages (or sequences of

symbols) coming out of a source to a destination point at as high a rate and accuracy as

possible. The source and the destination point are physically separated in space and a

communication channel of some sort connects the source to the destination point. The

channel accepts electrical/electromagnetic signals, and the output of the channel is usually a

smeared or distorted version of the input due to the non-ideal nature of the communication

channel. In addition to the smearing, the information-bearing signal is also corrupted by

unpredictable electrical signals (noise) from both man-made and natural causes. The

smearing and noise introduce errors in the information being transmitted and limits the rate at

which information can be communicated from the source to the destination. The probability

of incorrectly decoding a message symbol at the receiver is often used as a measure of

performance of digital communication system. The main function of the coder, the

modulator, the demodulator, and the decoder is to combat the degrading effects of the

channel on the signal and maximized the information rate and accuracy.

INFORMATION SOURCE:

Information sources can be classified into two categories based on the nature

of their outputs: Analog information sources, and discrete information sources. Analog

information sources, such as a microphone actuated by speech, or a TV camera scanning a

scene, emit one or more continuous amplitude signals (or functions of time). The output of

discrete information sources such as a teletype or the numerical output of a computer consists

of a sequence of discrete symbols or letters. An analog information source can be

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transformed onto a discrete information source through the process of sampling and

quantizing. Discrete information sources ate characterized by the following parameters:

1. Source alphabet (symbols or letters)

2. Symbol rate

3. Source alphabet probabilities

4. Probabilistic dependence of symbols in a sequence

From these parameters, we can construct a probabilistic model of the information

source and define the source entropy (H) and source information rate (R) in bits per symbol

and bits per second, respectively. The term bid is used to denote a binary digit.)

To develop a feel for what these quantities represent, let us consider a discrete

information source-a Teletype having 26 letters of the English alphabet plus six special

characters. The source alphabet for this example consists of 32 symbols. The symbol rate

refers to the rate at which the Teletype produces characters: for purposes of discussion, let us

assume that the Teletype operates at a speed of 10 characters or 10 symbols/sec. If the

Teletype is producing messages consisting of symbol sequences in the English language,

then we know that some letters will appear more often than others. We also know that the

occurrence of a particular letter in a sequence is somewhat dependent on the letters preceding

it. For example, the letter E will occur more often than letter Q and the occurrence of Q

implies that the next letter in the sequence will most probably be the letter U, and so forth.

These structural properties of symbol sequences can be characterized by probabilities of

occurrence of individual symbols by the conditional probabilities of occurrence of symbols.

An important parameter of a discrete source is its entropy. The entropy of a

source, denoted by H, refers to the average information content per symbol in a long message

and is given units of bits for symbol where bit is used as an abbreviation for a binary digit. In

our example, if we assume that all symbols occur with equal probabilities in a statistically

independent sequence, then the source entropy is five bits per symbols. However, the

probabilistic dependence of symbols in a sequence, and the unequal probabilities of

occurrence of symbols considerably reduce the average information content of the symbols.

Naturally we can justify the previous statement by convincing ourselves that in a symbol

sequence QUE, the letter U carries little or no information because the occurrence of Q

implies that the next letter in the sequence has to be a U.

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The source information rate is defined as the product of the source entropy

and the symbol rate and has the units of bits per second. The information rate, denoted by R,

represents the minimum number of bits per second that will be needed, on the average, to

represent the information coming out of the discrete source. Alternately, R represents the

Minimum average data rate needed to convey the information from the source to the

destination.

Source Encoder/Decoder:

The input to the source encoder (also referred to as the source coder) is a

string of symbols occurring at a rate of rs symbols/sec. The source coder converts the symbol

sequence into a binary sequence of 0’s and 1’s by assigning code words to the symbols in

input sequence. The simplest way in which a source coder can perform this operation is to

assign a fixed-length binary code word to each symbol in the input sequence. For the teletype

example we have been discussing, this can be done by assigning 5-bit code world 00000

through 11111 for the 32 symbols in the source alphabet and replacing each symbol in the

input sequence by its pre-assigned code word. With a symbol rate of 10 symbols/sec, the

source coder output data rate will be 50 bits/sec.

Fixed-length coding of individual symbols in a source output is efficient only

if the symbols occur with equal probabilities in a statistically independent sequence. In most

practical situation symbols in a sequence are statistically dependent, and they occur with

unequal probabilities. In these situations the source coder takes a string of two or more

symbols as a block and assigns variable-length code words to these block. The optimum

source coder is designed to produce an output data rate approaching R, the source

information rate. Due to practical constraints, the actual output rate of source encoders will

be greater than the source information rate R. the important parameters of a source coder are

black size, code word lengths, average data rate, and the efficiency of the coder (i.e., actual

output data rate compared to the minimum achievable rate R).

At the receiver the source decoder converts the binary output of the channel

decoder into a symbol sequence. The decoder for a system using fixed-length code words is

quite simple, but the decoder for a system using variable-length code words will be very

complex. Decoders for such systems must be able to cope with a number of problems such as

growing memory requirement and loss of synchronization due to bit errors.

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Communication Channel:

The Communication channel provides the electrical connection between the source

and the destination. The channel may be a pair of wires or a telephone link or free space over

which the information-bearing signal is radiated. Due to physical limitations, communication

channels have only finite bandwidth (B HZ), and the information-bearing signal often suffers

amplitude and phase distortion as it travels over the channel. In addition to the distortion, the

signal power also decreases due to the attenuation of the channel. Furthermore, the signal is

corrupted by unwanted, unpredictable electrical signals referred to as noise. While some of

the degrading effects of the of the channel can be removed or compensated for, the effects of

noise cannot be completely removed. From this point of view, the primary objective of a

communication system design should be to suppress the bad effects of the noise as much as

possible.

One of the ways in which the effects of noise can be minimized is to increase the

signal power. However, signal power cannot be increased beyond certain levels because of

nonlinear effects that become dominant as the signal amplitude is increased. For this reason

the signal-to-noise power ratio (S/N), which can be maintained at the output of a

communication channel, is an important parameter of the system. Other important parameters

of the channel are the usable bandwidth (B), amplitude an phase response, and the statistical

properties of the noise.

If the parameters of a communication channel are known, then we can compute the

channel capacity C, which represents the maximum rate at which nearly errorless data

transmission is theoretically possible. For certain types of communication channels it has

been shown that c is equal to B log2 (1+S/N) bits/sec. The channel capacity C has to be

greater than the average information rate R of the source for errorless transmission. The

capacity c represents a theoretical limit, and the practical usable data rate will be much

smaller than C. as an example, for a typical telephone link with a usable bandwidth of 3KHz

and S/N = 103, the channel capacity is approximately 30,000 bits/sec. At the present time,

the actual data rate on such channels ranges from 150 to 9600 bits/sec.

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Modulator:

The modulator accepts a bit stream as its input and converts it to an electrical

waveform suitable for transmission over the communication channel. Modulation is one of

the most powerful tools in the hands of a communication systems designer. It can be

effectively used to minimize the effects of channel noise, to match the frequency spectrum of

the transmitted signal with channel characteristics, to provide the capability to multiplex

many signals, and to overcome some equipment limitations.

The important parameters of the modulator are the types of waveforms used, the

duration of the waveforms, the power level, and the bandwidth used. The modulator

accomplishes the task of minimizing the effects of channel noise by the use of large signal

power and bandwidth, and by the use of waveforms that last for longer durations. While the

use of increasingly large amounts of signal power and bandwidth to combat the effects of

noise is an obvious method, these parameters cannot be increased indefinitely because of

equipment and channel limitations. The use of waveforms of longer time duration to

minimize the effects of channel noise is based on the well-known statistical law of large

numbers. The law of large numbers states that while the outcome of a single random

experiment may fluctuate wildly, the overall result of many repetitions of a random

experiment can be predicted accurately. In data communications, this principle can be used

to advantage by making the duration of signaling waveforms long. By averaging over

longer durations of time, the effects of noise can be minimized.

To illustrate the above principle, assume that the input to the modulator consists of

0’s and 1’s occurring at a rate of 1 bit/sec. The modulator can assign waveforms once every

second. Notice that the information contained in the input bit is now contained in the

frequency of the output waveform. To employ waveforms of longer duration, the modulator

can assign waveforms once every four seconds. The number of distinct waveforms the

modulator has to generate (hence the number of waveforms the demodulator has to detect)

increases exponentially as the duration of the waveforms increases. This leads to an increase

in equipment complexity and hence the duration cannot be increased indefinitely. The

number of waveforms used in commercial digital modulators available at the present time

ranges from 2 to 16.

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Demodulator:

Modulation is a reversible process, and the demodulator accomplishes the extraction

of the message from the information bearing waveform produced by the modulator. For a

given type of modulation, the most important parameter of the demodulator is the method of

demodulation. There are a variety of techniques available for demodulating a given

modulated waveform: the actual procedure used determines the equipment complexity

needed and the accuracy of demodulation. Given the type and duration of waveforms used by

the modulator, the power level at the modulator, he physical and noise characteristics of the

channel, and the type of demodulation, we can derive unique relationship between data rate,

power bandwidth requirements, and the probability of incorrectly decoding a message bit. A

considerable portion of this text is devoted to the derivation of these important relationships

and their use in system design.

Channel Encoder/Decoder:

Digital channel coding is a practical method of realizing high transmission reliability

and efficiency that otherwise may be achieved only by the use of signals of longer duration in

the modulation/demodulation process. With digital coding, a relatively a small set of analog

signals, often two, is selected for transmission over the channel and the demodulator has the

conceptually simple task of distinguishing between two different waveforms of known

shapes. The channel coding operation that consists of systematically adding extra bits to the

output of the source coder accomplishes error control. While these extra bits themselves

convey no information, they make it possible for the receiver to detect and/or correct some of

the errors in the information bearing bits.

There are two methods of performing the channel coding operation. In the first

method, called the block coding method, the encoder takes a block of k information bits from

the source encoder and adds r error control bits. The number of error control bits added will

depend on the value of k and the error control capabilities desired. In the second method,

called the convolution coding method, the information bearing message stream is encoded in

a continuous fashion by continuously interleaving information bits and error control bits.

Both methods require storage and processing of binary data at the encoder and decoder.

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While this requirement was a limiting factor in the early days of data communication, it is no

longer such a problem because of the availability of solid-state memory and microprocessor

devices at reasonable prices.

The important parameters of a channel encoder are the method of coding. Rate or

efficiency of the coder (as measured by the ratio of data rate at input to the data rate at the

output), error controls capabilities, and complexity of the encoder.

The channel decoder recovers the information bearing bits from the coded binary

stream. The channel decoder also performs error detection and possible correction. The

decoder operates either in a block mode or in a continuous sequential mode depending on the

type of coding used in the system. The complexity of the decoder and the time delay

involved in the decoder are important design parameter.

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CHAPTER – 6

THEORY RELATED TO DISTRIBUTION TRANSFORMERS

The transformer is a device, which transfers electrical energy from one electrical to

another electrical circuit through the medium of magnetic field and without a change in the

frequency. The electric circuit, which receives energy from the supply mains, is called

primary winding and the other circuit, which delivers electric energy to the load, is called the

secondary winding. Actually, the transformer is an electromagnetic energy conversion

device, since the energy received by the primary is first converted to magnetic energy and it

is then reconverted to useful electrical energy in the other circuits. Thus primary and

secondary windings of a transformer are not connected electrically, but are coupled

magnetically. This coupling magnetic field allows the transfer of energy in either direction,

from high voltage to low voltage circuits or from low voltage to high voltage circuits. If the

transfer of energy occurs at the same voltage, the purpose of the transformer is merely to

isolate the two electric circuits and this use is very rare in power applications. If the

secondary winding has more turns than the primary winding, then the secondary voltage is

higher than the primary voltage and the transfer is called a step-up transformer. In case the

secondary winding has less turns than the primary winding, then the secondary voltage is

lower than the primary voltage and the transformer is called a step-down transformer. Note

that a step-up transformer can be used as a step-down transformer, in which case the

secondary of step-up transformer becomes the primary of step-down transformer. Actually a

Transformer can be termed a step-up or step-down transformer only after it has been put into

service. Therefore, when referring to the windings of a particular transformer, the terms high-

voltage winding and low voltage winding should be used instead of primary and secondary

windings.

A transformer is the most widely used device in both low and high current circuits.

As such, transformers are built in an amazing range of sizes. In electronic, measurement and

control circuits, transformer size may be so small that it weighs only a few tens of grams

whereas in high voltage power circuits, it may weigh hundreds tones.

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There are two general types of transformers, the core type and the shell type. These

two types differ from each other by the manner in which the windings are wound around the

magnetic core. A transformer works on the principle of electro magnetic induction.

According to the principle, an e.m.f. is induced in a coil if it links a changing flux.

A distribution transformer should have a small value of voltage regulation, so that the

terminal voltage at the consumer’s premises doesn’t vary widely as the load changes. For a

transformer of large voltage regulation, the voltage at the consumer’s terminals will fall

appreciably with the increase in load. This has a detrimental effect on the operation of the

fluorescent tubes, TV sets, Refrigerator Motors etc., since these are designed to operate

satisfactorily at a constant voltage. Thus the distribution transformers should be designed to

have a low value of leakage impedance.

The transformer efficiency can be calculated if the total loses in the transformer are

known. Power transformers are used at the sending and receiving ends of a long, high voltage

power transmission line for stepping up or stepping down the voltage. These transformers are

manipulated to operate almost always at or near their rated capacity. Therefore, power

transformers are disconnected during light load periods. In view of this, a power transformer

is designed to have maximum efficiency at or near its full load KVA. Hence the choice of a

power transformer, out of a large numbers of competing transformers, should be based on

full load efficiency.

Distribution transformers are those, which change the voltage to a level suitable for

utilization purposes at the consumer’s premises. A power transformer does not come in direct

contact with the consumer’s terminals, whereas a distribution transformer must have its

secondary directly connected with the consumer’s terminals. The load on a distribution

transformer varies over a wide range during a 24-hour day. For example, a distribution

transformer in a residential colony may have practically little or no load during a

considerable portion of the daytime, but in the evenings, the load may be near its rated

capacity. Note that the primary of distribution transformers are always energized and,

therefore, the core loss takes place continuously. In view of this, the distribution transformers

are designed to have very low value of core loss. But for reduced core loss Pc (Pc is constant

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load voltage) the maximum efficiency may occur at about one-half of its rated KVA. Thus a

distribution transformer should not be judged by its full load efficiency, which is usually

much less than its maximum efficiency. However, the choice of a distribution transformer,

out of a large number of competing transformers, can be based on energy efficiency.

While testing the transformer polarity, on the primary side of two ending transformer,

one terminal is positive with respect to the other terminal at any one instant. At the same

instant one terminal of the secondary winding is positive with respect to the other terminal.

These relative polarities of the primary and the secondary terminals at any instant must be

known if the transformers are to be operated in parallel or are to be used in a polyphase

circuit.

A load test on a transformer is necessary if its maximum temperature rise is to be

determined. A small transformer can be put on full load by means of suitable load

impedance. But for large transformer, full load test is difficult, since it involves considerable

waste of energy and a suitable load, capable of absorbing full load power, is not easily

available. However, large transformers can be put on full load by means of sumpner’s or

back-to-back test. The sumpner’s test can also be used for calculating the efficiency of a

transformer, though the later can be determined accurately from open circuit and short-

circuited tests.

The back-to-back test on single Phase transformers requires to identical units, where

two primaries are connected in parallel, are energized at rated voltage and rated frequency.

For performing the load test on single-phase transformers, two identical units are

essential, whereas the load test on three phase transformers can be carried out on a single

unit.

A transformer, in which a part of the winding is common to both the primary and

secondary circuits, is called an autotransformer. In a two winding transformer, primary and

secondary windings are electrically isolated, but in an auto transformer the two windings are

not electrically isolated. The main dis-advantage of an autotransformer is due to the direct

electrical connection between the low tension and high-tension sides.

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CHAPTER – 7

DETAILS ABOUT ‘A’ TO ‘D’ CONVERTERS

The analog – to – digital converter (A.D) is used to convert an analog voltage or

current input to an output binary word that can be used by a computer. Of the many

techniques that have been published for performing an A/D conversion, only a few are of

interest to us: so we will consider only the voltage to frequency, signal – slope integrator,

duel-slope integrator, counter (or servo), successive approximation and flash methods. The

basic size of circuit that we will show is the 8-bit A/D converter, which for many purposes is

all that is needed. These same discussions are also useful for 10-bit, 12-bit or higher order

A/D converters.

INTEGRATION A/D METHODS:

Most digital panel Meters (DPM) and digital multi-meters (DMM) use either the

single integration or duel-slope integration methods for the A/D conversion process. The

single slope integrator is simple, but is limited to those applications that can tolerate accuracy

of one or two percent.

An example of single slope integrator A/D converter is shown in the next page, while

its timing diagram is shown below that.

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The following is the timing diagram

The single – slope integrator A/D converter consists of five basic sections: Ramp

generator, comparator, and logic. Clock and an output encoder consisting of a binary counter,

latch and display in the digital counter block. The ramp generator is an ordinary operational

amplifier Miller integrator with its input connected to a stable, fixed, reference voltage

source. This makes the input current essentially constant; so the voltage at Ramp o/p will rise

in a nearly linear manner, creating the voltage ramp. The comparator is an operational

amplifier that has an open feed back loop. The circuit gain is the open-loop gain (A vol) of

the device selected. Typically very high even in low cost operational amplifiers. When the

analog input voltage Vx is greater than the ramp voltage, the output of the comparator is

saturated at logic –HIGH level. The logic section consists of a main AND gate, a main gate

control, and a clock. The waveforms associated with this circuit are based on unknown input

Voltage Vx. The AND gate requires all three inputs to be high before its output can

be HIGH also. The output of the AND gate will go HIGH every time the clock signal is also

HIGH. The encoder, in this case an B-bit binary counter, will than see a pulse train with a

length proportional to the amplitude of the analog input voltage. If the A/D converter is

designed correctly, then the maximum range (full-scale) value of Vx. Several problems are

found in single-slope integrator A/D converters.

1) The ramp voltage may be Non-linear

2) The ramp voltage may have too steep or too shallow a slope

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3) The clock pulse frequency could be wrong

4) It may be prone to changes in apparent value of Vx caused by Noise

The duel-slope integrator corrects many of these problems. This circuit also consists

of five basic sections: integrator, comparator, control logic section, binary counter and a

reference current or voltage source. An integrator is made with an operational amplifier

connected with a capacitor in the negative feed back loop, as was the case in the single-slope

version. The comparator in this circuit is also the same sort of circuit as was used in the

previous example. In this case though, the comparator is ground referenced by connecting

+IN to ground. When a start command is received, the control circuit resets the counter,

resets the integrator to ‘O’ volts. The analog voltage creates an input current to the integrator,

which causes the integrator output to begin charging capacitor; the output voltage of the

integrator will begin to rise. As soon as this voltage rises a few milli volts above ground

potential the comparator output snaps HIGH- Positive. A HIG comparator output causes the

control circuit to enable the counter, which begins to count pulses.

Voltage to Frequency Converters:

These circuits are not A/D Converters in the strictest sense, but are very good for

representing analog data in a form that can be tape recorder on a low cost audio- machine, or

transmitted over radio. The V/F converter output can also be used for direct input to a

computer if a binary counter is used to measure the output frequency. Two forms of V/F

converter are common. One is a voltage-controlled oscillator (VCO), that is, a regular

oscillator circuit in which the output frequency is a function of an input controls voltage. If

the VCO is connected to a binary or binary coded decimal (BCD) counter, then the VCO

becomes a V/F form of A/D converter. The integrator, which causes the integrator output to

begin charging capacitor, the output voltage of the integrator will begin to rise. As soon as

this voltage rises a few milli-volts above ground potential the comparator output snaps HIGH

– Positive. A HIG comparator output causes the control circuit to enable the counter, which

begins to count pulses. The following is the block diagram of voltage to frequency converter

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Counter type A/D Converter:

A counter type A/D converter (Also called “servo” or “ramp” A/D converters)

consists of a comparator, voltage output DAC, binary counter, and the necessary control

logic. When the start command is received, the control logic resets the binary counter,

enables the clock, and begins counting. The counter outputs control the DAC inputs, so the

DAC output voltage will begin to rise when the counter begins to increment. As long as

analog input voltage Vx is less than Vref (The DAC output), the comparator output is HIGH,

when Vx and Vref are equal, however, the comparator output goes low, which turns off the

clock and stops the counter output at this time represents the value of Vx. The following is

the block diagram of binary A/D converter.

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SUCCESSIVE APPROXIMATION A/D CONVERTERS:

Successive approximation A/D conversion is best suited for many applications where

speed is important. This type of A/D converter requires only N+1 clock cycles to make the

conversion, and some designs allow truncation of the conversion process after fewer cycles if

the final value is found prior to N+1 Cycles. The successive approximation converter

operates by making several successive trails at comparing the analog input voltage with a

reference generated by a DAC.

PARALLEL OR “FLASH” A/D converters:

The parallel A/D Converter is probably the fastest A/D circuit known; indeed, the

very fastest ordinary commercial products use this method. Some sources call the parallel

A/D converter the “flash” circuit because of its inherent high speed. The parallel A/D

converter consists of a blank of (2N-1) voltage comparators biased by reference potential

Vref though a resistor Network that keeps the individual comparators 1-LSB a port. Since the

input voltage is applied to all the comparators simultaneously, the speed of conversion is

limited essentially by slow rate of the slowest comparator in the bank, and also by the

decoder circuit propagation time. The decoder converts the output code to binary code

needed by the computers. The A/D converter is a circuit that is used to produce a binary

number output that represents an analog voltage applied to the input.

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CHAPTER – 8

DETAILS ABOUT MICORCONTROLLER

The micro-controller is a chip, which has a computer processor with all its support

functions, memory (both program storage and RAM), and I/O built in to the device. These

built in functions minimize the need for external circuits and devices to be designed in the

final applications.

Most micro-controllers do not require a substantial amount of time to learn how to

efficiently program them, although many of them have quirks, which you will have to under

stand before you attempt to develop your first application.

Along with micro-controllers getting faster, smaller and more power efficient they are

also getting more and more features. Often, the first version of micro-controller will just have

memory and simple digital I/O, but as the device family matures, more and more part

numbers with varying features will be available.

With all the 8051 manufacturer’s products taken into account, there are over two

hundred different 8051 part numbers, each with different features and capabilities. For most

applications, we will be able to find a device within the family that meets our specifications

with a minimum of external devices, or an external but which will make attaching external

devices easier, both in terms of wiring and programming.

For many micro-controllers, programmers can be built very cheaply, or even built in

to the final application circuit eliminating the need for a separate circuit. Also simplifying

this requirement is the availability of micro-controllers with SRAM and EEPROM for

control store, which will allow program development without having to remove the micro-

controller from the application circuit.

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Different types of Micro-controllers:

Creating applications for micro-controllers is completely different than any other

development job in computing and electronic. In most other applications, we probably have a

number of sub systems and interfaces already available for our use. This is not the case with

a Micro-controller, where we are responsible

a) Power distribution

b) System clocking

c) Interface design and wiring

d) Systems programming

e) Application programming

f) Device programming

These work items might seem obvious, but having to do them all is really quite

profound in modern computing system development. In no other aspect of electronics are all

these requirements found. The process is also made more enjoyable by learning how to work

with the features built into the devices that are designed to simplify the task of directly

connecting to other devices. Often, very useful applications can be created using a micro-

controller and a few passive components.

Embedded micro-controllers:

When all the hardware required to run the application is provided on the chip, it is

referred to as an embedded micro-controller. All that is typically required to operate the

device is power, reset, and a clock. Digital I/O pins are provided to allow interfacing with

external devices. This complete hardware on a chip is extremely useful for some

applications.

Embedded micro-controllers are now replacing some very common devices like 555

timers because they are actually cheaper to use in applications and they are much more

precise and easier to control

Micro-controller memory types:

Memory is probably not something we normally think about when we create

applications for a personal computer. In a micro-controller, understanding how much

memory we have and how its architect is critical, especially when we are planning on how to

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implement the application code. In a micro-controller, memory for different purposes is

typically segregated and arranged to allow the device to execute most efficiently.

Control storage:

In a PC, when we execute an application, we read the application from disk and store

it into an allocated section of memory. In a micro-controller, this is not possible because

there is no disk to read from. The application that is stored in non-volatile memory is always

the only software the micro-controller will execute. Having the program always available in

memory makes the writing of its some what different than PC or work station applications.

Control store is known by a number of different names including program memory

and firmware (as well as some permutations of the various names). The name really is not

important. What is important is under standing that this memory space is the maximum size

of the application that can be loaded in to the micro-controller and that the application also

includes all the low-level code and device interfaces necessary to execute an application.

CHIP TECHNOLOGIES:

Micro-controllers, like all other electronic products, are growing smaller, running

faster, requiring less power, and are cheaper. This is primarily due to improvements in the

manufacturing process and technologies used (and not the adoption of different computer

architectures). Virtually all micro-controllers built today use CMOS (complementary metal

oxide semiconductor) logic technology to provide the computing functions and electronic

interfaces. CMOS is a push-pull technology in which a PMOS and NMOS transistor are

paired together. The following is the circuit diagram of push-pull configuration

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When the input signal is low, the PMOS transistor will be conducting and the NMOS

transistor will be ‘off’. This means that the switch (or transistor) at Vcc will be ‘ON’,

providing Vcc at the signal out. If a high voltage is input to the gate, then the PMOS

transistor will be turned off and the NMOS transistor will be turned on, pulling the output

line to ground. During a state transition, a very small amount of current will flow through the

transistors. As the frequency of operation increases, current will flow more often in a given

period of time (put another way, the charge transferred per unit time, which is defined as

“current”, will increase). This increased current flow will result in increased power

consumption by the device. Therefore, a CMOS device should be driven at the slowest

possible speed, to minimize power consumption.

An important point with all logic families understands the switching point of the input

signal. For CMOS devices, this is typically 1.4Volts to one half of Vcc. However, it can be at

different levels for different devices. Before using any device, it is important to understand

what the input threshold level is. CMOS can interface directly with most positive logic

technologies, although we must be careful of low voltage logic, to make sure that a high can

be differentiated from a low in all circumstances.

ATMEL 89C51 PROGRAMMING:

Programming the Atmel AT89Cx051 series of 8051 micro-controllers uses some

what of a different algorithm than what is used for the standard 40-pin devices. The

AT89C51 algorithm is actually quite simple to implement. This programmer hardware can

also be used to program AVR 20-pin micro-controllers.

The programming can be described as erasing the control store and then presenting

bytes to the micro-controller and latching it in. After the byte is latched in, the programmer

waits for the byte to be saved into control store before reading it back and incrementing the

AT89Cx051’s program counter to receive the next byte.

To begin the programming cycle, the AT 89C51 is powered up with the Reset and

XTAL1 pins held low. Then, +5V is applied to Reset and the PROG pin. At this point, the

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program counter inside the AT89C51 is reset to zero. After power up, the first thing we

should do is a chip erase, to prepare the control store for the next program (all the control

store bytes are loaded with 0FFh). This is accomplished by setting high and to low (this will

be characterized as HLLL to show how the control signals are set) and pulsing PROG low for

at least 10 msec.

With the chip erased, the control store can be programmed. Note that Reset is cycled

between +5V and +12V for writes and reads. This means that the Reset driver has to be a

circuit that can output 0V, 5V, and 12V to the Reset Pin.

The lock bits are used to limit access to the application in control store of a

programmed part. If lock bit 1 is programmed, then the flash control store cannot be updated

until it is erased again. If bit 2 is programmed, the verify fuction (read back) will return

invalid data (this is copy protection for the chip , there is no encryption array in the

AT89Cx51) again until the control store on the chip is erased. For obvious reasons, these two

bits should not be programmed until the application programming is complete.

Often in application programming, there will be gaps in the code, which means there

are areas that are not programmed. The AT89Cx51’s program counter can be incremented

(by pulsing XTAL1) to skip over these areas. To carry this out, the programmer’s control

software will have to keep track of the current value of the program counter as it works

through programming the device.

AT89Cx051

Programmer Circuit:

For many other devices (including the PIC Micro and even the 68HCxx), there are

actually quite a few simple circuits available for simply programming the Micro-controller.

While not attempting to fill the gap, a perfect programmer circuit can be design and it can be

used for all the AT89Cx51 applications.

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One nice feature of the programmer is its ability to be used in-circuit, it can be wired

into a prototype circuit and have the AT89Cx051 run without having to pull the chip in an

out of the programmer as circuits are being developed. Another feature is that this circuit

could be used for programming 20-pin Atmel AVR micro-controllers in parallel mode.

The circuit itself is pretty simple and can be blocked out, with the programmer

connected to an IBM –compatible PC via the parallel port. An adaptor with at least 16V

peak-to-peak supplies power. The power circuit provides switched +5 and +12V for the

8051’s Vcc and Reset (0 V, +5 V or +12 V). The programmer control block controls the

power circuit. If Reset is being driven by something other than 0 V, the programmer drivers

are active.

With this circuit, it is found that, when going from +12V to +5V on Reset, 30 micro

sec was needed. If we end up writing our own software for this circuit, we may have to make

sure that we have a long enough delay before attempting to read back what was written.

Going from 0 V to +5V or +12V (or from +5V to +12V) took less than a micro sec.

The programmer control block is used to control the power applied to the device

being programmed as well as to its Reset (as noted in the previous paragraph) and the

programming mode of AT89Cx51. A 74LS374 is used with data being latched in from the

PC’s parallel port. The output of the ‘374 is always enabled, but all the lines going to the

AT89Cx51 (with the exception of the power and Reset, which are independently controlled)

pass through a 74LS244, which allows the AT89Cx51 to be pulled from the circuit without

turning off the power to the programmer.

The ‘244 is also used to pass the RDY/_BSY signal back to the PC to allow the

programmer to poll the RDY/_BSY to determine when the programming operation has

finished.

The Data, which allows a programming byte to be passed to the Micro-controller or

read from it. It could have eliminated this pin and had the same functionality by simply using

the bi-directional features of the PC’s parallel port. However, to ensure that the AT89Cx51

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would run in-circuit, we wanted to make sure that we could disable the connection to the PC,

to make sure the cable wouldn’t affect the operation of the application and, more importantly,

make sure that invalid voltages or signals in the application circuit would not damage the PC.

The PC should have a parallel port capable of bi-directional I/O, and we used a

switch-box dual male DB-25 connector cable. This cable is used for connecting a PC’s

parallel port to a printer sharing switch box. On two of the Db- 25 connectors, each pin is

directly connected (i.e., pin 1 is connected to Pin 1, pin 2 to pin 2, and so on), which makes

wiring to the application easier.

The final circuit probably looks pretty complex; however, by following the nets, we

can find that it’s actually quite simple and easy to understand. What might be surprising is

the component reference numbers (they don’t go in any order in the schematic). They are not

in any kind of logical order because we developed this raw card.

ASSEMBLY LANGUAGE:

When we look at the different types of programming languages, we have to

understand the “pay menow, pay me later” rule that exists with programming costs.

Assembly language programming is generally the cheapest way to get into micro-controller

programming, but it is the most difficult to learn, requires the most effort, and is the least

portable to other platforms.

Conversely, using a high-level language (such as BASIC or C) can make it much

easier for a beginner to program a Micro-controller, but it is the most costly option. Code

written for a high-level language is, by definition, portable to other platforms.

Where the “ pay me now, pay me later” rule comes into effect is if we are developing

8051 applications professionally. Spending time on assembly language programming is

probably costing you money over doing it in a high-level language.

For learning the 8051 or any other Micro-controller or computer processor, assembly

language is, as per the author opinion, the best way of doing it. Before going to an

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experiment, we will get a good feeling for how the 8051 processes instructions and how it

works.

Assembly language programming is the process of writing code that uses assembler

statement, which are the actual instructions the 8051’s processor executes (the smallest unit

of granularity).

Along with assembler statement, directives are added to the source file to control the

operation of the assembly process. Macros and conditional assembly statements are types of

directives that can help you develop code unique to our application. Macros are labels that

are replaced with code; they’re similar to subroutines, except the subroutine code is copied

directly into the source before the assembly operation. Conditional assembly statements are

“if/else/end if” statements that execute during assembly and, depending on the conditions,

not allow certain sections of code to be assembled.

A completed assembly language source file is assembled into a listing file (showing

how the assembly program converted the source into bits for the processor) and an object, or

hex, file, which are the actual bits and bytes to be burned into the 8051. Assembly language

programming is the lowest form of: “human-readable” source code-processing possible.

Interpreters and compilers take high-level language statements and convert them directly into

processor instructions without the programmer being involved.

Now, if we are well heeled and don’t want to do the drudgery of assembly language

programming, we could buy a compiler, but we will never use the full potential of the 8051.

Knowing and being proficient in assembly language programming will allow us to enhance

our high-level language applications by allowing us to add code that will reduce the number

of cycles required to execute, reduce the number of bytes required for the program, or

enhance the operation of the application.

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CHAPTER – 9

HARDWARE DETAILS

The IC’s and other important components used in this project work, procured from

the Hyderabad Electronics Market. The details or data sheets of the IC’s are down loaded

from the Internet. The following are the web sites that can be browsed for collecting the data

sheets.

1. www. Texas Instruments.com

2. www. National semiconductors.com

3. www. Fairchild semiconductors.com

The following are the IC’s and other important components used in this project work

(1) ADC 0809 - Analog to Digital Converter IC

(2) 74LS 573 Octal Transparent D-type Latches

(3) LM324 - Quad Op-Amp IC (4) LM 555 Timer IC

(5) Voltage Regulator (6) Relay (7) Current Transformer

(8) 89C51 Micro-controller IC

(9) TEA 5591 AM/FM Radio Receiver IC

(10) 74LS 138 3-line to 8-line Decoder

(11) 74 LS 574 Octal D-type Flip-Flop (12) 74LS244 Octal Buffer

(13) CD 4046 PLL IC (14) CD 4053 Multiplexer IC

POWER SUPPLY:

The required DC levels are derived from the mains supply for this purpose a step-

down transformer of 12V-0-12V center tapped secondary transformer is used. The current

rating of the transformer is 750 ma at secondary. The secondary is rectified and filtered to

generate 12V smooth DC which is un-regulated voltage and which is required to drive the

buzzer and relay. With help of positive voltage regulators, a constant voltage source of +5V

and +9V are derived, for this purpose 7805 and 7809 3Pin Voltage regulators are used so

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that, though the mains supply varies from 170V to 250V, the output DC levels remains

constant. The following is the circuit diagram of power supply.

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CHAPTER-10

MICROCONTROLLER SOFTWARE

TEMP_ADC DATA 30H DSP_C DATA 31H DSP1 DATA 32H DSP2 DATA 33H DSP3 DATA 34H DSP4 DATA 35H BUF1 DATA 36H BUF2 DATA 37H BUF3 DATA 38H BUF4 DATA 39H LV1 DATA 3AH LV2 DATA 3BH LV3 DATA 3CH LV4 DATA 3DH T1_1 DATA 3EH T1_2 DATA 3FH T1_3 DATA 40H T1_4 DATA 41H T2_1 DATA 42H T2_2 DATA 43H T2_3 DATA 45H T2_4 DATA 46H CT1 DATA 47H CT2 DATA 48H CT3 DATA 49H CT4 DATA 4AH CNT DATA 4BH;> A0 BIT P3.0 A1 BIT P3.1 A2 BIT P3.2 ALE BIT P3.3 SOC BIT P3.4 OE BIT P3.5 EOC BIT P3.6 RLY BIT P2.0 buz bit p2.1`

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;> vvv BIT 00H ttt1 BIT 01H ttt2 BIT 02H ccc1 BIT 03H;>

ONE EQU 11111001B TWO EQU 10100100B THREE EQU 10110000B FOUR EQU 10011001B FIVE EQU 10010010B SIX EQU 10000010B SEVEN EQU 11111000B EIGHT EQU 10000000B NINE EQU 10010000B ZERO EQU 11000000B ;> ORG 0000H ;START OF PROG.. LJMP START ORG 000BH ;TIMER INT-0 PUSH ACC PUSH PSW LCALL DISPLAY POP PSW POP ACC RETI START: MOV P1,#0FFH MOV P2,#00H SETB P3.7 MOV P0,#00H MOV SP,#60H MOV DSP_C,#00H MOV TMOD,#01H MOV IE,#82H MOV buf1,#0C0H MOV buf2,#0C0H MOV buf3,#0C0H MOV buf4,#0C0H SETB TR0

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MOV R7,#01H

MAIN: CLR A0 ;\\SELECTING THE VOLTAGE CHANNEL-2\\ SETB A1 CLR A2 LCALL GET_ADC MOV A,TEMP_ADC LCALL H_D LCALL STR_SEG MOV LV2,DSP2 MOV LV3,DSP3 MOV LV4,DSP4 MOV A,TEMP_ADC CJNE A,#0F0H,L1 L1: JC li1 setb vvv ljmp here1 li1: clr vvv here1: CLR A0 ;\\SELECTING THE TEMP.. CHANNEL-0\\ CLR A1 CLR A2 LCALL GET_ADC MOV A,TEMP_ADC LCALL H_D LCALL STR_SEG MOV T2_2,DSP2 MOV T2_3,DSP3 MOV T2_4,DSP4 MOV A,TEMP_ADC CJNE A,#32H,L8 L8: JC li3 setb ttt2 ljmp here2 li3: clr ttt2 HERE2: SETB A0 ;\\SELECTING THE CURRENT CHANNEL-1\\ CLR A1 CLR A2 LCALL GET_ADC MOV A,TEMP_ADC LCALL H_D LCALL STR_SEG

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MOV CT2,DSP2 MOV CT3,DSP3 MOV CT4,DSP4 MOV A,TEMP_ADC CJNE A,#64H,LS3 LS3: JC li4 setb ccc1 MOV R7,#03H ljmp here3 li4: clr ccc1HERE3: JB P3.7,LAZ LCALL DELAY1 INC R7 LAZ: MOV A,R7 CJNE A,#01,LAZ1 MOV BUF1,#0C1H MOV BUF2,LV2 MOV BUF3,LV3 MOV BUF4,LV4 LAZ1: CJNE A,#00H,LAZ2 LAZ2: CJNE A,#02H,LAZ3 MOV BUF1,#0c6h MOV BUF2,T2_2 MOV BUF3,T2_3 MOV BUF4,T2_4 LAZ3: CJNE A,#03H,LAZ4 MOV BUF1,#88H MOV BUF2,CT2 MOV BUF3,CT3 MOV a,CT4 ANL a,#7Fh mov buf4,a LAZ4: CJNE A,#04H,LAZ5 MOV R7,#00H LAZ5: jb vvv,lt1 jb ttt2,lt3 jb ccc1,lt4 clr rly clr buz ljmp main lt1: setb rly SETB buz ljmp main

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lt3: setb rly SETB buz ljmp main lt4: setb rly SETB buz ljmp main ;>;> DISPLAY: MOV A,DSP_C CJNE A,#00H,H1 MOV P0,BUF4 SETB P2.6 CLR P2.5 CLR P2.4 CLR P2.3 H1: CJNE A,#01H,H2 MOV P0,BUF3 CLR P2.6 SETB P2.5 CLR P2.4 CLR P2.3 H2:CJNE A,#02H,H3 MOV P0,BUF2 CLR P2.6 CLR P2.5 SETB P2.4 CLR P2.3 H3:CJNE A,#03H,H4 MOV P0,BUF1 CLR P2.6 CLR P2.5 CLR P2.4 SETB P2.3 H4:INC DSP_C MOV A,DSP_C CJNE A,#04H,H5 MOV DSP_C,#00H H5:MOV TL0,#00H MOV TH0,#0F0H RET;> GET_ADC: SETB ALE

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NOP NOP SETB SOC LCALL D1 CLR ALE NOP NOP CLR SOC EOZ: JB P3.6,EOZ EOCZ: JNB P3.6,EOCZ SETB OE MOV A,P1 MOV TEMP_ADC,A NOP NOP CLR OE RET;> H_D: CLR A MOV R0,#00H ;\\STR THE VALUE UPPER\\ MOV R1,#00H ;\\STR VALUE LOWER\\ MOV R2,#00H MOV R2,TEMP_ADC MOV A,TEMP_ADC CJNE A,#00H,Z0 MOV R0,#00H MOV R1,#00H RET Z0: CLR A LA2: CLR C INC A ADD A,#00H DA A JNC LA1 INC R0 LA1: DJNZ R2,LA2 MOV R1,A RET;> STR_SEG: MOV A,R1 ANL A,#0FH LCALL SEGMNT

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MOV DSP2,A MOV A,R1 ANL A,#0F0H SWAP A LCALL SEGMNT MOV DSP3,A MOV A,R0 ANL A,#0FH LCALL SEGMNT MOV DSP4,A RET;> SEGMNT: CJNE A,#00H,LA3 MOV A,#ZERO LA3:CJNE A,#01H,LA4 MOV A,#ONE LA4:CJNE A,#02H,LA5 MOV A,#TWO LA5:CJNE A,#03H,LA6 MOV A,#THREE LA6:CJNE A,#04H,LA7 MOV A,#FOUR LA7:CJNE A,#05H,LA8 MOV A,#FIVE LA8:CJNE A,#06H,LA9 MOV A,#SIX LA9:CJNE A,#07H,LA10 MOV A,#SEVEN LA10:CJNE A,#08H,LA11 MOV A,#EIGHT LA11:CJNE A,#09H,LA12 MOV A,#NINE LA12:RET

;> D1: MOV R3,#01H DJNZ R3,$ RET;> DELAY: MOV R4,#0FFH

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DJNZ R4,$ RET;>DELAY3: MOV R4,#30H Z2: MOV R5,#20H Z1: MOV R6,#10H DJNZ R6,$ DJNZ R5,Z1 DJNZ R4,Z2 RET

;> DELAY1: MOV R5,#64H LX1: MOV R6,#54H DJNZ R6,$ DJNZ R5,LX1 RET

;>END

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CHAPTER-11

COMPUTER SOFTWARE

/* PC BASED SCADA MONITERING AND CONTROLING.*/

#include <stdio.h>#include <dos.h>#include <bios.h>#include <conio.h>#include <graphics.h>

#define LOWER_NIBBLE 3#define UPPER_NIBBLE 2#define ADC_CONTROL 1#define RESET 4#define HIGH 0xc0#define STC 0x01#define ALE 0x02#define OE 0x04#define IPRT 0x379#define OPRT 0x378#define CPRT 0x37A

void print(); /* DISPLAYS RECTANGLES*/void show(); /* DISPLAYS MENUS AND NAMES*/void rdadc(); /* READS ADC VOLTAGES*/int read_byte(); /* READS FROM PARALLEL PORT*/int read_sts(); /* READS STATUS OF ADC*/int send_byte(int ,int); /* SEND TO PARALLEL PORT*/

char ch;int maxx, maxy;int buz_sts;

main(){

int errorcode,posbak;int gdriver=DETECT, gmode;initgraph(&gdriver, &gmode, " "); /* chek path */errorcode = graphresult();if (errorcode != grOk){ printf("Graphics error: %s\n", grapherrormsg(errorcode));

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printf("Press any key to halt:"); getch(); exit(1); /* terminate with an error code */}

maxx = getmaxx();maxy = getmaxy();print();show();

while(ch!='x' && ch!='X'){

rdadc();}/*reset axxll modes and memorys*/closegraph();restorecrtmode();return 0;

}void print(){

cleardevice();setcolor(CYAN);

rectangle(1,1,maxx-1,maxy-1);setcolor(LIGHTCYAN);

rectangle(2,2,maxx-2,maxy-2);setcolor(BLACK);

rectangle(3,3,maxx-3,maxy-3);setcolor(LIGHTCYAN);

rectangle(4,4,maxx-4,maxy-4);setcolor(CYAN);

rectangle(5,5,maxx-5,maxy-5);

setcolor(CYAN);rectangle(6,6,maxx-6,maxy-6);

setcolor(LIGHTCYAN);rectangle(7,7,maxx-7,maxy-7);

setcolor(BLACK);rectangle(8,8,maxx-8,maxy-8);

setcolor(LIGHTCYAN);rectangle(9,9,maxx-9,maxy-9);

setcolor(CYAN);rectangle(10,10,maxx-10,maxy-10);

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setcolor(RED);rectangle(100, 400, maxx-100, maxy-200);

setcolor(LIGHTRED);rectangle(101, 401, maxx-101, maxy-201);

setcolor(YELLOW);rectangle(102, 402, maxx-102, maxy-202);

setcolor(LIGHTRED);rectangle(103, 403, maxx-103, maxy-203);

setcolor(RED);rectangle(104, 404, maxx-104, maxy-204);

setcolor(RED);rectangle(105, 405, maxx-105, maxy-205);

setcolor(LIGHTRED);rectangle(106, 406, maxx-106, maxy-206);

setcolor(YELLOW);rectangle(107, 407, maxx-107, maxy-207);

setcolor(LIGHTRED);rectangle(108, 408, maxx-108, maxy-208);

setcolor(RED);rectangle(109, 409, maxx-109, maxy-209);

}

void show(){

settextstyle(1,0,1);setcolor(LIGHTRED);outtextxy(maxx-(maxx-200),maxy-(maxy-40),"PC BASED SCADA

MONITERING");setcolor(7);line(200,62,465,62);

setcolor(7);line(200,64,465,64);

}

void rdadc(){

int temp;int ct1, ct2 = 0,ct3=0;int VOLT = 0;

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float x1, y1;float t2;

strt: while(!kbhit()){

flushall();VOLT = read_ADC(0);x1 = VOLT * 5;y1 = x1 / 255;setcolor(WHITE);gotoxy(13, 8);printf("Input voltage = %.1f volts",y1);

//delay(10);if(y1 <= 0.4 ){

buz_sts = 0; gotoxy(30,19);printf(" ");gotoxy(30,22);printf(" SYSTEM NORMAL CONDITION

");delay(10);

}else{ // gotoxy(30,19);printf(" SYSTEM ABNORMAL CONDITION ");if((y1 >= 0.8) && (y1 <= 1.5)){

if (ct2 >= 8) {buz_sts = 0xC0;gotoxy(30,22);printf(" SYSTEM OVERLOAD

");delay(10); ct2=0; } ct2++;

}

if((y1 >= 1.6) && (y1 <= 2.5)){

if(ct3 >= 8){buz_sts = 0xC0;

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gotoxy(30,22);printf(" TEMPERATURE HIGH ");

delay(10); ct3=0;}ct3++;

}if((y1 >= 2.8) && (y1 <= 4.3)){

buz_sts = 0xC0;gotoxy(30,22);printf("HIGH VOLATAGE ");delay(10);

}}

if(y1>=4.8 ){

buz_sts = 0; gotoxy(30,19);printf(" ");gotoxy(30,22);printf(" SYSTEM DISCONECT ");delay(1);

}

}

ch=bioskey(0);if(ch!='x'&&ch!='X')goto strt;

}int read_ADC(int cnt){

int temp, ct1;temp= cnt<<3;

send_byte(ADC_CONTROL,buz_sts & HIGH);delay(1);send_byte(ADC_CONTROL,(buz_sts & HIGH)|temp);delay(0);send_byte(ADC_CONTROL,(buz_sts & HIGH)|temp|ALE);delay(0);send_byte(ADC_CONTROL,(buz_sts & HIGH)|temp|ALE|

STC);delay(0);send_byte(ADC_CONTROL,(buz_sts & HIGH)|temp|STC);delay(0);send_byte(ADC_CONTROL,(buz_sts & HIGH)|temp);delay(0);while(read_sts()==0)

{if(kbhit()!=0)break;

}

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delay(10);send_byte(ADC_CONTROL,((buz_sts & HIGH)|temp)|OE);

delay(0);ct1=read_byte();return ct1;

}int read_byte(){

int lb,hb;outport(CPRT,LOWER_NIBBLE);delay(1);lb=inp(IPRT);delay(1);outport(CPRT,RESET);delay(1);outport(CPRT,UPPER_NIBBLE);delay(1);hb=inp(IPRT);delay(1);outport(CPRT,RESET);delay(1);return (hb&0xf0)^0x80+((lb&0xf0)>>4)^0x08;

}int send_byte(int addr,int dat){

int x;outp(OPRT,dat);delay(1);outp(CPRT,addr);delay(1);outp(CPRT,RESET);delay(1);

}int read_sts(){

int lb;lb=inp(IPRT);delay(1);return ((lb&0x08)>>3);

}

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CHAPTER – 12

FABRICATION DETAILS

The fabrication of one demonstration unit is carried out in the following sequence:

1. Finalizing the total circuit diagram, listing out the components and their sources of

procurement.

2. Procuring the components, testing the components and screening the components.

3. Making layout, preparing the inter connection diagram as per the circuit diagram,

preparing the drilling details, cutting the laminate to the required size.

4. Drilling the holes on the board as per the component layout, painting the tracks on the

board as per inter connection diagram.

5. Etching the board to remove the un-wanted copper other than track portion. Then

cleaning the board with water, and solder coating the copper tracks to protect the tracks

from rusting or oxidation due to moisture.

6. Assembling the components as per the component layout and circuit diagram and

soldering components.

7. Integrating the total unit inter wiring the unit and final testing the unit.

8. Keeping the unit ready for demonstration.

PCB FABRICATION DETAILS:

The Basic raw material in the manufacture of PCB is copper cladded laminate. The laminate

consists of two or more layers insulating reinforced materials bonded together under heat and

pressure by thermo setting resins used are phenolic or epoxy. The reinforced materials used are

electrical grade paper or woven glass cloth. The laminates are manufactured by impregnating thin

sheets of reinforced materials (woven glass cloth or electrical grade paper) with the required resin

(Phenolic or epoxy). The laminates are divided into various grades by National Electrical

Manufacturers association (NEMA). The nominal overall thickness of laminate normally used in

PCB industry is 1.6mm with copper cladding on one or two sides. The copper foil thickness is 35

Microns (0.035mm) OR 70 Microns (0.070 mm).

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The next stage in PCB fabrication is artwork preparation. The artwork (Mater drawing) is

essentially a manufacturing tool used in the fabrication of PCB’s. It defines the pattern to be

generated on the board. Since the artwork is the first of many process steps in the Fabrication of

PCBs. It must be very accurately drawn. The accuracy of the finished board depends on the

accuracy of artwork. Normally, in industrial applications the artwork is drawn on an enlarged scale

and photographically reduced to required size. It is not only easy to draw the enlarged dimensions

but also the errors in the artwork correspondingly get reduced during photo reduction. For ordinary

application of simple single sided boards artwork is made on ivory art paper using drafting aids.

After taping on a art paper and phototraphy (Making the –ve) the image of the photo given is

transformed on silk screen for screen printing. After drying the paint, the etching process is carried

out. This is done after drilling of the holes on the laminate as per the components layout. The

etching is the process of chemically removing un-wanted copper from the board.

The next stage after PCB fabrication is solder masking the board to prevent the tracks from

corrosion and rust formation. Then the components will be assembled on the board as per the

component layout.

The next stage after assembling is the soldering the components. The soldering may be

defined as process where in joining between metal parts is produced by heating to suitable

temperatures using non-ferrous filler metals has melting temperatures below the melting

temperatures of the metals to be joined. This non-ferrous intermediate metal is called solder. The

solders are the alloys of lead and tin.

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CHAPTER-13

CONCLUSION

The project work “Implementation of wireless communication in supervisory

control and data acquisition system of a distribution transformer using micro-

controller & computer” is successfully designed, tested and a demo unit is fabricated.

However, the limitation is being made in this project work is to monitor the three important

parameters, such as load current, temperature and input high voltage. Apart from these three

parameters, various other parameters, such as line frequency, power factor, power leakage,

Energy measurement etc; can be incorporated in this project work. Apart from using Micro-

controller at the transmitting end, Microprocessor or Computer also can be used. The

advantage of using PC is, the parameters not only monitored, but also periodically the data

can be logged and the same data can be stored. So that details of the parameters can be

monitored on the screen. There by this data can be used for taking suitable decisions.

In this project using the transistor does work temperature sensing casting as a

temperature sensor. For this purpose SL100 transistor (NPN – Silicon) is used as temperature

sensor. For better sensing, the casting or body of the transistor is firmly attached to the body

of the transformer whose temperature is to be monitored. The characteristics of the Transistor

changes according to the Temperature. Particularly, the gain of the transistor decreases with

increasing in the temperature. Similarly, the leakage current increases with the increase in the

temperature, due to the flow of minority carriers. To obtain the sufficient output and high

input impedance and low output impedance and driving current required to cascaded stages

of op-amps using LM 324 (Low power Quad op-amp) is designed. In this circuit instead of

using SL100 transistor, thermocouple can be used for measuring the higher degrees of

temperature.

The current transformer used in this project work, (for monitoring the load current

continuously) is designed for 3Amps i.e., the current flowing through the primary is

restricted for 3Amps because of the thickness of the copper wire. Increasing the thickness of

the primary wire can increase this current rating. Similarly ratio also can be increased or

decreased according to the circuit design.

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The relay used in this project work is rated for lower current, is that the contact rating

of the relay is less than 2amps, but in real applications suitable relays with higher rating

contacts can be used.

The control circuit used in this project work can be utilized for the real applications

with minimum modifications.

Radio communication is utilized in this project work and the radiating power of the

transmitter is very less, so that the range between the transmitter and receiver is less than 20

feet’s, however this range can be increased by increasing the radiating power of the

transmitter.

REFERENCES:The following are the references made during the development of this project

work.

Text Books:

(1) Linear Integrated Circuits – : D. Roy Choudhury, Shail Jain

(2) Power Electronics - By: SEN

(3) Relays and their applications - By: M.C.SHARMA

(4) Op-Amps Hand Book - By: MALVIND

(5) Mechanical and Industrial Measurements - By: R.K. Jain

(6) Computer Controlled System - By: Karl J.ASTROM

(7) Programming and Customizing the 8051 Micro-controller

- By: Myke Predko

(8) The concepts and Features of Micro-controllers - By: Raj Kamal

(9) C++ An Introduction to Programming -

By: JESSE LIBERTY . JIM KEOGH

(10) ‘C’ ALL Clear - By: RAVINDRA

(11) Basic Radio and Television. BY: S.P. SHARMA

(12) Fundamentals of Radio Communication BY: A. SHEINGOLD

(13) The IC 555 Timer applications source book

By: HOWARD M.BERLIN

Catalogs :

(1) TEXAS - LINEAR IC’s manual

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(2) SIGNETICS - DIGITAL IC’s manual

Journals:

(1) Electronic Design (2) Electronics for you

(3) Electronics Text. (4) Practical Electronics

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CHAPTER-14

COMPLETE CIRCUIT DIAGRAM WITH LIST OF COMPONENTS

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