Parking system using PLC SCADA

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CHAPTER 1

INTRODUCTION

Automatic multistoried car parking system is very essential in the modern

world where number of vehicles is increasing day by day and parking

spaces in public as well as private areas are not sufficient. This project

deals with a similar problem and as a solution, the system is developed

wherein anyone can park more number of vehicles in a smaller space.

Also by such arrangement, parking will be done systematically. Unlike

any other multistoried parking, this parking system is semicircular in

shape due to which availability of space for parking gets increased. Since

it is completely automated system human errors are negligible and hence

system is more reliable. This project makes use of a „DVP 14 SS „ PLC

for controlling purpose, simple DC geared motors for circular as well as

vertical movements of lift, Optical proximity sensor to sense entry of car

and Relay board to drive the motors. High torque motor is required for

rotational movement of lift.

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1.1 BACKGROUND

The automated parking management system has existed for a long time,

but is only now finding mass demand for the efficient and effective

parking solution. The demand for parking is constantly increasing while

the space for large parking lots is decreasing. As a result, automated

parking management systems have filled the void by parking more cars

in less space and improving profitability, safety, environment

considerations and all related expenses. With this in mind, knowing the

background of the parking garage can be an interesting topic.

The automated parking system was actually first developed in 1925 by

Max Miller in New York City. The designs original purpose was simple

to lift a vehicle off the ground, such as in the case of a stalled or broken

down car on a street. It was never used.

It was not until 1941, as cars crowded cities that the first attempt to

vertically park cars was attempted. O.A. Light created a device that

allowed three cars to park vertically, three on each side for a total

capacity of six. A year later,

E.W. Austin invented the automated garage. His invention became the

leader in automated parking during the 40s, 50s and 60s. These systems

were called Bowsers, Pigeon Holes and Roto Parks.

Throughout these years, developments and design changes were made to

continually improve the automated car park. In 1964, Eric Jaulmes

invented what is most similar to the automated parking management

systems of today. His system had a valet drive the car into an elevator.

The elevator would then take the car to a predetermined spot and the

valet would park the car in that space. Then on the return down, if it had

been requested, the valet would stop at another spot to get a car to be

returned. At the same time, the three former systems were revitalized to

remove the valet altogether allowing the lift to tip the car into place and

the opposite on retrieval.

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1.2 OBJECTIVE OF THE PROJECT WORK

a. The aim of this project (under an B.Tech. programme) is to

design and build a prototype car park system with PLC

SCADA.

b. To develop an intelligent, user friendly automated car

parking system which reduces the manpower, traffic

congestion and fuel consumption of the vehicle.

c. To offer safe and secure parking slots within limited area.

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CHAPTER 2

REVIEW OF EXISTING SYSTEM

2.1 DIFFICULTY IN FINDING VACANT SPACE

Quickly finding a vacant space for parking of car especially on weekend

or public holidays is very difficult task. Stadium or shopping malls are

crowed on holidays and weekends which results into insufficient area for

car parking.

2.2 IMPROPER PARKING

Improper car parking is, when a car is not parked correctly in allocated

parking area. Due Improper car parking the space allocated for parking

will not be used in proper manner. This may create traffic congestion.

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CHAPTER 3

WORKING PROTOTYPE

When car is entered in the pallet of escalator, it is detected by the

proximity sensor and it gives the 24 v signal to the PLC. After receiving

the signal, PLC checks the other sensor status and select the building no

and the floor no (Ground, 1st, 2nd floor) as per the programming of

PLC. After detection of parking slot, PLC gives the signal to relay

board. Relay board is used as a driver to drive low voltage dc motor.

High torque dc motor pulls the lift in upward direction with the help of

pulley. This motor brings the lift in front of designated floor. When lift

reach to the parking area then the PLC checks the status of the motor

driver and gives the signal to the motor system. motor system pushes the

pallet in the parking area. When the car is parked inside the parking area

then the sensor placed inside the parking area change its status and gives

the signal to the PLC. Then PLC again sends the signal to the motor

driver for reverse action of motor and system to regain original position.

Imagine the time that automatic smart parking systems would save you.

Every time you enter your office building you have to find a parking

space and spend time walking in and out of the lot as well. Imagine how

much time it is costing you. Even if you just spend 5 minutes a day to

park that translates to you spending more than a whole day just parking

every year. If you calculate the time you spend walking in and out of the

parking lot, searching for space and such it will be easily more than the

above amount. Through this system we can save a lot of time. Here,

PLC is used in the control of the prototype of the automated parking

system. DC motors and sensors are used to provide movements to

transport the vehicle in the parking system. The main advantage of this

system are space optimization, cost effectiveness and security.

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3.1 WORKING OF PLCs

A programmable logic controller is a specialized computer used to

control machines and processes. It therefore shares common terms with

typical PCs like central processing unit, memory, software and

communications. Unlike a personal computer though the PLC is

designed to survive in a rugged industrial atmosphere and to be very

flexible in how it interfaces with inputs and outputs to the real world.

The components that make a PLC work can be divided into three core

areas.

The power supply and rack

The central processing unit (CPU)

The input/output (I/O) section

PLCs come in many shapes and sizes. They can be so small as to fit in

your shirt pocket while more involved controls systems require large PLC

racks. Smaller PLCs (a.k.a. “bricks”) are typically designed with fixed

I/O points. For our consideration, we’ll look at the more modular rack

based systems. It’s called “modular” because the rack can accept many

different types of I/O modules that simply slide into the rack and plug in.

Figure 3.1:power supply rack

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Figure 3.2 : Back panel

The rack is the component that holds everything together. Depending on

the needs of the control system it can be ordered in different sizes to hold

more modules. Like a human spine the rack has a backplane at the rear

which allows the cards to communicate with the CPU. The power supply

plugs into the rack as well and supplies a regulated DC power to other

modules that plug into the rack. The most popular power supplies work

with 120 VAC or 24 VDC sources.

3.1.1 CPU

The brain of the whole PLC is the CPU module. This module typically

lives in the slot beside the power supply. Manufacturers offer different

types of CPUs based on the complexity needed for the system.

The CPU consists of a microprocessor, memory chip and other integrated

circuits to control logic, monitoring and communications. The CPU has

different operating modes. In programming mode, it accepts the

downloaded logic from a PC. The CPU is then placed in run mode so

that it can execute the program and operate the process.

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Figure 3.3 : CPU

Since a PLC is a dedicated controller it will only process this one

program over and over again. One cycle through the program is called a

scan time and involves reading the inputs from the other modules,

executing the logic based on these inputs and then updated the outputs

accordingly. The scan time happens very quickly (in the range of

1/1000th of a second). The memory in the CPU stores the program while

also holding the status of the I/O and providing a means to store values.

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3.1.2 I/O SYSTEM

The I/O system provides the physical connection between the equipment

and the PLC. Opening the doors on an I/O card reveals a terminal strip

where the devices connect.

INPUTS:

Input devices can consist of digital or analog devices. A digital input

card handles discrete devices which give a signal that is either on or off

such as a pushbutton, limit switch, sensors or selector switches. An

analog input card converts a voltage or current (e.g. a signal that can be

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anywhere from 0 to 20mA) into a digitally equivalent number that can be

understood by the CPU. Examples of analog devices are pressure

transducers, flow meters and thermocouples for temperature readings.

OUTPUTS:

Output devices can also consist of digital or analog types. A digital

output card either turns a device on or off such as lights, LEDs, small

motors, and relays. An analog output card will convert a digital number

sent by the CPU to it’s real world voltage or current. Typical outputs

signals can range from 0-10 VDC or 4-20mA and are used to drive mass

flow controllers, pressure regulators and position controls.

3.1.3 PRPGRAMMING A PLC

In these modern times a PC with specially dedicated software from the

PLC manufacturer is used to program a PLC. The most widely used form

of programming is called ladder logic. Ladder logic uses symbols,

instead of words, to emulate the real world relay logic control, which is a

relic from the PLC's history. These symbols are interconnected by lines

to indicate the flow of current through relay like contacts and coils. Over

the years the number of symbols has increased to provide a high level of

functionality.

The completed program looks like a ladder but in actuality it represents

an electrical circuit. The left and right rails indicate the positive and

ground of a power supply. The rungs represent the wiring between the

different components which in the case of a PLC are all in the virtual

world of the CPU. So if you can understand how basic electrical circuits

work then you can understand ladder logic.

In this simplest of examples a digital input (like a button connected to the

first position on the card) when it is pressed turns on an output which

energizes an indicator light.

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Figure 3.4

The completed program is downloaded from the PC to the PLC using a

special cable that’s connected to the front of the CPU. The CPU is then

put into run mode so that it can start scanning the logic and controlling

the outputs.

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3.2 WORKING OF SCADA

SCADA (Supervisory control and data acquisition) is an industrial

automation control system at the core of many modern industries,

including:

Energy

Food and beverage

Manufacturing

Oil and gas

Power

Recycling

Transportation

Water and waste water

And many more

SCADA systems are used by private companies and public-sector service

providers. SCADA works well in many different types of enterprises

because they can range from simple configurations to large, complex

projects.

Virtually anywhere you look in today's world, there is some type of

SCADA system running behind the scenes, whether at your local

supermarket, refinery, waste water treatment plant, or even your own

home.

A SCADA system performs four functions:

1. Data acquisition

2. Networked data communication

3. Data presentation

4. Control

These functions are performed by four kinds of SCADA components:

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1. Sensors (either digital or analog) and control relays that directly

interface with the managed system.

2. Remote telemetry units (RTUs). These are small computerized units

deployed in the field at specific sites and locations. RTUs (Remote

Telemetry Units) serve as local collection points for gathering reports

from sensors and delivering commands to control relays.

3. SCADA master units. These are larger computer consoles that serve

as the central processor for the SCADA system. Master units provide a

human interface to the system and automatically regulate the managed

system in response to sensor inputs.

4. The communications network that connects the SCADA master unit

to the RTUs in the field.

Figure 3.5

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3.3 WORKING OF SENSORS

A proximity sensor is a sensor able to detect the presence of nearby

objects without any physical contact. A proximity sensor often emits

an electromagnetic field or a beam of electromagnetic radiation (infrared,

for instance), and looks for changes in the field or return signal. The

object being sensed is often referred to as the proximity sensor's target.

Different proximity sensor targets demand different sensors. For example,

a capacitive or photoelectric sensor might be suitable for a plastic target;

an inductive proximity sensor always requires a metal target.

3.3.1 TYPES OF SENSORS:

Capacitive

Capacitive displacement sensor

Doppler effect (sensor based on effect)

Eddy-current

Inductive

Laser rangefinder

Magnetic, including Magnetic proximity fuse

Passive optical (such as charge-coupled devices)

Passive thermal infrared

Photocell (reflective)

Radar

Reflection of ionizing radiation

Sonar (typically active or passive)

Ultrasonic sensor (sonar which runs in air)

Fiber optics sensor

Hall effect sensor

3.3.2 APPLICATIONS

Parking sensors

Ground proximity warning system for aviation safety

Vibration measurements of rotating shafts in machinery

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Top dead center (TDC)/camshaft sensor in reciprocating engines.

Sheet break sensing in paper machine.

Anti-aircraft warfare

Roller coasters

Conveyor systems

Beverage and food can be making lines

Improvised Explosive Devices or IEDs

Mobile devices

3.3.3 CAPACITIVE PROXIMITY SENSING

Capacitive sensing is a noncontact technology suitable for detecting

metals, nonmetals, solids, and liquids, although it is best suited for

nonmetallic targets because of its characteristics and cost relative to

inductive proximity sensors. In most applications with metallic targets,

inductive sensing is preferred because it is both a reliable and a more

affordable technology.

Figure 3.6 Capacitive sensor components

The sensor consists of four basic components:

A capacitive probe or plate

An oscillator

A signal level detector

A solid-state output switching device

An adjustment potentiometer

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Capacitive proximity sensors are similar in size, shape, and concept to

inductive proximity sensors. However, unlike inductive sensors which

use induced magnetic fields to sense objects, capacitive proximity

generate an electrostatic field and reacts to changes in capacitance caused

when a target enters the electrostatic field. When the target is outside the

electrostatic field, the oscillator is inactive. As the target approaches, a

capacitive coupling develops between the target and the capacitive probe.

When the capacitance reaches a specified threshold, the oscillator is

activated, triggering the output circuit to switch states between ON and

OFF.

Figure 3.6 Capacitive proximity operation

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3.4 WORKING OF DC MOTORS

A DC motor is any of a class of electrical machines that converts direct

current electrical power into mechanical power. The most common types

rely on the forces produced by magnetic fields. Nearly all types of DC

motors have some internal mechanism, either electromechanical or

electronic, to periodically change the direction of current flow in part of

the motor. Most types produce rotary motion; a linear motor directly

produces force and motion in a straight line.

DC motors were the first type widely used, since they could be powered

from existing direct-current lighting power distribution systems. A DC

motor's speed can be controlled over a wide range, using either a variable

supply voltage or by changing the strength of current in its field

windings. Small DC motors are used in tools, toys, and appliances. The

universal can operate on direct current but is a lightweight motor used for

portable power tools and appliances. Larger DC motors are used in

propulsion of electric vehicles, elevator and hoists, or in drives for steel

rolling mills. The advent of power electronics has made replacement of

DC motors with AC motors possible in many applications.

Workings of a brushed electric motor with a two-pole rotor (armature) and permanent magnet stator.

"N" and "S" designate polarities on the inside axis faces of the magnets; the outside faces have opposite

polarities. The + and - signs show where the DC current is applied to the commutator which supplies

current to the armature coils

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3.4.1 GEAR MOTOR

A gear motor is a specific type of electrical motor that is designed to

produce high torque while maintaining a low horsepower, or low speed,

motor output. Gear motors can be found in many different applications,

and are probably used in many devices in your home.

Gear motors are commonly used in devices such as can openers, garage

door openers, washing machine time control knobs and even electric

alarm clocks. Common commercial applications of a gear motor include

hospital beds, commercial jacks, cranes and many other applications that

are too many to list.

3.4.1.1 USES:

Gear Motors are used in a lot of equipment including conveyor-belt

drives, home appliances, handicap and platform lifts, medical and

laboratory equipment, machine tools, packaging machinery and printing

presses, case erectors, box taper, hot melt glue pumps, heat shrink

tunnels, tape dispensers and conveyor drives.

Figure 3.7

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3.5 WORKING OF POWER SUPPLY

A power supply is an electronic device that supplies electric energy to

an electrical load. The primary function of a power supply is to convert

one form of electrical energy to another and, as a result, power supplies

are sometimes referred to as electric power converters. Some power

supplies are discrete, stand-alone devices, whereas others are built into

larger devices along with their loads. Examples of the latter include

power supplies found in desktop computers and consumer

electronics devices.

Every power supply must obtain the energy it supplies to its load, as well

as any energy it consumes while performing that task, from an energy

source. Depending on its design, a power supply may obtain energy from

various types of energy sources, including electrical energy transmission

systems, energy storage devices such as a batteries and fuel cells,

electromechanical systems such as generators and alternators, solar

power converters, or another power supply.

All power supplies have a power input, which receives energy from the

energy source, and a power output that delivers energy to the load. In

most power supplies the power input and output consist of electrical

connectors or hardwired circuit connections, though some power supplies

employ wireless energy transfer in lieu of galvanic connections for the

power input or output. Some power supplies have other types of inputs

and outputs as well, for functions such as external monitoring and

control.

To provide a useable low voltage the PSU needs to do a number of

things: -

Reduce the Mains AC (Alternating current) voltage to a lower

level.

Convert this lower voltage from AC to DC (Direct current)

Regulate the DC output to compensate for varying load (current

demand)

Provide protection against excessive input/output voltages.

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CHAPTER 4

CONSTRUCTION

4.1 PHASE I

a. Market survey

During this period detail market survey has been done to learn

available parking systems and their utility also their literatures of

different types of parking systems and its difference between have

been observed.

b. Problems in existing systems

The problems regarding the existing system have been found such as,

Complicated programming, High budgets, Unfeasible design, high end

robots, etc.

c. Conceptual Design

Taking problem statement from above and studying the fundamental

engineering concepts various concepts regarding modern parking

system are prepared and amongst those best concepts design has been

selected for further phases.

4.2 PRESENT PARKING SOLUTIONS

4.2.1 Integrated Car Parking Solution

Customize application suitable for various types of landscapes and

buildings Structures available below the ground. Ease control by

soft touch on the operation panel screen. When a vehicle stops in

front of the entrance, automatically door opens and trolley transfers

the vehicle to parking cell. Misleading of this solution is it should

be undergrounded. By this investment increases and lot much

space utilization is to be made.

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Figure 1 Integrated Car Parking Solution

4.2.2 Automated Car Parking

The driver will pull the car onto a computer- controlled pallet, turn it off,

and get out. The pallet is then lowered into the abyss of parking spaces,

much like a freight elevator for cars, except it can also move sideways,

not just up and down. There's an array of laser sensors that let the system

know if the car doesn't fit on the pallet (although it's big enough to fit a

mid-sized SUV),. The system retrieves the car when the driver returns,

although this might take some time and creative maneuvering. Cars are

parked two deep in some spots, so a specially tailored software system

has to figure out the logistics of shuffling the various vehicles around as

needed to retrieve a specific car. And for those, like me, who find it

difficult to turn their vehicle around after pulling out of a space, there's an

underground turntable that turns the car around before it is lifted to the

surface, so the car is facing out into the driveway, ready to go. Backing

out of garages or parking spaces is one of the most common causes of

accidents

Figure 2. Automated Car Parking

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4.2.3 Multi-Level Parking

A multi-level car parking is essentially a building with number of floors

or layers for the cars to be parked. The different levels are accessed

through interior or exterior ramps. An automated car parking has

mechanized lifts which transport the car to the different levels.

Therefore, these car parks need less building volume and less ground

space and thus save on the cost of the building. It also does away the

need for employing too many personal to monitor the place. In an

automated car parking, the cars are left at the entrance and are further

transported inside the building by robot trolley. Similarly, they are

retrieved by the trolley and placed at the exit for the owner to drive

away.

Figure 3. Multi- Level Parking

4.3 MATERIALS AND METHODOLOGY

4.3.1 Components

4.3.1.1 DC geared motor (24volts):

It’s a mechanically commutated electric motor, powered by

direct current (DC). Generally, DC geared motor runs in both

directions, but in this prototype model it is fixed uni- directionally

to avoid vibrations of the systems.

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4.3.1.2 Push buttons:

A push-button is a simple switch mechanism for controlling some

aspect of a machine or a process. Buttons are typically made out of

hard material, usually plastic or metal. There are totally 8

pushbuttons.

4.3.1.3 Capacitive proximity sensor:

Capacitive sensing is a noncontact technology suitable for

detecting metals, nonmetals, solids, and liquids, although it is best

suited for nonmetallic targets because of its characteristics and cost

relative to inductive proximity sensors. In most applications with

metallic targets, inductive sensing is preferred because it is both a

reliable and a more affordable technology.

4.3.1.4 Capacitive proximity sensor:

A freewheel or overrunning clutch is a device in a transmission that

disengages the driveshaft from the driven shaft when the driven

shaft rotates faster than the driveshaft. An overdrive is sometimes

mistakenly called a freewheel.

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CHAPTER 5

PROGRAMMABLE LOGIC CONTROLLER

A programmable logic controller (PLC), also referred to as

programmable controller, is the name given to a type of computer

commonly used in commercial and industrial control applications.

PLCs differ from office computers in the types of tasks that they

perform and the hardware and software they require to perform these

tasks. While the specific applications vary widely, all PLCs monitor

inputs and other variable values, make decisions based on a stored

program, and control outputs to automate a process or machine.

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Input

Module

Central Processing Unit

(CPU)

Programming

Device

Operator

Interface

5.1 BASIC PLC OPERATION

The basic elements of a PLC include input modules or points, a central processing unit (CPU), output modules or points, and a programming device. The type of input modules or points used by a PLC depends upon the types of input devices used.

Some input modules or points respond to digital inputs, also called discrete inputs, which are either on or off. Other modules or inputs respond to analog signals. These analog signals represent machine or process conditions as a range of voltage or current values. The primary function of a PLC’s input circuitry is to convert the signals provided by these various switches and sensors into logic signals that can be used by the CPU.

The CPU evaluates the status of inputs, outputs, and other variables as it executes a stored program. The CPU then sends signals to update the status of outputs.

Output modules convert control signals from the CPU into digital or analog values that can be used to control various output devices.

The programming device is used to enter or change the PLC’s program or to monitor or change stored values. Once entered, the program and associated variables are stored in the CPU.

In addition to these basic elements, a PLC system may also incorporate an operator interface device to simplify monitoring of the machine or process.

Output

Module

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5.2 HARD-WIRED CONTROL

Prior to PLCs, many control tasks were performed by contactors , control relays, and other electromechanical devices. This is often referred to as hard-wired control. Circuit diagrams had to be designed, electrical components specified and installed and wiring lists created. Electricians would then wire the components necessary to perform a specific task. If an error was made, the wires had to be reconnected correctly. A change in function or system expansion required extensive component changes and rewiring.

5.3 ADVANTAGES OF PLCs

PLCs not only are capable of performing the same tasks as hard-wired control, but are also capable of many more complex applications. In addition, the PLC program and electronic communication lines replace much of the interconnecting wires required by hard-wired control. Therefore, hard-wiring, though still required to connect field devices, is less intensive. This also makes correcting errors and modifying the application easier.

Some of the additional advantages of PLCs are as follows:

Smaller physical size than hard-wire solutions.

Easier and faster to make changes.

PLCs have integrated diagnostics and override functions.

Diagnostics are centrally available .

Applications can be immediately documented.

Applications can be duplicated faster and less expensively.

M OL

T1 L1

M

460 VAC L2

OL

T2

OL

T3

Motor

M

L3

OL

1 M

CR

24 VAC

Start Stop

2 CR

CR

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5.6 TERMINOLOGY

Developing an understanding of PLCs requires learning some basic terminology. This section provides an overview of commonly used PLC terms, beginning with the terms sensor and actuator.

5.6.1 SENSORS

Sensors are devices that convert a physical condition into an electrical signal for use by controller, such as a PLC. Sensors are connected to the input of a PLC. A pushbutton is one example of a sensor that is often connected to a PLC input. An electrical signal indicating the condition (open or closed) of the pushbutton contacts is sent from the pushbutton to the PLC.

5.6.2 ACTUATORS

Actuators are devices that convert an electrical signal from a

controller, such as a PLC, into a physical condition. Actuators are

connected to the PLC output. A motor starter is one example of an

actuator that is often connected to a PLC output. Depending on the

status of the PLC output, the motor starter either provides power to

the motor or prevents power from flowing to the motor.

5.7 DISCRETE INPUTS AND OUTPUTS

Discrete inputs and outputs, also referred to as digital inputs and outputs, are either on or off. Pushbuttons, toggle switches, limit switches, proximity switches, and relay contacts are examples of devices often connected to PLC discrete inputs.

Solenoids, relay and contactor coils, and indicator lamps are examples of devices often connected to PLC discrete outputs.

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In the on condition, a discrete input or output is represented internal to the PLC as a logic 1. In the off condition, a discrete input or output is represented as a logic 0.

5.8 ANALOG INPUTS AND OUTPUTS

Analog inputs and outputs are continuous, variable signals. Typical analog signals vary from 0 to 20 milliamps, 4 to 20 milliamps, or 0 to 10 volts.

In the following example, a level transmitter monitors the level of liquid in a storage tank and sends an analog signal to a PLC input. An analog output from the PLC sends an analog signal to a panel meter calibrated to show the level of liquid in the tank. Two other analog outputs, not shown here, are connected to current-to-pneumatic transducers that control air-operated flow- control valves. This allows the PLC to automatically control the flow of liquid into and out of the storage tank.

5.9 CPU

The central processor unit (CPU) is a microprocessor system that contains the system memory and is the PLC’s decision- making unit. The CPU monitors inputs, outputs, and other variables and makes decisions based on instructions held in its program memory.

5.10 MEMORY TYPES AND SIZE

Kilo, abbreviated k, normally refers to 1000 units. When talking about computer or PLC memory, however, 1k means 1024.

Random Access Memory (RAM) is memory that allows data to be written to and read from any address(location). RAM is used as a temporary storage area. RAM is volatile, meaning that the data stored in RAM will be lost if power is lost. A battery backup is required to avoid losing data in the event of a power loss.

Read Only Memory (ROM) is a type of memory used were it is necessary to protect data or programs from acc iden ta l erasure. The data stored in ROM can be read, but not changed. In addition, ROM memory is nonvolatile. This means that information will not be lost as the result of a loss of electrical power. ROM is normally used to store the programs that define the capabilities of the PLC.

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Erasable Programmable Read Only Memory (EPROM) provides a level of security against unauthorized or unwanted changes in a program. EPROMs are designed so that data stored in them can be read, but not easily altered. Changing EPROM data requires a special effort. UVEPROMs (ultraviolet erasable programmable read only memory) can only be erased with an ultraviolet light. EEPROM (electrically erasable programmable read only memory), can only be erased electrically.

5.11 SOFTWARE, HARDWARE AND FIRMWARE

Software is the name given to computer instructions, regardless of

the programming language. Essentially, software includes the

instructions or programs that direct hardware.

Hardware is the name given to all the physical components of a system. The PLC, the programming device, and the connecting cable are examples of hardware.

Firmware is user or application specific software burned into EPROM and delivered as part of the hardware. Firmware gives the PLC its basic functionality.

5.12 LADDER LOGIC PROGRAMMING

The degree of complexity of a PLC program depends upon the complexity of the application, the number and type of input and output devices, and the types of instructions used.

Ladder logic (LAD) is one programming language used with PLCs. Ladder logic incorporates programming functions that are graphically displayed to resemble symbols used in hard-wired control diagrams.

The left vertical line of a ladder logic diagram represents the power or energized conductor. The output coil instruction represents the neutral or return path of the circuit. The right vertical line, which represents the return path on a hard-wired control line diagram, is omitted. Ladder logic diagrams are read from left-to-right and top-to-bottom. Rungs are sometimes referred to as networks. A network may have several control elements, but only one output coil.

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5.12.1 WORKING PRINCIPLE

The ladder diagram was a diagram language for automation

developed in the WWII period, which is the oldest and most widely

adopted language in automation. In the initial stage, there were only

A (normally open) contact, B (normally closed) contact, output coil,

timer and counter…the sort of basic devices on the ladder diagram

(see the power panel that is still used today). After the invention of

programmable logic controllers (PLC), the devices displayable on

the ladder diagram are added with differential contact, latched coil

and the application commands which were not in a traditional power

panel, for example the addition, subtraction, multiplication and

division operations.

The working principles of the traditional ladder diagram and PLC

ladder diagram are basically the same. The only difference is that the

symbols on the traditional ladder diagram are more similar to its

original form, and PLC ladder diagram adopts the symbols that are

easy to recognize and shown on computer or data sheets. In terms of

the logic of the ladder diagram, there are combination logic and

sequential logic.

5.13 PLC SCAN

PLC utilizes a standard scan method when evaluating user

program.

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Scanning process:

Scan input status Read the physical input status and store the data in internal memory.

Evaluate user program

Evaluate the user program with data stored in internal memory. Program

scanning starts from up to down and left to right until reaching the end of

the program.

Refresh the outputs Write the evaluated data to the physical outputs

5.13.1 INPUT SIGNAL

PLC reads the ON/OFF status of each input and stores the

status into memory before evaluating the user program.

Once the external input status is stored into internal memory,

any change at the external inputs will not be updated until

next scan cycle starts.

Scan time:

The duration of the full scan cycle (read, evaluate, write) is

called “scan time.” With more I/O or longer program, scan

time becomes longer.

Read

scan time

PLC measures its own scan time and stores the value (0.1ms) in register D1010,

minimum scan time in register D1011, and maximum scan time in register D1012.

Measure

scan time

Scan time can also be measured by toggling an output every scan and then measuring

the pulse width on the output being toggled.

Calculate

scan time

Scan time can be calculated by adding the known time required for each instruction in

the user program. For scan time information of individual instruction please refer to

Ch3 in this manual.

5.13.3 OUTPUT

When END command is reached the program evaluation is

complete. The output memory is transferred to the external

physical outputs.

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CHAPTER 6

SCADA SCADA: Acronym for supervisory control and data acquisition, a

computer system for gathering and analyzing real time data. SCADA

systems are used to monitor and control a plant or equipment in industries

such as telecommunications, water and waste control, energy, oil and gas

refining and transportation. A SCADA system gathers information, such

as where a leak on a pipeline has occurred, transfers the information back

to a central site, alerting the home station that the leak has occurred,

carrying out necessary analysis and control, such as determining if the

leak is critical, and displaying the information in a logical and organized

fashion. SCADA systems can be relatively simple, such as one that

monitors environmental conditions of a small office building, or

incredibly complex, such as a system that monitors all the activity in a

nuclear power plant or the activity of a municipal water system.

SCADA systems were first used in the 1960s.

6.1 REAL TIME

Occurring immediately. The term is used to describe a number of

different computer features. For example, real-time operating systems are

systems that respond to input immediately. They are used for such tasks

as navigation, in which the computer must react to a steady flow of new

information without interruption. Most general-purpose operating

systems are not real-time because they can take a few seconds, or even

minutes, to react.

Real time can also refer to events simulated by a computer at the same

speed that they would occur in real life. In graphics animation, for

example, a real-time program would display objects moving across the

screen at the same speed that they would actually move.

computer

Last modified: Friday, January 04, 2002

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A programmable machine. The two principal characteristics of a

computer are:

It responds to a specific set of instructions in a well-defined

manner.

It can execute a pre-recorded list of instructions (a program).

Modern computers are electronic and digital. The actual machinery --

wires, transistors, and circuits -- is called hardware; the instructions and

data are called software.

All general-purpose computers require the following hardware

components:

a) memory : Enables a computer to store, at least temporarily,

data and programs.

b) mass storage device : Allows a computer to permanently

retain large amounts of data. Common mass storage devices

include disk drives and tape drives.

c) input device : Usually a keyboard and mouse, the input

device is the conduit through which data and instructions

enter a computer.

d) output device : A display screen, printer, or other device

that lets you see what the computer has accomplished.

e) central processing unit (CPU): The heart of the computer,

this is the component that actually executes instructions.

In addition to these components, many others make it possible for the

basic components to work together efficiently. For example, every

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computer requires a bus that transmits data from one part of the computer

to another.

Computers can be generally classified by size and power as follows,

though there is considerable overlap:

a) personal computer : A small, single-user computer based

on a microprocessor. In addition to the microprocessor, a

personal computer has a keyboard for entering data, a

monitor for displaying information, and a storage device for

saving data.

b) workstation : A powerful, single-user computer. A

workstation is like a personal computer, but it has a more

powerful microprocessor and a higher-quality monitor.

c) minicomputer : A multi-user computer capable of

supporting from 10 to hundreds of users simultaneously.

d) mainframe : A powerful multi-user computer capable of

supporting many hundreds or thousands of users

simultaneously.

e) supercomputer : An extremely fast computer that can

perform hundreds of millions of instructions per second.

operating system

Last modified: Friday, January 04, 2002

The most important program that runs on a computer. Every general-

purpose computer must have an operating system to run other programs.

Operating systems perform basic tasks, such as recognizing input from

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the keyboard, sending output to the display screen, keeping track of files

and directories on the disk, and controlling peripheral devices such as

disk drives and printers.

For large systems, the operating system has even greater responsibilities

and powers. It is like a traffic cop -- it makes sure that different programs

and users running at the same time do not interfere with each other. The

operating system is also responsible for security, ensuring that

unauthorized users do not access the system.

Operating systems can be classified as follows:

a) multi-user : Allows two or more users to run programs at

the same time. Some operating systems permit hundreds or

even thousands of concurrent users.

b) multiprocessing : Supports running a program on more than

one CPU.

c) multitasking : Allows more than one program to run

concurrently.

d) multithreading : Allows different parts of a single program

to run concurrently.

e) real time: Responds to input instantly. General-purpose

operating systems, such as DOS and UNIX, are not real-

time.

Operating systems provide a software platform on top of which other

programs, called application programs, can run. The application

programs must be written to run on top of a particular operating system.

Your choice of operating system, therefore, determines to a great extent

the applications you can run. For PCs, the most popular operating

systems are DOS, OS/2, and Windows, but others are available, such as

Linux.

6.2 What does SCADA MEAN?

SCADA stands for Supervisory Control And Data Acquisition. As the

name indicates, it is not a full control system, but rather focuses on the

supervisory level. As such, it is a purely software package that is

positioned on top of hardware to which it is interfaced, in general via

Programmable Logic Controllers (PLCs), or other commercial hardware

modules.

SCADA systems are used not only in industrial processes: e.g. steel

making, power generation (conventional and nuclear) and distribution,

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chemistry, but also in some experimental facilities such as nuclear fusion.

The size of such plants range from a few 1000 to several 10 thousands

input/output (I/O) channels. However, SCADA systems evolve rapidly

and are now penetrating the market of plants with a number of I/O

channels of several 100 K: we know of two cases of near to 1 M I/O

channels currently under development.

SCADA systems used to run on DOS, VMS and UNIX; in recent years

all SCADA vendors have moved to NT and some also to Linux.

6.3 ARCHITECTURE This section describes the common features of the SCADA products that

have been evaluated at CERN in view of their possible application to the

control systems of the LHC detectors.

6.3.1 HARDWARE ARCHITECTURE

One distinguishes two basic layers in a SCADA system: the "client layer"

which caters for the man machine interaction and the "data server layer"

which handles most of the process data control activities. The data servers

communicate with devices in the field through process controllers.

Process controllers, e.g. PLCs, are connected to the data servers either

directly or via networks or fieldbuses that are proprietary (e.g. Siemens

H1), or non-proprietary (e.g. Profibus). Data servers are connected to

each other and to client stations via an Ethernet LAN. The data servers

and client stations are NT platforms but for many products the client

stations may also be W95 machines. Fig.1. shows typical hardware

architecture.

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Figure 1: Typical Hardware Architecture

6.3.2 SOFTWARE ARCHITECTURE

The products are multi-tasking and are based upon a real-time database

(RTDB) located in one or more servers. Servers are responsible for data

acquisition and handling (e.g. polling controllers, alarm checking,

calculations, logging and archiving) on a set of parameters, typically

those they are connected to.

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Figure 2: Generic Software Architecture

However, it is possible to have dedicated servers for particular tasks, e.g.

historian, data logger, alarm handler. Fig. 2 shows a SCADA architecture

that is generic for the products that were evaluated.

6.3.3 COMMUNICATIONS

Internal Communication

Server-client and server-server communication is in general on a publish-

subscribe and event-driven basis and uses a TCP/IP protocol, i.e., a client

application subscribes to a parameter which is owned by a particular

server application and only changes to that parameter are then

communicated to the client application.

Access to Devices

The data servers poll the controllers at a user defined polling rate. The

polling rate may be different for different parameters. The controllers

pass the requested parameters to the data servers. Time stamping of the

process parameters is typically performed in the controllers and this time-

stamp is taken over by the data server. If the controller and

communication protocol used support unsolicited data transfer, then the

products will support this too.

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The products provide communication drivers for most of the common

PLCs and widely used field-buses, e.g., Modbus. Of the three fieldbuses

that are recommended at CERN, both Profibus and Worldfip are

supported but CANbus often not .Some of the drivers are based on third

party products (e.g., Applicom cards) and therefore have additional cost

associated with them. VME on the other hand is generally not supported.

A single data server can support multiple communications protocols: it

can generally support as many such protocols as it has slots for interface

cards.

The effort required to develop new drivers is typically in the range of 2-6

weeks depending on the complexity and similarity with existing drivers,

and a driver development toolkit is provided for this.

6.3.4 INTERFACING

Application Interfaces / Openness

The provision of OPC client functionality for SCADA to access devices

in an open and standard manner is developing. There still seems to be a

lack of devices/controllers, which provide OPC server software, but this

improves rapidly as most of the producers of controllers are actively

involved in the development of this standard. OPC has been evaluated by

the CERN-IT-CO group.

The products also provide

an Open Data Base Connectivity (ODBC) interface to the data in

the archive/logs, but not to the configuration database,

an ASCII import/export facility for configuration data,

a library of APIs supporting C, C++, and Visual Basic (VB) to

access data in the RTDB, logs and archive. The API often does not

provide access to the product's internal features such as alarm

handling, reporting, trending, etc.

The PC products provide support for the Microsoft standards such as

Dynamic Data Exchange (DDE) which allows e.g. to visualise data

dynamically in an EXCEL spreadsheet, Dynamic Link Library (DLL) and

Object Linking and Embedding (OLE).

Database

The configuration data are stored in a database that is logically

centralised but physically distributed and that is generally of a proprietary

format.

For performance reasons, the RTDB resides in the memory of the servers

and is also of proprietary format.

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The archive and logging format is usually also proprietary for

performance reasons, but some products do support logging to a

Relational Data Base Management System (RDBMS) at a slower rate

either directly or via an ODBC interface.

6.3.5 SCALABILITY

Scalability is understood as the possibility to extend the SCADA based

control system by adding more process variables, more specialised

servers (e.g. for alarm handling) or more clients. The products achieve

scalability by having multiple data servers connected to multiple

controllers. Each data server has its own configuration database and

RTDB and is responsible for the handling of a sub-set of the process

variables (acquisition, alarm handling, archiving).

6.3.6 Redundancy The products often have built in software redundancy at a server level,

which is normally transparent to the user. Many of the products also

provide more complete redundancy solutions if required.

6.4 FUNCTIONALITY

6.4.1 ACCESS CONTROL Users are allocated to groups, which have defined read/write access

privileges to the process parameters in the system and often also to

specific product functionality.

6.4.2 MMI The products support multiple screens, which can contain combinations

of synoptic diagrams and text.

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They also support the concept of a "generic" graphical object with links

to process variables. These objects can be "dragged and dropped" from a

library and included into a synoptic diagram.

Most of the SCADA products that were evaluated decompose the process

in "atomic" parameters (e.g. a power supply current, its maximum value,

its on/off status, etc.) to which a Tag-name is associated. The Tag-names

used to link graphical objects to devices can be edited as required. The

products include a library of standard graphical symbols, many of which

would however not be applicable to the type of applications encountered

in the experimental physics community.

Standard windows editing facilities are provided: zooming, re-sizing,

scrolling... On-line configuration and customisation of the MMI is

possible for users with the appropriate privileges. Links can be created

between display pages to navigate from one view to another.

6.4.3 TRENDING

The products all provide trending facilities and one can summarise the

common capabilities as follows:

the parameters to be trended in a specific chart can be predefined

or defined on-line

a chart may contain more than 8 trended parameters or pens and an

unlimited number of charts can be displayed (restricted only by the

readability)

real-time and historical trending are possible, although generally

not in the same chart

historical trending is possible for any archived parameter

zooming and scrolling functions are provided

parameter values at the cursor position can be displayed

The trending feature is either provided as a separate module or as a

graphical object (ActiveX), which can then be embedded into a synoptic

display. XY and other statistical analysis plots are generally not provided.

6.4.4 ALARM HANDLING Alarm handling is based on limit and status checking and performed in

the data servers. More complicated expressions (using arithmetic or

logical expressions) can be developed by creating derived parameters on

which status or limit checking is then performed. The alarms are logically

handled centrally, i.e., the information only exists in one place and all

users see the same status (e.g., the acknowledgement), and multiple alarm

priority levels (in general many more than 3 such levels) are supported.

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It is generally possible to group alarms and to handle these as an entity

(typically filtering on group or acknowledgement of all alarms in a

group). Furthermore, it is possible to suppress alarms either individually

or as a complete group. The filtering of alarms seen on the alarm page or

when viewing the alarm log is also possible at least on priority, time and

group. However, relationships between alarms cannot generally be

defined in a straightforward manner. E-mails can be generated or

predefined actions automatically executed in response to alarm

conditions.

6.4.5 LOGGING/ARCHIVING The terms logging and archiving are often used to describe the same

facility. However, logging can be thought of as medium-term storage of

data on disk, whereas archiving is long-term storage of data either on disk

or on another permanent storage medium. Logging is typically performed

on a cyclic basis, i.e., once a certain file size, time period or number of

points is reached the data is overwritten. Logging of data can be

performed at a set frequency, or only initiated if the value changes or

when a specific predefined event occurs. Logged data can be transferred

to an archive once the log is full. The logged data is time-stamped and

can be filtered when viewed by a user. The logging of user actions is in

general performed together with either a user ID or station ID. There is

often also a VCR facility to play back archived data.

6.4.6 REPORT GENERATION One can produce reports using SQL type queries to the archive, RTDB or

logs. Although it is sometimes possible to embed EXCEL charts in the

report, a "cut and paste" capability is in general not provided. Facilities

exist to be able to automatically generate, print and archive reports.

6.4.7 AUTOMATION The majority of the products allow actions to be automatically triggered

by events. A scripting language provided by the SCADA products allows

these actions to be defined. In general, one can load a particular display,

send an Email, run a user defined application or script and write to the

RTDB.

The concept of recipes is supported, whereby a particular system

configuration can be saved to a file and then re-loaded at a later date.

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Sequencing is also supported whereby, as the name indicates, it is

possible to execute a more complex sequence of actions on one or more

devices. Sequences may also react to external events.

Some of the products do support an expert system but none has the

concept of a Finite State Machine (FSM).

6.5 APPLICATION DEVELOPMENT

6.5.1 CONFIGURATION The development of the applications is typically done in two stages. First

the process parameters and associated information (e.g. relating to alarm

conditions) are defined through some sort of parameter definition

template and then the graphics, including trending and alarm displays are

developed, and linked where appropriate to the process parameters. The

products also provide an ASCII Export/Import facility for the

configuration data (parameter definitions), which enables large numbers

of parameters to be configured in a more efficient manner using an

external editor such as Excel and then importing the data into the

configuration database.

However, many of the PC tools now have a Windows Explorer type

development studio. The developer then works with a number of folders,

which each contains a different aspect of the configuration, including the

graphics.

The facilities provided by the products for configuring very large

numbers of parameters are not very strong. However, this has not really

been an issue so far for most of the products to-date, as large applications

are typically about 50K I/O points and database population from within

an ASCII editor such as Excel is still a workable option.

On-line modifications to the configuration database and the graphics is

generally possible with the appropriate level of privileges.

6.5.2 DEVELOPMENT TOOLS The following development tools are provided as standard:

a graphics editor, with standard drawing facilities including

freehand, lines, squares circles, etc. It is possible to import pictures

in many formats as well as using predefined symbols including e.g.

trending charts, etc. A library of generic symbols is provided that

can be linked dynamically to variables and animated as they

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change. It is also possible to create links between views so as to

ease navigation at run-time.

a data base configuration tool (usually through parameter

templates). It is in general possible to export data in ASCII files so

as to be edited through an ASCII editor or Excel.

a scripting language

an Application Program Interface (API) supporting C, C++, VB

a Driver Development Toolkit to develop drivers for hardware that

is not supported by the SCADA product.

6.5.3 OBJECT HANDLING

The products in general have the concept of graphical object classes,

which support inheritance. In addition, some of the products have the

concept of an object within the configuration database. In general the

products do not handle objects, but rather handle individual parameters,

e.g., alarms are defined for parameters, logging is performed on

parameters, and control actions are performed on parameters. The support

of objects is therefore fairly superficial.

6.6 EVOLUTION SCADA vendors release one major version and one to two additional

minor versions once per year. These products evolve thus very rapidly so

as to take advantage of new market opportunities, to meet new

requirements of their customers and to take advantage of new

technologies.

As was already mentioned, most of the SCADA products that were

evaluated decompose the process in "atomic" parameters to which a Tag-

name is associated. This is impractical in the case of very large processes

when very large sets of Tags need to be configured. As the industrial

applications are increasing in size, new SCADA versions are now being

designed to handle devices and even entire systems as full entities

(classes) that encapsulate all their specific attributes and functionality. In

addition, they will also support multi-team development.

As far as new technologies are concerned, the SCADA products are now

adopting:

Web technology, ActiveX, Java, etc.

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OPC as a means for communicating internally between the client

and server modules. It should thus be possible to connect OPC

compliant third party modules to that SCADA product.

6.7 ENGINEERING Whilst one should rightly anticipate significant development and

maintenance savings by adopting a SCADA product for the

implementation of a control system, it does not mean a "no effort"

operation. The need for proper engineering can not be sufficiently

emphasised to reduce development effort and to reach a system that

complies with the requirements, that is economical in development and

maintenance and that is reliable and robust. Examples of engineering

activities specific to the use of a SCADA system are the definition of:

a library of objects (PLC, device, subsystem) complete with

standard object behaviour (script, sequences, ...), graphical

interface and associated scripts for animation,

templates for different types of "panels", e.g. alarms,

instructions on how to control e.g. a device ...,

a mechanism to prevent conflicting controls (if not provided with

the SCADA),

alarm levels, behaviour to be adopted in case of specific alarms, ...

6.8 POTENTIAL BENEFITS OF SCADA

The benefits one can expect from adopting a SCADA system for the

control of experimental physics facilities can be summarised as follows:

a rich functionality and extensive development facilities. The

amount of effort invested in SCADA product amounts to 50 to 100

p-years!

the amount of specific development that needs to be performed by

the end-user is limited, especially with suitable engineering.

reliability and robustness. These systems are used for mission

critical industrial processes where reliability and performance are

paramount. In addition, specific development is performed within a

well-established framework that enhances reliability and

robustness.

technical support and maintenance by the vendor.

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For large collaborations, as for the CERN LHC experiments, using a

SCADA system for their controls ensures a common framework not only

for the development of the specific applications but also for operating the

detectors. Operators experience the same "look and feel" whatever part of

the experiment they control. However, this aspect also depends to a

significant extent on proper engineering.

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CHAPTER 7

RELAY

A relay is an electromagnetic switch operated by a relatively

small electric current that can turn on or off a much larger electric

current. The heart of a relay is an electromagnet (a coil of wire that

becomes a temporary magnet when electricity flows through it). You can

think of a relay as a kind of electric lever: switch it on with a tiny current

and it switches on ("leverages") another appliance using a much bigger

current. Why is that useful? As the name suggests, many sensors are

incredibly sensitive pieces of electronic equipment and produce only

small electric currents. But often we need them to drive bigger pieces of

apparatus that use bigger currents. Relays bridge the gap, making it

possible for small currents to activate larger ones. That means relays can

work either as switches (turning things on and off) or as amplifiers

(converting small currents into larger ones).

Figure 7.1

7.1 WORKING

Relays are switches that open and close circuits electromechanically or

electronically. Relays control one electrical circuit by opening and

closing contacts in another circuit. As relay diagrams show, when a relay

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contact is normally open (NO), there is an open contact when the relay is

not energized. When a relay contact is Normally Closed (NC), there is a

closed contact when the relay is not energized. In either case, applying

electrical current to the contacts will change their state.

Relays are generally used to switch smaller currents in a control circuit

and do not usually control power consuming devices except for small

motors and Solenoids that draw low amps. Nonetheless, relays can

"control" larger voltages and amperes by having an amplifying effect

because a small voltage applied to a relays coil can result in a large

voltage being switched by the contacts.

Protective relays can prevent equipment damage by detecting electrical

abnormalities, including overcurrent, undercurrent, overloads and reverse

currents. In addition, relays are also widely used to switch starting coils,

heating elements, pilot lights and audible alarms.

7.2 TYPES OF RELAYS

There are two basic classifications of relays: Electromechanical and Solid

State. Electromechanical relays have moving parts, whereas solid state

relays have no moving parts. Advantages of Electromechanical relays

include lower cost, no heat sink is required, multiple poles are available,

and they can switch AC or DC with equal ease.

7.2.1 ELECTROMECHANICAL RELAYS

Basic parts and functions of electromechanical relays include:

1. Frame: Heavy-duty frame that contains and supports the parts of

the relay.

2. Coil: Wire is wound around a metal core. The coil of wire causes

an electromagnetic field.

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3. Armature: A relays moving part. The armature opens and closes

the contacts. An attached spring returns the armature to its original

position.

4. Contacts: The conducting part of the switch that makes (closes) or

breaks (opens) a circuit.

Figure7.2

Relays involve two circuits: the energizing circuit and the contact circuit.

The coil is on the energizing side; and the relays contacts are on the

contact side. When a relays coil is energized, current flow through the

coil creates a magnetic field. Whether in a DC unit where the polarity is

fixed, or in an AC unit where the polarity changes 120 times per second,

the basic function remains the same: the magnetic coil attracts a ferrous

plate, which is part of the armature. One end of the armature is attached

to the metal frame, which is formed so that the armature can pivot, while

the other end opens and closes the contacts. Contacts come in a number

of different configurations, depending on the number of Breaks, poles and

Throws that make up the relay. For instance, relays might be described as

Single-Pole, Single-Throw (SPST), or Double-Pole, Single-Throw

(DPST). These terms will give an instant indication of the design and

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function of different types of relays.

Break -This is the number of separate places or contacts that a

switch uses to open or close a single electrical circuit. All contacts

are either single break or double break. A single break (SB) contact

breaks an electrical circuit in one place, while a double break (DB)

contact breaks it in two places. Single break contacts are normally

used when switching lower power devices such as indicating lights.

Double break contacts are used when switching high-power

devices such as solenoids.

Pole -This is the number of completely isolated circuits that relays

can pass through a switch. A single-pole contact (SP) can carry

current through only one circuit at a time. A double-pole contact

(DP) can carry current through two isolated circuits

simultaneously. The maximum number of poles is 12, depending

upon a relays design.

Throw -This is the number of closed contact positions per pole that

are available on a switch. A switch with a single throw contact can

control only one circuit, while a double-throw contact can control

two.

7.2.1.1 TYPE OF RELAYS

1. General Purpose Relays are electromechanical switches, usually

operated by a magnetic coil. General purpose relays operate with

AC or DC current, at common voltages such as 12V, 24V, 48V,

120V and 230V, and they can control currents ranging from 2A-

30A. These relays are economical, easy to replace and allow a wide

range of switch configuration.

2. Machine Control Relays are also operated by a magnetic coil.

They are heavy-duty relays used to control starters and other

industrial components. Although they are more expensive than

general purpose relays, they are generally more durable. The

biggest advantage of machine control relays over general purpose

relays is the expandable functionality of Machine Control Relays

by the adding of accessories. A wide selection of accessories is

available for machine control relays, including additional poles,

convertible contacts, transient suppression of electrical noise,

latching control and timing attachments.

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3. Reed Relays are a small, compact, fast operating switch design

with one contact, which is NO. Reed Relays are hermetically

sealed in a glass envelope, which makes the contacts unaffected by

contaminants, fumes or humidity, allows reliable switching, and

gives contacts a higher life expectancy. The ends of the contact,

which are often plated with gold or another low resistance material

to increase conductivity, are drawn together and closed by a

magnet. Reed relays are capable of switching industrial

components such as solenoids, contactors and starter motors. Reed

relays consists of two reeds. When a magnetic force is applied,

such as an electromagnet or coil, it sets up a magnetic field in

which the end of the reeds assume opposite polarity. When the

magnetic field is strong enough, the attracting force of the opposite

poles overcomes the stiffness of the reeds and draws them together.

When the magnetic force is removed, the reeds spring back to their

original, open position. These relays work very quickly because of

the short distance between the reeds.

7.2.2 SOLID STATE RELAYS

Solid state relays consist of an input circuit, a control circuit and

an output circuit. The Input Circuit is the portion of a relays frame

to which the control component is connected. The input circuit

performs the same function as the coil of electromechanical relays.

The circuit is activated when a voltage higher than the relays

specified Pickup Voltage is applied to the relays input. The input

circuit is deactivated when the voltage applied is less than the

specified minimum Dropout voltage of the relay. The voltage range

of 3 VDC to 32 VDC, commonly used with most solid-state relays,

makes it useful for most electronic circuits. The Control Circuit is

the part of the relay that determines when the output component is

energized or de-energized. The control circuit functions as the

coupling between the input and output circuits. In

electromechanical relays, the coil accomplishes this function. A

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relays Output Circuit is the portion of the relay that switches on the

load and performs the same function as the mechanical contacts of

electromechanical relays. Solid-state relays, however, normally

have only one output contact.

Figure 7.3

7.2.2.1 TYPE OF RELAYS

1. Zero-Switching Relays - relays turns ON the load when the

control (minimum operating) voltage is applied and the voltage of

the load is close to zero. Zero-Switching relays turn OFF the load

when the control voltage is removed and the current in the load is

close to zero. Zero-Switching relays are the most widely used.

2. Instant ON Relays - turns ON the load immediately when the

pickup voltage is present. Instant ON Relays allow the load to be

turned ON at any point in it's up and down wave.

3. Peak Switching Relays - turns ON the load when the control

voltage is present, and the voltage of the load is at its peak. Peak

Switching relays turn OFF when the control voltage is removed

and the current in the load is close to zero.

4. Analog Switching Relays - has an infinite number of possible

output voltages within the relays rated range. Analog switching

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relays have a built in synchronizing circuit that controls the amount

of output voltage as a function of the input voltage. This allows a

Ramp-Up function of time to be on the load. Analog Switching

relays turn OFF when the control voltage is removed and current in

the load is near zero.

7.3 A RELAYS CONTACT LIFE

A relays useful life depends upon its contacts. Once contacts burn out, the

relays contacts or the entire relay has to be replaced. Mechanical Life is

the number of operations (openings and closings) a contact can perform

without electrical current. A relays mechanical life is relatively long,

offering up to 1,000,000 operations. A relays Electrical life is the number

of operations (openings and closings) the contacts can perform with

electrical current at a given current rating. A relays Contact electrical life

ratings range from 100,000 to 500,000 cycles.

Figure7.4

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CHAPTER 8

SENSORS

A sensor is a device that detects and responds to some type of input from

the physical environment. The specific input could be light, heat, motion,

moisture, pressure, or any one of a great number of other environmental

phenomena. The output is generally a signal that is converted to human-

readable display at the sensor location or transmitted electronically over a

network for reading or further processing.

8.1 TYPES OF SENSORS:

Capacitive

Capacitive displacement sensor

Doppler effect (sensor based on effect)

Eddy-current

Inductive

Laser rangefinder

Magnetic, including Magnetic proximity fuse

Passive optical (such as charge-coupled devices)

Passive thermal infrared

Photocell (reflective)

Radar

Reflection of ionizing radiation

Sonar (typically active or passive)

Ultrasonic sensor (sonar which runs in air)

Fiber optics sensor

Hall effect sensor

8.2 APPLICATIONS

Parking sensors

Ground proximity warning system for aviation safety

Vibration measurements of rotating shafts in machinery

Top dead center (TDC)/camshaft sensor in reciprocating engines.

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Sheet break sensing in paper machine.

Anti-aircraft warfare

Roller coasters

Conveyor systems

Beverage and food can be making lines

Improvised Explosive Devices or IEDs

Mobile devices

8.3 CAPACITIVE PROXIMITY SENSING

Capacitive sensing is a noncontact technology suitable for detecting

metals, nonmetals, solids, and liquids, although it is best suited for

nonmetallic targets because of its characteristics and cost relative to

inductive proximity sensors. In most applications with metallic targets,

inductive sensing is preferred because it is both a reliable and a more

affordable technology.

Figure 8.1 Capacitive sensor components

The sensor consists of four basic components:

A capacitive probe or plate

An oscillator

A signal level detector

A solid-state output switching device

An adjustment potentiometer

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Capacitive proximity sensors are similar in size, shape, and concept to

inductive proximity sensors. However, unlike inductive sensors which

use induced magnetic fields to sense objects, capacitive proximity

generate an electrostatic field and reacts to changes in capacitance caused

when a target enters the electrostatic field. When the target is outside the

electrostatic field, the oscillator is inactive. As the target approaches, a

capacitive coupling develops between the target and the capacitive probe.

When the capacitance reaches a specified threshold, the oscillator is

activated, triggering the output circuit to switch states between ON and

OFF.

Figure 8.2 Capacitive proximity operation

8.4 DETECTION THROUGH BARRIERS

One application for capacitive proximity sensors is level detection

through a barrier. For example, water has a much higher dielectric than

plastic. This gives the sensor the ability to “see through” the plastic and

detect the water.

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SHIEDLNG The surface of the detection coil on Shielded Proximity Sensors is

covered with metal, so the flux is concentrated at the front of Sensors,

which reduces the influence of surrounding metal.

The surface of the sensing coil on Unshielded Proximity Sensors is

not covered with metal, so flux is also generated from the surface,

which makes Sensors easily influenced by surrounding metal.

Figure 8.3

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CHAPTER 9

MISELLANEOUS COMPONENTS

9.1 PUSH BUTTONS

push Button Switches consist of a simple electric switch mechanism

which controls some aspect of a machine or a process. Buttons are

typically made out of hard material such as plastic or metal. The surface

is usually shaped to accommodate the human finger or hand, so the

electronic switch can be easily depressed or pushed. Also, most Push

Button Switches are also known as biased switches. A biased switch, can

be also considered what we call a "momentary switch" where the user

will push-for "on" or push-for "off" type. This is also known as a push-to-

make (SPST Momentary) or push-to break (SPST Momentary)

mechanism.

Switches with the "push-to-make" (normally-open or NO) mechanism are

a type of push button electrical switch that operates by the switch making

contact with the electronic system when the button is pressed and breaks

the current process when the button is released. An example of this is a

keyboard button.

A "push-to-break" (or normally-closed or NC) electronic switch, on the

other hand, breaks contact when the button is pressed and makes contact

when it is released.

Figure 9.1

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9.1.1 TYPES OF PUSH BUTTONS

There are many different kinds of pushbutton switches and at Future

Electronics we stock many of the most common types. We carry some of

the top pushbutton switches manufacturers and suppliers including:

Altech, C & K, Carling, Cherry Electric, E-Switch, EECO, Grayhill,

Marquardt Switches, NKK Switches, Schurter and TE Connectivity

Best of all our electronic push button switch offering comes in a range of

sizes from miniature to industrial power switches. There are even

illuminated pushbutton switches available. Use our parametric filters to

refine your electric push button switch search on our website. You can

select by number of positions, by circuitry, by actuator style and by

termination among others.

9.1.2 USES OF PUSH BUTTONS

The "push-button" has been utilized in calculators, push-button

telephones, kitchen appliances, and various other mechanical and

electronic devices, home and commercial.

In industrial and commercial applications, push buttons can be connected

together by a mechanical linkage so that the act of pushing one button

causes the other button to be released. In this way, a stop button can

"force" a start button to be released. This method of linkage is used in

simple manual operations in which the machine or process have

no electrical circuits for control.

Pushbuttons are often color-coded to associate them with their function so

that the operator will not push the wrong button in error. Commonly used

colors are red for stopping the machine or process and green for starting

the machine or process.

Red pushbuttons can also have large heads (called mushroom heads) for

easy operation and to facilitate the stopping of a machine. These

pushbuttons are called emergency stop buttons and are mandated by the

electrical code in many jurisdictions for increased safety. This large

mushroom shape can also be found in buttons for use with operators who

need to wear gloves for their work and could not actuate a regular flush-

mounted push button. As an aid for operators and users in industrial or

commercial applications, a pilot light is commonly added to draw the

attention of the user and to provide feedback if the button is pushed.

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Typically, this light is included into the center of the pushbutton and

a lens replaces the pushbutton hard center disk. The source of the energy

to illuminate the light is not directly tied to the contacts on the back of the

pushbutton but to the action the pushbutton controls. In this way a start

button when pushed will cause the process or machine operation to be

started and a secondary contact designed into the operation or process

will close to turn on the pilot light and signify the action of pushing the

button caused the resultant process or action to start.

9.2 FREE WHEEL

A freewheel or overrunning clutch is a device in a transmission that

disengages the driveshaft from the driven shaft when the driven shaft

rotates faster than the driveshaft. An overdrive is sometimes mistakenly

called a freewheel, but is otherwise unrelated.

The condition of a driven shaft spinning faster than its driveshaft exists in

most bicycles when the rider holds his or her feet still, no longer pushing

the pedals. In a fixed-gear bicycle, without a freewheel, the rear wheel

would drive the pedals around.

Figure 9.2

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9.3 WHEEL

A wheel is a circular component that is intended to rotate on an

axle bearing. The wheel is one of the main components of the wheel and

axle which is one of the six simple machines. Wheels, in conjunction with

axles, allow heavy objects to be moved easily facilitating movement or

transportation while supporting a load, or performing labor in machines.

Wheels are also used for other purposes, such as a ship's wheel, steering

wheel, potter's wheel and flywheel.

9.3.1 WHEEL SPECIFICATION

Diameter - 7cm; Width - 4cm

Shaft Hole - 6mm

Easily fits into a 6mm shaft DC gear motor

Figure 9.3

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9.3 LED

A light-emitting diode (LED) is a two-lead semiconductor light source.

It is a p–n junction diode, which emits light when activated. When a

suitable voltage is applied to the leads, electrons are able to recombine

with electron holes within the device, releasing energy in the form

of photons. This effect is called electroluminescence, and the colour of

the light (corresponding to the energy of the photon) is determined by the

energy band gap of the semiconductor.

An LED is often small in area (less than 1 mm2) and integrated optical

components may be used to shape its radiation pattern.

Appearing as practical electronic components in 1962, the earliest LEDs

emitted low-intensity infrared light. Infrared LEDs are still frequently

used as transmitting elements in remote-control circuits, such as those in

remote controls for a wide variety of consumer electronics. The first

visible-light LEDs were also of low intensity, and limited to red. Modern

LEDs are available across the visible, ultraviolet,

and infrared wavelengths, with very high brightness.

Early LEDs were often used as indicator lamps for electronic devices,

replacing small incandescent bulbs. They were soon packaged into

numeric readouts in the form of seven, and were commonly seen in

digital clocks.

Recent developments in LEDs permit them to be used in environmental

and task lighting. LEDs have many advantages over incandescent light

sources including lower energy consumption, longer lifetime, improved

physical robustness, smaller size, and faster switching. Light-emitting

diodes are now used in applications as diverse as aviation, automotive

headlamps, advertising, general lighting, traffic signals, camera flashes

and lighted wallpaper. As of 2015, LEDs powerful enough for room

lighting remain somewhat more expensive, and require more precise

current and heat management, than compact fluorescent lamp sources of

comparable output.

LEDs have allowed new text, video displays, and sensors to be

developed, while their high switching rates are also used in advanced

communications technology.

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Figure 9.4

9.3.1 WORKING PRINCLIPLE

A P-N junction can convert absorbed light energy into a proportional

electric current. The same process is reversed here (i.e. the P-N junction

emits light when electrical energy is applied to it). This phenomenon is

generally called electroluminescence, which can be defined as the

emission of light from a semi-conductor under the influence of an electric

field. The charge carriers recombine in a forward-biased P-N junction as

the electrons cross from the N-region and recombine with the holes

existing in the P-region. Free electrons are in the conduction band of

energy levels, while holes are in the valence energy band. Thus the

energy level of the holes will be lesser than the energy levels of the

electrons. Some portion of the energy must be dissipated in order to

recombine the electrons and the holes. This energy is emitted in the form

of heat and light.

The electrons dissipate energy in the form of heat for silicon and

germanium diodes but in gallium arsenide phosphide (GaAsP)

and gallium phosphide (GaP) semiconductors, the electrons dissipate

energy by emitting photons. If the semiconductor is translucent, the

junction becomes the source of light as it is emitted, thus becoming a

light-emitting diode, but when the junction is reverse biased no light will

be produced by the LED and, on the contrary, the device may also be

damaged.

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9.4 CONVEYER BELT

Belt conveyor is a machine transporting material in a continuous way by

friction drive. It is mainly composed by rack, conveyor belt, belt roll,

tensioning device and gearing. It can form a material delivery process

between the initial feeding point and the final discharging point of jaw

crusher .

It can transport not only granular material, but also work piece. Besides

the pure material transporting, it can also form a rhythmic flow transport

line complying with the requirements of various industrial production

processes.

The belt conveyor can be used for horizontal transportation or inclined

transportation in a convenient way, and widely used in modern industrial

enterprises, such as: mine tunnel, mine surface transportation system,

open-pit and concentrator.

Figure 9.5

9.4.1 WORKING PRINCLIPLE

Belt conveyor is composed by two endpoint pulleys and a closed

conveyor belt. The pulley that drives conveyor belt rotating is called

drive pulley or transmission drum; the other one–only used to change

conveyor belt movement direction–is called bend pulley. Drive pulley is

driven by the motor through reducer, and conveyor belt dragging relies on

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the friction drag between the drive pulley and the conveyor belt. The

drive pulleys are generally installed at the discharge end in order to

increase traction and be easy to drag. Material is fed on the feed-side and

landed on the rotating conveyor belt, then rely on the conveyor belt

friction to be delivered to discharge end.

Feature:

The belt conveyor mainly has the following characteristics: the body can

flex easily with a belt-warehousing, the tail can elongate or shorten

complying with the coal face; directly lay on the roadway floor without

setting up foundation; compact structure, light and handy rack and

convenient disassembly. When the transmission capacity is big or

transport distance is far, we can meet the requirements by equipping with

intermediate drives. According to the requirements of transmission

process, it can be transported by single transmission and also can be

formed a horizontal or inclined transportation by multi-unit.

The belt conveyor is widely used in metallurgy, coal, transportation,

utilities, chemical and other departments because of its features of big

conveying capacity, simple structure, easy-to- maintenance, low cost and

versatility.

The belt conveyor is also used in building materials, electricity, light,

food, ports, ships and other departments.

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9.5 DC GEARED MOTOR

A gear motor is a specific type of electrical motor that is designed to

produce high torque while maintaining a low horsepower, or low speed,

motor output. Gear motors can be found in many different applications,

and are probably used in many devices in your home.

Gear motors are commonly used in devices such as can openers, garage

door openers, washing machine time control knobs and even electric

alarm clocks. Common commercial applications of a gear motor include

hospital beds, commercial jacks, cranes and many other applications that

are too many to list.

Figure 9.6

9.5.1 WORKING PRINCLIPLE

A gear motor can be either an AC (alternating current) or a DC (direct

current) electric motor. Most gear motors have an output of between

about 1,200 to 3,600 revolutions per minute (RPMs). These types of

motors also have two different speed specifications: normal speed and the

stall-speed torque specifications.

Gear motors are primarily used to reduce speed in a series of gears, which

in turn creates more torque. This is accomplished by an integrated series

of gears or a gear box being attached to the main motor rotor and shaft

via a second reduction shaft. The second shaft is then connected to the

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series of gears or gearbox to create what is known as a series of reduction

gears. Generally speaking, the longer the train of reduction gears, the

lower the output of the end, or final, gear will be.

An excellent example of this principle would be an electric time clock

(the type that uses hour, minute and second hands). The synchronous AC

motor that is used to power the time clock will usually spin the rotor at

around 1500 revolutions per minute. However, a series of reduction gears

is used to slow the movement of the hands on the clock.

For example, while the rotor spins at about 1500 revolutions per minute,

the reduction gears allow the final second hand gear to spin at only one

revolution per minute. This is what allows the second-hand to make one

complete revolution per minute on the face of the clock.

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CHAPTER 10

SWITCH MODE POWER SUPPLY

The electronic power supply integrated with the switching regulator

for converting the electrical power efficiently from one form to

another form with desired characteristics is called as Switch-mode

power supply. It is used to obtain regulated DC output voltage from

unregulated AC or DC input voltage.

Similar to other power supplies, switch-mode power supply is a

complicated circuit that supplies power from a source to loads.

switch-mode power supply is essential for power consuming

electrical and electronic appliances and even for building electrical

and electronic projects.

Figure10.1

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10.1 WORKING OF SMPS

Power supply is an electronic circuit that is used for providing the

electrical power to appliances or loads such as computers, machines,

and so on. These electrical and electronic loads require various forms of

power at different ranges and with different characteristics. So, for this

reason the power is converted into the required forms (with desired

qualities) by using some power electronic converters or power

converters.

Electrical and electronic loads work with various forms of power

supplies, such as AC power supply, AC- to-DC power supply, High-

voltage power supply, Programmable power supply, Uninterruptable

power supply and Switch-mode power supply.

10.2 TOPOLOGIES OF SMPS

There are different types of topologies for SMPS, among those, a few are

as follows

DC to DC converter

AC to DC converter

Fly back converter

Forward converter

10.2.1 DC TO DC CONVERTER SMPS

In a DC-to-DC converter, primarily a high-voltage DC power is directly

obtained from a DC power source. Then, this high-voltage DC power is

switched at a very high switching speed usually in the range of 15 KHz to

50 KHz.

And then it is fed to a step-down transformer which is comparable to the

weight and size characteristics of a transformer unit of 50Hz. The output

of the step-down transformer is further fed into the rectifier. This filtered

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and rectified output DC power is used as a source for loads, and a sample

of this output power is used as a feedback for controlling the output

voltage. With this feedback voltage, the ON time of the oscillator is

controlled, and a closed-loop regulator is formed.

Figure 10.2

The output of the switching-power supply is regulated by using PWM

(Pulse Width Modulation). As shown in the circuit above, the switch is

driven by the PWM oscillator, such that the power fed to the step-down

transformer is controlled indirectly, and hence, the output is controlled by

the PWM, as this pulse width signal and the output voltage are inversely

proportional to each other.

If the duty cycle is 50%, then the maximum amount of power is

transferred through the step-down transformer, and, if duty cycle

decreases, then the amount of power transferred will decrease by

decreasing the power dissipation.

10.2.2 AC TO DC CONVERTER SMPS

The AC to DC converter SMPS has an AC input. It is converted into DC

by rectification process using a rectifier and filter. This unregulated DC

voltage is fed to the large-filter capacitor or PFC (Power Factor

Correction) circuits for correction of power factor as it is affected. This is

because around voltage peaks, the rectifier draws short current pulses

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having significantly high-frequency energy which affects the power

factor to reduce.

Figure 10.3

It is almost similar to the above discussed DC to DC converter, but

instead of direct DC power supply, here AC input is used. So, the

combination of the rectifier and filter, shown in the block diagram is used

for converting the AC into DC and switching is done by using a power

MOSFET amplifier with which very high gain can be achieved. The

MOSFET transistor has low on-resistance and can withstand high

currents. The switching frequency is chosen such that it must be kept

inaudible to normal human beings (mostly above 20KHz) and switching

action is controlled by a feedback utilizing the PWM oscillator.

This AC voltage is again fed to the output transformer shown in the

figure to step down or step up the voltage levels. Then, the output of this

transformer is rectified and smoothed by using the output rectifier and

filter. A feedback circuit is used to control the output voltage by

comparing it with the reference voltage.

10.2.3 FLY-BACK CONVERTER TYPE SMPS

The SMPS circuit with very low output power of less than 100W (watts)

is usually of Fly-back converter type SMPS, and it is very simple and

low- cost circuit compared to other SMPS circuits. Hence, it is frequently

used for low-power applications.

The unregulated input voltage with a constant magnitude is converted

into a desired output voltage by fast switching using a MOSFET; the

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switching frequency is around 100 kHz. The isolation of voltage can be

achieved by using a transformer. The switch operation can be controlled

by using a PWM control while implementing a practical fly-back

converter.

Fly-back transformer exhibits different characteristics compared to

general transformer. The two windings of the fly-back transformer act

as magnetically coupled inductors. The output of this transformer is

passed through a diode and a capacitor for rectification and filtering. As

shown in the figure, the voltage across this filter capacitor is taken as the

output voltage of the SMPS.

Figure10.4

10.2.3 FORWARD CONVERTER TYPE SMPS

Forward converter type SMPS is almost similar to the Fly-back converter

type SMPS, but in the forward converter type, a control is connected for

controlling the switch and at the output of the secondary winding of the

transformer, and the rectification and filtering circuit is complicated as

compared to the fly-back converter.

It can be called as a DC to DC buck converter, along with a transformer

used for isolation and scaling. In addition to the diode D1 and capacitor

C, a diode D2 and an inductor L are connected at the output end. If switch

S gets switched ON, then the input is given to the primary winding of the

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transformer, and hence, a scaled voltage is generated at the secondary

winding of the transformer.

Figure 10.5

Thus, the diode D1 gets forward biased and scaled voltage is passed

through the low-pass filter preceding the load. If the switch S is turned

off, then the currents through the primary and secondary winding reach to

zero, but the current through the inductive filter and load can not be

change abruptly, and a path is provided to this current by the

freewheeling diode D2. By using the filter inductor, the required voltage

across the diode D2 and to maintain the EMF required for maintaining the

continuity of the current at inductive filter.

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CHAPTER 11

SOFTWARE AND CODING

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CHAPTER 12

CONCLUSION

Thus system designed is very precise and very easy in handling. This

system is advantageous for commercial as well as residential purpose.

The components used are readily available which makes construction

very easy. The structure is compact which allows the system to be

installed on any platform.

Here, PLC is used in the control of the prototype of the automated

parking system. Inductive sensors, DC motors are used to provide

movements to transport the vehicle in the parking system. The main

advantages are space optimization, cost effectiveness and security.

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REFERENCES

http://www.ijesit.com/Volume%204/Issue%202/IJESIT201502_52.

pdfMaizidi and Maizidi- Embeded system

http://www.slideshare.net/jermybsowmya/automatic-car-parking-

system-16284488

http://ijset.com/ijset/publication/v2s9/IJSET_2013_912.pdf

https://en.wikipedia.org/wiki/SCADA

https://en.wikipedia.org/wiki/Proximity_sensor

https://en.wikipedia.org/wiki/Push-button

http://en.wikipedia.org/wiki/Programmable_logic_controller

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