1

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.

2

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.

3

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.

4

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.

Figure 2.1

5

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.

6

7

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,

8

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

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

9

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.

Figure 3.3 CPU

10

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.

Figure 3.4

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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.

Figure 3.5

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 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 PROGRAMMING 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

12

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.

Figure 3.6

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:

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

14

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 3.7

15

3.3 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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3.3.1 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.

3.3.1.1 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 3.8

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3.4 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 4.1 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 4.2 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 4.3 Multi- Level Parking

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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.

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.

4.3.1.4 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.

22

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.

Figure 5.1

23

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.

Figure 5.2

Output

Module

24

5.2 HARD-WIRED CONTROL

Prior to PLCs, many control tasks were performed by c on ta c to r s , 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

25

5.4 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.

5.4.1 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.

5.4.2 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.

5.5 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.

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.

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5.6 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.

5.7 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.

5.8 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 a c c i d e n t a 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.

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.

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5.9 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.

5.10 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.

5.10.1 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.

28

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.

5.11 PLC SCAN

PLC utilizes a standard scan method when evaluating user program.

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

5.11.1 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.

29

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.

5.11.2 OUTPUT

When END command is reached the program evaluation is complete. The

output memory is transferred to the external physical outputs.

30

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 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.

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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 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.

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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, chemistry, but also in some

experimental facilities such as nuclear fusion. The size of such plants range from a

few 1000 to several 10 thousand 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 6.1: 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 6.2: 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.

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.

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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.

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).

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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.

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.

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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.

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.

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).

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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 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.

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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.

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.

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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.

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 contact is normally open (NO), there is

an open contact when the relay is not energized. When a relay contact is Normally

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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.

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.

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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 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

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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.

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

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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 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

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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 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.

Figure 7.4

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CHAPTER 8

MISELLANEOUS COMPONENTS

8.1 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 8.1

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8.1.1 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.

8.1.2 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. 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.

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8.2 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 8.2

8.3 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.

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8.3.1 WHEEL SPECIFICATION

Diameter - 7cm; Width - 4cm

Shaft Hole - 6mm

Easily fits into a 6mm shaft DC gear motor

Figure 8.3

8.4 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.

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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.

Figure 8.4

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8.4.1 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.

8.5 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

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in a convenient way, and widely used in modern industrial enterprises, such as: mine

tunnel, mine surface transportation system, open-pit and concentrator.

Figure 8.5

8.5.1 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 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,

55

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.

8.6 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 8.6

8.6.1 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.

56

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 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 9

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.

Figure9.1

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9.1 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.

9.2 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

9.2.1 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 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.

59

Figure 9.2

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.

9.2.2 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 having significantly high-frequency energy which affects the

power factor to reduce.

Figure 9.3

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

60

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.

9.2.3 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 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.

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9.2.4 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 transformer, and hence, a scaled voltage

is generated at the secondary winding of the transformer.

Figure 9.5

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 10

CODING

63

64

65

CHAPTER 11

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.

66

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

R. K. Rajput, Strength Of Meterials, S. Chand

http://www.parkingsystemsolutions.com/rotary

E. S. Kardoss, K. Baliant, I. Wahl, “Design of a Semi Aautonomous Park

Assist System,” Proceedings of The European Control Conference,2009, pp.

497-516

http://www.delta.com.tw/product/em/em_main.asp

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

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