Seminar Topics & Project Ideas On Computer Science Electronics Electrical Mechanical Engineering Civil MBA Medicine Nursing Science Physics Mathematics Chemistry ppt pdf doc presentation downloads and Abstract

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Presented by
N. D. Ramesh


Road Map
Introduction
Basic PLC components
Introduction to STEP 7 LITE
Programming PLC and Ladder logic
Exercises
SCADA
Future scope

Introduction
A digitally operating electronic apparatus which uses a programmable memory for implementing specific functions such as :
Logic sequencing
Timing
Counting
Arithmetic control
through digital or analog
input/output modules
Purpose of PLC & its functions
Initially designed to replace relay logic boards
Accepts input from a series of switches
Sends output to devices or relays

Functions
On-off control,
Sequential control,
Feedback control, and
Motion control
Basic PLC components

Power Supply
Every PLC has an external or internal Isolated Power Supply.
Isolated Power Supplies can have more than one isolated output.
Normally Power supplies are high voltage. Typically 24 Volts for industrial PLCs.
INPUTS & Outputs
These are the physical connections from the real world to the PLC.
Inputs can be limit switches, push buttons, and sensors, anything that can "switch" a signal on or off.
Outputs are solenoids, lamps, contactors, relays etc,.
The number of DI/Os can be increased by adding additional DI/O
modules
CPU
CPU module mainly classified into three different parts based on their operation.
Processor
program memory
serial communication ports
Scan cycle of PLC
STEP 7 LITE
STEP 7 LITE
Programming PLC
FBD (Function block diagram)
LD (Ladder diagram)
ST (Structured text, similar to the Pascal programming language)
IL (Instruction list, similar to assembly language)
SFC (Sequential function chart).

Ladder logic
Ladder diagram is a language which composes program using relay symbols as a base in an image similar to a hard-wired relay sequence.
A ladder logic program has a ladder look to it. The sides of the ladder are the power rail on the left and ground rail on the right. The rungs of the ladder consists of Virtual Relay Components.

Virtual Relay components
[ ] Normally Open Switch

[/] Normally Closed Switch

( ) Coil
And many more..


Exercises

Direct online starter
Sequential switching of motors
Fan control unit
Tank level controller
Traffic light control
Bottling Plant simulation

SUPERVISORY CONTROL AND DATA ACQUISTION (SCADA)

SCADA refers to combination of telemetry and Data acquisition. It consist of:
Collecting data
Transferring it back to control site
Carrying out necessary analysis and control
Displaying data on operator screens

TELEMETRY
It is the technique used in transmitting and receiving information or data over a medium. Information can be Voltage, speed, level, temp, flow etc. Data is transmitted to another location through cables, Telephone, radio. Information may come from multiple locations.
DATA ACQUISTION
It is method used to access and control information from equipment being controlled and monitored. The data accessed is then forwarded on to a telemetry system fro transfer to different sites.

Future scope
Study of :
Interrupts
Counters
Communication Protocol:
Profibus
How to use communications to communicate with other PLC,
smart actuators and sensors etc.

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PROGRAMMABLE LOGIC CONTROLLERS


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PLC: Characteristics

located near the plant (field level), require robust construction, protection against dirt, water and mechanical threats, electro-magnetic noise, vibration, extreme temperature range (-30C..85C)


programming: either very primitive with hand-help terminals on the target machine itself, or with a lap-top able to down-load programs.


• primitive Man-Machine interface, either through LCD-display or connection of a laptopover serial lines (RS232).


Modular PLC

housed in a 19" (42 cm) rack  (height 6U ( = 233 mm) or 3U (=100mm)


high processing power (several CPU)


large choice of I/O boards

interface boards to field busses

Protection devices


Protection devices are highly specialized PLCs that measure the current and voltages in an electrical
substation, along with other statuses (position of the switches,…) to detect situations that could endanger the equipment (over-current, short circuit, overheat) and triggers the circuit breaker (“trip”) to protect the substation.
In addition, it records disturbances and sends the reports to the substation’s SCADA.
Sampling: 4.8 kHz, reaction time: < 5 ms.


Discrete Plant (reminder)


The plant is described by variables which take well-defined, non-overlapping values.The transition from one state to another is abrupt, it is caused by an external event.
Discrete plants are normally reversible, but not monotone, i.e. negating the
event which caused a transition will not revert the plant to the previous state.

Example: an elevator doesn't return to the previous floor when the button is released.

Discrete plants are described e.g. by finite state machines or Petri nets.



Function Block library

The programmer chooses the blocks in a block library, similarly to the
hardware engineer who chooses integrated circuits out of the catalogue.


The programmer may extend the library by defining function block macros out of
library elements.

SCADA & PROGRAMMABLE LOGIC CONTROLLER


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Introduction

A Programmable Logic Controller, PLC, or Programmable Controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result.
PLC and Programmable Logic Controller are registered trademarks of the Allen-Bradley Company.
SCADA is Widely used in industry for Supervisory Control and Data Acquisition of industrial processes, SCADA systems are now also penetrating the experimental physics laboratories for the controls of ancillary systems such as cooling, ventilation, power distribution, etc. More recently they were also applied for the controls of smaller size particle detectors such as the L3 moon detector and the NA48 experiment, to name just two examples at CERN.

PLC compared with other control systems

PLCs are well-adapted to a certain range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations in ladder logic (or function chart) notation. PLC applications are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design. For high volume or very simple fixed automation tasks, different techniques are used.
A microcontroller-based design would be appropriate where hundreds or thousands of units will be produced and so the development cost (design of power supplies and input/output hardware) can be spread over many sales, and where the end-user would not need to alter the control. Automotive applications are an example; millions of units are built each year, and very few end-users alter the programming of these controllers. However, some specialty vehicles such as transit busses economically use PLCs instead of custom-designed controls, because the volumes are low and the development cost would be uneconomic

Digital and analog signals

Digital or discrete signals behave as binary switches, yielding simply an On or Off signal (1 or 0, True or False, respectively). Pushbuttons, limit switches, and photoelectric sensors are examples of devices providing a discrete signal. Discrete signals are sent using either voltage or current, where a specific range is designated as On and another as Off. For example, a PLC might use 24 V DC I/O, with values above 22 V DC representing On, values below 2VDC representing Off, and intermediate values undefined. Initially, PLCs had only discrete I/O.
Analog signals are like volume controls, with a range of values between zero and full-scale. These are typically interpreted as integer values (counts) by the PLC, with various ranges of accuracy depending on the device and the number of bits available to store the data. As PLCs typically use 16-bit signed binary processors, the integer values are limited between -32,768 and +32,767. Pressure, temperature, flow, and weight are often represented by analog signals. Analog signals can use voltage or current with a magnitude proportional to the value of the process signal. For example, an analog 4-20 mA or 0 - 10 V input would be converted into an integer value of 0 - 32767.

Programming

Early PLCs, up to the mid-1980s, were programmed using proprietary programming panels or special-purpose programming terminals, which often had dedicated function keys representing the various logical elements of PLC programs. Programs were stored on cassette tape cartridges. Facilities for printing and documentation were very minimal due to lack of memory capacity. More recently, PLC programs are typically written in a special application on a personal computer, then downloaded by a direct-connection cable or over a network to the PLC. The very oldest PLCs used non-volatile magnetic core memory but now the program is stored in the PLC either in battery-backed-up RAM or some other non-volatile flash memory.
Early PLCs were designed to be used by electricians who would learn PLC programming on the job. These PLCs were programmed in "ladder logic", which strongly resembles a schematic diagram of relay logic. Modern PLCs can be programmed in a variety of ways, from ladder logic to more traditional programming languages such as BASIC and C.

Ladder logic

Ladder logic is a method of drawing electrical logic schematics. It is now a graphical language very popular for programming Programmable Logic Controllers (PLCs). It was originally invented to describe logic made from relays. The name is based on the observation that programs in this language resemble ladders, with two vertical "rails" and a series of horizontal "rungs" between them.
A program in ladder logic, also called a ladder diagram, is similar to a schematic for a set of relay circuits. An argument that aided the initial adoption of ladder logic was that a wide variety of engineers and technicians would be able to understand and use it without much additional training, because of the resemblance to familiar hardware systems. (This argument has become less relevant given that most ladder logic programmers have a software background in more conventional programming languages, and in practice implementations of ladder logic have characteristics — such as sequential execution and support for control flow features — that make the analogy to hardware somewhat imprecise.)