all details about plc

1. Dr.Sunil Kumar Chaudhary
GCET, Department of Electrical Engineering
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2. Making products under the control of
computers and programmable controllers is
known as “INDUSTRIAL AUTOMATION”.
Examples---Manufacturing assembly lines
as well as stand alone machine tools (CNC
machines) and robotic devices fall under this
category.
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3. Advantages------Automation is delegation of
human control
functions to technical equipments for increasing
productivity, better quality, increasing safety in
working conditions reducing manpower and cost
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4. Sensors for sensing the input parameters
Transmitters for transmitting the raw signal
in electrical form
Control system which include PLC,DCS and
PID controllers
Output devices such as actuators, drives,
control valves, solenoid valves, coils,
indicating lamps.
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5. PID controller based controller system
PLC based control system
DCS based control system
PC based automation system
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6.  In old days, electrical control was mostly based
on relays(Contactors) (i.e. Relay logic). Since from
1970 PLCs(Programmable Logic Controllers) have
become most common choice for manufacturing
/ process control.
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7.  PLCs are programmable
 Many control relays can be replaced by software,
which means less hardware failure.
 It is easier to make changes in software than in
hardware.
 Special functions such as time delay actions, counters
are easy to produce in software.
 Reliability is more.
 There is almost no task limit to tasks for which PLCs
can be used.
 It is cost effective control system

8. 
PLCs are designed to be operated in industrial
environment with wide range of ambient
temperature, vibration and humidity conditions. It
is not effected by the electrical noise present in the
industrial environment
 In computer, the inputs are floppy drives and
CD ROMs and output is a printer, but in PLC
the inputs are signals from control elements
like push-buttons, limit switches,
temperature switches, pressure switch and
transducer etc., installed on the machines to
be controlled.
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9.  In PLCcs output are final control elements like
contactors, solenoids, positioning valves, indication
lights, an so forth.

The PLC is not a disc based system like PC. With a
disc
based system there is a continuous checking of
what to
do next. With a PLC the answer of what to do next
is
inherent, there is no consulting. The PLC program
is
stored in battery backed RAM or EPROM.
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10.  Another important difference between PLC and PC
is
that the PLC contains the operating systems and
application programs in ROM memory. The
operating
system does not have to load an application
program, as
it is already in ROM. It is difficult to differentiate
between
PLCs, ‘BIOS’, operating system and application
program.
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11.  Another major difference between PLC and
computer is the programming language. PLC is not
programmed in one of the high language used for
programming a computer. As PLC is designed to be
operated by plant engineers and maintenance
personnel with limited knowledge of computers, it
is designed to be programmed using RELAY
LADDER LOGIC. However some PLCs are available
which can be programmed using FORTRAN and
BASIC, but relay ladder logic programming is the
most popular. Some PLCs are also programmed
using, Boolean Algebra, Statement lists and Control
system flow chart languages.
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12.  – PLC were Designed for Relay Logic Ladder
and have
 Difficulty with some Smart Devices.
 – To maximize PLC performance and
Flexibility, a
 number of Optional Modules must be added
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14. A PLC is a solid state/computerized
industrial computer that performs
discrete or sequential logic in a factory
environment.
It was originally developed to replace
mechanical relays, timers, counters and
other such devices.
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Inputs
Outputs & Power Supply
Communication
Ports(RS-485)

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21. A typical PLC can be divided into four
components:
 Processor Unit
 Power Supply
 Input / Output Section
 The Programmable Device
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24. Pushbuttons
Switches
Limit Switches
Selector Switches
Proximity Sensors
Photo-electric Sensors
2)Input Devices-Analog
Resistance Temperature Detectors
Thermocouple
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25. The input module performs task
electronically as:
Determines the presence or absence of
input
Converts input signal to a DC level
useable PLC
Provides electronic isolation between
input signal and PLC
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26.  PLC output devices can usually be:
Solenoids
Relays-AC or DC powered
Contactors
Motor-Stators
Indication Lights
Valves
Alarms
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27. Stores the control program and data in its
memory.
Reads the status of connected input
devices.
Performs arithmetic and logical operations.
Executes the control program.
Commands connected to output to change
state based on program execution.
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28. For any execution of program, processor
has to scan the entire program. Scan
cycle consists of-
1) Input Scan: Detects the state of all input
devices that are connected to the PLC.
2) Program Scan: Executes the user
created program logic.
3) Output Scan: Energizes or de-energizes
all output devices that are connected to
the PLC.
4) Housekeeping: This includes
communications with programming
terminals, internal diagnostics etc.
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31. PLC’s are used successfully to execute
complicated control operations in a plant.
Its purpose is to monitor crucial process
parameters and adjust process operations
accordingly.
A sequence of instructions is programmed by
the user to the PLC memory and when the
program is executed ,the controller operates
a system to the correct operating
specifications.
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32. It is used for any application in industry that
requires electrical control.
Packing – Bottling and Canning
Material Handling – Machining
Power Generation – HVAC / building
automation
Security Systems – Automated Assembly
Paint Lines _ Water Treatment
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33. Cement Industry
Automation Industry
Chemicals Industry
Plastics Industry
Metals Industry
Paper Industry
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34. Allen Bradley USA
Siemens Germany
Modicon France
Mitshubishi Japan
GE Fanuc USA
Omron Japan
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35. PLC Saves
By
Material Cost : Reduced wiring and
associated
Installation : Less Space
Troubleshooting : No moving parts-
rugged
Labour Cost : Possibility of
reprogramming
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36. Reliability
Flexibility
Advance Function
Communication
Speed
Diagnostics
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37. Supervisory Control:-
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40.  Thanks
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