The document discusses the history and use of programmable logic controllers (PLCs) in industrial automation. It notes that PLCs were first specified in 1968 by General Motors to provide a solid-state, reusable system for controlling industrial processes more flexibly than relay-based systems. A PLC consists of a central processing unit, power supply, programming unit, memory, and input/output interfacing circuitry. It scans inputs, executes user-programmed logic instructions, and updates outputs on a continuous cycle. Common programming methods for PLCs include ladder logic, functional block diagrams, and structured text. PLCs communicate with field devices and one another using various interfaces and protocols.

1. Use of PLC in Industrial
Automation
Presented By
S Aloka Patro
Reg. No-13020034
DepartmentOf E&TC,VSSUT, Burla
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2. Manual Control:
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3. Behind the Invention:
 The Hydrometric Division of the General Motors Corporation specified the
design criteria for the first programmable controller in 1968. The primary
goal was to eliminate the high costs associated with inflexible, relay
controlled systems.
 The specifications required a solid-state system with computer flexibility
able to,
• survive in an industrial environment,
• be easily programmed and maintained by plant engineers and
technicians, and
• be reusable
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4. What is it ?
 PLCs can be thought of in
simple terms as industrial
computers with specially
designed architecture in both
their central units (the PLC
itself) and their interfacing
circuitry to field devices
(input/output connections to
the real world). They are
capable of storing
instructions, such as
sequencing, timing, counting,
arithmetic, data manipulation,
and communication, to
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5. What does the PLC consist?
 The Central processor unit
 The power supply unit
 The programming unit
 The memory unit
 The I/O interfacing Circuitry
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6. Operation:
 The operation of a programmable controller is relatively simple.
The input/output (I/O) system is physically connected to the field
devices that are encountered in the machine or that are used in
the control of a process. These field devices may be discrete or
analog input/output devices, such as limit switches, pressure
transducers, push buttons, motor starters, solenoids,etc. The I/O
interfaces provide the connection between the CPU and the
information providers (inputs) and controllable devices (outputs).
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7. I/O Module:
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9. PLC I/Os:
The PLC I/Os can be Analog or digital based upon the device.
 The AC modules and DC modules are not quite different though
all the present day devices have sensors and sensors work on DC
signals.
 The outputs may be a relay, transistor or aTRIAC.
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10. Switching:
 When an input command comes
from a field device, the signal
goes to the DI or AI card, where it
powers up the LED and through
optical coupling/switching the
Transistor is switched on & the
signal goes to the PLC processor
module through communication
interface module via profibus
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11. Memory Section:
 The total memory system in a PLC is actually composed of two different
memories:
1. The executive memory
2. The application memory
 The executive memory is a collection of permanently stored programs that
are considered part of the PLC itself.
 The application memory provides a storage area for the user-programmed
instructions that form the application program.
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12. Program Scan:
 This process of reading the inputs,
executing the program, and updating the
outputs is known as the Scan. The
scanning process is repeated over and over
in the same fashion, making the operation
sequential from top to bottom.
Sometimes, for the sake of simplicity, we
call the solving of the control program the
program scan and the reading of inputs
inputs and updating of outputs the I/O
update scan.
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13. Scanning Time:
 A typical PLC has repetitive cycle
of operations. First the PLC
sequentially scans the input
devices and updates memory
table as per the states of the
inputs. Then it executes a control
programming. After the
execution it updates the
memory table indicating
whether output devices should
be ON or OFF. This time comes
around 3 to 100 milliseconds.
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14. PLC Communication:
A PLC communicates with its interfaces using certain ways i.e.;
 Extension modules
 Remote I/O modules
 Serial communication modules(RS-232,RS-485)
 Parallel communication(IEEE 488)
 General twisted pair cables
 Ethernet cables
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15. Communication:
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16. How to program a PLC:
To program a PLC we need to know some of the basic languages
i.e.,
• Functional Block Diagram
• Ladder Logic
• StructuredText
• Instruction List
• Sequential Flow Chart
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18. Ladder Logic:
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19. Functional Block Diagram:
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22. Merits:
• Rugged and designed to withstand vibrations, temperature,
humidity, and noise.
• Have interfacing for inputs and outputs already inside the
controller.
• PLCs are easily programmed and have an easily understood
programming language.
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23. Future Research:
 Till now communication within a PLC hasn’t been wirelessly done, so
importance is given on making it wireless. Though a PLC needs more no of
cables to be erected, it should be of prime concern for us to reduce the no.
of cables for erection.
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24. References:
 www.jsl.com
 www.google.co.in
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