plc
TRANSCRIPT
Introduction
Programming is instructing a computer to do
something with the help of a programming
language. A programming language is an artificial
language designed to communicate instructions to
a machine. Programming languages can be used
to create programs that control the behavior of a
machine.
What is PLC ?
A programmable logic controller is a specialized
computer used to control machines process.
It uses a programmable memory to store
instructions and specific functions that include
ON\OFF functions, timing, counting,
sequencing, arithmetic and data handling
It can be programmed, controlled and
operated by a person unskilled in operating
(programming) computers.
Aim and Objectives of PLC
Its purpose is to monitor crucial process
parameters and adjust process operation
accordingly.
Eliminates much of the hard wiring.
It is reprogrammable, reusable and reliable.
Can be connected with plant computer systems
easily.
History
The first PLC systems evolved from conventional
computers in the late 1960s and early 1970s.
In 1990’s different ways of programming PLCs was
introduced and in some cases it took the place of PCs.
The first PLC systems evolved from conventional
computers in the late 1960s and early 1970s.
In the 1980's the lack of standardization were
improved and size of PLCs was also reduced.
In 1990’s different ways of programming PLCs was
introduced and in some cases it took the place of
pc’s.
How PLC works
Receives information's through different sensors.
Sequentially executes programs according to
the information from input sensors.
Gives the solution of problems and sends
appropriate commands as output.
Programming The PLC
It is mostly based on ladder logic. The sequential
approaches are:
Entry of the ladder logic diagram
Low-level computer-type languages
High-level computer type languages
Functional blocks
Sequential function chart
Concept of Ladder Logic
It is a programming language that represents a program by a graphical diagram.
Programs in this language resemble ladders, with two vertical rails and a series of horizontal rugs between them.
Symbols of ladder logic
-( )- A regular coil,
-(\)- A “ not” coil,
-[ ]- A regular contact,
-[ ]- A not contact
PLC Processor Scan
Three major tasks in a PLC processor scan are
executed in the following order :
Read the physical inputs
Scan the ladder logic program
Write the physical outputs
Application of PLC
Some remarkable sectors using PLC application:
In Traffic light Signal system
In automatic transfer switch
In Nano technology and robotics
In industrial manufacturing
In medical instruments and technologies
In machining, packaging, material handling,
automated assembly etc.
PLC
Designed for extreme
industrial environments
Integrated command
interpreter (proprietary)
No secondary memory
available
Optimized for Single
task
Computer
Designed mainly for data processing and calculation
Optimized for speed
Lost of secondary memory available
Multitasking capability
PLC Vs. Computer
Advantages
Flexibility
Large Quantities of Contacts
Lower Cost
Visual Observation
Reliability and Maintainability
Disadvantages
Single-function applications do not pay to use a
PLC that includes multiple programming
capabilities.
Their operational sequence is seldom or never
changed.
if the power fails, the system stops.
Future of PLC
Continuation of new product developments and
making integration of PLCs with other control.
PLC technology include features such as GUIs
and more human-oriented machine interfaces.
New PLC instructions are developed to add
intelligence to a controller.
Concept of the flexible manufacturing system
(FMS) will determine the control philosophy of the
future.
Conclusion
PLC applications are typically highly customized
systems. PLC is low compared to the cost of a specific
custom-built controller design. In general, PLCs are
more robust and require less maintenance, thus
making the things they control work better, in spite of
the environment. Overall, PLCs appear to be an
excellent solution for many different problems.