20-10-2012, 05:49 PM
SEMINAR ON PLC
SEMINAR ON PLC.pptx (Size: 246.52 KB / Downloads: 62)
What is PLC?
PLC is a digital computer designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. A PLC is an example of a real time system
History of PLC
First Programmable Logic Controllers was designed
and developed by Modicon as a relay replacer
for General Motors.
The first PLC, model name 084, was invented by
Morley in 1969 who is considered to be the "father" of
the PLC.
The first commercial successful PLC, the 184, was
introduced in 1973 which was designed by Michael
Greenberg.
PLC operation sequence
1) Self test: Testing of its own hardware and software
for faults.
2)Input scan: If there are no problems, PLC will copy all
the inputs and copy their values into memory.
3)Logic solve/scan: Using inputs, the ladder logic program is solved once and outputs are updated.
4)Output scan: While solving logic the output values
are updated only in memory when ladder scan is done,
the outputs will be updated using temporary values in
memory.
Ladder Logic
The ladder logic is the oldest programming
language for PLC.
It is well suited to express Combinational
logic
The main ladder logic symbols represent the
elements.
Advantages of PLCs:
Reliability.
Flexibility in programming and reprogramming.
Cost effective for controlling complex systems.
Small physical size, shorter project time.
High speed of operation.
Ability to communicate with computer systems in the plant.
Ease of maintenance /troubleshooting.
Reduced space.
Energy saving.
Disadvantages of PLCs
PLC devices are proprietary.
Fixed Circuit Operations.
PLCs manufacturers offer only closed architectures.