A Programmable Logic Controller (PLC) is a digital computer used to control electromechanical processes in factories. PLCs were introduced in the late 1960s to replace relay-based control systems. The first commercial PLC was developed by Modicon for General Motors. Later, as microprocessors became available, PLCs evolved to be more sophisticated. A PLC has components like a power supply, input/output modules, a processor, and a programming device to control inputs from sensors and outputs to devices. PLCs can operate in harsh industrial environments and use simple ladder logic programming. A Programmable Automation Controller (PAC) is similar but designed for more complex automation with greater flexibility, memory, and control

1. By
Bipin Likhar

2. PLC
 A Programmable Logic Controller (PLC) is a
digital computer used for automation of
electromechanical processes, such as control of
machinery on factory assembly lines, control of
amusement rides, or control of lighting fixtures.

3. PLC was introduced in late 1960’s to remove relay’s based
system.
First commercial & successful Programmable Logic
Controllers was designed and developed by Modicon as a
relay replacer for General Motors.
Earlier, it was a machine with thousands of electronic
parts.
Later ,in late 1970’s,the microprocessor became reality &
greatly enhanced the role of PLC permitting it to evolve
form simply relay to the sophisticated system as it is today.

4. 4
Major Components of a Common PLC
PROCESSOR
POWER
SUPPLY
I M
N O
P D
U U
T L
E
O M
U O
T D
P U
U L
T E
PROGRAMMING
DEVICE
From
SENSORS
Pushbuttons,
contacts,
limit switches,
etc.
To
OUTPUT
Solenoids,
contactors,
alarms
etc.

5. Major Components of PLC
 POWER SUPPLY
Provides the voltage needed to run the primary PLC components
 I/O MODULES
Provides signal conversion and isolation between the internal
logic level signals inside the PLC and the field’s high level signal.
 PROCESSOR
Provides intelligence to command and govern the activities of
the entire PLC systems.
 PROGRAMMING DEVICE
Used to enter the desired program that will determine the
sequence of operation and control of process equipment or
driven machine.

6. PLC Operation

7. Programming a PLC
 Ladder Logic
 Functional block diagram
 Structural text(similar to Pascal)
 Instruction list(similar to assembly language)

8. Why PLC ?....
• The controller is designed in modular form, so that sub-
assemblies could be removed easily for replacement or
repair.
• A PLC can work in the harsh and extreme conditions of the
industry where other systems such as a Micro-Controller
cannot.
• The system becomes reusable.
• The method used to program the controller is simple, so
that it can be easily understood by plant personnel.

9. Programmable Automation
Controller

10. PAC
 PAC stands for Programmable Automation Controller.
 PLC is best suited for machine control but has limited
memory and a focus on discrete I/O with on/off
control.
 On the other hand , a PAC is geared more toward
complex automation system architectures composed
of a number of PC-based software applications

12. Features of PAC
 Composed of a number of PC-based software
applications
 Including HMI (human machine interface) functions
 Architecture based on Ladder logic
 Provide greater flexibility in programming
 Larger memory capacity

13. Advantages of PACs over PLCs
 More open architecture
 Modular design
 More analog I/O options
 Better process control capabilities
 More built in communication ports
 Programming over USB ports
 Tag based programming (one software package
capable of programming multiple models )

14. Thank You