This document provides an introduction to programmable logic controllers (PLCs). It discusses that PLCs were first developed in the 1960s to replace unreliable relay systems for controlling industrial processes. A PLC typically consists of a central processing unit, input/output modules, and a power supply. PLCs are commonly programmed using ladder logic and are used widely in manufacturing, process control, building automation, and transportation applications due to their flexibility, reliability, modularity and cost-effectiveness. The document also notes some disadvantages of PLCs, such as complexity, security vulnerabilities, and lack of standardization.

1. Introduction to PLC
Dr. A. M. Takale
Mechanical Engineering Department
Sharad Institute of Technology College of Engineering.

2. • What is a PLC?
• A programmable logic controller (PLC) is a digital industrial
computer used for automating electromechanical processes,
such as control of machinery on factory assembly lines,
amusement rides, or light fixtures. PLCs are rugged, modular,
and adaptable, making them popular in a wide range of
applications.

3. • History of PLCs
• PLCs were first developed in the 1960s by Dick Morley of Allen-
Bradley. Morley was looking for a way to replace the complex
and unreliable relay systems that were then used to control
industrial processes. PLCs were an immediate success, and
they quickly became the industry standard for industrial
automation.

4. • PLC is typically made up of the following components:
• Central Processing Unit (CPU): The CPU is the brain of the
PLC. It is responsible for executing the user's program, which is
stored in memory.
• Input/Output (I/O) Modules: I/O modules allow the PLC to
communicate with the outside world. Input modules receive
signals from sensors and switches, while output modules send
signals to actuators and other devices.
• Power Supply: The power supply provides power to the PLC
and its components

5. • Ladder Logic
• Ladder logic is a graphical programming language that is
commonly used to program PLCs. Ladder logic diagrams are
made up of rungs, which represent the steps in a control
sequence. Each rung has two or more contacts, which
represent the conditions that must be met for the rung to be
activated. If all of the contacts on a rung are activated, then the
coil on the rung is energized. The coil then sends a signal to an
output module, which controls an actuator or other device.

6. • PLC Applications
• PLCs are used in a wide variety of applications, including:
• Manufacturing: PLCs are used to control machinery on factory
assembly lines.
• Process Control: PLCs are used to control processes such as
chemical reactions and wastewater treatment.
• Building Automation: PLCs are used to control HVAC
systems, lighting, and security systems.
• Transportation: PLCs are used to control traffic signals, train
systems, and aircraft systems.

7. • PLC Advantages
• PLCs have several advantages over other types of industrial control
systems, including:
• Flexibility: PLCs can be easily reprogrammed to change the control
sequence.
• Reliability: PLCs are very reliable and can withstand harsh industrial
environments.
• Modularity: PLCs can be easily expanded to add additional I/O
modules and other components.
• Cost-effectiveness: PLCs are relatively inexpensive, especially when
compared to other types of industrial control systems.

8. • PLC Disadvantages
• PLCs also have some disadvantages, including:
• Complexity: PLCs can be complex to program and troubleshoot.
• Security: PLCs are vulnerable to cyberattacks.
• Lack of Standardization: There is no single standard for PLC
programming languages and communication protocols.

9. • Conclusion
• PLCs are a powerful and versatile tool for industrial automation.
They are used in a wide variety of applications and offer many
advantages over other types of industrial control systems.

10. Thank You