HISTORY OF THE PLC

A Programmable Logic Controller (PLC) is an industrial computer designed for the

automation of electromechanical processes, such as those used in manufacturing, assembly
lines, robotic devices, or other control systems. Here’s a brief history of its development:
1. Origins (1960s)
 The concept of the PLC emerged in the 1960s due to the increasing complexity of
industrial control systems.
 Traditional control relied on relay-based systems, which were bulky, expensive, and
hard to modify. Engineers sought a more efficient and flexible alternative.

 1968: The first significant milestone was initiated when General Motors (GM) requested
a solution to replace relay systems in its Hydra-Matic automatic transmission
manufacturing plant.
 GM set four primary requirements for this solution:
o Programmable without needing rewiring.

o Compact, durable, and easy to maintain.

o Capable of processing logic operations efficiently.

o Economical compared to existing systems.

2. The First PLC (1969)

 The first PLC, Modicon 084, was developed in 1969 by Dick Morley, an innovator often
regarded as the "Father of the PLC."

Image of Dick Morley

Courtesy
of AutomationWorld.com
Richard E. Morley (December 1, 1932 – October 17, 2017) was an American inventor who was
considered one of the "fathers" of the programmable logic controller (PLC) since he was
involved with the production of the first PLC for General Motors, the Modicon, at Bedford and
Associates in 1968. The Modicon brand of PLC is now owned by Schneider Electric.

Modicon (MODular DIgital CONtroller) revolutionized manufacturing by providing a system that

could be programmed via a computer instead of physically altering wiring.
 The Modicon 084 used a simple programming language based on relay logic diagrams,
making it easy for technicians to adopt.
3. Early Adoption and Growth (1970s)
 During the 1970s, PLCs began to replace traditional relay logic systems across various
industries.
 Allen-Bradley (now Rockwell Automation) introduced its own PLCs and became a major
competitor to Modicon.
 Programming evolved from basic ladder logic to more complex capabilities, allowing
PLCs to handle larger processes.
 Memory capacity, reliability, and the ability to connect to peripherals were improved.
4. Advancements in Technology (1980s)
 With the development of microprocessors, PLCs became more powerful and compact.
  The introduction of networking capabilities allowed PLCs to communicate with other
devices and systems, facilitating distributed control systems (DCS).
 More sophisticated programming standards emerged, such as IEC 61131-3, which
defined languages like Ladder Logic, Function Block Diagrams, and Structured Text.
5. Integration with IT Systems (1990s)
 PLCs became more integrated with information technology systems during the 1990s,
enabling remote monitoring and diagnostics.
 The adoption of human-machine interfaces (HMIs) and SCADA (Supervisory Control
and Data Acquisition) systems enhanced control and visualization.
6. Modern PLCs (2000s and beyond)
 PLCs now support real-time processing, enhanced memory, and expanded
input/output (I/O) capabilities.
 Integration with IoT (Internet of Things) and Industry 4.0 principles allows PLCs to
participate in smart factories and cloud-based control systems.
 Modern PLCs support high-speed Ethernet communication, wireless control, and edge
computing for predictive maintenance and advanced analytics.
Key Manufacturers in PLC Development
 Modicon (Schneider Electric)  Siemens
 Allen-Bradley (Rockwell  Omron
Automation)
 Mitsubishi Electric

Figure – Siemens S7-1500 PLC

 EVOLUTION OF PLC

The evolution of programmable logic controllers (PLCs) has followed a path of increasing
functionality and capabilities, while becoming smaller, more powerful, and more cost-effective.
 First generation PLCs (1970s) were large, expensive, and used primarily to replace
relay-based control systems. They were based on custom logic circuits and could only
be programmed using proprietary software.
 Second generation PLCs (1980s) added more memory and processing power, and
began to use more standardized programming languages. They also started to
incorporate more advanced functions such as timers, counters, and data manipulation.
 Third generation PLCs (1990s) became more compact and efficient, and were able to
control a wider range of industrial processes. They also began to incorporate networking
capabilities, allowing PLCs to communicate with other devices and systems.
 Fourth generation PLCs (2000s) became even more powerful, with faster processors
and more memory. They also began to incorporate advanced features such as Ethernet
connectivity, support for industrial protocols such as Modbus and Profinet, and the ability
to handle large amounts of data.
 Fifth generation PLCs (2010s) became even more compact and efficient, with more
powerful processors and advanced features like built-in high-speed communication
interfaces, support for IoT and cloud connectivity, and advanced security mechanisms.
Currently, sixth-generation PLCs have a more compact design, even more powerful
processors and memory, more robust support for IoT, AI and Machine Learning, Cybersecurity,
and can be accessed remotely, offer more flexibility in terms of scalability.
As technology continues to advance, it is likely that PLCs will become even more powerful,
flexible, and cost-effective, and will continue to play an important role in industrial automation
and control.

APPLICATIONS OF PLC
Programmable logic controllers (PLCs) are used in a wide range of industrial control systems,
including:
1. Manufacturing: PLCs are used to automate and control a wide range of manufacturing
processes, including assembly lines, conveyor belts, and other types of industrial
machinery.
2. Power plants: PLCs are used to control and monitor a variety of systems in power
plants, including boilers, turbines, and other types of electrical and mechanical
equipment.
3. Water treatment: PLCs are used to control and monitor water treatment plants, including
processes such as filtration, chlorine addition, and pH adjustment.
4. Transportation: PLCs are used to control and monitor systems in transportation,
including traffic signals, automated trains, and other types of transportation
infrastructure.
5. Building automation: PLCs are used to control and monitor systems in buildings,
including heating, ventilation, and air conditioning (HVAC) systems, lighting, and security
systems.
6. Food and beverage: PLCs are used to control and monitor processes in the food and
beverage industry, including packaging, pasteurization, and quality control.
7. Oil and gas: PLCs are used to control and monitor processes in the oil and gas industry,
including drilling, refining, and transportation.
8. Agriculture: PLCs are used to control and monitor systems in agriculture, including
irrigation, fertilization, and pest control.

KEY FEATURES OF A PLC

A Programmable Logic Controller (PLC) is a type of computer specifically designed for
industrial control systems.
Some of the key features of a PLC include:
1. Reliability: PLCs are designed to operate reliably in harsh industrial environments, with
features such as redundant power supplies and robust hardware components.
2. Programmability: PLCs can be programmed using a variety of programming
languages, such as ladder logic or functional block diagrams, to control industrial
processes.
3. Flexibility: PLCs can be programmed to perform a wide variety of tasks, and can be
easily reconfigured to perform new tasks as needed.
4. Input/Output (I/O) capabilities: PLCs have a variety of input and output options,
including digital inputs, analog inputs, and a range of output options such as relays,
switches, and actuators.
5. Communication: PLCs can be connected to other devices, such as sensors and
actuators, using a variety of communication protocols, such as Ethernet, Modbus, and
Profibus.
6. Scalability: PLCs can be used in a variety of applications, from small standalone
systems to large, complex systems with hundreds of I/O points.
7. User-friendly programming: PLCs are designed to be user-friendly, with intuitive
programming software and graphical user interfaces.