Programmable Logic Controller (PLC) For Beginner

 A Programmable Logic Controller (PLC) is a type of computer-based control system used in industrial automation for controlling processes and machines. It is designed to replace traditional relay-based control systems and operate in harsh industrial environments.

Key features of PLC:

1.    Input/Output (I/O) modules to interface with sensors and actuators.

2.    A processing unit to execute a program stored in non-volatile memory.

3.    A programming language, usually ladder logic or function block diagram, used to create control logic.

4.    Communication interfaces for remote monitoring and control.

Benefits of PLC:

1.    High reliability and durability.

2.    Easy to program and modify control logic.

3.    Cost-effective solution for controlling industrial processes.

4.    Faster and more accurate control compared to traditional relay-based systems.


There are several types of PLCs based on their architecture, functionality and application:

1.    Compact PLCs: small and inexpensive, suitable for simple control applications.

2.    Modular PLCs: composed of individual modules that can be combined to meet specific control requirements.

3.    Standalone PLCs: designed for standalone operation and can also be integrated into a larger control system.

4.    Rack-mounted PLCs: designed for large control systems and require a backplane to connect multiple modules.

5.    Network PLCs: designed for communication over Ethernet or other communication networks.

6.    Motion Control PLCs: specialized in controlling motion-based systems, such as robots and conveyors.

7.    Safety PLCs: designed to meet safety requirements in hazardous environments and comply with safety standards.

It's important to choose the right type of PLC for the application based on its requirements, complexity, and environment.


PLCs use various programming languages to create control logic. The most commonly used programming languages are:
1.    Ladder Logic: based on electrical relay circuits, uses graphical symbols to represent control logic.
2.    Function Block Diagram (FBD): uses blocks and connections to represent control logic.
3.    Structured Text (ST): uses a high-level programming language, similar to Pascal or C.
4.    Sequential Function Chart (SFC): uses flowchart symbols to represent control logic.
Each language has its own advantages and disadvantages, and the choice of programming language depends on the application, the programmer's experience, and personal preference. Some PLCs support multiple programming languages, giving users the flexibility to choose the most suitable language for their application.

plc hardware architecture:

1.    PLC hardware architecture consists of the following main components:

2.    Processor Unit: contains the central processing unit (CPU), memory, and communication interfaces for input/output (I/O) and programming.

3.    Input/Output (I/O) modules: interface between the PLC and the physical world, converting signals from sensors and actuators into digital signals that the PLC can process.

4.    Power Supply: provides power to the PLC and its components.

5.    Memory: stores the control program, input/output data, and other information needed by the PLC.

6.    Programming Terminal: used to create, modify, and download the control program into the PLC.

7.    Communication Interface: enables communication between the PLC and other control devices, such as computers, HMI (Human Machine Interface), and SCADA (Supervisory Control and Data Acquisition) systems.

8.    Expansion Units: used to add additional I/O or communication capabilities to the PLC.

The architecture of a PLC can vary depending on the manufacturer and the specific model, but the basic components remain the same. The performance and capabilities of a PLC are determined by the processing power, memory size, and the number and type of I/O and communication modules.

Criteria for choosing a PLC

When choosing a PLC, it's important to consider the following criteria to ensure that the PLC is suitable for your application:

1.    Control Requirements: consider the complexity of the control task, the number of inputs and outputs, and the processing speed required.

2.    Environment: consider the operating environment, including temperature, humidity, vibration, and electromagnetic compatibility (EMC).

3.    Communication: choose a PLC with communication interfaces suitable for your application, including support for industrial networks such as Ethernet, Modbus, and CAN.

4.    Programming: choose a PLC with a programming language that is suitable for your application and matches your programming expertise.

5.    Expandability: consider the future expansion requirements, including additional I/O, communication, and processing capabilities.

6.    Support: choose a PLC from a manufacturer with a good reputation for technical support and reliability.

7.    Budget: choose a PLC that fits within your budget, but also consider the total cost of ownership, including the cost of programming, maintenance, and upgrades.

8.    Standards Compliance: consider whether the PLC complies with relevant industry standards, such as IEC 61131-3, and safety standards, such as EN 61508 or IEC 62061.

It's important to carefully evaluate your requirements and consider all of the criteria when choosing a PLC to ensure that it is suitable for your application and meets your needs.

Top 10 final year project ideas for PLC (Programmable Logic Controller) for Electrical Engineering students


 Types of Allen Bradley PLC

Ladder Logic (LAD) for S7-300 and S7-400 Programming 

Post a Comment

Previous Post Next Post