Evolution of PLC
PLC, or programmable logic controller, is a dedicated controller that is specially used in industries to control and automate industrial processes. It has become an integral part of every aspect of the industry, enhancing and expanding production. In the past, manual control was the norm, but it had its drawbacks. Manual control not only posed safety risks for the operators but also lacked precision and accuracy. To overcome these challenges, industries shifted to hardware control, specifically relay control systems.
The relay control system involved the use of hundreds and thousands of relays to create a simple control system. However, this system had its drawbacks as well. It required extensive wiring and made it difficult to identify and fix faults. Troubleshooting issues in a control system with thousands of wires was time-consuming and challenging. The industry referred to the relay control system as “five hours to find the fault and five minutes to fix it.”
To overcome the limitations of hardware control, industries moved towards electronics control, including PCB designing. However, troubleshooting and cost remained problematic. This led to the introduction of PLC control.
PLC, as a specialized computer, is designed to control machines and processes. It utilizes programmable memory to store instructions and execute various functions, such as on-off control, timing functions, counting functions, sequencing, logical arithmetic, and data handling. While the design of most PLCs is similar to personal computers, they are specifically tailored for manufacturing process equipment and machinery. Unlike office computers, PLCs are designed to operate in the industrial environment and can withstand the demanding conditions of continuous operation.
PLC Architecture
The architecture of a PLC consists of various components that work together to control and automate industrial processes. The key components include:
- Power Supply: The power supply is responsible for providing power to the CPU and other field devices.
- Input and Output Modules: These modules act as a bridge connecting input and output devices with the CPU. They enable communication between field instruments like push buttons, switches, transmitters, control walls, solenoid valves, and VFT.
- Optical Isolation: Optical isolation is an isolation barrier used to electrically isolate the internal components of the CPU from the I/O terminals. It ensures the protection of internal components from external factors.
- CPU: The CPU is the brain of the PLC system. It houses the processor responsible for performing logic and controlling communication among the modules. Users can enter desired circuits using a programming device, and the processor executes the program based on input data.
- Programming Device: The programming device allows users to write and modify programs. In the past, handheld devices were used, but now PCs and laptops with PLC software are commonly used for programming.
In addition to these core components, there are additional components that can be included in a PLC system, such as operator interface devices for data entry and monitoring, communication adapters for remote I/O, and network interfaces for interconnecting PLCs with other controllers and distributed control systems. These additional components enhance the functionality and connectivity of the PLC system.
Advantages of PLC
PLCs offer several advantages over previous control systems:
- Increased Reliability: Once a program is written and tested, it can be easily downloaded to the PLC. Since all the logic is contained within the PLC memory, the chances of making logical errors are minimized. Additionally, the program reduces the need for extensive external wiring, enhancing reliability.
- Flexibility: Modifying a program in a PLC is easy, providing flexibility to adapt to changing requirements. Users can modify programs in the field, and security measures like keylocks and passwords can be implemented to ensure authorized access.
- Communication Capability: PLCs can communicate with other PLCs and computer equipment, enabling seamless integration with SCADA systems, HMIs, and other PLCs. They also facilitate program uploading and downloading.
- Faster Response Time: PLCs operate in real-time, meaning events in the field trigger immediate output execution. This ensures faster response times and improved efficiency.
- Easier Troubleshooting: PLCs provide LED indications to identify faulty I/O and simplify troubleshooting. Users can monitor and watch the control program in real-time, aiding in problem identification and resolution.
PLCs have revolutionized industrial automation by offering reliable and flexible control solutions. Their ability to increase reliability, adaptability, communication capabilities, response times, and ease of troubleshooting make them invaluable in modern industrial processes.
This blog provided an introduction to PLCs, their evolution, architecture, and advantages. PLCs have become an integral part of industrial automation, enabling industries to enhance productivity, accuracy, and efficiency in their processes. In the next session, we will delve deeper into the world of PLCs.
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