History of PLC

Programmable Logic Controllers (PLCs) have been an integral part of industrial automation for several decades. The history of PLCs dates back to the late 1960s when the need arose for an automated solution to replace traditional relay-based control systems.

The hard-wired nature made it difficult for design engineers to alter the automation process. Changes would require rewiring and careful updating of the documentation. If even one wire were out of place, or one relay failed, the whole system would become faulty. Often technicians would spend hours troubleshooting by examining the schematics and comparing them to existing wiring. When general-purpose computers became available, they were soon applied to control logic in industrial processes. These early computers were unreliable and required specialist programmers and strict control of working conditions, such as temperature, cleanliness, and power quality.

The PLC provided several advantages over earlier automation systems. It tolerated the industrial environment better than computers, was more reliable and compact, and required less maintenance than relay systems. It was easily extensible with additional I/O modules, while relay systems required complicated hardware changes in case of reconfiguration. This allowed for easier iteration over manufacturing process design. A simple programming language focused on logic and switching operations was more user-friendly than computers using general-purpose programming languages. It also permitted its operation to be monitored. Early PLCs were programmed in ladder logic, which strongly resembled a schematic diagram of relay logic. This program notation was chosen to reduce training demands for the existing technicians. Other PLCs used a form of instruction list programming, based on a stack-based logic solver.

The Emergence of Digital PLCs

As computer technology advanced, digital PLCs began to emerge. In the early 1970s, the Allen-Bradley Company developed the first digital PLC, known as the Programmable Controller 1771 (PC-1771). The PC-1771 was a modular system that used a central processing unit (CPU) and a series of input/output (I/O) modules that could be added or removed as needed. The PC-1771 was an instant success and helped to popularize the use of digital PLCs in industrial automation.

The Advancements in PLC Technology

Over the years, PLC technology has continued to evolve and improve. Today’s PLCs are faster, more powerful, and more flexible than ever before. Modern PLCs use microprocessors and flash memory to store program instructions and support advanced features such as networking, real-time monitoring, and remote access. These advancements have enabled PLCs to be used in a wide range of applications, from manufacturing and process control to transportation and building automation.

The Future of PLCs

The future of PLCs looks bright, with continued advancements in technology and the increasing demand for automation in various industries. PLCs are expected to continue to play a crucial role in industrial automation, with new features and capabilities being developed to meet the changing needs of businesses. For example, the growing interest in the Industrial Internet of Things (IIoT) is driving the development of PLCs that can support advanced communication protocols and connect to cloud-based systems.

Conclusion

PLCs have come a long way since their humble beginnings in the late 1960s. From the first analog PLCs to the advanced digital PLCs of today, PLC technology has continued to evolve and improve. The future of PLCs looks bright, with continued advancements in technology and the increasing demand for automation in various industries. PLCs have played and will continue to play a critical role in industrial automation, helping to improve efficiency, reduce downtime, and increase safety in manufacturing, transportation, and other industries.

References:

Wikipedia

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