The Importance of PLCs in Manufacturing
The common definition one would find on Wikipedia describes a PLC or Programmable Logic Controller as the following: “ A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis. Dick Morley, considered to be the father of the device, invented the first PLC for General Motors in 1968”.
PLCs are occupying a central or pivotal place in much of the factory-based manufacturing being done these days. This is not by accident! Conceptually, PLCs are ideally suited to the needs of automation today. Let us take a moment to examine some of the reasons for this success.
Advantages Of Using PLCs In Factory-Based Manufacturing
For more than 50 years Programmable Logic Controllers have been slowly but surely cementing their reputation as the most rugged, cost effective, value for dollar industrial control system options in use today. The advantages inherent in the conceptual approach used with Programmable Logic Controllers has allowed them to evolve along with other key technologies and achieve and maintain a central role in modern day automation. Historically, PLCs were intended to provide a replacement for the physical time delay relays, coils, contacts, drum controllers and variety of Relay Logic devices used in the rigid and primitive control systems of days long past. The approach taken to implementing an effective replacement for these rigid systems provided a range of advantages that have proven to have lasting efficacy. These advantages have, in no small way, resulted in the dominance of Programmable Logic Controllers in todays ongoing march towards the automation of factory-based manufacturing. These lasting advantages are worthy of examination when attempting to understand the role of PLCs in modern day manufacturing.
The Key Lasting Advantages Of PLCs In Manufacturing
Programmable logic controllers are easy to program and to install. Most PLCs are provided with quick- release type screw connections for fast wiring of input and output devices. PLC editing features allow program changes, corrections, and loading procedures to be accomplished in a matter of seconds in most cases.
1. The speed with which internal timers, sequencers, and relays operate is much faster than conventional time delay relay systems. An assembly machine using a PLC would therefore have a higher productivity rate.
2. Access to PLCs is restricted by hardware features such as keylocks, and by software features, such as passwords. Timers and their timing values can also be protected through special commands.
3. Problem solving with PLCs is also a major advantage over any other type of control system. Many PLCs are provided with diagnostic indicators which monitor power supply, central processing unit faults, low battery power for memory backup, input/output conditions, forced output conditions, and so on.
4. Programmable controllers are designed with communications capabilities that allow them to converse with local and remote computer systems or to provide human interfaces. These interfaces range from simple light or annunciator systems with alpha- numeric displays to elaborate video screens that allow the current state of a process to be viewed.
5. PLCs are extremely reliable control devices and can be obtained in forms that can survive and function in harsh conditions. They can meet almost any set of installation code requirements.
6. A large base of trained maintenance personnel experienced in troubleshooting and servicing systems with ladder logic programming, a legacy language, as well as structured text, function blocks, and in recent years, C and C++.
7. More effective response to power interruptions and failures. Alarm routines and special function instructions allow for robust fault protection and system monitoring.
8. Facilities and instructions that make PLCs ideal for data acquisition, data transfer, and system monitoring. Modern PLCs take advantage of common network protocols allowing for seamless data integration between the plant floor and the front office. As a result, pertinent information regarding throughput, available resources, inventory status etc… being readily available in real time to the front office.
9. Suitability for Distributed Control applications as well as a Centralized control model. The flexibility and versatility of PLCs goes beyond the availability of programming options and techniques. The manner in which these devices can be employed is also wide ranging.
10. PLCs by their nature and design, are capable of taking advantage of any modern day advancements in materials sciences, new and better sensor technologies, advanced featured HMI devices as well as improved network technologies that allow for reliable real time control applications. The advantages listed above have evolved in their own way along with these other technologies and in doing so, have kept PLCs at the forefront of control systems technologies. Scalability has been key as applications have become more memory intensive. Modern day manufacturing has also resulted in a requirement for larger amounts of data to be transferred at faster rates. Information moving along with product through a controlled process is becoming common place in todays world.
As manufacturing organizations move to embrace the modern age, Programmable Logic Controllers will continue to demonstrate their utility and staying power. The advantages that lead to their widescale adoption since their advent over 50 years ago, will continue to provide a competitive advantage to any form of factory-based manufacturing. The ongoing automation of factory-based manufacturing combined with the wide variety of PLCs now available at affordable prices suggest that most other systems used for industrial control applications will continue to be slowly phased out as they become obsolete. More and more, these obsolete technologies are being replaced by modern PLCs as we move towards the new age of automation. In addition, automation is making its presence felt in a wide range of applications that until recently, have been the sole domain of human labour, so continued growth in this field is assured.
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