Programmable logic controllers or PLC's are digital computers that are used to automate electromechanical processes. The biggest difference between PLC's and standard computers is that the PLC is designed to survive extended temperature ranges, electrical noise, and has built in resistance to vibration and impact. All of this leads to a much more durable computer, which is necessary in the harsher environments that PLC's are often used in.
What Do Programmable Logic Controllers Do?
In order to understand exactly what they do, it is important to understand what they are. A PLC is used to both control and troubleshoot large machines. Think of the PLC as the brain for an automated machine, such as an assembly line. A single PLC can replace thousands of relays that were used in older electrical panels. This makes it much simpler for maintenance technicians to make changes, because no re-wiring is involved, only some minor reprogramming. The overall purpose of the PLC was to replace the electromechanical relays that were commonly found in industrial environments. As logic elements, they are able to emulate the interconnection of thousands of relays in order to perform designated tasks.
Where Are Programmable Logic Controllers Used?
Programmable logic controllers have been widely adapted to perform a variety of automation tasks. Normally, they will be found streamlining industrial processes in manufacturing plants. This is because the cost of developing and maintaining the automation system can be very high and changes to the system output is common. PLC's are highly customizable so that cost of a PLC is low, whereas a custom built controller is high. This is why custom built PLC's are primarily found in factories that mass-produce goods. With mass-produced goods, there can be millions of units produced without major changes. This can be seen in packaging plants, material handling plants, automated assembly lines, and much more.
To give you a better example of why PLC's are becoming much more common, let's look at a simple task that can be automated. Let's say that a solenoid needs to run for 3 seconds and then be turned off again. Traditionally, a simple external timer would be used to handle this process. However, what if you have 10 or 20 solenoids that need to be turned on and off for 3 seconds? You would need 10 or 20 external timers, and they would all have to be individually maintained. Using a PLC, you can replace all of the external timers at once. Additionally, if you need to modify the settings for a different project, you only need to change the settings of the single PLC, instead of all 20 external timers.
Programmable logic controllers were initially designed for the automotive industry and in 1968, was first implemented by General Motors. Since then it has spread to a variety of arenas from chemical plants to packing plants. PLC's have found their way into almost every industry, and will continue to be a mainstay as long as they remain durable and easily programmable.
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