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Practical Guide to Programmable Logic Controllers


The Programmable Logic Controller (PLC) has revolutionized the automation industry. Today, PLCs can be found in everything from factory equipment to vending machines, but prior to January 1, 1968, the programmable controller didn’t even exist. Instead, what existed was a unique set of challenges that needed a solution.

Before the days of the PLC, the only way to control machinery was through the use of relays, which work by utilizing a coil that, when energized, creates a magnetic force to effectively pull a switch to the ON or OFF position. When the relay is de-energized, the switch releases and returns the device to its standard ON or OFF position.

PLCs are often defined as miniature industrial computers that contain hardware and software used to perform control functions. More specifically, a PLC would be used for the automation of industrial electromechanical processes such as control of machinery on factory assembly lines, amusement rides, or food processing. They are designed for multiple arrangements of digital and analog inputs and outputs with extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact.

Typical PLCs have a wide range of I/O modules available to accommodate all kinds of sensors and output devices. The greatest benefit of automating with a PLC is the ability to repeat or change and replicate the operation or process while collecting and communicating vital information. Those making the buying decisions for programmable controller applications can have very different needs. Cost, power, speed, and communication are a few of the many considerations when choosing the right PLC for the job.

This Practical Guide to Programmable Logic Controllers Handbook has been improved with new, need-to-know information, making it a more comprehensive guide to the world of PLCs. Topics include basics of PLC history, PLC hardware and software, a deeper view into the ever-changing world of PLC communication, the importance of feedback loops, and cybersecurity – all topics that are a must-know for any PLC novice or seasoned automation professional.

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