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PLC Essentials

To enroll in the full course visit How to troubleshoot PLCs – Essential Training

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Introduction to PLC’s, before PLC’s there were relays the problem with relays was not only their size but they were extremely slow speeds were as slow as 20 to 60 milliseconds if changes had to be made rewiring would be required electricians had to understand relay logic and be able to troubleshoot electrical control systems using electrical schematics but the advancement of the transistors logic gates were replacing relay control circuits the digital revolution was born the explosion of digital control systems and computers place new demands on the technician as the digital age continued to accelerate so did the need for qualified electricians learning building algebra was a new skill maintenance electricians had to learn in order to troubleshoot most companies kept the relays until Hydromatic, a division of General Motors requested a device that would number one adapt to change number two be able to be placed on the factory floor and number three the programming had to be done in the form of relay logic it method that plant electricians engineers and technicians were already familiar with. Dick Morley is given credit with inventing the first PLC but Allen Bradley copyrighted the letter PLC in 1970 the first PLC was installed at General Motors Olds mobile plan at the Landis company in Landis Pennsylvania today PLC’s come in a variety of sizes based on Approximate I/O count so what exactly is a PLC? Best definition a PLC is a computer that takes the place of relays and wires relays with normally open and normally closed contacts are replaced with memory locations that reside in a processor the program in a PLC appears as a line diagram the symbol used mimic relay logic in each symbol has a specific memory address the normally open normally closed and relay coils is nothing but text on the keyboard symbols have a specific memory location it’s all virtual there is nothing real about it, relay logic has real voltages real normally-open normally closed contacts and real outputs ladder logic has symbols that mimic relay logic symbols has specific memory locations and the program appears as lying diagrams the challenge of troubleshooting PLC’s is the same as it was almost 50 years ago to realize although there are similarities between relay logic and ladder logic troubleshooting PLC’s cannot be approached with the same mindset that is used for troubleshooting relay logic failing to make a clear distinction between the two will only add confusion and frustration presently the PLC industry is and has been attempting to move away from relay logic programming but is finding to do so difficult because of its early marketing the analogy would be like saying if you speak Spanish fluently you should be able to speak Italian speaking and Spanish will only give you the chance to identify and understand some words and maybe host sentences but does not mean you can go to Italy and understand the language. Essentials for troubleshooting PLC’s we’ll introduce you to the six fundamentals for troubleshooting with success and confidence in a second course that is in development is designed for hands-on lab exercises this course will build on the foundation that is presented in essentials for troubleshooting PLC’s.