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Basics to electrical components help for PLCs and uCs

  1. Jul 14, 2014 #1
    I'm a non-electrical engineering student however want to gain knowledge and experience with different electrical programming systems. I'm confused however as to all the different components and their differences. For example, why/when would you choose a PLC over an Arduino board or do these two even compare? I'm primarily interested in things that will help in the construction of robots, automation tools, etc. so like how certain sensors work, circuitboards, etc. Any help is greatly appreciated, thanks!
  2. jcsd
  3. Jul 14, 2014 #2
    PLCs are industrially hardened to be able to withstand high amounts of electrical noise. They're preferred for industrial settings and other harsh locations.
  4. Jul 15, 2014 #3

    jim hardy

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    You'll learn by doing. Search for hobby sites like discovercircuits.com, sparkfun.com, amasci, tinaja, there are plenty around. Read up and build something.
  5. Jul 15, 2014 #4
    I recently discovered the Make Magazine electronics books. I think its pretty much what you are looking for. They give a lot of information without going into an engineering level of detail along with a bit of humor, historical footnotes, color photos, and equipment recommendations. Its very much geared toward a practical level of knowledge.
  6. Jul 17, 2014 #5
    I used to program PLCs to control the operation of riderless cranes used to store and retrieve pallets in warehouses. There are several advantages in addition to those already mentioned in such applications. First, the program is entered in as ladder logic, a representation of electrical diagram that electricians are already familiar with. This means it doesn't take a programmer to maintain the code, an electrician can do it. Second, with the PLC I used, the conduction path through the circuit lights up, that is to say the symbols change to bold font so that it is easy to follow exactly what is happening with the program as it is running.

    On these cranes there was a second computer programmed in assembler that did functions the PLC couldn't do such as translating commands from the mainfram to to PLC, maintaining lists of prohibited locations and so on. I spent perhaps a fifth the time working on and correcting my code than the other programmer did on his, and it wasn't because I was a better programmer. It's just a lot easier to program a PLC than it is a microcontroller.

    The advantages of a PLC over a uC are:
    Designed for harsh environments
    Ease of programming - if you understand relay circuits you can program PLCs
    Ease of maintenance and troubleshooting

    The advantages of a uC over a PLC are:
    Ability to perform much more complex tasks
    Able to do functions a PLC does with difficulty or not at all
    Last edited: Jul 17, 2014
  7. Jul 21, 2014 #6
    Great feedback, thanks for the replies. So my understanding is that PLCs are good for industrial control of certain processes while microcontrollers are used for more complex, in-depth operations. Is this correct? What are some more real-world examples of where a uC would be used in place of a PLC?
  8. Jul 21, 2014 #7
    a PLC is more of an application of microcontrollers. Its more of a complete system, with a power supply and an operating system and an easier to use interface, whereas a microcontroller is just a chip.
  9. Jul 21, 2014 #8
    So what other kinds of uC's are there like CPU's? Is a GPU considered a microprocessor?
  10. Jul 21, 2014 #9
    CPUs and GPU's are microprocessors, but not microcontrollers.

    A microcontroller sort of a general purpose self-contained computer. It has its own program memory, RAM, and input/output. Microprocessors have to get that functionality from other parts of the computer.

    To get a better idea of what to use them for, think of a car engine's fuel injection and ignition system. You'd have a table of data that would tell you how long to pulse the injectors at a certain throttle and certain RPM, and you'd have a optimal time to fire the spark plugs. It might also need some ability to change timings as the engine ages. But once you programmed it once, you'd probably never need to program it again. And certainly the average driver wouldn't need to program it. It doesn't need a operating system, or anything more than a tiny amount of memory and storage. Thus, it is a perfect application for a uC.
    Last edited: Jul 21, 2014
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