We all know that a Microcomputer is used to monitor and control various manufacturing processes in large process industries. When it gives some signal (in terms of information), control system components like actuators and valves act accordingly.

In entire of this process, I don't see any place for control systems engineering tools like Bode plots, Nyquist or Automatic feedback control.

Please explain this.

 

It seems that you have already formed an opinion. In the old analog control systems, you may be right. But in the new digital sampling systems that re-create analog, you may be wrong.

 

As long as you have a loop a Bode plot applies. As long as you sample, Nyquist applies. Automatic feedback control is a little vague, but follows number 1. Gain can be achieved by digital math, response by throughput. What's in the box is to a degree, immaterial. From the outside it looks the same and does the same things. Why wouldn't the same
tools apply?

Regards

cww

 

Understanding the Nyquist theorem is fundamental to using analogue signals with any modern digital control, data acquisition, or test system. If you don't understand the need for it, you can't use "a Microcomputer ... to monitor and control various manufacturing processes in large process industries". Or for that matter, to use a microcomputer in small process or any other industries. It also applies to reading analogue signals with a PLC.

You can't just stick components together without understanding how they interact. You will get readings, but they will be wrong.

 

Mr Griffin,
I am actually very confused with why we are taught control system engineering subjects in our curriculam. Actually the correct word you used "need for it"

and your email please !!

 

I'm not sure what your question is here. Are you asking for an explanation of what the Nyquist theorem is good for, or are you asking why you were taught it in the first place?

Nyquist tells you what cut off frequency you need for your front end low pass filter on an analogue input. If you do any work with something like a PC data acquisition board, this is fundamental. It is also applies to reading analogue signals with a PLC. If you are reading an analogue signal you need anti-aliasing filters. Some packaged sensors may come with appropriate filtering built in, but this is usually not the case.

As to why you were taught it, I presume your instructors taught it because it was something you need to know. Trust them, they've been doing this for years. You may not see the use for something until years later you need to solve a problem that relies on it. That applies to basic physics, algebra, and a lot of other subjects whose use is non-obvious.

As for my e-mail address, any questions you might have can be asked right here on Control.com.

 

At the risk of starting the "great debate"...

Engineering is defined as "the practical application of science to commerce or industry." (http://wordnet.princeton.edu/perl/webwn?s=engineering)

This implies 2 things:
1. An understanding of the fundamental science
2. The ability to apply it in practice

Many colleges and universities do a fine job covering the fundamentals, and all the associated math, but fall far short of addressing the practicalities. In fact, I have seen many university professors turn up their noses at subjects such as PLC programming. They see this as a "trade skill", or something that is somehow beneath them. Never mind that this is a "must have" skill at every manufacturing plant in the world. I have seen engineers graduate without ever having set foot in a plant. I have seen process and control engineers who could not identify a control valve.

Now, on the flip side: practice without fundamental understanding is quite dangerous. There have been many, many industrial accidents caused by failure to consider some fundamental aspect of the underlying science. All those fancy plots and the associated math were developed for a reason. They provide ways to explain and predict how the world works.

In my humble opinion, you must ALWAYS strike a balance between the appropriate science and its PRACTICAL application. Most engineers do not need to memorize all the various details of Nyquist plots. But you SHOULD know that they exist, and have an idea of what they are used for. Then they are another tool in your toolbox. A Nyquist plot is a tool that you can dust off and bring to the party when the time is right. They don't apply to every problem, and years may pass before you need Nyquist plots again.

Universities must, by their very nature, expose students to a broad array of tools, techniques, and thought processes. Students must seek out opportunities to develop the practical application of these skills. Personally, I recommend that every engineering student should participate in a co-op or similar work program before leaving the university. Universities and professors should REQUIRE this. Some do.

And, as practicing engineers, we should keep learning throughout our careers, and periodically refresh our knowledge of the fundamentals. Engineering, even a single discipline within engineering, is just too broad and deep for us to memorize and stay current on ALL the aspects of the technology. We must use our understanding of the fundamentals to develop and evaluate solutions to real-world problems. As needed, we need to dig in and strengthen our depth of knowledge on specific topics.

OK, I'll get off my soapbox now. Good luck in striking that balance between academics and practicality, and thanks for listening.

-George