Please help!

Hello everyone!!

I was hoping if anybody could help me.

I am sitting here ripping my hair out trying to do an assignment on PLC's for my Mechatronics corse!! Its not going to well!

I was searching around the net when I came across this site.

I was hoping someone would be able to put me in the right direction, maybe a good site to try or something, it would be brilliant!!!

The assignment is about differences between unitary, modular and rack mounted systems and loads of other questions along those lines - to me its all in a different language as I have only been doing this subject for a short while.

Please help a very stressed girl!!!!

Thank you!!!

Click on the learn plc's at the top of the page, follow that through, perhaps buy Phil's book.
also take a look at: http://www.freestudy.co.uk/plc.htm
and www.thelearningpit.com

Most people that come here have no problem with providing you assistance. A word of advise for fast answers is to post your question. Then post what you beleieve the answer is. The advantage of doing it this way is that it shows that you are trying to learn the answers for yourself.

as far as the above questions are concerned. They deal with how the total PLC is put together. For example rack mounted describes PLC's that mount on a rack with seperate I/O cards that also mount on a rack. Think of the above questions in similar terms and you should be able to answer your questions above.

One further trick is that the questions you are asking have been asked at least 20 times in the 5 months I've been visiting this site. If you do a search on the keywords your looking to define You will find those threads

Look at outcome 1 here: http://www.freestudy.co.uk/plc/

As a student you should definitely include your answer and then ask for corrections or comments. We tend to pick on students that give the slightest hint they want someone to do their homework for them. You seem to have put in some effort, and that is a good thing.

To be honest, the terms Unitary, Modular, Brick, Rack etc.. are not really common terms used in the real world of PLCs. After 20+ years of expierence I'm not sure of the answers myself.

Page 6 of this document seems to have the answers that your instructor may be looking for: http://www.freestudy.co.uk/plc/outcome1.pdf

Have fun..

Mike

elevmike said:

After 20+ years of expierence I'm not sure of the answers myself.

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There's probably a good reason for that. 20+ years ago, when the instructor for this class last touched a PLC, the lines were probably more clearly drawn. How would he classify the DL06, for example? It's kind of a Brick-Modular(Rack?) combo. Technically, I suppose it's modular. But, most of us use it like a brick. I wonder if this teacher's definition of "Rack" is the SLC style of PLC, or if he actually means a PLC that fits a 19" rack-mount enclosure. Are there any 19" rack PLCs? What category do we put touchscreen PLCs into?

The PLC/DCS/SCADA question is another good one. The lines have blurred so much now that PLCs are sometimes used to replace DCS systems, and two years later someone tries to sell the customer on a DCS again.

Rhiannon, tell your instructor that the answer to this question is useless trivia, at best. Very few marketing flyers or datasheets will describe a PLC in these terms. Instead, they use buzz words like "expandable," "7 slot," or "fixed IO." Good luck to you if you are ever asked to purchase a "Unitary PLC," and that's what you enter into the Google search window.

AK

I am not so sure that it is trivial. Most training begins with a history of some sorts, even Phil's learn PLCS. The idea may be to familiarze students with terms that have been and may be used with PLCS. Many work with MODICON but may not realize it is short for Modular Digital Controller.

Its a matter of perspective. PLCS have changed alot but "brick" is still used to identify a small controller even though that brick may have modular architecture.

Modular is definitely a common term for systems, even those that use racks.

The idea may be to get students to study the terms, learn the history and see how technology has changed the plc over time. Students with NO plc background develop a basic understanding of what they are, how they are used, what they were called, how they have changed...etc etc.

Its a matter of perspective:
Those working in the industry know the terms, types etc so the question is ridiculous.

Students or those that have never worked in the industry dont know terms, types etc so have to start somewhere.

We have seen a few here that have taken the HNC course that are very capable so the process must work.

rsdoran said:

We have seen a few here that have taken the HNC course that are very capable so the process must work.

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Thanks Ron,

I'll take that as a compliment!!

Paul

Out of all the topics covered in the HNC course, why is it that the "Unitary, Modular, Rack-Mounted" question is the one that gets asked here so often? I can think of a few possible explanations.

1. We're such arrogant, condescending, sarcastic SOBs that after seeing our answers to that first question, HNC students never come back.

2. When the typical HNC student that needs to ask for the answer to that question gets to chapter 2, he/she realizes that he/she is in so far over his/her head that he/she drops the course.

3. When the HNC student reads our answers, he/she realizes that taking a course that requires the student to memorize such insignificant trivia is a waste of time and money and drops the course.

Do other countries have standardized courses like these? If they do, why don't we get similar questions from Australia, New Zealand, India, Canada, South Africa? Why are they overwhelmingly from Great Britain?

rsdoran said:

PLCS have changed alot but "brick" is still used to identify a small controller even though that brick may have modular architecture.

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Which is why I said that there are certain buzz words which ARE important.

I understand the purpose of teaching history/background. But should it be an assignment, or worse yet, a TEST QUESTION? I'm still frustrated about what was or wasn't focused on in my own education. I took at least 6 credits of philosophy, because it was a required elective (oxymoron). Being exposed to Plato has only come in handy once or twice. I can always skip those ****tail parties...

Do I really need to know Isaac Newton on a personal level to understand physics? Not really, but I need to know what his discoveries were, so that I don't try to reinvent the wheel (or gravity).

AK

AK said...

"Being exposed to Plato has only come in handy once or twice."

AK, as long as you are alive and playing in "the game" (life), then you are being exposed and re-exposed to Plato, over, and over again.


Aristotle (and Newton) developed basic principles for understanding the nature of physical phenomena.

Socrates provided a means to analyze logical relationships (the fundamental basis of PLC logic).

Plato (a student of Socrates) provided a means to develop reasonable questions.


While it is true that Plato put a lot of effort into understanding the more esoteric questions of life, his efforts contributed greatly to the foundation of "Critical Thinking" as it applies to all aspects of life... including Process Control.

Socrates' effort was, of course, the basis for modern logic and the logic used in PLCs.

The contributions made by Aristotle were unsurpassed until Newton. Aristotle's principals were the only guiding principles in physical phenomena for many centuries until Newton came on the scene. Then Einstein showed up.

Not to belittle Newton, but Newton, as substantial as his work was, only added to the basic principles developed by Aristotle. Newton's work was based on Aristotle's work (along with the work of several others like Kepler, Copernicus, Tycho Brahe, etc.).

Einstein, on the other hand, while looking at the basic principles developed by Aristotle and Newton, turned the world upside-down by basing his developments on the concept that TIME, "THE FUNDAMENTAL CONSTANT", was not a fundamental constant after all! Of course, for most Earthly concerns, Time is pretty damned constant.

Modern Process Control activities rely heavily on the foundations established and further developed by these people. Each of these foundations are equally important. While developing a Process Control System we use all of the philosophies developed by these folks.

How often have you seen a reply-post asking the original poster to post a reasonable question? That is Plato talking!

Process Controls can be developed only through reasonable questions. The questions are every bit as important as the answers!

Plato plays more of a role in your life than you think.

Thanks to the efforts of those old, dead guys (and many others), we are able to do what we do now.

I wish I could learn eloquence.

My point was that students dont know the correct questions, they have nothing to use to relate to the plc world. Those in charge of the curriculum had to create a starting point to introduce students to plcs.

People learn something new everyday, will it all be useful? Maybe not but it may provide the information needed to learn something that is useful.

I read all the info on the freestudy site, not just the PLC section. Their is an abundance of relative information on each subject.

The PLC section starts on Architecture, hence unitary etc, but I believe they do this to give students an understand what they look like and to see what changes the industry has made.

I still think its perspective, you arent a student possibly without industrial background so this kind of information is meaningless to you.

It may be the kind of question though that piques a students interest and provides us with an PLucas.

BEAUTIFUL, Terry!!!

And your lesson was free. What do you suppose I paid to have it explained in a much more round-about way?

One thing I really grew tired of in school was being shown "POINT A" and "POINT B," and not being shown the connection. In fact, on a few occasions where I KNEW there was a connection, I was discouraged from taking advantage of it. Here's an example that still frustrates me:

In one of my programming (C++) classes, we had to write a program that prompted the user with a menu. Having done this a number of times in the past, I anticipated an invalid entry (although it wasn't in the assignment) and wrote code to deal with it. Sure enough, the TA tested our programs with an invalid selection. He down-graded me (one or two measly points) because my program repeated the menu. Not that it was really wrong, he admits. But, he grades our programs with a script. And his script hadn't anticipated this, and it sent the script into a loop. The printout blew itself up to 30 pages. Because the TA's code was short-sighted, I get penalized??? Somebody must've gotten an 'A' in Middle Management 101.

Let's not encourage creative thinking and problem solving in the engineering curriculum. Those aren't skills that matter, are they?

AK

I have a problem with the OP's (and other HNC student) type of question because it does very little to help students learn. Keep in mind, learning PLC is an vocational education, which is not the same as going to college and get your BS or BA.

I do agree with Terry on that a well rounded education is essential to career and life. Just not in a vocational class. Whoever give these type of questions out is just too lazy (or clueless) to be a good teacher in the subject. Yes, you can tell your teacher I said that too. Questions like these makes the PE Control (USA) looks good in comparsion.

Maybe it's just me but questions like these would have ended my interest in PLC had I encountered them in the beginning.

oh, was it Plato or Aristole that said "First seek to ask the right question"?

Here's an example from JK William:

The distinguished scholars of the British Royal Academy once were asked why it is that, when a live frog is immersed in a container filled to the brim with water, the water does not overflow. A lengthy and vigorous discussion resulted. Rival theories explaining this phenomenon were elaborated and analyzed. At long last, however, one member of the Academy filled a beaker with water, lowered a frog into it, and the problem which had so perplexed the scholars was solved. The water did overflow! The asking of a flawed question had spawned countless flawed theories!

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I am sure Paul and some others may want to get in on this.

I have a problem with the OP's (and other HNC student) type of question because it does very little to help students learn. Keep in mind, learning PLC is an vocational education, which is not the same as going to college and get your BS or BA.

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First off the HNC program is national so the curriculum is defined, the instructors probably have a guide to follow.

The HNC process can lead to a BS or BA degree, it is not just vocational training but that depends on the student.

They ask here about plcs because this is a plc site but that doesnt mean their main line of study is plc, its a module that could be part of several courses.

It was asked if other countries had certification like this, I dont know. I know the European's follow a free education system that is different from the US. Germany (and other countries) provide more vocational and technical training at the US High School level.

I totally dislike the US educational system because it doesnt offer young people training in vocational fields, or prepare them for vocational training. They graduate High School, many with the equivalent of an 8th grade education, with no training. One day I expect them to offer a Career class that teaches them to say "Would you like fries with that?"

Dislike the questions if you want but take time to look at the process. It is attempting to teach students, at an early age, skills that may be applied in an industrial world. As I stated before the process is successful for some.

Personally I applaud the European and UK on their educational process.

The land of opportunity. How fast can you run? Can you pass, throw or carry a ball? Can you sing?

You are smart but have no money? Can you say "Would you like fries with that"

The educated telling the uneducated a question is stupid or they are stupid. The only stupid question in the world is the one not asked.