The use of PLC in industrial automation

What is the Advantage & disadvantage of the use of PLC in industrial automation ?

It seems to me that I have seen the answer to that in a book some somewhere.

beginner answer

noise immunity - advantage

disadvantage: it's overkill - relays work just fine ... and they're cheaper too

I'm telling the truth here

Advantage - $$$
Disadvantage - $$$

The purpose of a technical education is not to learn facts, it is to learn analytical thinking processes.

I assume that if the direct answer is in your text book you would have read it. Therefore, apply analytical thinking to the question. Imagine an industrial process operated manually - say a towel laundry. Think about how people work: strengths and weaknesses and costs. Imagine the same process controlled by hardwired relays and timers and such. Think about how these devices work: strengths and weaknesses and costs. Imagine the same process with a PLC in control. Think about how PLCS work: strengths and weaknesses and costs.

Now put the three together to see the advantages and disadvantages of each.

Why use PLCs when a DCS would look so much cooler?

"Why use PLCs when a DCS would look so much cooler?"

WHAT!
BLASPHEMY!

I'm reporting you to the moderator

"Why use PLCs when a DCS would look so much cooler?"

Aaron, don't make me come down there!

Strewth

Cor blimey, this is far toooo technical for me!

I just don't get all the excitement about PLC's and DCS's.

Mankind has been studying the secrets of nature for a long time in an effort to bring those secrets out into the open for all to see! The use of PLC's and DCS's is completely contrary to that notion. They promote the idea of hiding all of the things that we've gone through so much effort to expose!

I agree, those chunks of plastic, metal and other exotic materials, do, somehow, seem to provide reasonable responses to reasonable conditions. BUT, Do you know why? I mean, Do you REALLY know why? Oh, sure you can throw around this theory and that theory in an effort to explain what is really happening... but my point is... you don't REALLY KNOW what is happening inside!

It's kinda like a thermos bottle... "It keeps COLD stuff COLD... It keeps HOT stuff HOT..." which raises the obvious question... "HOW THE HELL DO IT KNOW????"

And that raises the next obvious question... at any given time, "HOW DO YOU KNOW IT'S DOING THE RIGHT THING?" If you stick in some COLD stuff, hoping it will be COLD, later on, when you want it, you won't know if it's doing the right thing until it's time to see if it did the right thing!!! At which point, it might already be too late !!!

Is that insanity or what????

It's the "Schroedinger's Cat" thing... ANYTHING COULD BE HAPPENING IN THERE!

A PLC is pretty much like that thermos-bottle or the cat in the box... you simply don't REALLY KNOW what's happening on the inside!!!

Well, I don't like the idea of Magic and Smoke & Mirrors. I don't like the idea that someone has found these secrets and then hid them again. So, I went on a hunt to find all of the things that these PLC designers are trying to hide from our view.

I FOUND THEM !!! ....I FOUND THEM ALL !!!

I found individual items for each of the inner-parts of a PLC! These things are COOL!

The really neat thing about these things is that when you use them you can actually see them doing exactly what you told them to do! There is no guessing... no hoping that the right result will be produced!

YOU are in control of what they do !! YOU KNOW what they are doing, because YOU can see them doing it !!

If something goes wrong (it can happen!), then YOU can see where it went wrong AND then, YOU CAN FIX IT !!! Is that COOL, or what?

So, I'm currently involved in trying to get the budget passed for my next project. There does seem to be a lot of "zero's" in the numbers, but I'm pretty sure that when I show them what I found, they'll approve it! COOL !!

(That reminds me... I'll have to order an air conditioner for the cabinet... hmmm, and maybe a bigger cabinet.)

uh ... does anyone have a valium?

PLC and relays

PLC: u can connect I/O to it, can be analogue, digital and others. The program in the PLC that u need to program will do whatever u programmed with the outputs.

When u have a problem, something is not working, u can monitor your program and see what the problem is, an input that's not coming in for example.

PLC can these days control drives and peripheral stations with I/O. U can run a machine on a PLC concept; and when u have a problem or need to change somehting, u just program it on your desk, download it to the CPU from your desk and that's it. U didn't even moved from your desk.

No cables to care of when there needs to be a change in a sequence.


One thing that's less good: It's isn't cheap in the beginning, but...

If it can help optimize your finishing product and can reduce the down-times by this concept, u will win it back in no time.


Relays are good, but what about analogue control, a module for comparision, a module for pid, a module for timer, a module for that, etc... Will also cost, and u will need a stock of reserve modules !!!


Think about it !!


A life with PLC is a wonderfull life (not always )

Tom Jenkins said:

Aaron, don't make me come down there!

Click to expand...

BRING IT ON!

A DCS has sooooo many more blinking lights!

At least a couple of times, in the last couple of years, we Yanks have been accused, by a Brit or two, of not having a sense of irony.

I have been complimented by those Brits as having a good sense of irony.

Now... I too begin to feel like they do... you Yanks ain't got no sense of irony!

Doesn't ANYONE have a sense for what I said in this thread?

Not that I need feed-back on it... but, "You're out'a yer mind" would at least keep the thread going!