Just a general question about PLCs. As an engineering student I had experienced programming microcontrollers. I would assume that it is quite similar with PLCs, except that it is usually done in ladder logic.

As in any programming, practice will often lead to a more understanding of the certain microcontroller, as to how it will facilitate in solving our problem. In the market, there are so many PLC products available. However, how would everyone actually be able to learn so many types of PLCs? Would anyone out there, as an experienced person, think that knowing a lot of PLCs is important? If any PLCs are programmed the same way, why would there be so many problems waiting for answers?

Thank you.

 

Hello,

In my experience all plc's in principle operate in the same way. For instance we read the input mask, execute the program line by line according to the program structure and then we write the output mask.

Programming plc's facilitate the use of higher level languages (the programming software)which may use different terms and functions to come up with the same result from one plc to another. In the same way there are different methods in C++ or Pascal to program the same function in a microprocessor.

In essence what I am trying to say is that as long as the principle of operation of a PLC is understood (eg to have indepth knowlege of a particular brand like Siemens S7)then to swap from one brand to another, after the initial teething problems, is a transition and not a whole new learning process.

 

I feel that the major issue is not the lack of standardization across vendors (which is a problem) rather that there are so many different types of people programming PLCs.

Many of the questions regarding PLC programming result from lack of experience. Either programming inexperience (ie. electrician) or automation inexperience (ie. professional programmer).

IMHO, I think that the ideal PLC programmer should have a good basis in good programming style but should be well versed in automation concepts. A good PLC programmer should always keep in mind that the source code he/she develops is used every day as a trouble-shooting tool.

Good Luck,

(8{)} ( .)

[email protected]

 

Steve---

I've worked on projects that used various microcontrollers, and I've worked with most of the major brands of Relay Ladder Logic (RLL) programmable controllers. I'll opine that it is far easier to switch among RLL products than microcontroller products. The differences between Intel and Motorola microcontrollers, for example, are far greater than the differences between, say, Allen-Bradley and GEFanuc programmable controllers.

Most of my OEMs and integrators are prepared to handle any PLC brand their customer specifies, within reason. While I can always make a case for my own products, my clients seem to handle brand shifts reasonably well. I think this is because they are good at their own specialties.

While knowing a lot of programmable controllers is a valid resume builder for a consultant, knowing how to solve applications is far more important in general. You can do a transfer line, a palletizer, or a roller coaster with the same programmable controller, but there are very few people that can do even one of those with ANY programmable controller. Those are the people that have those jobs!

I believe the real talent in automation is in the application, not in the tools. As someone said, using the same word processor as Stephen King does not make you a successful novelist.

Hope this helps!

Larry Lawver
Rexel / Central Florida

 

Hi Steven:

I have a little pratice on programming a few PLC types and I have teach PLC programming too. The first thing I ever say to people is: "I will not teach you how to program THIS PLC, I will teach you HOW TO PROGRAM PLC's"

I think the most important tip on PLC programming is not to know how to program one or more PLC models. In my opinion, the most important thing is to have clear ideas about how you can do things (emergency behaviour, signals monitoring, securities, data management, program structures, alarms, etc) No matter what the PLC model is, it is only a tool. A good PLC programmer will always find the way to solve the problem (the magic word is Improvisation).

Important: A good PLC programmer should know too a little about the neighborhood.
>From the novel "Ender's Game":
"If you want to win your enemy, you must know him before..." (or something like that)

(I mean: electronics, electricity, mechanics...)

Hope useful.

Aquilino

 

Knowing many different PLCs can be quite a challenge but is a very powerfull tool to have on your resume. As an OEM we try to stay with the same brand PLC, it makes life alot easier when all you have to know is one type of PLC. However there are multiple cases were the customer specs in a PLC that we have never used or have had little experence with. The the choice then becomes either get learn the PLC or loose the sale, so the more plc's you learn the better. There is not alot of difference in PLC programing from one to another. Think about this, most are done in ladder or fuction block, all (that I know of) use windows to program, its a matter of learning the addressing and certain "tricks" of each PLC. The hard part is trying to decide what the PLC is capible of before you start a job, question like does it have enough memory? Will it crap out on you in the middle of the night? Will the PID functions work correctly? So if you are good at one brand of PLC its not so hard to switch to another.

 

All PLC ladder logic regardless of manufacturer is pretty much the same, much like the various flavors of C++ are pretty much the same. The learning curve for learning a new PLC is about a week or less if you're comfortable with ladder logic in general. Some of the newer PLCs like AB ControlLogix and SoftLogix use ladder logic but are more "object oriented" in the addressing structure. The biggest headache of most PLC projects is getting all the various hardware components to communicate and play nice together.

 

Most PLCs are pretty much the same, the biggest differences are in the program developmental software and they usually don't vary all that much. maybe one company calls an instruction by a different name, or they may offer fewer or more advanced instructions to make programming quicker. Once you get the hang of one (AB is probably the best to learn if you only learn one) its not very difficult to pick-up on a new one. It took me very little time to make the switch from AB RSLogix to Modicon Concept, when I changed jobs 2 years ago. If you are a field Programmer for an Automation company you are going to end up learning a lot of different software since different clients are going to use different systems. But other than that, you will most likely end up with whatever your company has decided on. Due to the cost of Software most companies will pick one "Line" of PLC for 99% of there applications.
What type of answers are you having trouble finding? I have never had any real problems with tech support from AB or SquareD. I don't personally care much for GE software but there again I would think their tech support would be fairly decent.
In my experiance changing versions of Autocad is worst than changing PLC brands.

 

Simple - try to abstract the process so that it doent matter what the controlling device is. Apply the concepts, then the details based on the hardware selected. The reason for IEC61131 is for this reason - multiple hardware platforms similar software and details.

Cheers from: Jeremy Pollard, CET The Crazy Canuckian!
Integration and Automation Training, Consulting, and Software

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To everyone whom had given informative reasons to me, I have one final question.

Since PLC programming requires experience, how can a student learn more about PLCs, given that we do not have the tools to experiment with. I had studied about motor control, and other small applications. However, I do not know anything about emergency behaviour, signals monitoring, securities, data management, program structures, alarms, etc as pointed by Aquilino.

How far more is there to learn about PLCs? What about networking? Data gathering? Communication between ports or PLCs?

Thank you.

 

Hi Steven,

I am an undergraduate engg student myself.I also faced the same problem of learning to program a diferent PLCs particularly after coming from a Microcontroller background.

I would suggest that you take the online tutorials on
www.plcs.net

When you have got a basic understanding of the underlying principles, download "RSLOGIX" software for simulation from the Allen Bradley site or Rockwell Automation site.It wil be very helpful in simulating real-time conditions and also you can test your programming skills.

I found these to be very informative and I hope you will too.


Best of Luck
Gaurav
[email protected]

 

Steven---

PLCs are tools. In the hands of trained users, tools work to accomplish the goal. Goals are things you actually get paid for, whether they are automobiles assembled, loaves of bread shipped, or guests safely moved through a theme park ride.

I am the guru for my brand of PLCs in my market, but I was never formally trained on them. In fact, my employer in 1982 paid to have me trained on a different brand, and I have worked on my current brand ever since, through three careers. This was not planned, it just happened. Even worse, my career changes were attempts to get away from the entire business, but I just kept stumbling into better jobs in the same business.

My most successful colleague, meanwhile, is a microbiologist who has never worked a day in his field. Next is a guy who never finished college. Next is a guy who started in our warehouse with no training at all, ... just like the very successful person that hired all of us!

What all of us have done to be successful is: Solve problems.

You need a framework in which to do that. You might find that by offering to intern at systems integrators in your area. They'll expect you to know little about PLCs and motors, but a lot about PCs and networking...

Automation is a business about solving problems. The solution might require mechanical, electronic, electrical, chemical, computer, or political actions. If PLCs are part of the solution, you'll learn that once you're in the business of solving problems. At that point, you'll get the on-the-job training that has been the real history of PLCs.

Hope this helps!

Larry Lawver
Rexel / Central Florida