How many PLCs should a PLC programer be familiar with?

Dear pals,

I am trying to pursue a career as a PLC programmer or a control technician. I know there are lots of PLCs out there on the market. Most of the time, as a technician, you are supposed to be familiar with all the technical stuff and know how to play with them. But for me, it seems that every PLC is different from others. Siemens has a different way of thinking; Allen-bradley use its own programming structure; Mitsubishi uses a different and confusing way of addressing arrangement... Every one claims that they are ¡°IEC 1131 compatible¡±. But, do you see any kind of compatibility?

My question are:

How many PLCs should a PLC programmer be familiar with?
How can you manage?

Any input(DC or AC) is welcomed.

Stupid answer. You should know all the plcs you are required to know. If you have only one manufacturer in your plant knowing more realy dosn't help. I am an integrator I have to know too many. It realy comes down to what you are working with.

Thats just my two cents

The question for you should be "If I pursue a career as a programmer or technician, then what brands should I learn to give me the best shot at employment". Learning too many brands right away will over load you. Try Siemens and Allen Bradley to start. I thought Allen Bradley was easiest to learn. Siemens has a good market share up there. With those two on your resume' you will get many interviews.

Looooongshot...

Godfrey has done well to suggest Siemens and Allen-Bradley. I agree, but for different reasons.

First...
I think new programmers need to learn at least two PLC's (three would probably be better).

AND, those PLC's should be as far apart from each other in their programming styles as possible.

The idea is, to learn that...
If you can program those two or three PLC's, then you should be able to program any PLC.

I am not suggesting that being an A-B (or Siemans) expert means you can be an expert in (or even program) other PLC's.

The lesson you have to learn is that, fundamentally (no matter how much you might LOVE(TI)/HATE(AB) ( <--bias-based sub-liminal message!) one brand over another), they are all the same in one unifying respect - LOGIC.

To get to the point where you can program any PLC, you first have to get to the point where you can understand and develop LOGIC.

Once you know LOGIC, it then becomes a relatively simple matter of learning the secret codes, winks and hand-shakes for any given PLC.

Once you think in terms of logical concepts, you simply look for the secret code that delivers on the concept - in any PLC!

Now, a history lesson (or, maybe it should be called a Brief Auto-Biography)...

My very first PLC experiences were with Allen-Bradley.

WOW! PLC's ARE COOL!!!

I worked with Allen-Bradley for about 3-years. Then I went to college for Electrical Engineering. When I got out of school, I went to work for a prominent (at the time) specialized computer manufacturer.

All of my programming experience was based on direct interaction (or at least, relatively more so than with PLC's) with the CPU (Assembly, FORTRAN, C... and a few of the other weird ones like COBOL).

The point is, I was dealing with the processor. There were no high-level interface layers - such as those that are typically presented by all PLC's. (Yes, there are now some PLC's that let you into that level, but that is so now, it wasn't so then.)

In dealing with the processor, I learned to look at things from the processors' point of view. From the processor-point-of-view, things are a lot different! (more later)

So, economic bust came in, Hi-Tech went out...

I went back to work on my Electricians License in a lo-tech manufacturing plant. They didn't have a slot for a Process Engineer, but they did have a job for an Electrician/PLC Programmer. So, I took it.

They had some Allen-Bradley PLC's that I thought I would slip right into. I did... sorta... My previous experience was hindering me a bit. I didn't know why.

Then they brought in a few machines that had the GE Series-One. I was expected to pick up on them. I read the books a couple of times, played games with the spare CPU we ordered and, frankly, I was astounded!

The difference between the Allen-Bradley PLC and the GE PLC was like Day-vs.-Night! The GE was simply more intuitive! I had a ball with the GE and became less enthralled with the Allen-Bradley.

Time goes on, jobs change, and I find myself doing Process Controls at a place that has a Texas Instrument PLC (TI-505) running the big show. (It's fairly well understood by Human Resource-types that good PLC programmers can program any PLC - so I get, and take, the job).

It takes me 6-months to figure out the system (it's 4 stories tall and 2 city-blocks long). Meanwhile, I'm reading the manuals - 2 or 3 times.

I couldn't believe it... this TI stuff is even more intuitive than the GE stuff! Not just more intuitive, but even closer to the CPU-talk that I experienced a few years back.

Like Day-vs.-Night-vs.???

And therefore, my bias against AB.

Others might have gone through the same experience... maybe not.

The point is, learn PLC's that are as far removed, in style, from each other as possible.

So, I suggest...

Allen-Bradley and Siemens Simatic 505 (TI-505) or the Siemens S7-2xx series (a TI-Spawn) - not the S7-3xx, -4xx.

And possibly, the Honeywell System - it's not quite like either the AB or the Siemens.

For all of the potential Flame-Throwers out there... It's just my opinion... find a way to get over it.

Good Terry,You have done well..will be useful for all

Regards...SpRai

Longshot,

I agree with Terry. Pick a couple of brands that are as different as possible. I started out with Mitsubishi FX, then learned Allen-Bradley SLC, and most recently I have been using Siemens S7-300. Each time I learned a new system, I thought "Wow, this is different - I've really been missing out!" While the logic is basically the same, each plc manufacturer has its own little way of doing things.

Good Luck with the job hunt.

Terry,

Tangent - I've heard others say that they prefer TI505 stuff over S7-300/400. What are the differences between the two? I have never programmed a 505 - I've been using S7-300s. I like Step-7 for some of the same reasons that you state that you prefer the TI stuff. Just wondering what I'm missing out on.

Kevin Hammond

"What's a Modicon?"

Man, did I hear that one... My first programming experience was with a modicon, and ONLY with a modicon. When the company went to Mexico, my Modicon expertise and 50 cents wouldn't get a cup of coffee at McDonalds. All anybody wanted was AB!

Ironically, I landed a job in a plastics plant working with about 4 different types of pick+place robot, but little PLC. But that got my foot in the door, and I eventually landed where I am today, a programmer / electrician.

In short, I agree with Terry - learn more than one PLC, but for God's sake, make one of them an AB!

Ahem. I am now versed in Omrons, ABs, Modicon, and Mitsubishi, with more all the time. Currently puzzling out a B+R programmed in German, but that may be a little more versatility than I was looking for

Just my two bits.

TM

Look at local job listings. Most ads for PLC type people list the desired platform experience. Watch them for a while. You should be able to figure out what is most popular in you area. Try to concentrate on those.

Knowing AB (at least in North America) is like knowing Windows. Like it or hate, you have to know how to use it at most jobs.

Remember, it's all just ones and zeroes
and how they are manipulated.
Here lately though, I've been running a
little short on ones.
Any suggestions?

Just a few friendly thoughts.

I fully agree with Rick Densing who suggested that you watch the local job listings to see what’s going on in your area. After all, why learn something you can’t use? As he pointed out, Allen-Bradley is probably going to pop up more often than a lot of the other brands in most areas. But even beyond that, there’s another thing you have to keep in mind: AB is a brand – they manufacture several different platforms. Specifically: the PLC-5 family; the SLC-500 family; the MicroLogix family; the ControlLogix family; and others. While all of these AB platforms do the same type of job, they have some MAJOR differences which tend to keep life interesting for a newcomer (and for many old timers too). Most beginners assume that an AB is an AB is an AB. This is not so. Allow me to offer just one simple (true story) illustration.

Suppose, for the sake of argument, that you’re fully versed in SLC-5/04 programming. Let’s say that you know this particular AB model inside and out. You decide to answer a local add for an “Allen-Bradley PLC programmer” and show up for your initial interview. The interviewer’s first question is: “How would you go about processing 4-20mA analog input and analog output signals in a PLC-5/20”. Since all of your experience is based solely on the SLC platform, all of a sudden you’re in big trouble. (In the SLC platform, the analog signals pass directly through the input and output tables. In the PLC-5 platform, the analog signals must be moved in and out of the INTEGER files by using block transfer reads and block transfer writes to communicate with the analog I/O modules). In our hypothetical job interview, you’re now in the position of a truck driver who’s driven only automatic transmissions all of his life. Suddenly you’re being interviewed for a stick-shift job. That clutch pedal and shift lever are going to be significant problems.

The point that I’m trying to make is that you need to do your homework on not only what BRANDS are being used but also on the specific PLATFORMS within those brands. My personal suggestion is that you initially concentrate on learning one particular platform within one particular brand until you feel more or less comfortable with it. Then when you move on to something else, you’ll be able to compare the differences and the similarities between the previous system and the new one.

Now let me say this: none of what I have said (or any other responder has said or will say) should discourage you (or any other reader) from proceeding with your stated career objectives. This is all do-able. But it’s bound to be a whole lot easier in the long run if you approach it systematically from the very beginning. Which is why, I assume, you posted your initial question.

And as for your specific question: “How many PLC's do I need to know?” I doubt that anyone will argue with the idea that the more you know, the more you’ll be worth. Just try to make sure that you're learning the systems that will get you hired and keep you hired. Find out what's being used in your area and start learning and then keep learning.

Best of luck.

Kevin,

With respect to the differences between TI-505 (Simatic 505) and S7-300, -400...

I could point to this and that difference, here and there. Peter could point out many very specific differences that have a big impact on his programming. Peter has to deal with the interfacing between his products and all (or at least, almost all) of the PLC's out there.

Each difference on its own probably won't seem like such a big deal. You find a difference here and there, and you find a way to get over it - no big deal. Before you know it, the differences aren't that big at all... the individual differences, that is.

What I have a problem with is the shear volume of differences. You can only have that many differences for one reason... there is a major difference in the programming philosophy!

The best way I have found to illustrate the difference is the difference between the Hewlett-Packard (HP) Hand Calculator (very AB-like) and the Texas Instruments (TI) Hand Calculator.

The HP uses a method called RPN (Reverse Polish Notation, the RPN might actually stand for something else, but the Reverse Polish Notation phrase is attributed to HP Engineers.)

Wow, it's been a while since I used it. HP was something like...

"2 Enter, 3 ENTER, ADD" = RESULT

The TI used "English"...

"2 + 3 =" RESULT

The difference was in the programming philosophy. HP went closer to the processor but moved further from the normal language of the user.

TI opted to move closer to the native language of the user. TI uses (used) the same philosophy in their PLC's.

Tangent off a Tangent...
AB data files impose the same kind of restraints on users that "C++" imposes. "C" does not impose those restraints. "C" is certainly more dangerous in the hands of a rookie than "C++" is... but raw "C" is much more powerful! There is NOTHING that can be done in "C++" that can not be done in "C".

If you want to reference an integer, you simply do so by means of its location in memory. You don't have to go through any file-handling to gain access to the value.

Same thing with Analog I/O. Simply reference the memory location containing the value.

These values are kept in special locations - but, to the user, the special handling is essentially transparent!

AND... you do not have to shut-down the system to do any data-manipulation ("file-manipulations"). You can do it all on-line!

There are no "special files" other than what are really sub-routines; Analog Alarms, etc.

Back to the 505 vs. S7-300, -400....
The S7-200 series is a direct spawn from the TI-505 line. If you were to read up on the S7-200 series you would get a pretty damned close picture of the TI-505.

I have read the manuals for S7-300, -400 and have gone to "S7" classes where the subject was primarily S7-200, but also included some -300 & -400 stuff.

The differences were glaring! The -300 & -400 are from Siemens, after all.

Hi terry !

Thanks for your explenations regarding S7-300 400 and 200 , english is not my mother tongue besides I am a rather slow guy being taught therefore I would need more explenation.

As young as a begginer I must admire that I do not have any experience with S7200 (telling you the truth been engaged as a team member in a big S7300 S7400 project is my only experience) From the manuales ( That are not completely correct most of the time) I got that the S7 200 is widely used in projects with little amount of I/Os and communication, S7300 for medium scale and S7400 for real projects.but how is how ? and what realy a small project means?

My boss thinks that the experience will give me enough clue to selectamong the brands then among the models and at last among cpus. I wonder if you have experiences to shar regarding the matter.

Let us get a bit further than programming talks ! I am interested to know if you had an experience using S7200 ontroling a medium size project (i.e. pipe production mills,light rolling mills) or you just suggest them over S7400-300 for machine control purposeses ?

I am not sure about legal problems it might have for the professionals (Daddy always take care of these things) But I am wondering if the kind phil can make a separate post index for compeleted projects with some details (I/Os, Communication, CPUs and a little discription about the project) I think this will help not only the beginners but also the big guys in CPU and model selection.

OH GOD look ! How much did I write ! Let's call it a day

Thank you everybody
Thank you tery

RPN is a legitamate term. The system was developed by a Polish mathematician, I never knew his name. I still use my HP28S. It's about 15 years old now.

Terry -

Thanks for the reply. I have wondered about the S7-200s, but most of my projects have loads of I/O, so I went down the S7-300 path.

By the way, I have had an HP calculator for 15 years. And I must say, when you get your brain thinking in RPN calculator mode, it's very hard to shift back into "normal" calculator mode. Maybe that's why I like Step 7.

Kevin Hammond