SLC 5/02,03, 04, 05 - VS Siemens S-?? Similar Logic / workings???????

[soop7667]

Hello!

My Company utilizes the SLC 5/00 PLC's extensively and exclusively in our Manufacturing plants. I've had a couple training courses with RS Logix 500 and Linx, and after setting up a spare rack I've taught myself extensively. Experience has also taught me a lot.

I've never seen a Siemens PLC and I was wondering how similar they are to the Allen Bradley SLC's. Obviously they'll need different programming / communication software - and the corresponding hardware, but as far as the logic is structured - I have no clues.

I've read some post and learned of some differences in the data file structures and timers but does it look like a ladder? Does it scan line by line? I'm thinking for some reason it may scan all the lines at the same time...is that the case?

I'm considering a job change and the company is looking for:
"Industrial Electrical / Sensor / Siemens / PLC troubleshooting - Programming experience a plus"
I'm currently in a supervisory position but my main focus of duties is Logic changes, electrical and PLC troubleshooting, And I have done some pretty good things by adding sensors on some of our machines. They're not seeking someone for a supervisory / managerial role however, seeing as though I can make wire and PLC's do what I want better than the 20 people I supervise...I think I might like the change.

Also since they're looking for someone in this particular field I would assume that they have some issues with their PLC's. Salary would probably be the determining factor in this decission...what's the going pay for someone who posesses these skills in the Southeast US?

 

[Tom Jenkins]

The answer varies with which Siemens model. The most common is the S7 series.

Siemens has a number of languages, including ladder logic. Their ladder for discrete logic is fundamentally similar to A-B. Any analog data or math or advanced operations is totally different, and uses a lot of function blocks and such.

I strongly recommend getting Siemens training if you start to work with them - their software is definitely NOT intuitive.

 

[PLucas]

soop7667,

I have posted this link before, but you might of missed it.

click here for Siemens S7 training manuals. You might find them useful.

Paul

 

[JesperMP]

I assume that your potential new employer means S7-300/S7-400. The S7-200 is the smaller type PLC and is quite a bit different from the other two.

But here goes:
RSLogix 500 ladder and STEP7 LAD is very similar.
Despite what Tom says, math is also similar.

There are MANY differences between the two platforms, but "regular" ladder code can be ported with relatively little effort.

Just to prepare you, I have compiled the most important differences:

1. SLC500 code is only ladder, whereas S7 code can be STL (statement list), FBD (function blocks), LAD (ladder), SCL (pascal like), Graph, Higraph ....
STL is what is really running "inside" the S7. All the others are just an additional layer on top of STL.
Stay with LAD, and STAY THERE. Only when you are comfortably safe with LAD should you start with any of the others. In the end, knowledge of STL will be usefull to you, but not in the beginning. Ignore the smartasses who claim that they program in STL only.

2. SLC500 data is segmented into files of different type (i.e. integers, floating point numbers, timers, etc.).
S7 data is not separated in that way. Data must be declared variable for variable. In a file there can be any type of data next to each other.
To complicate it further, there are two separate areas of data: Merkers and DBs.
Each CPU has a predefined amount of Merker memory.
The Merker memory cannot be expanded. If you remove the battery and shut down the CPU, the contents of the Merkers will set to zero (!).
You can setup as many DBs as the CPU memory will allow (actually there is a limit on the number of DBs). If you remove the battery and shut down the CPU, the contents of the DBs will set to the socalled "initial values" that you can define yourself.
A beginner will start to use Merker memory only. But for separating the data into blocks and for using the "initial values" consider to use DBs.

3. S7 timers are quite different from SLC timers.
There are basically two types: S5 timers and IEC timers. They both have merit.
S5 timers use a special BCD like format for the setpoint "S5TIME". And they time down from the setpoint to zero. An S5 timer can be placed any where in a LAD network, it will simply take the logical state at that position and use that as the condition for its execution. There is a predefined number of S5 timers in each CPU. So the dont use up any DB memory.
IEC timers uses a "TIME" format for bot setpoint and actual value. This "TIME" is really just the time in milliseconds. But it will be displayed as "2H20M15S100MS" for 2 hours 20 minutes 15 seconds and 100 milliseconds for example. They time up from zero to the setpoint.
An IEC timer will require its own LAD network as it is really a call to a built in subroutine in the CPU. Each IEC timer require that you assign a DB to it (or use "multiple instances", come back here if you need to know how).

4. Math and comparisons in S7 is split into math for Integers, Double Integers and Reals. In SLC500, conversion between integers and floating points is done automatically. Not so in S7. As it is not so easy to combine different type math in LAD, you must define early on which to use (math is actually easier in STL, but even so stay with LAD as long as possible).

come back for more help if you need it

 

[JesperMP]

Wait - there is more !

About data:

SLC500 counts data and i/o in words (i.e. N7:0 .. N7:1 .. N7:2 .. one word each).
S7 counts data and i/o in bytes. That means that an integer (= 1 word = 2 bytes) can have the address MW0 (Merker Word 0), actually contains the two bytes MB0 and MB1.
A double word like MD0 contains the four bytes MB0, MB1, MB2 and MB3.
This means that adresses can overlap !
For example M3.3, MB3, MW2, MD1 all overlap each other !

If you do NOT want adresses to overlap, you must laboriously check in the XREF that you havent used overlapping adresses.

Alternatively, use symbols for each adress (recommended anyway), and use DB memory in stead of Merker memory. Step7 will not allow DB addresses with symbols to overlap.

If you DO want adresses to overlap, it is easiest to do it with Merkers.

 

[soop7667]

WoW! I thought I was really smart tille I read the past two posts...now I'm not feeling so smart. Either way though...Considering my life's happennings in the past few days especially...I think I had better leave where I'm at and seek employment with this company I'm looking at. The hours and time which I'm currently required to work here has got my home life in a real mess....for REAL. I wish this forum were about relationships...unfortunately this is not the case or I could allow all of my life problems to spill out onto your PC screens. My only hope is that I'll be able to do the job in which they want durin hours which work to provide more time for my family and less stress at home. If your reading this do me a favor...pray for me.

I'm not sure I understand much of what you spoke of there Jesper...I got the just of it...but that's sounding pretty far from RSLogix...I'm by no means an expert programmer - being self taught by experimentation and experience has enabled me to modify some logic here and there and I can come up with some raw logic to run something if I need...but I think This other company is really looking for someone with talents like I have. They're making Pavers...I make block...not to much difference between the machines or processes involved...the thing that I like is that they're specifically looking for someone with these skills which I posess. I'm not sure yet what I will do...I suppose I should set up an interview and see exactly what I may get myself into.

I will continue to check here for posts, and I'll upsate as well. Thank you all very much for shedding some light on the workings of Siemens Stuff...I think I'm going to need a little toying around with it to see what I can do.

 

[JesperMP]

soop7667,
dont be intimidated by S7. It is easy to be, but its a mind thing.
The trouble with S7 is the documentation that really doesnt help a beginner. I know because I have been there.
The trick is to go boldly forward, and when the stumbling blocks appear, ask someone who knows the answer to the problem (maybe someone on PLCs.net) and then continue as before. The points I wrote to you were some of the stumbling blocks that a person that needs to convert from SLC500 to S7 will meet.

SLC500 ladder and S7 LAD is really very similar. My standard PLCs are SLC500 and S7. I write my code so that it can be ported with relative ease between the two.

 

[PLucas]

The trouble with S7 is the documentation that really doesnt help a beginner.

Nor a 'more experienced' user, especially when you come across a function you want to use for the first time. For example FC51.

Soop7667,

As Jesper said, go boldly forward, then post here anything that you need help with. There are a good few of us here with S7 experience, at least one of us will be able to answer your questions (I hope).

Paul

 

[BobB]

You either love or hate Siemens. I HATE 'EM. Sorry Paul but they are the least intuitive of all the PLCs I have programmed.

Place a send at the beginning of the program and a receive at the end or it will not work. Or is it the other way around. Cannot remember, thanfully.

 

[JesperMP]

There are a few posters here that cannot ignore a thread with Siemens in it. They just have to jump in and state something like "I hate Siemens". What does that do for advancing the subject I wonder ...

I neither hate nor love Siemens. Same with AB. They are both tools in my huge box of instruments that I have to master (well, to a certain degree that is) for making a project.
I have stated in many threads that Siemens indeed have a problem with its documentation. Combined with the pequliar quirks that Siemens have, it is indeed not easy to get into. But if you use it regularly for a living, the initial difficulty will fade.

I have some collegues that have just converted a huge PLC5 program to S7. They were relative newcomers to S7 and they did indeed have a tough going in the start. But after they are finished, they are actually satisfied and are NOT talking about going back.

As I said, a helpful person that can jump in and answer your questions will do more than anything else to speed up your learning of S7. As you new company (*) allready use S7, there will be someone there who will help you I am sure. If not, you know where else you can ask.

*: Good luck with getting that job !

 

[BobB]

Sorry JesperMP. Perhaps I am being unkind but I have been caught with "undocumented" features such as the processor could not recognise an expansion rack etc and a decidedly dodgy support system from Siemens in Ozz. They decided to spend some days proving that the PLC would work. It did not!!! By the way, I had to go to the MD (a friend) to get any help at all as they were all in a "training session". I offered to help the training session by giving them something to train on but they declined. I do not think it would have impressed the customers in training. Guess it makes you a bit bitter.

I might add that a sales clerk helped by giving me a different processor and that solved the problem. Says a lot for the techos.

Cost me 1 1/2 weeks of farting around, lots of accomodation costs (out of town) , 3 plane trips trying to get the thing resolved and several threats of liquidated damages. Would have sent me broke in a big way.

Plus i got caught with their first attempt at Windows based software. What a bomb.

Yes, the documantation is terrible.

Regards

 

[JesperMP]

BobB,
I know from other threads that you are not unkind
I must say that your experiences are awful, I can understand your point of view.