Some basic Step 7 questions

flowdam

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We have no Siemens in our plant and very little within the company, but we are looking at a German integrator who will be using this platform. We asked if he would be programming in ladder and his reply was that yes he would be programming in ladder logic with AWL and SCL. By the limited research I have done, it does not look like either of these are true ladder programming. I know the SCL is structured text and it appears the AWL is some kind of flow diagram. My questions are as follows:

  1. Exactly what format is the AWL?
  2. Is it possible to convert the above mentioned formats to Ladder? (I would think not on the SCL)
  3. Can the Step7 send motion commands like ControlLogix?
  4. If so how reliable is a Step7 system with motion on Profibus?
Thanks.
 
flowdam said:
1. Exactly what format is the AWL?
AWL = AnWeisungsListe. It's basically the PLC's processor language. It consists of mnemonics and operands. All higher programming languages are first converted into AWL before being executed. When it comes short cycle times, AWL is the way to go, readability is something else...

flowdam said:
flowdam said:
Is it possible to convert the above mentioned formats to Ladder? (I would think not on the SCL)
All ladder and SCL can be converted into AWL. The other way around is NOT that obvious: Certain steps need to be followed when writing AWL that is to be re-converted.

flowdam said:
flowdam said:
Can the Step7 send motion commands like ControlLogix?
Sorry, I'm not familiar with ControlLogix 'extended' commands.

flowdam said:
flowdam said:
If so how reliable is a Step7 system with motion on Profibus
Siemens-S7 and Profibus are two of a kind! Siemens can be called the founder of Profibus (right?).
 
AWL is the German for STL, SCL as you suspect is Structured Text. If you want him to program in ladder, tell him you want him to program in KOP. You may find that he doesn't want to or says he can't. If he says he can't, he's not necessarily being difficult, there are a lot of things in Step7 that can only be done in STL.

You'll find that most Germans (and I suspect most Step7 programmers in general) tend to program in STL, probably because it's the only way to access the full power of the machine.

A possible solution may be function block, known as FUP in German. Most Germans I know are happier with FUP than KOP (if for some reason they can't or don't want to use STL) and about 95% of FUP programming can be switched to display in KOP (ladder) with a mouse click. The other way round, if I remember correctly, everything you can program in KOP will display in FUP.

If you write STL/AWL programs in a special way, you can get a lot of it to show in ladder, but obviously not those functions which only work in STL. A possible solution may be to persuade your supplier to package those functions which must be written in STL in FBs or FCs and then call these blocks in a Ladder or Function Block (KOP or FUP) main program.

Can't help you with motion control, I suspect there may be some special hardware, known as Function Modules - FMxyz - (and possibly associated S/W) to do this though.

Step7 works perfectly with Profibus, which you might expect since Siemens were heavily involved in the development of Profibus.
 
In addition to the previous replies.

Absolutely try to specify LAD (aka KOP) to be used for the major part of the program. A LAD program will be very similar to a Ladder program in ControlLogix.
SCL will be exactly the same as Structured Text in a ControlLogix.

Motion with S7 will typically be done with the special "T" versions of the S7-300 CPUs. T=Technological functions. The CPUs are the 315T-2DP and 317T-2DP. These have onboard Profibus interfaces.
 
Thanks everyone,

Your explanations and ideas are most helpful. Just got back from the local Siemens dealer and they were very helpful as well.

Right now the vendor is planning on using the 317-2DP and sending messages to the Siemens servos via Profibus. Jesper would you say it would be worth the difference to have the vender use the 317T instead?
 
If you go with Sinamics, then the motion controller would be part of the Sinamics drive system and a 317T is not required. If using master drive servos, then the 317T would be used. Sinamics is bleeding edge.
 
I would recommend the 317T-2DP with the Sinamics drives. It is a totally integrated system similar to the AB kinetix system. You will need the technology add on package for S7 manager. Everything is managed through S7 manager. The 317T-2DP has two profibus channels, a 1.5 meg and a 12 meg. The Sinamics drives reside on the 12 meg network. The motion system is really easy to set up. Use the siemens motors with absolute encoders if possible. The positive and negative overtravel switches for the servos wire directly into a rack of ET200S I/O that sits on the same 12 meg profibus network that the Sinamics drive is on. Once everything is powered up, you start S7 and run the technology package. It uses a wizard that walks you through the setup. It's divided up in two sections: A drive section and an axis section. You have to do the drive section first to setup the velocity loop then just work your way through each motor. Next do the axis setup to do the position loop. You can go online with the drives at any time for adjustments. Once you are finished you will save that configuration and the system creates a DB for each motor and places them in Step 7. At that point you just use the the ladder motion instructions just like Controllogix. If you need camming or gearing, it's no problem. Conversely, if you just hang some profibus drives out there on the 1.5 meg network then coordination probably won't work. The sinamics also supports a system called safe standstill which is a redundant safety rated circuit.

Also the TP270 HMIs are great too.

Good luck.
 
flowdam said:
Jesper would you say it would be worth the difference to have the vender use the 317T instead?
I am glad that someone else could step in and provide the answer, but then I see that the two responses seem to contradict each other.

L D[AR2 said:
]If you go with Sinamics, then the motion controller would be part of the Sinamics drive system and a 317T is not required.
SD_Scott said:
I would recommend the 317T-2DP with the Sinamics drives.
 
To clarify, you can use the 317T with Sinamics, but you can also get a motion controller that forms part of the Sinamics system.

I have looked at the general requirements of a 12 axis electronic "gearbox" system recently. The current implementation is 317 with MasterDrives + simolink for the electronic gearing.

Alternatives considered were:
1. 317T for supervision and motion control with "dumb" sinamics drives.
2. A 317 for supervison with motion control in the sinamics system.
 
It really depends on what you (and the machine builder) are more comfortable with. The T processor integrates the motion control into the PLC program using function blocks. It's a good fit when there's a mix of PLC and motion control, and the builder/maintenance are more comfortable with PLC programming than motion control.
 
Once again, thank you all for your help.

Sinamics is bleeding edge.

We like the blood as long as someone else has absorbed a few blows first. It's not so new that they'll have to have 10 different firmware upgrades?

I would recommend the 317T-2DP with the Sinamics drives. It is a totally integrated system similar to the AB kinetix system.

This is the system I envision. If we're going to have to make the multi$$$ investment for software at least give me something similar to what we already know.

One last question, SD-Scott. You stated you would go with the Siemens motors, but vendor is stating that with the design of their system they had to go with a third-party vendor that could produce high torque in small package. Other than manual setup of the motors in Step 7, this should not pose a problem in utilizing the 317T with motion commands, correct?
 
flowdam said:
Once again, thank you all for your help.



We like the blood as long as someone else has absorbed a few blows first. It's not so new that they'll have to have 10 different firmware upgrades?



This is the system I envision. If we're going to have to make the multi$$$ investment for software at least give me something similar to what we already know.

One last question, SD-Scott. You stated you would go with the Siemens motors, but vendor is stating that with the design of their system they had to go with a third-party vendor that could produce high torque in small package. Other than manual setup of the motors in Step 7, this should not pose a problem in utilizing the 317T with motion commands, correct?


The Sinamics system uses motors with two different cables. One is for the power and brake like normal. The other cable is called "Drive cliq". It reports the position back to the Sinamics drive plus other data also. It looks kinda like a cat 5 cable. I really don't know of any other motor brand that would work. We also had an issue where a group wanted to use a different motor, and we basically conviced them otherwise. I would highly recommend staying with a totally matched system. I don't have a feel for what kind of motor you need, but I was impressed with the power of the siemens motor. Siemens has a motor sizer package called Micromaster sizer. It produces an Excel spreadsheet BOM. I attached an example.

 
Yes, the Siemens motors send position feedback to the drives using Ethernet. I'm sure you could get a resolver/encoder module for the sinamics drive to control a motor using more conventional feedback.
 

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