Siemens Simatic/s7 for Dummies? 3

[thenkel]

I'm currently involved in a materials handling project using an s7-300 controller. I have done similar work in the past with AB and Modicon controllers.

Having started the project, I find myself questioning the use of FB's or FC's for certain parts. Then I question whether i'm headed in the right direction at all...

I guess my question would be:

1. Anyone have a quick and dirty howto on the differences between OB, FB, FC's? The manual isn't real clear on usage cases.

2. Would it be possible for anyone to email a working program (i'm using step 5.2) that I may look at and see how it all works together?

I know I may be asking a lot here, but hopefully I can repay the favor when someone else asks this question again.

Thank you.

Todd

 

[Macbeth]

Quick rundown

Consider Organization Blocks (OB's) the same as Modicon’s Segments or AB’s Program files, OB's execute on events, such as Errors (OB122), Interrupts (OB40), Timed (OB20), or good old cyclic cycle (OB1). An OB would contain FB” and FC.

FC are sections of code you create that don’t require stored memory for the next program scan an example would be an ADD block two registers are added together to produce a result that is then used.

FB work like FC But have assigned memory to them a DB, they then would remember the data from scan to scan. An exanple would be a PID loop.

 

[thenkel]

First, thank you for the quick response.....

Let me see if I have this straight,

The OB's contain the logic to call the FB and FC's.

FC's would be used for basic device control, say if switch is ON turn ouput ON

FB's on the other hand, would be used to determine if a liquid level is greater or less than the previous scan.

I must say this experience has proved to be quite humbling. I consider myself better than average as a programmer, but this has thrown me for a loop. Overthinking things perhaps?

I have been slogging my way through to the best of my knowledge, however, I am at a point in the software where I have to route a pallet based on a number. If the number is greater than the previous number it goes one way, if less than it goes the other way. Seems simple enough. I just can't figure the way to store/retrieve/use this data.

 

[JWSC]

Todd,

Talk to your distributor. There is a CD with movie files that describe all of this. It is call Step 7- Step by Step.
Siemens give these away.

 

[thenkel]

Thank you, i'll check that out.

 

[PLucas]

If you will be working a lot with Step 7, then it might be worth purchasing the books by Hans Berger (Automating with Step 7 in LAD and FBD or Automating with Step 7 in STL)

Paul

There are 10 types of people in this world.....
Those that understand binary and those that don't!