Simatic

Hello Can any one tell me in detail the merits and demerits of using Block diagrams over ladder logic. Which when is best suited for automation environment??????/

Simatic STEP7 program representation in LAD or FBD?
It is a matter of personal taste. Both are applicable for representing industrial automation programs.

My personal taste is to prefer LAD over FBD. LAD is slightly easier to overlook in a hurry. I think the reason is that LAD is 100% graphical, whereas you have to interpret the ">=" (for OR) and "&" (for AND) when using FBD so it is not exactly as graphical as LAD.

In most cases (but not all) a LAD program can be viewed as FBD and vice-versa.

KUMARAN said:

Hello Can any one tell me in detail the merits and demerits of using Block diagrams over ladder logic. Which when is best suited for automation environment??????/

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Look's like a homework question to me!

I will just add one thing to JesperMP's comments:

The maximum number of elements ( -| |- or -|/|- ) allowed in ladder is 12.

When you use an AND gate in FBD you can have a lot more than 12.

I don't know the exact number but I do know that it is more than is allowed in ladder.

This applies to Step 7, other manufacturers may vary

Paul

The number of elements allowed in a ladder rung is not limited to 12 in most other platforms in case you were wondering. In most cases you are limited only by the amount of processor memory. You wouldn't want to put 300 elements on a rung because it would get rather confusing, but there are times when more than 12 elements in a rung is much nicer than making more variables to keep track of portions of logic. Most of the time you won't find a need to go more than 12...but sometimes its nice.

On to the original question...well most block diagram logic developed these days has the capability to run C/C++, sometimes VB, sometimes executables....it all depends on the software used, and almost all of them give you the option of viewing or writting in ladder format.

You pretty much never see any of these added features in a package that dosn't offer the block FBD formats.

A real big advantage to LAD is that your more likely to have a machine electrican understand the logic. Lots more people read ladder diagrams the logic flow charts.