Ladder Logic or Function Block (was SOFT: O/S Churn and Open Source)

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Thread Starter

Brian E Boothe

I'd like to Inquire on what everyone likes to use Ladder logic Or Function Block in there Programming...
Me myself Love Function Block its much easier to follow and Implement


----- Original Message -----
> From: Jake Brodsky
> To: [email protected]
> Subject: Re: SOFT: O/S Churn and Open Source
>
> > Whereas, my old copy of 16 bit MS-Money has run quite happily
> > throughout several Windows upgrades.
> >
> > Sample size one, of course, but like I say, Microsoft is not all bad,
> > and Open Source is not all good.
>
> Congratulations. You found something Microsoft did well. Now, let's look at the REST of the story ....<clip>
 
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Robert Ackerman

I'd say it's probably just a matter of what you're used to. Everybody (okay, a broad brush here but it serves the point) who uses ladder logic (i.e. Allen Bradley) will jump on the ladder logic side. Everybody who uses function blocks (i.e. Siemens) will jump on the function block side.

I've used both (although I have more experience with function blocks) and really haven't seen a real difference, only a conceptual one. Subjectively I like function blocks more, but this is probably just a function of my experience level.

Rob Ackerman
automationX Canada
www.mnrcan.com

> I'd like to Inquire on what everyone likes to use Ladder logic Or Function Block in there Programming...
> Me myself Love Function Block its much easier to follow and Implement
>
 
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It entirely depends on what I am doing. Analog is SOMETIMES easier with FB, but LD is much simpler and faster to code for logic.
 
I find that when I design a machine, I have to use LD more often than not because it's the only thing the maintenance personel understand and can work on.
 
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Rajesh kenge

I do accept with most of u that it's a question of experience and with what one is used to.

For last 5 years I have been using ladder as my main tool for programming. I was able to program almost all kind of logics.

Ladder is a better option as it has all the electrical conventions in contact's coil's etc. So is preferred by most of the customers. Also if programmed using ladder the program are more debuggable. My preference is for ladder.

Rajesh kenge
 
> I find that when I design a machine, I have to use LD more often than not because it's the only thing the maintenance personel understand and can work on.<

I totally agree with the previous post. Ladder is about as close that you can come to an electrical diag. The best instruction course I ever took was not a plc course but a machine tool circuitry course. After that ladder logic made more sense to me. by the way I am "maintenance personel".
 
I agree that we all like best that what we are most familiar with.
However, to be the most productive and efficient a combination of the two is used. This is called SFC or Sequencial Function Control. It uses flow blocks that have ladder in them. If you get the opportunity try it, it is VERY efficient (fewer rungs of logic) and fast developing and debugging.
 
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Joe Jansen/ENGR/HQ/KEMET/US

Since most of my work is done on a SLC 500 platform, I do not have the option. However all of our program flow diagrams are done using a
simplified form of grafcet. Repeating someone else's opinion, I think that the ideal would be a grafcet diagram where each transition and function
could be 'zoomed into' and ladder logic, IL, C, or whatever language of choice could be entered to define the operation of that point.

If I had my choice, I would probably prefer FB, as I understand it is similar to the above(?).

--Joe Jansen
 
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Robert Ackerman

Again, experience aside, I personally don't see too much of a difference between ladder logic and FB logic. To me, a coil and a digital point are pretty much the same thing. A maintenance/electrical personnel might see this differently of course :)

I've also found that debugging is not so much a function of what style of code you are using as it is which system you are using it on. Some systems have very good debugging tools, some don't.

Rob Ackerman
V.P. Engineering Development
automationX
www.mnrcan.com
 
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Michael Griffin

An "FB" is a "Function Block", while an "FBD" is a "Function Block Diagram". These are two completely different things.

Function Block Diagram is like linking together AND and OR gates in an electronic schematic. The Function Block Diagram "networks" I have seen are approximately equivalent to a rung of ladder. I have used programming software that supports both ladder and FBD, and it allows you to toggle between programming modes. I have only experimented with it, but a rung of FBD seems to normally translate to ladder, but ladder will often not translate into FBD.
FBD seems to appeal to people in some types of process industry, or to people who are more comfortable wiring together chips than they are with programming software. You used to be able to buy hardware "logic modules" which you would wire together to perform various control functions, in a manner analogous to wiring together relays. Just as relay control became
ladder logic programming, these hardware "logic modules" have a software equivalent in FBD.
I am sure that there are things you can do in FBD more easily than you can in ladder (especially continuous control equations), but I think the above gives you the gist of it.

In both IEC and Siemens terminology, an FB is a "Function Block", which is something entirely different from "Function Block Diagram". Whereas FBD is a programming language, FB is simply a type of subroutine. Within the FB, you
can write your program in ladder, instruction list, or even function block diagram, if you so wish, and then call the FB from elsewhere in your program. There is really nothing special about an FB subroutine that is worth mentioning here.

It is unfortunate that FBD and FB have similar names, as this no doubt produces a fair bit of confusion among people who are not familiar with them. However to summarise, there is no relationship between FBD and FB, they are
two completely different things.

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Michael Griffin
London, Ont. Canada
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