Function Block Diagrams

[geniusintraining]

For all you FB people..draw this..
D

A(
O Q A
ON F C
)
AN F B
= F C

My 1st pick would be STL, faster to write, but harder to trouble shoot

 

[Mehdi]

dont get me wrong..but from a simplistic point of view..ladder wins hands down..For all you FB people..draw this..

A B

-----------| |------|/|----------(c)

| |

|-|c|--|

Seems easy enough but would like to see a FB diagram that was as straight forward as that..

D

Did you mean this one?

 

[Sheldn]

Relay Ladder Logic (RLL) works good for digital and sequential systems and devices such as a motor starter and associated logic or a sequencer. Function Block (FB) is great for process type stuff such as a flow totalizer or PID block. I have had difficulty trying to implement state type logic and one shots in FB. The nice thing with newer products that support multiple languages running concurrently is you can select the specific language for the specific need.

The specifics of implementation for each manufacturer's product needs to be taken into account and may effect some users opinion. Order of execution in RLL is usually straight forward (except the old Modicons), understandable and dependable. Order of execution and propogation of data for FB can matter for time critical logic and the user needs to know how the specific hardware/software combination they are using works.

 

[ushidayo]

Did you mean this one?

Nice Picture! May I use it as an example of why I don't use FBD for boolean logic?

Most ladder logic editors are quite friendly to use. They will let you insert columns to make space for new contacts, or insert rows for new branches. On the other hand most FBD editors are clumsy when it comes to editing. For instance if you wanted to change the logic in the diagram above to "C=((A.D)+C).B" it would take a ridiculously long time in FBD compared to LD.

 

[Mehdi]

On the other hand most FBD editors are clumsy when it comes to editing. For instance if you wanted to change the logic in the diagram above to "C=((A.D)+C).B" it would take a ridiculously long time in FBD compared to LD.

I'm sure lots of you people here have not experience on using ABB PLCs / DCSs and their FBD editors (DigiTool or Control Builder F) in your projects to see how user friendly they are. It is Siemens Simataic which has a clumsy configuration tools and environment.

 

[ushidayo]

Happy New Year Everyone.

I'm sure lots of you people here have not experience on using ABB PLCs / DCSs and their FBD editors (DigiTool or Control Builder F) in your projects to see how user friendly they are. It is Siemens Simataic which has a clumsy configuration tools and environment.

No I haven't used either DigiTool or Control Builder F, so I can't comment on their useability. I find the most useful PLC program editors have "F Key" shortcuts for entering instructions (I find it extremely annoying to have to continuously use the mouse when writing software!).

I've found that with some editors, the ladder logic editor is dreadfully slow or the display is inadequate. Often with these editors it is just as easy, if not more easy, to use FBD instead.

Here in Japan, on larger projects, the useability of the editor will have a bigger affect on the project cost than the price of the PLC hardware.

Has anyone noticed that in some cases the original DOS editor, for a PLC, is better that the Windows version that replaced it (it terms of productivity)? I'll admit that the learning curve has probably been reduced due to the common feel that Windows gives. But once you've learned how to use an editor, you want to be able to write code quickly so that you can spend more time thinking about the structure and integrity of the program.

 

[Mehdi]

HI Ushidayo,


I suggest you all try ABB software and enjoy it all. They are really fantastic and easy to use. I love them all!


Cheers
Mehdi

 

[patriot]

I know ladder well enough to write programs for most applications. To me, Function block programming looks terribly difficult. I've never attempted to do anything in it. Then again, I learned from old hard wired relay machines, then jumped to ladder logic. Function block stuff doesn't seem very logical to me.

 

[darrenj]

Function block stuff doesn't seem very logical to me.

Wow That statement is sure to get some response!!!Function Block is logical if you are used to dealing with IC or other programming languages..I agree with you however in i find it difficult..I am sure its because i just haven't spent enough time with it..That being said i have vowed that my next small project will be written in FB just to get an idea..Hell i will try anything once..(Now if i could just get the wife to think like that!!! )

 

[Peter Nachtwey]

Arguments over 9th and 10th best.

Has anyone noticed that in some cases the original DOS editor, for a PLC, is better that the Windows version that replaced it (it terms of productivity)?

I still use my old DOS editor, Brief. I am looking to get DOSEMU working on my Linux machine. I still have products to support that were developed using DOS tools. The windoze versions did not work near as well probably because they use windoze. Give me mean and lean with symbolic debugging and I am happy.

Function Block is logical if you are used to dealing with IC or other programming languages.

Even the IC guys are going to VHDL and other text representations. Think about it folks. Most of the worlds software is not written in ladder or function block, it is written in C or C++. Why is that? Because entering code using a good text editor is the most efficient way of entering code. I bet most of the tools you are using is written or C or C++. FDB has a place, but only if it can replace SFC and LD.

beat this:

c := ( a or c ) and not b;		(* ST *)
c = ( a || C ) && !b;			// C or C++
 
LD A						 ; Instruction list
OR C						 ; I don't see why
ANDN B						; Siemen's STL is 
ST C						 ; so much more verbose

I did not have to touch a mouse or hit a arrow key or otherwise move my hands from the normal typing or 'home' position. Can't beat that for speed. I can single step throuh the code and see the state of the variables change. I do think PLCOPEN blew it when they designed ST. I hate (* *) for comments.

We do a lot of Nation Instruments LabView programming which is basically function block programming. I find it tedious and clumsy. The only benefit is that it is very graphical and it shows the signal paths, but I wonder if it couldn't have been written in VB faster or perhaps the new C#.net. BTW, we use Labview for our bed of nails test systems, not to control any machinery.

 

[ndzied1]

I still use my old DOS editor, Brief.

Ever try KEDIT? It was based on an old CMS editor called XEDIT that ran on IBM mainframes

For a windows text editor I'm partial to UltraEdit 32.
http://www.ultraedit.com/

I do think PLCOPEN blew it when they designed ST. I hate (* *) for comments.

I always find myself wanting to use end of line comments like the // in C. The (* *) are a pain!!!!!!! I don't think the // is used anywhere in IEC so I think the change could be implemented but seems like they'd balk at taking suggestions from Yankees

 

[ushidayo]

The windoze versions did not work near as well probably because they use windoze. Give me mean and lean with symbolic debugging and I am happy.

One thing that I do find useful in Windows is Excel. For creating huge blocks of repetitive code (where only the device addresses are changing), Excel is a God-send. With "Ctrl-D" and "Alt-E I S" you can save hours of typing and then concatenate it and cut and paste the results to the PLC editor. The pedantic may suggest that a For-Next loop will do it for you, but I prefer ladder logic to be written verbatim.

 

[Peter Nachtwey]

I always find myself wanting to use end of line comments like the // in C. The (* *) are a pain!!!!!!!

(* WHO NEEDS TO COMMENT CODE? *)

Using (* *) is a violation of Delta rule #1. Make it easy to do the right thing. (* *) will make everyone think it is a pain to comment.

I use SlickEdit. It is VERY powerful. SlickEdit now needs 256 MB just to edit. What ever happened to lean and mean?

 

[LadderLogic]

(I find it extremely annoying to have to continuously use the mouse when writing software!).

Yesss! "The AutoCAD syndrome". Right hand on the keyboard-right hand on the mouse-keyboard-mouse-keyb... Darn, some newer programming packages seem to miss this important issue entirely.

 

[Peter Nachtwey]

Ladderlogic, I have a marketing question.

1. Early keyboards did not have direction keys. Editors like UNIX's VI or VIM use J for left, H for left, K for up and L for right in screen mode. Shift J, K, K and L would add solid bars. Would you be willing to use these key to move around the screen?

2. I have a philosophy about keys. I feel it is much easier to hit the same key twice than to hit a bunch of different keys. For instance, if I were to design a ladder editor I would use the C key to enter a contact. If you didn't like a NO contact then you hit the C key again to get a NC contact. If you want a rising edge key you hit the C key again and if you want a falling edge contact you hit the C key again. Likewise outputs would only require hitting the O key until you got the output you want such as ( ), (\), (R), or (S). A function would be entered using a f key and then you would enter text to select the function you wanted. I might add some short cut keys but the basic most things should be done with just knowing and hitting a few keys.

This would requires very little movement of the hands and memorizing very few keys. I think it would be much faster than those LD editors that have a whole bunch of different function keys. Keys like ^C, ^X and ^V can be used for cut and paste.

You can see this would be radically different and minimal, yet I feel this would be faster and easier to learn than other LD editors. Especially for those that can't type. This could also apply to FBD editors as well.