Ladder OR????

rsdoran

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Join Date
Apr 2002
Location
Birmingham, AL
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This is a topic I have thought about alot recently because of having to deal with IEC 1131 conventions.

I have been accused of wanting to DUMB down code so the maintenance/electricians can understand it.

A post was made earlier about Siemens and STL, one of the reasons I have come to like Siemens is that it combines ladder and STL..ie gives you the option of using either to perform what is needed or transforming STL into ladder and vice versa...at least as much as possible.

What I (as a maintenance/electrician) do not understand is the need to use languages that are totally foreign to us.

I understand that ladder has limits BUT

Ladder is graphical...all electricians and most maintenance personnel have to deal with drawings. LD a AND b OR c = x is NOT graphical. A BTR/BTW is within some of our grasp, thats just reading and writing...most of us learn how to do that kinda young.

On a daily basis I have to deal with plc's and the code that I can not obtain...thats another issue. What I would like to see is graphical representation (ladder representation) of items that arent existing now but are in things like STL, IL , SFC etc etc al.

I do NOT want the code DUMB nor the code to make the PERSONNEL made DUMB because they cant understand it. I seek a fair medium...maybe prejudiced to the ladder/graphical side.

NOTE: The fact of documentation is not an issue here...no matter how a program is written, if not documented well then even the best can be kinda DUMB.

I know for OEM's etc the issue is to protect (another issue)...but is there a way to PROMOTE a graphical/ladder combination of the methods used today?...ie combine the advantages of ladder with STL, IL, stage, etc etc al

For alot of OEM's this wouldnt be feasible because some of your income comes from parts/service...but for some of us end users this would make life alot easier. NOTE PERSONAL RANT NOW: You dont know how much it aggrevates me not to be able to do my job because a company withholds vital info (of course the company that buys a machine with that limitation has to deal with that fact) BUT at the same time it makes me look incompetent.

Just curious why some of the best couldnt be combined with the OLD.
 
Rsdoran,

From looking at posts made by you, I do not think you should refer to anything you do as dumb. Code written is all up to the programmer.
The time spent to learn code never ends. To know every instruction and it's function is not even common among people that program for a living. Styles and methods change. If management only knew what we go through to maintain systems!
 
Ron

I am in full agreement with you regarding 'dumbing' down code. As far as I am concerned the best way to program a PLC is with ladder, because then nearly every technician/electrician who comes in contact with it can understand it. unfortunately, as you say, ladder does have it's limits, then that is the time to go into statement, providing your annotation is good this should not present too many problems for people to understand. There is nothing worse than having to decipher someones code beacuse they haven't put any annotation with it.

A little while ago, we had a problem with one of our ship to shore cranes (S5 PLC), the problem lay in one of the function blocks, written in statement, this block was well annotated but, the annotation was in German! Not being a German speaker this block took me a long time to understand, although I got there in the end, I knew roughly what the block done, I felt that I had wasted a lot of time deciphering the block. Needless to say I have now annotated the said block in english.

Paul
 
Hi Rsdoran,

No problem in dumbing down the code, in fact if the sparky can solve the problem by himself, he won't be calling you at 2am in the morning.

The problem I sometimes get is exactly the opposite, I'm told to dumb down my code, and I'm usually happy to oblige (I'm an end user too).

For a fair while, we've been specifying that the OEM/contractor will use ladder, if not - to discuss it with us first. This usually works because most (99%) of what you need to do can be done in ladder.
You can probably eliminate most of the STL with a little thought.
Since you're going for IEC code (S7 I presume), you could fork out a little more and use SFC (S7Graph), it's entirely graphical, usually easier to understand than ladder, and stops the pesky OEMs from writing their sequences in STL.
I have to mention that my main experience with SFC is from Modicon's Concept 2.0, so I don't know how good S7Graph is, although I'm evaluating it at the moment.


Hope this helps,

Doug
 
I tend to agree that simpler is better.

Any average PLC programmer can come up with a complex solution to a simple problem, but it takes a really good programmer to come up with a simple solution to a complex problem.
 
You can sometimes have your cake and eat it too!
Some PLC platforms allow you to 'roll your own' function blocks.
(G&L Pic900 Family comes to mind). You can write a very complicated function block, compile it, and the result is a very easy to follow function with mininal inputs and outputs.

One function block example that I have created is a ramp generator with a discrete input to enable the function, two numeric inputs for setpoint and ramp rate and a single output for the ramped value. That's all you see. Very simple and easy to follow! If you are the curious type and you want to see the code inside the function, you can 'zoom' in on the function and see the dozens of networks of ladder code that make up the function. You can also use the function over and over again inside the main program.
 

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