begginer's qustion

kiran_deodhar

Member
Join Date
Apr 2003
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1
i am totally new to this field.can anybody tell me is there any other approach than ladder logic for plc programming?
is there any, which one is better?
:(
 
Sure there are several different approachs. Some plc's such as the WINPLC sold by AutomationDirect.com use flowchart logic as their programming style. Still others use a structured text or a BASIC type programming. Some even use a combination of the above such as TRiLOGI . 👨🏻‍🏫 All the ladder code is used for is to act as the GUI for the programmer. Most all platforms convert the ladder logic that you draw into some type of lower level code when it is compiled. This code is what the PLC's processor can understand. As far as which type is better that would depend on the person doing the programming. Which type do they understand and follow the best. I am just as comfortable writing code in ladder as I am in flowchart but some people cant follow ladder but can follow a flowchart. Some can hash out code in basic better so they may choose a package that uses that type of coding. So it all depends on the programmer. :D I hope that I have helped.
 
Last edited:
IEEE 61131-3

There are 5 programming languages officially defined by the standard IEEE 61131-3.
Instruction List
Structured Text
Ladder Diagram
Function Block Diagram
Sequential Function Chart

As far as which one is "better" - that's impossible to answer. It is both a matter of personal preferrence, and suitablilty to the task (and the PLC - not all languages are supported by all PLCs)

I personnally prefer ladder in most cases, as it provides a nice graphical representation of what's going on. I don't see too much difference between LD and FBD, other than in the latter the "wires" can carry analog information (e.g., numbers) instead of just digital info (True/False).

The mindset of SFCs is a good one to acquire when creating sequences, and since only the active step is scanned, can be faster than ladder equivalents. But SFCs do not handle exception logic well (you wind up with so many branches that it becomes nearly impossible to follow the intended main flow of the program.

I don't have much experience with IL and ST to offer good opinions. Programs written in them are typically more efficient than those in ladder.
 
Other than all the above options, a rather abstruse option is assembly language. Now programming in assembly has its advantages of compactness, superior use memory, and high degree of control. Last year I constructed a small PLC and programmed the micro controller directly using an EPROM Programmer. However, It's not the best option in any sense. Above all because it makes reprogramming a very difficult task. Still a viable option for a low budget hobby project. Any buyers...
 
There is a good reason PLCs are programmed in ladder logic, and if you read about the reason they were first created you will see why. If you don't like ladder, go program a PC, and leave PLCs alone. PLCs were created to replace banks of hard wired timers, counters, relays, etc, for production workers to use and maintenance electricians to maintain, and not for engineers and programmers to sit around and feel good about themselves. Sorry guys.

OK, bring it on.......

Vetteboy
 
Can't we all...just get along? :(

for production workers to use and maintenance electricians to maintain, and not for engineers and programmers to sit around and feel good about them. Sorry guys.

Well Vetteboy, are you saying that RLL is the only language that a maintenance electrician can, or is smart enough to understand? :rolleyes: Is it the job of most electrical maintenance guys to write code for PLCs? As a former electrical/electronics maintenance tech I think I can safely say that in many plants the maintenance guys don’t get to modify the code much less sit down and write new code for the PLCs in the plant. In fact many of them may never even see any PLC code. So at one point or another there has to be an "InJuNeer" or "PoGrammer" sitting round feeling good about themselves. The code just doesn't grow in there, and if it did, who says it has to be RLL?
That’s all I’ve got to say bout that.
 
Above all confrontations....

Well Kiran, if you are all too confused with all these discords; remember just this - "The most important part is to develop a logic that works and works well under any circumstance imaginable. If someone ( be it an 'InJuNeer' or a 'PoGrammer' or a 'MAINtenance' guy)is smart enough to come out with such a logic; he is smart enough to implement that logic in any language."
So Kiran, instead of pondering over what language is superrior to what, work on your ability to analyze and solve engineering problems. As for the languages, apart from the superficial difference, they are all the same.

Last words: Kalle, man, you can do with some patience.
 
I suspect that Kalle doesn't hold the copyright to that movie.
For motion pictures there is a fair use clause that allows up to 30 seconds to be used. Also, since we aren't making any money off it, the concern of the interested party is probably nil.
 
Rick

My comment was very much 'tongue in cheek' and it was a reference to a comment that Ron Doran received on his website.

I did not mean it to sound like I was preaching, or indeed to offend anyone.

Paul
 

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