Ladders are more popular among sparkies while signal flow is gaining ground and used for more ambitious projects than opening/closing the factory gate.
BTW: There is a policy regarding students. We are not supposed to help you out with homework. But this question is obviously not homework.
There are a lot of legacy LL out there. If your question is regarding more used as in installed base, instead of current usage, I would think that LL would be a higher percentage.
In any case, it doesn't hurt to know LL.
For exaple, I came across both APL and SOPL recently. Haven't seen either for 15 years - neither have the client - but I could translate it (okay, sort of). One of those old useless skills that comes in handy one in a while.
Ladder Logic will always be around. I'm in all sorts of factories, research facilities, pipelines, skids, cabinets, systems, cities - you name it, and LL is always there and usually predominant.
Obviously the more complex, the more the other languages are used - rightly so. But you have to program to the level of the person who has to maintain and/or troubleshoot the system. Ladder Logic can always make sense at 3am, waken from a deep sleep, thrown into an emergency situation.
I'll go so far as to say that great programmers will actually use 10 lines of simple code rather than 1 complex line of code for that very reason. Obviously structure and grouping are critical.
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All's well that Ends!
For a sequence, one SFC chart is far easier to follow than the equivalent in ladder. For a simple piece of logic the ladder may be easiest.
The two should coexist, they are not meant to be alternatives.
And the other 1131/3 things too, like Function Blocks for loops have their place too.
Lets not forget ST, I find writing modular structured code very easy with it.
I am not sure that LL will always be around, as the younger techs, engineer and so forth 'come of age' I think LL will gradualy die off. I think thats due to computer introduction at an earlier age. Us graybeards grew up with relay control, so LL was a natural progression. The youger grew up with controllers, and I see the upward trend in controller capibilities I think as a result.
All languages will perform and come up with the same (or similar) end result. The most important thing to remember is your audience (i.e. who will work on the system after it is commissioned?). If you are called back to work on the system in 2 years or 5 years from now, how long will it take you to come up to speed?
I have worked at facilities where SFCs were banned (i.e. you would get fired for programming in that language). I generally try to make things as easy as possible so that anyone can work on it.
