The end of ladder logic?

How many of you are looking to the future and seeing the trend towards SFC's and Structured Text (ST) becoming the way of the future?

For example Schneider's new Unity Pro package is 100% optimised to run ST, but by contrast the Ladder (LD) editor is a clumsy afterthought. Even when using the LD it encourages you to write all you Operations and Compares in little ST fragments.

Right now Ladder accounts for 80-90% of the automation code installed base, but do you see this percentage staying the same or declining? And if so, will it be a gradual change or possibly a rapid one?

I'm quite happy using SFC's, FBD and ST. But in my heart of little PLC hearts, I prefer Ladder. I can do everything in it that I have ever needed to do. It is one universal tongue we all understand. Is there actually any real benefit in the proliferation of languages that IEC1131 mandates?

Are we going to see text based code churned out by IT graduates flicked over from web-design, grinding out the big projects? These kind of people have no trouble modelling process in text-based languages. OK so I'm being a little provocative, but I guess I am asking a serious question about whether or not us hands on people will have a place in larger automation projects, other than yanking cables and belling out IO.

PhilipW said:

But in my heart of little PLC hearts, I prefer Ladder. I can do everything in it that I have ever needed to do. It is one universal tongue we all understand.

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This is one of the main reasons why ladder isn't going anywhere, anytime soon. If that Unity Pro software has a lousy ladder editor, then us ladder folks ain't gonna be using it. We can only wait to see how well it fairs...

This is the only "End of Ladder" in my mind...





-Eric

The non-ladder IEC languages, in my experience, are more prevalent in Europe. That's why Modicon and Siemens PLCs in some ways treat ladder as the ugly step-sister. Conversely, in the states ladder is king, and SFC and so on are the neglected aspects.

I think we will see more SFC and ST in the process industries. I think we'll see ladder in the discrete industries. That's because these languages have some real advantages in these respective applications. To some extent the process industries drove the development of SFC, and discrete manufacuring drove ladder.

I think that we'll see the market winners be the companies that enable smooth integration of the two types of languages. I want my alarm interlocks and some machine sequencing to be done in ladder, but I kind of like writing function blocks for analog control. I should be able to call one from the other and vice versa. I could do that OK in Concept on the Modicon - I haven't seen Unity. And I wouldn't put too much stock in Modicon as a trend setter anyway.

As far as job security, any damn fool could always write code. Knowing what it is supposed to accomplish and wringing out the field sensor and wiring problems at commissioning is where the skill comes in. A bit weenie from IT will go home with his tonque hanging out and babbling senselessly after half a day trying to keep up on a system start-up!

As I understand it, ladder is not anything like as widespread in Europe as in America, not sure where the Antipodes is placed in this respect. As far as I'm concerned I program in SFC by preference, followed by FB, but then I'm a Process Control Engineer not a "Maschinenbauer". The only time I use ladder is when FB is too big to fit comfortably on the screen and when viewing process operation ladder usually shows a bit more.

Whenever things get more complicated I revert to STL, but I'm not enough of a programmer to be comfortable with ST (I hope I've got those two the right way round, I work in German, so I'm never quite sure which is which! I mean I'm not comfortable with the Pascal like language.)

I can well imagine that things might move in that direction for larger projects or for Process Control as the PLCs become ever more powerful, it makes it easier to use higher level languages to achieve the desired result.

For pure machine control, I can't see things changing so fast. There, I think it will be a case of using whatever you are comfortable with. That may well mean that younger, computer-literate entrants to the branch may well tend more to the high level language direction, but people coming in from the electrical side will still tend to prefer ladder. Somewhere in the middle will be those who, for whatever reason, prefer function block (I prefer FB as a result of a background in H/W design, it reminds me of designing IC circuits).

I work mainly with Europeans and China, and ladder really isn't that common. I've personally never used it during my 15 years of programming, but it's because of how I learned. But I can say that all of the people I know who learned STL, FBD, and SCL after first programming in ladder, would never go back to ladder. Other languages are just much faster to code, and makes us more competitive. At least that has been my experience.

Hey Roy, I'm back in Germany again. If you don't get those timers figured out, come down to Stuttgart and I'll help you out.

I was working a project using Step 7. The main operator controls were written by the guru for the company that did the operator controls. My company did the switch gear. During start-up, a couple of changes needed to be made. I watch the man do all text programming, while my engineer did mostly ladder on our side. I was amazed to see how it worked. I did a bunch of reading and question asking on the benefits of text programming versus ladder. Seems like it depended on wether you learned old time relay logic and basic PLC or went to programming school as what the different folks on the project prefered.

One thing I have noticed in most newer equipment, both PLC and Drives, there is the ability to program in text for those that do that.

I have to agree that the younger crowd that had a computer for a toy instead of Mr. Machine or an Atari will probably like text programming over ladder logic.

I truly enjoy watching a computer nerd, excuse me IT type, go bonkers at a real world start up of equipment. I love it when they say it is programmed to do this, and I have to say it does not and actually does this instead. Then I get to watch as they go into critical mass.

Simply another opinion...

Here in Mexico, I don't see ladder going away... Thinking about the maintanence electrical types who understand thier electrical scematics the ladder is an easy evolution... Not going to see too many maintanence electricians with any other coding back ground or the ability to troubleshoot most other programming languages...

Tom Jenkins said:

And I wouldn't put too much stock in Modicon as a trend setter anyway.

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Scary thing to say seeing as they are credited with the first PLC!!!

My 2c on the subject...

FB and ST are cool are work realy nice..(Havnt done ST yet but from playing around it looks nice)However i look at it like this..

Windows XP is easy to use (Dont bash me untill you read everything!!) Compared to DOS..However windows is a dosshell

Anyone who has ever had to realy tweek or seen the "Blue screen of death" knows that dos will get you running again.. I view FB and ST the same way..They are nice but if you realy want to know whats happing in a process then look at the ladder..(Now thats probably the Sparky in me comeing out).. I like to see that Bold green line telling me where power is rather than looking for a #1 or a #0 above an output or input!

Again i like FB it has some way cool features that take Tons of time in ladder such as PID and Motion..but i still come back to ladder..

C:\old_farts\*.*

Darrenj

I tried to be silent

However windows is a dosshell

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Not for a long time.

Alas, ladder will diminish and the Euro (or WORLD) will be our currency.

I don't think ladder will die.

It is good for handling glue logic for inputs that must be polled. ST can do this too but it isn't as visual. Also, can ST be change on-line? Can you single step? How do you debug ST?

I do think those die hard ladder fans just haven't done a project complicated enough so they can see the benefits of SFC and ST. Using SFC and ST together should result in very efficient code for those applications that use state machines.

BTW, I do most of my programming in assembly, C, and Mathcad.

As an old tutor of mine once said...
'The mechanic with only one spanner (wrench) in his tool box is probably not going to do as good a job as one who's box is full!'
Just my 2 bobs worth

It is good for handling glue logic for inputs that must be polled. ST can do this too but it isn't as visual. Also, can ST be change on-line? Can you single step? How do you debug ST?

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As a C programmer, I can imagine you feel most at home in ST, I most definitely do not! I'm therefore not certain of the answer to your questions, but I would think (assume, guess?) that you can probably neither edit online nor single-step in ST. However, I would expect that in S7 at least, just as you can open an S7-GRAPH block in STL, that you can probably open an SCL/ST block online in STL and there you would be able to both edit online and set Breakpoints to single step through your program. Obviously a bit of a cludge and not as comfortable as being able to work directly in ST, but I reckon anybody who is comfortable in ST (not to mention assembler) should have no problems working in STL.

BTW, I noticed somebody reading your "Stupid S7 question" Thread from 2003 yesterday and had a look at it myself, made interesting reading - I guess you're probably a lot more comfortable in S7 nowadays!

How many of you are looking to the future and seeing the trend towards SFC's and Structured Text (ST) becoming the way of the future?

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Not here!!!

For example Schneider's new Unity Pro package is 100% optimised to run ST, but by contrast the Ladder (LD) editor is a clumsy afterthought. Even when using the LD it encourages you to write all you Operations and Compares in little ST fragments.

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That is why I will not use it by choice!!!

I'm quite happy using SFC's, FBD and ST.

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Good for some things!!!

But in my heart of little PLC hearts, I prefer Ladder.

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Here here!!!

Are we going to see text based code churned out by IT graduates flicked over from web-design, grinding out the big projects? These kind of people have no trouble modelling process in text-based languages.

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Pity the poor maintenance guys that have to sort things aout after the boffins have left the site. Perhaps that is why they do it!!! Call them back at ridiculous hourly rates. Good for business!!!

That's why Modicon and Siemens PLCs in some ways treat ladder as the ugly step-sister.

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I have heard it suggested that these things came about from a very heavy Siemens push to compensate from a lousy function set in Siemens PLCs. That was suggested to me by a Siemens rep no less!!!!

I think that we'll see the market winners be the companies that enable smooth integration of the two types of languages. I want my alarm interlocks and some machine sequencing to be done in ladder, but I kind of like writing function blocks for analog control. I should be able to call one from the other and vice versa. I could do that OK in Concept on the Modicon - I haven't seen Unity. And I wouldn't put too much stock in Modicon as a trend setter anyway.

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I thought Concept was lousy and Unity is even worse!!!!

Whenever things get more complicated I revert to STL, but I'm not enough of a programmer to be comfortable with ST (I hope I've got those two the right way round, I work in German, so I'm never quite sure which is which! I mean I'm not comfortable with the Pascal like language.)

I can well imagine that things might move in that direction for larger projects or for Process Control as the PLCs become ever more powerful, it makes it easier to use higher level languages to achieve the desired result.

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Omron developed a PLC where one could describe a function block and write everything in the block in a high level language. It did not sell!!!! No value going there for sure if the company cannot make a bob. But it was still a PLC with the good checks that ere built in.

April (swallowed up by Schneider) had a "PLC" that could be programmed in a high level language and one even had to program in things like watchdog timers, checks on program integrity etc. No use calling that device a PLC.

For pure machine control, I can't see things changing so fast. There, I think it will be a case of using whatever you are comfortable with. That may well mean that younger, computer-literate entrants to the branch may well tend more to the high level language direction, but people coming in from the electrical side will still tend to prefer ladder. Somewhere in the middle will be those who, for whatever reason, prefer function block (I prefer FB as a result of a background in H/W design, it reminds me of designing IC circuits).

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I was having discussions with a client today about programming languages etc. He is a mechanical and electrical engineer and also has written hard code in Fortran, C, C++, VB, and machine code. Only a young guy perhaps 28 years old. The project in question is being implemented by the 2 of us conjointly. We have a lot of respect for each other and that is really good. He is off on the road of FB, ST and STL due to his programming background. As I pointed out to him, when he is finished with the job he has gone to something else. The poor cows that are left to trouble shoot the job will not understand what he has done. I suggested that I would have to support the job by phone and try to explain things to the maintenance people, not easy in ST and STL but FB could probably be managed. All of a sudden the penny dropped and there was an immediate understanding that the way he wanted to go was not practical from a maintenance point of view.

By the way, the project is a complete re-hash of the control system for the maintenance cranes on the Sydney Harbour Bridge. Get sick and tired of bridge climbs for which people pay a lot of money. My old legs do not like it any more, particularly at 2AM!!!

I truly enjoy watching a computer nerd, excuse me IT type, go bonkers at a real world start up of equipment. I love it when they say it is programmed to do this, and I have to say it does not and actually does this instead. Then I get to watch as they go into critical mass.

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How true is that??????

Here in Mexico, I don't see ladder going away... Thinking about the maintanence electrical types who understand thier electrical scematics the ladder is an easy evolution... Not going to see too many maintanence electricians with any other coding back ground or the ability to troubleshoot most other programming languages...

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Here, here!!!!!!!

Again i like FB it has some way cool features that take Tons of time in ladder such as PID and Motion..

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Why??? I am used to using an autotune PID function (2 degree of freedom) function that does it all for me.

It is good for handling glue logic for inputs that must be polled. ST can do this too but it isn't as visual. Also, can ST be change on-line? Can you single step? How do you debug ST?

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Pain in the backside!!!!

I do think those die hard ladder fans just haven't done a project complicated enough so they can see the benefits of SFC and ST. Using SFC and ST together should result in very efficient code for those applications that use state machines.

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Have always been able to do what I want with ladder and higher end stuff for motion etc. A good PLC motion set of software will look after whatever you wish to do quite comfortably from my experience - but it has to be good!!!

Pilip, you are definately a provocative stirrer, but a good one. Excellent food for thought here. A lot of people with their own opinions. There should be much more of this sort of discussion in the forum.

CONGRATULATIONS for intoducing a subject that I am sure will not go away.

Y'all just want let it die. I was not going to rant...

I do think those die hard ladder fans just haven't done a project complicated enough so they can see the benefits of SFC and ST. Using SFC and ST together should result in very efficient code for those applications that use state machines.

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I am an avid ladder proponent. These werent alwasy available and some complicated processes managed to survive and more people were easily able to learn.

Ladder is a graphical representation similar to relay ladder logic therefore its easier for most electrician/maintenance types to follow the programming. Relay logic itself is not gone nor will be for a long time (if ever)...basically electricity, because of the LAWS of PHYSICS, can not change therefore it will still be wired the same for a long long time.

Personal opinion the advent of all these languages has actually put the field a step backwards. Instead of ONE COMMON language being truly developed for ALL PLCs now they have to conform to 5 different languages WITH NOTHING to decide HOW each language is actually developed.

Another OPINION, why create new languages? If you are going to do this then why not just allow the use of HIGH LEVEL languages, C, BASIC etc. I could understand this better than a bunch of languages specifically created for it that can be different overall depending on who creates the instructions for the language. I think at least one may have to conform to a pre-made set of instructions which is good but not sure that it can not have variations to some degree.

It has been stated that electrician/maintenance types need to learn more so "programmers" dont have to "dumb down" code. ALL people need to learn more but some people develop trades as their carrers, if they have to learn to "PROGRAM" then why be a tradesman.

Its better, its faster.....Why? You save an hour or 2 creating a program? It cuts down a few milliseconds of scan time (maybe)? It may save memory? Who exactly does that benefit in the long run?

If LADDER had been a SINGLE COMMON LANGUAGE by now there would be so much "generic" code developed and so many "enhancements" that the above would be meaningless. OF course that would mean "the uneducated could do it...can not have that now can we?

The machine/system goes down. Inhouse personnel attempt to troubleshoot using the plc software...its in a NON-ladder language...OOOPPPPSSS...WE dont understand so have to HIRE someone, machine is down until we can get someone.

A simple modification is needed...OOOPPPSS its not in ladder so have to HIRE someone because we dont know how.

Personally I believe all the "languages" were created for financial reasons. It makes it harder for the end user to work with therefore they have to contact the OEM or use a "programmer". It makes it easier in many cases to "lock out" the code so the end user is forced to deal with the OEM. It provides a "job security" feature for some. It allows those without electrical or machine knowledge do programming which may be cheaper for the OEM.

Laddder may not die but it is falling by the wayside rapidly.

Even though I may one day have to use one or more of these languages I will always believe that LADDER is the best. As was mentioned the ability to SEE that ladder rung of code go "TRUE" is a picture that is worth a THOUSAND WORDS.

My first programming experience at the age of twelve was BASIC (TRS-80 Model 1 Level 1). I quickly learned that if I wanted to control the details better, machine language was the way to go. The same holds true with ladder logic vs. other PLC languages.

I learned many kinds of BASIC, C++, Assembly code, and a little bit of about everything else. Then, when I was trained on PLCs and found out we were using ladder logic to control multi-million dollar machines I was stunned! I figured there had to be a better more standardized high level system in charge of it all.

Well, even if there was, you still need the "nuts and bolts" of ladder logic or a similar low level language to get the flexibilty and performace that industry demands. Just like I needed machine language to make my BASIC programs do certain things faster and better on my old Atari.

Ladder isn't going away. It is too versatile, allows online editing and allows electrician comprehension.