You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old April 18th, 2017, 11:04 AM   #31
keshik
Lifetime Supporting Member
Canada

keshik is offline
 
Join Date: Jun 2011
Location: Portland, OR
Posts: 323
Quote:
Originally Posted by daba View Post
Really ? Is that why it has become one of the most popular, if not the most popular PLC language since the 1960's.

As a visual representation of the running program, it suits the widest audience, from seasoned programmers to low-skilled maintenance techs....
Keep in mind that he is (I believe) using a Codesys based editor. Codesys does not have a very good ladder editor. Meanwhile, with Rockwell the reverse is true - good ladder editor, bad ST editor.
  Reply With Quote
Old April 18th, 2017, 10:17 PM   #32
Mara
Member
Finland

Mara is offline
 
Join Date: Jan 2017
Location: Finland
Posts: 19
Quote:
Originally Posted by daba View Post
Really ? Is that why it has become one of the most popular, if not the most popular PLC language since the 1960's.

As a visual representation of the running program, it suits the widest audience, from seasoned programmers to low-skilled maintenance techs....
Like i said, it's just my opinion. I feel that ST is very simple because you can just write the code you think. IF this AND this OR that AND this THEN...

By the way, was there any other programming languages at the 60's ?
  Reply With Quote
Old April 19th, 2017, 02:09 AM   #33
Hundikoer
Member
Estonia

Hundikoer is offline
 
Hundikoer's Avatar
 
Join Date: Jul 2003
Location: Tallinn
Posts: 268
Quote:
Originally Posted by Mara View Post
By the way, was there any other programming languages at the 60's ?
Instruction List kind of things?
  Reply With Quote
Old April 19th, 2017, 03:35 AM   #34
JesperMP
Lifetime Supporting Member + Moderator
Denmark

JesperMP is offline
 
JesperMP's Avatar
 
Join Date: Feb 2003
Location: Copenhagen.
Posts: 13,012
Quote:
Originally Posted by Mara View Post
I am not sure about other PLC's but a i am using Beckhoff with TwinCat 3 and i can see active variables in ST. Same thing with with FBD. I can't see any advantages in Ladder. Of course this is just my opinion but i feel that Ladder is very unclear.
A good ladder editor will not only show the status of the online variables, but also the status of the logic result, even in the middle of a ladder rung (* not sure if Twincat does this).
That makes it very easy to follow the logic, especially when the logic changes quickly.
And, you have to admit that it is very intuitive that you can just follow the green status through an entire rung in order to immediately understand why the rung is true or not true.

edit:
The above is to argue that the online view of ladder is more immediately informative than ST or IL.
But even when viewing or editing code offline, Ladder is better than ST or IL for logic (boolean algebra).
This because Ladder is a visual language with no need to perform an interpretation in ones own mind, whereas text-based languages such as Structured Text and Instruction List require that you read, understand and interpret the logic in your mind.
It is good that ST uses immediately understandable mnemonics (IF, THEN, AND, OR etc), but Ladder is still better. ST has a tendency to become verbose for logic code.

The advantage of ST is that you can perform more complex tasks in a compact and efficient manner.
For example, to perform loops in Ladder is possible, but will take many rungs, which may be less readable and less easy to maintain than loops in ST.
__________________
Jesper
3 strikes and you're out

Last edited by JesperMP; April 19th, 2017 at 03:47 AM.
  Reply With Quote
Old April 19th, 2017, 07:30 AM   #35
Helliana
Member
United States

Helliana is offline
 
Join Date: Nov 2011
Location: Arkansas
Posts: 536
Quote:
Originally Posted by Mara View Post
By the way, was there any other programming languages at the 60's ?
Relay logic ladder prints that looks very similar to PLC ladder programming.
  Reply With Quote
Old April 19th, 2017, 07:38 AM   #36
Geoff White
Member
Australia

Geoff White is offline
 
Join Date: Oct 2005
Location: Brisbane
Posts: 162
Horses for courses.

ST for anything even vaguely algorythmic.
  Reply With Quote
Old April 19th, 2017, 08:08 AM   #37
JeremyAdair87
Member
United States

JeremyAdair87 is offline
 
Join Date: Jun 2014
Location: Ozark Mountains
Posts: 39
In ladder if it is in a straight line it is an "and statement" if it branches down it is an "or statement"

Do it in ladder. Structured text is not as flexible, easy to read, or as simple as ladder. Do it right or don't do it at all.

I've programmed in RISK assembly languages, java, python, C++, ladder and flow... You can see the green bars light up on contacts in ladder. Don't do it in C.

Last edited by JeremyAdair87; April 19th, 2017 at 08:10 AM. Reason: typos
  Reply With Quote
Old April 19th, 2017, 08:15 AM   #38
jstolaruk
Member
United States

jstolaruk is offline
 
Join Date: Dec 2004
Location: Detroit, SE Michigan
Posts: 2,898
Quote:
Originally Posted by Mara View Post
By the way, was there any other programming languages at the 60's ?
I would not be surprised to hear that FORTRAN was used at one point. Developed in the 50's it was very popular.
__________________
"You can live to be a hundred if you give up all the things that make you want to live to be a hundred." Woody Allen
  Reply With Quote
Old April 19th, 2017, 08:16 AM   #39
JeremyAdair87
Member
United States

JeremyAdair87 is offline
 
Join Date: Jun 2014
Location: Ozark Mountains
Posts: 39
Quote:
Originally Posted by Geoff White View Post
Horses for courses.

ST for anything even vaguely algorythmic.
Algorithms are a step by step way of doing things in code right? I'm not sure what your statement means please clarify.

Thanks,
  Reply With Quote
Old April 19th, 2017, 09:30 AM   #40
Tom Jenkins
Lifetime Supporting Member
United States

Tom Jenkins is offline
 
Tom Jenkins's Avatar
 
Join Date: Apr 2002
Location: Milwaukee, WI
Posts: 5,734
Quote:
Originally Posted by ladderlogic View Post
i should say that in my experience "jumping" the regular program scan order is considered in the plc world just as bad practice as using go to statement used to be considered in basic, visual basic etc. Each has its use but better to be avoided for clarity.

Modern plc processors are typically fast enough so not to worry about the execution times and not to skip sections of the code with jumps. Just my two cents.
+1
  Reply With Quote
Old April 19th, 2017, 09:47 AM   #41
Epy
Lifetime Supporting Member
United States

Epy is offline
 
Epy's Avatar
 
Join Date: Jul 2012
Location: Allen-Bradley Valley
Posts: 356
+ Regarding ST: depends on what you're used to, to ordinary computer programmers most written programming languages are easy to read, as you start to readily recognize indented blocks as significant (loop, if, etc). The crappy Renu HMC's I've been using lately show the current values in the ST when online in an intuitive way; showing online tag state is not exclusive to LD.
+ Regarding Mara's point about languages in the 60's, guessing the options were ladder logic or something resembling assembly. The PC didn't really come along until the late 70's, so before that programming was done with handheld programmers (highly doubt the ladder logic was nice looking, or even graphical, or had the ability to go online), and the workstations of the time. Keep in mind, talking about actual PLCs of the time, not computers used in a control capacity.
__________________
Quote:
Originally Posted by ganutenator View Post
customers:
I don't know how to do it so it must be easy
  Reply With Quote
Old April 19th, 2017, 10:41 AM   #42
ndzied1
Lifetime Supporting Member
United States

ndzied1 is offline
 
ndzied1's Avatar
 
Join Date: Aug 2002
Location: Chicago, Illinois
Posts: 2,308
Quote:
Originally Posted by Epy View Post
so before that programming was done with handheld programmers (highly doubt the ladder logic was nice looking, or even graphical, or had the ability to go online), and the workstations of the time. Keep in mind, talking about actual PLCs of the time, not computers used in a control capacity.
Yup, this was how the SLC150's were programmed when I started in this crazy field:
__________________
nOrM
======================
nOrM=Norman Dziedzic Jr.
"I decry the current tendency to seek patents on algorithms. There are better ways to earn a living than to prevent other people from making use of one's contributions to computer science." Donald Knuth
  Reply With Quote
Old April 19th, 2017, 10:45 AM   #43
jstolaruk
Member
United States

jstolaruk is offline
 
Join Date: Dec 2004
Location: Detroit, SE Michigan
Posts: 2,898
The T3 with the built-in ladder programming. Often, each panel had its own T3 dedicated to it. Too big to move without a cart.
__________________
"You can live to be a hundred if you give up all the things that make you want to live to be a hundred." Woody Allen
  Reply With Quote
Old April 19th, 2017, 10:47 AM   #44
ndzied1
Lifetime Supporting Member
United States

ndzied1 is offline
 
ndzied1's Avatar
 
Join Date: Aug 2002
Location: Chicago, Illinois
Posts: 2,308
Quote:
Originally Posted by JeremyAdair87 View Post
Do it in ladder. Structured text is not as flexible, easy to read, or as simple as ladder. Do it right or don't do it at all.
The "Right Way" is not the same for all applications. I once had to parse an ASCII string coming from a gauge in ladder logic in an SLC500 so that I could pull the measurement numbers from the string.

It took a couple days to figure out and probably 15-20 rungs after optimization. 3-4 lines of ST (which didn't exist for me at the time and never did on the SLC500) would have been much faster, easier to understand and readable for that application.

While everyone has their favorite flavor of programming, what I like about the current direction of PLC programming is that you CAN pick a language that makes sense for the application. And, you can use them in the same program. My programs are almost always a combination of routines in Ladder and ST.
__________________
nOrM
======================
nOrM=Norman Dziedzic Jr.
"I decry the current tendency to seek patents on algorithms. There are better ways to earn a living than to prevent other people from making use of one's contributions to computer science." Donald Knuth
  Reply With Quote
Old April 19th, 2017, 10:57 AM   #45
cardosocea
Member
United Kingdom

cardosocea is offline
 
Join Date: Nov 2016
Location: London
Posts: 260
Quote:
Originally Posted by Mara View Post
By the way, was there any other programming languages at the 60's ?
I learned PLC's with an OMRON PLC and no software or computer... just a portable console. And there was no way of inputting ladder into it. You'd basically write down your ladder and convert it into the language that would describe the ladder (very similar to Assembly in fact).

After a while, me and others wouldn't even think in ladder, but went straight away to that language to save time.

This being said, ladder and to a certain extent FBD are the best when it comes to digital logic as there is zero mental effort in understanding why an output is on or off.

One company I worked for had a few locations and one would program everything in STL (Siemens) and the other had everything in FBD for Siemens also... and the stupidest arguments arose between people from both these offices about which language was the best.

For some reason, they would not agree that it's painful to troubleshoot a long sequence of And's and Or's in STL and the other would not agree on how silly it was to perform complex calculations in FBD and how much scrolling there would be to visualize the entire code.
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
Which programming method is better - ladder logic or structured text sinha_nsit LIVE PLC Questions And Answers 32 February 29th, 2016 11:47 AM
RS Logix Structured Text JasonWade LIVE PLC Questions And Answers 22 July 28th, 2014 04:19 PM
why use structured text and function block over Ladder spidermonkey LIVE PLC Questions And Answers 46 January 8th, 2013 10:02 AM
Structured Text on a PLC-5 antjon1 LIVE PLC Questions And Answers 6 March 30th, 2006 01:05 PM
Documentation on Structured Text cmulder LIVE PLC Questions And Answers 13 June 11th, 2003 10:10 AM


All times are GMT -5. The time now is 11:37 AM.


.