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PLC Programming
- Thread starter Pali
- Start date
- Replies 10
- Views 4,004
There are various methods out there, the most common format is ladder representation of boolean logic.
Many manuf. allow the programming in either ladder or in direct mnemonics of boolean functions, which generally is faster.
There are also enhanced methods using SFC (sequential flow chart) if the software allows it.
Ladder representation is usually also used for status/diagnostic checking using a diagnostic display of the ladder.
If you want to make chages to an exsisting ladder, you generally need the software and sometimes the interface unit,
You would need to obtain a programming manual and read it over.
Minder.
Many manuf. allow the programming in either ladder or in direct mnemonics of boolean functions, which generally is faster.
There are also enhanced methods using SFC (sequential flow chart) if the software allows it.
Ladder representation is usually also used for status/diagnostic checking using a diagnostic display of the ladder.
If you want to make chages to an exsisting ladder, you generally need the software and sometimes the interface unit,
You would need to obtain a programming manual and read it over.
Minder.
Last edited:
PLC ladder logic can be extremely difficult to modify if it is not documented. If you intend to modify the code in an existing machine you may have trouble. Most builders strip out all internal comments from the code to make it difficult for others to understand.
Many builders also lock the PLC to prevent unauthorized changes.
Well i dont' want to mess around with existing plc,
just wanted to understand how it is done.
Boolean logic sounds familiar, but no clue as to what it is.
do we type this in English or numbers.
can any of you type few lines for me to understand better.
I'v seen PLC units in machine and pictures, but never really gone into the ladder.
as a hobbyist can we do it ourselves for small projects.
regards & cheers
Pali
just wanted to understand how it is done.
Boolean logic sounds familiar, but no clue as to what it is.
do we type this in English or numbers.
can any of you type few lines for me to understand better.
I'v seen PLC units in machine and pictures, but never really gone into the ladder.
as a hobbyist can we do it ourselves for small projects.
regards & cheers
Pali
Pali
If you have any experience with programming languages then ladder logic will be easy to understand. Think of it as a list of IF-THEN statements running in an endless loop. The language is graphic instead of text-based.
Automationdirect.com sells a small PLC (model DL-05) for about $100USD. I think they still have a free version of the programming software for this model.
Automation Direct PLC manuals are very well written and easy to learn from. I taught myself enough in two weeks to build and program my first automated machine.
Here is a webpage that explains the basics of ladder logic:
http://openbookproject.net//electricCircuits/Digital/DIGI_6.html
Good luck
Pali, If you study a schematic of a machine displaying the typical "Ladder" format for the control logic.
In N. America it is shown as two vertical power lines each side of the page with the logic functions in between.
Europe uses a top and bottom horizontal line and the logic flows down, instead of left to right.
For e.g. http://www.me.ua.edu/me360/fall05/Misc/Logic_Control_Systems.pdf
If you look at the first very simple rung one typical PLC may describe this as:
LD PB-1
LD CR-1A
AND LS-1
OR LD
OUT CR-1
LD being a Mnemonic for load.
The result of the two rungs being OR'd decide the status of the output.
There are variations according to the PLC designer, but the basis of the instruction mnemonics are based on the Boolean arithmetic, which has the basic instructions of
AND, NOT, NOR, NAND etc.
Ironically this is a form of mathematics originated by an Englishman, George Boole in the 19th century, unfortunately there was no use for it at the time until the advent of computers!.
Minder.
In N. America it is shown as two vertical power lines each side of the page with the logic functions in between.
Europe uses a top and bottom horizontal line and the logic flows down, instead of left to right.
For e.g. http://www.me.ua.edu/me360/fall05/Misc/Logic_Control_Systems.pdf
If you look at the first very simple rung one typical PLC may describe this as:
LD PB-1
LD CR-1A
AND LS-1
OR LD
OUT CR-1
LD being a Mnemonic for load.
The result of the two rungs being OR'd decide the status of the output.
There are variations according to the PLC designer, but the basis of the instruction mnemonics are based on the Boolean arithmetic, which has the basic instructions of
AND, NOT, NOR, NAND etc.
Ironically this is a form of mathematics originated by an Englishman, George Boole in the 19th century, unfortunately there was no use for it at the time until the advent of computers!.
Minder.
Thanx Friends.
The problem with Indian education system is that it more of Theory, than practical.
Only heard of this and done on paper, no practical stuff.
now that I'm financially independent, want to try out practically few tings as hobby and also my 4 year son is more technically bent like his Grandfather.
Thank you all again for your patience and time.
warm regards & seasons greetings [the festival of lights begins in India]
Pali
The problem with Indian education system is that it more of Theory, than practical.
Only heard of this and done on paper, no practical stuff.
now that I'm financially independent, want to try out practically few tings as hobby and also my 4 year son is more technically bent like his Grandfather.
Thank you all again for your patience and time.
warm regards & seasons greetings [the festival of lights begins in India]
Pali
dkmc
Diamond
- Joined
- Jan 13, 2002
Whew...-that- simplifies the whole thing now doesn't it !
WarrenD
Aluminum
- Joined
- Nov 22, 2006
- Location
- Vacaville, CA
Another alternative
Although I have a background and advanced education in computer programming and electrical engineering, I still try to avoid devices which require a lot of effort to get up to speed. I have found the easiest PLC's to program are the Millenium (now III) series from Crouzet. Programming is just a matter of dragging items (logic elements, timers, input devices, output devices, etc) from a toolbar and drawing lines to connect them. If you prefer, you can use ladder logic or sequential functions also. I find that I can do most programming in a matter of minutes rather than hours (or days!)
Although I have a background and advanced education in computer programming and electrical engineering, I still try to avoid devices which require a lot of effort to get up to speed. I have found the easiest PLC's to program are the Millenium (now III) series from Crouzet. Programming is just a matter of dragging items (logic elements, timers, input devices, output devices, etc) from a toolbar and drawing lines to connect them. If you prefer, you can use ladder logic or sequential functions also. I find that I can do most programming in a matter of minutes rather than hours (or days!)
