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Ladder Logic Fundamentals and Programming Examples - PLC Tutorial

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Ladder Logic Fundamentals and Programming Examples - PLC Tutorial

Logical continuity vs. electrical continuity
I/O Mapping
Mastering examine onon and examine off instructions
The PLC scanning process

PLC Programming Languages

  • In the United States, ladder logic is the most popular
    method used to program a PLC
  • This course will focus primarily on ladder logic programming
  • Other programming methods include:
    … Function block diagrams (FBDs)
    … Structured text (ST)
    … Instruction List (IL)
    … Sequential function charts (SFCs)

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PLC programming languages
Anatomy of a ladder program
Logic functions

Anatomy of a Ladder Program


  • Input instructions are entered on the left
  • Output instructions are entered on the right
  • The power rails simulate the power supply lines
    L1 and L2 for AC circuits and +24 v and ground for DC circuits
  • Most PLCs allow more than one output per rung
  • The processor (or “controller”) scans ladder rungs from top-to-bottom and from left-to-right.
    The basic sequence is altered whenever jump or subroutine instructions are executed.

Logic Functions

  • PLC programming is a logical procedure
  • In a PLC program, “things” (inputs and rungs) are either TRUE or FALSE
    If the proper input conditions are TRUE:The rung becomes TRUE and an output action occurs (for example, a motor turns on)
    If the proper input conditions are not TRUE:The rung becomes FALSE and an output action does not occur
  • Ladder logic is based on the following logic functions:
    AND,  OR,  Sometimes called “inclusive OR”, Exclusive OR.


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For much more download  here (PLC Downloads -> Usefull PLC PDF's -> Ladder Logic Fundamentals PLC tutorial).


Last Updated ( Sunday, 27 December 2009 18:51 )  


#62 2013-04-28 01:35
I want to lean basic plc
#61 2013-04-25 05:26
i required more information to teach programming so,please help me
#60 2013-04-10 19:08
I have a Robopack 1010 casing machine. I am not PLC litterate I am in need of a functional ladder program. Any help would be appreciated.
#59 2013-03-12 14:44
we need more exsamples
#58 2013-01-23 15:43
in ompanies a person need graduation licence called degree, to wok on these stuffs. i love internet, it gives knowledge in free.......
#57 2013-01-10 15:32
If you guy leaving coments and asking for some of the help that I am seeing asked for. Can't you figure it out on your own? If you are the new learning class of tomorrow, real scary.
#56 2012-09-27 15:42
design a ladder diagram for following condition. in a car manufacturing company a car is to painted shell body of car to be washed for 1 min and after washing is dipped in a chemical solution for 2 min after chemical dip a counter is used to count the no of cars painted and after 5 cars the counter generates an alarm
#55 2012-09-27 12:49
i need logo pdf wright some basic file
#54 2012-09-26 10:50
writing logic easy but in output is difficult
#53 2012-08-07 11:49
i want to learn plc ladder diagrams using simple concepts,please giving some simple examples

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