Programming Languages for PLC

Programming Languages for PLC

Hi Friends, today we are going to discuss three most used
programming languages for PLC these are Ladder Logic programming, Instruction
List and Functional Block Diagram.

 Ladder Logic Programming 

 A program
consists of instructions that accomplish specific tasks. The degree of
complexity of a PLC program depends upon the complexity of the application, the
number and type of input and output devices, and the types of instructions
used. Ladder logic (LAD) is one programming language used with PLCs. Ladder
logic incorporates programming functions that are graphically displayed to
resemble symbols used in hard-wired control diagrams.  The left vertical line of a ladder logic
diagram represents the power or energized conductor. The output coil
instruction represents the neutral or return path of the circuit. The right vertical
line, which represents the return path on a hard-wired control line diagram, is
omitted. Ladder logic diagrams are read from left-to-right and top-to-bottom.
Rungs are sometimes referred to as networks. A network may have several control
elements, but only one output coil.
Ladder Logic Programming

Statement List and Function Block Diagrams:

While ladder
logic programs are still common, there are many other ways to program PLCs. Two
other common examples are statement list and function block diagrams. Statement list (STL) instructions
include an operation and an operand. The operation to be performed is shown on
the left. The operand, the item to be operated on, is shown on the right.
Function block diagrams (FBD) include rectangular functions
with inputs shown on the left side of the rectangle and outputs shown on the
right side. In the following example, the program segments perform the same
In addition
to LAD, STL, and FBD, multiple other types of programming languages are used for
PLCs. Each type of programming has its advantages and disadvantages. Factors
such as application complexity, types of programming available for a specific
PLC model, and user standards and preferences determine which type of
programming is used for an application.

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