10
2.5.1
Functional block diagram
Function Block Diagram (FBD) is a programming language defined in
IEC61131-3. FBD is a graphical representation of an Industrial
programmed control system and adopts a set of symbols and
conventions defined in IEC-1131-3. It represents a control system in
terms of signal flow between processing elements similar to the
methodology adopted for signal flow in electronic circuits. By using
interconnected graphical blocks, it expresses the behavior of functions,
function blocks and a composite program.
An example of FBD is shown in the figure below.
Figure 11 – FBD
You can find detailed information about creating FBD in PLC
Configurator in chapter
3.9.
2.5.2
Ladder diagram
Ladder Diagram (LD) is a programming language defined in IEC61131-
3. Ladder diagrams are derived from electrical circuit diagrams, which
have been conventionally used to represent relay logic operations. Many
of the symbols and terminology have also been adopted from the circuit
diagrams. In other words, Ladder Diagrams are graphical
representations of Boolean expressions, but they can also include other
information normally not possible with Boolean expressions.
A ladder diagram has two vertical power rails, one on the left and
another on the right side of the diagram. The left vertical rail carries the
power to the coil (notionally) through the contacts. The contacts are
arranged along horizontal 'rungs' and the power flows through these
rungs to energize the coil, which is on the right hand side of the logic
diagram, when the logic condition represented by the contacts is TRUE
