Ladder (LD) is a visual programming language defined by the IEC 61131 standard. It includes components:
Function AND - (X . Y) :
|---------| |----| |---------|
X Y
Function OR - (X + Y) :
|------|---| |--|------------|
| X |
|---| |--|
Y
Logical function - F=(X.Z + /Y) :
|---|---| |---| |---|----( )-|
| X Z | F
|---|/|---------|
Y
Inputs : - Instruction normally open : --| |-- - Instruction normally close : --|/|-- - Instruction with rising edge : --|P|-- - Instruction with falling edge : --|N|-- Outputs : - Coil normally open : --( )-- - Coil normally close : --(/)-- - SET Coil : --(S)-- - RESET Coil : --(R)--
It allows to realize logical functions graphically:
Function AND - (X . Y) :
|---------| |----| |---------|
X Y
Function OR - (X + Y) :
|------|---| |--|------------|
| X |
|---| |--|
Y
Logical function - F=(X.Z + /Y) :
|---|---| |---| |---|----( )-|
| X Z | F
|---|/|---------|
Y