Ladder Diagram Languages-Programmable Logic Controller
- 2. Flowchart
- 3. Ladder Diagram Primary programming language for PLCs. Other programming methods include: Function block diagrams (FBDs) Structured text (ST) Instruction List (IL) Sequential function charts (SFCs) Visual and Graphical language unlike textual high-level, such as C, C++, Java… Derived form relay logic diagrams Primitive Logic Operations OR AND NOT
- 5. Ladder Diagram Power Rails - Pair of vertical lines Rungs - Horizontal lines Contacts A, B, C, D… arranged on rungs Note in PLC Ladder Logic: No Real Power Flow (like in relay ladder) There must be continuous path through the contacts to energize the output Terminologies Power Rails Rungs
- 6. Ladder Diagram Binary Input Devices Device One/Zero Interpretation Limit switch Contact/no contact Photodetector Contact/no contact Pushbutton switch On/off Timer On/off Control relay Contact/no contact Circuit breaker Contact/no contact
- 7. Ladder Diagram Binary Output Devices Device One/Zero Interpretation Motor On/off Alarm buzzer On/off Lights On/off Control relay Contact/no contact Valves Closed/open Clutch Engaged/not engaged Solenoid Energised/not energised
- 8. Anatomy of Ladder Diagram o
- 9. Anatomy of Ladder Diagram 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 +24V 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.
- 10. Basic Ladder Logic Symbols
- 11. 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
- 15. Relay to Ladder Diagram
- 16. Relay to Ladder Diagram