Define order of operations (e.g., pump startup, conveyor chain) with interlocks and delays.
🔧 Sequence Logic Design (Ladder/ST/Function Blocks):
| Step | Action |
|---|---|
| 1 | List steps (e.g., Step 1 – Close valve, Step 2 – Start pump, etc.). |
| 2 | Define step enable conditions (AND of prior step complete, safety interlock, manual request). |
| 3 | Use step memory bits (e.g., Seq_Step_1_Active) and advance using R_TRIG or Timers. |
| 4 | Add reset or fault override logic. |
| 5 | Use structured logic blocks per step: avoid spaghetti code. |
🔧 Example: Step Transition Condition
ladderCopyEditIF Step_1_Complete AND Start_Command THEN Step_2_Enable
🧠Tip:
Use SFC (Sequential Function Charts) for more advanced sequence control and visual logic.
âś… Final Pro Tips:
- Document everything: Every fail-safe condition, state logic, and sequence should be in the FDS (Functional Design Spec).
- Modularize your code: Keep state machines, sequence logic, and safety logic separate but coordinated.
- Use simulation tools (like Siemens PLCSIM, Codesys Visualizations) to test logic before going on-site.