Learning outcomes
- Explain the key principles of sequences, state machines and interlocks.
- Carry out a structured practical check or configuration task.
- Recognise common faults, risks and evidence needed for diagnosis.
Module 7 · Lesson 2
Sequences, state machines and interlocks
Program reliable automatic sequences with explicit states, transitions, timeouts and recovery paths.
Before you begin
Sequence narrative and simulator.
Safety: Use site procedures, approved test equipment and competent supervision. Never bypass a protection or interlock without formal control.
Step-by-step learning
- List all states and the permitted transition from each.
- Define transition conditions, timeout alarms and safe abort behaviour.
- Program manual, automatic and maintenance modes with clear authority.
- Test abnormal transitions, power failure and restart from every state.
Ian's practical tips:
- State machines make complex processes easier to test than scattered latches.
- Every sequence needs a defined safe destination when something goes wrong.
Fault-finding questions
- What should be happening, and what evidence proves it?
- Where is the last known correct signal, voltage, state or process condition?
- What changed immediately before the fault?
- Can the system be divided into smaller testable sections?
Practical activity
Create a one-page test record for this lesson. Include expected values, measured results, equipment used, risks controlled, defects found and the final proven condition.