The big idea: Every control system is the same loop — sense, decide, act, measure again. What changes between applications is the consequence of getting it wrong.
That consequence is what decides how the system must be engineered.
| System | Senses | Acts on | Failure means |
|---|---|---|---|
| Cruise control | Wheel speed | Throttle | Uncomfortable, or unsafe |
| Traffic lights | Vehicle loops, timers | Light phases | Congestion, or collisions |
| Pacemaker | Heart rhythm | Electrical pulse | Death |
| Smart heating | Room temperature | Boiler, valves | Discomfort, wasted energy |
| Production line | Position, weight | Motors, arms | Damaged goods, injury |
Free preview
This is the free notes preview
You're reading the free notes. Aimnova Pro unlocks the full study experience — and you can try it with your first topic free to keep:
- FlashcardsLock in vocabulary and key terms with spaced repetition.
- Practice questionsAnswer exam-style questions and get instant AI marking.
- Mock exams & past-paper vaultSit full mocks and see exactly how examiners award marks.
- Personalised study planA daily plan built around your exam date and weak areas.
Safety-critical
- Redundant sensors, so one failure is detected not obeyed
- A fail-safe state defined in advance
- Hard real-time — a missed deadline is a failure
- Certified, and deliberately simple code
Important but not critical
- One sensor, with plausibility checks on its readings
- Degrade gracefully — fall back to a timer
- Soft real-time — late is worse, not fatal
Convenience
- Cheap sensors, best effort
- A failure is an annoyance
- Cost dominates the design
A failed sensor reading zero looks like a real zero: A disconnected temperature sensor may report 0°C. The controller obeys it and heats at full power into an already warm room.
This is why critical systems use more than one sensor and compare them — a reading that disagrees with its neighbours is treated as a fault, not as truth.
See how examiners mark answers
Access past paper questions with model answers. Learn exactly what earns marks and what doesn't.
What changes as systems take more decisions
- A thermostat's mistake costs comfort; a vehicle's costs lives
- Responsibility blurs — the manufacturer, the programmer, the operator, or the owner?
- Deskilling: operators who never intervene lose the ability to when they must
- Automation bias: people trust a usually-correct system and stop checking it
- And the failure may be in software that was never physically inspected
Tie the ethics to the mechanism: The strongest answers connect the two: "because the system acts without asking, a sensor fault becomes a physical action before any person can intervene — which is why redundancy is a safety requirement and not an optimisation."
That sentence is doing both halves of the question at once.
How this is tested — you must apply the same loop to an unfamiliar scenario and engineer it for the consequence of failure. It comes up two ways:
Paper 1 Section A
- Explain the use of control systems in real-world applications, 3-5 marks
- Identify sensors and actuators in a described system
- State one benefit of automation here
Paper 1 Section B — case study
- Evaluate a safety-critical design
- Discuss responsibility when it fails
The classic trap: Listing components and stopping. The marks in this statement are for why this application is engineered the way it is — and that follows from what happens when it gets the answer wrong.
Explain how a control system keeps a train at a safe distance from the one ahead, and why its design differs from a domestic thermostat.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.