Computer Science · Cheatsheet
Topic 6 · Control Systems (HL)
Chapter 1 · Open vs closed loop
📋 Reference · always available
Control system
Uses input commands to MANAGE the behaviour of another (usually physical) system.
Open loop
Runs a fixed action; NO feedback. Simple, cheap, BRITTLE. Toaster timer, microwave, traffic lights.
Closed loop
Sensor measures output → controller compares to target → adjusts. Self-correcting. Thermostat, cruise control.
4 parts (closed-loop)
SENSOR → CONTROLLER → ACTUATOR → PROCESS → (back to sensor). MEMORISE IN ORDER.
Setpoint
The TARGET value (e.g. 20°C on thermostat). Error = setpoint − measured.
When open-loop is right
Predictable system + small disturbances + low cost of error + sensors too expensive.
When closed-loop is required
Disturbances common + accuracy matters + stakes high (flight, medical, vehicle).