Real-world control systems monitor an environment, process input against a desired state, and produce an output through actuators. Most repeatedly use feedback so that they can detect change and adjust their behaviour automatically.
The Control-System Mechanism
A sensor measures a physical condition, such as temperature, position, light, or distance. The measurement is converted into data and sent to a controller, which applies an algorithm to decide what action is required.
An actuator then changes the physical system. A new sensor reading indicates the effect of that action, forming a feedback loop.
These systems require real-time processing: data must be processed within a deadline for safe operation.
| System | Inputs and processing | Outputs and feedback |
|---|---|---|
| Thermostat | A temperature sensor compares room temperature with the set point. | Heating is switched on or off; later readings show whether the target has been reached. |
| Elevator | Position, speed, door, load, and button sensors provide data to the controller. | Motors move the lift; brakes and doors operate; sensors confirm safe position and movement. |
| Traffic lights | A fixed system follows timed instructions, while an adaptive system also processes vehicle or pedestrian data. | Lights change state; sensors provide feedback about traffic flow. |
| Self-driving car | Cameras, radar, lidar, GPS, and other sensors model the surroundings. Algorithms support perception, decision-making, and path planning. | Steering, braking, and acceleration actuators respond; continuous feedback allows rapid correction. |
A common misconception is that every control system uses feedback. A fixed-time traffic light can be an open-loop system because its output does not depend on measured traffic, whereas an adaptive light is a closed-loop system.
Exam Technique
For an IB response, trace the complete sequence from input to processing, output, and feedback. Apply each component to the named scenario, and explain why real-time response, reliability, or safety is important rather than merely listing hardware.
