Control (HL): Sensors, Feedback and Embedded Systems
What the exam tests
Control tests how systems sense, decide and act. HL questions cover sensors, actuators, controllers, feedback, open- and closed-loop systems, embedded systems and the social implications of automation.
Core rules
- A control system has a sensor, a processor/controller, an actuator and an output; feedback compares the measured output with a target.
- Open-loop systems act without checking the result; closed-loop systems use feedback to correct error.
- A microcontroller is a self-contained chip with CPU, memory and I/O, often embedded in a device; a microprocessor is a CPU without that integration.
- Hysteresis creates a dead band so an actuator does not switch rapidly near the set point.
- Control systems raise issues of safety, reliability, privacy, employment and accountability.
Worked example
A thermostat has set point 21 °C. The sensor reads 19 °C; the controller turns the heater on. When the sensor reads 22 °C, the controller turns it off. Reasoning: this is closed-loop because the sensor feeds back the actual temperature. Without hysteresis the heater might switch on and off repeatedly around 21 °C; a 1 °C dead band reduces wear.
Traps
Calling a sensor an actuator; saying a thermostat is open-loop because it has a setting; ignoring feedback delay and oscillation; treating embedded systems as general-purpose PCs; forgetting ethical and safety implications.