Control systems
Trace input–process–output–feedback and explain how controllers, sensors, actuators, transducers and algorithms automate real systems.
A control system turns measurements into actions
- describe input, process, output and feedback in open- and closed-loop systems;
- describe controller, sensor, actuator, transducer and control-algorithm roles;
- explain control systems in several real-world applications;
- decide when feedback is essential to meeting a target condition.
Rapid Recall Deck
Attempt each card first. If a term is new, flip and study it, then answer it again without looking. Mark only secure recall as “Know it”.
Closed loop = action + measured consequence
Target temperature
│
v
[ Controller / control algorithm ] ──> [ Heater actuator ]
^ │
│ v
[ Temperature sensor ] <──── room temperature
feedbackTrace the closed loop
The target is 21°C and the sensor measures 18°C. Describe the role of each component until the room moves toward the target.
The temperature sensor/transducer measures the physical temperature and converts it into an input signal. The controller applies the control algorithm, compares the measurement with the 21°C target and sends an output signal to the heater actuator. The actuator changes the physical environment by heating. The sensor measures the resulting temperature again, providing feedback so the controller can reduce/stop heating as the target is reached.
Feedback changes the decision after observing the result
Open-loop timer
A garden sprinkler runs for exactly 10 minutes every morning and never measures soil moisture. Explain why this is open-loop and identify one limitation.
The controller produces an output based on a schedule but does not measure whether the soil actually needs water or whether watering achieved the target condition. Therefore no feedback corrects the action; it may over-water after rain or under-water during very dry conditions.
Close the loop
How could the sprinkler be redesigned as a closed-loop system?
Add a soil-moisture sensor and a target moisture level. The controller repeatedly compares measured moisture with the target and operates/stops the valve/pump actuator accordingly, using the new measurement as feedback.
Use terminology by mapping it to a real mechanism
Map the components
An automatic door uses a proximity sensor, a controller and an electric motor. Describe the input, process, output and the roles of sensor, transducer, controller, control algorithm and actuator.
The proximity sensor detects a person and transduces the physical condition into an electrical/digital input. The controller runs a control algorithm deciding whether the door should open/close. The motor is the actuator that converts the controller’s output signal into physical movement. The door movement is the output; a more advanced closed-loop door could also use position/safety sensors as feedback.
Transfer the same control model to different applications
Autonomous vehicle
Sensors measure surroundings/vehicle state; the controller processes these inputs and sends commands to steering/braking/throttle actuators. Feedback updates the next control decision.
Traffic signals
A controller can use timers and vehicle/pedestrian sensors to determine signal phases; adaptive systems use feedback about traffic demand.
Elevator
Position/door/load sensors provide inputs; the controller schedules movement and commands motor/door actuators while safety feedback constrains operation.
An explanation should show the signal/action chain
Explain one complete application
Choose home security, automatic washing machine or irrigation control. Explain how the system uses at least one sensor, a controller/control algorithm and an actuator. State whether feedback is used and why.
Example — irrigation: a moisture sensor measures soil state and transduces it to an input. The controller compares the reading with a threshold/target. If soil is too dry, it activates a pump/valve actuator; later moisture readings provide feedback and allow watering to stop when the target is reached. This is a closed-loop design because measured results alter later outputs.
Name the component, then explain what it does in the loop
Paper 1-style mini-set
1. Describe the role of a sensor and an actuator in a control system.
2. Distinguish open-loop from closed-loop control.
3. Explain how a home thermostat uses feedback.
- A sensor measures/detects a physical condition and provides an input; an actuator converts a controller output into physical action.
- Open-loop output is not corrected using measured consequences; closed-loop systems feed measured state/result back to the controller and adjust future output.
- The thermostat measures current temperature, compares it with the target, switches heating/cooling, then re-measures the changed temperature and adjusts output until the target range is maintained.
Finish the learning cycle
IA — main task
Continue Criterion D wrap-up and make sure your final implementation evidence is clearly linked to techniques and testing.
Paper 1 — short practice
Draw one open-loop and two closed-loop real-world control systems. Label sensor/transducer, controller, algorithm, actuator, input, output and feedback where applicable.