Automated and Emerging Technologies · 4 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 3% of your exam marks.
Sensor to microprocessor to actuator control loop questions. Usually 3 to 4 marks.
An automated system that just keeps running forever is only useful if it can respond to changes in the environment. The key idea that makes this possible is the feedback loop.
A feedback loop is the cycle by which the output of a system is fed back as an input, so that the system can compare its current state with the target state and adjust accordingly.
In an automated control system, the loop usually looks like this:
The output of the actuator changes the very thing that the sensor is measuring; that change feeds back into the next reading. This makes the system self-correcting.
A common distinction:
| Open-loop control | Closed-loop control | |
|---|---|---|
| Does the system use a feedback loop? | No | Yes |
| How does it decide what to do? | Follows a fixed sequence, regardless of what is actually happening | Continually checks the result and adjusts |
| Reacts to changes in the environment? | No | Yes |
| Example | A microwave running for exactly 30 seconds and then stopping (no sensor checking the food) | A central-heating thermostat that adjusts to the room temperature |
Almost every automated system in the syllabus is closed-loop, because the whole point of automation is that the machine adapts to its surroundings.
Example — A funfair attraction lines up several motion sensors along a track; each time a runner passes a sensor, the system fires a jet of water at them. Describe how the components cooperate to make this happen.