A control system manages or regulates another system by receiving input, processing data and producing an output. In a closed-loop control system, feedback allows the system to compare the actual result with the desired result and make automatic adjustments.
How a control system works
A control system operates as a repeating sequence:
- Input: A sensor or user supplies data about the environment or the required state.
- Process: A controller applies programmed rules or an algorithm to the input data. It may compare a measured value with a set point, which is the desired value.
- Output: The controller sends a signal to an actuator, such as a motor, heater, valve or alarm.
- Feedback: A sensor measures the effect of the output and returns this information to the controller. The next output can then be adjusted.
For example, a heating system may have a set point of 22°C. A temperature sensor reports 19°C, so the controller activates the heater. Feedback from the sensor eventually reports 22°C, causing the controller to switch the heater off or reduce its output.
| System type | Operation | Example |
|---|---|---|
| Open-loop system | Produces output without measuring its effect; there is no feedback loop. | A toaster operating for a fixed time |
| Closed-loop system | Uses feedback to compare the actual state with the set point and correct deviations. | A thermostat-controlled heating system |
A common misconception is that every automated system uses feedback. An automated open-loop system can follow programmed instructions, but it cannot detect whether its output achieved the intended result.
Exam technique
For an IB question asking you to explain a control system, identify the input device or sensor, describe the processing decision, name the output device or actuator, and show how feedback changes later processing. Do not merely list the four stages; apply each stage explicitly to the given scenario and distinguish feedback from ordinary input data.
