7.3. Closed Loop Control

A closed-loop control system uses feedback: it measures the output of the system, the process variable, and compares it to the desired goal (the setpoint). If there is an error, the controller adjusts the actuator until the output matches the target more closely.

Unlike open-loop systems, closed-loop systems can adapt to disturbances, changes in load, or variations in the environment. They are more complex, but they allow for much more accurate, reliable, and stable operation.

Examples:

• A thermostat keeps a room at a set temperature. When the temperature falls below the target, the heater switches on; when it rises above the target, the heater switches off.

• A car cruise control system measures the car’s speed and automatically adjusts the throttle to hold the speed constant, even on hills.

• A drone flight controller constantly measures its tilt and altitude, adjusting the motors to stay level and hover.

In each case, the system measures what’s happening, compares it to the setpoint, and uses that feedback to correct its actions.

Note

More details about specific closed-loop algorithms are found on the following pages.