Systems Thinking
Feedback & Control
14 minStudent plan
Open loop versus closed loop, why feedback can make a system worse, and what makes a control system stable.
After this lesson you can
- Tell open loop from closed loop, and pick one
- Say why a system oscillates
- Explain what stability margin buys you
Open loop and closed loop
An open-loop system acts without checking the result. A motor given 60% power turns at whatever speed that produces, which changes with battery voltage, load and temperature.
A closed-loop system measures the result and corrects. It compares the measured value with the target, and the difference is the error. The controller's job is to drive that error to zero.
Closed loop is not automatically better. It costs a sensor, and it introduces the possibility of instability that open loop simply does not have. Where the disturbance is small and predictable, open loop is often the right engineering answer, a stepper motor holds position perfectly well without a position sensor.
In the full lesson
- Open loop and closed loop
- Why systems oscillate
- Gain, stability and margin
This lesson comes with the Student plan. The first module of Engineering Foundations is free.