IntermediateTopic 44 of 101Signals, Control & Comms
Open-loop vs closed-loop
Closed-loop systems use measured output to correct error.
In depth
Open-loop control applies a predetermined input without measuring output (washing machine timer): simple but sensitive to disturbances. Closed-loop (feedback) measures output, compares with reference and corrects error: more accurate and robust but can become unstable and needs sensors.
Key points
- Sensitivity to parameter changes
- Loop gain
- Feedback and noise
ExampleA toaster is open loop; an oven with a thermostat is closed loop.
Closed-loop control reduces sensitivity to disturbances and model errors, but it can also cause instability, so the design must balance both.
What is Open-loop vs closed-loop?
Closed-loop systems use measured output to correct error.
Why is it important to understand open-loop vs closed-loop?
Closed-loop control reduces sensitivity to disturbances and model errors, but it can also cause instability, so the design must balance both.
What is open-loop control?
A system with no measurement of the output, so it cannot correct for disturbances or errors in the model.
What is the risk of feedback?
High gain or delay can make the loop oscillate or become unstable, so the design must check margins.
How is Open-loop vs closed-loop used in practice?
Typical applications include comparing a toaster timer that runs open loop with a thermostat that uses feedback, holding a cruise control speed on a hill and correcting an error in a robot joint from encoder feedback.
What should I learn before Open-loop vs closed-loop?
Study "Introduction to control systems" first (topic 43 of 101 in Signals, Control & Comms). It covers the groundwork this topic builds on.
What are the key points of Open-loop vs closed-loop?
Sensitivity to parameter changes. Loop gain. Feedback and noise.
Can you give an example of Open-loop vs closed-loop?
A toaster is open loop; an oven with a thermostat is closed loop.
What comes after Open-loop vs closed-loop?
The next topic is "Plant, sensor, controller, actuator", which builds directly on this one.
How difficult is Open-loop vs closed-loop?
It is classed as Intermediate in Signals, Control & Comms (topic 44 of 101). It is an intermediate topic. Work through the beginner topics in Signals, Control & Comms first.