Closed loop

Closed loop or closed-loop may refer to:

• Loop (topology), topological path whose initial point is equal to its terminal point
• Closed curve, the image of a continuous mapping of a circle

• Closed-loop controller, control law that uses knowledge of the state or output
  • Closed-loop transfer function, mathematical function describing the net result of the effects of a feedback control loop on the input signal to the plant under control
  • Electronic feedback loop
  • Proportional–integral–derivative controller (PID), type of feedback controller using three terms (P, I, and D)
• Closed ecological system, ecosystem that does not exchange matter with the exterior
• Closed-loop communication, communication technique in which every received message is confirmed by the sender
• Ecological sanitation systems (or ecosan), approach to sanitation provision which aims to safely reuse excreta in agriculture

• Circular economy, with materials recycled
• Closed time loop, a paradox of time travel
• Knot loop, in a knot