Closed loop

Closed loop may refer to:

• A feedback loop, often found in:
  • Control theory#Closed-loop transfer function, where a closed-loop controller may be used
  • Electronic feedback loops in electronic circuits
  • PID controller, a commonly used closed-loop controller
• Closed ecological system not relying on matter exchange outside of the system, as opposed to open loop
• Ecological sanitation systems or ecosan, intended to close the nutrient and water cycle
• Pulling water from one area of a reef aquarium and pumping it immediately elsewhere in the tank to create higher flow and minimize dead spots