What characteristic defines a closed loop system?

A closed loop system is characterized by its use of feedback to control input, allowing for adjustments based on the system's output. In such systems, the output is continually monitored, and this information is fed back into the system to modulate its performance, ensuring that it operates within desired parameters. This feedback mechanism is crucial for maintaining stability and accuracy in various applications, such as temperature control in reactors or speed regulation in machinery.

For instance, in a nuclear power plant, the control rods are adjusted based on the readings from sensors measuring the core temperature and fission reactions. This ensures that the reactor operates safely and efficiently by responding dynamically to the conditions present within the system.

In contrast, systems that operate in isolation do not interact with or adjust based on their surroundings, meaning they lack the feedback mechanism essential to closed loops. Similarly, relying solely on initial conditions would imply a predictive model without any adaptive changes based on real-time data. Lastly, a system that prevents any energy input would hinder performance by not allowing necessary adjustments, ultimately leading to inefficiency and potential failure. Therefore, the defining characteristic of a closed loop system is its reliance on feedback to control and optimize input.