How is a "feedback loop" defined in control systems?

A feedback loop in control systems is defined as a circuit where the output is fed back into the system. This concept is fundamental in control theory, where the purpose of the feedback is to compare the output of a system to the desired reference or setpoint. By sending output information back into the system, control mechanisms can adjust the input based on the disparity between the actual output and the desired output. This self-regulating feature allows the system to maintain stability, improve accuracy, and correct any deviations from the setpoint.

In contrast, relying solely on external inputs, as suggested in one of the choices, does not encapsulate the essence of feedback; feedback requires interaction between output and input. Similarly, while having a process that maintains a constant output is beneficial, it does not alone define a feedback loop. Maintaining constant output can occur without any feedback mechanism. The idea of reducing system complexity does not speak to the function of feedback loops either, as feedback loops can introduce complexity into a system while enhancing its control capabilities. Thus, the concept of feeding output back into the system is what distinctly characterizes feedback loops in control systems.