Which of the following defines the concept of "steady-state error"?

The concept of "steady-state error" is defined as the difference between the desired output and the actual output of a control system when the system has stabilized and reached equilibrium. In other words, once a control system is subjected to a specific input and allowed to reach a steady state, the performance of the system can be evaluated by comparing the setpoint (desired output) with the output it actually achieves. Steady-state error is crucial for understanding the accuracy and performance of control systems, as it shows how well the system can maintain the desired output level over time, despite any disturbances or variations that may occur.

In contrast, fluctuations during the control process relate more to the transient response of the system rather than steady-state performance. The time taken for the system to stabilize refers to the transient response time, which does not directly measure the difference between desired and actual outputs at equilibrium. The initial response describes how the system reacts immediately after an input change, again focusing on the transient behavior rather than steady-state conditions. Thus, the correct definition highlights the importance of steady-state conditions in evaluating system performance.