What is the settling time in a control system?

• A. The time required for the response to reach the final value for the first time.
• B. The time required for the response to remain within a specified band around the final value after the transient.
• C. The time taken to reach the maximum overshoot.
• D. The time until the error first crosses zero.

Answer: (B)

Settling time is the time after a disturbance or input change when the system’s output stays within a chosen tolerance band around its final steady-state value, once the transient behavior has died out. You typically specify a band like ±2% or ±5% of the final value, and settling time is the moment after which the response remains inside that band for all following time. It’s not the time to first reach the final value (that’s rise time), nor the time to reach the maximum overshoot (peak time), nor the time when the error first crosses zero. For many second-order systems, settling time scales with damping and natural frequency, often described as a few time constants.