During a step test for a FOPDT model, which value represents the dead time L?

• A. The delay before the response starts
• B. The final steady-state gain
• C. The rise time
• D. The bandwidth limit

Answer: (A)

Dead time in a FOPDT model is the pure delay between when you apply a change to the input and when the process output first starts to respond. In a step test, you look for the moment the output begins to move after the input step; that interval is L. The final steady-state gain is the gain K you reach after the transient, the rise time is set by the time constant T, and bandwidth limit isn’t part of the standard FOPDT description. So the value that represents dead time is the delay before the response starts.