What does dead time mean in process dynamics?

What does dead time mean in process dynamics?

• A. A delay in sensor power-up.
• B. The time for the PV to reach final value.
• C. A delay between an input change and the corresponding PV response.
• D. The rate of change of the PV.

Answer: (C)

Dead time is the pure delay between changing an input and when the process variable first starts to respond. It comes from things like transport, sensing, or actuator lags, so nothing observable changes during that interval even though the input has changed. For example, opening a valve may take several seconds before the flow affects the level in a tank. This is modeled as a time delay in the process transfer function. It’s different from a lag, where the PV changes more slowly or is attenuated, and from settling time (the time to reach a final value) or rate of change (the derivative). So the best description is a delay between the input change and the PV response.

Dead time is the pure delay between changing an input and when the process variable first starts to respond. It comes from things like transport, sensing, or actuator lags, so nothing observable changes during that interval even though the input has changed. For example, opening a valve may take several seconds before the flow affects the level in a tank. This is modeled as a time delay in the process transfer function. It’s different from a lag, where the PV changes more slowly or is attenuated, and from settling time (the time to reach a final value) or rate of change (the derivative). So the best description is a delay between the input change and the PV response.