Glossary · Automation fundamentals, platforms and components
Dead time
Also known as: Transport delay, Time delay
German: Totzeit
In control engineering, dead time is the interval between a change of an input to a system and the start of the system's response, typically caused by transport of material or signals.
- Automation components
- Standards
- Process industry
In one sentence
Dead time is the delay between a change at a system's input and the start of its response, often caused by transport of material.
Example
A conveyor carries material from the dosing screw to a weighing belt in 20 s, so the weight controller sees the effect of a change only after this dead time.
How it applies
- Engineering: Dead time makes control loops harder to tune and can cause oscillation. Remedies include moving sensors closer, feedforward, Smith predictors or Model predictive control (MPC).
- Commissioning: Step tests reveal dead time as the period before the process variable moves.
- Documentation: Loop descriptions can note significant dead times and why tuning is deliberately slow; operators then understand why the process reacts late.
- Operation: Operators who adjust setpoints manually should wait for the dead time to pass before correcting again, otherwise they overshoot.
Dead time vs. time constant
Dead time is a pure delay with no response at all. A time constant describes how quickly a response develops once it has started. Many processes show both, and the ratio between them strongly influences controllability.