Dead time
The delay between a change at the output and the first sign of a response in the measurement.
What it means
Dead time is the interval during which absolutely nothing happens. Move the valve, and for some period the measurement does not change at all — the fluid has to travel, the heat has to conduct, the sample has to reach the analyser.
It is the single most important number in tuning, because it sets a hard limit on how well any controller can perform. A controller cannot correct for a disturbance it has not been told about, and dead time is exactly the period during which it has not been told. Loops with long dead time relative to their time constant are difficult regardless of tuning.
Dead time is also the reason reset can be set too fast. If integral action repeats faster than the dead time, the controller keeps adding correction while the previous one is still in transit, and the loop cycles by construction.
Also called
On a plant you will hear this called transport delay. They mean the same thing.
Related
Where this comes up
- Control valve hunting
- PID loop oscillating
- Valve position oscillates but the process variable barely moves
- Sluggish control loop
- Flow loop unstable
- Pump speed loop hunting
- Noisy PV and valve chattering
- DeltaV PID parameters explained
- Ovation PID parameters explained
- SIMATIC PCS 7 PID parameters explained
- Rockwell PIDE PID parameters explained
- Yokogawa Centum PID parameters explained
- Honeywell Experion PID parameters explained
- Foxboro I/A PID parameters explained
- ABB 800xA PID parameters explained
- GE Mark VIe PID parameters explained
- Mitsubishi MELSEC PID parameters explained
- Allen-Bradley PID parameters explained
- Schneider Modicon PID parameters explained
- How to tune a DeltaV PID
- How to tune a Rockwell PIDE
- How to tune a Honeywell PID
- PID tuning calculator
- FOPDT calculator
- Reset units converter
- Feedforward gain calculator
- Bump test procedure
- PID tuning cheat sheet
- How to tune a PID loop on a running plant
- Tuning flow control loops
- Tuning temperature control loops
- Tuning pump and fan speed loops
- Tuning pH control loops
- How to tune a cascade PID
- Fired heater and heat exchanger temperature
- Tuning analyzer and composition loops
- Time constant
- Process gain
- Cascade control
- Lambda tuning
- Bump test
- Ultimate gain
- First-order plus dead time (FOPDT)
- Cohen-Coon tuning
- Sample time
- Feedforward control
- Shrink and swell
- Derivative on the process variable
- Measurement filtering
- Smith predictor
Last reviewed 2026-09-18.