Deadband

A range of signal change that produces no movement at the valve at all. On a trend that is the flat spot on the PV at every output reversal: lost motion, not a constant you retune.

Trend showing backlash: the process variable stays flat while the controller output reverses, then follows once the deadband has been taken up. Flat spots on the process variable exactly where the output changes direction. The width of the flat spot is the size of the deadband. This is lost motion in the linkage or the actuator coupling, not a tuning problem.

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What it means

Deadband is the amount the controller output has to change before the valve responds. It is most visible on reversals, where lost motion in the linkage has to be taken up before the stem moves in the new direction.

On a trend it shows as a flat section on the process variable occurring exactly where the output changes direction. The width of that flat spot, as a percentage of output travel, is the size of the deadband — a number worth measuring, because it is what the mechanical trade will want. That is the deadband meaning that matters on a plant: how much signal is lost before the stem moves. Searches for what is dead band in control system are the same idea: a range of command that produces no travel.

PID deadband on a Honeywell or similar block is a configured gap the controller ignores. Valve deadband is mechanical lost motion. Mixing the two is how a loop gets detuned for a packing problem. Measure the flat spot on a reversal; if it matches the configured gap, the block is doing what it was told. If it is larger, the valve is.

Also called

On a plant you will hear this called backlash, lost motion, dead band. They mean the same thing.

Questions that come up

What is deadband in a control valve?

A range of signal change that produces no movement at the valve. On a trend it is the flat spot on the PV at every output reversal: lost motion, not a constant you retune.

What is dead band in a control system?

The same idea as valve deadband: a range of command that produces no travel. Measure the width of the flat spot as a percent of output — that is the number the mechanical trade wants.

What is PID deadband?

On some faceplates, a configured gap the controller ignores so noise does not move the valve. That is not valve deadband. Valve deadband is lost motion in the stem; the configured gap is a choice. Measure the flat spot before you retune.

Glossary

Where this comes up

Written by PIDSnap control engineering. Published 2026-08-01, last reviewed 2026-10-22.