EKS-HUM-024 / Condensation, measurement and control

Control Deadband

控制死区

A control deadband is a defined range of the controlled variable or error within which the controller makes no new corrective action or does not switch state.

Aliases: control dead band, neutral zone, switching differential

QUANTITY, SYMBOL AND UNIT

Quantity / objectControl dead band

SymbolΔx_db

UnitNot applicable

Definition

A control deadband is a defined range of the controlled variable or error within which the controller makes no new corrective action or does not switch state.

In two-position humidity control, separate on and off thresholds can reduce rapid cycling. In other controllers, a neutral zone or error dead band may have a different implementation, so the upper threshold, lower threshold and action direction must be stated.

Formula and variables

Δx_db = x_upper - x_lower

Conditions: Use only after defining which thresholds are upper and lower and whether the controller is two-position, neutral-zone or digital error-dead-band control. Units follow the controlled variable.

Symbol	Meaning	Unit
`Δx_db`	dead-band width	same as controlled variable
`x_upper`	upper action threshold	same as controlled variable
`x_lower`	lower action threshold	same as controlled variable

Relations and distinctions

Dead band and setpoint

The setpoint is the desired value; the dead band describes a range of no action or separated switching thresholds around the control logic.

Dead band and uncertainty

Dead band is a deliberate control setting. Measurement uncertainty describes doubt associated with the measured value.

Engineering meaning

Choose switching thresholds with sensor noise, process lag, equipment cycling limits and acceptable humidity variation in view.
Document whether the stated value is total width, plus/minus half-width, hysteresis or an on/off differential.

Common misconceptions

MisconceptionA narrow deadband always gives more accurate and stable humidity control.

Accurate explanationIf it is too narrow for the sensor noise and process lag, equipment may cycle excessively without improving the actual space condition.

Application boundaries

Dead-band terminology and display conventions vary by controller manufacturer.
Dead band does not correct sensor bias, poor location, insufficient capacity or long process delays.

Supporting sources

ASHRAE / SRC-ASHRAE-F17-CH07

ASHRAE Handbook - Fundamentals, Chapter 7: Fundamentals of Control ↗

2017 IP edition / Chapter 7, two-position differential lines 50–55, dead-band thermostat lines 345–354 and digital error dead band line 698
Supports: Two-position controller differential is the difference between action settings; A dead band is a neutral range without control action; Digital error dead bands can suppress unnecessary actions near set point

Maintenance record