In alarm management, what is deadband?

• A. The threshold value for a high-priority alarm
• B. The time delay before an alarm activates
• C. The minimum change required to re-arm or clear an alarm
• D. The maximum allowed deviation before an alarm trips

Answer: (C)

Deadband is the defined minimum change the process variable must undergo after an alarm has occurred before the alarm can re-arm or clear. This creates a little hysteresis, so small fluctuations near the trip point don’t keep causing alarms. After an alarm trips, you either need the value to move back into a safe region by a sufficient amount to clear, or to move beyond the alarm point again by a sufficient amount to re-arm. This helps prevent nuisance alarms and rapid on/off cycling in noisy or fluctuating systems.

The threshold for triggering an alarm is not deadband itself—it’s the point that starts the alarm. A time delay describes how long the condition must persist before the alarm activates, not the amount of change required to reset. And a maximum deviation before tripping defines how far the signal can wander before the alarm trips, which is about initial triggering, not what’s needed to re-arm or clear afterward.