What is a 'hard alarm' vs 'soft alarm' in a DDC system?

• A. Hard alarm is a defined fault with immediate audible/visual alert; soft alarm is a programmable condition that may not trigger hardware interlocks.
• B. Hard alarm always silent; soft alarm triggers hardware interlocks.
• C. Hard alarm is a software notification; soft alarm is a physical interlock.
• D. Hard alarm and soft alarm are identical.

Answer: (A)

In a DDC system, alarms are used to warn operators about conditions that require attention, and they come in two main flavors: hard alarms and soft alarms. A hard alarm represents a defined fault that demands immediate notice and action. It has a clear, built-in response in the control logic, typically with audible or visual alerts to grab attention, and it often engages hardware interlocks or trips to protect equipment and safety. Think of a sensor failure or a valve stuck in a fault condition—these are situations where the system must stop or take a protective action right away.

Soft alarms are programmable conditions or notifications that indicate something to monitor, but they aren’t necessarily faults. They usually appear on the operator screen, are logged, and can be acknowledged or silenced. They may be used to flag trends, abnormal but non-critical deviations, or conditions that don’t require automatic shutdown unless the operator decides to escalate. Because they’re not tied to mandatory safety interlocks, soft alarms generally don’t trigger hardware interlocks by themselves.

So, the best way to describe the distinction is that a hard alarm is a defined fault with immediate alerts and potential interlocks, while a soft alarm is a configurable condition that may not trigger hardware protections.