What is the role of alarms and fault diagnostics in DDC systems?

• A. Alarms notify operators of abnormal conditions.
• B. Fault diagnostics identify root causes of sensor or actuator failures.
• C. Alarms identify root causes of sensor or actuator failures.
• D. Fault diagnostics log energy usage.

Answer: (C)

In DDC systems, alarms and fault diagnostics play complementary roles in keeping the system healthy. Alarms are thresholds or event signals that alert operators when something is out of the normal range, so a human can respond quickly to potential issues. Fault diagnostics, on the other hand, digs deeper into the data from sensors and actuators to pinpoint the underlying cause of a failure—like a faulty sensor reading, a stuck actuator, or a degraded control loop. This targeted diagnosis lets maintenance teams identify what needs fixing rather than just knowing that something is wrong.

That’s why fault diagnostics is the right description here: it focuses on identifying the root causes of sensor or actuator failures, which is essential for efficient troubleshooting and repair. Alarms alert you to abnormal conditions, which is useful for immediate awareness, but they don’t explain why the condition occurred. Logging energy usage isn’t the primary role of fault diagnostics; energy data is typically handled by separate monitoring or analytics features.