What is diagnostic coverage in safety-related systems?

• A. The total number of sensors in a system
• B. The fault-detection capability of safety components; higher coverage reduces residual risk
• C. The speed of fault detection
• D. The physical size of safety components

Answer: (B)

Diagnostic coverage is the fault-detection capability of safety components; higher coverage reduces residual risk. In functional safety, it measures how many potential faults in the system are detectable by built-in diagnostics, self-tests, and monitoring. When more faults are detected and corrected before they can cause unsafe behavior, the likelihood of a dangerous, undetected fault is lower, which lowers the residual risk of the safety function. This concept guides how much testing, monitoring, and redundancy a design needs to meet a given safety target. It isn’t about the number of sensors, the speed of fault detection, or the physical size of components.