In a periodic test plan for a pressure switch, what potentially dangerous failure is NOT detected if the differential pressure is not raised?

• A. Shorted switch contacts
• B. Plugged pressure ports
• C. Switch movement jammed
• D. Broken switch housing

Answer: (A)

The correct answer indicates the failure mode that would not be detected when the differential pressure is not raised. A shorted switch contact scenario typically results in a situation where the switch falsely indicates either an open or closed position without relying on the differential pressure change. This means that even if the pressure difference remains unchanged, the switch's output could still indicate a fault state due to the contact being shorted, effectively masking the actual condition of the system.

In a well-designed testing framework, other failure modes like plugged pressure ports, which would prevent the pressure switch from properly sensing changes in pressure, and switch movement jamming, which would impede the actual mechanism needed for response, would be more likely to be detected through a rise in differential pressure. The broken switch housing could lead to external issues impacting functionality, which may be identified via other testing or monitoring methods as well.

Thus, it's the nature of shorted contacts to be undetectable under unchanged pressure conditions, which highlights why this particular failure mode is not identified when the differential pressure is not raised.