The correct answer is C. The explanation is as follows: 1. Confirm the correct answer: The correct answer is C) The detector mechanism consists of an armature suspended on a flexure pivot and restrained from motion by a permanent magnet acting through a small air gap. 2. Explain the reasoning: This description accurately depicts the typical vibration sensing device used with centrifugal separators on diesel vessels. The armature suspended on a flexure pivot and the permanent magnet restraint are the key components that allow the detector to sense abnormal vibrations and trigger an alarm or automatic shutdown. 3. Explain why the other options are incorrect: Option A is incorrect as vibration sensors are commonly used with centrifuges on diesel vessels. Option B is incorrect as the vibration switch is typically mounted to detect vertical vibrations, not horizontal. Option D is incorrect as the detector's purpose is to sense abnormal vibrations, not prevent critical speed range issues. 4. Concise explanation: The correct answer C accurately describes the vibration sensing device used with centrifugal separators on diesel vessels, which consists of an armature suspended on a flexure pivot and restrained by a permanent magnet to detect abnormal vibrations.