Abstract: The present invention is a tuning fork oscillator for detection and measurement of corrosive or foreign materials. The elements include a means for mechanical excitation, and a mechanical oscillator, wherein said mechanical oscillator has a resonant frequency, f, and a quality factor, Q. A fuse fixed to the oscillator to change oscillator amplitude to or from essentially zero to resonance amplitude. In a preferred embodiment, the tuning fork has one region compatible with the service fluid and the other region is incompatible with the service fluid or other contaminant. The sensor alarms when a measured amount of the incompatible material has been removed or deposited.