Monitoring blade passage in turbomachinery through the engine case (no holes)

It is possible to detect passage of turbomachinery blades without penetrating the engine case. This "look through the wall" eddy current sensor eases the addition of a PHM system to an engine. This paper introduces this sensing concept, summarizes the physics, and presents results of preliminary tests. Blade material and geometry, case material, thickness and temperature, blade tip clearance, sensor detail and design and blade tip velocity all affect the strength and quality of the signal detected.