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The paper presents fundamentals of a new method for monitoring of technical condition demonstrated by blades of rotor machines during operation thereof. The method involves the diagnostic model expressed as a quotient of the amplitude amplification for the diagnostic signal y(t) that results from the blade impact and the signal x(t) produced by the blade surrounding when the blade tip approaches the sensor, divided by the amplitude amplification of these signals when the blade tip has already passed the sensor position and moves away. The adopted diagnostic model takes account for current surrounding of the blade x(t) with no need of measurements of its parameters [12,14,15]

The paper reviews features and applications of the modified inductive sensor, able to operate in contact with exhaust gases of temperature even as high as 1200 K. The new design includes the metal-ceramic housing ensuring proper heat transfer, the magnetic circuit containing set of permanent magnets with various magnetic field values and Curie temperatures, the completely redesigned windings and current/voltage converter used instead of the electromotive force amplifier. Its principle of operation is based on electrodynamical interaction and therefore it may be referred as a passive eddy-current sensor. Two applications of the technique are presented such as blade vibration measurement in High Pressure Turbine of military turbofan (tip-timing) and speed monitoring of roller-element bearing supporting the shaft in a turbojet engine.