19 th World Conference on Non-Destructive Testing 2016 1 License: http://creativecommons.org/licenses/by/3.0/ Structural Health Monitoring of Compressor Blades with the use of Variable Reluctance Sensor and Impedance Method Miroslaw WITOS 1 , Michal WACHLACZENKO 1 1 Air Force Institute of Technology, Warsaw, Poland, Fax +48 261851612 Contact e-mail: witosm@itwl.pl; michal.wachlaczenko@itwl.pl Abstract. The comprehensive approach for rotating compressor blades diagnostic has been introduced in the paper: slow- and high-speed rotating fluid-flow machinery running at risk of mechanical damage (by foreign objects and erosion), corrosion and other forms of material fatigue (LCF, HCF, VHCF). Objects with variations of its magnetization due to Villari effect. For blades’ real operating condition and technical state monitoring purposes a impedance method has been used. Signal from magnetic reluctance sensor (VR) mounted above supervised rotating blade row has been recorded creating sort of an encoder which output signal contain simultaneous information about: - blade vibration induced by aerodynamic and mass force input; - instantaneous rotor rotation speed; - rotor vibration and unbalance; - coupling conditions of reluctance sensor with vibration and rotating blades. The sensor output voltage and current signal is measured which is used to instantaneous impedance Z(t) as well as reflectance coefficient Γ(t). On the basis on mentioned above measurements a numerical analysis was conducted to determine coupling conditions of sensor with blades and extract diagnostic symptoms representing blades’ stress magnetization level and sensor clearance. For numerical analysis purposes blade material was represented by real inductor – 5 element substitute circuit providing true transformation of Z(ω) and Γ(ω) characteristics in wide band of angular frequency ω. Discussed problem is supported with experimental data showing potential possibilities for blade tip-timing method development without necessary modifications of existing measurement system. Introduction Rotating fan, compressor and turbine blades are critical elements of the rotary machine. The blades are exposed to accelerated fatigue and operational degradation – Figure 1, resulting from:  influence of complex real working loads (quasi-static and dynamic), including adverse dynamic phenomena (stall, flutter, surge);  modal properties of the blade (resulting from its geometry and material parameters), including very low damping of vibration in resonance ranges;  influence of the environment and operating conditions on the health of the blade surface (corrosion, erosion, foreign objects, icing, salinity); More info about this article: http://ndt.net/?id=19613