On-line compensation of axial fan blade angle in blade tip timing measurement

This article deals with the BTT method of blade vibration measurement used for condition monitoring of variable pitch axial fan blades. The efficiency of axial fans with variable pitch is controlled by adjustment of blade angle. BTT analysis may lead to incorrect results when only one BTT sensor is used for blade TOA measurement without consideration of the current blade angle and at least two sensors must be used. The method of blade vibration monitoring based on multiple BTT sensors is described in this paper. The suitability of the designed method is verified by a case study.