A calibration technique for non contact measurement systems of jet engine blades vibration during operation

Blade tip timing (BTT) measurement systems enable the measurement of blade vibrations by means of contactless sensors mounted in the engine casing. Despite this sophisticated and expensive instrumentation is commercially available since years, there is no simple and standard laboratory procedure to calibrate a tip timing system. Performance of BTT measurement systems sensors and processing methods are often referred to contact measurements performed by strain gauges glued on the rotating blades. This paper describes a BTT signal simulation software and a calibration bench both useful for any kind of BTT measurement systems. The structure and the concepts behind the calibration technique are presented. The calibration bench it is based on the blade motion decomposition. Numerical and experimental simulations of typical cases are presented. Advantages and limitations of the proposed simulations tools and calibration test bench are pointed out.