Measurement Methodology: Blade Tip Timing: A Non-Contact Blade Vibration Measurement Method

Abstract

Rotor blades are widely used in large turbine equipment such as aero-engines and gas turbines. The stable operation of these machines is largely dependent on the condition of the blades. In gas turbines and compressors, blade failure is mostly caused by foreign object damage (FOD), manufacturing defects and material defects. To ensure the rationality of blade design and the stability of the whole system, reliable blade on-line monitoring is the foundation [1]. Blade tip timing (BTT) is a potential method of blade vibration monitoring. It does not need to contact the blade, which can realize the whole-stage blade vibration monitoring by a few numbers of probes. The traditional method of vibration monitoring with strain gauges requires the complex telemetry system and even adjustment of the rotor structure. In contrast, the BTT method is simple and efficient; however, the disadvantage is that the signal is under-sampled. Various methods have been developed in recent decades to overcome undersampling. In this article, you will see how to sample blade tip displacement using the BTT method, what constitutes a BTT measurement system, and how to overcome undersampling and extract the vibration parameters from BTT signals.