Constant speed tip deflection determination using the instantaneous phase of blade tip timing data

Abstract

Blade Tip Timing (BTT) is a non-intrusive measurement technique that can be used to estimate the vibration characteristics of rotor blades during turbomachine operation. BTT uses proximity probes mounted into the turbomachine casing to measure the Time-of-Arrival (ToA) of rotor blades at these proximity probes. The ToAs are determined using a triggering criterion on the proximity probe signal. Rotor blade tip displacements are then calculated from these ToAs. It is therefore imperative that the triggering criterion be as accurate as possible. This article proposes a new method to determine the tip displacement of rotor blades from a proximity probe signal. The method first converts the signal into the angular domain and then obtains the tip deflection through manipulation of the instantaneous phase in the signal. Three experimental tests are conducted where existing triggering criteria are compared to the proposed method. It is found that the proposed method is highly accurate in determining the tip deflections for a constant rotor speed.