Noninterference blade-vibration measurement system for gas turbine engines

A noninterfering blade-vibration measurement system has been demonstrated in tests of a gas turbine firststage fan. Conceptual design of the system, including its theory, design of case mounted probes, and data acquisition and signal-processing hardware, was done in a previous effort. The current effort involved instrumentation of an engine fan stage with strain gages; data acquisition using shaft-mounted reference and casemounted optical probes; recording of data on a wideband tape recorder; and posttest processing using both off-line analysis in a facility computer and a minicomputer-based readout system designed for near-real time readout. Results are presented in terms of true blade-vibration frequencies, timeand frequency-dependent vibration amplitudes, and comparison of the optical noninterference results with strain-gage readings.