Performance comparison of robust laser interferometer (RLI) and contact accelerometer technology in aviation health monitoring

Accelerometer systems are commonly employed in aviation health and usage monitoring systems (HUMS) and other aviation diagnostic and prognostic system approaches. Over the past decade, an research and development (R&D) robust laser interferometer (RLI) has been employed in a variety of aviation component health measurement situations, and in a variety of functional measurement situations of potential significance for aviation system health. Examples of RLI measurement data are taken from gearbox and turbine jet engine test cell measurements and from laboratory measurements that involve both controlled and empirical experiments. Selected simulation data is also used to validate aspects of the differences in performance that are anticipated when comparing both a quality contact (accelerometer) system implementation and the non-contact (RLI) measurement system. Dynamic and environmental parameters of concern were selected from an article by Jon Wilson in Sensor Magazine (March 1999) entitled "Dynamic and Environmental Effects on Performance Parameters". The dynamic parameters include: sensitivity/signal-to-noise; dynamic range; amplitude frequency response; phase frequency response; amplitude non-linearity; transverse sensitivity; and mass and size. The environmental parameters include: temperature; thermal transmit sensitivity; base strain sensitivity; electromagnetic sensitivity; acoustic sensitivity; radioactive environments; humidity; grounding/electrical isolation; and placebo/noise monitor control. Additionally, other factors are addressed including bandpass differences in terms of total bandpass, high frequency performance and low frequency performance. Observations are also included that address potential user interest beyond performance. Examples include implementation alternatives, integration considerations, cost considerations and an outline of the remaining work that need to be accomplished for introducing a new generation of "advanced health and usage monitoring systems".