Andreas Zeisberger

Modern Telemetry Systems and Rotating Instrumentation

The knowledge of component stresses and operating conditions (pressure, temperature, vibration) within the rotating parts of aircraft engines and other turbomachines is essential to evaluate performance and load conditions. The rotating data acquisition is accomplished using telemetry systems that have to fulfill extremely high mechanical and thermal requirements. Despite these restrictions, an increasing number of measurement positions have to be recorded simultaneously with a very high bandwidth to resolve oscillations up to 50 kHz or even more. In the following, the requirements on a modern telemetry system will be presented in detail. In addition to the analogue systems used today MTU Aero Engines and Manner Sensortelemetrie have developed a new digital system that enables the simultaneous measurement of 48 dynamic channels with a bandwidth of 50 kHz and improved signal quality. The data is transmitted from the rotating to the stationary side using a high frequency carrier while the electric power is supplied inductively.Copyright

Total Temperature Measurement of Fast Air Streams With Fiber-Optic Bragg Grating Sensors

The suitability of using fiber Bragg gratings (FBG) as sensor elements in total temperature probes for turbine compressor applications is shown. A series of five FBG-based probes was built and characterized experimentally in the harsh environment of an open-jet test bench at air stream velocities of up to Mach 0.8. The performances of the FBG-based probes were compared with that of a conventional thermocouple-based total temperature sensor. All fiber-optic probes showed good mechanical robustness and recovery factors in the range of 0.79-0.99. Employing fiber-optic sensor elements allowed a significant reduction of the diameters of the stagnation tubes of the transducers. Because of the smaller probe design and thinner signal transmission cables, less distortion of the air stream is expected with the fiber-optic sensors, when compared with the conventional instrumentation.

Miniaturized total temperature probe based on fibre Bragg gratings

A miniaturized design of a fibre-optic based total temperature probe is presented which is intended to be used for aircraft engine testing. The FBG-based probes were experimentally characterized in the harsh environment of an open jet test bench at air stream velocities up to Mach numbers of 0.8 and they showed similar performance as conventional sensing techniques. The reduction of the size of the transducer was possible by using small sized FBG-based temperature sensors. Due to the smaller probe design and thinner signal transmission cables, less distortion of the air stream is expected with the fibre-optic sensor, when compared to conventional instrumentation. This allows a higher density of instrumented sensors and thus a higher spatial resolution of the measurement. This is, to our knowledge, the first demonstration of total temperature measurements at high air stream velocities with FBG-based transducers.