2.2 - Robust and Miniaturized Non-Incremental Fiber-Optic Distance Sensor for Turbo Machine Rotor Deformation and Vibration Monitoring

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings OPTO 2011
O2 - 3D and Calibration
P. Dreier, T. Pfister, J. Czarske - Technische Universität Dresden (Germany)
42 - 47


In order to improve the safety, the lifetime, and the energy efficiency of turbo machines, the dynamic behaviour of the rotor has to be analyzed and optimized. Thus, rotor unbalances, dynamic deformations, and blade vibrations as well as blade tip clearance changes have to be monitored during operation for optimizing the rotor design and to validate numerical models. However, these are big challenges for metrology, since small, robust, and noncontact measurement techniques are required offering both micrometer accuracy and microsecond temporal resolution.
We recently developed a non-incremental laser Doppler distance sensor (LDDS) employing two superposed fan-shaped interference fringe systems with contrary fringe spacing gradients. Via the resulting two independent measuring channels, it measures simultaneously the in-plane velocity and the out-of-plane position of laterally moving objects with micrometer precision and concurrently with high temporal resolution. The outstanding feature of the LDDS is that its measurement uncertainty is generally independent of the object velocity, which enables precise deformation and vibration measurements also at high rotor speed. Moreover, this sensor does not require an in situ calibration and it allows measuring tip clearance as well as radial and lateral rotor vibrations simultaneously. Employing a rugged LDDS prototype with integrated water cooling, successful test measurements were accomplished at a transonic centrifugal compressor as well as at a vacuum high-speed rotor test rig.
In this contribution, we introduce a novel miniaturized and robust fiber-optic sensor setup employing diffractive micro-optics in combination with a special dispersion management scheme.The resulting sensor head is only 20 mm in diameter and less than 100 mm in length. A thermostable housing allows measurements at high ambient temperatures without active cooling which is crucial for application inside turbo machines.
We will give a thorough description of the innovative sensor design and of its numerical optimization using the software tool ZEMAX. In addition, experimental results will be presented demonstrating the capability of this sensor to measure deformations and vibrations of fast rotating objects, such as turbo machine rotors, even at high speed and at high ambient temperatures.