Tip timing measurements using fiber optic sensors

Turbine blades are critical parts of aeronautic engines. They are subjected to high mechanical stresses at very high temperatures. In the event of breakage, the integrity of the engine, or even of the aircraft, can be compromised.

We use what we call “on/off probes” made out of bundles of fibers to perform the optical measurement that relies on the photon-emission/photon-reception principle.

An emitting fiber is used to illuminate the blades. The reflection on the blades is captured by the collecting fibers placed around the emitting fiber. The optical signals are then analyzed and interpreted using specific algorithms.

In aircraft engines, turbine blades are parts that operate at very high temperatures. SEDI-ATI designs quality optical probes that can withstand +600°C.

Tip-timing is involved in the qualification of engines and turboshafts. This technique enables to monitor the vibratory modes of turbine blades in operation and to detect possible blade deformations.

The campaign of tests consists in mounting optical sensors on the engine casing, in front of the blades, in order to measure their time of passage. The amplitude of vibration of each blade as it passes in front of the sensors can be deducted from the passage times of the blades and the speed of rotation.