Field of Application
- To measure and characterize blade vibrations in turbomachinery
- Crack detection
- Mistuning detection
- Resonance frequency
- Resonance speed
- Engine Order
- Nodal diameter
The Tip Timing System is used for non-contact measurement and characterization of rotor blade vibrations in turbomachinery. The Tip Timing System at the TFD uses optical laser probes that operate according to the photo barrier principle. Several probes are mounted throughout the entire casing diameter. Each probe sends laser signals that are reflected by the blade tips when the blades pass through. This scattered light is transferred to a detector though an optical fiber. In this manner the time of arrival (TOA) of the blade is measured at the sensor position. When blade vibrations occur, the TOA of the blade deviates from the reference blade TOA due to the deflected blade tip, depending on the vibration mode. The time difference is then used to estimate the blade deflection. The system has eight probes and can measure on each rotor blade up to three blade vibrations simultaneously in the measured stage. By using comprehensive online and offline software, synchronous vibrations (forced response) as well as non-synchronous vibrations (flutter, stall/surge) can be analyzed in great detail. The system can also be used for crack detection, as cracks change the vibration characteristics of a blade, which then can be measured.
The TFD system can be also equipped with high temperature probes for measurements under high temperature conditions, e.g. turbocharger.
The advantages of Tip Timing Systems in comparison to conventional DMS measurements are:
- The non-invasiven method, which prevents a mechanical and/or aerodynamic influence on the vibration system
- All blades can be measured without any elaborate instrumentation. This system is especially suitable for mistuning measurements
- No telemetry is necessary because the probes are mounted in the casing
The TFD’s system is mobile and can be used at all test benches in the institute.
This measurement system is also described in the literature under the following terminology: Non-Intrusive Stress Measurement (NSMS), Arrival Time Analysis (ATA), Blade Tip Timing (BTT) or non-contact blade vibration measurements (Berührungslose Schaufelschwingungsmessung, BSSM).
You can find more information on the Tip Timing System of the TFD in the internet site of the production firm, Agilis Measurement Systems, Inc.