FOCIS thumbPrime Photonics' FOCIS™ system is the most capable blade vibration measurement system available today.  This optical system times the passage of each blade and analyzes the data to determine blade vibrations.

 

FOCIS™ Optical Blade Vibration Monitoring System

The FOCIS™ system is an optical blade vibration monitoring system which measures blade tip timing. It detects the time of arrival of each blade by shining a laser at the blade tip and capturing the reflected light from the passage of every blade. Optical blade tip timing is the most accurate blade tip timing method, allowing quality blade vibration data that surpass any other method.

The FOCIS™ blade vibration monitoring system displays blade vibration data in real time and offers post-processing analysis capabilities for in-depth understanding of blade dynamics and blade vibration events.  The FOCIS™ system measures both synchronous and asynchronous blade vibrations for detection of blade deflection, vibration amplitude and frequency, flutter and stall events.

Campbell
Campbell Diagram displaying synchronous blade vibration

For more information about the FOCIS™ system, please read Details of FOCIS™ Blade Vibration Monitoring System.

Blade Vibration

Rotor blade vibration occurs in all turbomachinery including aircraft engines, steam and gas turbines, compressor systems and turbochargers. Undesired blade vibration can lead to high cycle fatigue (HCF) blade failures, low cycle fatigue (LCF) blade failures, flutter or be an indicator of an equipment health problem such as failing bearings. Understanding blade vibration is essential to validating new turbomachinery designs, making decisions about future designs, and in understanding how to operate equipment efficiently and safely.

Blade Vibration Monitoring Systems

Blade vibration has historically been measured via strain gauges.  This requires attaching strain gauges to the blades, which is not ideal because the mass of the strain gauge in itself might introduce perturbations.  Strain gauges also require wiring to carry the signal back to the stator portion.  Advancements have been made through the use of telemetry which offer an alternative to slip ring assemblies, but strain gauge measurement methods still require instrumentation of the blades and rotor.

Blade tip timing is a non-contact measurement method for determining blade vibration.  It relies on the measurement of the time of passage, also called Time Of Arrival (TOA), of every blade.  If the blades were not deflecting or vibrating, they would always have the same time of arrival.  Because they vibrate, the time of arrival varies.  Time of arrival is different for different sensing positions around the rotor, and it is also different at every turn for the same measurement position.  Precise timing of blades at several positions around the rotor gives a complete picture of blade vibration.

Due to its non-intrusive nature, blade tip timing is widely used for rotor blade vibration measurements, both as standalone tool and in conjunction with strain gauge-based vibratory analysis.   

For More Information

Details of FOCIS™ Blade Vibration Monitoring System