Signal Processing

Sensor signals are processed by its controller, which gives complete angular velocity information. In short, the frequency of the analog output signals from both interferometers are separated into a static component (dc fraction) and a dynamic component (ac fraction) of rotational speed.

After signal conditioning, the output signals of both interferometers are merged in a mixer stage, followed by a preprocessing block. Here, static and dynamic frequency components are sent to separate decoders, which operate as frequency-to-voltage converters.

Then, the static rpm and dynamic signal Δω are fed to separate outputs:

• Dc stationary rotation ω _DC : A constant component of the tangential velocity, which is proportional to the speed or rpm. Together, the beams yield correctly scaled rpm information, independent of radius.

• Ac rotational vibration Δω: The fluctuating component of the shaft rotation, which indicates angular or rotational vibration.

• The vibrational velocity signal Δω is also sent to an integrator block to provide angular displacement Δφ.

Any gross, lateral, non-vibration movement of the shaft is not measured, because it's detected by both laser beams, and discarded in the differencing process.

Data Processing

Rotational vibrometers together with data processing software can identify individual vibration frequencies, solve problems with noisy signals (and closely spaced and crossing orders) and plot the situation.

Software can generate contour plots, to help identify trouble frequencies.

Angular vibrational velocity, displacement, and rpm are sent downstream as analog output. These outputs can be used by signal processing software, such as order tracking analyzers. Or, some software analyze noise and vibration from time waveform and tachometer signals. This generates post-process vibration data and high-resolution spectral and order-based analyses for detailed diagnosis of machinery problems. Other features include spectrograms, color-contour plots, phase plots, 2 and 3D plotting, and Bode diagrams.

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Measuring all types of motion
	Measuring out-of-plane single-point vibration Single-point vibrometers measure the vibrations of an object in the laser beam direction. If aligned at a right angle to the object surface, it’s termed an out-of-plane vibrometer.
	Measuring out-of-plane differential vibration Differential vibrometers measure vibration between two points vibrating relative to each other. Specialized fiber-optic probes even examine locations difficult to access.
	Measuring in-plane vibration Measurements of vibrations in the surface plane — for example, at right angles to the optical axis. Some sensor-controller combinations can even monitor vee belts or pistons.
	Measuring rotational vibrations For measuring torsional vibrations of continuously rotating surfaces or angular vibrations of fixed surfaces. Output is independent of the surface shape.
	Measuring 3D vibration Three independent laser beams intersecting at the focus point allow vibration characterization in three dimensions.
	Mapping out-of-plane vibration over a surface: Deflection shapes Scanning vibrometers automate surface vibration measurement and visualization. Productivity is enhanced, eliminating the gluing, wiring, and processing of other methods, and improving accuracy.
	Mapping 3D vibration over a surface: Deflection shapes Complete 3D structural dynamics can be captured for an entire test object. This is useful for FE correlation and model validation; animations give excellent visualization of experimental results.