Rotational ODS+OMA


The Rotational ODS+OMA package is a Soft- and Hardware solution to determine the modal values (natural frequencies, damping and mode shapes) of rotating parts under operating conditions. Required for the measurements are one or more vibration transducers that rotate with the shaft. The identification of the modal values is processed by the Operational Modal Analysis Software (OMA) named ARTeMIS Extractor. Non rotating measurements points can also be considered in the identification of modal values.


The  Rotational  OMA+ODS  System  is  especially designed  and  developed  to  do  structural  testing  of rotating  parts  during operation.  Next  to  the  classic operation  deflection  shape  method  (ODS)  it‘s  now possible  to  evaluate  the  modal  values  (natural  frequencies,  damping  and  mode  shapes)  by  using operational  modal  analysis  algorithms  (OMA).  The vibration  measurements  are  done  by  transducers which  are  mounted  on  the  rotating  shaft.

The measurement signals can be transmitted either by telemetry or by slip ring. As an alternative for slow rotating components MAUL-THEET offers compact autonomous front ends, which can be applied directly to the rotating test object and which transmit the signals via WLAN.

Because the angular position is measured the position of the rotating sensors can be calculated to any time. So the signal blocks can be build and analyzed for the local angle ranges. This data is saved and can be evaluated later with the analysis program MAUL-THEET ODS or ARTeMIS Extractor (OMA).

By the Rotational operation deflection shapes analysis (Rotational ODS) time blocks of different length can be extracted, because it can be chosen how the circle of sensor position should be divided. These blocks can be weighted by FFT Windows (Hanning for example) and than be transformed into frequency domain by FFT. Under consideration of the angular position of the sensors a coordinate transformation is done and as by a usual ODS the Auto- and Cross spectra can be calculated.

Next  to  the  calculation  and  animation  of  vibration shapes Rotational ODS offers additional useful tools and displays:

Polar plot Amplitude vs. Rotation Angle

Amplitude Ration vs. Rotation Angle

Frequency vs. Rotation Angle

Phase vs. Rotation Angle

Waterfall– and contour plots

Rotational OMA

The Rotational OMA Module can generate complete data sets for the operational modal analysis software ARTeMIS Extractor. This data sets contains:

Wire frame model geometry by points, lines and surfaces

The channel assignment for each measurement,

The vibration data as time series.

This data sets can directly be transferred to the ARTeMIS Extractor. For the estimation of the modal values all known algorithms offered by ARTeMIS Extractor are available:

FDD (Frequency Domain Decomposition),

EFDD(Enhanced FDD),

SSI (Stochastic Subspace Identification).

The calculated modal values can be listed charts and mode shapes can be animated by an extensive animation module. In addition to that ARTeMIS Extractor offers various tools to validate the modal data:

Overlay of mode shapes,

Stabilization plots,

Modal Assurance Criteria (MAC).


The Rotational package can be used to analyse

Brake Discs

Wind Mills

Diesel Engines


Industrial Fans

Ship Tansmissions

Ship Propeller


The OMA+ODS package was developed in close cooperation with our customer Continental Teves AG (hydraulic breaking systems, Frankfurt) for the use at rotating breaking disks. We are glad that the fully developed Rotational OMA+ODS package is now available for all our customers.