Generating an SoR Test Using Recorded Data (STAG)

February 23, 2021

A Sine-on-Random (SoR) test is the most accurate test method for replicating an environment with rotational components. However, there is no standard method of SoR test development, and the process of generating and accelerating both sine and random test profiles can be time-consuming and prone to error. Vibration Research released the Sine Tracking, Analysis and Generation tool (STAG) as an accurate and efficient option for SoR test development using recorded data.

Sine Tracking, Analysis and Generation (STAG)

SoR is a mixed-mode test with sine tones superimposed on a random background. The STAG tool uses recorded time history data from an engine run-up or coast down to generate the sinusoidal portion of the SoR test. Then, the data are exported to VibrationVIEW, where the random test profiles are generated and accelerated with the fatigue damage spectrum (FDS). Together, the sinusoidal and random test profiles constitute an accelerated SoR test that is the damage equivalent of the original environment.

As discussed in the previous lesson, the sinusoidal test profiles are processed separately with STAG because the FDS assumes all vibrations to be random. The STAG tool ensures that the sinusoidal vibration in the original environment is included in the SoR test and represented accurately.

Sinusoidal Test Profiles

Sinusoidal vibration from the rotating component(s) is processed with STAG in the ObserVIEW software package. The order content from the recorded time-history waveform is analyzed, and the vibration generated from the rotational source is identified. A reference RPM trace is required as it correlates to the measured vibration on the rotational equipment.

Frequencies corresponding to the reference RPM and its harmonics are designated as orders. The dominant orders are extracted to separate the sinusoidal content from the random. With STAG, the ten most significant orders are identified automatically, thereby saving processing time.

Sine test profile development in STAG

Using the dominant orders, the frequency ranges relating to the sinusoidal vibration are defined, and the sinusoidal test profiles are accelerated automatically. If necessary, the test engineer can review/adjust the automated profiles. Then, the parameters used to accelerate the sine profiles are copied to VibrationVIEW for the remainder of the SoR test development process.

Random Test Profiles

The remaining random vibration is processed with FDS in VibrationVIEW. As discussed in the FDS lesson, the FDS is used to generate an accelerated random test with time history data.

Using a rain flow algorithm and cycle counting, the FDS accounts for the damage from every peak-to-valley stress cycle in the time waveform and converts the damage into an appropriate relative damage number for each frequency bin. When combined, the relative damage numbers constitute the FDS-generated power spectral density.

Lastly, the accelerated sine and random test profiles are combined to create the final SoR test.


STAG can be used to generate an accurate representation of an environment with dominant sinusoidal vibration and background random vibration, such as an engine environment.

STAG reduces the processing time from tens of hours to seconds and generates an SoR test with a high level of accuracy. Developing an SoR test otherwise is achievable but requires specialized knowledge and significant time. The STAG tool reduces processing time, minimizes potential user error, and directly exports the data to a test profile that can be run on a shaker controller.

Download a free demo of the ObserVIEW software.