Sine on Random (SoR) Test
Some vibration environments are characterized by quasi-periodic excitation from reciprocating or rotating machines (like rotor blades, propellers, or pistons). A good way to simulate this is with one or more high-level narrow-band or sinusoidal vibration components superimposed on a low-level broadband random profile. These are called mixed-mode random tests.
There are two types of mixed mode random tests supported in EDM: Sine on Random (SoR) and Random On Random (RoR). In each of these test types, an additional vibration profile is placed on top of the regular broadband random profile. In Sine On Random, this additional profile consists of one or more sine waves that sweep through a specified frequency range. The random profile may represent a base excitation or background noise level, and the sine waves represent strong single-frequency excitation. This mimics some real-world situations better than a random test by itself.
A typical profile of SoR described in Mil-810F is shown below. Note that the random broadband profile is defined in units of Power Spectral Density, or g2/Hz, while the sine components are specified as amplitudes in units of g.
When SoR is running, the sine tone or tones will be shown superimposed on the broadband random profile.
Crystal Instruments Spider controller has powerful Sine on Random function that allows to have up to 12 independent sine tones, or up to 20 harmonic tones. The sine tone operation can be controlled manually using control buttons, or through a predefined schedule. Each sweeping tone can has its own sweeping range and speed. A hardware system with up to 512 input channels can be constructed using Spider-HUB switch connection.
When signals are displayed, it can be either displayed in G2/Hz the power spectral density, which is suitable for measuring the random signals, or displayed in G-peak which is more suitable for measuring the amplitudes of sine tones.