Which name is best applied to a peak at 3.1x in a vibration spectrum?

A peak at 3.1x in a vibration spectrum is best characterized as a non-synchronous peak. This terminology is used to describe frequency components that do not align with the fundamental rotational frequency of the machine or system being analyzed.

In many vibration analysis scenarios, the fundamental frequency corresponds to the rotational speed of the machinery, which would typically be referred to as 1x. Therefore, a peak at precisely 3.1x suggests a frequency that is not a direct harmonic of the fundamental frequency—instead, it reflects interactions or phenomena occurring at a different rate or due to other influences such as harmonics from other sources or modulating factors affecting the system.

Understanding this context is key in distinguishing between synchronous and non-synchronous vibrations. Synchronous peaks arise directly from periodic events in line with the fundamental frequency, while non-synchronous peaks indicate various potential issues or behaviors in mechanical systems, such as nonlinear effects, interactions among components, or the influence of external vibrations, making the term "non-synchronous" particularly fitting for a peak at 3.1x.