For the life of me, I can't remember what these lines are called on typical Waterfall plots. I had a document explaining them in detail, including why they occur and issues surrounding their presence, but I cannot find the document without remembering what they're called.
They appear on Waterfall plots, most often when plotting Sound or Vibration, versus RPM, versus Frequency. I have highlighted an example in the plot below. If anyone can simply tell me their technical term, I'd very much appreciate it.
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I think they're call Pulse Width Modulation, usually happen in electric motors.
Here I found two FAQs:
Wow. Thanks for the quick reply.
That's a little different that the (non-Siemens) document I remember reading on these, but that document may have been dealing more with IC engines. Your explanation makes more sense in my application, because we do use PWM for driving our electric motors.
Now that you have provided the definition of these lines, I can research potential issues of operating in a range where one of the normal (non-offset) orders crosses one of these PWM (offset) orders (like operating at a resonance).