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Beat Frequencies

Beat Frequencies

Beat Frequencies

I am trying to understand a ventilation module here. It contains six fans, and it is attached through anti-vibration mounts. The fans are capable of disturbing the system that is being cooled. I am assuming that the fans all do not run at exactly the same speed, so there should some sort of beat frequency. I have modeled and graphed this in Excel and I can see beat amplitudes varying at somewhere between around 5Hz to around 1/10Hz. The actual vibration is at about 50Hz. I am accounting for centrifugal force. If the vibrations are at the frequency of the impeller blades, things are way more complicated.

Are these beat amplitudes equivalent to vibrations, or is this just a 50Hz system with varying amplitude?


RE: Beat Frequencies

I spent about a year working on a heterodyning problem. In that time I never got a good handle on an analytical method that could differentiate between a variable amplitude single frequency and a heterodyning pair of frequencies. I actually knew the root causes of the two signals so this was not an issue for me on that problem. I don't know if that helps!


Greg Locock

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RE: Beat Frequencies


I am not surprised that you couldn't. My spreadsheet model generates crazy shapes that are wildly different every time I run it. The results look really cool.


RE: Beat Frequencies

Are these actual fans?
Can you measure their respective rpms to a few cpm ?
Are there actual vibration measurements , made with enuff resolution to see a fraction of a Hz/ a few cpm ?

RE: Beat Frequencies


There are actual fans, but I cannot get at them at the moment. They are being ant-vibration mounted, so there is a history of them disturbing the system. I am not certain the anti-vibration mounts will work, and I am trying to understand the system.


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