How to Interpret Multiple Peaks in a Bode Plot?

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Discussion Overview

The discussion revolves around the interpretation of multiple peaks in a Bode plot, specifically in the context of a nanopositioning system's frequency response. Participants explore the significance of these peaks, particularly the first peak, and whether subsequent peaks indicate noise or other system characteristics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the first peak represents a resonance frequency, while the significance of subsequent peaks remains unclear.
  • Others argue that determining whether the peaks are real or just measurement noise requires more detailed information about the system and the measurements taken.
  • A participant mentions that the graph measures the x-axis frequency response for nominal and payload conditions, suggesting that the nominal response is for an unloaded state compared to a maximum load state.
  • It is noted that increasing the load lowers the frequency of the first peak, which aligns with expectations for a loaded resonant system, and that a phase shift of 180° at that frequency confirms resonance.
  • Some participants suggest that the other peaks may correspond to additional system modes, such as transverse modes.
  • There is a suggestion that staying well below the first peak is advisable for achieving good closed-loop control.
  • Questions are raised about how the open-loop response will be utilized in closed-loop applications.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the peaks, with no consensus on whether the additional peaks are noise or indicative of other system behaviors. The discussion remains unresolved regarding the exact nature of these peaks.

Contextual Notes

Participants acknowledge limitations in the information provided, such as the definitions of nominal load and payload, and the need for more details to draw definitive conclusions about the measurements and their implications.

skyhj105
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I think that first peak of the graph represent a resonance frequeny but i don`t know some peaks which are located after first peak.
Is it a just noise? or some other?
 

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The measurement is what it is regardless of the names you assign to the peaks, so I'm not sure what you're really asking.

To determine if the plots are real or just measurement noise, one needs much more detail than you provided.
 
anorlunda said:
To determine if the plots are real or just measurement noise, one needs much more detail than you provided.

Thank you for your answer.
I `ll tell you more detail. The value what this plot measure is x-axis frequency response for nominal and payload.(I don`t konw meanig of nominal load and payload exactly... what is this?)
x-axis is one axis of nanopositioning system.
 
Sorry, that is still not enough information to answer your question.
 
skyhj105 said:
I `ll tell you more detail. The value what this plot measure is x-axis frequency response for nominal and payload.
The graph text suggests nominal response when unloaded, compared to response with a maximum load.
Payload is not mentioned. I would expect it to be somewhere between the two.

It appears that when the load is increased to the maximum, the frequency of the first peak is lower, which is what is expected from a loaded resonant system. The fact that the phase cleanly changes by 180° degrees at that frequency confirms that it is a resonance.

Can you give a reference for the scanned figure.
 
skyhj105 said:
I think that first peak of the graph represent a resonance frequeny but i don`t know some peaks which are located after first peak.
Is it a just noise? or some other?
The simple answer is that you should stay well below the first peak if you want good closed loop control.

The other peaks are other system modes probably, transverse modes etc...
 
MRFMengineer said:
The simple answer is that you should stay well below the first peak if you want good closed loop control.

The other peaks are other system modes probably, transverse modes etc...

You are looking at the open loop response of the system, how are you planning to use it? Closed loop?
 

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