why are phase plots important?

Discussion in 'General Electronics Chat' started by jmdejoanelli, Mar 25, 2011.

  1. jmdejoanelli

    Thread Starter New Member

    Mar 13, 2011
    10
    1
    Hi all,

    I've been doing a lot of bode plots lately in my electronics classes and so far we are only ever really interested in the gain part of the plot.

    Can someone please explain to me why the phase part of the plot is important and perhaps an example where the phase plot is just as useful as the gain plot.

    Thanks,
    Josef
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    An interesting issue is the effect of using filtering for de-noising of signals. Filters (e.g. low pass) are often used to remove noise from signals. The 'problem' is that while the filter is good at removing the unwanted noise from the important signal information, the filtering process also produces phase changes in the signal of interest.

    Phase errors may or may not be important. A phase error may be important if one is using the filtered signal as part of a feedback control system - where, for instance, the filtered signal is coming from a noise prone process sensor. This phase error may influence the process stability or accuracy.

    Phase errors don't matter if one is only interested in the signal magnitude. For instance, if you only want to know the mean value of a noisy signal.
     
    Last edited: Mar 25, 2011
  3. jmdejoanelli

    Thread Starter New Member

    Mar 13, 2011
    10
    1
    Ok thanks mate, that actually makes sense now that I'm thinkin about feedback.

    Cheers!
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    I've actually been dealing with a practical problem of late that requires a de-noising filtering function without introducing time (phase) delays in observed data.

    I've played around with techniques such as Hilbert Transform, Savitzy-Golay filtering and (so-called) filt-filt (forward-reverse) functions. These produce reasonable results each with their strengths and limitations.

    You've asked an important question from my perspective. It bears some thinking about. As the the famous Bob Pease might put it - "What's all this phase plotting stuff, anyhow?"

    Cheers.
     
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