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Signal behavior with function generator
Circlotron:
DG1022Z with two sine waves locked together in frequency and phase. Was using it to drive two audio power amplifiers powering a small induction motor. Made life difficult to say the least.
https://youtu.be/Qg6sqLdAIs0
mawyatt:
--- Quote from: 2N3055 on December 06, 2022, 09:50:47 pm ---I looked at what Martin and Mike has shown, and couldn't reproduce it.
Then I went and checked: In Utility/Phase mode I had it set for INDEPENDENT phase mode. It perfectly transitions from frequency to frequency without discontinuity.
But...
If I set it for DEPENDENT phase mode it resets phase every time , because it has to start both CH from same phase..... There is no other good simple way to keep phase relationship for different channels (with different frequency and waveform) but to reset from change.
Thanks Mike for noticing "phase resets to zero on each frequency update" which made me look there...
Best,
--- End quote ---
That makes prefect sense with what you've described. When changed to "Independent" in the Phase Mode under Utility vs. "Phase-Locked" we get the phase continuous as you've shown earlier :)
Thanks for fretting this out and enlightening us as usual :-+
Best,
mawyatt:
So why does this discontinuous phase matter?
Normally it doesn't but one scenario comes mind, I'm sure there are others as well.
Consider making a Bode Plot of a Closed Loop System to retrieve the Open Loop Response. If the system under study is active and has resonances, or highly non-linear behavior, then this discontinuous nature could induce the resonance or invoke the non-linearities, all of which may have very long time constants to recovery of "Steady State". When the measurements are acquired during the Bode Plot if these effects are not allowed to die down to noise levels, then corrupted measurements are likely. Since the Bode function is generally not a true frequency "Sweep" but "Stepped" either linearly or logarithmically in frequency, this Phase Discontinuous behavior would occur at even step along the way potentially corrupting the results.
If one envisions doing Bode Plots utilizing a given AWG, then it may be wise to investigate wether the Phase Continious Mode/Feature/Behavor is available.
We found this discontinuous behavior "unsettling" at first (pun intended), but thanks to 2N3055 we are now less concerned!!
Best,
2N3055:
--- Quote from: mawyatt on December 06, 2022, 10:58:27 pm ---We found this discontinuous behavior "unsettling" at first
--- End quote ---
LOL!!
2N3055:
--- Quote from: mawyatt on December 06, 2022, 10:58:27 pm ---So why does this discontinuous phase matter?
Normally it doesn't but one scenario comes mind, I'm sure there are others as well.
Consider making a Bode Plot of a Closed Loop System to retrieve the Open Loop Response. If the system under study is active and has resonances, or highly non-linear behavior, then this discontinuous nature could induce the resonance or invoke the non-linearities, all of which may have very long time constants to recovery of "Steady State". When the measurements are acquired during the Bode Plot if these effects are not allowed to die down to noise levels, then corrupted measurements are likely. Since the Bode function is generally not a true frequency "Sweep" but "Stepped" either linearly or logarithmically in frequency, this Phase Discontinuous behavior would occur at even step along the way potentially corrupting the results.
If one envisions doing Bode Plots utilizing a given AWG, then it may be wise to investigate wether the Phase Continious Mode/Feature/Behavor is available.
We found this discontinuous behavior "unsettling" at first (pun intended), but thanks to 2N3055 we are now less concerned!!
Best,
--- End quote ---
I put up a setup where one scope monitors frequency transitions while other scope performs FRA.. Just out of curiosity.
Internal gen in SDS2000X HD performs seamless transition. Same will be for SDS2000X+.
SDG6000X needs to be in Phase independent mode.. Then transitions are seamless.
If in Phase dependent mode it creates short pause between frequences, i.e. signal goes to zero and restarts exactly 1ms later with next frequency at phase 0° .
FRA II Siglent code waits for signal to settle (that includes a DUT too) a bit anyways..
It seems like someone did their homework.
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