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Waveform generation and phase angle
06-21-2019 11:59 AM
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I don't see voltage affect reading here. Higher frequency will have higher error.
Kevin_Price
Proven Zealot
06-21-2019 12:54 PM
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Just a quick followup: on your 6216, analog INPUTS are multi-plexed with a small time delay between channels. Analog OUTPUTS are simultaneous. There's no *additional* phase angle to explain away due to (temporarily) generating both signals as analog outputs. Well, not unless you assign different phase values when generating the waveforms.
Come to think of it though, maybe a worthwhile troubleshooting step is to feed the same waveform to both AO channels. Then there can be no doubt that the generated signals will have the same phase.
-Kevin P
CAUTION! New LabVIEW adopters -- it's too late for me, but you *can* save yourself. The new subscription policy for LabVIEW puts NI's hand in your wallet for the rest of your working life. Are you sure you're *that* dedicated to LabVIEW? (Summary of my reasons in this post, part of a voluminous thread of mostly complaints starting here).
06-21-2019 01:27 PM
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Kevin,
Thanks for the explanation. I think the two signals generated are synced to each other, I have a vi to measure the phase angle, it's exact as set angle, the problem is after the generation, write, in transit, read and process.
Bob_Schor
Knight of NI
06-22-2019 08:05 AM
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A followup to Kevin Price's
@Kevin_Price wrote:
Just a quick followup: on your 6216, analog INPUTS are multi-plexed with a small time delay between channels. Analog OUTPUTS are simultaneous. There's no *additional* phase angle to explain away due to (temporarily) generating both signals as analog outputs. Well, not unless you assign different phase values when generating the waveforms.
A tiny followup: in the Very Old Days (before LabVIEW), Multi-channel Analog Boards had something called a "Sample-and-hold" circuit on each input channel that "captured the voltage" and held it constant for the length of time it took the Multiplexer to sample all 8 (or 16 or however many) channels, thus eliminating the phase difference between the channel samples. By the time inexpensive DAQ boards came along, the multiplexers were faster, the circuits were (physically) tinier, and S&H circuits were often eliminated, to be removed in post-processing if the User realized this could be an issue ... [I confess that I've not ever considered doing this, but my sampling rates are relatively low ...].
Bob Schor
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