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What's in the Buffer?

Posted: Thu Feb 13, 2020 2:35 pm
by MrCJ
when measuring low freuencies wit the highest decimation factor (and therefore with a sampling rate of 7,6 kS/s), I stumbled across a rather bizarre phenomenon:
There seems to be some kind of data already stored in the buffer, before aquiring the data and it doesn't seem to be the previous measurment. The following image contains a screen shot from a simple matlab script that captures a OUT1 Sin on both input chanels.
Basically the code looks like the example code from the docs.
After trying to figure out what this undesirable is and where it comes from I discovered, that the pause between starting to aquire and enabling the trigger, is not only necessary (since the red pitaya won't capure usable data with a pause of 0s), but can also prevent this described phenomenon from happening.
It seems like it takes a pause with a length of about 9s to capture only the desired part of the data. And it also seems like this is the "time scale" mentioned in the table . But how come this time scale is so long, as the "direct" calculations from my other post say otherwise?

Thanks in advance.

Confused regards

Re: What's in the Buffer?

Posted: Wed Feb 19, 2020 11:01 am
by redpitaya
Thank you for your post.
Please be advised that at very low decimation it takes time for data to fill the buffer, before and after the trigger event, so this delay is necessary before setting the trigger or reading data out.