OZ2CPU found some strange looking noise with the Siglent SPD3033X power supply during his investigations.
We tried to analyze it a little bit more. For this we both made some recordings with the SDM3055X (oz2cpu) and I (SDM3065X) for further FFT with EXCEL.
You find the results in the SPD3033X thread.
https://www.eevblog.com/forum/testgear/how-to-calibrate-siglent-spd1000x-spd3303x-spd3303x-e-series-power-supplies/msg3923762/#msg3923762During this tests I discovered some strange behavior of the SDM3065X (the SDM3055X seems to be better) which I want to point out.
Problem:
If you record continuous measurements to USB with SDM3065X, the time interval between measurements is not constant, there are big deviations.
I tried several series with different USB-drives and different settings. As you can see in the attached photos, we find a distribution pattern. (y-axis: time interval between single measurements in seconds)
But for low frequency FFT we need a nearly constant interval or with other words a constant acquisition frequency.
Surprisingly the SDM3065X behaves during very fast recording (0.05 PLC, acquisition frequency up to 1 kHz) best.
It's not a problem of the USB transfer speed, one data set is 32 byte, at 1 kHz acquisition frequency we need only 32 kByte/s.
The problem with the not constant triggering was pointed out here long ago.
https://www.eevblog.com/forum/testgear/siglent-new-bench-dmm-sdm3055/msg3466342/#msg3466342I tried external triggering as well but found no improvement.
Attached you find the distribution pattern of different recording (4096 measurements - limit for Excel FFT) of the 3055X and the 3065X.
btw: in one of the first Siglent Operating Tips from March 2018 it was shown that there is no time stamp with recordings to the internal storage
https://siglentna.com/operating-tip/sample-and-store-sdm3000/Now we have 2022! Siglent - why?
My wish/expectations to Siglent for the next firmware update:
#1 time stamp for internal recordings
#2 (nearly) constant acquisition/internal triggering frequencies, as with the 3055X, in best case controlled by user
As mentioned this would enable some interesting possibilities (low frequency noise measurements etc.)
Thanks to oz2cpu for his support.
Tautech, I will be very grateful if you can direct this to someone who is in charge of this product. Thanks.