Oscilloscope Low Sampling at uHz Sinus Signal

Question

I tried to measure a sinus signal at 1000 µHz with my R&S RTC1000 oscilloscope (bandwith 300 MHz). The function generator that I used was the EDU33212A. I set the T/div=100s and the oscilloscope shows that it's sample rate was 5samples/sec at the top edge of the screen.

So, the total sample count will be 100s x 12divisions x 5samples/sec = 6000samples.

Do you know why it reduced the sample memory depth so far?

It has a memory capacity of 2 Mpts (2,000,000 samples - in 1-channel mode), so in theory it could capture many more samples. The interpolation mode that the oscilloscopes use was the "sin(x)/x" and for this I believe I saw a smooth sinus signal, with only a small amount of aliasing.

Does the sample depth automatically increase if you reduce the scan rate (e.g: to ~1sec/div or less) and then reduce if you return to 100s/div, or is it a perhaps separate option in the menu? — Attie
– Attie, Commented Jun 11, 2024 at 20:27
Note also that the signal you've shown is ~1 mHz, not 100 µHz — Attie
– Attie, Commented Jun 11, 2024 at 20:30
Technically the sample rate and buffer size are completely independent parameters, in a normal scope. Some scopes offer some automatic scaling (why? is a different question), but there should be a way to decouple the two parameters. You just need to find a way how to do this on your scope. — Ale..chenski
– Ale..chenski, Commented Jun 11, 2024 at 21:16

qrk · Accepted Answer · 2024-06-11 22:58:11Z

According to the manual, Section 5.3.3.1 and Table 5-1, you most likely have the Record Mode set to Automatic. Automatic tries to set up the sample rate to some reasonable number.
Your other options are Maimum Waveform Rate and Maximum Sample Rate.

Try setting it to Maximum Sample Rate and report back.

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