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Siglent SDS1x04X-E BodePlot II (SFRA) features and testings
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Pitrsek:
Any clue as to why is the low limit set to 10Hz?
tautech:

--- Quote from: Pitrsek on January 05, 2020, 01:46:54 am ---Any clue as to why is the low limit set to 10Hz?

--- End quote ---
Offer a valid use case for under 10 Hz and we'll send this request to Siglent.
n3mmr:

--- Quote from: tautech on January 05, 2020, 07:17:07 am ---
--- Quote from: Pitrsek on January 05, 2020, 01:46:54 am ---Any clue as to why is the low limit set to 10Hz?

--- End quote ---
Offer a valid use case for under 10 Hz and we'll send this request to Siglent.

--- End quote ---

For really-high-quality audio power amplifiers, a bode plot of the range 0.1 Hz to, say, 100 Hz will enable a designer to accurately predict the audibility of artefacts coming from attempts to limit the vlf range by steep slope high pass filtering of subsonics.
mrprecision:

--- Quote from: mrprecision on January 04, 2020, 11:26:49 am ---I have tested the Bode Plot Function of my scope (SDS1104X-E) and have been very enthusiastic about it so far. I connected the scope to the generator (DG2042X) via Ethernet, this worked without any problems right away. However, there seems to be a problem with the Bode Plot function.
In the simple example I tested a passive filter of the 1st order with 100Hz at -3dB. The sweep for the Bode Plot function was chosen from 10Hz to 1kHz with 10 points per decade. "Channel Gain Auto" was selected under the channel settings.
Then the Bode Plot measurement was started. The first run is as expected. However, the first point in the Bode Plot is incorrectly determined in all further runs. In my view, this is a mistake. However, if you select "Channel Gain Hold" under the channel settings, this incorrect measurement does not occur. It also appears to occur only at low start frequencies.

Video
http://www.schaeck.eu/download/eev/siglent_bode_2_error.mp4

--- End quote ---

Back to my Question: But why is the already existing function only working for the first run?
Performa01:

--- Quote from: mrprecision on January 05, 2020, 08:04:54 am ---
--- Quote from: mrprecision on January 04, 2020, 11:26:49 am ---I have tested the Bode Plot Function of my scope (SDS1104X-E) and have been very enthusiastic about it so far. I connected the scope to the generator (DG2042X) via Ethernet, this worked without any problems right away. However, there seems to be a problem with the Bode Plot function.
In the simple example I tested a passive filter of the 1st order with 100Hz at -3dB. The sweep for the Bode Plot function was chosen from 10Hz to 1kHz with 10 points per decade. "Channel Gain Auto" was selected under the channel settings.
Then the Bode Plot measurement was started. The first run is as expected. However, the first point in the Bode Plot is incorrectly determined in all further runs. In my view, this is a mistake. However, if you select "Channel Gain Hold" under the channel settings, this incorrect measurement does not occur. It also appears to occur only at low start frequencies.

Video
http://www.schaeck.eu/download/eev/siglent_bode_2_error.mp4

--- End quote ---

Back to my Question: But why is the already existing function only working for the first run?

--- End quote ---
Yes, there's a timing problem whenever the vertical gain of the measurement channel exceeds 1V/div.

There is a base range up to 100mV/div that doesn't require an input attenuator.
For the vertical gain settings up to 1V/div the first 20dB attenuator is activated.
For the vertical gain settings up to 10V/div the scond 20dB attenuator is activated on top of that.

These attenuators are relay operated and quite obviously the 2nd attenuator causes additional time delays that are not allowed for in the Bode plot firmware.

Knowing this, the workaround is simple. Just lower the stimulus level by 3dB, so that the vertical gain of the measurement channel (Ch.2) never exceeds 1V/div. With this setting you can have glitch-free measurements over more than 100dB dynamic range (the first attenuator doesn't pose a problem):


SDS1104X-E_Bode_LP100Hz_10-10MHz+3dBV

In the screenshot above, the 100Hz lowpass filter is measured up to 10MHz. As can be seen, my filter works as expected up to some 2MHz, then there is a resonance with a maximum attenuation of about 100dB and after that, the attenuation is decreasing again. The phase plot also clearly documents this.

Numerous passes have been made and the data at 10Hz have always been correct. Of course I've also tried lower spans, including the setting that you've used (10Hz to 1kHz). It all works fine.
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