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Using (and living with) Siglent SDS1000X-E Series Oscilloscopes

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bdunham7:

--- Quote from: SimonM on June 30, 2021, 12:31:11 am ----29.35ns seems a lot to adjust something. A few 10's ps would be acceptable.

--- End quote ---

Agreed, that sounds broken.  I have no idea how it is broken or what malfunction would cause that.  29ns is roughly the equivalent of 20 feet of coax.  It is possible that there is some calibration setting that is grossly off, so contact Siglent to see if they have some method of changing that or if they want to exchange it.


--- Quote ---de-skew (is that a verb?)

--- End quote ---

delime, delouse, deskew....sounds good to me.

StillTrying:
It's odd, we've never seen that one before, with 4 near identical probes all the 4 channel skews on 0 should do.
Did you remove all 4 probes for the warmed up self-cal.

SimonM:

--- Quote from: StillTrying on June 30, 2021, 12:46:53 am ---It's odd, we've never seen that one before, with 4 near identical probes all the 4 channel skews on 0 should do.
Did you remove all 4 probes for the warmed-up self-cal?

--- End quote ---
Thanks. All the probes are the ones supplied and the type is pp510. For the warmed-up self-cal, I followed the instructions to remove all the probes. I would assume that, if the skew between different channel pairs can be set up and measured, then it can also be calibrated down to close to zero during a self-cal.

Simon

tautech:
Channel skew is specified on P9 in the datasheet:
Channel Skew <100 ps
https://www.siglenteu.com/wp-content/uploads/dlm_uploads/2020/12/SDS1000X-E_DataSheet_DS0101E-E04C.pdf

Whenever you strike something that doesn't look right use Default to bring settings back to factory then run Self Cal and revisit the measurement.
For BNC connections an unmatched pair of cables can often produce different results.

SimonM:

--- Quote from: tautech on June 30, 2021, 04:35:06 am ---Channel skew is specified on P9 in the datasheet:
Channel Skew <100 ps
https://www.siglenteu.com/wp-content/uploads/dlm_uploads/2020/12/SDS1000X-E_DataSheet_DS0101E-E04C.pdf

Whenever you strike something that doesn't look right use Default to bring settings back to factory then run Self Cal and revisit the measurement.
For BNC connections an unmatched pair of cables can often produce different results.

--- End quote ---

Thanks.

I am returning the scope to the factory setup and running Self Cal before revisiting the measurements.

The BNC connections are with/without the 50-ohm termination. Results are unchanged.

The cables are pretty well matched - they are the 4x PP510 probes. Swapping the probes around, the results are unchanged.

Here is what I did to simplify the setup (one channel of FG directly connected via two probes to the scope)

I have removed the 50-ohm terminator and setting the FG to Hi-Z. The setup is about as simple as it can be.

There is a setting for Quick-Cal on the scope. I hadn’t noticed it before and it was switched ON. I switched it OFF because the condition of varying temperature doesn’t apply.

I have reset the scope as follows:

1. Reset to factory defaults;
2. Use the scope Self Cal calibrate operation (takes about 5 minutes);
3. Press default button;
4. Set all four probes to 10X;
5. Set all four channels to the same 2V/div, 0V offsets;

Without anything connected, the four channels are overlain at 0V.

Set the FG to 10MHz and Hi-Z. Channel 2 is off. There is no 50-ohm terminator.

1. Channel 1 is triggered and displays the waveform with a probe point directly off the FG;
2. Channel 2 is added and the probe is connected to the same FG output. Both channels are in phase;
3. Move the 2nd probe from channel 2 to channel 3. The scope is out of phase;
4. Move the 2nd probe from channel 3 to channel 4. The scope is out of phase;
5. Move the 2nd probe from channel 4 back to channel 1. The scope is in phase;

When the scope is in phase the 2nd trace covers the first trace, otherwise, they are out of phase.

I can manually skew a second channel to overlay the first trace. -29.35ns is required.

NB without the 50-ohm terminator the results are as before, there is one difference that is expected: displayed trace doubles (Vp-p) because there is a change in the load impedance when connecting/disconnecting a second probe.

At 1MHz and probes set to 1X, timebase altered and scope input channels set to 1X, 2V/div, 0V offsets, it shows the same waveform.

Adding the second channel, overlays in phase, moving 2nd probe to channel 3 and then to channel 4 also shows the channels out of phase.

At 1MHz the amount of phase shift on the screen is reduced e.g. to 1/10. Skew to correct this is again best at -29.35ns.

Switching between probes doesn’t vary/alter the result.

Observations and conclusions

1. Removing the 50-ohm terminator doesn’t vary the out of phase outcome;
2. Varying which probes are used doesn’t vary the outcome;
3. Changing frequency e.g. between 10MHz and 1MHz and using probes 1X doesn’t vary the outcome;
4. The scope doesn’t show phase alignment between channels (1 & 2) with channels (3 & 4) after calibration;
5. The scope is remarkably aligned within the channels (1 & 2) or channels (3 & 4);
6. The scope can measure skew and offsets between channels, it just treats them separately e.g. scope is 2 + 2 channels.

rf_loop provided a review of the scope and his analysis of skew indicated a very high degree of alignment (see page 76):



NB the only mismatch is with attenuation (might be expected) and not with skew - each channel is very well aligned.

Simon

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