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Siglent SDS1104X-E Quick Cal Question

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TomKatt:

--- Quote from: bdunham7 on June 28, 2022, 05:21:00 pm ---Also, it does look like Siglent has intentionally made the calibrator output pretty much exactly 0-3V.

--- End quote ---
I always thought that's why they were called 'Calibration' terminals as opposed to 'Compensation' terminals...  It seems reasonable to assume (to me) that both amplitude and frequency would be calibrated.  I'd be surprised if any Tek or Keysight scope did not specify their calibration point parameters.

Edit - N/M, wrong again.  Apparently nobody specifies voltage any longer, they just specify frequency and 'approximate' voltage.  Older CRO documentation specifies amplitude, but modern gear is all listed as ~ (Tek 465 even species available calibration signal current as 30ma +/- 2% based on a +/- 1% 300mv amplitude at an approximate 1KHz frequency)

I'll take some screenshots of my tests later this afternoon for comparison.

Thanks again!

tautech:

--- Quote from: TomKatt on June 28, 2022, 05:29:11 pm ---
--- Quote from: bdunham7 on June 28, 2022, 05:21:00 pm ---Also, it does look like Siglent has intentionally made the calibrator output pretty much exactly 0-3V.

--- End quote ---
I always thought that's why they were called 'Calibration' terminals as opposed to 'Compensation' terminals...  It seems reasonable to assume (to me) that both amplitude and frequency would be calibrated.  I'd be surprised if any Tek or Keysight scope did not specify their calibration point parameters.

Edit - N/M, wrong again.  Apparently nobody specifies voltage any longer, they just specify frequency and 'approximate' voltage.  Older CRO documentation specifies amplitude, but modern gear is all listed as ~ (Tek 465 even species available calibration signal current as 30ma +/- 2% based on a +/- 1% 300mv amplitude at an approximate 1KHz frequency)

I'll take some screenshots of my tests later this afternoon for comparison.

Thanks again!

--- End quote ---
While this may be so the old CRO probe compensation outputs were notoriously all over the place especially when these scopes had a bit of age on them.  :scared:
Without means for adjustment a probe compensation output can only be described as suitable for compensating probes and for a sanity check.
However for some of the ooooold Teks the output bar also served as calibration output for current probes for which they indeed were very useful however I'm unaware of any modern scope that provides a current probe calibration/check output and instead many now use fixtures:
https://siglentna.com/product/power-analysis-deskew-fixture/

As far as how measurements perform in the modern DSO it is certainly how you drive them and another data point for you to consider is my old SN#0012 SDS1104X-E, just cold booted, unknown when Self Cal was last run, Quick Cal = Off and using BNC Croc clip leads to the probe compensation terminal and some Stats running for good measure.

Now tell me how you might measure more precisely with a CRO considering the parallax error they can introduce ?

TomKatt:

--- Quote from: tautech on June 28, 2022, 10:18:23 pm ---Now tell me how you might measure more precisely with a CRO considering the parallax error they can introduce ?

--- End quote ---
Please do not misunderstand me - I fully appreciate modern DSO scopes and believe their abilities far exceed CRO's in virtually every respect.  If anything, I guess that's why I got confused on this topic expecting a 3.00V measurement to display on the screen.   Believe me I know there is no "precision" to my CRO because everything is based on visual estimation.

Anyways....  I ran a few more tests yesterday and I am now convinced the comments about sampling and noise affecting the readings are correct and that the scope is reporting what it is seeing pretty accurately.  I see now that the Pk-Pk parameter is not the best one to convey the signal - when I looked at ALL the measurements I see that the Amplitude parameter displayed exactly 3.00V with 10X probe and 3.02V with the 1X probe.  And despite limiting the BW to 20MHz, I can see that the sensitivity of the scope is seeing noise that affects the measurements.

Thanks again for helping an old dog learn a few new tricks.

Edit - If the new Siglent only displayed waveforms like my CRO (no digital measurements), I would have looked at that signal and thought "yup - 3V / 1KHz square wave as expected" in my CRO mindset.  The actual measurement differing from that threw me off a bit.

bdunham7:
I let my scope warm up for at least half an hour and then ran the Self-Cal.  This is what I got using only a 1X probe.  Comparing the pictures you can see ever so slightly more noise on the BW full setting.  I included StDev and RMS as another demonstration of how measurements on the scope may not mean exactly what you would think at first.

TomKatt:
Forgot to mention that my results also allowed >30 min warmup followed by a Self Cal. 

My results seem virtually identical to yours.  Good to know.

Thanks for the follow up  8)

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