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LCR Impedance Viewer for Picoscope+Keysight+R&S Bode Plot Data (open source)

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Hans Polak:
P.S. I forgot to mention that this correction was with the 100R series resistor that I used.
For other resistors, a new correction file should be made.

Hans

_Wim_:

--- Quote from: Hans Polak on May 14, 2021, 10:47:33 am ---I think we should leave the subject, because we are not coming together as it seems.

--- End quote ---

Hi Hans, I would rather come to a conclusion, as now we have created doubt whether the results are correct or not. If incorrect, I will make the modification, but until now I am not convinced it is the case. Hopefully some other members here can share their opinion also.


--- Quote from: Hans Polak on May 14, 2021, 10:47:33 am ---Look at the first image below how the Bode diagram looks in my case.
And altough this doesn't look to bad, only 0.06dB and 6 degrees removed from the ideal, the effect of this can be quite massive as we will see.

Now store this Bode diagram as a .csv file, open it in Excel and make a second set with Log Freq, -1*Gain in dB  and -1*Phase.
This second set will be your future correction set.
To show the effect, I took a 1x probe as a DUT.
Without any correction, results are shown in the second image.
But when correcting this recording in Excel by adding the gain in dB and phase of the correction set, the now corrected data produces quite a different plot, see the the third image.
So this is way more accurate than just specifying the capacity of the measuring probe.
What you see are resp. Impedance, Resr and two plots for the Capacity, one is using 1/B as in FRA and the second using B/(A^2+B^2),  [with A and B being resp. the RE and IM part of Z].
Result is very good after correctio,  isn't it.

Hans

--- End quote ---

I you read the beginning of this thread, this is how I initially saw the calibration also. But after reading a bit more on the subject, I somehow convinced myself this was not fully correct, however I am not sure of this. Did you check if this also works ok with a complex DUT? Typically LCR meters do both an open and a short calibration to correct for errors.

Hans Polak:
Wim,
When you propose a complex DUT, composed out of various components, I can solder this together and show the results without and with correction.
I'm looking forward to do this test.

Hans

_Wim_:

--- Quote from: Hans Polak on May 14, 2021, 05:07:08 pm ---Wim,
When you propose a complex DUT, composed out of various components, I can solder this together and show the results without and with correction.
I'm looking forward to do this test.

Hans

--- End quote ---

Hi Hans,

To test the calibration routine, I would do the following:
1) run the calibration routine, and measure a complex load => this give you the reference waveform of the complex load
2) "modify" your scope input channel by adding a parallel capacitor [and series capacitor bypassed by a resistor] [=optional]
3) run the calibration routine again with the "modified" scope input, and remeasure the same complex load
4) ideally the measurement result should be equal to your reference waveform.

Hans Polak:
Hi Wim,

As I understand your proposal,

Make cal. file 1 with only the scope probe attached.
Measure a complex load and correct it with cal. file 1.
Make a new cal. file 2, now with an added cap over the probe.
Measure the same complex load again but now with the added cap and correct the result with cal. file 2.
Corrected result for the complex load should be the same in both cases.

That's easy to perform, and I will certainly do, but before doing that two questions:
1) Is there a reason why you attached an image of a probe, or do you suggest this to be used as a complex load 
2) what capacity do you suggest to place in par. to the probe for cal. file 2 ?

Hans

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