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Capacitive & Inductive Impedance Plots with SDS2104X Plus Bode Function
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mawyatt:
Here's a simple technique to utilize the Bode Function to create some nice Impedance Plots of various capacitors.

The idea is to have the scope plot Ch2/Ch1, or Vo/Vi as it does with the Bode function. Using an external AWG (SDG2042X) to create the stimulus under LAN control from the SDSX+, place the AWG output signal thru a reference resistor R (1K 2W 1% in our case). The DUT capacitor is placed from the Resistor to Local Ground, and Ch1 senses the AWG side of R and Ch2 senses across the DUT.

Here's a little math behind this, Vo is the voltage across the DUT and Vi is the voltage from the AWG source.

Impedance of DUT Z = Vo/I, where I is the DUT thru current.

I = (Vi-Vo)/R, where R is the sense resistor

Z = Vo/[(Vi-Vo)/R] = R/( Vi/Vo -1), if Vi/Vo is >> 1, then

Z ~ R(Vo/Vi) and Vo/Vi is what the Bode function plots.

So simply scaling the Bode Function dB scale by R revels the ~ Magnitude of DUT Impedance and the Phase is as indicated.

For the magnitude in ohms |Z| ~ R[ 10^(dB/20)], C ~ 1/(|Z|*2pi*F)

Here's a few capacitor examples:



Edit: Added (Calculated from graphs and Tonghui LCR Meter TH2830 Measured values).

#28 680uF Electrolytic     (634uf, 641.5uF @ 100Hz)

#31 470uF Polymer          (459uF, 469uF @ 1KHz)

#32 10uF Mylar               (9.59uF, 9.72uF @ 1KHz)

#33 5uF Polypropylene    (4.89uF, 4.84uF @1KHz)

#34 0.1uF Polystyrene (poor quality)



Added these:

#35 1uF Mylar                 (981.3nF, 994.5nF @ 10KHz)             

#37 2uF Polypropylene     (1.985uF, 1.975uF @ 10KHz)

#38 10nF Polystyrene      (10.28nF, 10.086nF @ 100KHz)

#39 100nF Disc Ceramic   (95.9nF, 92.81nF @ 10KHz)

The SDSX+ does a respectable job with it's nice low noise front end and good overall dynamic range, and the Bode Function is "Icing on the Cake" ;D

Anyway, hope some folks find this interesting.

Best,


Martin72:
Interesting thing I want to recreate on my scope.  :-+
mawyatt:
See post #130 here.

https://www.eevblog.com/forum/testgear/east-tester-et4410-esr-measure/125/

Some Plots added.

Note because of the superb noise and DR of the Siglent SDSX+ and even better SDSX HD, a decent Wide-Band Impedance Analyzer is lurking in the background ::)

This has a very good chance of being a "decent" Analyzer because of the low noise front end and high DR due to dynamic input scaling as well as the Frequency Selective (FS) feature utilized within the Bode Function. This FS isn't as good as a quality LCR meter since these employ Synchronous Sampling which is the ultimate in signal processing techniques for recovering synchronous signals from noise, however the FS seems to do a very good job with our experience. You can judge this with the various plots and lower impedance levels achieved with a 1K source impedance.

Anyway, lets hope Siglent is listening ;D

Best
tautech:
Just stumbled on a vid from Chris doing much the same stuff with a SVA1015X:

TopQuark:
Very interesting test  :-+ . Decided to have a go myself.

I see myself using this trick in the future, so I wanted to make a dedicated jig for this. I used a nanoVNA test board and soldered a 1k 0.1% resistor and a couple of probe sockets to it. Scrapped away some of the solder mask to expose a bit more copper for bigger parts.

Ran the test with a 10uF MLCC and a 100nF PPS film cap. The 100nF film cap is quite tricky to test, as its SRF is around 20-30MHz, so 10x probing is strongly preferable and 20M BW limit can't be used. The SDS2000X HD performed respectably in this test.

I'll see if I can jerry rig together some code in Python to produce capacitance and impedance graphs out of the bode plot data.
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