Problems to compare impedance AD5933 and Agilent LCR meter E4980A

[Daphne (daphnepaag)]

Hello,

I´m currently working with the impedance converter AD5933. I´m having 
some problems to compare the data that I get from the AD5933 with a LRC 
meter.
I start my measurement by configurating my frequency start, the 
increment and number of increments. In my case I´m running frequency 
sweep with a range from 1kHz to 100kHz.

I started by calculating the gain factor with a know impedance, and then 
I start my measurement. I get the real and the imaginary data from the 
register specify at the datasheet, then I calculate the magnitude and 
the impedance also with the formulas that are in the datasheet.

However when I want to compare the impedance that I get with a LCR 
meter, the data is different and I don´t really know why. I have done 
some examples as explained in the datasheet but I don´t know if there is 
any detail that I´m missing.

To double check my data I also got the resistive and reactive from my 
impedance convertor and the phase (as specify in the datasheet) but I 
have not yet have any success.

Have someone had something similar?

Thanks
Daphne

[Hp M. (nachtmix)]

Daphne schrieb:
> However when I want to compare the impedance that I get with a LCR
> meter, the data is different and I don´t really know why.

Have you ever tested the readings with a pure ohmic resistor?

[Christoph M. (mchris)]

>However when I want to compare the impedance that I get with a LCR
>meter, the data is different and I don´t really know why.

Can you show a graph which compares the two impedance curves and phase 
curves? What device under test do you use?
It could be a could idea to use a well known circuit like a LCR 
resonance circuit to test the measurement setup and compare it to the 
reference LCR meter.

[Daphne (daphnepaag)]

Yes, I have try to read just ohmic resistance and I get the values 
right, I try with different resistances and I had no problem, however 
when I add a capacitor in parallel and then I run a frequency sweep and 
try the same with the LRC meter the results are not matching any more.

[Daphne (daphnepaag)]

so from the datasheet 
(https://www.analog.com/media/en/technical-documentation/data-sheets/AD5933.pdf) 
I´m following the "measuring the phase across an impedance" section.

The first step says that I should add a know impedance between the Vin 
and Vout, in my case I´m using a 200K resistor. From this value I should 
get the impedance phase of the system, my result is the chart attach.
Once this step is done, it says in the datasheet that I should use an 
unknow impedance and also run a frequency sweep.

Once I have those values I need to get the Impedance phase from the 
"unknow impedance", and to do so rest the impedance from the unknow 
resistance - phase from the system.

I did this calculation and my results are the charts label "Unknow 
impedance phase". Once that part was done I compare with my LRC meter 
and the results were not that far from each other.

However!! I run the same measurement with a capacitor, in this case a 
4.3nF and did the same procedure and in the datasheet it says that the 
difference between capacitor to resistance should be -90. But I don´t 
get those results and the data that I obtain from the impedance 
converter AD5933 is not matching with the data from the LRC meter.

I have check my calculations and the data but I have not been success on 
finding the error.

Maybe if you see something that I´m not seeing you could please let me 
know :)

Thanks!
Daphne

[Christoph M. (mchris)]

>However!! I run the same measurement with a capacitor, in this case a
>4.3nF and did the same procedure and in the datasheet it says that the
>difference between capacitor to resistance should be -90

-90 .. what unit?

[Christoph M. (mchris)]

Do you understand what phase means? It is important to not confuse the 
phase angle given in degrees and the phase angle given in radiants.