Question

There is a bug in the export of data from the impedance analyzer from Waveforms (specifically from Waveforms 3.8.2 using the Analog Discovery 2, but I have seen it with earlier releases of Waveforms 3 also).

The problem is that the frequencies are reported as if they were from a linear sweep, even though a logarithmic frequency sweep was done:

#Date Time: 2018-07-01 16:50:47.258
#Trace: Trace
#Start: 100 Hz
#Stop: 1e+06 Hz
#Steps: 101
#Resistor: 10000 Ω
#Average: 10
#ProbeCapacitance: 1.04e+06 Ω
#ProbeResistance: 4.3e-11 F
#Compensation: Open Short
#Wavegen: Wavegen1
#Amplification: 1 X
#Settle: 20 ms
#MinPeriods: 32
#Channel: Channel 1
#Range: 5.49577 V
#Offset: -0.000318847 V
#Attenuation: 1 X
#Channel: Channel 2
#Range: 5.51181 V
#Offset: -0.000280998 V
#Attenuation: 1 X

Frequency (Hz)	Trace θ (°)	Trace |Z| (Ω)	Trace Ls (H)	Trace Cs (F)
100	0.00067832392258167652	9971.9407134030535	0.00018789460945304077	-0.013481119008321029
10099	0.0018260127183053441	9972.4554790954317	0.00046132118972998595	-0.0045670615004842902
20098	0.0026165423173400044	9972.2098918719494	0.00060286028271848858	-0.0029068564833067186

Many of my students had problems with this bug last quarter, and we had to create a work-around in our gnuplot plotting scripts:

#if the frequencies in your data file don't follow log increments use the code below 
# Written by Ali Fallahi
#example: use plot 'data' u (correct($1)):3 instead of plot 'data' u 1:3
 freq_u=1e6 #last frequency
 freq_l=10 #first frequency
 NoOfSamples=101 #number of samples 
 indexno(f)=(NoOfSamples-1)*(f-freq_l)/(freq_u-freq_l)
 correct(f)=10**(log10(freq_l)+indexno(f)/(NoOfSamples-1)*log10(freq_u/freq_l))
##

plot 'measuring-10kohm-buggy-freq.txt' u (correct($1)):3 title  '10k{/Symbol W}±0.1%'               

It would be nice not to need to correct the data files.

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2 answers to this question

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Posted (edited)

Hi @gasstationwithoutpumps

Thank you for the observation and sorry for the issue.
It is fixed for the next software release.

As workaround you could also export Trace (or Ref) data (these will be with less detail in comments) or view (Impedance, Capacitance...), which have correct logarithmic scale.

image.png.789988ebc2b4cb4ba2467f3408067065.png

Edited by attila

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