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Bug: AD2 Impedance Meter export


gasstationwithoutpumps

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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