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Accuracy specifications of Impendance Analyzer


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Although there are no specs, I have made some measurements of the Impedance Analyzer board, reported at https://gasstationwithoutpumps.wordpress.com/2018/07/01/analog-discovery-impedance-analyzer/

It seemed to me that the Impedance Analyzer was built using 0.2% tolerance resistors (or that they got lucky with 1% tolerance resistors).  The 10Ω reference had lower accuracy than the others, possibly because of contact resistance in the relays.

If you are careful to pick the right size reference resistor and do open/short compensation, you should be able to get 1% accuracy from the measurements.

I don't use the Ls, Cs, … numbers reported from the tool, but take the |Z| and phase recording and fit my own models to the data using gnuplot (I'm often fitting devices like loudspeakers or electrodes, which are not well modeled by the simple linear models used by the impedance analyzer).

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46 minutes ago, gasstationwithoutpumps said:

Although there are no specs, I have made some measurements of the Impedance Analyzer board, reported at https://gasstationwithoutpumps.wordpress.com/2018/07/01/analog-discovery-impedance-analyzer/

It seemed to me that the Impedance Analyzer was built using 0.2% tolerance resistors (or that they got lucky with 1% tolerance resistors).  The 10Ω reference had lower accuracy than the others, possibly because of contact resistance in the relays.

If you are careful to pick the right size reference resistor and do open/short compensation, you should be able to get 1% accuracy from the measurements.

I don't use the Ls, Cs, … numbers reported from the tool, but take the |Z| and phase recording and fit my own models to the data using gnuplot (I'm often fitting devices like loudspeakers or electrodes, which are not well modeled by the simple linear models used by the impedance analyzer).

Thank you very much for your information, very useful !!

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1 hour ago, gasstationwithoutpumps said:

I don't use the Ls, Cs, … numbers reported from the tool, but take the |Z| and phase recording and fit my own models to the data using gnuplot (I'm often fitting devices like loudspeakers or electrodes, which are not well modeled by the simple linear models used by the impedance analyzer).

Hint: The Matlab / Octave function "fminunc" or "fminsearch" can work miracles in finding parameters of an equivalent network. In the past, I've used Maxima CAS to get the Laplace-domain input/output equation from nodal equations, then "stringout" to import the result into Matlab and "fminunc" to fit the parameters to measured data. This doesn't even need phase, just magnitude data (as long as it's minimum-phase type)

 

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4 hours ago, xc6lx45 said:

Hint: The Matlab / Octave function "fminunc" or "fminsearch" can work miracles in finding parameters of an equivalent network. In the past, I've used Maxima CAS to get the Laplace-domain input/output equation from nodal equations, then "stringout" to import the result into Matlab and "fminunc" to fit the parameters to measured data. This doesn't even need phase, just magnitude data (as long as it's minimum-phase type)

 

I've needed to use non-linear devices to model loudspeakers (for example, an inductor-like device with impedance (j 𝜔)^𝛼 M (instead of j 𝜔 L).  I'm sure that Octave, Matlab, and SciPy can be set up to optimize parameters for complicated functions, but I've found it simpler to use (and teach) gnuplot's model fitting command.  

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