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Impedance Analyzer "resistor too high!?"


I do not understand the algorithm being used for reporting "resistor too high!?" in the impedance analyzer.

It seems to pop up whenever the phase is close to 0°, which makes no sense to me.  The resistor is too large when the magnitude of impedance measured is less than about 0.01 times the reference resistance—the phase isn't really a relevant parameter.  A slightly more sophisticated algorithm might look at the voltages of the two measurements and report the resistance being too large or too small when the relevant voltage (across the resistor or across the DUT) gets down to only a few bits in the ADC.

Speaking of voltages—shouldn't the impedance analyzer warn the user when too much current is being asked of the function generator?  With a 10Ω reference resistor, the short compensation calls for 100mA/V, but the output stage of the function generator is limited to about ±35mA so even the default ±1V is too much amplitude.  Detecting that the voltage measured does not match the voltage requested should not be very difficult.

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Hi @gasstationwithoutpumps

You are right but unfortunately the raw data (scope voltage reading) is not kept in the IA, only the further processed values for each step.

In the beta version you can disable the warnings under Options. https://forum.digilentinc.com/topic/8908-waveforms-beta-download/

The AWG can output up to 50mA. The 10 and 1MOhms on the IA adapter are extreme limits for the AD device but it can be useful.
Here you can see a 2.2mF capacitor which requires 10 Ohms reference.


I will look into providing better warnings, measurement qualitative information for each step and current limitation, signal drop warning.

Thank you for your observations. 

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I have used the 10Ω setting and found it useful, albeit a bit risky unless the voltage is reduced to stay within current limits.

The resistor too-large/too-small warning could be based on the computed magnitude of impedance, compared to the known magnitude of the reference resistor.  If the resistor is not within a factor of 100 of the measured magnitude of impedance, then it is too big or too small.  That isn't as good a test as looking at the measured voltages, but should come fairly close.

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