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Impedance Analyzer design flaw


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Hi, I think I found a design flaw in the Impedance Analyzer and would appreciate the thoughts of others. The load resistors R2 thru R7 are switched one at a time into circuit via the software select in Waveforms. Their values are each decade from 10 Ohms to 1 Meg. All good so far. However these resistors are effectively in parallel with the input impedance of Ch2 of the Analog Discovery, which is 1 Meg. Therefore when 100k is selected the effective load is about 90.9 k Ohms. And when 1 Meg load is selected the effective load is 500k Ohms i.e. half what you expect. For 10k and lower load resistance this issue is immaterial. The open and short compensation function may correct some error in the reading, but especially at 1 Meg setting, the load is much different to what is expected and that could impact secondary readings such as parallel capacitance.

Have others noticed this? Or am I missing something?

 

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Hi @bmac_2780

The software takes in account the probe-IA-PCB impedance and subtracts this from the measurement results.
Additional to this, the open/short compensations should help to improve the results further.

image.png.bc775fd2cc98b033105414abf04fa3a3.png

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