impedance analyzer questions

[gasstationwithoutpumps]

Why does the impedance analyzer only allow 10Ω, 100Ω, 1kΩ, 10kΩ, 100kΩ, and 1MΩ reference resistors?  I might have a precision 510Ω resistor that I want to use for a reference.  Or, as happened for me today, I might want to use a 1Ω resistor as a reference (I was trying to determine the saturation current for an inductor, so I needed a large DC current, plus a small signal to measure impedance with.)  I added an external transistor to provide gain from the function generator, but the 10Ω constraint meant that I couldn't raise the current much without hitting voltage limits.  (I'll have to use the network analyzer and do my own fitting, rather defeating the advantage of the impedance analyzer)

I found the impedance analyzer a bit non-intuitive to use and almost completely undocumented.  It is a bit annoying that compensation needs to be redone any time the sweep is changed, and there there is no way to store a number of different compensation sets, switching between them as needed.

I was also wondering why the impedance analyzer used a shared ground, rather than taking advantage of having differential inputs to measure the voltage across the resistor and the unknown impedance separately.  Using the differential channels, one can have a larger difference in |Z| between the reference and the unknown, since you don't have to compare R with R+Z, but only with Z.

[attila]

Hi @gasstationwithoutpumps

We tried to keep the interface simple.
The exact resistor value can be entered in the Compensation dialog, like for 10Ω label you can specify 1.001Ω

You can perform the compensation on larger number of samples than the measurement is done, like 1k and 100.
You can also open multiple Impedance windows or use separate workspaces for analysing different frequency ranges or for various circuit setups.

The structure/computations use ground reference to be compatible with single ended devices.

[gasstationwithoutpumps]

Thanks.  It had not occurred to me that compensation dialog box would allow changing the presets.  Of course, the name for the resistor in the menu is still the original name, which is confusing.  One of the things I liked about Waveforms 2015 was the ability to type in numbers in almost any box (sampling rate, time/division, volts/division, …), so having the impedance menu being a fixed list seemed a little inconsistent with the rest of the user interface.

The resistor-too-high and resistor-too-low hints often seem incorrect.  I was getting resistor-too-low hints when, in fact, the resistor was too high.

I guessed that the structure using ground reference was so that people could use conventional probes, but it would be nice to have an option to use the differential channels when they are available—the use of high gain for lower impedance can increase the range over which the impedance meter can work with a given reference.

[attila]

Hi @gasstationwithoutpumps

Thank you for your observations.