Network Analyzer versus Impedance Analyzer

[Cleber Borges]

Hello everyone,

Reading about the EIS area - Electrochemcical Impedance Spectroscopy - I found that currently commercial potentiostats implement Impedance analysis by the method:
FRA - Frequency Response Analyzer, also referred to as Transfer Function Analysis.

As far as I understand, this method would be the same as the one implemented by the Network Analyzer tool in AD2 (am I right? ? ), since in its description it consists of:
"The Network Analyzer is used to analyze transfer functions (the ratio between an output function and an input function)"

If I can have the Impedance Analysis (measurement) implemented by the two tools: (i) Network Analyzer and (ii) Impedance Analyzer;
with differences observed between the two tools, for example, in the frequency range:
Network Analyzer = 2 mHz up to 10 MHz - and no "open" and "short" compensation option
Impedance Analyzer = 200 uHz up to 25 MHz - and with "open" and "short" compensation option

Which made me have the following doubts:

[1] - What is the fundamental difference between them?
[2] - I saw that the Impedance Analyzer tool forces the current calculation while the Network Analyzer emphasizes the voltage attenuation. But what is the implication of this?

In the literature, I saw the defense of the FRA method based on measurement accuracy. The source signal is multiplied by the attenuated signal and the result is given from this combination.

[3] - Does the Network Analyzer tool algorithm follow this form?
[4] - In the WaveForm examples, there is the use of reference resistors for use of the Network Analyzer tool. Is it mandatory to use them or can you close the circuit by connecting to Ground-GND?

Many thanks for your attention and patience!
These details may be basic to those trained in electronics, but it is difficult to find them in referrals from other areas. And it certainly makes all the difference trying to do the measurement correctly.
Once again: thank you!

Cleber Borges

 

 

[Andras]

Thanks @attila, that's good to know!

I might use my PC soundcard as a signal generator, it looks an easier workaround for now

[attila]

Szia @Andras

The WaveForms Sound Card option is solution for free... in case the audio IO limitations are suitable for the requirements.

Here some IA measurements are compared between AD2 and Sound Card:

 

[Andras]

Thanks @attila for the tips!

I would like to ask for your help: what would you do if you wanted to measure two (fluid) samples at the same time over and over? For my current experiments I would need to measure the capacitance of one sample and another sample as a control. I'm willing to build a small hardware if I need to, but I really would like to use AD2 and WaveForms to make it happen.

Plan A is that I start up two WaveForm instances, one with AD2 and one with the Sound Card option, and I would create a small extension (with fixed resistance) to my soundcard following the diagram you showed me, and I would measure the impedance with both at the same time.

Plan B would be that I build/buy a small digitally controlled switch (a small multiplexer basically) for the Impedance Analyzer, have the two probes on its inputs, and control the whole process with a WaveForms script (select the probe, make a measurement, select the other probe, make a measurement, repeat).

What do you think?

[attila]

Hi @Andras

A. Comparing two different tools might not be the best option, it could give different results.

B. At the moment the Impedance Analyzer interface takes control over the Supplies and DIO lines to control the IA Adapter.
On the Adapter the negative supply and some DIO lines are unused.
In the next software version I will add option to be able to control these.
Having these you could use a small signal relay with ~5V control, similar to the ones on IA adapter but non-latching, to switch between the measured and control DUTs.
https://reference.digilentinc.com/_media/reference/instrumentation/analog_discovery_impedance_analyzer_sch.pdf

Edit:
You could use the current software for plan B.
First, in the Impedance interface using the Adapter option select the needed resistor value, then select "W1-C1-DUT...". This will release the Supplies and DIO lines to be used from other interfaces, and the latching relays on the Adapter will remain unchanged. Then you can use the Static IO or Negative supply for other purposes, to control the external relay...

Edited August 12, 2019 by attila

[Pop Alexandra]

Thanks for the clarifications, guys! Really useful thread. 

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Alexandra from Ci Analytics