EIS Experimentation with AD2-IA

[EzeStare]

Hello.

We are working in a research project about electrochemical non-faradic biosensors development. Similar to the forum question made by Borges Cleaver (AD2 as a Electrochemical Impedance Meter: Is possible?) we want to characterize our systems by EIS technique, using the digilent AD2-IA. We can avoid the reference electrode because the non-faradic nature of our electrochemical system.

We have some questions that are difficult to solve reading the manuals or the forum (may be, we miss something of course).

Indeed:
1- In order to select the wires to adapt the system impedance correctly. What is the real value of the impedance at the Wave Generator?

2- If we set the Adapter (IA) configuration to perform an impedance analyzer measure (BODE). It automatically fixed only ONE resistor during all the measure or it may be changing among the time?

3- Taking into consideration that yielded wires could be better in order to avoid noise (inductive and capacitive) in the frequency-dependent DUT impedance measurement, why the IA was builded without BNC connector (for example)? Does Digilent offer some alternative solution or recommendation to this topic?

[attila]

Hi @EzeStare

1. The Wavegen output has zero impedance.
https://reference.digilentinc.com/reference/instrumentation/analog-discovery-2/reference-manual#awg_iv

2. By default the selected Resistor is used, but you can select Constant Voltage/Amplitude or Custom Mode which change the Resistor value.

3. The shorter cables are better and open/short compensations can be used to reduce the effects of the wiring.

 

[EzeStare]

Hi Attila, thank you very much for your answer. 

1- Thanks. I had already read it, but we have doubts whether it is possible. 

2- I explain it better, because I think the question is not very precise.

Using  the Impedance Analyzer, when I set the Adapter Option, the resistor is restricted  to the user modification:

At online reference manual it said: The Impedance Analyzer Instrument in WaveForms is made easier to use by the reference resistors and relays that come pre-loaded on the Impedance Analyzer board. The Analog Discovery can automatically select the most appropriate component for the job that it needs to do. 

For the AD2-IA and ‘Adaptar’ configuration at WaveForm, I want to know:

a ) HOW it automatically selects the reference resistor?

b) Is the resistor changed automatically every time the software thinks it is necessary along ONE RUN? Or is it the same during the “run”? (For example, it may select 1 MOhm, since 1 Hz till 1 kHz, and 1 Ohm since 1kHz till 100 kHz)

c) is the resulting graph (BODE) corresponding to the impedance behaviour of the: ‘DUT’ or the ‘DUT + reference resistor arrangement’ system? 

 Thank you
best regards

[attila]

Hi @EzeStare

The Constant Voltage and Current options will change the Wavegen Amplitude and with Adapter also the Resistor value.
The Custom lets you write script to control the Amplitude, Offset, Resistor based on frequency step and reading. The editor provides some examples.

[mmachtey]

Hi @attila

Thanks for your reply and sorry for the delay.
So we have two ways to analyze the bode behavior of our DUT.

First way: the automatic constant voltage mode
1- When we use this configuration, the "resistance too low" or "resistance too high" alarm turn on. We don't know why that happened. AD2-IA was unable to select internal resistance? Can we trust the results under the red alarm signal?

2- There is an ecuation to know HOW the AD2-IA change numerically "the Wavegen Amplitude and ... also the Resistor value".

3-Please, Can you explain the next equation (what are these parameters?)
 

https://forum.digilentinc.com/topic/19370-ad2-accuracy-of-impedance-analyzer/#comment-52514

         

second way: custom mode

4- Please, Can you give us some script code example to select the reference resistor by our criteria?

Thank You very much!

Matías

 

Edited June 16, 2021 by mmachtey

[attila]

Hi @mmachtey

1. The low/high warning are shown where the reference resistor and DUT impedance are different by magnitudes, so the result resolution/accuracy may be low.
Try reducing the rms voltage value.

2,4. The Constant Voltage/Current implementations are similar to examples, see pic below.

3. The function is for the open/short compensation.
https://forum.digilentinc.com/topic/21746-discovery-2-impedance-measurement-and-compensation-issues/?do=findComment&comment=62830