AD2 as a Electrochemical Impedance Meter: Is possible?

[Cleber Borges]

Dear all,
Good afternoon!

In electrochemistry, a system of 3 electrodes is used to:

1 - measure the Potential (V) between the Working Electrode (WE) and the Reference Electrode (RE)
2 - measure the current (i) between the Working Electrode (WE) and the Counter-Electrode (CE)

The RE is constructed so that no electric current must flow between WE and RE.

My question is:
If I use the schematic of figure B, the tool: Impedance Analyzer, implemented in Waveform,
will it use the potential difference of the channels of the Scope1 (+) port and the (-) port?

My goal is to characterize the Impedance in WE (Working Electrode) as a Randle Cell (Figure C) without the interference of the other two electrodes - RE and CE.

(Figure (A) illustrates the electrochemical cell in use in conventional potentiostats for voltammetric study)

Thanks in advance for your attention and comments.
Thank you very much
Cleber Borges

 

 

 

[attila]

Hi @Cleber Borges

The Scope inputs on Analog Discovery are differential, so these always measure the voltage between positive and negative inputs.

The Impedance Analyzer is not suitable for such measurements. You could eventually use math/script in Custom One/Two plots of the Network Analyzer.

The IA interface supports single ended setups and calculates series or parallel equivalent circuits, such Rs-Rp/Xp approximation is not supported.
In the calculations the probe impedance (R/C of 2+) is taken in account.
I have tested support for differential setup, but the results were not so good at high frequency and low capacitance values. Probably the circuit was to complex, the math to cancel out the effect of two scope wires (1- and 2+) was not sufficiently complete, or the measurements is highly sensitive to minor positive/negative input bandwidth differences...

[Cleber Borges]

Many thanks @attila,
But if you say you tested in the differential configuration, I will not try to do it because I do not have much experience or material for these tests.
And logically for the use of 3 electrodes I would necessarily need to use differential mode.
In any case, it would be very useful for electrochemistry if it worked.

[attila]

Hi @Cleber Borges

The Impedance Analyzer takes in account the probe R/C and open/short compensation in the measurements. With differential setup the inaccuracy/non-linearity raises at high frequency and high resistance/low current, when measuring R/C comparable to 1M/20pF of the Scope input at ~MHz like pF capacitance with 100k-M resistor.

In case you are working with low frequency and reference resistor value, like Hz to 10kHz and Ohms to 10kOhms, the Scope probe impedance has minimal/negligible effect on the measurement results.

Here you have WaveForms beta v3.8.22 supporting differential setup in the Impedance Analyzer, but you can also use the Network Analyzer which does not take in account the scope probe impedance.

 

[Cleber Borges]

Hi @attila,

Good Morning!
As far as I understand, this implementation: W1-C1P-DUT-C1N-C2-R-GND was tailor-made for the example I mentioned! Thank you very much because it will be much easier to do chemistry tests.
In general, in Chemistry, the frequencies of  ~ 1kHz - 100kHz are more usual and values of ~ nanofarad

Thanks :-)

Cleber Borges

[Cleber Borges]

 

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[Cleber Borges]

Hi @attila,

Is there any future revision possibilities for the IA-adapter to be able to contemplate these three electrodes?

Since minimizing the connectors, wires, welding ... And always using the same precision resistors greatly improve the accuracy of measurements.

It would be an interesting platform for use in electrochemistry with the use of 3 electrodes.

thanks
Cleber Borges

 

ps.: (here in Brazil I never found resistor 0.1% to buy)  :-(

 

[attila]

Hi @Cleber Borges

For the time being we have no plans for another IA module, it depends on the demand...

I think it would be useful to have IA with differential option and  4 wire connector, current/voltage.

Thank you for sharing your request.

[attila]

Hi @Cleber Borges

....
The exact value of the reference resistor can be specified in the compensation dialog of IA.

[momo]

I am also interested in this impedance differential setup introduced in the latest beta version. Although I have no idea how frequently beta version updated, I hope x86 version will be available soon.

Thanks in advance, momo

[attila]

Hi @momo

In case you are looking for the 32bit Windows build, I just added it:
https://forum.digilentinc.com/topic/8908-waveforms-beta-download/

[momo]

Thank you very much for your quick action.