Cleber Borges

Before I continued my tests with beer, I wanted to make sure of two things:
a, the amount of the sample fluid does not influence the impedance values
b, the measurement itself does not change the sample fluid so that its impedance is changed at every measurement
For case A, I made 3 references with 1 cup, 2 cups and 3 cups of tap water.  I used the same source and the same container for all the measurements.

 
Then I made 3 other measurements of the same 3 cups of water.

 
At this point I can conclude that the measurements are fairly harmless, there is only a small amount of change on the dataset after each consecutive measurement. I could probably use lower voltages, which could theoretically reduce the impact further.
The amount of the test fluid does change the dataset somewhat, so I will keep that in mind when I go ahead with my further tests and I will try to keep the volume of the fluid fixed.
As we could see from my previous post, the temperature is very important, so that's another parameter I will try to manage and keep constant between the tests.

Hey guys,
I've made some experiments that could be interesting for your as well. I put tap water into my ceramic container, I heated it to different temperatures and measured the impedance every 5 degrees.
You can see the values between 60 ° Celsius (140 ° Fahrenheit) and 5 ° Celsius (41 ° Fahrenheit). Red is 60 Celsius, blue is 5 Celsius and there are 10 steps between them.

hello @Andras ...
My IA board (impedance analyzer) arrived a few days ago, but I did not even test it ... But now I have the AI board in my hands. Thanks for your attention.
The IA board does not allow a reference electrode (RE) such as figure-item B. Such a scheme would be to not pass current between the working electrode (WE)  and a reference electrode (RE). It would be to measure more accurately and discount several other effects in a more automated way. This scheme is not necessarily mandatory.

You can use the scheme of just two electrodes as you mention.
I am a chemist and I do not have much knowledge of the electrical / electronic part. I imagine that your measurements reflect well the salinity of the water tested.
 
Actually, I think this device - AD2 - could provide a lot of chemical information of Impedance measurement, but I just started reading about it.
It's great to know that more people are interested in AD2 and EIS ... so we can build a source of information.
Regards,
Cleber
 

Hello @attila
Good Morning
Thanks for your response and patience :-)
I am a Professor of Chemistry  (University Researcher in Brazil) and I am interested in the area of:
EIS - Electrochemical Impedance Spectroscopy  ( below SITE reference in [1] ).
In an EIS study, the frequency region of 100kHz to 1uHz is very common.
It is the current practice of this area.
The amplitude of the signal is a few millivolts. Usually it's 10mV.
So my interest in low frequencies and low amplitudes
In WaveForms Help - AD2 (item 5: AWG) says:
The resolution is ~0.7 mV for amplitudes above 1 V, and ~0.18 mV for amplitudes of 1 V and lower.
Does the AD2 and sound card achieve a higher resolution than this?
Because I see that the low frequency is not limiting but the signal resolution at 10mV seems to me to be near the limit.
I am a layman in the subject and I am still starting in EIS
but I think that the hardware and the software could also be very useful in this field :-) !!!
Thanks again for your dedication!
Cleber Borges
[1] - https://en.wikipedia.org/wiki/Dielectric_spectroscopy