Water conductivity measurement

[north2012]

Thanks! I will inform you about results. Regards, John

 

[D.A.(Tony)Stewart]

I am uncertain as to the polarity of ε'' as there are two definitions with opposing polarity.

as defined elsewhere in Wiki


But whatever polarity is assigned, the Conductivity value is related to the Charge Current Density and the Electric Field

If jε'' = ε' + jσ/ω then the imaginary term σ/ω → ∞ as ω → 0

I realize , this only adds more questions than answers but I wonder if an interdigital filter can properly measure the Charge current density, J and the Electric Field, E with such close proximity effects. I wonder if this is why they tend to be large parallel plates with a big gap to minimize the distortion effects of surface charge gradient fields with the dipole moments of the electrolyte..

But then again, Maybe its a better way. I'm not sure.

 

[FvM]

I am uncertain as to the polarity of ε'' as there are two definitions with opposing polarity.

Yes, the negative polarity corresponds to the usual representation of AC quantities by complex numbers.

I copied the expression from Wikipedia without thinking about the convention. Respectively you get
B = +Aε'ω (leading current of a capacitor is represented as postive susceptance)

In any case, after putting in the ε'' term, you should get positive resistance and conductance, otherwise the cell would act as an energy source.

The frequency dependency of ε'' isn't but a natural consequence of roughly constant conductivity. I wonder if the complex ε representation is of any practical use for conductivity measurement and calculations.

Regarding interdigital conductivity probe, I think the disadvantages are the non-uniform current distribution and high field-strength at electrode edges, also that it's almost impossible to get an accurate geometry factor by calculations, because small variation of electrode distance and even edge shape have a large effect. Long-term stability is probably poor.

 

[north2012]

When sample is in the air I have impedance change shown in next figure



and when sample is in water