How linear is brine?

[Mark Tillotson]

For fun I decided to test a small glass of salt water for linearity as a resistance. The electrodes were strips of stainless steel (in fact the spring strips from old windscreen wiper blades!). This was added to a divider circuit with 680 ohms as the lower leg. My QA403 was used to plot various aspects of this resistor's performance:

At the standard 1kHz the typical distortion v. level curve shows up:

The linearity increases with frequency:

This might be due to impedance falling, or polarization or perhaps something else (scope for further investigation), I forgot to check if the gain varied with frequency

Seems to be mainly 3rd harmonic (makes sense as the cell is symmetric):

Residual at 60Hz:

 

[MarcelvdG]

THD or THD+N?

 

[cvanc]

Some audiophile somewhere will pay good money for saline resistors.

Just sayin' 🤣

 

[stellavox]

Per this post, I immersed my preamp in salt water. It sounded more liquid!

Until it shorted out. Then it sounded dry and grainy.

 

[HeyBill]

Values may change with different electrodes. Anyway, back to the salt mine.

 

[cvanc]

That's why Mark is already planning a Rhodium version.

Dude I think you just found your retirement plan 👍

 

[Elvee]

I suspect that most of the non-linearity is caused by the metal to electrolyte interface. To avoid that, a 4-wire setup would be preferable, with the sensing electrodes being as neutral as possible, carbon rods for example

 

[cvanc]

You are of course correct, and I retract my earlier comments.

One should clearly reserve Rhodium to make the case out of.