Sean,

> Did you observe this change from 6500 Hz to 7000Hz just once or does it
> happen consistently? What do you have to do to get the circuit to go back
> to 6500Hz? Does it just go back to 6500Hz on its own if left until the
> night time?

I recalibrate it and then the next day I see it change. Going back I=20
have not observed. Good point. I will need more time to carry out this=20
experiment.

> What kind of caps are you using for the AC coupling to the probes? Could
> there be leakage current through these which is presenting a small DC
> voltage between the probes, leading to an electrochemical reaction?

Metal polyester. At low frequency, the waveform is 50% duty cycle. At=20
higher freq the duty cycle changes. This also could be one of the=20
issues. I will investigate more on this.

> I would think that, even in the absence of a DC bias, the surface of the
> probes would change chemically after a few hours in the salt water, or ev=
en
> pure water. This change might sequester some of the salt out of the
> solution and change the conductivity. It also might change the conductivi=
ty
> by insulating the probes partially or changing the ion
> mobility/permeability.

This also I have to investigate. For me to get at the bottom of this. I=20
will need a couple of weeks :-), but I will do it and check out all=20
permutations and combinations.

Cheers

Ravi

--=20
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