> I was wondering if there is anyone that
> has ever had any experience with measuring
> either of these two. The conductivity
> is measured using two probes in the solution.
> An AC signal is passed between the two
> to prevent any build-up on one of the electrodes.
> I presume the volt drop is then measured to
> determine the conductivity which is measured
> in micro-Siemens/cm.
>
> pH is usually measured with a glass probe, but
> I'm not sure what to expect at the other end of
> the probe, as I have not come across any data
> sheets on them.

From my impression, there are a number of ways of measuring pH; one very
simple method is to use two disimilar metal probes and measure the current
generated by the created cell.  I don't know what problems there are with
either probe aging or with solution contamination; you'd probably want to
have the probes open-circuit when you weren't actually taking measurements
or maybe even run a very small reverse current through them (to reduce the
effects of current leakage through the solution).  Perhaps others here know
more about such things.