Hi Gavin,

>I was wondering if there is anyone that
>has ever had any experience with measuring
>either of these two.
you are lucky, I work with both

>The conductivity
>is measured using two probes in the solution.
Right. Use inert material, like stainless steel or graphite, platinum used
in laboratory applications is probably unnecessary for you.

>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
AC signal correct, several hundred Hz up to units of kHz. Better work with
constant (and small, <1V effective) AC voltage and measure current, which is
proportional to conductivity.

>determine the conductivity which is measured
>in micro-Siemens/cm.
Yes. You have to calibrate your measuring cell constant using KCl solution
of known conductivity. Use destiled water to adjust zero.

>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.
Its output is voltage, most probes give zero voltage at about 7 pH and
change its output by about -58 mV/pH (negative slope, voltage decreases with
increasing pH value). Slope is temperature and probe dependent, also changes
with time. You may need adjustment pots (or adjust in software) for both
zero point and slope or zero point only, and calibrate using solution(s) of
known pH (buffer solutions). Last but not least, the output inpedance is
several hundred megaohms, so you need a FET OpAmp right after the probe.

>
>Any help would be most appreciated.
No problem. You may also try to call Omega company and request pH and
conductivity handbook. Besides all their wanderful product info with even
more wanderful price-tags you will get a short overview of pH and
conductivity measurement in the book.
Omega phone: (203)539-1660
fax: (203)539-7700
Toll-free: 1-800-TC-OMEGA
email:info@omega.com

Josef
mailto:euroclass@pha.pvtnet.cz