Most have ruled it out already but I think a conductivity probe could
still be worth trying out.

A few years back I made conductivity probe circuits for use in dairy
sheds (milking sheds). If set too sensitive they would act on milk
froth, which in that case was an undesireable characteristic
because we wanted to read milk level.

Perhaps a couple of narrow stainless steel probes placed as far
apart as possible to prevent froth hanging between them.You could
add another probe to measure liquid level too if that is an
advantage. Increasing the frequency of the AC bias applied to the
probes to a few hundred khz allows capacitve sensing (or even a
hybrid capacitance/conductance method), so you could use a metal
plate under the cup for the earth instead of an earth probe.

Regards,

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  brent.brown@clear.net.nz

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