>I'm looking for some way to measure when a probe is in
>or out of the water.
...
>A couple of people on this list suggested that capacitance
>might be a better way to go, and I'm looking to try that route.

You might try and manufacture your own dielectric measurement sensor. This
is what is being used on the Huygens probe that is going to be set adrift
from the Cassini space probe that has just gone into orbit around Saturn.

The sensor consists of a number of thin plates (it looks like about 10 thou
stainless steel) about 4 or 5 square inches, and formed up like the old air
spaced tuning capacitors in radios. There is a bolt through each corner, and
odd numbered plates connected to one bolt, even numbered plates to another
bolt, making a capacitor. The whole thing was then dipped into a plastic
like stuff to put an extremely thin insulating coating on all the surfaces,
so there can be no electrical contact with the liquid.

The presence of liquid between the plates will now change the capacitance,
due to the different dielectric properties of the liquid. Different liquids
will produce different levels of capacitance change.

Not clear what you are trying to measure, but you may need to have a large
enough gap between the plates to ensure that when the sensor comes out of
the water, the plates are far enough apart that there is no water retained
by capillary action.

Have fun experimenting.

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