>> You place a resistor and a thermistor in close proximity at the end 
>> of an
>> insulated probe. You shroud it slightly with a plastic shield to 
>> trap
>> the heat
>> except that water can still flow into the shield easily.
>>
>> When the water is NOT touching the probe, the resistor heats the
>> thermistor to a steady-state point, above normal ambient.

With some thought this could serve to both measure water temperature 
AND to detect absence of water.

Heat resistor (or PTC) enough to raise its temperature in air to say 
80 C +.

When water is present sensor temperature will drop to a known 
temperature above water's temperature. The better the heat transfer 
provisions the better they match.

Air cooling rate will also vary as water cooling ability is varied. 
Calibration probably required.

A Peltier device may be useful here.

A pulsed sensor where delta temperature rise with time is sensed would 
allow liquid temperature measurement AND detection of liquid absence 
without having to operate the sensor at a high temperature in air.


        RM 

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