How to condition a NTC of very low resistance?
I assume you want to keep power dissipation low in the sensor, say, well below 1 mW.

If you maintain a voltage of 10 mV across the sensor, the current will range between roughly 2.8 and 20 mA, and the power dissipation will range from 28 to 200 &micro;W.

A circuit to do this would look something like this:







simulate this circuit &ndash; Schematic created using CircuitLab

The output voltage will be highest when the temperature is lowest, about 3.2V when the sensor is at 0.5&Omega; and about 0.5V when the sensor is at 3.5&Omega;. You can deal with this in software after the ADC or add additional conditioning circuitry to get what you want.

The key parameter for the opamp is its input offset voltage. There are specialized devices on the market that have extremely low values for this parameter. Also, if you want to operate from a single power suplly, keep an eye on the input common mode range.