>The current is 200uA. I try to display the temperature data on an LCD, but
the
>reading takes more than 10 minutes to be stable, meaning the change is very
>little. Why is this so?

How big are the variations you are getting? remember that if you could do a
step change of the temperature the resistance of the thermistor is going to
follow a curve similar to the charge or discharge curve of a capacitor
because of thermal inertia, that is to say the thermistor will not
instantaneously change temperature, but will take a certain time to reach
the new temperature.

Also if the thermistor is not thermally bonded to a (relatively) large mass
any draft of air around it will cause it to change temperature (typically
cool off) which may show on your readout if it is sensitive enough. This
will easily change the temperature 0.1C and often up to 0.5C just by waving
your hand to disturb the air around it.

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