Quote Originally Posted by amodpathak View Post
Temperature goes above ZERO.Positive temperature is displayed correctly.When i keep thermistor in freezeo then temperature does't go below ZERO.
Try some basic measurements. remove the thermistor from the board and place it in your freezer with wires connected. Measure the resistance using a digital volt meter and note it down, together with the temperature. Repeat the measurement when the thermistor is placed in ice water, and again when under a lamp or something that you can measure the temperature with. This may help you calibrate the routine better.

One possible issue could be that your chosen thermistor is positive only, ie at zero degrees C it's resistance is zero ohms (or as near to as dam it).