I am trying to use in built ADC of PIC 18F4520. The input is a voltage signal by an analog sensor whose output varies with temperature. It comes to be about 5.2 V at a certain temperature. Now, i am getting fluctuating values of ADC output (I checked the ADC output by printing the result with 4 seven segment display unit). When the output is 60 it fluctuates between 60-70. I am unable to understand the cause of this fluctuation. As i intend to measure temperature via the output of this analog sensor the fluctuation in ADC output is causing trouble. What can be the reason and please provide it's solution also. Also, is there a way to know the output that 10 bit ADC will show for a particular input?

I am also confused that if i had set the reference voltage VFG0 to VDD i.e. 5 V. and VFG1 to VSS i.e. 0 . So will my ADC be able to measure 5.2 or any voltage above 5 V ? Please answer, thanks in advance.