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?
[![The image gives the ADCON 1 register details. ][1]][1]


  [1]: https://i.sstatic.net/5TG4n.jpg
**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.