Re: temperature sensor
Configure your op amp as a buffer ( Unity gain amplifier ) and you will get the same vtg. at the output.
Make calibration as per below, before you go.
1. Rise the temperature of LM35 to the maximum you want to measure. This gives the highest o/p voltage. Set your +ve reference vtg. of PIC slightly above this value.
2. Lower the temperature to the least, and do the same, for -ve ref. voltage.
Now you may go ahead. You have calibrated your sensor.