You need to provide more information. What is the name/brand of this IR sensor you are using?
What is its expected output in output in volts for various temperatures? Unless it behaves like an RTD, thermistor, or thermocouple, then you will have errors in using any of those Temperature choices.
See what kind of calibration curve the sensor has. Read the sensor in volts and apply custom scaling based on the calibration curve to get a reading in degrees.
