A tip assembly for an IR thermometer apparatus includes a heat sink having a heat sink cavity and a tip section and a fluid path and at least one hydraulic port. The tip assembly also includes an IR sensor mechanically seated in the tip section and thermally coupled to the heat sink. The tip assembly also includes an electrical connector configured to provide an electrical connection to the tip assembly. A fluid having a fluid temperature is introduced into the fluid path via the hydraulic port. The fluid causes the heat sink and the IR sensor to substantially reach one or more pre-determined temperatures by thermal conduction during calibration of the tip assembly. Another tip assembly having an internal heat source is described. Another tip assembly having an internal heat pump is described. A method to calibrate a tip assembly is also described.