A process temperature estimation system includes a mounting assembly configured to mount the process fluid temperature estimation system to an external surface of a process fluid conduit. A hot end thermocouple is thermally coupled to the external surface of the process fluid conduit. A resistance temperature device (RTD) is spaced from the hot end thermocouple. Measurement circuitry is coupled to the hot end thermocouple and is configured to detect an emf of the hot end thermocouple and a resistance of the RTD that varies with temperature and provide sensor temperature information. A controller is coupled to the measurement circuitry and is configured to measure a reference temperature based on the resistance of the RTD and employ a heat transfer calculation with the reference temperature, the emf of the hot end thermocouple, and known thermal conductivity of the process fluid conduit to generate an estimated process temperature output.