A novel high temperature thermal instrument is proposed, which utilizes a dual-sensing platinum resistor encased in a mono-crystalline alpha-alumina (sapphire) substrate. The instrument is comprised of four platinum trace elements, oriented with 90° rotational symmetry atop a 1120 oriented crystal lattice substrate. All four of these sensors measure temperature directly via 4-wire ohm measurement of the absolute resistance, while two sets of orthogonal sensors measure the differential strain created by the axially dependent thermal expansion coefficient of a sapphire substrate via a WSB measurement. The RTD temperature measurement calibration is then monitored for drift and corrected by comparing the differential strain-derived measurement of temperature to the temperature derived from the RTD measurement. This allows the instrument to self-calibrate via comparison of two functionally independent measures of electron mobility and operate in extreme environments which have previously caused RTD sensors to drift from their initial calibration and introduce an undefined measurement error. The intended deployment configuration and instrument construction is defined in terms of MEMS fabrication processes and performance of the sensor is simulated to evaluate and confirm the functional applicability of the instrument for operation in pebble bed HTGR thermal environments
