UEI Test Equipment ATT31 External Temperature Probe for The Dth31 UEi Test Instruments has over 45 years experience designing and manufacturing a broad range of Test and Measurement Tools. Professionals recognize the UEi brand for quality and innovative features designed to solve real-world problems. UEi backs its products with dedicated technical support, service and repair teams. UEi Test Instruments has over 45 years experience designing and manufacturing a broad range of Test and Measurement Tools. UEi backs its products with dedicated technical support, service and repair teams.