Abstract: An insulated probe assembly is disclosed for use with a process instrument adapted to detect a condition of a material in a process vessel. The probe assembly includes an adaptor receivable in an opening of the process vessel. The adaptor includes a through opening having an enlarged counterbore at an outer end defining an inner shoulder. A probe extends through the adaptor into the process vessel. The probe narrows from an outer process end to an inner end at a sloped shoulder positioned in the counterbore of the adaptor. An insulator sleeve surrounds the probe and has an inner end extending into the adaptor counterbore and engaging the shoulder, and an opposite outer end extending beyond an outer end of the probe. A plug is provided for sealing the probe in the insulator sleeve at the sleeve outer end. A tubular insulating probe cover surrounds the sloped shoulder of the probe and is at least partially received in the adaptor end of the insulator sleeve and extends beyond the shoulder.