Mineral insulated thermocouples consist of an outer metal sheath that houses the thermocouple conductors; the sheath is then filled with a highly compacted magnesium oxide powder to prevent the conductors contacting at any point other than the fixed junction.
This construction allows the sheaths to be bent or formed to shape as required by the user, but remain rigid during use. The whole assembly is hermetically sealed giving the conductors full protection from the operating environment.
Available in 2 core (simplex) or 4 core (duplex) with a range of outer sheath materials including Grade 25/20 (310) stainless steel (corrosion resistant and suitable for use in sulphur bearing atmospheres), Alloy 600 (severely corrosive atmospheres to high temperatures) and Nicrobel D (recommended with type K and N thermocouples with good high temperature strength and excellent performance in oxidising, carburising, reducing and vacuum atmospheres).
Reference : sterlingsensors