Measurement of high temperatures, higher than 1000 C, using ceramic based thermocouples can be a well established process. To carry out this successfully the resistance wires throughout the thermocouple must be insulated and guarded.
The use of Ceramic materials to protect the platinum based wire is a technique which has been used for many years, because of the exceptional heat resistant properties of those materials. The thermocouple temperature sensor is easily the most frequently used heat measurement implement and it is useful for measuring the temperature within a furnace, typically used for the melting or heat treatment of metal or indeed for manufacturing ceramic products.
The ceramic components inside a typical thermocouple device will be the outer protection tube which is subjected to the furnace. Occasionally multiple tubes are used inside one another to deliver the level of insulation and protection required.
Ceramic insulators (Tubes with 2 or more core holes through them) will also be used to isolate the a couple of wires that proceed to the bi-metallic joint on the head the point through which sens0rs temperature is measured.
The common materials used for that tube can be a 99.7% alumina material, impervious tube, which can be attached typically into a metal thermacouple head, containing a terminal block which is used for connecting to some standard wire to the instrumentation. In a less demanding heat atmosphere a mullite tube can be utilized being a cheaper alternative, which will work sufficiently up to 1600 ‘oc. The mullite tube is also an impervious tube and it has 60% alumina content.