Measurement of high temperatures, greater than 1000 C, using ceramic based thermocouples can be a well established process. To do this successfully the resistance wires within the thermocouple need to be insulated and protected.
Using Ceramic materials to protect the platinum based wire is a technique that has been used for many years, as a result of exceptional heat resistant properties of these materials. The thermocouple controller is the most commonly used heat measurement implement which is used for measuring the temperature on the inside of a furnace, typically being used for the melting or heat treatment of metal or indeed for manufacturing ceramic products.
The ceramic components in the typical thermocouple device would be the outer protection tube which is subjected to the furnace. In some cases multiple tubes are utilized inside the other to provide the degree of insulation and protection required.
Ceramic insulators (Tubes with 2 or higher core holes through them) are also accustomed to isolate the 2 or more wires that go to the bi-metallic joint with the head the point that sens0rs temperature is measured.
The typical materials used to the tube is a 99.7% alumina material, impervious tube, which is attached typically to a metal thermacouple head, containing a terminal block which is used for connecting into a standard wire towards the instrumentation. In a less demanding heat atmosphere a mullite tube may be used being a cheaper alternative, that will work sufficiently up to 1600 ‘oc. The mullite tube is likewise an impervious tube and contains 60% alumina content.