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 have to be insulated and guarded.
The application of Ceramic materials to safeguard the platinum based wire is a technique which has been used for many years, because of the exceptional heat resistant properties of these materials. The cartridge heater with thermocouple is easily the most commonly used heat measurement implement and it is employed for measuring the temperature inside of a furnace, typically being utilized for the melting or heat therapy for metal or indeed for manufacturing ceramic products.
The ceramic components within a typical thermocouple device will be the outer protection tube which is open to the furnace. Sometimes multiple tubes are utilized inside one another to deliver the level of insulation and protection required.
Ceramic insulators (Tubes with 2 or maybe more core holes through them) may also be used to isolate the two or more wires that go to the bi-metallic joint in the head the point from which sens0rs temperature is measured.
The common materials used for that tube is a 99.7% alumina material, impervious tube, which happens to be attached typically into a metal thermacouple head, containing a terminal block that is utilized in order to connect to your standard wire to the instrumentation. In a less demanding heat atmosphere a mullite tube may be used as a cheaper alternative, which can work sufficiently around 1600 ‘oc. The mullite tube is also an impervious tube and has 60% alumina content.