Use of Thermocouples in Industrial Ceramics Applications
Measurement of high temperatures, greater than 1000 C, using ceramic based thermocouples is a well established process. In order to do this successfully the resistance wires within the thermocouple need to be insulated and protected.
The use of Ceramic materials to protect the platinum based wire is a method that has been used for many years, due to the exceptional heat resistant properties of these materials. The thermocouple is the most commonly used heat measurement implement and is used for measuring the temperature 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 a typical thermocouple device are the outer protection tube that is exposed to the furnace. In some cases multiple tubes are used inside each other to provide the level of insulation and protection required.
Ceramic insulators (Tubes with 2 or more core holes through them) are also used to isolate the two or more wires that go to the bi-metallic joint at the head which is the point from which the temperature is measured.
The typical material used for 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 to connect to a standard wire to the instrumentation. In a less demanding heat atmosphere a mullite tube may be used as a cheaper alternative, which will work sufficiently up to 1600 ‘oc. The mullite tube is also an impervious tube and has 60% alumina content.
Ceramic materials are ideal for many high temperature applications but are also ideally suited to aggressive wear and chemical situations.