Wednesday, 12 September 2018
Skin Type Thermocouple is designed to measure the temperature of the body. It is bonded to the surface of the body to which temperature is to be measured through an insulating pad so that it collects temperature. This model of the thermocouple is typically used within the high-temperature industry and/or corrosive environments where fast and accurate temperature measurement is critical.
The most important consideration for effective Skin Type Thermocouple is its design which can provide repeatability, durability, and accuracy. To achieve these functions thermocouple must incorporate with its design which should provide excellent insulation properties, material compatibility and good physical contact with the tube and it should also have the ability to withstand high radiant temperatures and stresses and in some cases harsh combustion chemistry.
Mostly Skin Type thermocouple is directly welded to the surface to which we have to measure the temperature with a thermally insulating pad so that only surface temperature is collected rather than surrounding air temperature. For a thermocouple to work at its optimum range, the thermocouple sheath must remain in close contact with the tube. The weld pad should be positioned at the critical point and the remaining cable should be routed away from the direct heat – along with the coolest side of the vessel. This installation technique is important as it allows the thermocouple to utilize the process tube as a heat sink.
In addition to the weld pad, expansion loops design can be considered. A furnace can experience a movement of between 50 mm and 350 mm, from startup, to reach its process temperature. If such incremental expansions are not considered through the integration of expansion loops, the Skin Type Thermocouple will be subjected to strain and even breakage. Expansion loops are therefore recommended to ensure the optimum life of the thermocouple helping to reduce commissioning and maintenance problems.
In Skin Type thermocouple there is no need for thermowell whereas in other thermocouple thermowell is required. Skin Type thermocouple has low mass as compared to other thermocouples. Skin Type thermocouple is never used as a shield they are directly connected to the surface of the body to which temperature is to be measured whereas other thermocouples cannot show this property.