Closely measuring the temperature of various aircraft components allows both the aircraft and its passengers to fly safely and with greater fuel efficiency.
How Thermocouples Are Used to Monitor Aircraft Temperature
Thermocouple Types Used In Aircraft
The thermocouple type is decided by the combination of metals used across the two wires (referred to as legs) within the device. Typically, two thermocouple types are suitable and commonly used within aircraft – these pertain to type J and type K although the use of Type N thermocouples in place of Type K has been seen to be increasing.
Type J is made of a positive iron leg, and a negative constantan (copper/ nickel alloy) leg; it operates within a temperature range of 0°C and 750°C, and is suitable for measuring the cylinder head in reciprocating, or piston, engines. The hot end of the device is usually located within the cylinder head, where it can measure the temperature with immediate effect.
Type K is an established and commonly used thermocouple type, since it can withstand a great temperature range. Consisting of a positive Nickel/ Chromium leg and a negative Nickel/ Aluminium leg, type K works in temperatures from -200°C to 1250°C. It can be located in turbine engines, measuring the temperature of exhaust gas as it leaves the turbine.
Type N thermocouples consist of a positive leg of a Nickel Chrome Silicon alloy and a negative leg of a Nickel Silicon alloy. Type N thermocouples work over the same temperature range as Type K but have a slightly enhanced resistance to corrosion and significantly better repeatability characteristics around 400°C; a known issue with Type K.