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Closely measuring the temperature of various aircraft components allows both the aircraft and its passengers to fly safely and with greater fuel efficiency.

This needs to be achieved in real time so as to accurately portray the status of the aircraft engine and other instruments necessary for flight.

How Aerospace Thermocouples Are Used to Monitor Aircraft Temperature

How Is Aircraft Air Temperature Controlled?

The International Civil Organization (ICAO) has set a standard aircraft temperature for aviation, which is often referred to as the ICAO Standard Atmosphere Standard by the Federal Aviation Administration (FAA). This standard temperature must be maintained throughout air travel; applying to the cockpit, engine and cabin to ensure that on-board passengers and airline staff are kept safe while in the air. This rule applies to every flight of both non-domestic and commercial aircrafts.

But how is an aircraft temperature controlled? Measuring this can be difficult. Because of the pressurisation caused by fluctuating high altitudes, the density and temperature of the outside air will drastically fluctuate from the temperature and pressure within the plane itself.

Several devices can be used to measure the air temperature of aircraft components, including both the engine and cabin. Two of the most common devices are Electrical Resistance Thermometers, or devices, which work on the principle of measuring resistance to a flow of electricity. As the wires inside the device heat up, the resistance to the flow of electricity increases. They are highly sensitive, but cannot withstand extreme temperatures.

Thermocouples, on the other hand, can. Thermocouples are another commonly used device within aircrafts, and so often offer an alternative to Electrical Resistance devices for measuring aircraft temperature.

What Is a Thermocouple and How Is It Used in Aviation?

A thermocouple is capable of immediately registering changes in thermostat temperature and atmospheric pressure, so finds its use amongst many industries and a peppering of applications – acting as a controller and monitor of aircraft temperature in a range of settings; from domestic homes to aircraft cabins. When it comes to air travel, thermocouples can be used to measure the cold on aeroplanes and how it compares to the outside air temperature.

Thermocouples can also be used to measure the ventilation, pressure and temperature of the cabin air. This applies to all flights, across the total air flight - as the plane speed increases and decreases through takeoff and landing.

How Does a Thermocouple Work?

A thermocouple operates by two wires of dissimilar metals, or metal alloys, in a closed circuit. These wires are sealed together at one end (referred to as the hot end) whilst left separated at the other (the cold end). When a difference in temperature is registered between the hot and cold end, a voltage is sparked within the circuit, which is measured by a device located at the cold end; taking the measurements of both the voltage and the known temperature of the cold end, the temperature at the hot end can be calculated. The hot end of this circuit can be placed in the aircraft component which is to be monitored, thus measuring its temperature.

Aerospace Thermocouples Used In Cabin and Aircraft Control Systems

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 aircraft 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 engine thermocouples, measuring the aircraft 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.

Thermocouple Wire Suppliers

Scott Precision Wire has been established since 1923, and manufactures industry-leading thermocouple wire for use within aircraft temperature monitoring systems. With our years of experience and dedication to perfecting our products, we can offer high quality aerospace thermocouples which has undergone rigorous testing to ensure it is of a premium class.

Scott Precision Wire provides thorough in-process checks and testing to ensure our thermocouple wire is suitable for your applications. Our thermocouple laboratory is devoted to testing against customer EMF specifications as well as other variables such as surface hardness and resistance.

A custom range of sizes is available, from small sample lengths to full-length reels – all of which is manufactured to the same impeccable standard. We provide the resources for a variety of different uses of thermocouples, so whatever your requirements, we can meet them.

We understand getting your thermocouple aviation wire right is crucial; sample product batches are available for sampling and testing before you commit to full production.