How Are Thermocouples Used on Aircraft?
There are a few common devices used to measure the temperature of different aircraft sections like the engine and cabin. An electrical resistance thermometer (ERT) is one such type of device, and it works on the principle of measuring resistance to a flow of electricity. ERTs are useful because they are highly sensitive, but they cannot withstand extreme temperatures. In contrast, thermocouples operate on a similar principle, but are able to work in a wider temperature range. As such, thermocouples are very often used in aircraft where temperatures can reach very high, like in the engine, as well as below freezing, like at high altitudes. Consequently, it is important to understand how these crucial components function on aircraft..
What Is a Thermocouple?
A thermocouple is a device which consists of two wires of dissimilar metals, or metal alloys, in a closed circuit. These wires form a sealed junction at one end, referred to as the hot end, while they are left separated at the other, called the cold end. When a difference in temperature is registered between the hot and cold end, a voltage is sparked within the circuit. This voltage spark is then measured by a device located at the cold end which takes both the voltage and the known temperature of the cold end to calculate the temperature of the hot end. The hot end of this circuit can be placed in the aircraft component which is to be monitored, measuring its temperature in return.
Thermocouple Types Used in Aircraft
The exact combination of metals used across the two wires of a thermocouple determines its type. Generally, two thermocouple types are suitable and commonly used in aircraft: type J and type K. However, Type N thermocouples have been seeing use as a replacement for Type K in recent years.
Type J is made of a positive iron wire and a negative constantan (copper-nickel alloy) wire which operate within the temperature range of 0 to 750 degrees Celsius. As such, it is suitable for measuring the cylinder head in piston engines. The hot end of this device is usually located within the cylinder head where it can measure the temperature as it changes.
Type K is a frequently used thermocouple type that can withstand a great temperature range. Made from a positive nickel-chromium wire and a negative nickel-aluminum wire, Type K works in temperatures from -200 to 1250 degrees Celsius. Due to this capability, they are often used in turbine engines to measure the temperature of exhaust gas as it leaves the turbine.
Type N thermocouples consist of a positive wire made of nickel chrome silicon alloy and a negative wire of a nickel silicon alloy. These thermocouples work over the same temperature range as Type K, but have slightly better resistance to corrosion. They also have much better repeatability characteristics around 400 degrees Celsius, a temperature which Type K is known to have issues with.
Choosing a Thermocouple for an Assembly
When considering your options for a thermocouple device in your aircraft, there are many different suppliers to choose from. To simplify your search, Aerospace Aces invites you to browse our vast catalog of available products which are all sourced from trusted suppliers on our Approved Vendor List (AVL). As a premium aircraft parts distributor, we provide thorough quality evaluation for all our items, along with expedited shipping to meet our customers’ strict operational requirements. When you are in need of high-caliber items, including thermocouples, Aerospace Aces is here to assist you with all that you require.
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