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Composition
Type T thermocouples are made from a combination of copper and constantan. Constantan is an alloy of copper and nickel. The copper is used for the positive side, and the constantan for the negative one. One advantage is that these materials give Type T thermocouples a homogeneity or uniformity that some of the other thermocouples do not have. Homogeneity is important because otherwise there would be an increased probability of temperature gradients, where the temperature inside of the metals would vary based upon location.
Temperature Measurements
Type T thermocouples' composition make them ideal for environments where there is moisture or extreme cold. They are preferred for these types of measurements because of their ability to resist corrosion and rust. Type J thermocouples, for instance, are made using iron-constantan, and the iron makes them susceptible to rust. Also, Type T models will not become brittle at temperatures below zero, which is yet another problem with Type J. The ideal measurement range for Type T is from --200 degrees Celsius to 350 degrees Celsius, which is --328 Fahrenheit to 662 Fahrenheit. In actuality, typical measurements are done in the --70 degrees Celsius to 400 degrees Celsius ranges. This is --94 degrees Fahrenheit to 752 degrees Fahrenheit. These are the ranges where Type T tends to be most accurate.
Magnetism
Type T thermocouples are not magnetic, which is another advantage. This is because users needing to take measurements in environments where magnetic fields are present do not have to worry about Type T sensors changing their properties. Thermocouples made from magnetic materials such as iron or nickel lose their magnetism when they are heated above certain temperatures, and this affects their ability to take measurements. Type J thermocouples are magnetic, because of the presence of iron. Type K thermocouples are also magnetic, because they are made using chromel and alumel. Chromel is an alloy made from nickel and chromium. Alumel is an alloy made using nickel and aluminum, although small amounts of manganese and silicon are often present.
Considerations
Compared with other thermocouples, such as rare earth ones, Type T models are inexpensive. However, despite their advantages, they do have some weaknesses. Type T thermocouples cannot be used in extreme temperature environments, because they will become damaged and melt. As with other thermocouples, their output signals are small, making them are prone to noise, and so they must be calibrated before usage.
Other applications include generators, medicine and scientific research. They are also used to take temperature measurements in animals, and in environments such as tissue, liquids, powders and food.