Thermometrics is the science of measuring temperature. The accurate measurement of temperature is crucial in many settings, including industrial processes in manufacturing, engineering applications, technology, research science, medicine, and even everyday applications such as cooking. Due to its wide variety of applications, thermometrics is a broad field. A number of different thermometric devices have been developed, ranging from the common mercury or digital thermometers used in households to highly sensitive thermistors used in automotive and industrial processes. Temperature can be measured through a variety of different methods. Thermometric devices work because a rise or fall in temperature affects their physical structure in a specific and predictable way. Since heat is a form of energy, it can be transferred from one object to another in situations where there is a difference of temperature between the two objects — a temperature gradient. This principle is known as conduction. Thermometers register a given temperature because heat is transferred from the environment to a material inside the thermometer. For example, a mercury thermometer consists of mercury, a metal that is a liquid at room temperature and pressure, inside a glass tube. The glass tube is either filled with nitrogen gas or kept at a vacuum. When heat is transferred to the mercury in a bulb at the base of the thermometer, the mercury expands into the space above it. This expansion in volume is due to the transfer of heat energy from the environment to the particles of mercury, which move farther apart from each other when energized. Since the change in volume caused by heating the mercury occurs in a predictable and constant way, the thermometer can be calibrated and used as a temperature-measuring instrument. Other types of thermometers, though they vary in sensitivity and in the types of materials they use, work based on the same principles of heat transfer. In advanced thermometrics, however, it is sometimes necessary to use a different type of device with greater sensitivity, called a thermistor. Like a thermometer, a thermistor can also be used to measure temperature, but functions through a slightly different mechanism. Thermistors are made of metallic or ceramic materials that increase or decrease in resistance to electrical current along with increases or decreases in temperature. Since the relationship between resistance and temperature in these devices is predictable based on the materials the devices are made of, thermistors can be used to measure temperature changes. Thermistors are used widely in thermometrics and manufactured in many different styles. A few practical areas in which thermometrics are important include the automotive industry, medicine, and the home appliance market. In automobiles, precise measurements of temperature are necessary to ensure that engines are properly cooled. In medicine, a high body temperature can indicate disease and is monitored closely. Medical appliances such as incubators also rely on thermometric devices for operation. In home appliances, such as ovens, temperature must be controlled so that meats and other food can be properly cooked.
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