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A thermometer is a device capable of measuring temperature, by using a temperature sensor (conductive wire, mercury, alcohol, etc.) in which some physical change occurs with temperature, such as dilation and a way of converting this physical change into a numerical value (like the thermometer scale).
The classical thermometer, uses a liquid, such as mercury, Galinstan, alcohol, which deforms when exposed to different temperatures. Main disadvantage is that they cannot operate at very low temperatures, as their liquid will freeze.
Lab scale thermometers can be either simple, or with a ground glass joint. They are either mercury or alcohol-based.
Similar in operation to the scale thermometers, they use a piece of metal instead of a liquid, which deforms depending on the temperature, deformation which is translated to a dial scale, displaying the temperature. Bimetallic thermometers are the most common type.
Come in two main types:
- Resistance thermometers: determine the temperature by measuring the change in the electrical conductivity of a metal wire.
- Thermocouples: thermocouples produce a temperature-dependent voltage as a result of the thermoelectric effect, which can be interpreted to measure temperature.
Infrared thermometers can measure the temperature using a laser beam. Useful to measure extreme temperatures from distance, without exposing the thermometer and its user to hazardous environment.
Thermometers, both scale-based and mechanical can be found in most hardware and dollar stores. Electronic and infrared thermometers can be bought from electronic and construction suppliers.
Lab thermometers can be bought from lab suppliers.
Mercury-based thermometers have been phased out in most of EU, though occasionally some street vendors may still sell such thermometers, usually coming from former Soviet block countries where such items are still being manufactured. Mercury-based lab thermometers are also getting harder to find.