Liquid thermometers The principle of operation of such a thermometer is based on the expansion and contraction of the liquid that fills the bulb changes its volume when oscillating at its own tempetature. Mechanical thermometers The principle of operation of such thermometers is also based on expansion. Such thermometers differ in the special accuracy of measurements.
Gas thermometers In contrast to liquid thermometers in gas, some kind of inert gas is used. Digital thermometers These mercury free thermometers are easy to use and the reading is displayed in a more convient form.
Infared thermometers These thermometers ude a crystal which is sensitive to infared or heat radiation. One of the exclusive qualities of it is that it is based on non-contact mechanism which makes them really easy to use.