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“Other Means Of Measuring Temperature Than Thermocouples” 1. Thermometers One of the most popular methods of measuring temperatures is using a thermometer. The bulb thermometer is the most common glass thermometer. It contains some type of liquid, which is generally mercury. The principle, that bulb thermometers work, is that a liquid changes its volume relative to its temperature. Therefore, liquids occupy less space when they are heated. Galileo invented the first thermometer. It was an air thermometer consisting of a glass bulb with a long tube attached. When, the dupe was dipped into a cooled liquid the bulb was warmed, expanding the air inside. As the air continued to expand, some of it escaped. When the heat was removed, the remaining air contracted causing the liquid to rise in the tube indicating a change in temperature. However, the Galileo type thermometer is very sensitive, it is not too practical because it can be affected by small changes it atmospheric pressure. After Galileo, Fahrenheit invented a new type of thermometer, the alcohol and the mercury thermometers, which was not affected by atmospheric pressure changes. Mercury thermometer consists of capillary tube, which after being filled with mercury is heated to expand the mercury and expel the air from the tube. The tube is then sealed, leaving the mercury free to expand and contract with temperature changes. One disadvantage of this type of thermometer is that it is not so sensitive, compared to the air thermometer.
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