Types of Thermometer and Working Principles

            TYPES OF THERMOMETERS AND  WORKING PRINCIPLES INTRODUCTION A  thermometer  is a device that  measures temperature  or a  temperature gradient  (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a  mercury-in-glass thermometer  or the pyrometric sensor in an  infrared thermometer ) in which some change occurs with a change in temperature; and (2) some means of converting this change into a numerical value (e.g. the visible scale that is marked on a mercury-in-glass thermometer or the digital readout on an infrared model). Thermometers are widely used in technology and industry to monitor processes, in  meteorology , in medicine, and in scientific research. Any substance that somehow changes with alterations in its temperature can be used as the basic component in a thermometer. Gas thermometers work best at very low temperatures. Liquid thermometers were once the most common type in use. T