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W A T L O W

Application Guide catalog - 7347 Application Guide

The Art of TemperatureSensing

Defining Temperature— What Is It?

Temperature is the degree of “hotness”or “coldness” of a body or substance as indicated on, or referenced to a standard scale.Another way to think of temperature isin terms of heat energy. Heat energy is the amount of molecular activity which is the sum of an atom’s subatomic par-ticle vibration, oscillation and friction with other subatomic particles in thesame molecule.The greater the molecular activity, the greater the amount of heat energy.Conversely, less molecular activity results in less heat energy.The theoretical point, or “temperature,”at which there is no molecular activity is called absolute zero.To measure “temperature” or the rela-tive amount of heat energy, temperature scales have been devised to definearbitrary increments.There are four temperature scalescommonly in use today: •Celsius—commonly usedthroughout the world [°C =
Temperature Sensors 5 �
9 (°F - 32)]•Kelvin—used in conjunction withthe Celsius scale for scientific and engineering equations[K =

Temperature Sensing Methods

5 �
9 (°R - 0.6°); K = °C + 273]•Fahrenheit—commonly used inNorth America (°F = 1.8°C + 32)•Rankine—used in conjunction withthe Fahrenheit scale for scientific and engineering equations[°R = 1.8K + 0.6°; °R = °F + 460°] Contact temperature sensing brings the sensor in physical contact with a substance or object. Contactsensing can be used with solids, liquids or gases. Non-contact temperature sensing (infrared temperature sensing or IRsensing) measures temperature byintercepting a portion of the electro- magnetic energy emitted by an object or substance (most notably the energycontained in the infrared portion of theelectromagnetic spectrum) and detect-ing its intensity. This method is used to sense the temperatures of solidsand liquids. IR sensors cannot be usedto sense the temperature of gases due to their transparent nature. 33