Temperature measurement - Temperature measurement Metrology...

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Temperature measurement Metrology and Instrumentation August 4, 2011 Dr. Belal Gharaibeh
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Introduction to temperature measurement We can measure temperature change rather than absolute (single) temperature at a certain location Previously we explained how that a measurand (input) is measured by comparing to a standard Example: unknown mass is compared to a universal kg prototype Temperature change, unlike all other properties, is measured by observing the changes in another temperature depended physical property Temperature is gauged by its affect on quantities like: volume, pressure, resistance, and radiation energy Example: change in volume of liquid in glass thermometer indicates the temperature change
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Temperature sensing techniques 1. Change in physical dimensions 1. Liquid in glass thermometer 2. Change in gas pressure or vapor pressure 1. Pressure thermometer 3. Change in electrical properties 1. Resistance thermometer 2. Thermistors 3. Thermocouples 4. Change in emitted thermal radiation 1. Infrared pyrometer 5. Change in chemical phase 1. Liquid crystals
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°Kelvin is the basic temperature unit and is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water For the SI (metric) units: °Celsius = °Kelvin 273.15 For the imperial (English) units: ° Fahrenheit = °Rankin 459.67 Conversion from SI to English units ° F= 9/5*(°C) +32 Conversion from English to SI units °C = 5/9*[(°F) 32] temperature units and conversion
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Liquid in glass thermometer This temperature measuring devise consists of: Large bulb at lower end A capillary tube with scale Liquid filling bulb and portion of the tube (before the scale) Small safety bulb at the end of the tube if temperature range is exceeded bulb Capillary tube Liquid Safety bulb will be on top
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Operation method of liquid in glass thermometer If temperature is increased then greater expansion in liquid will happen As the liquid expands it will rise in the
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