Johann Maier, winter semester 2015/16


Introduction and basics

Temperature is a physical quantity or more specifically a comparative measure of hot or cold. It is measured by a thermometer, which may work through the bulk behavior of a thermometric material, detection of thermal radiation, or particle kinetic energy. There exist several scales and units […], the most common being Celsius (denoted °C ,[…]), Fahrenheit (denoted °F), and, especially in science, Kelvin (denoted K). [1]

The coldest theoretical temperature is absolute zero, at which the thermal motion in matter would be zero. […] Absolute zero is denoted as 0 K on the Kelvin scale, −273.15 °C on the Celsius scale, and −459.67 °F on the Fahrenheit scale. […] Temperature is important in all fields of natural science and engineering – consequently also in non-destructive testing. [1]

Temperature Measurement

History

Temperature measurement describes the process of measuring a current local temperature for immediate or later evaluation.[…] Attempts at standardized temperature measurement prior to the 17th century were only crude. For example in 170 AD, physician Claudius Galenus [2] mixed equal portions of ice and boiling water to create a "neutral" temperature standard. The modern scientific field has its origins in the works by Florentine scientists in the 16th century including Galileo constructing devices able to measure relative change in temperature, but subject also to confounding with atmospheric pressure changes. These early devices were called thermoscopes. The first sealed thermometer was constructed in 1641 by the Grand Duke of Toscani, Ferdinand II. [2] The development of today's thermometers and temperature scales began in the early 18th century, when Gabriel Fahrenheit produced a mercury thermometer and scale, both developed by Ole Christensen Rømer. [3]

Measurement Technologies

Many methods have been developed for measuring temperature. Most of these rely on measuring some physical property of a working material that varies with temperature. One of the most common devices for measuring temperature is the liquid-in-glass thermometer. This consists of a glass tube filled with mercury or some other liquid, which acts as the working fluid. Temperature increase causes the fluid to expand, so the temperature can be determined by measuring the volume of the fluid. Such thermometers are usually calibrated so that one can read the temperature simply by observing the level of the fluid in the thermometer. [3]

Other important devices for measuring temperature include: Thermocouples , thermistors, resistance temperature detectors (RTD), Pyrometers and thermographic cameras (both using infrared radiation). [3]

One must be careful when measuring temperature to ensure that the measuring instrument (thermometer, thermocouple, etc.) is really the same temperature as the material that is being measured. Under some conditions heat from the measuring instrument can cause a temperature gradient, so the measured temperature is different from the actual temperature of the system. In such a case the measured temperature will vary not only with the temperature of the system, but also with the heat transfer properties of the system. [3]

Thermocouple Type K ready for usePyrometer used for temperature measurement in friction-stir-weldingThermographic camera in use


Non-invasive thermometry

During recent decades, many thermometric techniques have been developed. The most promising and widespread non-invasive thermometric techniques are based on the analysis of magnetic resonance images, computerised tomography images and echotomography images. These techniques allow monitoring temperature within tissues without introducing a sensing element. [4] [3]

Literature

  1. https://en.wikipedia.org/w/index.php?title=Temperature&oldid=700791526 January 27th, 2016
  2. T. J. Quinn (1983). Temperature. London: Academic Press.
  3. https://en.wikipedia.org/w/index.php?title=Temperature_measurement&oldid=695261147 January 2nd, 2016
  4. Hyperthermal Procedure". Measurements and Biomedical Instrumentation Lab. Università Campus Bio-Medico di Roma.; http://www.mtmbilab.com/hyperthermal-procedure.html