Physical Properties and Temperature Measurement

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Chapter 2

• Physical Properties and Temperature Measurement

Physical Properties Temperature Measurement
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• Physical properties vary widely between different
  metals and alloys.

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• Specific melting points and ranges are an asset
  in certain applications.

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• Coefficient of linear expansion is a property of
  primary importance in many applications, such as
  loops in steam lines.

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• Alloying of a metal increases the electrical
  resistivity of the metal.

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• Ferromagnetic metals have high values of magnetic
  susceptibility, paramagnetic metals have low
  values, and diamagnetic metals have low negative
  values.

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• A magnetizing curve is a plot of the magnetism
  induced in a metal when a magnetizing force is
  applied.

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• There is a 1.8F change on the Fahrenheit scale
  for every 1.0C change on the Celsius scale.

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• The Rankine scale is used for absolute
  temperature calculations in relation to the
  Fahrenheit scale. The Kelvin scale is used for
  absolute temperature calculations in relation to
  the Celsius scale.

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• When heat is applied, the helical coil in the
  bimetallic coil pyrometer unwinds, causing rotary
  motion of a pointer and producing a temperature
  reading.

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• In a liquid expansion or gas or vapor pressure
  pyrometer, the expansion of the medium in the
  bulb produces movement in the Bourdon tube, which
  moves the temperature indicator.

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• An EMF is produced in response to the temperature
  difference between the hot junction and cold
  junction of the thermoelectric pyrometer.

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• Thermocouple ends are fused together unless the
  medium to be measured provides the electrical
  connection.

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• Homogeneity of the wires of a thermocouple can be
  tested by passing a small flame along the wires
  that are connected to a galvanometer.

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• Thermowells introduce a time lag in temperature
  measurement when the temperature is fluctuating.

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• Radiation pyrometers focus the radiant energy on
  a thermopile, which generates an EMF that is
  translated into temperature.

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• Optical pyrometers match the brightness of a lamp
  filament with the brightness of the hot source.

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• Melting characteristics of temperature-indicating
  crayons are used to measure the surface
  temperature of an object.