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Surface Material
Emissivity
Coefficient
Surface Material
Emissivity
Coefficient
Concrete, rough
0.94
Steel Oxidized
0.79
Concrete tiles
0.63
Steel Polished
0.07
Cotton Cloth
0.77
Stainless Steel, weathered
0.85
Copper electroplated
0.03
Stainless Steel, polished
0.075
Copper heated and covered
with thick oxide layer
0.78
Stainless Steel, type 301
0.54 - 0.63
Steel Galvanized Old
0.88
Copper Polished
0.023 - 0.052
Steel Galvanized New
0.23
Copper Nickel Alloy, polished
0.059
Tile
0.97
Glass smooth
0.92 - 0.94
Water
0.95 - 0.963
Glass, Pyrex
0.85 - 0.95
Wood Beech, planned
0.935
Granite
0.45
Wood Oak, planned
0.885
Gypsum
0.85
Wood, Pine
0.95
Ice smooth
0.966
Wrought Iron
0.94
Figure 2 - Reference Table for Emisivity of Materials and finishes
Caution:
Values in emissivity tables are only ever guideline values.
Understanding the basic concept of Thermal Imaging:
It is important to understand that a thermal image represents the temperature distribution on the
surface of an object. This is important to understand when looking for concealed objects, such as
pipes embedded within floors or walls. You cannot look through objects with a thermal camera,
but rather you can detect a transfer of hot or cold from behind or within a surface material. As
this temperature differentiation is absorbed within the surface material the ability to detect a
thermal image of a concealed temperature variation will diminish. It may be necessary to (for
instance) to start with a very cold floor, before turning on the heating element embedded within
the floor, in order to detect a temperature gradiant of the heating coils within. Once the floor
tile absorbs the heat with even distribution, it will no longer possible to detect the temperature
variations with your thermal camera. This would also apply to hot/cold pipes concealed within
walls.
NOTE:
Actual temperature accuracy will vary, as the heat / cold is absorbed within the surface
material, as you are actually measuring the temperature on the surface material (not the pipe
concealed within).
Emissivity (
ε
) is a coefficient to measure the ability of a material to emit infrared radiation. This is
a critical setting within any thermal camera, in order to provide an accurate calculation of vastly
different materials (see attached table above). There are numerous factors taken into account
when selecting the proper Emissivity, which include color, finish and texture. Generally speaking,
polished surfaces reflect more strongly than rough or matt surfaces made of the same material. It
is important to select the proper Emissivity in order to obtain the greatest thermal accuracy.
NOTE:
Where the human eye can look through glass, glass has a reflective property to infrared
radiation. Your Thermal Imager therefore measures thermal radiation reflected off the glass, and
cannot detect temperature of viewed materials from behind the glass.
NOTE:
Where the Thermal Imager will always visually indicate temperature variations through the
user’s choice of color pallets, the accuracy of actual temperature readings may vary when viewing
a variety of object with varying color and texture.
Remember
– every surface has a specific
Emissivity for optimum accuracy of temperature readings.
