Wuhan Guide IR136 Manuel d'utilisateur télécharger pdf (Page 84)

Thermografie in der Theorie und Praxis (INTERNET: www.irPOD.net / e-MAIL: [email protected] ) © Bernd Schindel 2007

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Shading

A measure of the non-uniformity of signal in an infrared system. Shading is measured by exposing the

system to a wide area, constant temperature target and measuring the variations around a mean value.

Shading may be identified by source - for example optical shading will be characterized by strong

responses in the center and weak responses in the corners (vignetting). Channel to channel variations in

response can also be a source of shading (Channel balance).

Specific Heat

A property of materials. The specific heat of a material indicates how much thermal energy (in joules) is

required to increase a mass (in grams) of material a small temperature difference (degree C). Specific heat

is one of the principal factors in determining heat capacity, conduction rates in a material ' and the thermal

time constant of an object subject to heating.

Spectral

Pertaining to the electromagnetic spectrum, depending on wavelength or frequency, varying based on

wavelength.

Spectral Absorption

The ability a filter or gas has of transmitting radiation of some wavelength while absorbing materials of

other wavelength. The atmosphere is a spectral absorber for relatively long infrared path lengths.

Spectral Emission

A source which radiates thermal energy is specific bandwidths and emits little or no radiation in others. An

incandescent light is a gray body radiator while a quartz iodine light is a selective radiator. Hot pipes are

gray body radiators while flames are selective (spectral) radiators.

Spot Size

The minimum size of object which can be resolved at a given distance by an optical device.

Standards, Secondacy

Secondary standards are physical standards and references. which have been calibrated directly off of the

NIST primary standard. These standards are normally maintained by the more sophisticated testing

laboratories and used to calibration reference standards.

Stirling Refrigerator

A component used for cooling detectors to cryogenic temperatures. A stirling cycle refrigerator operates on

compression and expansion of gasses like a home refrigerator. However, the refrigerator uses the Stirling

cycle and Helium gas instead of Freon.

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Wuhan Guide IR136 Manuel d'utilisateur Page 84