Therma/infrared Testing (IR)

• Thermal resistance is a material`s impedance to heat flow
• Conductive heat transfer cannot take place across the vacuum
• the infrared/thermal energy emitted from a target surface is proportional to the fourth power of the absolute surface temperature
• thermal radiation reaching the surface of a thermally opaque object will only be absorbed and reflected by the surface
• the following spectral band is included in the infrared spectrum 0.75-100um
• As a surface cools, the peak of its radiated infrared energy shifts to longer wavelengths
• A gray body surface with an emissivity of 0.04would almost a perfect reflector
• if a surface has an emissivity of 0.35 and a reflectivity of 0.45 its transitivity would be 0.20
• the spectral band in which glass transmits infrared radiation most efficiently is the 2-3um region
• Infrared thermal detectors have a broad, flat spectral response
• a diffuse reflecting surface is a surface that scatters reflected energy in many directions
• The minimum resolvable temperature difference is a subjective measurement that depends on the infrared imagining system`s thermal sensitivity and spatial resolution
• the spatial resolution of an instrument is related to the instantaneous field of view and the working distance
• the noise equivalent temperature difference (NETD) of a thermal infrared imager tends to improve as the target temperature increases
• the 3-5um spectral region is well suited for the inspection of materials that exhibit targets warmer than 200ºC
• When measuring the temperature of glass while using a mid-wave (3-5um) infrared imaging system, use a 3.9um bandpass filter is necessary
• Aline scanner is best used for applications requiring online real-time process monitoring and control of a linear thermal process
• Most infrared focal plane array imagers offer better spatial resolution than scanning radiometers
• When measuring the temperature of a non gray target errors may occur when using a variety of instruments
• thermal diffusivity is high for metals and low for porous materials
• The term used to describe a material`s surface temperature response to a given energy input is called thermal effusivity