Glossary – A

Absolute Temperature: On the Fahrenheit scale, this is the temperature as indicated by any means plus 459.72 (460). On the Centigrade scale, this is the temperature as indicated by any means plus 273.18.


Active Infrared Thermography: Technique employed where the surface of the material is examined while heat flows are produced by way of applying an external heating or cooling source and observing the thermal pattern as the surface radiates infrared energy. Examples of active infrared thermography include solar loading, heating and cooling with airflows, pulsed energy from laser or light sources, and energy from vibrations or ultrasonics.


Air Leakage: The unintended movement of air from a location where it is intended to be to another location.


Alternating Current (AC): An electric current that reverses its direction many times a second at regular intervals, typically used in power supplies.


Ambient Conditions: The prevailing environmental conditions such as the surrounding air temperature, sky conditions, barometric pressure, and relative humidity.


Ampere: Unit of measurement for electrical current. An ampere is equal to 1 coulomb of electrons flowing by a given point in 1 second. Also known as coulomb/second.


ANSI: American National Standards Institute, Washington D. C.


Aperture Device: A mechanical device that is opaque to infrared radiation and has an opening through
which an infrared imaging radiometer is sighted during testing


Asphalt: A dark bituminous substance that is found in natural beds, or is obtained as a residue in the petroleum refining process. It consists chiefly of hydrocarbons. Asphalt may be further refined to conform to various roofing grade specifications.


Asphalt Roof Cement: A trowelable mixture of solvent-based bitumen, mineral stabilizers, other fibers and/or fillers. Classified by ASTM Standards D 2822-1 Asphalt Roof Cement, and D 4586-2 Asphalt Roof Cement, Asbestos-Free, Types II and I. Type I is sometimes referred to as “plastic cement” and is made from asphalt characterized as self-sealing, adhesive and ductile, and conforming to ASTM Specification D 312, Type I; Specification D 449, Types I or II, or Specification D 946. (See Plastic Cement and Flashing Cement.) Type II is generally referred to as “vertical-grade flashing cement”, and is made from asphalt characterized by a high softening point and relatively low ductility, and conforming to the requirement of ASTM Specifications D 312, Types II or III; or Specification D 440, type III. (See Plastic Cement and Flashing Cement.)


ASTM: American Society for Testing and Materials, West Conshohocken, PA.


Attenuating Medium: A semi-transparent solid, liquid or gas, such as a window, filter, external optics or an atmosphere that attenuates infrared radiation.