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Glossary of Thermography Terms


A temperature scale based on 32°F as the freezing point of water, and 212°F as the boiling point of water at standard atmospheric pressure; a relative scale related to the Rankine scale

[0°F = 459.67R; 1F° (ΔT) = 1 R(ΔT)]

Used in the USA only. Relation to the Kelvin scale is: 100K = 180R

Field of View (FOV)

The angular subtense over which an instrument will integrate all incoming radiant energy. In a radiation thermometer this defines the target spot size; in a scanner or imager this defines the scan angle or picture size.

Fibre Optic, Infrared

A flexible fibre made of a material that transmits infrared energy, used for making non-contact temperature measurements when there is not a direct line of sight between the instrument and the target.

Filter, Spectral

An optical element, usually transmissive, used to restrict the spectral band of energy received by an instrument’s detector.

Flame Filter

A filter of a specific waveband used to minimize the effects of flame, enabling the IR camera to “see through” the flame. The specific waveband is a region where the contents of CO2 and H2O does not reduce transmittance. The center wavelength is 3.2µm, the bandwidth is less than 0.25µm.

Focal Plane Array (FPA)

A linear or two-dimensional matrix of detector elements, placed in the focal plane of an instrument. In thermography, rectangular FPAs are used in “staring” (non-scanning) infrared imagers. These are called IRFPA imagers.

Focal Point

The point at which the instrument’s optics image the infrared detectors at the target plane. In a radiation thermometer, this is where the spot size is the smallest.

Frame Repetition Rate

The image update frequency- how many times per second the infrared imager delivers a complete IR picture.

Full Scale

The span between the minimum value and the maximum value that an instrument is capable of measuring at a selected measurement range.

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