December 2006

Infrared terms

Infrared terms

FOV: This refers to field of view, a measurement of the angle seen by the camera; the specification typically is given in degrees horizontal and vertical, such as 22 degrees vertical by 22 degrees horizontal.

FPAs: Focal plane array systems have a matrix of individual detectors.

Detector array: A detector array is composed of a number of individual detectors, typically 320 x 240 or 160 x 120 in size.

Microbolometer: An FPA with a thermal detector that responds to a voltage change is a microbolometer.

Millikelvin (mK): The specification for a camera's thermal sensitivity typically is quoted in mK, or one thousandth of a kelvin (or centigrade) degree. As an example, a 50-mK camera can, in theory, distinguish between a 30 C surface and a 30.05 C surface. A smaller value means the camera has greater thermal sensitivity.

Radiometric: The response of the detector to infrared radiation is calibrated so temperatures can be inferred from the amount of radiation detected. If a camera is fully radiometric, temperatures can be read anywhere in the image. Others have only a center spot calibrated for measurement.

Sensitivity: This refers to a measure of the minimum temperature difference (in millikelvins) that can be detected at a given temperature, typically 30 C.

Spatial resolution: This measures the ability of a detector to resolve small-sized details; the term instantaneous field of view (IFOV) may be used with the specification quoted as an angular measurement in milliradians (mRad). A smaller value means the camera has higher or better resolution.

Spot radiometer: These tools are temperature "guns" that measure radiation for a given spot and convert the data into a radiometric temperature value without a thermal image. Although useful, for instance to check kettle temperatures, these inexpensive ($100-$1,000) devices can have severe limitations with regard to spatial resolution and emissivity correction.

This Web exclusive information is a supplement to Infrared cameras come of age.