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Glossary of Thermography Terms


The object surface to be measured or imaged.


A measure of the thermal energy contained by an object; the degree of hotness or coldness of an object measurable by any number or relative scales; heat is defined as thermal energy in transit, and flows from higher temperature to objects of lower temperature.

Temperature Conversion

Converting from one temperature scale to another; the relationships are: Celsius: 0 °C = 273.15 Kelvin;

Temperature Measurement Drift

A reading change (error), with time, of a target with nonvarying temperature, which may be caused by a combination of ambient changes, line voltage changes and instrument characteristics.

Temperature Resolution

See minimum resolvable temperature (difference), MRT(D).

Thermal Conductivity

See Conductivity, Thermal.

Thermal Detector, Infrared

A type of infrared detector that changes electrical characteristics as a function of temperature. Typically, thermal detectors have slow response, (on the order of milliseconds) broad spectral response and usually operate at room temperature. Thermal detectors are commonly used in infrared radiation thermometers and in some imagers. See Bolometers, Microbolometers.

Thermal Sensitivity

See Minimum Resolvable Temperature (Difference), MRT(D).

Thermal Viewer

A nonmeasuring thermal imager that produces qualitative thermal images related to thermal radiant distribution over the target surface.

Thermal Wave Imaging

A term used to describe an active technique for infrared non-destructive material testing, in which the sample is stimulated with pulses of thermal energy, and where the time-bases returned thermal images are processed to determine flaw dept and severity; also called “pulse-stimulated imaging”.


A temperature detector, usually a semiconductor, whose resistivity decreases predictably with increasing temperature.

Thermistor Bolometer, Infrared

A Thermistor so configured as to collect radiant infrared energy; a type of thermal infrared detector.


A device for measuring temperature based on the fact that opposite junctions between certain dissimilar metals develop an electrical potential when placed at different temperatures, typical thermocouple types are;

  • J Iron/constantan
  • K Chromel/alumel
  • T Copper/constantan
  • E Chromel/constantan
  • R Platinum/platinum – 30% rhodium
  • S Platinum/platinum – 10% rhodium
  • B Platinum – 6% rhodium/platinum – 30% rhodium
  • G Tungsten/tungsten – 26% rhenium
  • C Tungsten – 5% rhenium/tungsten – 26% rhenium
  • D Tungsten – 3% rhenium/tungsten – 25% rhenium


A thermal map or image of a target where the grey tones or colour hues correspond to the distribution of infrared thermal energy over the surface of the target (qualitative Thermogram); when correctly processed and corrected, a graphic representation of surface temperature distribution (quantitative Thermogram).


Another word used to describe an infrared thermal imager.


Any device used for measuring temperature.


A device constructed by the arrangement of thermocouples in series to add the thermoelectric voltage. A radiation thermopile is a thermopile with junctions so arranged as to collect infrared radiant energy from a target, a type of thermal infrared detector.

Time Constant

The time it takes for any sensing element to respond to 63.2% (1-1/e) of a step change at the target being sensed. In infrared sensing and thermography, the time constant of a detector is a limiting factor in instrument performance, as it relates to respond time.

Total Field of View

(TFOV) – In imagers, the total solid angle scanned, usually rectangular in cross sections; usually called FOV, field of view.


Any device that can convert energy from one form to another. In thermography, an infrared detector is a transducer that converts infrared radiant energy to some useful electrical quantity.

Transfer Calibration

A technique for correcting a temperature measurement or a Thermogram for various errors by placing a radiation reference standard adjacement to the target.

Transfer Standard

A precision radiometric measurement instrument with e.g. NIST traceable calibration used to calibrate radiation reference sources.

Transmissivity, (Transmittance)

(τ) – The proportion of infrared radiant energy impinging on an objects surface, for any given spectral interval, that is transmitted through the object. (τ = 1 – ε – ρ) For a blackbody, Transmissivity = 0. Transmissivity is the internal transmittance per unit thickness of a nondiffusing material.

Two–colour Pyrometer

See Ratio Pyrometer.

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