ITC Level II key terms

Heat transfer through direct contact between molecules, moving from hotter regions to cooler ones without any bulk movement of the material. In solids it is the dominant heat-transfer path and it drives temperature equalisation across joints and hardware.

Heat carried away or delivered by a moving fluid such as air or water, either naturally through buoyancy or forced by fans and wind. It cools surfaces and can hide or mimic faults during an infrared inspection.

Energy emitted as electromagnetic waves by any object above absolute zero, needing no medium in which to travel. Between roughly 0.7 and 1000 micrometres it is called infrared, and a camera measures only this emitted portion.

A number between 0 and 1 describing how efficiently a real surface radiates compared with a perfect blackbody at the same temperature. Low-emissivity surfaces such as shiny metal emit little and are hard to measure accurately.

An idealised object that absorbs all incoming radiation and emits the maximum possible energy at every wavelength for its temperature. Its behaviour defines the reference curves used to calculate temperature from measured infrared radiance.

The fraction of incoming infrared energy a surface bounces back rather than absorbs or transmits. For an opaque object reflectivity roughly equals one minus emissivity, so shiny surfaces reflect their surroundings into the camera.

The fraction of infrared energy that passes through a material instead of being absorbed or reflected. Most solids are opaque in the thermal infrared, but gases and special windows transmit, which matters for distance and window corrections.

At a given wavelength and temperature, a surface emits exactly as strongly as it absorbs. Because good absorbers are good emitters, low-emissivity metals that reflect much of the radiation falling on them also radiate poorly.

The change in temperature across a unit of distance within a material or between adjacent components. Steep gradients drive faster heat flow and appear as sharp temperature boundaries in a thermal image.

The ability of an object to store thermal energy, equal to its mass multiplied by its specific heat. Components with high capacitance heat and cool slowly, so they reach steady temperature later and can mask developing faults.

The extra thermal resistance where two surfaces meet imperfectly, restricting heat flow across that boundary. In electrical joints it also adds electrical resistance, which is why loose connections appear as localised hot spots.

An uncooled infrared detector element whose electrical resistance changes as it warms from absorbed radiation. Microbolometer arrays run at ambient temperature, need no cryogenic cooling and are the sensor used in most handheld thermal cameras.

The two-dimensional grid of detector elements placed at the camera's focal plane. Its number of rows and columns, such as 320 by 240, sets how many individual temperature samples each image contains.

The pixel count of the detector array, expressed as horizontal by vertical elements. It limits the finest detail the camera can resolve and, combined with lens and distance, determines the smallest target that can be measured.

Noise equivalent temperature difference, the smallest temperature change a camera can detect against its own noise, usually quoted in millikelvin. Lower values mean better sensitivity for resolving small thermal contrasts.

The range of infrared wavelengths to which a detector responds, commonly 8 to 14 micrometres for long-wave uncooled cameras. Waveband affects atmospheric transmission, how well glass blocks radiation and which materials may be viewed.

Instantaneous field of view, the angular width seen by a single detector element, usually expressed in milliradians. Multiplying it by the working distance gives the size of one pixel on the target.

The area on the target that supplies radiation to the detector, comparable to the projected pixel size at that distance. The spot should fit inside the component being measured or the reading will average in the surroundings.

Adjusting the lens so the target's infrared image is sharp on the detector array. Poor focus blurs the image and spreads energy between pixels, causing incorrect temperature readings even when the picture looks acceptable.

Two display settings that control which temperatures are mapped to the colour scale. Level sets the centre or upper value of the displayed range and span sets its width, together controlling image contrast.

The colour scale used to convert measured temperatures into visible shades on the display. The choice affects how easily a thermal pattern is seen but never changes the underlying measurement data.

A camera input describing the infrared radiation arriving from the surroundings and bouncing off the target. Setting it correctly compensates for background reflections, especially on low-emissivity surfaces.

The value entered in the camera to tell it how strongly the target emits, so that measured radiance can be converted into temperature. An incorrect entry is one of the most common sources of measurement error.

Camera inputs for distance, air temperature and relative humidity that estimate how much infrared energy is absorbed along the air path. They matter for long-distance work and for accurate absolute temperature measurement.

The temperature difference between a suspect area and a reference area, such as a similar phase or an adjacent healthy component. It is the usual basis for judging how serious a finding is.

The amount of current flowing through equipment at the moment of inspection. Fault heating rises with the square of current, so heavily loaded circuits show problems clearly while lightly loaded ones may reveal nothing.

Heating of outdoor equipment by direct sunlight, which can create large apparent temperature differences unrelated to any fault. Surveys are usually scheduled to avoid it or to allow adequate cooling time beforehand.

Heat removal by airflow over a surface, which varies with wind speed and direction. Wind can suppress a genuine hot spot or make one side of equipment look cooler than the other.

Heat generated where moving parts rub, such as bearings, belts and couplings, because mechanical energy converts into thermal energy. Rising temperature over time signals wear, misalignment or inadequate lubrication.

The characteristic shape, size and temperature pattern that a particular fault or component produces. Recognising signatures lets an inspector separate genuine anomalies from reflections and other misleading patterns.

A display function that highlights all pixels falling within a chosen temperature band in a single colour. It helps show the extent of a hot or cold area and compare it with the surrounding material.

Measurement-based inspection in which actual temperatures or temperature differences are recorded, corrected for emissivity and background, and used to assign severity. It contrasts with purely pattern-based qualitative surveys.

An apparent hot or cold area caused by something other than the fault being sought, such as a reflection, airflow or a different surface finish. It must be ruled out before a finding is reported.

Adjusting level, span and palette while viewing so that a subtle thermal pattern becomes visible. It changes how data is displayed on screen but not the measured values stored with the image.

A scheme that ranks findings by severity, usually combining temperature difference above reference with the criticality of the equipment. It tells maintenance what to repair immediately, soon or at the next planned outage.

An initial inspection that records normal operating temperatures for equipment so later readings can be compared against it. Trending against a baseline reveals gradual deterioration that a single survey might miss.

The international standard defining competence categories, training and examination requirements for infrared thermographers. It sets out what Category I, II and III personnel are expected to know and be able to do.

A standard guide for examining electrical and mechanical equipment with infrared thermography, covering equipment condition, safety, qualitative and quantitative use, and the reporting of results.

The documented deliverable of a survey, containing equipment identification, thermal and visible images, measured temperatures, severity ranking and recommended actions. It must be clear enough for a reader who did not attend the inspection.