ITC Thermographer Level III flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Stefan-Boltzmann law

Total radiant exitance of a blackbody equals the Stefan-Boltzmann constant times absolute temperature to the fourth power: M = σT⁴. Radiated power rises steeply with temperature.

Wien displacement law

Peak emission wavelength equals 2898 micrometre-kelvin divided by absolute temperature. A 300 K surface peaks near 9.7 micrometres, favouring longwave cameras for ambient targets.

Kirchhoff's law

For an opaque body, emissivity equals absorptivity at each wavelength and direction, and reflectivity equals one minus emissivity. Low-emissivity surfaces mostly reflect background radiation.

Apparent temperature

The temperature a camera reports after applying its emissivity and background settings. It equals true surface temperature only when those inputs match the actual scene.

Emissivity of polished aluminum

Roughly 0.05, so polished aluminum is a poor emitter and strongly reflects its surroundings. Accurate measurement usually requires a high-emissivity coating or tape.

Cavity effect

Enclosed geometries such as furnace openings and deep holes trap reflections, raising apparent emissivity toward one. They behave closer to a blackbody than a flat surface.

ISO 18434-1 scope

Standard covering condition monitoring and diagnostics of machines using thermography. It addresses survey methods, measurement conditions, and interpretation of thermal results.

ISO 18436-7 categories

Defines thermographer categories: Level I performs basic measurements, Level II interprets per established techniques, Level III develops procedures and manages the program.

ASTM E1934

Standard guide for examining electrical and mechanical equipment with infrared thermography. It covers survey conditions, qualitative and quantitative interpretation, and reporting.

Written practice

Program document defining training hours, experience, examination content, acceptance criteria, and recertification intervals for each thermographer category. It controls qualification.

Baseline trending conditions

Record load, ambient temperature, wind, solar load, distance, and emissivity settings for every survey so later measurements are comparable to the baseline.

Acceptance criteria

Pre-agreed thresholds for judging a finding, such as delta-T over similar components, absolute temperature limits, or trend deviation. They must be written before the survey.

Reflected temperature method

Measure apparent temperature of crumpled aluminum foil near the target with emissivity set to one. Enter that value as the background temperature for the target.

Emissivity by reference tape

Apply black tape or paint of known emissivity to the target, allow equilibration, and compare its reading with the bare surface to derive the surface emissivity.

Thermal resistance analogy

Heat flow equals temperature difference divided by thermal resistance. A rising delta-T across the same path at constant load indicates increasing resistance.

Severity classification

Ranking findings by combining delta-T, load, component criticality, and trend history. A small delta-T on a critical component can outrank a large one elsewhere.

Envelope leak detection

Moisture and air leaks are visible only when a temperature difference is created by heating, cooling, or pressure difference. Without a driving force no pattern appears.

Report content elements

Object and location, survey conditions, camera and settings, radiometric image, temperature values and method, severity, limitations, and recommended action with priority.

Microbolometer detector

Uncooled longwave detector array, typically 8 to 14 micrometres, lower cost and slower response than cooled photon detectors. Common in handheld cameras.

IFOV formula

Instantaneous field of view equals detector pitch divided by focal length, in milliradians. It gives the pixel footprint at distance and drives spot-size calculations.

Spot-size pixel rule

The target should cover at least three by three pixels for a measurement, and ten by ten pixels for critical work, to avoid dilution by background temperature.

Camera accuracy specification

Usually stated as plus or minus two degrees Celsius or two percent of reading, whichever is greater, within a defined ambient range. Outside that range a temperature coefficient applies.

NETD

Noise equivalent temperature difference: the smallest resolvable temperature difference at a stated target temperature and averaging. Lower values indicate better sensitivity.

Spectral band selection

Longwave suits ambient targets and outdoor work; midwave suits high-temperature targets, through-flame measurement, and some plastics and glass. Match band to target temperature.

Focus as measurement parameter

Defocus spreads target energy over more pixels and biases the reading toward background temperature. Correct focus is required before capturing radiometric data.

Spot-size calculation example

With IFOV 1.3 milliradians at 10 metres, the pixel footprint is 13 millimetres. The three-by-three rule then requires a target of about 39 millimetres.

Load correction for electrical

Resistive losses scale roughly with the square of current. If the survey load differs from rated load, record it because delta-T changes with load.

Uncertainty budget

Combine emissivity, reflected background, atmospheric transmittance, distance, and camera accuracy contributions to state an expanded measurement uncertainty with a coverage factor.

Level III duties

Per ISO 18436-7, Level III develops procedures, manages the program, performs advanced analysis, and qualifies Level I and II personnel. Recertification is required at defined intervals.

Blackbody verification

Check camera measurement against a blackbody reference at multiple temperatures across the working range, at defined intervals and after repair or firmware change.

Solar loading artifact

Solar heating creates false hot indications and wind cooling creates false cold ones. Survey after solar load decays and record wind speed, ideally below about five metres per second.

Thermal lag

Thick, high-thermal-mass objects respond slowly to internal faults. Allow time for steady-state conditions before measuring to avoid understating the fault.