ITC Thermographer Level III cheat sheet

Stefan-Boltzmann law: total exitance M = εσT⁴, σ = 5.670×10⁻⁸ W·m⁻²·K⁻⁴; radiated power scales with the fourth power of absolute temperature, so a 2× rise in kelvin gives 16× the exitance.

Wien displacement law: λmax = 2898 μm·K / T; a 300 K surface peaks near 9.7 μm, so longwave 8–14 μm cameras match ambient-temperature targets.

Planck's law gives spectral exitance per wavelength; real cameras integrate it over their spectral band and detector response, which is why band choice changes apparent temperature.

Kirchhoff's law: for an opaque body ε = α at each wavelength and direction; reflectivity ρ = 1 − ε, so low-emissivity surfaces mostly show reflected background radiation.

Emissivity is directional and spectral; polished metals show strong angular variation near grazing angles (above roughly 60° from normal), so aim near-normal to the surface.

Total radiation from a real target = emitted (ε·Lbb) + reflected (ρ·Lbackground) + transmitted (τ·Lbehind); most field targets are opaque, so τ = 0 and the reflected term dominates errors.

Apparent temperature is what the camera reports after applying an emissivity and background setting; it equals true temperature only when those inputs match reality.

Conduction, convection, and radiation combine at a surface; a hot component under forced convection or with a low-emissivity coating can read far below its internal temperature.

A written procedure must define the standard, acceptance criteria, camera class, emissivity/background settings, target preparation, environmental limits, and reporting format before inspections begin.

ISO 18434-1 covers condition monitoring and diagnostics of machines using thermography; ISO 18436-7 defines thermographer categories and qualification requirements.

ASTM E1934 gives the standard guide for examining electrical and mechanical equipment with infrared thermography; ASTM E2509 addresses temperature measurement performance of IR systems.

Acceptance criteria should be tied to a reference: ΔT above a defined baseline, absolute temperature limits from the manufacturer, or comparison to similar loaded components under equal conditions.

Baseline trending requires stable, repeatable conditions: record load, ambient temperature, wind, solar load, distance, and emissivity settings so later surveys are comparable.

Personnel qualification routes include ISO 18436-7 categories (Level I, II, III) and employer certification programs such as ASNT SNT-TC-1A or ISO 9712; the written practice defines the route.

Program records should retain raw radiometric images, not only compressed reports, so later reanalysis with corrected emissivity or background is possible.

Route and survey planning: define inspection points, safety permits, required load (typically equipment energized at normal operating load), and access before arriving on site.

For electrical connections, a ΔT between similar components under equal load is more diagnostic than absolute temperature; report the load current with every finding.

Reflected temperature compensation: measure apparent temperature of a crumpled aluminum foil target near the object with emissivity set to 1.0, then enter that value as background.

Emissivity estimation by reference: apply black electrical tape or paint of known ε to the target, let it equilibrate, and compare readings to derive the surface ε.

Thermal resistance analogy: heat flow q = ΔT/R; a rising ΔT across the same path at the same load indicates increasing resistance (loose lug, corroded joint, failing bearing).

Severity classification should combine ΔT, load, criticality of the component, and trend history; a small ΔT on a critical busbar can outrank a large ΔT on a non-critical panel.

Moisture and air-leak detection requires a deliberate ΔT across the building envelope, created by pressure difference or heating/cooling; without a driving force, no pattern appears.

Report content: object and location, conditions (load, ambient, wind, distance), camera and settings, radiometric image, temperature values and method, severity, and recommended action.

Detector types: microbolometer (uncooled, LWIR, lower cost, slower response) versus cooled photon detectors (InSb MWIR, MCT or QWIP LWIR, higher sensitivity, faster frame rates).

Instantaneous field of view: IFOV = detector pitch / focal length (mrad); the spot-size ratio uses IFOV in milliradians to give the smallest resolvable target at distance.

Measurement field of view rule: the target should cover at least 3×3 pixels, and for critical measurements 10×10 pixels, so the reported temperature is not diluted by background.

Spatial resolution and the slanted-edge or line-spread method quantify how many pixels a target spans; below the 3×3 pixel threshold, readings tend toward background temperature.

Accuracy specifications are usually stated as ±2 °C or ±2% of reading, whichever is greater, at a defined ambient range; outside that range, add the stated temperature coefficient.

Atmospheric transmission losses rise with distance and humidity; most cameras include distance, relative humidity, and ambient temperature inputs for transmittance correction.

Emissivity setting errors dominate field uncertainty; a 10% ε error on a low-emissivity target can shift the reading by tens of degrees, so verify ε rather than assume it.

Level III duties per ISO 18436-7 include procedure development, program management, advanced analysis, and qualification of Level I and II personnel; recertification is required at defined intervals.

Blackbody: ε = 1, α = 1, ρ = 0; it is the reference radiator against which real surfaces are compared.

Graybody approximation assumes ε is constant across the camera band; it fails for metals and for thin films with spectral features.

Radiance contrast between target and background drives detectability; a low-ε target can still be seen if its reflected background differs strongly from its emitted radiance.

Transmissivity of the atmosphere varies with band; water vapor and CO₂ absorption create windows, which is why LWIR 8–14 μm and MWIR 3–5 μm are used.

Thermal time constant: surfaces with low thermal capacitance and low conductivity (thin metal, insulation) heat and cool fast, producing transient artifacts.

Solar loading and wind cooling create false hot or cold indications; surveys should be run after solar load has decayed and with wind below about 5 m/s or recorded.

A qualification program needs a written practice defining training hours, experience, examination content, and recertification interval for each category.

ISO 18436-7 categories: Level I performs basic measurements with a defined procedure; Level II performs and interprets per established techniques; Level III develops procedures and manages the program.

Document control: procedures, acceptance criteria, and report templates must be version-controlled and traceable to the standard cited.

Audit trail for measurements should include camera serial number, calibration date, and the settings used, so results are defensible.

Calibration verification: check the camera against a blackbody reference at defined intervals and after any repair or firmware change.

Safety integration: electrical thermography requires arc-flash and shock risk assessment, PPE, and permit-to-work before opening energized panels.

For rotating equipment, compare bearings and couplings at equal load and speed; a ΔT rise at constant load signals lubrication loss, misalignment, or wear.

For refractory and insulation, the temperature profile across the shell indicates lining thickness loss; map the pattern and trend it rather than reporting single points.

For solar panel and electronics inspection, use the highest spatial resolution available and record irradiance or load current, since output and heating scale with it.

Image processing: isotherm bands, line profiles, and region-of-interest statistics support quantitative analysis; report the statistic used (max, mean, min) and the region.

Uncertainty budget: combine emissivity, reflected background, atmospheric transmittance, distance, and camera accuracy to state a defensible measurement uncertainty.

Corrective action tracking: each finding should have an owner, a deadline, and a re-inspection record confirming the repair.

NETD (noise equivalent temperature difference) is the smallest resolvable temperature difference at a stated target temperature and averaging; lower is better.

Spectral band selection: LWIR for ambient targets and outdoor work; MWIR for high-temperature targets, through-flame measurement, and some plastics and glass.

Frame rate and integration time trade off with sensitivity; fast-moving targets or transient events need short integration and high frame rates.

Lens choice changes IFOV and the spot-size ratio; a telephoto lens increases pixels on target at distance, a wide lens reduces it.

Focus is a measurement parameter: defocus spreads the target's energy over more pixels and biases the reading toward background temperature.

Recertification and requalification intervals are set by the certifying scheme; records must show the date, scope, and examiner for each qualification.

Severity ranking for electrical findings commonly uses ΔT over similar components at equal load, with thresholds defined in the written procedure, not assumed.

For building envelope surveys, report the indoor–outdoor ΔT, pressure difference (if used), wind, and time of day, since these determine whether a leak pattern is visible.

Report language should separate observation (measured ΔT) from interpretation (probable cause) from recommendation (action and priority).

Radiometric JPEG or TIFF data should be archived alongside the report so a reviewer can re-run analysis with corrected parameters.

Follow-up inspection should repeat the same load, distance, and settings to make the comparison valid.

Temperature conversions: T(K) = T(°C) + 273.15; ΔT in kelvin equals ΔT in degrees Celsius.

Radiant exitance units: W/m²; radiance: W/(m²·sr); the camera measures radiance and converts to temperature using calibration curves.

Emissivity of common surfaces: polished aluminum about 0.05, oxidized aluminum about 0.3, black electrical tape about 0.95, matte black paint about 0.95, human skin about 0.98.

The reflected apparent temperature term grows in importance as ε falls; for ε below about 0.5, background measurement is mandatory for accurate readings.

Thermal contrast is reduced by any intervening material with partial transmission (glass, plastic film, mesh); most glass is opaque in LWIR and blocks measurement.

Standard references to cite in procedures: ISO 18434-1 (machine condition monitoring), ISO 18436-7 (personnel), ASTM E1934 (electrical/mechanical inspection guide).

Acceptance criteria must be written before the survey and agreed with the asset owner; criteria invented after the measurement are not defensible.

Record retention periods should be defined in the program document and aligned with the asset owner's maintenance record policy.

Training hours and experience requirements differ by scheme; the written practice states them explicitly for each category.

Program performance metrics: findings confirmed on repair, false-positive rate, and time from finding to corrective action.

Spot-size calculation: at distance d with IFOV θ (mrad), the pixel footprint is d·θ/1000 in metres; multiply by the pixel-count rule for the minimum measurable target.

Example: IFOV 1.3 mrad, distance 10 m gives a pixel footprint of 13 mm; a 3×3 rule requires a target of at least about 39 mm.

Averaging frames reduces noise and improves NETD but blurs transient events; state the averaging used when reporting small ΔT.

Camera calibration should be traceable to a blackbody source; a calibration certificate states the temperature range and uncertainty.

Environmental inputs (ambient temperature, humidity, distance) must be entered in the camera or the analysis software, not left at defaults.

For electrical panels, measure with the panel closed where possible to preserve normal convection; opening the panel changes the thermal pattern.

Load correction: if the survey load differs from rated load, note it, because ΔT scales roughly with the square of current for resistive losses.

For mechanical systems, compare at equal speed and load; a bearing ΔT rise of a few kelvin at constant conditions can indicate incipient failure.

Report images should include a visible-light reference image and the radiometric image with the temperature scale and cursor values.

Uncertainty statement example: ±2 °C camera accuracy plus emissivity and background contributions, reported as an expanded uncertainty with coverage factor.

Procedure content checklist: scope, references, personnel qualification, equipment and calibration, survey conditions, measurement method, acceptance criteria, reporting, records.

Nonconformance handling: findings that exceed criteria require documented notification, escalation, and re-inspection after repair.

Supplier and subcontractor thermographers must meet the same written practice and provide qualification records.

The program manager (Level III) reviews reports for technical accuracy and consistency before release.

Periodic program review should check whether acceptance criteria still match asset criticality and failure history.

Detector resolution (e.g., 320×240, 640×480) sets the field-of-view pixel count; combined with lens focal length it determines IFOV.

Cooled detectors require periodic cooler service; cooler failure or degraded vacuum raises noise and reduces accuracy.

Battery and environmental ratings (IP rating, operating temperature range) determine where the camera can be used safely.

Verification of measurement accuracy should be done at multiple temperatures across the working range, not at a single point.

Personnel records should include training certificates, examination results, experience log, and the date of last requalification.

Kirchhoff's law applies per wavelength and direction; a surface can be a good emitter at one band and a poor one at another.

Cavity effect: enclosed geometries (furnace openings, holes) approach blackbody behavior because reflections are trapped, raising apparent ε toward 1.

Thermal lag: thick, high-thermal-mass objects respond slowly to internal faults; allow time for steady-state conditions before measuring.

Convective heat transfer coefficient rises with air speed, so wind increases heat loss and lowers surface temperature for a given internal heat generation.

Phase change and latent heat (moisture evaporation, condensation) create temperature plateaus that can mask or mimic faults.

For pipeline and tank inspection, look for thermal gradients indicating level, sludge, or insulation loss; report the gradient and the assumed conditions.

For electronics, power the board at normal load and allow warm-up; a shorted or high-resistance component shows a localized hot spot relative to neighbors.

For predictive maintenance, trend the same measurement point over time; a rising trend at constant load is stronger evidence than a single reading.

Report severity should reference the procedure's classification scheme and state the basis (ΔT, absolute temperature, or trend).

Re-inspection intervals should be set from severity and failure consequence, and recorded in the maintenance system.

Uncertainty and accuracy claims in reports must be consistent with the camera specification and the conditions of measurement.

Standard operating procedures should state which camera class and lens are acceptable for each measurement type.

Data management: name files with asset ID, date, and point ID so images can be retrieved for trending.

Training records must show the syllabus covered, including theory, equipment, and the specific applications the thermographer is qualified for.

Ethical reporting: state limitations and conditions honestly; do not present an apparent temperature as a true temperature without stating the assumptions.

Spectral response of a microbolometer is broad in LWIR (roughly 8–14 μm); a cooled InSb detector responds in MWIR (roughly 3–5 μm).

Measurement range and accuracy are specified separately; a camera may have a wide range but reduced accuracy at the extremes.

Emissivity tables are approximate; verify ε on the actual surface when accuracy matters.

Focus and distance must be set before capturing radiometric data; post-processing cannot recover spatial resolution lost to defocus.

Qualification examinations should test both theory and practical measurement, with a defined pass mark in the written practice.

Radiation emitted by a surface is proportional to ε times the blackbody radiance at that temperature and wavelength.

Reflected radiation from surroundings enters the camera along with emitted radiation; the background temperature input corrects for this term.

Apparent temperature error from an emissivity mismatch is larger at low ε and when the background differs strongly from the target temperature.

The camera's calibration converts incident radiance to temperature assuming a blackbody; emissivity and background settings adjust that conversion.

Transmission through the atmosphere reduces signal with distance; the correction uses humidity and distance inputs.

For roof and envelope surveys, the best time is when the indoor–outdoor ΔT is largest and solar load is absent, often early morning or after sunset.

For electrical busbar and switchgear, compare phases and like phases under equal load; one phase hotter than the others indicates a connection or balance problem.

For motors, compare frame and bearing temperatures to baseline at the same load; a rise indicates cooling loss, overload, or bearing wear.

Report temperature values with the statistic (max, mean, spot) and the emissivity and background settings used.

Include a limitations section stating what the survey could not assess (e.g., concealed components, low-emissivity surfaces).

The written practice is the controlling document for qualification; it must be approved and dated.

Qualification is not the same as certification; certification is issued by a certifying body, qualification by the employer.

Recertification requires evidence of continuing work in the category and, in some schemes, a re-examination.

Program audits should verify that procedures are followed and that records are complete.

Acceptance criteria changes must be communicated to all thermographers and reflected in the procedure version.

NETD is measured at a stated target temperature and frame averaging; compare cameras at the same conditions.

Spatial resolution is limited by detector pitch and lens; a smaller pitch gives finer IFOV for the same focal length.

A camera's temperature measurement uncertainty is separate from its image quality; a sharp image can still have a biased reading.

Blackbody verification should be performed at the temperatures actually used in service.

Qualification records should be retained for the period defined in the written practice and made available to the asset owner.

Emissivity values below about 0.2 make measurement highly sensitive to background; apply a high-emissivity coating or tape for reliable readings.

Thermal contrast between a fault and its surroundings is what makes it visible; a fault with no ΔT is not detectable regardless of camera quality.

Heat flow direction determines whether a fault appears hot or cold; moisture in a wall can appear cold from outside in winter and warm from inside.

Solar reflection can create false hot spots on low-emissivity surfaces; change the viewing angle or time of day to confirm.

The atmosphere is not fully transparent; absorption bands reduce signal and the camera's distance/humidity inputs compensate approximately.

For condition monitoring, a baseline image at commissioning gives the reference for all later comparisons.

For electrical findings, record the load current and the panel's rated current; ΔT without load context is not actionable.

For mechanical findings, record speed and load; a bearing ΔT at no load is not comparable to one at full load.

Report images should be saved in a radiometric format with the temperature scale visible.

Corrective actions should be verified by re-inspection at the same conditions and the result recorded.

Standard references for building thermography include ISO 6781 and ASTM C1060, which address qualitative and quantitative envelope inspection.

Acceptance criteria for buildings are usually qualitative (pattern presence) or based on a defined ΔT between suspect and reference areas.

Survey conditions for buildings must include indoor–outdoor ΔT, wind, solar load, and pressure difference.

Records should include the weather conditions and the time of survey, since they determine whether the pattern is valid.

Program documentation should state which standards apply to which asset class.

Camera warm-up time affects stability; allow the stated warm-up before measurement.

Ambient temperature outside the specified range requires a temperature coefficient correction.

Lens transmission losses are included in the camera calibration; adding filters or windows changes the calibration and must be accounted for.

A protective window or IR-transparent sight glass must be characterized for transmission before use in measurement.

Personnel should be trained on the specific camera model and software used in the program.

Stefan-Boltzmann and Wien laws are the basis for band selection and for the strong temperature dependence of radiated power.

Planck's law describes the spectral distribution; the camera integrates it over its band and detector response.

Emissivity, reflectivity, and transmissivity sum to 1 for each wavelength and direction.

Opaque targets have τ = 0, so ε + ρ = 1.

The reflected background term is corrected using the measured background temperature and the surface reflectivity.

For tank level detection, the thermal gradient between liquid and vapor space indicates level; report the gradient and the assumed conditions.

For refractory inspection, map the shell temperature and compare to the design profile; local hot bands indicate lining loss.

For solar modules, a hot cell or bypass diode shows a localized temperature rise; record irradiance and load.

For electronics, a thermal map with region statistics supports fault isolation; report the region and statistic.

For all applications, state the measurement uncertainty and the assumptions behind the reported temperatures.

The program should define the frequency of surveys per asset class based on criticality and failure history.

Findings should be entered into the maintenance management system with a unique ID for tracking.

Reports should be reviewed and approved by a qualified Level III before distribution.

Program metrics should be reviewed periodically to confirm the program is delivering value.

Changes to standards or camera technology should trigger a procedure review.

Detector pixel pitch and lens focal length determine IFOV; both must be known to compute spot size.

The 3×3 pixel rule is a minimum; critical measurements need more pixels on target.

Averaging and frame rate affect noise and the ability to capture transients.

Calibration and verification records must be traceable and retained.

Qualification must match the applications the thermographer performs, not just the category level.

Temperature is a state variable; radiated power depends on absolute temperature to the fourth power.

A small temperature difference at high absolute temperature produces a large change in radiated power.

At ambient temperatures, the peak wavelength is in LWIR; at high temperatures, it shifts to MWIR and SWIR.

Band selection should match the target temperature and the required spatial resolution.

Emissivity and background settings must be verified for each measurement, not assumed from a table.