ITC Level II cheat sheet

Fourier's law: q = −kA(dT/dx), with k in W/(m·K); steady one-dimensional conduction is proportional to area and temperature gradient.

Convection: q = hA(Ts − T∞); h combines natural and forced effects and rises steeply with air velocity.

Radiation: q = εσA(Ts⁴ − Tsurr⁴), σ = 5.67×10⁻⁸ W/(m²·K⁴); absolute temperatures in kelvin are required.

Wien's displacement law: λmax(μm) ≈ 2898/T(K); a 300 K surface peaks near 9.7 μm, inside the LWIR band.

Kirchhoff's law: at a given wavelength and temperature ελ = αλ, so low-emissivity surfaces emit little and reflect much.

Emissivity spans 0–1: polished aluminium ≈ 0.05, oxidised steel ≈ 0.80, matte black paint ≈ 0.95, human skin ≈ 0.98.

Thermal diffusivity α = k/(ρcp) governs transient response speed; thermal resistance of a slab is R = L/k.

A temperature difference of 1 K equals 1 °C; K = °C + 273.15, and heat flux is expressed in W/m².

Natural convection on a vertical air-facing plate typically gives h = 3–10 W/(m²·K); forced air raises this to 10–100 W/(m²·K).

LWIR (8–14 μm) suits near-ambient targets and transmits well in humid air; MWIR (3–5 μm) suits hot targets and high-temperature ranges.

Uncooled microbolometers operate at ambient temperature with NETD typically 30–80 mK and frame rates of 30–60 Hz.

Cooled photon detectors (InSb, MCT, QWIP) run at cryogenic temperature, giving NETD below 20 mK, short integration times and high frame rates.

IFOV (mrad) = FOV (mrad) / horizontal detector pixels; at working distance d the pixel footprint equals IFOV × d.

Focal length and detector size set the field of view; a narrower FOV shrinks spot size and increases resolvable detail.

NETD is the target-to-background difference producing a signal equal to detector noise; lower NETD means better sensitivity.

Germanium optics are opaque to visible light and transmit well from about 2 to 12 μm, so visual and thermal alignment differ.

Water vapour and CO₂ absorption reduce received signal; cameras compensate using distance, relative humidity and air temperature inputs.

Detector warm-up and stabilisation must complete before radiometric accuracy meets the manufacturer's published specification.

Radiometric accuracy requires four inputs: emissivity, reflected apparent temperature, distance/atmospheric transmission, and relative humidity with air temperature.

Reflected apparent temperature is measured with a crumpled aluminium foil reflector placed in front of the target and assigned ε ≈ 1.

A spot measurement is valid only when the target fills at least 3×3 pixels; smaller targets read a blend of target and background.

Defocus enlarges the effective spot and blends target with background, lowering the peak apparent temperature of small hot spots.

Level and span remap the display window to the colour scale; stored radiometric values are unchanged.

Palette choice (rainbow, iron, greyscale) affects display only and never changes measured temperatures.

For low-emissivity targets, matte tape or paint of known ε ≈ 0.95 provides a reliable comparison surface.

Isotherms and colour alarms highlight all pixels above, below or between set thresholds, enabling fast scanning of large areas.

Published emissivity tables are indicative; the assigned value must match surface condition, viewing angle and the camera's spectral band.

High-resistance joints, loose lugs and corroded contacts produce I²R heating that scales with the square of load current.

Electrical surveys are informative only under load; 40% of nominal current is a widely used minimum, with higher load giving better fault contrast.

Severity is graded by ΔT against a similar component under similar load: about 1–3 °C possible, 4–15 °C probable, above 15 °C major deficiency.

Phase imbalance shows as one phase or the neutral running hotter; all phases and the neutral are compared at the same load.

Solar loading and wind distort outdoor electrical scans; night or shaded surveys reduce the solar error.

Bearing defects, inadequate lubrication, misalignment and belt slip appear as elevated housing temperature relative to sister units.

Motor overheating arises from overload, voltage imbalance, single phasing or blocked cooling passages.

Steam trap failure, missing insulation, refractory damage and moisture ingress are located by abnormal surface temperature patterns.

Mechanical friction heating appears on the loaded side and shifts with rotational speed, so speed and load are recorded with each image.

Low-emissivity shiny surfaces mirror nearby sources; the false pattern moves with the camera and is a reflection, not a real temperature.

A genuine thermal anomaly persists in shape and location as viewing angle changes and correlates with an expected heat source.

Reported temperature is apparent; correcting emissivity, reflected temperature and atmospheric transmission yields true surface temperature.

Comparative analysis of similar components under similar load is more reliable than absolute temperature thresholds.

Thermal bridges appear warm in heating season because framing conducts heat through the envelope faster than adjacent insulation.

Wet building materials have high thermal mass and evaporative cooling, appearing cooler by day and warmer at night than dry material.

Wind above roughly 5 m/s reduces surface temperature differences and can hide envelope insulation defects.

Minimum detectable ΔT is set by NETD plus scene noise; small targets need a larger temperature difference to be resolved.

Baseline images taken from fixed positions with fixed settings and load allow deterioration to be trended over time.

ISO 18436-7 defines three thermographer certification categories: Category 1 assistant, Category 2 practitioner, Category 3 programme leader.

ISO 18434-1 gives guidance on infrared thermography for condition monitoring and diagnostics of machines.

ASTM E1934 is the standard guide for examining electrical and mechanical equipment with infrared thermography.

ASTM C1060 covers qualitative thermographic surveys of building envelope insulation; ASTM E1186 covers air leakage detection.

A report records ambient temperature, wind, solar load, humidity, emissivity and reflected temperature settings, equipment ID and load.

Each finding includes paired visual and thermal images, measured temperatures, ΔT, severity class and a recommended action.

Camera calibration is verified against a blackbody reference at intervals set by the manufacturer or programme procedure, commonly annually.

A written programme procedure defines inspection routes, severity criteria, acceptance limits, reporting format and corrective-action tracking.

NFPA 70E governs electrical safe work practice, including arc-flash PPE, when thermographers open energised panel covers.