ITC Level II flashcards

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

Fourier's law

One-dimensional conduction heat rate is q = −kA(dT/dx), where k is thermal conductivity in W/(m·K), A is cross-sectional area and dT/dx is the temperature gradient.

Newton's law of cooling

Convective heat transfer is q = hA(Ts − T∞), where h is the convection coefficient, A the surface area and Ts − T∞ the surface-to-fluid temperature difference.

Stefan-Boltzmann law

Total radiant power emitted per unit area by a grey body is εσT⁴, where σ = 5.67×10⁻⁸ W/(m²·K⁴) and T is absolute temperature in kelvin.

Wien's displacement law

Peak emission wavelength shifts inversely with absolute temperature, λmax ≈ 2898/T in μm·K, so a 300 K object peaks near 9.7 μm.

Kirchhoff's law

At a specified wavelength and temperature, spectral emissivity equals spectral absorptivity, so good absorbers are good emitters and poor emitters reflect strongly.

NETD

Noise equivalent temperature difference: the target-to-background temperature difference producing a signal equal to detector noise. Lower NETD means better thermal sensitivity.

Microbolometer

An uncooled detector element whose electrical resistance changes with absorbed infrared radiation; arrays of these operate near ambient temperature across roughly 8–14 μm.

IFOV

Instantaneous field of view: the angular subtense of a single detector pixel, which multiplied by working distance gives the pixel footprint on the target.

Cooled photon detector

A semiconductor detector held at cryogenic temperature by a Stirling or Dewar cooler, giving short integration times and very low noise in MWIR or LWIR bands.

MWIR versus LWIR

MWIR spans roughly 3–5 μm and suits hot targets; LWIR spans 8–14 μm, matches near-ambient emission peaks and transmits well through humid air.

Reflected apparent temperature

The temperature assigned to background radiation reflected from a low-emissivity target, measured with a crumpled foil reflector set to near-unit emissivity.

Distance-to-spot ratio

The ratio of working distance to the diameter of the area measured; a valid reading requires the target to fill at least three by three pixels.

Level and span

Display settings that map a temperature window onto the colour scale. They change image contrast only and do not alter stored radiometric data.

Emissivity tape method

Applying matte tape or paint of known high emissivity, about 0.95, to a shiny target creates a reliable surface for comparative temperature measurement.

Atmospheric transmission compensation

A camera setting that uses distance, relative humidity and air temperature to correct for absorption by water vapour and carbon dioxide along the optical path.

I²R heating

Resistive heating that grows with the square of current, which is why loose, corroded or undersized electrical connections become hot only under load.

Forty percent load rule

Electrical thermography is informative only when the circuit carries appreciable current; a common minimum threshold is forty percent of nominal rated load.

Phase imbalance signature

Unequal currents between phases cause one conductor or the neutral to run hotter than its counterparts under the same connected load.

Delta-T severity classification

Electrical faults are graded by temperature rise above a similar component: about 1–3 °C possible, 4–15 °C probable and above 15 °C major deficiency.

Bearing friction heating

Lubrication failure, misalignment or wear raises bearing housing temperature, identified by comparison with identical bearings at the same speed and load.

Solar loading error

Direct sunshine heats surfaces unevenly and can mimic or mask faults, so outdoor electrical and envelope surveys are best performed at night or in shade.

Reflected thermal artifact

A false hot or cold pattern produced when a low-emissivity surface mirrors a nearby source; it changes with viewing angle and is not an equipment fault.

Thermal bridge

A path of low thermal resistance through the building envelope, such as framing or slab edges, that appears warmer in heating season than adjacent insulated areas.

Apparent temperature

The uncorrected temperature the camera reports from received radiance; correcting emissivity, reflected temperature and atmosphere yields true surface temperature.

Comparative thermography

Judging equipment by comparing similar components operating under similar load and conditions, rather than relying on absolute temperature thresholds alone.

Moisture thermal signature

Wet material has high thermal mass and evaporative cooling, so it appears cooler than dry material by day and warmer than dry material at night.

Wind limit for envelope surveys

Surface temperature differences used to detect insulation defects are reduced when wind exceeds roughly five metres per second, lowering defect contrast.

ISO 18436-7

The standard defining three categories of infrared thermographer certification, from Category 1 assistant through Category 2 practitioner to Category 3 programme leader.

ISO 18434-1

The standard giving guidance on infrared thermography applied to condition monitoring and diagnostics of machines, including measurement and analysis procedures.

ASTM E1934

The standard guide for examining electrical and mechanical equipment using infrared thermography, covering qualitative and quantitative survey practice.

Thermography report content

A report states ambient conditions, wind, solar load, emissivity and reflected temperature settings, equipment identification, load, paired visual and thermal images, and severity.

Programme written procedure

A documented method defining inspection routes, severity criteria, acceptance limits, reporting format, calibration intervals and corrective-action tracking for the thermography programme.