ASNT Level III IR flashcards

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

Wien's displacement law

The peak wavelength of blackbody emission is inversely proportional to absolute temperature, lambda_max = 2898/T micrometres. At 300 K the peak is near 9.7 micrometres.

Stefan-Boltzmann law

Total radiant exitance of a blackbody equals sigma times T to the fourth power. For real surfaces multiply by emissivity, making exitance strongly sensitive to temperature.

Kirchhoff's law

For an opaque body in thermal equilibrium, spectral emissivity equals spectral absorptivity at each wavelength and temperature. Good absorbers are good emitters.

Emissivity definition

Ratio of radiation emitted by a real surface to that of a blackbody at the same temperature and wavelength. Values range from 0 to 1.

Graybody assumption

A body whose emissivity is constant across wavelength but less than one. Simplifies radiometric temperature calculation but is an approximation for most real materials.

Atmospheric IR windows

Wavelength bands where atmospheric transmission is high, principally 2-5.6 micrometres and 8-14 micrometres. Outside these bands water vapor and CO2 absorb strongly.

Reflected apparent temperature

The temperature of radiation reflected from the target into the camera, used by the camera to correct indicated temperature. Set it from a diffuse reflector near the target.

Blackbody reference source

A calibrated cavity radiator with known high emissivity used to verify or calibrate infrared cameras and confirm radiometric accuracy in the field or lab.

NETD

Noise-equivalent temperature difference: the target temperature change producing a signal equal to RMS noise. Lower values indicate better thermal sensitivity.

Detectivity D*

Normalized measure of detector sensitivity that accounts for detector area and bandwidth. Higher D* indicates a more sensitive detector.

Microbolometer

Uncooled thermal detector array whose resistance changes with absorbed infrared energy. Common in LWIR handheld and fixed cameras.

Photon detector cooling

Photon detectors such as InSb and MCT require cryogenic or thermoelectric cooling to reduce thermal noise and achieve high sensitivity and fast response.

IFOV

Instantaneous field of view: the angular subtense of one detector element, equal to detector size divided by focal length. Determines smallest resolvable target at a distance.

Measurement field of view

The area over which the camera averages temperature, commonly taken as three by three pixels. The target should fill at least this area.

Radiometric accuracy

Camera specification stating maximum temperature error under defined conditions, often plus or minus two degrees Celsius or two percent of reading.

Active thermography

Inspection technique that applies external energy to the target and observes the resulting thermal response, enabling detection of subsurface features and defects.

Passive thermography

Inspection that observes natural temperature differences without added excitation, commonly used for electrical, mechanical, and building envelope surveys.

Pulsed phase thermography

Technique that transforms pulsed thermal data into phase images via Fourier analysis, reducing sensitivity to emissivity variation and non-uniform heating.

Lock-in thermography

Periodic excitation at a fixed frequency with synchronous detection to extract amplitude and phase images, improving signal-to-noise for subtle defects.

Building envelope delta-T

Minimum steady indoor-outdoor temperature difference, often about ten degrees Celsius, needed for meaningful infrared surveys of insulation and air leakage.

Electrical load requirement

Thermographic inspection of electrical equipment should be performed under load near normal operating levels so abnormal heating is detectable.

Comparative analysis

Evaluating a component's temperature relative to similar components under similar load and conditions, rather than relying only on absolute temperature.

False indication causes

Reflections, emissivity variation, solar loading, and wind can create thermal patterns unrelated to defects. Verify by changing angle or repeating the inspection.

Thermal bridge

A localized path of high heat flow through an assembly, producing a distinct thermal pattern that must be distinguished from defects during interpretation.

Severity classification

Assigning a significance level to an anomaly based on pattern, temperature rise, and comparison to criteria, with the basis documented in the report.

Detection limit

The smallest defect or temperature difference reliably detectable under stated conditions; should be acknowledged in the inspection report.

ASTM E1934

Standard guide for examining electrical and mechanical equipment using infrared thermography, covering procedures, equipment, and reporting.

ASTM E1933

Standard practice for measuring and compensating for emissivity when using infrared imaging radiometers, including reference and contact methods.

ASTM E1186

Standard practice for air leakage detection in building envelopes using infrared thermography, addressing conditions and interpretation.

ISO 18434-1

Standard covering condition monitoring and diagnostics of machines using thermography, providing general procedures and guidance for industrial applications.

SNT-TC-1A

ASNT recommended practice for employer-written personnel qualification and certification programs in nondestructive testing, including training and examination guidance.

Level III responsibilities

Establishing and interpreting procedures and standards, administering the qualification program, and providing technical direction for the method within the employer's organization.