Thermography

Gamma rays - Shortest
X-rays- Go through flesh but not bone

Visible light- 400 nm - 700 nm

Length of wavelength peak to peak.

Infrared- William Herschel, 1750-1848, German astronomer and composer. Found that different colors had different temperatures. Red was the hottest, but are abelow red was hotter, but he could not see that. Objects, as they heat up, irradiate the absorbed infrared radiation.

Infrared radiation is a shadow of Heat

Calorie or BTU
Calorie: Heat to raise 1 gram of water 1 C
BTU: Heat to raise 1 lb of water 1 F
It is measured by its effect on a body

Basic Thermodynamics
Energy - Potential to do work
Potential energy= Stored
Kinetic Energy = motion of waves

Heat vs Temperature
Heat is energy in thermal form
Heat is the transfer of thermal energy from one object to another
Temperature is the average kinetic energy of the molecules in an object
0 Kelvin - Theoretical condition where there is NO IR radiation

Heat Transfers in 3 ways
Conduction - Through contact
Convection - Heat moving through a fluid ( Air is a fluid)
Radiation - Heat movement through electromagnetic waves

Thermal Capacity: The amount of energy needed to change the temperature. Impacted by Mass and its specific heat

Specific Heat: The ability of a material to hold heat.
Often expressed as a ratio when compared with water

Water:
Very dense:
High specific heat:
Abundant:
Can Change Phase: Fluid to vapor
Latent Heat of Vaporization: 1000 BTU's per lbs

Temperature Measurement Conversions
T = Measure vibration of Molecules T = Measure of "Hotness" and "Absence of hotness" T is NOT the equivalent to energy. 1 lb of steam has 1000 BTUs, more than a lb of water.

Fahrenheit = (C x 1.8) +32, i.e, Example 25 C = (25 X 1.8) +32 = 77 F
Celsius = (F-32)/1.8, i.e, Example 95 F = (95-32)/1.8= 35 C
Kelvin = C + 273, i.e, Example 35 C = 35 C+273 = 308 K

DELTA T

DELTA C to Delta F Conversion
DELTA F = Delta C X 1.8

DELTA F to Delta C Conversion

DELTA C = Delta F / 1.8

Radiant Energy
Incident Energy = A+R+T
Absorbed:

Reflected:

Transmitted: Ignored with IR Thermography. Transmissivity is generally ignored

Radiant energy is transmitted through smoke, which is why Thermography is of benefit in search and rescue

Emissivity Values Engineeringtoolbox.com

Question 5

Score: 2/4

In building envelope thermography, a required minimum temperature differential (delta-T) between inside and outside refers to:

Effective building envelope thermography requires adequate heat flow through the building shell to create detectable thermal patterns at the surface. This is driven by the delta-T between the conditioned interior and the exterior ambient. Most practitioners and standards (e.g., ASTM E1186, ITC guidelines) recommend a minimum delta-T of 10 °C (18 °F) for 3–4 hours prior to and during the inspection to ensure stable, detectable thermal patterns.

Question 6

Which of the following best explains why infrared thermography is classified as a 'non-destructive testing' (NDT) method?

NDT methods by definition examine materials or components without damaging or altering them, so the component can continue in service after inspection. Infrared thermography detects thermal patterns caused by anomalies (electrical resistance, moisture, insulation voids) without physical contact, without applying external stress, and without altering the component. This allows inspection during normal operation and repetitive trending over time.

Question 7

Which type of infrared camera lens material is most commonly used for LWIR cameras operating in the 8–14 μm band?

Germanium (Ge) is the most common lens material for LWIR cameras in the 8–14 μm band because it is highly transparent to LWIR radiation (transmission > 45% without coating, >95% with anti-reflection coating) and has a high refractive index (~4.0) allowing compact lens designs. Standard optical glass (borosilicate, crown glass) and polycarbonate are opaque in the LWIR band and cannot be used as IR lens elements.

Question 8

The primary purpose of PPE during an infrared electrical survey includes which of the following?

NFPA 70E requires thermographers working near energized electrical equipment to wear appropriate arc-rated PPE (arc-rated clothing, face shield, gloves) rated for the incident energy level of the task. PPE protects against arc-flash burns (radiant heat), arc blast, and electrical shock. The specific PPE category is determined by the incident energy analysis.

Question 9

Glass and most plastics are described as 'IR-opaque' or 'IR-blocking' materials because:

Glass, most plastics, and many polymers are opaque to long-wave infrared (8–14 μm). They absorb LWIR radiation from objects behind them and then re-emit radiation corresponding to their own surface temperature. A standard thermal camera cannot 'see through' a glass window — it measures the glass surface temperature, not the object behind the glass. Specialized IR-transmissive materials (e.g., germanium, zinc selenide optics, polyethylene film) are required for transmission windows.

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