CPR Infrared Thermography 2 — Questions and Answers
Question 1: What does emissivity refer to in the context of infrared thermography?
- The camera's lens focal length
- A material's efficiency at emitting infrared radiation relative to a blackbody (Correct answer)
- The temperature range of the IR camera sensor
- The reflectivity of a surface to visible light
Correct answer: A material's efficiency at emitting infrared radiation relative to a blackbody
Emissivity is a dimensionless value (0–1) describing how efficiently a material emits infrared energy compared to a perfect blackbody at the same temperature.
Question 2: Which emissivity value setting should a thermographer use when imaging a highly polished metal surface?
- 0.95
- 0.10–0.20 (Correct answer)
- 1.00
- 0.75
Correct answer: 0.10–0.20
Polished metals have very low emissivity (typically 0.05–0.20), so the camera must be set accordingly to avoid inaccurate temperature readings.
Question 3: In building moisture investigations, infrared thermography detects wet areas primarily because wet materials exhibit:
- Higher reflectivity than dry materials
- A thermal mass difference causing evaporative cooling (Correct answer)
- Greater emissivity than surrounding dry materials
- Lower density visible to IR sensors
Correct answer: A thermal mass difference causing evaporative cooling
Wet materials appear cooler in IR images during evaporation because evaporative cooling lowers the surface temperature relative to dry surroundings.
Question 4: What is the recommended minimum temperature differential (ΔT) between indoor and outdoor environments for effective building envelope IR scanning?
- 3°F (1.7°C)
- 10°F (5.6°C) (Correct answer)
- 25°F (13.9°C)
- 50°F (27.8°C)
Correct answer: 10°F (5.6°C)
A minimum 10°F (5.6°C) delta-T is generally required to create enough thermal contrast to reveal insulation defects and moisture patterns.
Question 5: Which type of IR camera detector does NOT require cooling and is most commonly used in field restoration work?
- Indium antimonide (InSb)
- Mercury cadmium telluride (MCT)
- Microbolometer (uncooled FPA) (Correct answer)
- Quantum well infrared photodetector (QWIP)
Correct answer: Microbolometer (uncooled FPA)
Microbolometer-based uncooled focal plane array detectors are rugged, affordable, and require no cryogenic cooling, making them ideal for field use.
Question 6: When performing an IR scan after a water loss event, the BEST time to scan is:
- Immediately during active rainfall or flooding
- Several hours after drying equipment has been running to create thermal contrast (Correct answer)
- During midday sun exposure for maximum ambient heat
- After all visible moisture has been removed and surfaces appear dry
Correct answer: Several hours after drying equipment has been running to create thermal contrast
Running drying equipment for several hours creates a temperature differential that makes residual moisture visible as cooler anomalies on IR images.
Question 7: What artifact in an IR image is caused by the thermographer's own body heat reflecting off a low-emissivity surface?
- Thermal bridging
- Reflected apparent temperature (RAT) artifact (Correct answer)
- Blooming
- Thermal gradient banding
Correct answer: Reflected apparent temperature (RAT) artifact
Reflected apparent temperature artifacts occur when the IR camera captures the thermographer's body heat reflected off a mirror-like low-emissivity surface, distorting readings.
CPR Infrared Thermography 2
What does emissivity refer to in the context of infrared thermography?