Interpretation and Evaluation of Results
Interpreting Thermal Images
Interpretation involves distinguishing true thermal anomalies from artifacts. Common artifacts include reflections (from low-emissivity surfaces), solar loading, wind cooling, and emissivity variations. A true anomaly typically shows a pattern consistent with the heat source (e.g., loose connection heating). Quantitative analysis requires correcting for emissivity, distance, and atmospheric transmission. Temperature measurement uncertainty should be considered; factors include emissivity uncertainty, reflected temperature, and camera accuracy. Severity assessment often uses ΔT between the anomaly and a reference, or absolute temperature limits. Standards like NFPA 70B or ASTM E1934 provide guidance.
Traps in Questions
- Misinterpreting reflections as hot spots; reflections often move with camera angle.
- Ignoring the effect of wind or convection cooling, which can mask or alter patterns.
- Assuming all hot spots are problems; some are normal (e.g., equipment operating at higher load).
- Overlooking the need for a reference temperature; absolute temperature alone may be misleading.
- Failing to consider the thermal time constant; some anomalies take time to develop.
Worked Example / Rule of Thumb
A useful rule: If a hot spot disappears or moves when the camera angle changes, it is likely a reflection. For severity, a common criterion: ΔT = 1-3°C may be minor, 4-15°C intermediate, >15°C serious (depends on application). Always document environmental conditions and load at time of inspection.