glossary
Infrared thermography glossary
By Ashton Bott, Level III Certified Master Thermographer. Updated 2026.
Plain definitions for the terms in your inspection report.
Delta T
The temperature difference between a component and a reference, either a similar component under similar load or the ambient air. Delta T is how severity is judged, because absolute temperature alone can mislead.
Qualified thermographer
A person trained to perform and interpret thermal inspection, typically following ASNT or ISO-based thermography training frameworks. Training levels run from Level I through Level III, with Level III representing the most advanced training.
Energized inspection
Inspection performed while equipment is under load, which is necessary because heat producing faults only show under current.
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