Test Procedures, Techniques, and Applications
Procedures and Techniques
Infrared testing procedures must be tailored to the application, whether predictive maintenance, building diagnostics, or electrical inspections. Key steps include: defining the objective, selecting appropriate equipment (spectral range, sensitivity, lens), preparing the scene (cleaning, minimizing reflections, ensuring proper emissivity), and establishing environmental conditions (temperature, humidity, wind, solar loading). Techniques include qualitative thermography (identifying anomalies) and quantitative thermography (measuring temperatures). For electrical inspections, loads should be at least 40% of nominal to ensure detectable heating. For mechanical systems, compare similar components under similar conditions. Active thermography (e.g., pulsed or lock-in) uses external excitation to reveal subsurface defects.
Traps in Questions
- Neglecting to account for emissivity variations and reflections; these cause false indications.
- Performing inspections under unfavorable environmental conditions (e.g., high wind, direct sunlight).
- Failing to ensure adequate load on electrical equipment; low load may not produce detectable heat.
- Using the wrong spectral band for the temperature range (e.g., using 3-5 μm for low-temperature targets).
- Forgetting safety procedures, especially for electrical inspections.
Worked Example / Rule of Thumb
A common rule for electrical inspections: a temperature rise (ΔT) of 10°C above a similar component under similar load is often considered a potential problem, but severity criteria depend on standards. For example, a ΔT of 10-20°C may require investigation, while >40°C may indicate immediate action. Always compare to a reference (similar component or historical data). Also, for outdoor inspections, avoid times when solar loading is high; early morning or evening is preferred.