Infrared thermography is a powerful non-contact diagnostic technique widely used in condition monitoring, electrical inspections, building diagnostics and predictive maintenance. However, accurate temperature measurement using infrared technology is not as simple as pointing a camera and reading a value. It involves a complete measurement chain that must be clearly understood.
The Journey of Infrared Energy
In any practical infrared measurement, thermal energy follows a specific path:
- It originates from the target surface
- Travels through a transmitting medium (usually the atmosphere)
- Finally reaches the measuring instrument
This journey is critical because the energy detected by the infrared camera is not purely from the object, it is influenced at every stage.
Key Insight:
- The temperature displayed by the thermal camera is affected by all three components, not just the target.
The Three Critical Components
To ensure accurate thermographic measurements, three sets of characteristics must always be considered:
Target Surface Characteristics
The target is the object whose temperature you want to measure. Its properties significantly influence the emitted infrared radiation.
Important Factors:
- Emissivity: Ability of a surface to emit infrared energy
- Surface condition: Rough, oxidized, polished, or painted
- Material type: Metal vs non-metal
Example:
- A painted surface gives accurate readings
- A polished metal surface reflects surrounding temperatures, causing errors
Transmitting Medium Characteristics
Between the target and the camera lies the medium usually air. This medium can absorb, emit, or scatter infrared radiation.
Important Factors:
- Atmospheric conditions: Humidity, dust, smoke
- Distance between camera and object
- Temperature of surroundings
Example:
- High humidity can absorb infrared energy, reducing measurement accuracy
- Long distances can cause signal loss
Measuring Instrument Characteristics
The infrared camera or sensor itself also plays a vital role in accuracy.
Important Factors:
- Calibration accuracy
- Detector sensitivity (NETD)
- Optics and resolution
- Settings (emissivity, reflected temperature, distance)
Example:
- Incorrect emissivity setting can lead to large temperature errors
- Poor resolution may miss small hotspots
Why This Concept is Important
Many beginners assume that thermography is straightforward but ignoring any one of these three factors can result in:
- Incorrect temperature readings
- Misdiagnosis of faults
- Missed critical failures
- False alarms
Real-World Application Example
Electrical Inspection
- Target: Busbar connection
- Medium: Air (possibly humid or dusty)
- Instrument: Thermal camera
If the busbar is shiny (low emissivity) and surroundings are reflected, the camera may show false temperature readings, leading to incorrect conclusions.
Key Takeaway
Infrared measurement is not just about the object. It is a complete system involving:
- Target
- Medium
- Instrument
Accurate thermography requires understanding and controlling all three.
