Infrared Thermography Exam Notes

Camera Spot Size Ratio

  • A camera with a spot size ratio of 60:1 can measure a 2-inch target from 60 inches away.
  • If the target is larger, the camera can be further away (e.g., a 4-inch target can be measured from 120 inches away).

Heat Energy and Temperature Scales

  • Heat energy does not exist below zero Kelvin (absolute zero).
  • Zero degrees Celsius is simply the freezing point of water.

Infrared (IR) Transmissivity

  • Ordinary glass windows have low IR transmissivity.
  • Materials like polycarbonate and clear plastics can also block IR.
  • Certain materials, like some trash bags, can act as lenses for IR.

Infrared Imaging

  • An infrared image displays differences in thermal radiation.
  • Hotter objects emit more IR radiation.
  • The camera assigns colors to represent different levels of IR emission.
  • Insulated materials (e.g., multiple-pane windows, insulated water bottles) slow down heat transfer.

Emissivity

  • Low emissivity targets do not show apparent temperatures that are close to true temperatures.
  • The emissivity setting on the IR camera must be adjusted to match the target material for accurate readings.

Emissivity, Reflectivity, and Transmissivity

  • The sum of emissivity, transmissivity, and reflectivity of an object equals 1 (or 100%). Emissivity+Reflectivity+Transmissivity=1Emissivity + Reflectivity + Transmissivity = 1
  • If the IR camera's emissivity setting is lower than the object's actual emissivity, the object will appear warmer.
  • To get accurate temperature readings, match the camera's emissivity setting to the target's emissivity.
  • Material charts and databases can provide emissivity values for various materials.

Factors Affecting Emissivity

  • Glossy vs. Matte Surfaces: Glossy surfaces have lower emissivity, while matte surfaces have higher emissivity.

Modifying Image Attributes After Capture

  • Only the emissivity can be modified after a picture has been taken.
  • Focus, range, and distance must be set correctly before taking the picture to get the correct spot size ratio

Distance and Spot Size Ratio

  • Distance from the target is irrelevant until the maximum spot size ratio is reached.
  • Exceeding the maximum spot size ratio compromises the accuracy of the temperature reading.

Targeting Cavities

  • Targeting a cavity can provide more accurate results than targeting a shiny object, although it may be tricky due to size and distance constraints.

Emissivity of Oxidized Copper

  • Oxidized copper has an emissivity value somewhere between shiny and non-shiny materials.

Safety

  • Do not look directly at the sun.