Thermography and Infrared Radiation Notes

FLIR Cameras

  • FLIR cameras are often used and can cost around 5,0005,000. They are considered robust.

Thermography and Infrared Radiation

  • Infrared radiation (IR) is a form of electromagnetic (EM) radiation.
  • Other forms of EM radiation include radio, X-ray, ultraviolet, gamma rays, and microwaves.
  • IR travels at the speed of light.
  • The difference between these forms of EM radiation is their wavelengths.
  • Wavelength: Measurement of the distance between cycles, like in a sine wave.
  • IR wavelengths are longer than visible light but close on the spectrum.
  • Visible light occupies a narrow band in the middle of the EM spectrum.

Color Temperature

  • Color temperature is measured in Kelvins (K).
  • Relates to the electromagnetic spectrum.
  • Typical range for lighting: 2,0002,000 - 6,0006,000 K.
  • Lumens: Measure the brightness or intensity of light in an area.
  • Visible light and infrared are next to each other on the spectrum.
  • Eyes perceive visible light as different colors reflecting off surfaces.
  • Infrared is emitted by everything but is outside the visible spectrum.
  • Technology enables devices to "see" IR and assign colors based on emitted energy to judge temperature.

AI Image Generation

  • AI can generate images depicting wavelength differences of visible light and infrared radiation.
  • Tools like NextEra AI can be used with prompts to create such images.
  • AI can also be used to create backgrounds with random electrical components.

Temperature and Metal Colors

  • Heating metals can change their color based on temperature.
  • Blacksmiths use the color of heated metal to judge its workability.
  • Plastics, wood, and other combustibles don't change color predictably with temperature.

Properties of Infrared Radiation

  • IR is emitted by everything above absolute zero.
  • Absolute zero: −460-460 degrees Fahrenheit.
  • Kelvin scale: 0 K is absolute zero.
  • Absolute zero: All atomic movement stops; no energy is emitted.
  • IR is generated by the acceleration of electrically charged particles.
  • As an object gets hotter, particle movement increases, emitting more IR energy.
  • Temperature differences on the same surface indicate varying energy emission.
  • Absolute zero has never been reached and is, by definition, impossible to reach.
  • Liquid nitrogen is around −200-200 to −300-300 degrees Fahrenheit.

Kirchhoff's Law

  • Kirchhoff's law: Deals with infrared energy emitted, transmitted, or reflected by a surface.
  • Emissivity, transmissivity, and reflectivity are important measurements for IR scans.
  • Cameras read emitted energy.
  • Different material properties result in different readings.
  • Metal surfaces can be difficult for cameras to read due to their shininess.
  • Emissivity (e), transmissivity (t), and reflectivity (p) must equal 1 (or 100%).

e+t+p=1e + t + p = 1

  • If transmissivity is zero, focus on emissivity and reflectivity.
  • Reducing reflectivity (e.g., by scuffing a surface) increases emissivity.

Examples of Emissivity and Reflectivity

  • Mirror: High reflectivity.
  • Glass: High transmissivity.

Black Body Emitter

  • Black body: Theoretical object emitting 100% IR with no reflectivity or transmissivity.
  • Vantablack: Paint that absorbs nearly 100% of light.
  • Surfaces painted with Vantablack appear distorted due to the lack of reflection.
  • High emissivity: Non-glossy surfaces allow cameras to easily read temperature.
  • The emissivity of a surface is considered around 0.950.95 when high.

High and Low Emissivity Materials

  • High emissivity: Plants, animals, people (non-glossy), black electrical tape, asphalt, water, soil, non-metallic paints, rubber.
  • Black electrical tape: Useful tool.
  • For glossy surfaces, apply tape to create a target spot.

Transmissivity

  • Transmissivity: Amount of IR energy that can pass through an object.
  • Assume transmissivity is zero if you can't see through an object.
  • Good IR transmitters: Germanium, open air, calcindride, zinc selenide, thin plastics.
  • Polycarbonate shielding: Surprisingly reflective to IR.
  • Germanium: Material used for IR lenses.

Reflectivity

  • Reflective materials: Shiny, glossy materials like bus bars.
  • Specular reflectors: Mirrors.
  • Diffuse reflectors: Scuffed surfaces.
  • Scuffing a surface lowers reflectivity and increases emissivity.

Measuring Low Emitted Objects

  • Apply tape.
  • Scuff the surface to lower reflectivity.
  • Paint the surface.
  • Take advantage of surface geometry (cavities).
  • Take temperature readings from high emittance objects in contact with the target.

Surface Geometry

  • Targeting a cavity may provide better results due to reflections.
  • This can be difficult and may require getting too close to energized equipment.

Demonstrations with Metallic Cans

  • Can with hot water, half painted with high emissive paint: Accurate temperature reading on the painted side.
  • Empty can: Reflects surroundings, appearing hot.
  • Can with hot water and a strip of tape: Accurate reading on the tape.
  • Cans partially filled with hot water: Camera can see where the hot water is.

Adjusting Camera Settings

  • Emissivity settings can be changed to get better results on low emissive targets.
  • Glossy surfaces require considering reflected temperature.

Camera Features and Settings

  • Cameras can capture images.
  • Focus, temperature range, and operating distance cannot be adjusted after capturing an image.
  • Emissivity can be adjusted after the image has been captured using FLIR software.
  • Focus: Important for accurate temperature readings.
  • Temperature range: Min and max temperatures should encompass the object's temperature.
  • Operating distance: How far you are from the target.

Spot Size Ratio

  • Spot size ratio: Indicates how close you need to be to a target of a specific size for an accurate reading.
  • Example: 245:1 ratio means you can accurately read a 1-inch target from 245 inches away.

External Factors Affecting Readings

  • Roughness or smoothness of the surface.
  • Load passing through the object.
  • Weather: Rain, moisture, and grease can lower emissivity.
  • Wind: Can affect temperature readings.

Emissivity Guidelines

  • Shiny or glossy objects: Low emissivity.
  • Oxidized or corroded metals: Varying emissivity.
  • Ceramics: High emissivity (if not glazed).
  • Nonmetals, paints, and tapes: High emissivity.

Taking Readings of Energized Equipment

  • May need to wait until the equipment is at 50% or greater load.
  • Process:
    1. Deenergize and verify safety.
    2. Remove covers.
    3. Reenergize and wait for load.
    4. Take scans.
    5. Deenergize and verify safety.
    6. Reapply covers.

Interpreting Results

  • Compare temperature differences within the same equipment.
  • Compare to similar objects.
  • Refer to schematics to determine expected current.

Substation Examples

  • Temperature differences in splices should not exceed 3 degrees.
  • Significant temperature differences indicate potential problems.

Comparing Targets

  • Compare to similar objects operating on a different phase or circuit.
  • Determine expected current and compare to actual current.
  • Follow the same process from inverter to inverter without changing settings and give results to engineer to be interpreted.

Abnormally Cold Objects

  • HVAC units, liquid-cooled inverters, and batteries.
  • Leaks in systems or blockages in radiators can cause abnormally cold spots.
  • Escaping refrigerant can cause frost.
  • Radiant heat can help to identify areas that may be affected.