Thermography and Infrared Radiation Notes

FLIR Cameras

• FLIR cameras are often used and can cost around 5,000. 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: 2,000 - 6,000 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 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 to -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 = 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 0.95 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.