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Thermal Imaging Cameras: Applications, Uses and Features

Quick Tips #345

Temperature is very important in our everyday lives and is used for many applications: to check for illness, to determine if food is cooked thoroughly or if your car is overheating. Thermal imaging cameras take measuring temperature to the next level—instead of getting a number for the temperature, you get a picture showing the temperature differences of a surface. Thermal imaging, also known as thermography, is a technique for producing an image of invisible infrared light emitted by objects with the use of a thermal imaging camera. Thermal imaging cameras provide rapid scanning of a surface that is nondestructive and environmentally friendly, which allows for quick detection of potential problems or defects that will reduce troubleshooting time and preventative maintenance.

What do thermal imaging cameras see?

Thermal imaging cameras don't actually see temperature. Instead, they capture the infrared (IR) energy transfer from an object to its environment and produce a real-time image in a color palette where hotter objects appear brighter and cooler objects appear darker. IR energy is generated by the vibration of atoms and molecules and behaves similarly to visible light where it can be reflected, refracted, absorbed and emitted. The more these atoms and molecules move, the higher the temperature of the object.

Thermal Imaging Camera Applications and Uses

Thermal imaging cameras are becoming a common tool in the home inspection industry where they are being used to verify building performance to specifications, to determine insulation condition, locate leaks, verify structure design and locate moisture intrusion. Of course, these are not the only thermal imaging camera applications. Their use is limited only by the imagination of the user. Primarily, thermal imaging cameras are used where the identification of thermal patterns can be used to find something or diagnose a condition, such as poor insulation in a home or an overloaded electrical circuit. Some examples of thermal imaging camera applications include:

  • Substation electrical inspections
  • Thermal heat loss inspections of buildings
  • Locate radiant heating wires or pipes
  • Locate potential areas for mold growth
  • Flat-roof leak detection for buildings
  • Detect thermal patterns on boiler tubes
  • Mechanical bearing inspections
  • Detect insulation leaks in refrigeration equipment

Thermal Imaging Camera Features

Basically, a thermal imaging camera is capable of saving the thermal image to either its internal memory or to a memory card, depending on the camera capabilities. Once the user is done taking the photos, they can be viewed and edited on the camera or downloaded to a PC where the images can be formatted on a report with the included software. Thermal imaging cameras can be purchased with the bare minimum of features that will only read the temperature of the fixed center crosshairs on the display, where other cameras will allow the user to select multiply moveable crosshairs and compare the temperatures between them or the box area feature that will show the high, low and average temperature within a box on the display. Thermal imaging cameras will have multiple color palettes, such as black/white, iron or rainbow, that are user selectable. The iron palette is most commonly used by home inspectors. The black/white palette helps identify details on an image, and the rainbow palette has the best thermal sensitivity for displaying the differences in temperature. See sample images below of some color palettes.

Iron palette of fuse bus bar Iron palette of fuse bus bar
Black/White/Gray palette Black/White/Gray palette
Rainbow palette Rainbow palette
Hot metal palette Hot metal palette
Amber palette Amber palette

More sophisticated cameras may include:

A color alarm feature that allows the user to select a temperature. The camera will only display a color thermal image of anything that is either above or below the selected temperature.
A picture-in-picture feature that will display a color thermal image (which is a quarter of the size of the display) inside a standard digital image. Temperature readings are limited to the thermal portion of this feature.
A fusion or blending feature allows the user to blend either the maximum, minimum or average temperature of the thermal image with a standard digital image.


How do I get a good image?

Using a thermal imaging camera is quite simple, but interpreting the captured image takes knowledge and experience. To help a user obtain the best thermal image to analyze, there are four adjustments that can be made to the camera: focus, emissivity setting changes, reflective temperature setting changes and thermal tuning.

1. Just like a standard camera, the lens of the thermal imaging camera needs to be focused to enhance the clarity of the image. Most cameras can be focused by twisting the lens, where more sophisticated cameras will have a push-button focus.

2. Emissivity is the amount of radiation emitted from an object compared to that of a perfect emitter of radiation when both are at the same temperature. A lower emissivity setting is used for highly reflected objects, and a high-emissivity setting is used for low-reflective objects. Objects that are nonmetal or that have a rough surface will have a higher emissivity. Adjusting the emissivity is important when taking temperature measurements or when comparing two different objects' temperatures. Incorrect emissivity settings will make objects appear hotter or colder than what they really are. Not all cameras will allow the user to adjust the emissivity of the camera and will be defaulted to wood or drywall.

3. The reflective temperature setting allows the user to compensate for surrounding objects' temperature reflecting on an object. If reflecting thermal energy from surrounding objects is suspected, move the camera around in the area of the target and see if the hot or cold spot moves with the camera. If it does, it is a reflection from another object, if it does not, it is a true hot or cold spot. In order to find out what the reflective temperature is, the user will need to adjust the emissivity of the camera to 1.0, then place a piece of crinkled aluminum foil on a piece of cardboard. Hold the foil between the camera and the object you intend to view, and note the temperature of the foil. Then input the temperature of the foil in the reflective temperature setting on the camera. Just like emissivity, reflective temperature is important when taking temperature measurements or comparing two objects' temperatures. Not all cameras will allow the user to input reflective temperature.

4. Thermal tuning the camera involves adjusting the span or temperature range that the camera sees while in manual viewing mode. Thermal imaging cameras have an automatic viewing mode and manual viewing mode. When the camera is in automatic mode, the camera will automatically adjust the temperature scale to what is being viewed, which causes the display to change colors frequently when the camera is moved. Manual mode allows the user to adjust the span to a desired range, and the camera will always display this temperature range. Using the manual mode is best when used to bring out temperature differences of the object being viewed.

Thermal Imaging Camera Limitations

Because thermal energy can be reflected off shiny surfaces, thermal imaging cameras can not see through glass. If you stand in front of a window while looking at a thermal imaging camera, you will see yourself in the window because of the thermal energy reflecting off the glass. Regardless of what Hollywood movies may show, thermal imaging cameras can not see through walls. It is also important to know that thermal imaging cameras should not be used as the deciding factor that a problem exists. Using other instruments, such as a borescope, moisture meter, multimeter or blueprint drawing of the building should always be used to confirm the problem.

Commonly Asked Questions

Q.   Can thermal imaging cameras see through walls?
A.   No. While hi-resolution and hi-sensitivity cameras can create the appearance of seeing through walls, what you are actually seeing is transmitted thermal energy. For example, if you look at the interior walls of a home when it is cold outside, you will likely see the studs in the wall. What is showing on the surface is cold transmitted from the outside, through the studs, to the surface of the drywall. It appears that you can see into the wall, but you are actually only seeing the different temperatures on the surface.
Q.   Can thermal imaging cameras detect plumbing leaks?
A.   Yes. Thermal cameras are a useful plumbing leak locator. Most cameras have a temperature difference sensitivity of .10 degree Centigrade or better. It doesn't take a big temperature difference for the camera to see the leak. The issue is allowing that thermal energy difference enough time to transfer through the flooring to the surface.
Q.   Can thermal imaging cameras detect air leaks?
A.   Yes. Similar to plumbing applications, this ties directly to the camera sensitivity. Because the temperature change required is so slight, you can detect draft areas around doors, windows, and attic access points.
Q.   Will thermal imaging cameras detect moisture?
A.   Yes. Moist materials retain thermal energy differently, allowing the camera to pick up the differences. You should always double check a potential spot of moisture with a moisture meter since there are several things that can create the thermal anomaly you are seeing.
Q.   What is the biggest difference between a $3,000 and $10,000 camera?
A.   The biggest difference is typically resolution. The higher the resolution, the better the picture clarity. This translates to a better picture at a greater distance as well—similar to the megapixels of a regular digital camera.
Q.   What is PIP?
A.   Picture-in-Picture (PIP) technology in thermal cameras allows you to overlay a thermal image on top of a regular digital image. Depending on the camera, you may be able to resize the thermal image box. Some cameras also allow for fusion or blending, which allows you to fade the thermal image out over the digital image, increasing visibility of what is below the thermal image. This capability can permit reading machine labels to identify the specific device being checked or can be used to add detail to exactly where an image was taken.
Q.   What is emissivity, and why is it important to thermal cameras?
A.   Emissivity is the amount of thermal energy an object either emits or absorbs. This is relevant to thermal cameras because highly reflective materials absorb thermal energy; thus, the camera can not get an accurate reading of temperature. For example, if you heat a black, PTFE resin-lined frying pan that has a chrome exterior, the black side will read a temperature value closer to the actual temperature, whereas the chrome side will give you values that are far from actual. Most materials fall close to the common preset emissivity value in the camera, but this setting can be changed to accommodate different materials.
Q.   What are important criteria to look for in a camera?
A.   Price is a common consideration, but there are few key features to look for. First is resolution. Are you viewing small parts and motors or is the camera for home energy inspection or moisture detection? Motor inspection might require a higher resolution where home energy and moisture can be detected with a slightly rougher image. Another consideration may be whether the unit has a field changeable battery or a car charger. Depending on the application, you may be running the camera for significant periods of time.

One last feature to look for is temperature range. Some cameras are ideally suited for industrial applications and will have a higher temperature range for reading electrical panels, motors, heat processes, etc. Other cameras have a range (–4 to 248 degrees Fahrenheit, for example) that is better suited for home inspections. Moisture and residential energy loss detection can typically be accomplished with a lower temperature range camera.


Sources

http://www.infraredtraining.com

(Rev. 1/2012)


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