Message Board Thread - "Image and Object Parameters in IR Camera"

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Image and Object Parameters in IR Camera sj 12/2/2010
Hello,

I have recently started working with IR camera for building envelope thermal imaging. After generating report, I found out that my camera is showing object distance of 3.3 feet in all the images.Is there any fault? Also, is it okay to take default 68.0 F reflected apparent temperature for the interiors in a building? For the exteriors, how to set reflectd apparent temperature as foil test is not feasible outside the building. Finally, will the emmissivity value affect my camera temperature readings?
Thanks in advance!
 
Re:Image and Object Parameters in IR Camera IRJay 12/3/2010
The camera does have defaults. the FLIR cameras default to .95 emissivity, 68 F for Trefl and 3.3 feet for distance.
Now all of these parameters have an effect on a measurement. The most critical is the emissivity. Learning this parameter is as important as learning what amperage is to an electrician. This must be adjusted in most cases to the effective emissivity of the surface being measured. Higher e objects such as building components of paint, wood, masonry can have some varience but the measurement might not be greatly effected. Bare metal components such as copper or stainless steel have low E and can make great errors with the wrong E setting.
Now the Trefl value has more impact as the E of the object is low. A good cutoff value of E to measure above is .7. Below this the Trefl value set wrong in the camera can have great influence on the measurement. The value in the camera represents the average of all the infrared energy that can relfect off the object of interest.
The distance is one part of 3 values to account for atmospheric absorbtion. Not a big factor under 20-30 feet from a surface
Not setting these correctly will at times produce wrong measurements. Your camera is calculating from the entered values the correct meaurement. Wrong values produce wrong answers. Garbage in garage out analogy.
Consider a thermography class to fully understand the practice of thermography. For more information, email me at jay.bowen@infraredtraining.com
 


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