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ati ati 12/29/2009
I am new to thermography. Can someone explain to me the proper outdoor RAT measuring for the average residential structure. In daytime I have been using the air temp, and air or building temp for night time measurements.Can your explanation include clear and cloudy nights sky, and any other information you deem important.
 
Re:ati Rey 1/5/2010
ati wrote:
w to thermography. Can someone explain to me the proper outdoor RAT measuring for the average residential structure. In daytime I have been using the air temp, and air or building temp for night time measurements.Can your explanation include clear and cloudy nights sky, and any other information you deem important.
Hi, hope I can help. It is important to note that your ambient temperatures are not the same as RAT. RAT stands for Reflective Apparant Temperature. I.e. thermal radiation reflected of your target and this thermal radiation should not be used by the scanner for temperature calculation. Two methods exist for calculating RAT according to DIS ISO 18434-1.
1. Reflector Method
2. Direct Method

Reflector method is most accurate.
Step 1 - Set Emissivity to 1
Step 2 - Use any type of reflector material. My favorite is aluminium foil.
Step 3 - Hold the reflector in front of the scanner at the same angle as the target.
Step 4 - Hold the reflector as close to the target as safely possible.
Step 5 - It is advised to toggle the focus to get a more average temperature.
Step 6 - Take a temperature reading of the reflector and set your scanner to this value. Normally on the scanner or software it is called T(Refl).

First calculate RAT and then emissivity. Take ambient values (T atmosphere) and humidity seperately and add to your software to calculate accurate temperatures.

I hope the above helped. For more info you can contact me at rey@hentus.co.za
 
Re:ati Scott Wood Associates 1/5/2010
ATI, Rey has provided a great way to determine the RAT. This value and all other parameter settings Rey mentioned is a good start for temperature corrections. My question to you would be why are you looking at specific temperatures unless you are performing conductive temperature measurements such as R or U-values?
Usually building investigations using thermography as an investigative tool are to evaluate; energy movement through the building enclosure providing thermal anomalies or patterning due to ; thermal capacitance difference (trapped moisture, grout fill of CMU), thermal conductance (insulation variation, structural changes such as filled-in windows or thermal bridging), evaporative cooling (moisture location), to mention a few. All these use thermography to look at patterns or thermal anomalies not typically present within the building materials being observed. Thermal patterning is not influenced by changes to the parameter setting of an infrared camera and in most cases does not require actual temperatures.
For additional information regarding the use of infrared thermography in buildings training can be found with ITC’s building science thermography class. That class provides a certification in the use of infrared in building enclosure evaluations as well as a strong background in building sciences necessary to properly interpret the thermograms generated in the inspection process.
Please feel free to contact me at scott@buildingsciencethermography.com if you have an interest or further questions.
 


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