| Title | By | Posted On |
| Temperature Span vs. actual ambient temperature |
ed@RBinfrared |
5/16/2011 |
I have an ir image of a roof membrane showing a span of 40-34F. However the roof scanned was exposed to temperatures through the day of 66 - 46F The temperature that night never got below 46F.
Tref=50 and Tatm=69 Span of -40 - +250 ane e=0.98
How can this be? |
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| Re:Temperature Span vs. actual ambient temperature |
dandersen |
5/16/2011 |
Where did you come up with: Tref=50
Are you sure it wasn't -50? |
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| Re:Temperature Span vs. actual ambient temperature |
ldapkus |
5/16/2011 |
ed@RBinfrared wrote:
an ir image of a roof membrane showing a span of 40-34F. However the roof scanned was exposed to temperatures through the day of 66 - 46F The temperature that night never got below 46F.
Tref=50 and Tatm=69 Span of -40 - +250 ane e=0.98
How can this be? Radiant cooling from the atmosphere? |
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| Re:Temperature Span vs. actual ambient temperature |
dandersen |
5/17/2011 |
Reflection?
Radiant cooling actually cools the surface.
You need to make correct camera corrections to get correct measurements.
How did you measure Tref?
Also you have Tatm=69 but you said it never got over 66F?
I can only assume you scanned at night (46F), set the camera Tatm and Tref above that ambient temp and got an odd span.
Why are you worried about the numbers in a roof scan?
If you do need the actual measurement you must correct the apparent temperature.
e=0.98, what angle did you take the scan at?
e changes with angle.
The sharper the angle the greater the reflection.
Nothing is adding up here.
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