Survey And Analysis - FLIR InfraCAM User Manual

12.3.8.6

Survey and analysis

The following provides some operational guidance to the thermographic operator.
The survey must collect sufficient thermographic information to demonstrate that all
surfaces have been inspected in order that all thermal anomalies are reported and
evaluated.
Initially, environmental data must be collected, as with any thermographic survey in-
cluding:
Internal tempetarture in the region of the anomaly.
■
External temperature in the region of the anomaly.
■
Emissivity of the surface.
■
Background temperature.
■
Distance from the surface.
■
By interpolation, determine the threshold temperature to be used.
For internal surveys the threshold surface temperature (T
■
+ T . The thermographer will be looking for evidence of surface temperature below
so
this threshold.
For external surveys the threshold temperature (T
■
The thermographer will be looking for evidence of surface temperature above this
threshold.
Images of anomalies must be captured in such a way that they are suitable for analysis:
The image is square to any features of the wall or roof.
■
The viewing angle is nearly perpendicular to the surface being imaged. Interfering
■
sources of infrared radiation such as lights, heat emitters, electric conductors, re-
flective elements are minimised.
The method of analysis will depend somewhat on analysis software used, but the key
stages are as follows:
Produce an image of each anomaly or cluster of anomalies.
Use a software analysis tool to enclose the anomalous area within the image, taking
■
care not to include construction details that are to be excluded.
Calculate the area below the threshold temperature for internal surveys or above
■
the threshold temperature for external surveys. This is the defect area. Some
anomalies that appeared to be defects at the time of the survey may not show defect
areas at this stage.
Add the defect areas from all the images ∑A
■
Calculate the total area of exposed building fabric. This is the surface area of all
■
the walls and roof. It is conventional to use the external surface area. For a simple
shape building this is calculated from overall width, length and height.
Publ. No. 1558299 Rev. a200 – ENGLISH (EN) – February 12, 2007
12 – Introduction to building thermography
) is T
sia sia
) is T = f
soa soa so
.
d
= f (T – T )
si si so
(T – T ) + T .
so si si
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