Conditions And Equipment - FLIR InfraCAM User Manual

12 – Introduction to building thermography
12.3.8.5
To achieve best results from a thermal insulation survey it is important to consider
the environmental conditions and to use the most appropriate thermographic technique
for the task.
Thermal anomalies will only present themselves to the thermographer where temper-
ature differences exist and environmental phenomena are accounted for. As a mini-
mum, the following conditions should be complied with:
Temperature differences across the building fabric to be greater than 10℃ (18℉).
■
Internal air to ambient air temperature difference to be greater than 5℃ (9℉) for
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the last twentyfour hours before survey.
External air temperature to be within ±3℃ (±5.4℉) for duration of survey and for
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the previous hour.
External air temperature to be within ±10℃ (±18℉) for the preceding twentyfour
■
hours.
In addition, external surveys should also comply with the following:
Necessary surfaces free from direct solar radiation and the residual effects of past
■
solar radiation. This can be checked by comparing the surface temperatures of
opposite sides of the building.
No precipitation either just prior to or during the survey.
■
Ensure all building surfaces to be inspected are dry.
■
Wind speed to be less than 10 metres / second (19.5 kn.).
■
As well as temperature, there are other environmental conditions that should also be
taken into account when planning a thermographic building survey. External inspec-
tions, for example, may be influenced by radiation emissions and reflections from
adjacent buildings or a cold clear sky, and even more significantly the heating effect
that the sun may have on surface.
Additionally, where background temperatures differ from air temperatures either inter-
nally or externally by more than 5 K, then background temperatures should be mea-
sured on all effected surfaces to allow surface temperature to be measured with suf-
12
ficient accuracy.
For this type of survey infrared cameras must have a sufficiently high resolution to
detect small anomalies at a resonable distance. Typically, cameras use detectors
with 320 × 240 (= 76,800) pixels. The total pixel count should be at least 40,000 for
good results, and the camera should have a temperature sensitivity of at least 0.2℃
(0.36℉) (usually specified as NETD or noise equivalent temperature difference) so
that surface anomalies with small temperature differences can be detected.
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Conditions and equipment

Publ. No. 1558299 Rev. a200 – ENGLISH (EN) – February 12, 2007