FLIR ThermaCAM P20, Руководство оператора

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19 The measurement formula
As already mentioned, when viewing an object, the camera receives radiation not
only from the object itself. It also collects radiation from the surroundings reflected
via the object surface. Both these radiation contributions become attenuated to
some extent by the atmosphere in the measurement path. To this comes a third
radiation contribution from the atmosphere itself.
This description of the measurement situation, as illustrated in the figure below,
is so far a fairly true description of the real conditions. What has been neglected
could for instance be sun light scattering in the atmosphere or stray radiation
from intense radiation sources outside the field of view. Such disturbances are
difficult to quantify, however, in most cases they are fortunately small enough to
be neglected. In case they are not negligible, the measurement configuration is
likely to be such that the risk for disturbance is obvious, at least to a trained oper-
ator. It is then his responsibility to modify the measurement situation to avoid the
disturbance e.g. by changing the viewing direction, shielding off intense radiation
sources etc.
Accepting the description above, we can use the figure below to derive a formula
for the calculation of the object temperature from the calibrated camera output.
10400503;1
Figure 19.1 A schematic representation of the general thermographic measurement situation. 1:
Surroundings; 2: Object; 3: Atmosphere; 4: Camera
Assume that the received radiation power W from a blackbody source of temper-
ature
T
source
on short distance generates a camera output signal
U
source
that is
proportional to the power input (power linear camera). We can then write (Equation
1):
Publ. No. 1 557 536 Rev. a35 – ENGLISH (EN) – January 20, 2004
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