Measurement Principle - Jenoptik VARIOSCAN high resolution Series Manual

and apparent object temperature (the temperature that an object of
emissivity ε = 1 would have without atmospheric absorption).
3. Finally, a generally applicable radiation-physical term takes into
account the measuring conditions at the real object (object
emission, extraneous radiation, atmospheric transmission).
Steps 2 and 3 must be accomplished during the run time of the system
with every change and output of temperature-relevant parameters
(range, level, object emissivity and distance, air and ambient
temperature, pixel temperature, temperature scale, isotherm). The
camera is controlled by selecting mean temperature (level) and span
(range) of the measuring range. By selecting level and range, the
brightness and contrast of the thermogram are defined. Using these
two parameters and based on the temperature model, the system
calculates from the detector signal that has been digitised with 16 bits a
current assignment table (Look Up Table) for 256 possible colours. The
temperature scale corresponds to a linear colour curve.
9.2

Measurement principle

The radiation received by the camera in the scanning phase consists of
the following fractions:
– Characteristic radiation emitted by the measured object,
– Radiation of surfaces in the ambience of the measured object
reflected by it,
– Characteristic radiation of the atmosphere between object and
camera.
All these fractions are considered for total radiation with a weighting
factor that corresponds to their emission and transmission factors each.
At short measuring distance (transmission of air path = 1) and an object
emissivity of 1 the received total radiation only depends on the
temperature of the measured object. The influence of extraneous
radiation is taken into account under real conditions by calculating the
total radiation from the apparent object temperature and subtracting
from it the fractions of ambience and air path.
Temperature measurement
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